A.Chernogorov

Beam pipe influence on the STS performance

A.Chernogorov, S.Belogurov,ITEP, Moscow

14th CBM Collaboration Meeting, October 6.-9. 2009, Split, Croatia

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 2

Outline:• Introduction

• Simulation conditions

• Layout of the stations

• Pipe configurations

• Detailed results for one configuration

• Comparative analysis for all configurations

• ConclusionsLeading effect: additional hits produced by delta electrons

This part I will speak about

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 3

Simulation conditions• 100 Central UrQMD Events (Au+Au@25AGeV/c)

(UrQMD1.3 input file14: http://www-linux.gsi.de/~cbmsim/cbm_vmc_doc/input.htm)

• Specially prepared geometry of STS stations (2.5° hole). Previous standard geometry had rectangular holes with constant height and was not suitable for our study.

• Several geometries for Al and Be beam pipe• Track simulation with Geant3 (generation

threshold 30 keV, Energy loss threshold 70 keV) /u/sbelogur/cbm/run/sts_sim_my.C based on standard sts_sim.C

(July09 Cbmroot version)• Track reconstruction using

L1Performance class /u/sbelogur/cbm/run/sts_reco_my.C based on recUrQMD_only.C by I.Vassiliev

• Selection condition of tracks passing near the pipe: not less than one point of a track should belong to the cone with 5° vertex angle (MCTracks&RECOTracks)

• Two level observables – excess hits due to pipe, quality of tracks reconstruction

Selection conditionof tracks near the pipe

for analysis

in order to separate effects of tracking algorithm

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 4

Layout of stationsSpecial geometry was created for us by Anna with square holes of 2.5° aperture. Set of sensors 2, 4, 6, 12, 18 cm. For central ones sizes were introduced manually to follow the 2.5° requirement.

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 5

Layout of stations We have found that with previous geometry hit probability per strip >10% i.e. too many fakes. We introduced a new geometry with sensors of 1.4, 2, 4, 6, 12 cm and all central sensors 2 times shorter than before.

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 6

Pipe configurations

For mechanical stability should be: h~D/E, where h is the thickness of the pipe;D is diameter of the pipe;E is the Young's modulus;E(Be)=300GPa, E(Al)=70GPa

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 7

Hit density for 1, 4, 8 STS stationsDetailed results for Be tube Ø28mm h0.5mm configuration

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 8

Detailed results for Be tube Ø28mm h0.5mm configuration

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 9

Comparative analysis for all configurations

A.Chernogorov 14th CBM Collaboration Meeting , Split, Croatia October 6-9 2009 10

Conclusion

• Effects of pipe are visible for all configurations, especially for reconstruction of secondary tracks and for ghosts

• Lowest effects are observed for cylindrical tube Ø20mm, largest ones for pipe having 2.5° cone’s shape

• Usage of the Be allows to reduce considerably pipe’s effects in comparison with Al