electron identification in cbm

Electron Identification in CBM

Semeon Lebedev GSI, Darmstadt and LIT JINR, Dubna

Gennady OsoskovLIT JINR, Dubna

Electron Identification CBM Collaboration Meeting, 15.10.2008 2

Outline

• Electron Identification in RICH

• Electron Identification in TRD

• Global Electron Identification


Electron Identification in RICH


Improvements

• Hough Transform ring finder was improved especially for high ring density environment.

• Algorithm for electron identification in RICH based on ANN was implemented


Standard and Compact RICH geometry

Large Compact

radiator gas N2 CO2

reflective index 1.000298 1.00045

pth [GeV/c] 5.6 4.65

radiator length [m] 2.5 1.5

full length [m] 2.9 1.8

mirror radius [m] 4.5 3

mirror size [m2] 22.8 11.8

photodetector size [m2] 9 2.4

No. of channels 200k 55k

The length of the compact RICH radiator was calculated in order to keep mean number of hits in electron ring equals to 22. This is a requirement of the ring reconstruction algorithm.

See talk by E. Belolaptikova in RICH session.


Hit density normalized to one event

Standard RICH Compact RICH


High ring density test for ring finder (1)

120 e+ and 120 e- in 120 e+ and 120 e- in each eventeach event



• 500 events500 events• histogram cell size is 10x10 histogram cell size is 10x10

cmcm22

• 1) RD < 70 cm1) RD < 70 cm350 rings/500 events/100 cm350 rings/500 events/100 cm22

-> -> 0.7 rings/event/100 cm0.7 rings/event/100 cm22

-> -> 0.930.93 rings/event/ring arearings/event/ring area• 2) 70 < RD < 110 cm2) 70 < RD < 110 cm250 rings/500 events/100 cm250 rings/500 events/100 cm22


-> -> 0.670.67 rings/event/ring arearings/event/ring area• 3) RD > 110 cm3) RD > 110 cm< 150 rings/500 events/100 cm< 150 rings/500 events/100 cm22


-> -> 0.400.40 rings/event/ring arearings/event/ring area

1122

33

For the red area in the histogram majority For the red area in the histogram majority of rings are overlapped.of rings are overlapped.

RD = radial positionRD = radial position

RDRD



min min #hits#hits

IntegratedIntegrated

efficiencyefficiency

55 91.0791.07

1010 92.7192.71

1515 95.2895.28

Old version of ring finder showed only 78%Old version of ring finder showed only 78%


PMT collection efficiency

• 70% collection efficiency might be realistic because of the H8500 construction

Mean number of hits in electron ring:Mean number of hits in electron ring: 100 % CE =100 % CE = 21.14 hits/ring21.14 hits/ring 70% CE = 15.8 hits/ring70% CE = 15.8 hits/ring

100 % CE -> Mean efficiency = 91.07 %100 % CE -> Mean efficiency = 91.07 %70% CE -> Mean efficiency = 88.10%70% CE -> Mean efficiency = 88.10%

240 e+ and e- in each events240 e+ and e- in each events


Efficiency vs. number of hits

240 e+ and e- in each event240 e+ and e- in each event

100 % Collective efficiency 100 % Collective efficiency 70% Collective efficiency70% Collective efficiency


Efficiency vs. B/A

B/A distribution for e+ and e-

100 % Collective efficiency 100 % Collective efficiency 70% Collective efficiency70% Collective efficiency

In 1% ellipse fitter In 1% ellipse fitter goes wrong.goes wrong.

BB

AA

Important parameter for Compact RICH design.


Electron Identification in RICH based on ANN (1)

Input parameters for ANN:• A axis• B axis• Ring-track distance• Chi2• Number of hits• Momentum• Radial position• Ellipse rotation angle• Azimuthal angle

B axisRing-track distance Chi 2


Electron Identification in RICH based on ANN (2)

pions electrons


Electron Identification in TRD


Two different TRD geometries

Sum of energy loss for pions (solid line) and electrons (dashed line).

Munster-Bucharest0.3 Mev

Standard 0.15 Mev

Munster-Bucharest

Standard

Gas layers


Improvements in Electron Identification algorithm

• Different geometries• Detector inefficiency• Track passes through not

all layers

4-4-4Standard setup

4-2-234% saving

• Electron Identification algorithm based on ANN allows to identify electrons which have from 6 to 12 hits in TRD. Two different TRD geometries are supported.


Pion suppression vs. # of hits in track

Nof hits in track 1212 1111 1010 99 88 77 66

Pion Pion suppression, suppression,

standardstandard geometrygeometry

331188 250250 148148 9494 5757 3434 2323

Pion Pion suppression, suppression, MB geometryMB geometry

10k10k 6k6k 21002100 12001200 550550 370370 155155

• Electron efficiency 90%Electron efficiency 90%• Algorithm based on ANN was usedAlgorithm based on ANN was used• Integrated pion suppression for all momentum range Integrated pion suppression for all momentum range (1-10 GeV/c) is shown(1-10 GeV/c) is shown


Pion suppression in dependence on momentum

Momentum, Gev/c 1 1.5 2 3 4 5 7 9 11 13

ANN cut -0.17 0.48 0.69 0.81 0.85 0.88 0.89 0.91 0.91 0.91

Pion supression

101 331 425 424 410 479 330 323 264 235

• To keep 90% of electron efficiency one To keep 90% of electron efficiency one need to chose cut in dependence on need to chose cut in dependence on momentum according to plot.momentum according to plot.

• Fitted with fractionally rational functionFitted with fractionally rational function• Model: y = a+b/(x-c)Model: y = a+b/(x-c)• a = 0.955; b = -0.379; c = 0.663;a = 0.955; b = -0.379; c = 0.663;

Electron efficiency 90%Electron efficiency 90%

Standard TRD geometry is used


Global Electron Identification


Matching efficiency (1)


Matching efficiency (2)


Note: besides “true” matching losses also losses due to geometry come in (tracks not accepted in TRD)


Recall, Electron Identification in CBM

A axis B axis Ring-track distance

RICH

TRD

RICH:• ring-track distance < 1 cm; • A and B +- 3sigma around mean value; • Artificial Neural NetworkArtificial Neural NetworkTRD:• ANN output > 0.8

Dashed line – piSolid line - el


Electron identification, standard RICH (1)

Cuts: ring-track distance < 1 cm; A and B +- 3sigma; TRD ANN > 0.8


Electron identification, standard RICH (2)

RICH ANN > -0.3; TRD ANN > 0.8RICH ANN > -0.3; TRD ANN > 0.8


Electron identification, compact RICH (1)

Cuts: ring-track distance < 1 cm; A and B +- 4sigma; TRD ANN > 0.8


Electron identification, compact RICH (2)

RICH ANN > -0.3; TRD ANN > 0.8RICH ANN > -0.3; TRD ANN > 0.8


Summary table


Standard RICH cuts*

RICH Ann Standard RICH cuts*

RICH Ann

RICH, efficiency % 87.1 90.3 81.9 83.8

RICH, pi supression 240 250 110 250

RICH+TRD, efficiency % 81.0 83.3 73.4 74.6

RICH+TRD, pi supression 9800 10500 6800 13000

*ring-track distance < 1 cm; A and B +- 3sigma around mean value;*ring-track distance < 1 cm; A and B +- 3sigma around mean value;


Summary

• Hough Transform ring finder was improved especially for high ring density environment. Efficiency for the standard RICH is more than 95%, for the Compact RICH about 90.5%

• Algorithm for electron identification in RICH based on ANN was implemented. It has shown better results in comparison to standard cuts.

• Electron Identification algorithm in TRD allows to identify electrons which have from 6 to 12 hits in TRD. Two different TRD geometries are supported (Munster-Bucharest and standard).

• Routines for electron identification and quality check were implemented. Standard and Compact RICH layout were tested.

• Results are very good:– for standard RICH geometry pion suppression factor of 10k can be

reached at 83.3% electron efficiency using RICH and TRD.

– for compact RICH geometry pion suppression factor of 13k can be reached at 74.6% electron efficiency using RICH and TRD.

electron identification in cbm

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