Difference between revisions of "Particle Identification"
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Pion contamination in the electron sample (without cuts) =<br> | Pion contamination in the electron sample (without cuts) =<br> | ||
<math> = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =</math><br> | <math> = \frac {Integral(gauss(0))}{Integral(gauss(0) + landau(3) + gauss(6))} =</math><br> | ||
− | <math> = \frac{ | + | <math> = \frac{? \times 10^?}{ ? \times 10^? + ? \times 10^? + ? \times 10^?} = </math> <br> |
− | <math> = | + | <math> = ? </math><br> |
{|border="2" colspan = "4" | {|border="2" colspan = "4" |
Revision as of 22:06, 13 March 2008
EG1 run database
run summary
polarization info
Particle Identification
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
where
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[1]
after deriving the Taylor expansion of our function and considering only the first two terms, we get
The gas used in the CLAS Cerenkov counter is perfluorobutane
with index of refraction equal to 1.00153.
Electrons
The calculation of the number of photoelectrons emitted by electrons is shown below.
Electron mass
The Hall B cherenkov detector is 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.
=
- For the number of photoelectrons we have the following
That means the number of photoelectrons should be about 13.
Used file dst27095_05.B00 energy=5.7GeV and torus=2250(B>0). Target NH3
Pions( )
The threshold energy for pions is ~2.5 GeV and for electrons 9 MeV.
- Example for
where
The Hall B cherenkov detector is
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.
=
- For the number of photons we have the following(for pions)
Used file dst27095_05.B00 energy=5.7GeV and torus=2250(B>0). Target NH3
CLAS Cherenkov signal
Electrons
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.
- PE Fit equation
File:Gaussian fitting function.pdf
C.Lanczos, SIAM Journal of Numerical Analysis B1 (1964), 86. File:C.Lanczos SIAM Journal of Numerical Analysis B1 1964 86.pdf
//__[2] [3] ____________________________________________________________________________ Double_t TMath::Landau(Double_t x, Double_t mpv, Double_t sigma, Bool_t norm) { // The LANDAU function with mpv(most probable value) and sigma. // This function has been adapted from the CERNLIB routine G110 denlan. // If norm=kTRUE (default is kFALSE) the result is divided by sigma 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}; 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}; static Double_t p3[5] = {0.1788544503, 0.09359161662,0.006325387654, 0.00006611667319,-0.000002031049101}; 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; }
Fitting the Histograms
root [13] e_numb_of_photoelectrons->Draw();
root [2] g3= new TF1("g3","gaus(0)+landau(3)+gaus(6)",0,20);
To get fit parameters for g3 we should fit individually each of them(gaus(0),landau(3),gaus(6))
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)
root [11] e_numb_of_photoelectrons->Fit("g3","R+");
- e_Momentum_vs_Number_of_Photoelectrons
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. .
- Number of photoelectrons
Data | |||
---|---|---|---|
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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 |
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).
Experiment | B>0 | without cuts | flag>10 | 5<nphe<15 | 5<nphe<15 and flag>10 |
---|---|---|---|---|---|
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Pions( )
- _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
Experiment | B>0 | without cuts | e_flag>10 | 0<e_nphe<5 | 0<nphe<5 and e_flag>10 |
---|---|---|---|---|---|
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Calorimeter
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
without cut | _vs_nphe( ) | _vs_nphe ( ) | _vs_nphe( ) |
---|---|---|---|
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_vs_nphe( ) | _vs_nphe( and ) | _vs_nphe ( and ) |
---|---|---|
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From the EC_tot/P_vs_Number_of_Photoelectrons histogram one can see that the released energy fraction( ) at ~1.5 nphe peak is much smaller than it should be for electrons. In conclusion, the ~1.5 nphe peak is produced by the tail of negatively charged particles(pions). To eliminate negatively charged pions cut is applied on Calorimeter. After the cut was applied the number of entries decreased by ~33.47%.
Plot to 25 PEs. Have a histogram with total sum of three distributions. Use the fits from the cherenkov spectrum to estimate
how many pions are stil in the electron sample after the E/P cut.
Pion contamination in the electron sample (without cuts) =
with cut( | )with cut( | )with cuts( | and )|
---|---|---|---|
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Distributions | amplitude | mean | width | amplitude | mean | width | amplitude | mean | width |
---|---|---|---|---|---|---|---|---|---|
with cut( | )with cut( | )with cuts( | and )|||||||
gauss(0) | p0=1919+/-17.8 | p1=3.593+/-0.233 | p2=8.269+/-0.134 | p0=2025+/-9.4 | p1=3.44+/-0.05 | p2=8.442+/-0.037 | p0=1732+/-8.4 | p1=3.886+/-0.050 | p2=8.069+/-0.037 |
landau(3) | p3=8600+/-1.4 | p4=-3.063+/-1.414 | p5=-7.138+/-0.000 | p3=8600+/-3648.7 | p4=-3.092+/-1.414 | p5=-10.91+/-0.000 | p3=8600+/-5160.0 | p4=-2.821+/-1.414 | p5=-7.986+/-1.414 |
gauss(6) | p6=5568+/-69.1 | p7=1.164+/-0.006 | p8=0.543+/-0.008 | p6=5773+/-76.6 | p7=1.162+/-0.008 | p8=0.5562+/-0.0052 | p6=4301+/51.3 | p7=1.189+/-0.008 | p8=0.5299+/-0.0059 |
e_numb_of_photoelectrons with the following cuts
, . To eliminate the photons produced by the negatively charged pions was used the cut on the momentum e_momentum<3 GeV. Because the high energy pions are able to produce photons, which are misidentified with photoelectrons.Electron
Cuts
Calorimeter based cuts
The distributions below represent two types of cuts applied to improve the electron particle identification (PID) using a 4 GeV electron beam incident on an NH3 target. The electron calorimeter is segmented into an inner
and an outer region. The total energy absorbed by the calorimeter system is recorded in the variable . The momentum ( ) is calculated using the reconstructed track and the known torus magnetic field. The distributions of and are shown below where both have been divided by the electron momentum and no cuts have been applied.
Without any cuts we have 181018 entries. After using the following cut
After the cut on the energy deposited into inner part of electron calorimeter, number of entries decreases by 22%.
Both cuts and
In case of using the cuts of the total deposited energy and the energy deposited into inner calorimeter number of entries decreases ~36%
summary table
The "# of triggers" columns represents the number of events which generated a signal above threshold in the calorimeter and the scintillator. The expected # of events column represents the number of reconstructed events with tracks that also make it through the cuts defined in the table.
The semi-inclusive analysis will focus on the 4 GeV and 6 GeV data which have both inbending and outbending torus settings. Specifically runs 28074 - 28579 ( 4 GeV) and Runs 27356 - 27499 and 26874 - 27198 (6 GeV)
Beam Energy | Torus Current | Begin Run | End Run | file used | cuts | # trig( | )expected # evts( | )p<3, | , (%)p>3, | , (%)||
---|---|---|---|---|---|---|---|---|---|---|---|
and | |||||||||||
1606 | 1500 | 25488 | 25559 | dst25504_02.B00 | 64% | 49.5% | 78% | 60 | 3.2 | ||
1606 | 1946 | 25560 | 25605 | 44 | |||||||
1606 | 1500 | 25669 | 25732 | dst25669_02.B00 | 64% | 49% | 78% | 226 | 10 | ||
1606 | 1500 | 25742 | 26221 | dst25754_02.B00 | 21% | 11% | 24% | 3154 | 13.3 | ||
1606 | -1500 | 26222 | 26359 | dst26224_02.B00 | 4.6% | 3% | 6.6% | 703 | 13.1 | ||
1724 | -1500 | 27644 | 27798 | dst27649_02.B00 | 4.8% | 2.2% | 5.9% | 211 | 20 | ||
1724 | 1500 | 28512 | 28526 | 159 | |||||||
1724 | -1500 | 28527 | 28532 | 93 | |||||||
2288 | 1500 | 27205 | 27351 | dst27225_02.B00 | 20.2% | 13% | 25.6% | 1647 | 16.1 | ||
2562 | -1500 | 27799 | 27924 | dst27809_02.B00 | 5.7% | 4.6% | 8.6% | 1441 | 13.1 | ||
2562 | -1500 | 27942 | 27995 | dst27942_02.B00 | 6.1% | 4.4% | 8.9% | 841 | 32.3 | ||
2562 | 1500 | 28001 | 28069 | dst28002_02.B00 | 27.8% | 13% | 29.6% | 1013 | 30.7 | ||
2792 | -1500 | 27936 | 27941 | dst27937_02.B00 | 6.7% | 5% | 9.9% | 69 | 20.6 | ||
3210 | -2250 | 28549 | 28570 | 436 | |||||||
4239 | 2250 | 28074 | 28277 | dst28075_02.B00 | 35.3% | 23.9% | 40.5% | 2278 | 19.6 | ||
4239 | -2250 | 28280 | 28479 | dst28281_02.B00 | 9.1% | 9.4% | 13.6% | 2620 | 15.2 | ||
4239 | 2250 | 28482 | 28494 | 7 | |||||||
4239 | -2250 | 28500 | 28505 | 107 | |||||||
4239 | 2250 | 28506 | 28510 | dst28509_02.B00 | 29.5% | 22% | 36% | 75 | 18.1 | ||
5627 | 2250 | 27356 | 27364 | dst27358_02.B00 | 33.2% | 27.8% | 41.3% | 56 | 19.4 | 44.6 | 40.1 |
5627 | -2250 | 27366 | 27380 | dst27368_02.B00 | 12.6% | 14.8% | 19.5% | 130 | 13.6 | 25.3 | 8.8 |
5627 | 2250 | 27386 | 27499 | dst27388_02.B00 | 33.4% | 27.8% | 41.4% | 1210 | 20.2 | 44.8 | 40.1 |
5627 | 965 | 27502 | 27617 | 493 | |||||||
5735 | -2250 | 26874 | 27068 | dst26904_02.B00 | 13% | 15% | 20% | 1709 | 19.9 | 25.6 | 9.1 |
5735 | 2250 | 27069 | 27198 | dst27070_02.B00 | 33.3% | 28.8% | 42.2% | 1509 | 15 | 46 | 40.2 |
5764 | -2250 | 26468 | 26722 | dst26489_02.B00 | 12.2% | 14.4% | 19.1% | 1189 | 10 | 24.6 | 9.3 |
5764 | 0 | 26723 | 26775 | 268 | |||||||
5764 | -2250 | 26776 | 26851 | dst26779_02.B00 | 13.5% | 15.5% | 20.5% | 662 | 15.9 | 26.4 | 9.2 |
Cut on the number of photoelectrons
In this case is used a cut on the number of photoelectrons, which is
Used cuts and
Used file dst28181_03(energy 4.2GeV). In this case was applied cuts on the polar angle(
Plot of vs
In this case is used file dst27070(Energy 5.735 GeV and Torus 2250) and are applied the following EC cuts: For ECtotal -
P<3
After using above cuts the number of entries decreases ~46%
0.5<P<1
The number of entries decreased by ~51.8%
1<P<1.5
The number of entries decreased approximately by 47.8%
1.5<P<2
In this case the number of entries decreased by 46.1%
2<P<2.5
In this case the number of entries decreased by 38%
P>3
Used file dst27070(Energy 5.735 GeV and Torus 2250) and are applied the following EC cuts: For ECtotal -
The number of entries decreased by~40.2%
Plot of EC_tot/P vs nphe for Electrons
Used file dst27070(Energy 5.735 GeV and Torus 2250)
p<3 GeV
The graphs below represents all electron candidates having a momentum smaller than 3 GeV. Negatively charged pions are the most likely particle to be misidentified as an electrons by the tracking software. A negatively charged pion having a momentum of 3 GeV would generate less than ?? photons in the cerenkov counter. As a result the electron candidates which
- chi_sqr for pions
Used file:27095_05.B00(energy=5.735GeV and torus=2250), everything is done for
p<3 GeV and
p<3 GeV, and
p<3 GeV, , and nphe>2.5
Plot of EC_total vs EC_inner
In this case file dst28181_03.B00 was used(Energy 4.2 GeV and Torus +2250).
The following cuts were applied: , , ec_chi_sqr<0.1 and nphe>3.
Raster and vertex correction
A raster calibration and a cut on the vertex distribution was made in order to select electrons from the polarized target, also the ones scattered from other materials in the beam path. A plot of the uncorrected vertex distribution is presented below for dst27070_02.B00 file(energy=5.7GeV Torus=2250)
Pion
Summary Table
Beam Energy | Torus Current | Begin Run | End Run | file used | # trig( | )expected # evts( | )p>3, | , (%)p<3, | , (%)
---|---|---|---|---|---|---|---|---|
1606 | 1500 | 25488 | 25559 | dst25504_02.B00 | 60 | 3.2 | ||
1606 | 1500 | 25669 | 25732 | dst25669_02.B00 | 226 | 10 | ||
1606 | 1500 | 25742 | 26221 | dst25754_02.B00 | 3154 | 13.3 | ||
1606 | -1500 | 26222 | 26359 | dst26224_02.B00 | 703 | 13.1 | ||
1724 | -1500 | 27644 | 27798 | dst27649_02.B00 | 211 | 20 | ||
2288 | 1500 | 27205 | 27351 | dst27225_02.B00 | 1647 | 16.1 | ||
2562 | -1500 | 27799 | 27924 | dst27809_02.B00 | 1441 | 13.1 | ||
2562 | -1500 | 27942 | 27995 | dst27942_02.B00 | 841 | 32.3 | ||
2562 | 1500 | 28001 | 28069 | dst28002_02.B00 | 1013 | 30.7 | ||
2792 | -1500 | 27936 | 27941 | dst27937_02.B00 | 69 | 20.6 | ||
4239 | 2250 | 28074 | 28277 | dst28075_02.B00 | 2278 | 19.6 | ||
4239 | -2250 | 28280 | 28479 | dst28281_02.B00 | 2620 | 15.2 | ||
4239 | 2250 | 28506 | 28510 | dst28509_02.B00 | 75 | 18.1 | ||
5627 | 2250 | 27356 | 27364 | dst27358_02.B00 | 56 | 19.4 | 36.1 | 31.5 |
5627 | -2250 | 27366 | 27380 | dst27368_02.B00 | 130 | 13.6 | 25 | 43.8 |
5627 | 2250 | 27386 | 27499 | dst27388_02.B00 | 1210 | 20.2 | 39.8 | 32.4 |
5735 | -2250 | 26874 | 27068 | dst26904_02.B00 | 1709 | 19.9 | 22.5 | 46.4 |
5735 | 2250 | 27069 | 27198 | dst27070_02.B00 | 1509 | 15 | 34.6 | 32.9 |
5764 | -2250 | 26468 | 26722 | dst26489_02.B00 | 1189 | 10 | 25.2 | 44.3 |
5764 | -2250 | 26776 | 26851 | dst26779_02.B00 | 662 | 15.9 | 21.3 | 44 |
Table for Pions
I used the pion id code(both subroutines):
Beam Energy | Torus Current | Begin Run | End Run | file used | events remaining after cuts | # trig( | )expected # evts( | )|
---|---|---|---|---|---|---|---|---|
first(%) | second(%) | |||||||
1606 | 1500 | 25488 | 25559 | dst25504_02.B00 | 96.8 | 99 | 60 | 3.2 |
1606 | 1500 | 25669 | 25732 | dst25669_02.B00 | 98.1 | 98.9 | 226 | 10 |
1606 | 1500 | 25742 | 26221 | dst25754_02.B00 | 13.4 | 22.8 | 3154 | 13.3 |
1606 | -1500 | 26222 | 26359 | dst26224_02.B00 | 11.3 | 15.3 | 703 | 13.1 |
1724 | -1500 | 27644 | 27798 | dst27649_02.B00 | 15.3 | 18.7 | 211 | 20 |
2288 | 1500 | 27205 | 27351 | dst27225_02.B00 | 16.4 | 18.9 | 1647 | 16.1 |
2562 | -1500 | 27799 | 27924 | dst27809_02.B00 | 11.1 | 14.2 | 1441 | 13.1 |
2562 | -1500 | 27942 | 27995 | dst27942_02.B00 | 11.1 | 14.2 | 841 | 32.3 |
2562 | 1500 | 28001 | 28069 | dst28002_02.B00 | 22.4 | 23.1 | 1013 | 30.7 |
2792 | -1500 | 27936 | 27941 | dst27937_02.B00 | 12.3 | 15.4 | 69 | 20.6 |
4239 | 2250 | 28074 | 28277 | dst28075_02.B00 | 16.7 | 14.3 | 2278 | 19.6 |
4239 | -2250 | 28280 | 28479 | dst28281_02.B00 | 10.4 | 12.6 | 2620 | 15.2 |
4239 | 2250 | 28506 | 28510 | dst28509_02.B00 | % | % | 75 | 18.1 |
5627 | 2250 | 27356 | 27364 | dst27358_02.B00 | 40.5 | 40.8 | 56 | 19.4 |
5627 | -2250 | 27366 | 27380 | dst27368_02.B00 | 9.7 | 12.7 | 130 | 13.6 |
5627 | 2250 | 27386 | 27499 | dst27388_02.B00 | 14.1 | 15.5 | 1210 | 20.2 |
5735 | -2250 | 26874 | 27068 | dst26904_02.B00 | 12.1 | 14.5 | 1709 | 19.9 |
5735 | 2250 | 27069 | 27198 | dst27070_02.B00 | 19.5 | 22.9 | 1509 | 15 |
5764 | -2250 | 26468 | 26722 | dst26489_02.B00 | 9.6 | 13.3 | 1189 | 10 |
5764 | -2250 | 26776 | 26851 | dst26779_02.B00 | 10.3 | 13.9 | 662 | 15.9 |