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Geometry layout studies of the RICH detector in the CBM experiment

Elena Belolaptikova

Dr. Claudia HoehneDr. Claudia Hoehne

Moscow State Institute of Radioengineering, Electronics and Automation (TU)

GSI, Darmstadt

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Outline

Studies of the RICH material budget Compact RICH design Summary

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Studies of additional material budget

in the CBM RICH detector

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Motivation

Study the influence of the RICH material budget to the STS, TRD and global (STS+TRD) track reconstruction.

Thick mirror easy and cheap construction.

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The simulation

UrQMD events, Au-Au central collisions at 25 AGeV Additionally 50 electrons were embedded in each event;

Detailed simulations have been performed in order to study the material of the RICH mirrors. The standard RICH geometry was tested with different mirror

thicknesses – 3 mm, 6 mm and 10 mm; 3 mm (idealistic); 6 mm (realistic); 10 mm (safety factor)

The mirror support structure was simulated. The L1 STS track reconstruction algorithm was used; Two different methods were used for TRD track reconstruction:

LIT and L1.

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The support structure for the mirrors

material – Al; distance between tubes – 40 cm

The first version radius – 3 cm; thickness – 5 mm;

The second version radius – 1.5 cm; thickness – 2 mm;

(proposal of E. Vznuzdaev, PNPI St. Petersburg)

The support structure

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TRD track finding efficiency for electrons

Without support structure With support structure

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Track finding results

STS tracking efficiency doesn’t depend on the presence of the grid support structure.

For all tested RICH geometries efficiency for all tracks is about 82%, and for electron tracks – 87%.

The TRD track finding efficiency drops down on 2-2.5% with increasing mirror thickness

Difference between presence of the first version of the support structure and its absence is roughly 1.5 – 2.5 % .

For the second version – less than 1%.

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Summary table for the TRD track finding

No support structure With support structure

3 mm 6 mm 10 mm 3 mm 6 mm 10 mm

LIT L1 LIT L1 LIT L1 LIT L1 LIT L1 LIT L1

All, % 93.8 87.2 93.6 86.0 93.0 84.6 93.3 85.8 93.0 84.5 92.5 83.1

Electrons,% 89.3 91.0 88.1 89.6 87.0 88.4 87.6 88.8 86.4 87.3 85.2 85.8

Ghosts, #/ev. 13.7 38.1 14.7 40.1 16.2 41.7 15.1 40.0 16.0 42.3 17.4 43.5

Mismatches, % 0.68 0.09 0.68 0.10 0.68 0.12 0.71 0.09 0.77 0.11 0.76 0.15

Designation of the summary table: All – TRD tracks with 12 hits; Electrons – embedded primary electrons in UrQMD; Ghost – wrongly found tracks; Mismatch – wrong matches with STS tracks.

realisticidealistic

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Compact RICH design

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Motivation

CBM RICH is an expensive detector. In order to save money the optimization of size

and geometry is needed. The most important and expensive component

is the photodetector. The dimensions of this part should be

minimized.

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Comparison of large and compact RICH

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.

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The compact RICH layout optimization

A design of the compact RICH detector was implemented;

The detector layout was not optimized – rings have strong distortions

and elliptical shapes in the PMT plane reduction of the ring

reconstruction efficiency and increase in ring radius resolution bad

electron identification performance.

Optimization of the photodetector and

mirrors positions is needed.

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Optimization parameters

The following parameters are chosen to be optimized: RICH detector acceptance; A, B and B/A ratio; Hit and ring density; Electron ring distribution on the PMT plane. Number of hits;

Special routines for the calculation and visual representation of the parameters were implemented.

The RICH event display was used to visualize hits and rings in the PMT plane.

A

B

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The Compact RICH

Different compact RICH geometries were implemented, simulated and investigated to find the best one.

Analyses of these geometries were done by the parameters mentioned above.

The most appropriate geometry was chosen with the best correlation of the selected parameters.

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Chosen compact RICH geometry

PMT plane (divided into 4 panels) rotation around x-axis: 5°

rotation around y-axis: - 5°

z position - 1800 mm

y position - ±1275 mm

∆y = ±300 mm

Mirror tilted by -1° around x-axis

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Standard vs. Compact RICH Hits distribution

PMT area = 9 m2 PMT area = 2.4 m2

Number of hits in primary electron ring.

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Standard vs. Compact RICHAcceptance

.. ,

Acc eAcc

simulated e

Acceptance for primary electrons in dependence on momentum.

eAcc. ― electrons which have RICH ring with >=5 hits

Mean acceptance = 88.88% Mean acceptance = 83.86%

Parameters of BoxGenerator are following:

Pt (0., 3.)

Phi (0., 360.)

Theta (2.5, 25.)

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Standard vs. Compact RICH, Distributions of A, B and B/A

compact RICH

standard RICH

AB

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Standard vs. Compact RICH, Electron ring distributions on the PMT plane

Standard

Compact

(selected region shown)

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Standard vs. Compact RICH, Ring reconstruction efficiency.

Au-Au at 25 AGeV UrQMD + 5 e- and 5 e+ in each event

Mean efficiency = 95.04%

Standard RICHStandard RICH Compact RICHCompact RICH

Fakes/event = 1.50

Mean efficiency = 90.63%

Fakes/event = 3.55

,.

.

eacc

erecoEfficiency eacc. ― electrons which have RICH ring with >=5 hits

and track projection on PMT plane

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Summary RICH geometries with different mirror thicknesses were

simulated. The mirror support structure was implemented. Having only changes on few percent level in the track finding efficiency reassure for planning a “standard” RICH mirror of 6 mm glass thickness and aluminum support. This will save money and efforts.

RICH geometry testing routines were implemented and different compact RICH geometries were simulated and investigated. Better positions of PMT and mirrors were found.

The best compact RICH geometry was tested with UrQMD events. Obtained results are very promising.

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Thanks for your attention!Thanks for your attention!