Höhne, C.

Lebedeva, E.

GSI Repository

Status of low-mass di-electron simulations in the CBM experiment ∗E. Lebedeva1 and C. Ho¨hne11JLU Gießen University, Gießen, GermanyThe reconstruction of low-mass vector mesons is oneof the main goals of the CBM experiment at FAIR. TheCBM experiment will be able to reconstruct low-mass vec-tor mesons in di-electron and di-muon decay channels. Thecurrent status of low-mass di-electron simulations in cen-tral Au+Au collisions at 8 AGeV (SIS100) and 25 AGeV(SIS300) beam energy is presented in this report.Results were obtained with the latest version of theCBMROOT software (January 2013) which includes re-alistic detector descriptions. The background was gener-ated using the transport code UrQMD including di-electronpairs from γ-conversions, π0- and η- Dalitz decays. Di-electron pairs from ρ, ω, φ, and ω-Dalitz decays were sim-ulated by the PLUTO event generator and embedded intoUrQMD events. The detector setup includes STS, RICH,TRD and TOF detectors. For 8 AGeV beam energy theTRD detector was excluded from simulations. A 25 μmthick gold target was used in order to avoid additional back-ground from γ-conversions in the target.An electron candidate has to be reconstructed and iden-tified in all detectors, namely RICH, TRD and TOF. Sincethe TRD is not used for 8 AGeV beam energy simula-tions, an additional momentum cut at 5.5 GeV/c was im-plemented in order to reject large momentum pions.The background rejection strategy includes several cuts.The first cut is based on the assumption that all pairs withMee < 25 MeV/c2 stem from γ-conversion and they arefully removed from further combinatorics. The aim of thenext two cuts is to reject e± pairs where one partner is re-constructed only in the STS (segment track) or was fullyreconstructed but not identified as electron. The last cut isa transverse momentum cut.The dominant background source are random combi-nations of e± from π0-Dalitz decays and γ-conversions.For 8 AGeV beam energy the main contributions to back-ground pairs come from combinations of e± from π0-Dalitz decays and other particles (35%), e± from π0-Dalitzand γ-conversion (23%) and e± from different π0-Dalitzdecays (18%). For 25 AGeV beam energy the numbers are23%, 31% and 29%, respectively.The invariant mass spectra after applying all cuts are pre-sented in the upper plot for 8 AGeV and in the lower plotfor 25 AGeV beam energy in Figure 1.The final S/B ratio and reconstruction efficiency for ρ0,ω and φmesons and for different invariant mass regions arepresented in Table 1.∗Work supported by BMBF and HIC for FAIR]2 [GeV/ceeM0 0.5 1 1.5 2Yield-810-710-610-510-410-310-210]2 [GeV/ceeM0 0.5 1 1.5 2Yield-810-710-610-510-410-310-210Figure 1: Invariant mass spectra after applying all cuts forcentral Au+Au collisions at 8 AGeV (above, 100k events)and 25 AGeV (below) beam energy.Table 1: S/B ratio and reconstruction efficiency after ap-plying all cuts.8AGeV 25AGeVS/B Eff.[%] S/B Eff.[%]ρ - 3.12 - 4.39ω 0.64 4.11 0.31 5.53φ 0.04 4.89 0.11 7.08Mee:0.0-0.2 1.94 - 1.44 -Mee:0.2-0.6 0.031 - 0.019 -Mee:0.6-1.2 0.067 - 0.053 -PHN-NQM-EXP-54 GSI SCIENTIFIC REPORT 201284

Status of low-mass di-electron simulations in the CBM experiment

http://repository.gsi.de/record/51988/files/PHN-NQM-EXP-54.pdf

Status of low-mass di-electron simulations in the CBM experiment

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