Sevil Salur for STAR Collaboration, Yale University

1. Au-Auat sNN =200GeV Significance =20±3 STAR Preliminary X ~0.5-1.5  per event for AuAu from theoretical prediction (1,2,3) L(1520) S*± Signal Mixed Event Background p+p √s=200GeV Signal after Background Subtraction preliminary Reconstruction OUTPUT Monte Carlo INPUT preliminary p+p K p D p e d-Auat sNN =200GeV p-pat s =200GeV NEntries X+X Significance =60±4 Significance =15±2 X+X STAR Preliminary STAR Preliminary S*± +S*± S*± +S*± ± Star Preliminary p+p Star Preliminary d+Au Star Preliminary Au+Au Counts ? Minv [GeV/c2] Minv [GeV/c2] Minv [GeV/c2] Pentaquark Searches with STAR at RHIC Sevil Salur for STAR Collaboration, Yale University WHAT IS A PENTAQUARK? It is a five-quark system. SIMULATION STUDIES gp→(nK+) K−d gd→(nK+) K−p K+Xe→(pK0) X nd,Ne→(pK0) K0 Nentries Nentries Antidecuplet from Chiral Soliton Model Nentries gC→(nK+) K−X gp→(nK+) K0 M inv (p+K0) [GeV/c2] M inv (p+K0) [GeV/c2] e+d→(pK0) X p+p→(Xp) XYZ… One Monte Carlo Q Pentaquark with a full TPC simulation per event with a distribution of Tinv slope =250 MeV is embedded in real p+p events. Only 3% of these Q’s could be reconstructed. The width and the mass remains consistent with the Monte Carlo input after the reconstruction. A similar Monte Carlo study yields a X5 acceptance of 2% for STAR. Describing Pentaquarks with Models: Chiral Soliton Model:Chiral dynamics generated narrow K+n resonance (partial motivation of experiments). Uncorrelated Quark Model:Q 4Q in the lowest orbital of a mean field. Bag, NRQM… Correlated Diquark Description:Quarks are correlated in an antisymmetric color, flavor and spin state. Rapidity vs PT Acceptance Left plot shows the TPC acceptance which is defined as the ratio of Q that are possible to reconstruct compared to simulated input. Right plot shows the phase space population of the Q after reconstruction. WHICH PENTAQUARKS WE ARE LOOKING FOR Q can be reconstructed in this PT and y range Good opportunity to observe antipentaquarks (antibaryon/baryon ~ 1 at RHIC) THE ANALYSIS AND TECHNIQUES preliminary STAR at RHIC, BNL measures charged particles via Time Projection Chamber . Due to the very short lifetime of pentaquarks, topological analysis, which is used to analyze long lived particles such as L, Ks0 and X cannot be used. An alternative method is use a mixing technique which we use to identify resonances in STAR. In this technique, Ks0 ‘s are identified with topological analysis. The identifiedKs0 are mixed with a p to get Q. The background is achieved by mixing p’s from one event with the Ks0 candidates from another event. Optimizing Momentum Cuts via Monte Carlo Tracks Upper and lower momentum cuts are applied in agreement with the momentum distributions of the decay particles of the Monte Carlo Q + to maximize the signal over background. preliminary Counts Counts Counts p+p Momentum distribution of the protons and kaons decayed from Monte Carlo Q and in real events p [GeV/c] p [GeV/c] Charged particles are identified by p and dE/dx information obtained by the TPC. STAR Time Projection Chamber (TPC) Ks0’s are identified by the decay topology technique due to their relatively long lifetime. FEASIBILITY STUDIES WITH THE CURRENT DATA • Preliminary dN/dy in p+p of L(1520)  0.004 per event • 8 Million X 0.004  32 K L(1520) • 0.1-1 X 32 K  3-32 K 0.5-1.5 X 1.5 Million 0.8-2.3M • Efficiency 3%  90-960  25-70K • Branching Ratio 50%  45-480  10-25K • B R 50% from K0s  22-240  5-18K Background pairs per event in the mass range of  is 0.0004  2 • 0.0004 X 8 Million  3200 2 X 1.5 Million  3M Significance  = Signal/√(2 X Background+Signal)  0.25-3  2-7 Mixing Technique Works. This technique has been successfully used in STAR to identify resonances such as K*, S(1385), L(1520), and X(1530), etc… (See talk by Christina Markert (Friday Parallel 2: Strangeness Spectra) “Strange Baryon Resonance Production in p+p, d+Au and Au+Au Collisions at RHIC energies” and below …)S(1385)L+p, as in the case of Q+,L’s are identified by decay topology similarly to K0 due to their long life time and p’s are identified by dE/dx information. We can repeat the same study for the d+Au collisions. To estimate the yield we assume Npart scaling. The number of participants in d+Au is 8 while in p+p it is 2 and in Au+Au it is 350 for most central collisions. The lower limit is obtained from p+p scaling while the upper limit is from Au+Au yield estimates. • 0.0016-0.034 X 10M Q  20-340K Q • Efficiency 3 % 600-10000 • Branching Ratio 50% 300-5000 • B R 50 % from K0s  150-2500 • Background pairs per event in the mass range of Q is 0.001 • 0.001 X 10 Million  10000 • s = Signal/ √(2X Background +Signal) 1-16 Clear signals of X and S(1385) have been observed in all three systems. X shares the same decay channel with S(1385) so does S5, one of the non exotic members of the antidecuplet. • SUMMARY AND FUTURE PLANS • Pentaquarks are observed in 6 different experiments. • Preliminary acceptance and efficiency studies show that we should be able to find pentaquarks at the few % level. Resonances can be clearly reconstructed via event mixing techniques in p-p, d-Au and Au-Au central collisions. Optimization of cuts to improve the signal over background is in progress. • Possibility of measuring the anti pentaquarks at RHIC (antibaryon/baryon~1). • Much more data from Run 4 which has just started !!! • Au+Au at √sNN=200 GeV 100 Million Events planned (70 times the Current Data). The significance will increase to 20-84 with the above estimations. First Look at the Invariant Mass Spectrum of Q  K0+ p : Signal ? Mixing Background After Background Subtraction REFERENCES 1) W. Liu, C.M. Ko, Phys. Rev. C68, 045203 (2003) 2) J.Letessier, G.Torrieri, S.Steinke and J.Rafelski, hep-ph/0310188 3)Jorgen Randrup, nucl-th/0307042 4) D. Diakonov, V. Petrov, and M. Ployakov, Z. Phys. A 359, 305 (1997) More studies needed. No strong signal yet. Signal to background depends highly on the selection of events and applied cuts. To improve cuts and understand the decay mechanism we can do simulation studies. 5)R. Jaffe and F.Wilczek, hep-ph/0307341 6) T. Nakano et al., AAPPS Bull.13:2-6,2003 7) V.V. Barmin et al, hep-ex/0304040