Difference between revisions of "EG1 Teleconferences DeltaDoverD"

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−
=15-1-09=
+
=2/26/09=
−
==Cherenkov==
 
−
===Cherenkov Theory===
 
−
   
 
−
When the velocity of a charged particle is greater than the local phase velocity of light or when it enters a medium  with different optical properties the charged particle will emit photons.  The Cherenkov light is emitted under a constant angle <math>\theta_c</math> - the angle of Cherenkov radiation relative to the particle's direction. It can be shown geometrically that the cosine of the Cherenkov radiation angle is anti-proportional to the velocity of the  charged particle<br>
 
  
−
<math>cos \theta_c=\frac{1}{n \beta}</math><br>
 
  
−
where <math>\beta c</math> is the particle's velocity and n - index of refraction of the medium.The charged particle in time t travels <math>\beta c t</math> distance, while the electromagnetic waves - <math>\frac{c}{n}t</math>. For a medium with given index of refraction n there is a threshold velocity <math>\beta_{thr}=\frac{1}{n}</math>, below <math>\beta_{thr}</math> no radiation can take place.  This process may be used to observe the passage of charged particles in a detector which can measure the produced photons.<br>
+
[http://www.jlab.org/Hall-B/secure/eg1/EG2000/nevzat/UPGRADE_DST/cuts/OSICuts.h OSICuts]
  
−
The number of photons produced per unit path length of a particle with charge ze and per unit energy interval of the photons is proportional to the sine of the Cherenkov angle[http://pdg.lbl.gov/2007/reviews/passagerpp.pdf] <br>
+
=2/12/09=
  
−
<math>\frac{d^2 N}{dEdx}=\frac{\alpha z^2}{\hbar c}sin ^2 \theta_c=\frac{\alpha z^2}{\hbar c}[1-\frac{1}{\beta^2 n^2 (E)}]</math><br>
+
An estimate of the pion contamination in the electron candidates from the 5 GeV data set appears below.  Cuts are applied on the electron candidates based on the ratio of the energy deposited by the electron candidate in the electron calorimeter to the particles momentum measured by track reconstruction using hits in the drift chamber <math>\left ( \frac{E}{p} \right )</math>.
 +
As reported at the last teleconference on 1/20/09, these cuts were taken from [[Media:Yelena_Prok_Measurement_of_The_Spin_structure_Function_of_The_Proton_in_The_Resonance_Region_Thesis.pdf]]
 +
and applied to the 5 GeV data sample.  The number of photoelectrons measured by the cherenkov detector is shown below.  The goal is to estimate the number of pions which contaminate the electron candidate sample.  This is done
 +
by fitting the photoelectron distribution to 2 gaussian distributions and a Landau distribution.  Integrals of the fits over the region of interest are used to determine the pion contamination to the electron candidates.
  
 +
[http://www.jlab.org/Hall-B/secure/eg1/EG2000/josh/pion.cc Josh's Pion cuts code]
  
−
<math>\frac{d^2 N}{d\lambda dx} = \frac{2 \pi \alpha z^2}{\lambda^2}[1-\frac{1}{\beta^2 n^2 (\lambda)}]</math><br>
+
==Number of photoelectrons and EC_tot/P vs nphe for Pions and Electrons when e_momentum < 3 GeV==
  
−
<math>\beta=\frac{v}{c}=\frac{pc}{\sqrt{(pc)^2 + (mc^2)^2}}</math><br>
 
  
−
after deriving the Taylor expansion of our function and considering only the first two terms, we get<br>
 
−
<math>\frac{d^2 N}{dEdx}=\frac{\alpha z^2}{\hbar c}sin ^2 \theta_c=\frac{\alpha z^2}{\hbar c}[\beta^2 n^2 (E) - 1]</math>
 
  
−
The gas used in the CLAS Cerenkov counter is perfluorobutane <math>C_4 F_{10}</math> with index of refraction equal to 1.00153.  
+
[[Image:e_momentum_vs_ec_tot_without_cuts.gif|300px]][[Image:e_momentum_vs_ec_tot_with_cuts.gif|300px]]
  
  
 +
{| border="1"  |cellpadding="20" cellspacing="0
 +
|-
 +
| Momentum (GeV) || <math>EC_{tot}</math>/P || <math>EC_{inner}</math>/P || Cherenkov cut
 +
|-
 +
| e_momentum<3 || >0.2 ||>0.08|| nphe>2.5
 +
|}
  
−
====Electrons====
 
  
−
The calculation of the number of photoelectrons emitted by electrons is shown below.
+
{| border="1"  |cellpadding="20" cellspacing="0
−
Electron mass <math>m_e = 0.000511GeV</math>, <math>n=1.00153</math> and <math>\beta=\frac{p}{E} = 1</math>, because mass of the electron is negligible and also <math>\frac{\alpha}{\hbar c}=370[ eV^{-1} cm^{-1}] </math><br><br>
+
|-
−
The Hall B cherenkov detector is <math>\sim \; 0.7</math> m thick radiator.  We assume the PMTs used to  collect light have a constant quantum efficiency of 8% for photons with wavelength between 300 and 600 nm.
+
|[[Image:electrons_nphe_without_cuts_all_data_with_fits.gif|300px|thumb|The number of photoelectrons without cuts]] || [[Image:electrons_nphe_with_cuts_ecinner_0.08p_ectotal_0.2p_emomentum_3_all_data_with_fits.gif|300px|thumb|The number of photoelectrons after cuts on <math>EC_{tot}/P</math>, <math>EC_{inner}/P</math> and e_momentum]] || [[Image:electrons_nphe_with_cuts_ecinner_0.08p_ectotal_0.2p_emomentum_3_nphe_2.5_all_data_with_fits.gif|300px|thumb|The number of photoelectrons after cuts on <math>EC_{tot}/P</math>, <math>EC_{inner}/P</math>, e_momentum and nphe]]
 +
|}
  
−
<math>\frac{dN}{dx} </math> <math>= 2 \pi \alpha z^2 [{\beta^2 n^2 (\lambda)} - 1]\int_{300nm}^{600nm} \frac{1}{\lambda^2} d\lambda \times (0.08)=</math>  <br>
 
−
<math>= 2 \pi \alpha z^2 [{\beta^2 n^2 (\lambda)} - 1] (\frac {1}{\lambda})|_{600nm}^{300nm} \times (0.08) </math>=<br>
 
−
<math>= 2\times 3.14 \times \frac{1}{137} \times 1^2 \times [1.00153^2 - 1] \times \frac{1}{600} \times 0.08 [nm^{-1}] = </math> <br>
 
−
<math>= 19 \times 10^{-9} [nm^{-1}]</math> <br>
 
  
−
;For the number of photoelectrons we have the following <br>
+
{|border="2" colspan = "4"
−
<math> N = 19 \times 10^{-9} \times 0.7 m [\frac{10^9}{m}] = 13.3 </math><br>
+
!Distributions||amplitude|| mean || width ||amplitude|| mean || width
 +
|-
 +
|  || colspan="3" align="center"| without cuts || colspan="3" align="center" | with cuts(<math>EC_{inner}/P>0.08</math>, <math>EC_{tot}/P>0.2</math>, e_momentum<3 GeV)
 +
|-
 +
| gauss(0)|| p0=8.788e+06 +\-12727  || p1=6.139 +\-0.010 || p2=5.824 +\-0.004  || p0=4.604e+06 +\-6281 || p1=6.956 +\-0.010 || p2=6.056 +\-0.005
 +
|-
 +
| landau(3)|| p3=3.872e+07 +\-112178 || p4=3.19 +\-0.01  || p5=2.488 +\-0.003 || p3=1.426e+07 +\-56395 || p4=4.032 +\-0.008 || p5=2.497 +\-0.004
 +
|-
 +
| gauss(6)|| p6=2.727e+07 +\-8868 || p7=1.094 +\-0.000 ||p8= 0.5347 +\-0.0002  || p6=9.694e+06 +\-4903 || p7=1.116 +\-0.000 ||  p8= 0.5185 +\-0.0004
 +
|}<br>
  
−
That means the number of photoelectrons should be about 13.<br>
 
  
−
Used file dst27095_05.B00 energy=5.7GeV and torus=2250(B>0). Target NH3<br>
+
;1.) Electrons in the sample
  
−
[[Image:e_momentum_vs_numb_of_photoelectrons_27095_theory.gif|200px]]
+
[[Image:gauss_0_2.gif|200px]][[Image:landau_3_2.gif|200px]][[Image:gauss_6_2.gif|200px]]
  
−
====Pions(<math>\pi^-</math>)====
+
Electrons in the sample(using all cuts except nphe>2.5) =<br>
 +
<math> = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =</math><br>
 +
<math> = \frac{6.104 \times 10^9 + 2.925 \times 10^9}{ 6.104 \times 10^9 + 2.925 \times 10^9 + 1.241 \times 10^9} = </math> <br>
 +
<math> = 87 % </math><br>
  
  
−
The threshold energy for pions is ~2.5 GeV and for electrons 9 MeV.  <br>
+
;2.) Electrons in the sample using all cuts including nphe>2.5 cut
  
−
;Example for <math>\pi^-</math> <br>
+
[[Image:gauss_0_3.gif|200px]][[Image:landau_3_3.gif|200px]][[Image:gauss_6_3.gif|200px]]
  
−
<math>m_{\pi^-}=139.57[\frac{MeV}{c^2}]</math>, momentum <math>p=mv=3 [\frac{GeV}{c}]</math> and n=1.00153<br>
+
Electrons in the sample(including nphe>2.5 cut) =<br>
 +
<math> = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =</math><br>
 +
<math> = \frac{5.367 \times 10^9 + 2.434 \times 10^9}{ 5.367 \times 10^9 + 2.434 \times 10^9 + 4.928 \times 10^6} = </math> <br>
 +
<math> = 99.9 % </math><br>
  
−
where <math>\frac{\alpha}{\hbar c}=370[ eV^{-1} cm^{-1}] </math><br>
 
  
−
The Hall B cherenkov detector is <math>\sim \; 0.7</math> m thick radiator.  We assume the PMTs used to  collect light have a constant quantum efficiency of 8% for photons with wavelength between 300 and 600 nm.
+
;Conclusion: Using only EC cuts, electrons in the sample are 60 %, after using the cut on the number of photoelectrons the pion contamination decreased and 69 % of the particles are electrons, that means pion contamination is 31 %. It decreased by 9 %.
 +
If we assume that the photoelectrons from electrons are described by the Gaussian and landau distribution and that the pions are only in the gaussian distribution then
 +
we would expect our electron candidates to have a pion contamination of <math>\frac{4.928 \times 10^6}{5.367 \times 10^9 + 2.434 \times 10^9 } \times 100 %=  0.06 %</math>.
  
−
<math>\frac{dN}{dx} = \frac{2 \pi \alpha z^2}{\lambda^2}[1-\frac{1}{\beta^2 n^2 (\lambda)}]=</math> <br>
+
;For Pions
−
<math>= 2 \pi \alpha z^2 [1-\frac{1}{\beta^2 n^2 (\lambda)}]\int_{300nm}^{600nm} \frac{1}{\lambda^2} d\lambda \times (0.08)=</math>  <br>
 
−
<math>= 2 \pi \alpha z^2 [1-\frac{1}{\beta^2 n^2 (\lambda)}] (\frac {1}{\lambda})|_{600nm}^{300nm} \times (0.08) </math>=<br>
 
−
<math>= 2\times 3.14 \times \frac{1}{137} \times 1^2 \times [1-\frac{1}{0.998919^2 \times 1.00153^2}] \times \frac{1}{600} \times 0.08 [nm^{-1}] = </math> <br>
 
−
<math>= 5.465 \times 10^{-9} [nm^{-1}]</math> <br>
 
  
−
;For the number of photons we have the following(for pions) <br>
+
In this case, Josh's pion cut code was used. The number of entries decreased by ~ 20 %.
−
<math> N = 5.465 \times 10^{-9} \times 0.7 m [\frac{10^9}{m}] = 3.8255 </math><br>
 
  
−
Used file dst27095_05.B00 energy=5.7GeV and torus=2250(B>0). Target NH3<br>
+
{| border="1"  |cellpadding="20" cellspacing="0
 +
|-
 +
|[[Image:EC_tot_P_vs_nphe_for_pions_all_data_without_cuts_2.gif|300px|thumb|<math>EC_{tot}</math>/P vs nphe for pions without cuts]] ||[[Image:EC_tot_P_vs_nphe_for_pions_all_data_with_cuts_2.gif|300px|thumb|<math>EC_{tot}</math>/P vs nphe for pions using Josh's pion cuts code]]
 +
|}
  
−
[[Image:pi_momentum_vs_numb_of_photons_27095_theory.gif|200px]]
+
;For Electrons
 +
In order to remove the peak around ~ 1.5 PE and some high energy pions which have enough energy to cause the Cherenkov radiation the cut on nphe was applied.
 +
The number of entries after applying the following cuts -  <math>EC_{inner}/P>0.08</math> <math>EC_{tot}/P>0.2</math>, e_momentum < 3 GeV and nphe > 2.5 decreased by 65.31 %.
  
−
===CLAS Cherenkov signal===
+
{| border="1"  |cellpadding="20" cellspacing="0
−
====Electrons====
+
|-
 +
|[[Image:EC_tot_P_vs_nphe_for_electrons_all_data_without_cuts_2.gif|300px|thumb| <math>EC_{tot}</math>/P vs nphe for electrons without cuts]] || [[Image:EC_tot_P_vs_nphe_for_electrons_all_data_with_cuts_2.gif|300px|thumb| <math>EC_{tot}</math>/P vs nphe for electrons after cuts on <math>EC_{tot}/P</math>, <math>EC_{inner}/P</math>, e_momentum and nphe]]
 +
|}
  
−
The cherenkov signal measured in CLAS for particles identified as electrons by the tracking algorithm is shown below.  There are two distributions present.  One distribution is centered around 1.5 PEs and the second distribution is at 8 PEs when two gaussians and a Landau distribution are combined and fit to the spectrum.  As we will show below, the first peak is due to the misidentification of a negative pion as an electron.
+
==Number of photoelectrons and EC_tot/P vs nphe for Pions and Electrons when e_momentum > 3 GeV==
  
−
;PE Fit equation
 
−
;<math>N_{pe}= p_0 e^{-0.5 \left (\frac{x-p_1}{p_2} \right )^2} + p4\frac{1}{1-\left(\frac{x-p5}{p6}\right )} + p_6 e^{-0.5 \left (\frac{x-p_7}{p_8} \right )^2}</math>
 
  
−
  [[Image:gaussian_fitting_function.pdf]]
+
{| border="1" |cellpadding="20" cellspacing="0
 +
|-
 +
| Momentum (GeV) || <math>EC_{tot}</math>/P || <math>EC_{inner}</math>/P || Cherenkov cut
 +
|-
 +
| e_momentum<3 || >0.24 ||>0.06|| nphe>0.5
 +
|}
  
−
C.Lanczos, SIAM Journal of Numerical Analysis B1 (1964), 86.
 
−
[[Image:C.Lanczos_SIAM_Journal_of_Numerical_Analysis_B1_1964_86.pdf]]
 
  
 +
{| border="1"  |cellpadding="20" cellspacing="0
 +
|-
 +
|[[Image:electrons_nphe_without_cuts_all_data_with_fits_1.gif|300px|thumb|The number of photoelectrons without cuts]] || [[Image:electrons_nphe_with_cuts_ecinner_0.06p_ectotal_0.24p_emomentum_3_all_data_with_fits_1.gif|300px|thumb|The number of photoelectrons after cuts on <math>EC_{tot}/P</math>, <math>EC_{inner}/P</math> and e_momentum]] || [[Image:electrons_nphe_with_cuts_ecinner_0.06p_ectotal_0.24p_emomentum_3_nphe_0.5_all_data_with_fits_1.gif|300px|thumb|The number of photoelectrons after cuts on <math>EC_{tot}/P</math>, <math>EC_{inner}/P</math>, e_momentum and nphe]]
 +
|}
  
−
[http://ific.uv.es/informatica/manuales/root_v4.04/src/TFormula.cxx.html normalized fitting functions]
 
−
[http://wwwacs.gantep.edu.tr/guides/programming/root/htmldoc/TMath.html#TMath:Landau Landau and Landaun difference]
 
−
[http://support.adobe.com/devsup/devsup.nsf/docs/50023.htm for me]
 
  
−
  //__[http://lcgapp.cern.ch/project/cls/work-packages/mathlibs/mathTable.html] [http://root.cern.ch/root/html/src/TMath.cxx.html#fsokrB] ____________________________________________________________________________
+
{|border="2" colspan = "4"
−
Double_t TMath::Landau(Double_t x, Double_t mpv, Double_t sigma, Bool_t norm)
+
!Distributions||amplitude|| mean || width ||amplitude|| mean || width
−
{
+
|-
−
  // The LANDAU function with mpv(most probable value) and sigma.
+
| || colspan="3" align="center"| without cuts || colspan="3" align="center" | with cuts(<math>EC_{inner}/P>0.06</math>, <math>EC_{tot}/P>0.24</math>, e_momentum>3 GeV)
−
  // This function has been adapted from the CERNLIB routine G110 denlan.
+
|-
−
  // If norm=kTRUE (default is kFALSE) the result is divided by sigma
+
| gauss(0)|| p0=8.788e+06 +\-12717  || p1=6.139 +\-0.01 || p2=5.824 +\-0.004  || p0=3.087e+06 +\-1393 || p1=7.038 +\-0.002 || p2=4.573 +\-0.001
−
  static Double_t p1[5] = {0.4259894875,-0.1249762550, 0.03984243700, -0.006298287635,  0.001511162253};
+
|-
−
  static Double_t q1[5] = {1.0        ,-0.3388260629, 0.09594393323, -0.01608042283,    0.003778942063};
+
| landau(3)|| p3=3.872e+07 +\- 112058 || p4=3.19 +\-0.01  || p5=2.488 +\-0.003 || p3=1.774e+07 +\-12968 || p4=3.797 +\-0.002 || p5=1.398 +\-0.001
−
  static Double_t p2[5] = {0.1788541609, 0.1173957403, 0.01488850518, -0.001394989411,  0.0001283617211};
+
|-
−
  static Double_t q2[5] = {1.0        , 0.7428795082, 0.3153932961,  0.06694219548,    0.008790609714};
+
| gauss(6)|| p6=2.727e+07 +\- 8869 || p7=1.094 +\- 0.000 ||p8= 0.5347 +\- 0.0002  || p6=3.285e+06 +\-3512 || p7=1.198 +\-0.000 ||  p8= -0.4637 +\-0.0005
−
  static Double_t p3[5] = {0.1788544503, 0.09359161662,0.006325387654, 0.00006611667319,-0.000002031049101};
+
|}<br>
−
  static Double_t q3[5] = {1.0        , 0.6097809921, 0.2560616665,  0.04746722384,    0.006957301675};
 
−
  static Double_t p4[5] = {0.9874054407, 118.6723273,  849.2794360,  -743.7792444,      427.0262186};
 
−
  static Double_t q4[5] = {1.0         , 106.8615961,  337.6496214,    2016.712389,      1597.063511};
 
−
  static Double_t p5[5] = {1.003675074,  167.5702434,  4789.711289,    21217.86767,    -22324.94910};
 
−
  static Double_t q5[5] = {1.0         , 156.9424537, 3745.310488,    9834.698876,      66924.28357};
 
−
  static Double_t p6[5] = {1.000827619,  664.9143136,  62972.92665,    475554.6998,    -5743609.109};
 
−
  static Double_t q6[5] = {1.0        , 651.4101098,  56974.73333,    165917.4725,    -2815759.939};
 
−
  static Double_t a1[3] = {0.04166666667,-0.01996527778, 0.02709538966};
 
−
  static Double_t a2[2] = {-1.845568670,-4.284640743};
 
−
  if (sigma <= 0) return 0;
 
−
  Double_t v = (x-mpv)/sigma;
 
−
  Double_t u, ue, us, den;
 
−
  if (v < -5.5) {
 
−
      u  = TMath::Exp(v+1.0);
 
−
      if (u < 1e-10) return 0.0;
 
−
      ue  = TMath::Exp(-1/u);
 
−
      us  = TMath::Sqrt(u);
 
−
      den = 0.3989422803*(ue/us)*(1+(a1[0]+(a1[1]+a1[2]*u)*u)*u);
 
−
  } else if(v < -1) {
 
−
      u  = TMath::Exp(-v-1);
 
−
      den = TMath::Exp(-u)*TMath::Sqrt(u)*
 
−
            (p1[0]+(p1[1]+(p1[2]+(p1[3]+p1[4]*v)*v)*v)*v)/
 
−
            (q1[0]+(q1[1]+(q1[2]+(q1[3]+q1[4]*v)*v)*v)*v);
 
−
  } else if(v < 1) {
 
−
      den = (p2[0]+(p2[1]+(p2[2]+(p2[3]+p2[4]*v)*v)*v)*v)/
 
−
            (q2[0]+(q2[1]+(q2[2]+(q2[3]+q2[4]*v)*v)*v)*v);
 
−
  } else if(v < 5) {
 
−
      den = (p3[0]+(p3[1]+(p3[2]+(p3[3]+p3[4]*v)*v)*v)*v)/
 
−
            (q3[0]+(q3[1]+(q3[2]+(q3[3]+q3[4]*v)*v)*v)*v);
 
−
  } else if(v < 12) {
 
−
      u  = 1/v;
 
−
      den = u*u*(p4[0]+(p4[1]+(p4[2]+(p4[3]+p4[4]*u)*u)*u)*u)/
 
−
                (q4[0]+(q4[1]+(q4[2]+(q4[3]+q4[4]*u)*u)*u)*u);
 
−
  } else if(v < 50) {
 
−
      u  = 1/v;
 
−
      den = u*u*(p5[0]+(p5[1]+(p5[2]+(p5[3]+p5[4]*u)*u)*u)*u)/
 
−
                (q5[0]+(q5[1]+(q5[2]+(q5[3]+q5[4]*u)*u)*u)*u);
 
−
  } else if(v < 300) {
 
−
      u  = 1/v;
 
−
      den = u*u*(p6[0]+(p6[1]+(p6[2]+(p6[3]+p6[4]*u)*u)*u)*u)/
 
−
                (q6[0]+(q6[1]+(q6[2]+(q6[3]+q6[4]*u)*u)*u)*u);
 
−
  } else {
 
−
      u  = 1/(v-v*TMath::Log(v)/(v+1));
 
−
      den = u*u*(1+(a2[0]+a2[1]*u)*u);
 
−
  }
 
−
  if (!norm) return den;
 
−
  return den/sigma;
 
−
}<br>
 
  
−
Fitting the Histograms<br>
 
  
−
root [13] e_numb_of_photoelectrons->Draw();   <br>
+
;1.) Electrons in the sample
−
root [2] g3= new TF1("g3","gaus(0)+landau(3)+gaus(6)",0,20); <br>
 
  
−
To get fit parameters for g3 we should fit individually each of them(gaus(0),landau(3),gaus(6))<br>
+
[[Image:gauss_0_2_1.gif|200px]][[Image:landau_3_2_1.gif|200px]][[Image:gauss_6_2_1.gif|200px]]
  
−
root [3] g3->SetParameters(2.3e3,8,8.1,8.6e+3,8.6e-1,1.6,8.6e+3,8.6e-1,1.6,8.6e3)<br>
+
Electrons in the sample(using all cuts except nphe>0.5) =<br>
−
root [11] e_numb_of_photoelectrons->Fit("g3","R+");
+
<math> = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =</math><br>
 +
<math> = \frac{3.32 \times 10^9}{ 3.32 \times 10^9 + 2.291 \times 10^9 + 3.8 \times 10^8} = </math> <br>
 +
<math> = 55 % </math><br>
  
−
;e_Momentum_vs_Number_of_Photoelectrons
+
;2.) Electrons in the sample using all cuts including nphe>0.5 cut
  
−
The flag cut applied on the number of photoelectrons means that in CLAS detector instead of 5 superlayers were used 6 of them in track fit. As one can see from the histograms of the Number of photoelectrons, the cut on flag does not have effect on the peak around 1.5phe and decreases the number of entries by 37.17 %. The peak is due to a high energy pions(>2.5GeV), which have enough momentum to emit Cherenkov light and also because of the bad collection of light, there are a particular polar and azimuthal combination of angles where The Cherencov Detector cannot receive emitted light. .<br>
+
[[Image:gauss_0_2_2.gif|200px]][[Image:landau_3_2_2.gif|200px]][[Image:gauss_6_2_2.gif|200px]]
  
−
;Number of photoelectrons
+
Electrons in the sample(all cuts) =<br>
 +
<math> = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =</math><br>
 +
<math> = \frac{ 3.269 \times 10^9}{ 3.269 \times 10^9 + 2.285 \times 10^9 + 3.571 \times 10^8} = </math> <br>
 +
<math> = 55 % </math><br>
  
 +
;Conclusion: The pion contamination is this case is the same as it was before using the cut nphe>0.5 cut. The pion contamination is 45 % in the sample.
 +
If we assume that the photoelectrons from electrons are described by the Gaussian and landau distribution and that the pions are only in the gaussian distribution then
 +
we would expect our electron candidates to have a pion contamination of <math>\frac{3.571 \times 10^8}{3.269 \times 10^9 + 2.285 \times 10^9  } \times 100 %=  0.06 %</math>.
  
−
{|border="2" colspan = "4"
+
;For Pions
−
!Data||||||
+
 
 +
In this case, Josh's pion cut code was used. The number of entries decreased by ~ 20 % .
 +
 
 +
{| border="1" |cellpadding="20" cellspacing="0
 
|-
 
|-
−
| ||[[Image:e_number_of_photoelectrons_27095_1.gif|200px]]  
+
|[[Image:EC_tot_P_vs_nphe_for_pions_all_data_without_cuts_2.gif|300px|thumb|<math>EC_{tot}</math>/P vs nphe for pions without cuts]] ||[[Image:EC_tot_P_vs_nphe_for_pions_all_data_with_cuts_2.gif|300px|thumb|<math>EC_{tot}</math>/P vs nphe for pions using Josh's pion cuts code]]
−
|| [[Image:e_number_of_photoelectrons_27095_fits.gif|200px]]  
+
|}
 +
 
 +
;For Electrons
 +
In order to remove the peak around ~ 1.5 PE and some high energy pions which have enough energy to cause the Cherenkov radiation the cut on nphe was applied.
 +
The number of entries after applying the following cuts -  <math>EC_{inner}/P>0.06</math> <math>EC_{tot}/P>0.24</math>, e_momentum > 3 GeV and nphe > 0.5 decreased by 73 %.
 +
 
 +
{| border="1"  |cellpadding="20" cellspacing="0
 
|-
 
|-
−
| ||[[Image:e_number_of_photoelectrons_27095_flag_10_1.gif|200px]]  
+
|[[Image:EC_tot_P_vs_nphe_for_electrons_all_data_without_cuts_2_1.gif|300px|thumb| <math>EC_{tot}</math>/P vs nphe for electrons without cuts]] || [[Image:EC_tot_P_vs_nphe_for_electrons_all_data_with_cuts_2_1.gif|300px|thumb| <math>EC_{tot}</math>/P vs nphe for electrons after cuts on <math>EC_{tot}/P</math>, <math>EC_{inner}/P</math>, e_momentum and nphe]]
−
|| [[Image:e_number_of_photoelectrons_27095_flag_10_fit_with_cut.gif|200px]]  
+
|}
−
|}<br>
+
 
 +
 
 +
Repeat the above calculation using Nevzat's cuts.
 +
http://www.jlab.org/Hall-B/secure/eg1/EG2000/nevzat/GEOM_CC_CUTS/
 +
 
 +
=1/29/09=
 +
 
 +
We are interested in measuring the semi-inclusive pion asymmetry for both proton and deuteron targets using the 5-6 GeV EG1b data set.  Our goal will be to investigate fragmentation and establish a procedure for extracting <math>\frac{\Delta d}{d}</math> within the CLAS 12 GeV program.  We begin the analysis using the EG1 DSTs created from "cooked" data files.  Our first goal is evaluate the cuts used by others to improved the identification of scattered electrons in the data sample.
 +
 
 +
==Cherenkov signal==
 +
===Cherenkov PE Calculation===
 +
As shown in the wiki section, [[Particle_Identification#Cherenkov]],
 +
the expected  number of photoelectrons produced by electrons traversing the CLAS cherenkov detector would be <br>
 +
<math> N = 19 \times 10^{-9} \times 0.7 m [\frac{10^9}{m}] = 13.3 </math><br>
 +
 
 +
if you assume a <math>\beta</math> of 1 for the detected electrons in our data sample.
 +
 
 +
The expected number of photoelectrons in the CLAS cherenkov detector for reconstructed pion energies in the EG1 data set is shown in the graph below.
 +
 
 +
[[Image:pi_momentum_vs_numb_of_photons_27095_theory.gif|200px]]
 +
 
 +
 
 +
Our theoretical expectation, based on the description of the CLAS cherenkov detector suggests, that pions can generate up to about 10 photoelectrons compared with the 13 photoelectrons that can be generated by electrons.  While the cherenkov detector can distinguish  a 4 photoelectron signal generated by pions of momentum 3 GeV or less from the 10 photoelectrons generated by the typical detected electron, high momentum pions would generate photoelectron signals which are comparable to the photoelectrons generated by an electron.
 +
 
 +
===Measured CLAS Cherenkov signal===
 +
====Electrons====
 +
 
 +
[[Image:e_number_of_photoelectrons_27095_fits.gif|200px|thumb|track reconstructed using 5 superlayers]]
 +
The cherenkov signal measured in CLAS for particles identified as electrons by the tracking algorithm is shown below.  There are two distributions present.  One distribution is centered around 0.7 PEs and the second distribution is at 5.3 PEs when two gaussians and a Landau distribution are combined and fit to the spectrum. 
 +
 
 +
;PE Fit equation  (Osipenko's CLAS Note 2004-20 [[Image:CLAS_Note-2004-020.pdf]])
 +
;<math>N_{pe}= p_0 e^{-0.5 \left (\frac{x-p_1}{p_2} \right )^2} + p4\frac{1}{1-\left(\frac{x-p5}{p6}\right )} + p_6 e^{-0.5 \left (\frac{x-p_7}{p_8} \right )^2}</math>
 +
 
 +
 
 +
<pre>
 +
The CLAS note above says 2 Poisson convolution by a gaussian are used to fit NPE histogram. 
 +
The Poisson distribution starts to look like a gaussian when the Poisson mean value is larger
 +
than 4.  Our electron candidates theoretically have NPE = 13 and pions have NPE>4 when the
 +
pion energies are above 3 GeV.
 +
 
 +
We seem to get good fits if we use 2 Gaussians convoluted with a Landau.
 +
 
 +
</pre>
 +
 
 +
As we will show below, the first peak is due to the misidentification of a negative pion as an electron.
 +
 
 +
[[Image:e_number_of_photoelectrons_27095_flag_10_fit_with_cut.gif|200px|thumb|track reconstructed using 6 superlayers]]  
 +
 
 +
Reconstruction of an electrons trajectory through the CLAS drift chambers can be done using either 5 or 6 super layers.  Do tracks reconstructed using 5 superlayers generate cherenkov signals which differ from tracks reconstructed using all 6 DC superlayers?  The track reconstruction algorithm records the number of superlayers used for the track reconstructions.  This number is recorder in the EG1 DST files within the "flag" variable.  If the "flag" variable in the DST is larger than 10, then 6 superlayers were used for the track reconstruction. 
 +
The cherenkov spectrum below is observed for particles identified as electrons in the EG1 data in which 6 superlayers have been used to determine their trajectory.
 +
 
 +
The table below compares the cherekov spectrum fit values for particles identified as electrons with and without the 6 superlayer requirement.  If 6 superlayers are required for the electron reconstruction, the high PE gaussian distribution mean changes from 5.3 PEs to 3.8 PEs and is not not consistent within 2 standard deviations of the fit errors.  The LOW PE gaussian distribution, the suspected pion contamination, mean changes from 0.7 to 1.0 PEs. 
 +
The cuts decreases the number of entries by 37.17 %. It is believed that the Gaussian distribution centered around 1 PE is due to high energy pions(>2.5GeV).  Neither of these distributions is consistent with the theoretical predictions made above suggesting that there are some light collection inefficiencies within the cherenkov detector.<br>
  
 
Table: Cherenkov fit values
 
Table: Cherenkov fit values
Line 191: Line 227:
  
  
−
When flag cut(flag>10 cut means that 6 superlayers were used in track fit) was applied the number of entries decreased by 37.17 % and the mean value for the number of photoelectrons is about 7-8. After 5<nphe<15 cut, the number of entries decreased by 66.63 %.The mean value of the nphe is ~9 which agrees with theory(mean value ~13).<br>
+
The plots below show the event population intensity as a function of the electron candidates momentum measured by tracking and the number of photoelectrons observed in the cherenkov detector
  
  
Line 197: Line 233:
 
!Experiment||B>0||without cuts||flag>10||5<nphe<15||5<nphe<15 and flag>10
 
!Experiment||B>0||without cuts||flag>10||5<nphe<15||5<nphe<15 and flag>10
 
|-
 
|-
−
| || ||[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_1.gif|200px]]
+
| || || [[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_2.gif|200px]]
−
[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_2.gif|200px]]
+
||[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_2.gif|200px]]
−
[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_3.gif|200px]]
 
−
|| [[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_1.gif|200px]]
 
−
[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_2.gif|200px]]
 
−
[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_3.gif|200px]]
 
 
|| [[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_?_nphe_?.gif|200px]]
 
|| [[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_?_nphe_?.gif|200px]]
 
||[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_5_nphe_15_flag_10.gif|200px]]
 
||[[Image:e_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_5_nphe_15_flag_10.gif|200px]]
Line 211: Line 243:
 
;<math>\pi^-</math>_Momentum_vs_Number_of_Photons
 
;<math>\pi^-</math>_Momentum_vs_Number_of_Photons
  
−
After e_flag>10 cut, the number of entries decreased by 30.45 % and the mean value for the number of photons is ~9
+
The histograms presented below show the event population intensity for the pion momentum and the number of photoelectrons generated by the pions. One can see that after applying cuts on NPhE and flag the mean value is around 1.
  
  
Line 217: Line 249:
 
!Experiment||B>0||without cuts||e_flag>10||0<e_nphe<5||0<nphe<5 and e_flag>10
 
!Experiment||B>0||without cuts||e_flag>10||0<e_nphe<5||0<nphe<5 and e_flag>10
 
|-
 
|-
−
| || ||[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_1_1.gif|200px]]
+
| || ||[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_2_1.gif|200px]]
−
[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_2_1.gif|200px]]
+
|| [[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_2_1.gif|200px]]
−
[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_without_cuts_3_1.gif|200px]]
 
−
|| [[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_1_1.gif|200px]]
 
−
[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_2_1.gif|200px]]
 
−
[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_flag_10_3_1.gif|200px]]
 
 
|| [[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_?_nphe_?.gif|200px]]
 
|| [[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_?_nphe_?.gif|200px]]
 
||[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_0_nphe_5_flag_10.gif|200px]]
 
||[[Image:pi_momentum_vs_numb_of_photoelectrons_27095_exp_with_cuts_0_nphe_5_flag_10.gif|200px]]
 
|}
 
|}
 +
 +
== Electron-pion contamination==
 +
Osipenko's CLAS Note 2004-20 [[Image:CLAS_Note-2004-020.pdf]]
 +
 +
;EC_tot/P_vs_Number_of_Photoelectrons and EC_inner/P_vs_Number_of_Photoelectrons
 +
 +
Two types of cuts were applied on the distributions below, one on the energy deposited to the inner calorimeter <math>EC_{inner}/P>0.08</math> and another one on the total energy absorbed by the calorimeter <math>EC_{tot}/P>0.2</math>, to improve the electron particle identification. In this case we used the DST file dst27095_05, the beam energy is 5.735 GeV and target NH3.<br>
 +
 +
{|border="2" colspan = "4"
 +
! without cut || <math>EC_{tot}/P</math>_vs_nphe(<math>EC_{tot}/P>0.2</math>)|| <math>EC_{inner}/P</math>_vs_nphe (<math>EC_{inner}/P>0.08</math>)|| <math>EC_{tot}/P</math>_vs_nphe(<math>EC_{inner}/P>0.08</math>)
 +
|-
 +
|[[Image:ec_tot_momentum_vs_numb_of_phe_27095_without_cut.gif|200px]]
 +
|| [[Image:ec_tot_momentum_vs_numb_of_phe_27095_with_cut.gif|200px]]
 +
|| [[Image:ec_inner_momentum_vs_numb_of_phe_27095_with_cut_ec_inner_momentum_0.08.gif|200px]]
 +
|| [[Image:ec_tot_momentum_vs_numb_of_phe_27095_with_cut_ec_inner_momentum_0.08.gif|200px]]
 +
|}<br>
 +
 +
{|border="2" colspan = "4"
 +
! <math>EC_{inner}/P</math>_vs_nphe(<math>EC_{tot}/P>0.2</math>) || <math>EC_{tot}/P</math>_vs_nphe(<math>EC_{tot}/P>0.2</math> and <math>EC_{inner}/P>0.08</math>)|| <math>EC_{inner}/P</math>_vs_nphe (<math>EC_{tot}/P>0.2</math> and <math>EC_{inner}/P>0.08</math>)
 +
|-
 +
|| [[Image:ec_inner_momentum_vs_numb_of_phe_27095_with_cut_ec_tot_momentum_0.2.gif|200px]]
 +
|| [[Image:ec_tot_momentum_vs_numb_of_phe_27095_with_cut_ec_inner_momentum_0.08_and_ec_tot_momentum_0.2.gif|200px]]
 +
|| [[Image:ec_inner_momentum_vs_numb_of_phe_27095_with_cut_ec_tot_momentum_0.2_and_ec_inner_momentum0.08.gif|200px]]
 +
|}<br>
 +
 +
 +
=21-07-2010=
 +
 +
==Cuts==
 +
 +
The correct identification of an electron and a pion is the main requirement for a semi-inclusive analysis. unfortunately, the pion is able to generate cerenkov radiation an as a result be misidentified as an electron.  This contamination of the electron sample is removed using the cuts on the energy deposited in the electromagnetic calorimeter, the number of photoelectrons in the Cherenkov counter and fiducial cuts on the detector acceptance.
 +
The energy deposition in the calorimeter for electrons and pions is different. Pions are minimum ionizing charge particles depositing into the calorimeter which is independent of the pion's momentum once the momentum is above ~ 0.08 GeV. On the other hand, electrons produce photoelectrons and create electromagnetic shower releasing the energy into the calorimeter which is proportional to their momentum. In order to remove contamination due to the energy deposition in the calorimeter the following cut was introduced: <math>EC_{total}>0.2*p</math>. The cut was also applied to the energy collected in the inner part of the calorimeter: <math>EC_{inner}>0.06*p</math> , because the ratio of the energy deposited in the total to the inner calorimeter depends on the thickness of the detector and is a constant.<br>
 +
[[Image:e_total_vs_e_inner1_before_cuts_file_dst27070.gif|200px]][[Image:e_total_vs_e_inner1_after_cuts_file_dst27070.gif|200px]]<br>
 +
In addition to the cut on the energy deposited into the electromagnetic calorimeter, the misidentified electrons were excluded requiring a signal in the threshold CLAS Cherenkov detector.  Pion's misidentified as electrons have been shown to produce around ~1.5 photoelectons in the cherenkov detector, as shown below. Geometrical cuts on the location of the particle at the entrance to the cerenkov detector were applied to reduce the pion contamination. The second histogram below shows that after cuts the peak around 1.5 is substantially reduced. <br>
 +
{| border="1"  |cellpadding="20" cellspacing="0
 +
|-
 +
| No cuts || OSI Cuts
 +
|-
 +
| [[Image:electrons_nphe_without_cuts_all_data_with_fits.gif|200px|thumb|The number of photoelectrons without cuts]] || [[Image:electrons_nphe_with_OSIcuts_all_data_with_fits.gif|200px|thumb|The number of photoelectrons with OSI cuts]]
 +
|}
 +
 +
==phi_angle_in_CM_Frame_vs_Relative_Rate==
 +
 +
Because of wide range of kinematics, <math>{\varphi_{\pi}}^*</math> was measured only for certain lepton scattering <math>\theta_e</math> angles and invariant mass (W). Applying above described cuts: EC_inner>0.06, EC_tot/p>0.2, nphe>2.5 and <math>0.9<M_x<1.1</math>, for the following invariant mass <math>1.44<W<1.46</math> and <math>0.4<cos\theta_{pion}^{CM}<0.6</math> the <math>{\varphi_{\pi}}^*</math> vs relative rate distribution is shown below on the graph and compared with E99-107 data, which by itself is in agreement with the models.<br>
 +
{| border="0" style="background:transparent;"  align="center"
 +
|-
 +
|
 +
[[Image:phi_angle_in_CM_Frame_vs_Relative_Rate_cos_theta_0-4_0-6_W_1-45.jpg|400px|thumb|<math>{\varphi_{\pi}}^*</math> vs Relative rate for fixed <math>cos\theta_{pion}^{CM}=0.5</math> and <math>W=1.45 GeV</math> <ref name="Park2008" > Bogus text</ref> <ref> http://clasweb.jlab.org/cgi-bin/clasdb/msm.cgi?eid=14&mid=16&data=on </ref> ]]
 +
|}<br>
 +
 +
The EG1b data for kinematics chosen above show the same shape as E99-107 data.
 +
 +
 +
'''If you follow the link below, you can find the comparison for the wide range of kinematics:'''
 +
 +
[[Phi_angle_in_CM_frame_for_different_runs]]
 +
 +
==Electron Efficiency Ratio==
 +
 +
Used NH3 target runs with positive and negative torus. EC , nphe and OSI cuts are applied. Only electron was required.
 +
 +
{| border="1"  |cellpadding="20" cellspacing="0
 +
|-
 +
| File number || electron || electron
 +
|-
 +
| B<0 || [[File:electron26990_4.gif|200px]]  || [[File:electron26990_5.gif|200px]]
 +
|-
 +
| B>0  || [[File:electron27113_4.gif|200px]]  || [[File:electron27113_5.gif|200px]]
 +
|}
 +
 +
 +
Below is the graph of electron efficiency ratio when electron_paddle_number=7 for positive torus(Bp) and electron_paddle_number=11 for negative torus(B_n)
 +
 +
[[File:electronefficiencyratioBp7Bn11.jpg|300px]]
 +
 +
[[Media:electronefficiencyratioBp7Bn11.txt]]
 +
 +
 +
In this case we required positive pion and electron and applied cut on <math>Q^2</math>(<math>1.05<Q^2<1.15</math>)
 +
 +
{|border="5"
 +
!X_bj ||B_n/B_p Rates
 +
|-
 +
| 0.14 || 0.25 <math>\pm</math> 0.55
 +
|-
 +
| 0.15 || 0.74 <math>\pm</math> 0.27
 +
|-
 +
| 0.17 || 1.07 <math>\pm</math> 0.18
 +
|-
 +
| 0.19 || 1.3 <math>\pm</math> 0.13
 +
|-
 +
| 0.2 || 1.4 <math>\pm</math> 0.14
 +
|}
 +
 +
 +
 +
[http://wiki.iac.isu.edu/index.php/EG1 Go Back] [[EG1]]

Latest revision as of 05:50, 21 July 2010

2/26/09

OSICuts

2/12/09

An estimate of the pion contamination in the electron candidates from the 5 GeV data set appears below. Cuts are applied on the electron candidates based on the ratio of the energy deposited by the electron candidate in the electron calorimeter to the particles momentum measured by track reconstruction using hits in the drift chamber [math]\left ( \frac{E}{p} \right )[/math]. As reported at the last teleconference on 1/20/09, these cuts were taken from Media:Yelena_Prok_Measurement_of_The_Spin_structure_Function_of_The_Proton_in_The_Resonance_Region_Thesis.pdf and applied to the 5 GeV data sample. The number of photoelectrons measured by the cherenkov detector is shown below. The goal is to estimate the number of pions which contaminate the electron candidate sample. This is done by fitting the photoelectron distribution to 2 gaussian distributions and a Landau distribution. Integrals of the fits over the region of interest are used to determine the pion contamination to the electron candidates.

Josh's Pion cuts code

Number of photoelectrons and EC_tot/P vs nphe for Pions and Electrons when e_momentum < 3 GeV

E momentum vs ec tot without cuts.gifE momentum vs ec tot with cuts.gif


Momentum (GeV) [math]EC_{tot}[/math]/P [math]EC_{inner}[/math]/P Cherenkov cut
e_momentum<3 >0.2 >0.08 nphe>2.5


The number of photoelectrons without cuts
The number of photoelectrons after cuts on [math]EC_{tot}/P[/math], [math]EC_{inner}/P[/math] and e_momentum
The number of photoelectrons after cuts on [math]EC_{tot}/P[/math], [math]EC_{inner}/P[/math], e_momentum and nphe


Distributions amplitude mean width amplitude mean width
without cuts with cuts([math]EC_{inner}/P\gt 0.08[/math], [math]EC_{tot}/P\gt 0.2[/math], e_momentum<3 GeV)
gauss(0) p0=8.788e+06 +\-12727 p1=6.139 +\-0.010 p2=5.824 +\-0.004 p0=4.604e+06 +\-6281 p1=6.956 +\-0.010 p2=6.056 +\-0.005
landau(3) p3=3.872e+07 +\-112178 p4=3.19 +\-0.01 p5=2.488 +\-0.003 p3=1.426e+07 +\-56395 p4=4.032 +\-0.008 p5=2.497 +\-0.004
gauss(6) p6=2.727e+07 +\-8868 p7=1.094 +\-0.000 p8= 0.5347 +\-0.0002 p6=9.694e+06 +\-4903 p7=1.116 +\-0.000 p8= 0.5185 +\-0.0004



1.) Electrons in the sample

Gauss 0 2.gifLandau 3 2.gifGauss 6 2.gif

Electrons in the sample(using all cuts except nphe>2.5) =
[math] = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =[/math]
[math] = \frac{6.104 \times 10^9 + 2.925 \times 10^9}{ 6.104 \times 10^9 + 2.925 \times 10^9 + 1.241 \times 10^9} = [/math]
[math] = 87 % [/math]


2.) Electrons in the sample using all cuts including nphe>2.5 cut

Gauss 0 3.gifLandau 3 3.gifGauss 6 3.gif

Electrons in the sample(including nphe>2.5 cut) =
[math] = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =[/math]
[math] = \frac{5.367 \times 10^9 + 2.434 \times 10^9}{ 5.367 \times 10^9 + 2.434 \times 10^9 + 4.928 \times 10^6} = [/math]
[math] = 99.9 % [/math]


Conclusion
Using only EC cuts, electrons in the sample are 60 %, after using the cut on the number of photoelectrons the pion contamination decreased and 69 % of the particles are electrons, that means pion contamination is 31 %. It decreased by 9 %.

If we assume that the photoelectrons from electrons are described by the Gaussian and landau distribution and that the pions are only in the gaussian distribution then we would expect our electron candidates to have a pion contamination of [math]\frac{4.928 \times 10^6}{5.367 \times 10^9 + 2.434 \times 10^9 } \times 100 %= 0.06 %[/math].

For Pions

In this case, Josh's pion cut code was used. The number of entries decreased by ~ 20 %.

[math]EC_{tot}[/math]/P vs nphe for pions without cuts
[math]EC_{tot}[/math]/P vs nphe for pions using Josh's pion cuts code
For Electrons

In order to remove the peak around ~ 1.5 PE and some high energy pions which have enough energy to cause the Cherenkov radiation the cut on nphe was applied. The number of entries after applying the following cuts - [math]EC_{inner}/P\gt 0.08[/math] [math]EC_{tot}/P\gt 0.2[/math], e_momentum < 3 GeV and nphe > 2.5 decreased by 65.31 %.

[math]EC_{tot}[/math]/P vs nphe for electrons without cuts
[math]EC_{tot}[/math]/P vs nphe for electrons after cuts on [math]EC_{tot}/P[/math], [math]EC_{inner}/P[/math], e_momentum and nphe

Number of photoelectrons and EC_tot/P vs nphe for Pions and Electrons when e_momentum > 3 GeV

Momentum (GeV) [math]EC_{tot}[/math]/P [math]EC_{inner}[/math]/P Cherenkov cut
e_momentum<3 >0.24 >0.06 nphe>0.5


The number of photoelectrons without cuts
The number of photoelectrons after cuts on [math]EC_{tot}/P[/math], [math]EC_{inner}/P[/math] and e_momentum
The number of photoelectrons after cuts on [math]EC_{tot}/P[/math], [math]EC_{inner}/P[/math], e_momentum and nphe


Distributions amplitude mean width amplitude mean width
without cuts with cuts([math]EC_{inner}/P\gt 0.06[/math], [math]EC_{tot}/P\gt 0.24[/math], e_momentum>3 GeV)
gauss(0) p0=8.788e+06 +\-12717 p1=6.139 +\-0.01 p2=5.824 +\-0.004 p0=3.087e+06 +\-1393 p1=7.038 +\-0.002 p2=4.573 +\-0.001
landau(3) p3=3.872e+07 +\- 112058 p4=3.19 +\-0.01 p5=2.488 +\-0.003 p3=1.774e+07 +\-12968 p4=3.797 +\-0.002 p5=1.398 +\-0.001
gauss(6) p6=2.727e+07 +\- 8869 p7=1.094 +\- 0.000 p8= 0.5347 +\- 0.0002 p6=3.285e+06 +\-3512 p7=1.198 +\-0.000 p8= -0.4637 +\-0.0005



1.) Electrons in the sample

Gauss 0 2 1.gifLandau 3 2 1.gifGauss 6 2 1.gif

Electrons in the sample(using all cuts except nphe>0.5) =
[math] = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =[/math]
[math] = \frac{3.32 \times 10^9}{ 3.32 \times 10^9 + 2.291 \times 10^9 + 3.8 \times 10^8} = [/math]
[math] = 55 % [/math]

2.) Electrons in the sample using all cuts including nphe>0.5 cut

Gauss 0 2 2.gifLandau 3 2 2.gifGauss 6 2 2.gif

Electrons in the sample(all cuts) =
[math] = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =[/math]
[math] = \frac{ 3.269 \times 10^9}{ 3.269 \times 10^9 + 2.285 \times 10^9 + 3.571 \times 10^8} = [/math]
[math] = 55 % [/math]

Conclusion
The pion contamination is this case is the same as it was before using the cut nphe>0.5 cut. The pion contamination is 45 % in the sample.

If we assume that the photoelectrons from electrons are described by the Gaussian and landau distribution and that the pions are only in the gaussian distribution then we would expect our electron candidates to have a pion contamination of [math]\frac{3.571 \times 10^8}{3.269 \times 10^9 + 2.285 \times 10^9 } \times 100 %= 0.06 %[/math].

For Pions

In this case, Josh's pion cut code was used. The number of entries decreased by ~ 20 % .

[math]EC_{tot}[/math]/P vs nphe for pions without cuts
[math]EC_{tot}[/math]/P vs nphe for pions using Josh's pion cuts code
For Electrons

In order to remove the peak around ~ 1.5 PE and some high energy pions which have enough energy to cause the Cherenkov radiation the cut on nphe was applied. The number of entries after applying the following cuts - [math]EC_{inner}/P\gt 0.06[/math] [math]EC_{tot}/P\gt 0.24[/math], e_momentum > 3 GeV and nphe > 0.5 decreased by 73 %.

[math]EC_{tot}[/math]/P vs nphe for electrons without cuts
[math]EC_{tot}[/math]/P vs nphe for electrons after cuts on [math]EC_{tot}/P[/math], [math]EC_{inner}/P[/math], e_momentum and nphe


Repeat the above calculation using Nevzat's cuts. http://www.jlab.org/Hall-B/secure/eg1/EG2000/nevzat/GEOM_CC_CUTS/

1/29/09

We are interested in measuring the semi-inclusive pion asymmetry for both proton and deuteron targets using the 5-6 GeV EG1b data set. Our goal will be to investigate fragmentation and establish a procedure for extracting [math]\frac{\Delta d}{d}[/math] within the CLAS 12 GeV program. We begin the analysis using the EG1 DSTs created from "cooked" data files. Our first goal is evaluate the cuts used by others to improved the identification of scattered electrons in the data sample.

Cherenkov signal

Cherenkov PE Calculation

As shown in the wiki section, Particle_Identification#Cherenkov, the expected number of photoelectrons produced by electrons traversing the CLAS cherenkov detector would be
[math] N = 19 \times 10^{-9} \times 0.7 m [\frac{10^9}{m}] = 13.3 [/math]

if you assume a [math]\beta[/math] of 1 for the detected electrons in our data sample.

The expected number of photoelectrons in the CLAS cherenkov detector for reconstructed pion energies in the EG1 data set is shown in the graph below.

Pi momentum vs numb of photons 27095 theory.gif


Our theoretical expectation, based on the description of the CLAS cherenkov detector suggests, that pions can generate up to about 10 photoelectrons compared with the 13 photoelectrons that can be generated by electrons. While the cherenkov detector can distinguish a 4 photoelectron signal generated by pions of momentum 3 GeV or less from the 10 photoelectrons generated by the typical detected electron, high momentum pions would generate photoelectron signals which are comparable to the photoelectrons generated by an electron.

Measured CLAS Cherenkov signal

Electrons

track reconstructed using 5 superlayers

The cherenkov signal measured in CLAS for particles identified as electrons by the tracking algorithm is shown below. There are two distributions present. One distribution is centered around 0.7 PEs and the second distribution is at 5.3 PEs when two gaussians and a Landau distribution are combined and fit to the spectrum.

PE Fit equation (Osipenko's CLAS Note 2004-20 File:CLAS Note-2004-020.pdf)
[math]N_{pe}= p_0 e^{-0.5 \left (\frac{x-p_1}{p_2} \right )^2} + p4\frac{1}{1-\left(\frac{x-p5}{p6}\right )} + p_6 e^{-0.5 \left (\frac{x-p_7}{p_8} \right )^2}[/math]


 The CLAS note above says 2 Poisson convolution by a gaussian are used to fit NPE histogram.  
The Poisson distribution starts to look like a gaussian when the Poisson mean value is larger 
than 4.  Our electron candidates theoretically have NPE = 13 and pions have NPE>4 when the 
pion energies are above 3 GeV.

We seem to get good fits if we use 2 Gaussians convoluted with a Landau.

As we will show below, the first peak is due to the misidentification of a negative pion as an electron.

track reconstructed using 6 superlayers

Reconstruction of an electrons trajectory through the CLAS drift chambers can be done using either 5 or 6 super layers. Do tracks reconstructed using 5 superlayers generate cherenkov signals which differ from tracks reconstructed using all 6 DC superlayers? The track reconstruction algorithm records the number of superlayers used for the track reconstructions. This number is recorder in the EG1 DST files within the "flag" variable. If the "flag" variable in the DST is larger than 10, then 6 superlayers were used for the track reconstruction. The cherenkov spectrum below is observed for particles identified as electrons in the EG1 data in which 6 superlayers have been used to determine their trajectory.

The table below compares the cherekov spectrum fit values for particles identified as electrons with and without the 6 superlayer requirement. If 6 superlayers are required for the electron reconstruction, the high PE gaussian distribution mean changes from 5.3 PEs to 3.8 PEs and is not not consistent within 2 standard deviations of the fit errors. The LOW PE gaussian distribution, the suspected pion contamination, mean changes from 0.7 to 1.0 PEs. The cuts decreases the number of entries by 37.17 %. It is believed that the Gaussian distribution centered around 1 PE is due to high energy pions(>2.5GeV). Neither of these distributions is consistent with the theoretical predictions made above suggesting that there are some light collection inefficiencies within the cherenkov detector.

Table: Cherenkov fit values

Distributions amplitude mean width amplitude mean width
without cuts with cut(flag>10)
gauss(0) p0=2144+/-44.0 p1=5.342+/-0.343 p2=7.761+/-0.188 p0=1580+/-8.1 p1=3.75+/-0.06 p2=8.486+/-0.042
landau(3) p3=4.349e+04+/-2894 p4=1.049+/-0.026 p5=0.2197+/-0.0257 p3=8600+/-3648.7 p4=-3.861+/-1.414 p5=-4.88+/-1.41
gauss(6) p6=4960+/-270.6 p7=0.7345+/-0.0983 p8=0.8885+/-0.0594 p6=6219+/-54.2 p7=1.088+/-0.006 p8=0.6037+/-0.0052



The plots below show the event population intensity as a function of the electron candidates momentum measured by tracking and the number of photoelectrons observed in the cherenkov detector


Experiment B>0 without cuts flag>10 5<nphe<15 5<nphe<15 and flag>10
E momentum vs numb of photoelectrons 27095 exp without cuts 2.gif E momentum vs numb of photoelectrons 27095 exp with cuts flag 10 2.gif E momentum vs numb of photoelectrons 27095 exp with cuts ? nphe ?.gif E momentum vs numb of photoelectrons 27095 exp with cuts 5 nphe 15 flag 10.gif

Pions([math]\pi^-[/math])

[math]\pi^-[/math]_Momentum_vs_Number_of_Photons

The histograms presented below show the event population intensity for the pion momentum and the number of photoelectrons generated by the pions. One can see that after applying cuts on NPhE and flag the mean value is around 1.


Experiment B>0 without cuts e_flag>10 0<e_nphe<5 0<nphe<5 and e_flag>10
Pi momentum vs numb of photoelectrons 27095 exp without cuts 2 1.gif Pi momentum vs numb of photoelectrons 27095 exp with cuts flag 10 2 1.gif Pi momentum vs numb of photoelectrons 27095 exp with cuts ? nphe ?.gif Pi momentum vs numb of photoelectrons 27095 exp with cuts 0 nphe 5 flag 10.gif

Electron-pion contamination

Osipenko's CLAS Note 2004-20 File:CLAS Note-2004-020.pdf

EC_tot/P_vs_Number_of_Photoelectrons and EC_inner/P_vs_Number_of_Photoelectrons

Two types of cuts were applied on the distributions below, one on the energy deposited to the inner calorimeter [math]EC_{inner}/P\gt 0.08[/math] and another one on the total energy absorbed by the calorimeter [math]EC_{tot}/P\gt 0.2[/math], to improve the electron particle identification. In this case we used the DST file dst27095_05, the beam energy is 5.735 GeV and target NH3.

without cut [math]EC_{tot}/P[/math]_vs_nphe([math]EC_{tot}/P\gt 0.2[/math]) [math]EC_{inner}/P[/math]_vs_nphe ([math]EC_{inner}/P\gt 0.08[/math]) [math]EC_{tot}/P[/math]_vs_nphe([math]EC_{inner}/P\gt 0.08[/math])
Ec tot momentum vs numb of phe 27095 without cut.gif Ec tot momentum vs numb of phe 27095 with cut.gif Ec inner momentum vs numb of phe 27095 with cut ec inner momentum 0.08.gif Ec tot momentum vs numb of phe 27095 with cut ec inner momentum 0.08.gif


[math]EC_{inner}/P[/math]_vs_nphe([math]EC_{tot}/P\gt 0.2[/math]) [math]EC_{tot}/P[/math]_vs_nphe([math]EC_{tot}/P\gt 0.2[/math] and [math]EC_{inner}/P\gt 0.08[/math]) [math]EC_{inner}/P[/math]_vs_nphe ([math]EC_{tot}/P\gt 0.2[/math] and [math]EC_{inner}/P\gt 0.08[/math])
Ec inner momentum vs numb of phe 27095 with cut ec tot momentum 0.2.gif Ec tot momentum vs numb of phe 27095 with cut ec inner momentum 0.08 and ec tot momentum 0.2.gif Ec inner momentum vs numb of phe 27095 with cut ec tot momentum 0.2 and ec inner momentum0.08.gif



21-07-2010

Cuts

The correct identification of an electron and a pion is the main requirement for a semi-inclusive analysis. unfortunately, the pion is able to generate cerenkov radiation an as a result be misidentified as an electron. This contamination of the electron sample is removed using the cuts on the energy deposited in the electromagnetic calorimeter, the number of photoelectrons in the Cherenkov counter and fiducial cuts on the detector acceptance. The energy deposition in the calorimeter for electrons and pions is different. Pions are minimum ionizing charge particles depositing into the calorimeter which is independent of the pion's momentum once the momentum is above ~ 0.08 GeV. On the other hand, electrons produce photoelectrons and create electromagnetic shower releasing the energy into the calorimeter which is proportional to their momentum. In order to remove contamination due to the energy deposition in the calorimeter the following cut was introduced: [math]EC_{total}\gt 0.2*p[/math]. The cut was also applied to the energy collected in the inner part of the calorimeter: [math]EC_{inner}\gt 0.06*p[/math] , because the ratio of the energy deposited in the total to the inner calorimeter depends on the thickness of the detector and is a constant.
E total vs e inner1 before cuts file dst27070.gifE total vs e inner1 after cuts file dst27070.gif
In addition to the cut on the energy deposited into the electromagnetic calorimeter, the misidentified electrons were excluded requiring a signal in the threshold CLAS Cherenkov detector. Pion's misidentified as electrons have been shown to produce around ~1.5 photoelectons in the cherenkov detector, as shown below. Geometrical cuts on the location of the particle at the entrance to the cerenkov detector were applied to reduce the pion contamination. The second histogram below shows that after cuts the peak around 1.5 is substantially reduced.

No cuts OSI Cuts
The number of photoelectrons without cuts
The number of photoelectrons with OSI cuts

phi_angle_in_CM_Frame_vs_Relative_Rate

Because of wide range of kinematics, [math]{\varphi_{\pi}}^*[/math] was measured only for certain lepton scattering [math]\theta_e[/math] angles and invariant mass (W). Applying above described cuts: EC_inner>0.06, EC_tot/p>0.2, nphe>2.5 and [math]0.9\lt M_x\lt 1.1[/math], for the following invariant mass [math]1.44\lt W\lt 1.46[/math] and [math]0.4\lt cos\theta_{pion}^{CM}\lt 0.6[/math] the [math]{\varphi_{\pi}}^*[/math] vs relative rate distribution is shown below on the graph and compared with E99-107 data, which by itself is in agreement with the models.

[math]{\varphi_{\pi}}^*[/math] vs Relative rate for fixed [math]cos\theta_{pion}^{CM}=0.5[/math] and [math]W=1.45 GeV[/math] <ref name="Park2008" > Bogus text</ref> <ref> http://clasweb.jlab.org/cgi-bin/clasdb/msm.cgi?eid=14&mid=16&data=on </ref>


The EG1b data for kinematics chosen above show the same shape as E99-107 data.


If you follow the link below, you can find the comparison for the wide range of kinematics:

Phi_angle_in_CM_frame_for_different_runs

Electron Efficiency Ratio

Used NH3 target runs with positive and negative torus. EC , nphe and OSI cuts are applied. Only electron was required.

File number electron electron
B<0 Electron26990 4.gif Electron26990 5.gif
B>0 Electron27113 4.gif Electron27113 5.gif


Below is the graph of electron efficiency ratio when electron_paddle_number=7 for positive torus(Bp) and electron_paddle_number=11 for negative torus(B_n)

ElectronefficiencyratioBp7Bn11.jpg

Media:electronefficiencyratioBp7Bn11.txt


In this case we required positive pion and electron and applied cut on [math]Q^2[/math]([math]1.05\lt Q^2\lt 1.15[/math])

X_bj B_n/B_p Rates
0.14 0.25 [math]\pm[/math] 0.55
0.15 0.74 [math]\pm[/math] 0.27
0.17 1.07 [math]\pm[/math] 0.18
0.19 1.3 [math]\pm[/math] 0.13
0.2 1.4 [math]\pm[/math] 0.14


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