Kisel, I.

Kulakov, I.

Lebedev, A.

Vassiliev, I.

Zyzak, M.

GSI Repository

Multi-strange baryon decay reconstruction in the CBM experimentI. Vassiliev1,2, I. Kisel1,3, I. Kulakov1,3, A. Lebedev1,4, M. Zyzak1,3, and the CBM Collaboration1Goethe-Universita¨t, Institut fu¨r Kernphysik, Frankfurt am Main; 2GSI, Darmstadt; 3FIAS. Frankfurt am Main; 4JINR,DubnaOne of the predicted signatures of the phase transitionfrom nuclear matter to deconﬁned quark gluon plasma isthe enhanced production of multi-strange particles. Alsothe yield of particles carrying strange quarks is expectedto be sensitive to the ﬁreball evolution. The CBM detectorwill provide an unique opportunity to measure yields, di-rect and elliptic ﬂows, excitation functions of multi-strangebaryons at different energies and sizes of the collidingheavy ions. Ω− baryon consists of 3 strange quarks, Ξ−baryon contains 2 strange quarks and Λ — one strangequark. Multi-strange baryons will be measured in CBM byits decay into charged hadrons, which are detected in theSilicon Tracking System (STS) and in the Time-of-Flightdetector (TOF).To study the feasibility of multi-strange baryons decayreconstruction in the CBM experiment, a sets of 106 cen-tral Au+Au UrQMD events at 2, 4, 6, 8, 10, 15, 20, 25, 30and 35 AGeV were simulated. High statistic allows to cal-culate even Ω± reconstruction efﬁciency directly, avoidingsignal embedding into the UrQMD events. Together withwide range of the beam energies, it allows to investigatesystematic behavior of different physics observables likedirect and elliptic ﬂows, excitation functions, antibaryon tobaryon ratios and many others. In Fig. 1 the reconstructedmulti-strange antibaryon to baryon production ratios versusbeam energy is shown. Strange quarks number hierarchy isclearly visible. Black points correspond to Ω+ to Ω− ra-tios (S = 3), red points are Ξ+ to Ξ− ratios (S = 2) and bluepoints are Λ¯ to Λ ratios (S = 1).The Ω− decays into Λ+K− with branching ratio 67.8%and cτ = 2.46 cm., the Ξ− decays toΛ+π− with branchingratio 99.89% and cτ = 4.92 cm decays ofΛ happen most of-ten in the STS detector. The STS geometry with 8 double-sided segmented strip detectors, cables and support frameswere used for event reconstruction. Particle identiﬁcationwith TOF was applied. The KFParticle Finder package wasused to reconstruct about 50 particles and resonances in-cludingΩ±, Ξ±, Λ and Λ¯. Typical invariant mass spectrumis shown in Fig. 2. The Ω− reconstruction efﬁciency isabout 1.8% for central UrQMD events. The reconstructedmass value 1.672 ± 0.003 GeV/c2 is in a good agreementwith the simulated PDG’s data. The Ω− invariant mass res-olution is 2.3 (MeV/c2).The Ω± or Ξ± are accepted if they have good qualitygeometrical and topological detached vertex with (χ2geo <3σ, χ2topo < 3σ) and z-vertex farther than 3 cm down-stream of the target plane.Figure 1: Recalculated ratios of anti-baryon to baryonsyields versus beam energyFigure 2: Reconstructed invariant mass distribution ofΛ K− pairs in central Au+Au collisions at 35 AGeV. Redline is polynomial background plus signal Gaussian ﬁt.PHN-NQM-EXP-52 GSI SCIENTIFIC REPORT 201282 FAIR@GSI

Multi-strange baryon decay reconstruction in the CBM experiment

http://repository.gsi.de/record/51986/files/PHN-NQM-EXP-52.pdf

Multi-strange baryon decay reconstruction in the CBM experiment

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