Kisel, I.

Kulakov, I.

Vassiliev, I.

Zyzak, M.

GSI Repository

Antihyperon decay reconstruction in the CBM experimentI. Vassiliev1,2, I. Kisel1,3, I. Kulakov1,3, M. Zyzak1,3, and the CBM Collaboration1Goethe-Universita¨t, Institut fu¨r Kernphysik, Frankfurt am Main; 2GSI, Darmstadt; 3FIAS. Frankfurt am MainOne of the most challenging tasks of the CBM experi-ment is to measure yields, excitation functions and ﬂowsof antihyperons. Antihyperons like Ω+ and Ξ+ will bemeasured in the CBM-detector by its decay into chargedhadrons, which are detected in the Silicon Tracking Sys-tem (STS) and in the Time-of-Flight detector (TOF). Thekey role of the TOF detector is antiproton selection invery dense negative pions and Kaons environment. On theFig. 1 is shown calculated by TOF tracks m2 vs particlemomentum. Negative track with | m2 − m2p |< 2σ and| m2 −m2K |> 3σ and | m2 −m2π |> 3σ was used as anantiproton candidate to reconstruct Λ¯.Figure 1: Tracks m2 vs particle momentum calculated byTOF.On the Fig. 2 is shown invariant mass distribution ofp¯ π+ pairs. Clear Λ¯ peak is visible. Λ¯ reconstruction ef-ﬁciency is above 14% for 35 AGeV and achieve its maxi-mum about 22% at 8 AGeV. One or two antiproton track-candidates per event allows signiﬁcantly decrease the com-binatorial background. Signal to background ratio is above3.4 for central Au + Au collisions at 35 AGeV. KFParticleﬁnder was used in order to reconstruct Λ¯ combining sec-ondary p¯ and π−.Then, combining Λ¯ with positive secondary Kaon orpion, the Ω+ and Ξ+ candidates were tested. The Ω+ orΞ+ was accepted if it has good quality geometrical andtopological detached vertex: (χ2geo < 3σ, χ2topo < 3σ) andz-vertex greater than 3 cm downstream the target plane.To study the feasibility of multi-strange antihyperondecay reconstruction in the CBM experiment, a sets of106 central Au+Au UrQMD events at 2, 4, 6, 8, 10, 15,Figure 2: Reconstructed invariant mass distribution of p¯ π+pairs in central Au+Au collisions at 35 AGeV. Red line ispolynomial background plus signal Gaussian ﬁt.20, 25, 30 and 35 AGeV were simulated. Typical in-variant mass spectrum is shown in Fig. 3. The Ξ+ re-construction efﬁciency is about 3.1% for central Au +Au UrQMD events at 35 AGeV. The reconstructed massvalue 1.321 ± 0.003 GeV/c2 is in a good agreement withthe simulated PDG’s data. Invariant mass resolution is2.3 (MeV/c2).Figure 3: Reconstructed invariant mass distribution ofΛ¯ π+ pairs in central Au+Au collisions at 35 AGeV. Redline is polynomial background plus signal Gaussian ﬁt.GSI SCIENTIFIC REPORT 2012 PHN-NQM-EXP-51FAIR@GSI 81

Antihyperon decay reconstruction in the CBM experiment

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Antihyperon decay reconstruction in the CBM experiment

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