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Pentaquark Searches at the Relativistic Heavy Ion Collider

Pentaquark Searches at the Relativistic Heavy Ion Collider. Sonia Kabana University of Nantes and SUBATECH, Nantes, France. EINN 2005 Milos, Greece, 20 Sept. 2005. Outline. Introduction Pentaquark Searches in STAR theta++ Xi0/N0 theta+ Xi-- Pentaquark Searches in PHENIX

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Pentaquark Searches at the Relativistic Heavy Ion Collider

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  1. Pentaquark Searches at the Relativistic Heavy Ion Collider Sonia Kabana University of Nantes and SUBATECH, Nantes, France EINN 2005 Milos, Greece, 20 Sept. 2005

  2. Outline • Introduction • Pentaquark Searches in STAR theta++ Xi0/N0 theta+ Xi-- • Pentaquark Searches in PHENIX anti-theta- • Conclusions and outlook

  3. Introduction Relativistic Heavy Ion Collider at Brookhaven Lab: RHIC energy <= sqrt(s)=200 GeV per NN collisions Collisions studied: AuAu, pp, dAu, CuCu Four experiments: Phenix, Star, Phobos, Brahms Physics goals: -QCD phase transition at Tc 200 MeV new signature seen: jet quenching -Spin of the nucleon

  4. STAR PHENIX PRL 92 (2004) 052302; PRL 91 (2003) 182301 What is special about RHIC for exotic particle searches ? Measurements from Heavy Ion Collisions at SPS and RHIC suggest strongly that a new state of matter is formed in these collisions made by (100eds) of deconfined quarks and gluons STAR, PHENIX: Elliptic flow of hadrons scales with the nr of quarks --> Data suggest hadron formation through quark coalescence --> quark coalescence as new production mechanism opens up for multi-q/g states RHIC may be a unique source of multiquark and gluon states made by coalescence possibly out of a hadronizing QGP

  5. STAR STAR identification capabilities used in this study: TPC inside a magnet, dE/dx id, topological id for decays in the TPC STAR is able to detect many strange particles in large acceptance (full phi, =-1,1): , , 0s, , , (1530),(1520), K+- etc. Dedx plot One event p+p with a Xi or L embedded to illustrate the topological cuts

  6. STAR theta++/+, Xi-- Searches Xi-- -> pi- Xi- Q+  p + KS Q++  p + K+ H. Huang, Y. Ma, S. Salur, C. Markert Results shown in : J Ma, APS april 2005, H Huang Beijing june 2005, H Huang, DNP Hawai 19-25 Sept 2005 Data Set: Au + Au 200 GeV run 2 (~1.7 M, 30-80%) p + p data 200 GeV run 2 (~6.5 M, Z<75cm) d + Au 200 GeV run 3 (18.6 M) Au + Au 63 GeV run 4 (5.6 M) Cu + Cu 63 GeV run 5 (16.5 M) Au + Au 200 GeV Run 4 (10.7 M, 20-80%)

  7. pK+ and pK- from 18.6 M d+Au at 200 GeV dAu results M (GeV/c2)

  8. dAu results The invariant mass distribution is fitted to a Gaussian plus a linear function. A 3.5-5.0 sigma signal is seen Measured mass is about 1.53 GeV/c2. Full width is about 15 MeV

  9. D++p+p and using p as K Q p  K Q D Slope depends on the level of pion contamination (p cut) ! D

  10. Other PID Cuts Kaon 0.2<p&pt<0.7, Proton 0.3<p&pt<1.0

  11. AuAu 62.4 GeV Results • AuAu 62 GeV data • 20-80% centrality bin • 5.6 M events • Weak Signal (3sigma) if any Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5)

  12. AuAu 200 GeV Run 4 Results • Year 4 AuAu 200 GeV data • 20-80% centrality bin • 10.7 M events • No Significant Signal (2s) Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5)

  13. Cu+Cu 62.4 GeV Run 5 Data • Year 5 CuCu 62 GeV data • 0-70% centrality bin • 16.5 M events • No signal at all !! Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5)

  14. Is There an Obvious Contradiction ? The signal is not significant in Au+Au systems d+Au a favored system ?: signal strength and low combinatorial background --> RHIC should have another long d+Au run Q++ L(1520)

  15. A Stringent Limit from HERA-B HERA-B hep-ex/0408048 sqrt(s) 42 GeV pA (C,Ti,W) 200 M inelastic events q+/L <0.92%; 95%CL q+/L(1520) <2.7%; 95% CL Our Estimate in STAR d+Au sqrt(s) 200 GeV q++/L ~ 0.35% Does this imply L(1520)/L ~ 34%? STAR L(1520)/L ~ 10% (corrected for branching ratio) !

  16. Spectrum? After acceptance and efficiency correction Assuming 100% branching ratio Spectrum includes ++and -- Mt-exponential fit yields: dN/dy= 0.0012 +- 0.0006 T= 315 +- 30 MeV Yields for some particles in dAu Ks: 0.321 +- 0.006 +- 0.03 L+Lbar: 0.339 +- 0.007 Xi+Xibar: 0.0251 +- 0.0006 Phi: 0.0642 Q++/f ~ 2%

  17. Xi-- STAR searches Jingguo Ma, UCLA APS Meeting 05/01/2004 From 14,000 - STAR Preliminary Invariant Mass (GeV/c2) Invariant Mass (GeV/c2) From 11,600 + Invariant Mass (GeV/c2) Invariant Mass (GeV/c2) Data: dAu MinBias, 15M events. Black lines are from event mixing. Clear signals were seen for the (1530) particle. No signal for the -- has yet been seen.

  18. Sevil Salur, Yale Univ. APS Meeting 05/01/2004 STAR theta+ --> pK0s searches Star Preliminary p+p Counts 2 MeV bin size ? Signal Mixed Event Background ? Star Preliminary p+p Star Preliminary d+Au Minv [GeV/c2] Minv [GeV/c2]

  19. J Ma, APS april 2005 STAR Preliminary • dAu data, Ks0 was identified by topological method • There is some excess at invariant mass around 1540 MeV/c2, but it is not too significant statistically.

  20. STAR Xi0/N0 --> L K0s search S. Kabana, R. Witt, M. Heinz S. Kabana, 20th Winter Workshop on Nuclear Dynamics Jamaica, 15-20 March 2004

  21. Identification of  and K0s in the present study • Topological cuts: • - Search for   p - and K0s  + - decay pattern (V0, requiring sec. decay vertex) • - Distance of Closest Approach (DCA) between daughters < 0.8 cm • - DCA of V0 to primary vertex < 0.4 cm, V0 Decay Length > 6 cm • - DCA of V0 daughters to primary vertex > 1.3 cm (K0s), 1.0 cm p(), 2.5 cm () • Accept only unambiguous K0s and , namely satisfying only one hypothesis • Quality cuts: Nr. of hits(track) > 15 (out of max 45), Avoid same tracks used in both V0s STAR Au+Au coll. 200 GeV preliminary

  22. …..Identification of  and K0s in the present study • De/dx cuts: • De/dx(tracks) < 3  from expected De/dx • Momentum(proton) < 0.7 GeV, Momentum(pion) < 0.5 GeV • Data sample: • Au + Au collisions at s(NN)=200 GeV Trigger: minimum bias, 1.45 Million events • Require a defined primary vertex, with |Z| <25 cm • Mass range used around the mean to select K0s and : K0s: +-35 MeV, : +-10 MeV STAR Au+Au coll. 200 GeV preliminary

  23. Preliminary results of STAR pentaquark searches in the  K0s channel Observation of a possible narrow peak at 1734 MeV in  K0s inv.mass Au+Au min. bias (s)NN=200 GeV Cut out upper ~10% of (tot) to suppress background Region +- 3 MeV (~1.5 ) around maximum: S/(B)=30.6/ ( 35.4)= 5.15, S/(S+B)=3.77, Mass = 1733.6 +-0.5 MeV +-5 MeV (syst), < 4.6 +-2.4 MeV (Gauss,1 MeV bin) STAR Au+Au coll. 200 GeV preliminary Bin size 3 MeV Blue line: mixed event background Best Significance obtained in semiperipheral ev.: S/(B)=19.36/ (10.64)=5.93

  24. No cut on centrality STAR Au+Au coll. 200 GeV preliminary S/(B)=40.55/ (83.45)= 4.44

  25. (1232) p() pi-(K0s) + K0s(pi+ pi-) = 1232+497.67 = 1729.7 MeV • Could fake possibly a peak near 1734 MeV ? Note STAR syst. error ~ 5 MeV • - Difficult to result to a narrow peak ( width ~120 MeV) • -Test 1: Cut more on DCA(p,pi) to primary vertex  does not destroy the peak STAR Au+Au coll. 200 GeV preliminary Test 2: Cut Inv.Mass( p() pi-(K0s) ) out of  mass +- 30 MeV does not destroy the peak

  26. PHENIX pentaquark searches Phenix is the only experiment which could search up to now for the anti-theta- --> anti-n K- Decay channel, thanks to its ability to identify antineutrons in the electromagnetic calorimeter Antiparticle/particle ratios at RHIC are high: >=0.7

  27. Dch+PC1 K- PC2 EMC+PC3 Anti Pentaquarks in PHENIX SimulatedQ- K-+n Q+ K0+p Fairly hopeless due to small acceptance (three particles in small aperture) Q+ K++n Neutron difficult to identify in PHENIX But how about the Anti Particle? `n Q- K-+n Looks fairly straightforward: Search for a big cluster in the electromagnetic calorimeter caused by ann annihilation and combine it with a K-

  28. PHENIX anti-theta- --> K- anti-n identification capabilities C. Pinkenburg, QM2004 EMCal response for p and anti-p. The annihilation energy of anti-p leads to larger clusters, which is a signature also for anti-n identification. K identification up to p=1.5 GeV using TOF (EMCAL), momentum from central tracker

  29. 200 GeV p+p 200 GeV p+p n + - n + + Counts / bin No pT cut No pT cut • Same event • Mixed event • MinBias trigger - + 1.11.21.31.41.51.6 1.11.21.31.41.51.6 Invariant mass [GeV/c2] Marker : Data Dash line : MC + mass peak[GeV/c] mass from PDG - pT [GeV/c] Reliability of Anti-n Candidate • Invariant mass peak ofS • -(1189.4)n + - : R.R. 99.85%, c-= 2.396cm • +(1197.4)n + + : B.R. 48.31%, c+= 4.434cm • Mass shift due to no TOF calibration for n in EMCal is <~5% • Quick check by Monte-Carlo shows agreement with data

  30. C. Pinkenburg, QM2004 K+ anti-n inv. mass No signal seen in the channel K+ anti-n, in which no signal is expected.

  31. C. Pinkenburg, QM2004 K- anti-n inv. mass While a signal was visible near 1.53 GeV without a needed timing correction for the anti-n in EMCAL, after this correction was done the signal dissapeared. --> Anti-sigma- signal is 2 times larger without timing correction • No signal seen for anti-theta- --> K- anti-n with timing correction Remaining Mystery: why no signal in K+ anti-n without timing correction?

  32. dAu @ s=200GeV ~500*106 Events pp @ s=200GeV ~50*106 Events AuAu @ s=200GeV ~36*106 Events From rough simulations we estimate a 0.2% reconstruction efficiency for theQ- Data Sets C Pinkenburg RHIC AGS meeting may 2004

  33. Q-K- +n (pp) Statistically challenged analysis, So far no signal (we hope for the many pp events we are going to take in Run5) Courtesy of Hisayuki Tori

  34. Q-K- +n (AuAu) 30-50% Top 30% central 50-92% work-in-progress work-in-progress work-in-progress Small plots but trust me there is currently no signal either We now have 50 times more AuAu events from Run4! Masashi’s thermal model predicts Q-/S+~0.1 for central events (assuming J=1/2 for the Q-). Testing this should be within reach. Courtesy of Masashi Kaneta

  35. Future plans • We probably can reduce the background in our K-n invariant mass distribution • Improve the EMCal Hadron timing, that will hopefully bring the S masses closer to pdg • We can recover nearly a factor of 2 of Anti Neutrons by recovering broken upclusters • TheS look very promising, we can do upper limits on ratios since the p and K efficiencies are known and the difficult Anti Neutron efficiency drops out • 1.5*109 fresh AuAu Events @ s=200 are waiting for us

  36. Comment: Present limit of momentum of K- to enable TOF id and related pi contamination, allows for AntiSigma- detection, but is this good enough for a much rarer pentaquark signals ? --> Small searched signal implies need to reduce the background more than needed for detection usual hadrons (Lambdas, Sigmas..) --> Would be clearly of interest to select K- in the momentum region with the smallest possible contamination and look for pentaquarks with this sample !

  37. Conclusions and outlook • Heavy Ion collisions at RHIC may offer a unique opportunity to produce multi-q/g states through coalescence out of a QGP • - PHENIX: searches for anti-theta- --> K- anti-n • --> no signal found in dAu, pp anf AuAu collisions at sqrt(s)=200 GeV • --> studies with lower pi contamination important, higher stat AuAu to be analysed • STAR: - Peak seen in theta++ and theta-- channel in d+Au collisions at sqrt(s)=200 GeV consistent with detector resolution, and below UL of HERA for theta+ • - Low significance in Au+Au at 62 and 200 geV • - No peak seen in Cu+Cu 62 GeV

  38. Conclusions cont theta+ --> p K0s : No significant peak seen in pp, dAu and AuAu collisions --> Ongoing work N0/X0 --> LK0s : peak seen at m=1734 MeV, width consistent with the det. Resolution and S/sqrt(B)=5-6 in Au+Au collisions at 200 GeV Future plans for both Phenix and STAR include analysis of more data : 2004 AuAu 200 GeV 2005 Cu+Cu 62 and 200 GeV, pp at 200 GeV To search and confirm or reject the seen candidates: Theta++(1530) and N0/Xi0(1734) and search for anti-theta- , theta+ and Xi--

  39. --------- THE END

  40. STAR Au+Au Collisions at RHIC Central Event (real-time Level 3)

  41. Possible Sources of Background Double Conversion of p0 photons p0 gg  e+e- e+e- Same-sign e’s within the K and p bands mostly in the low mass region opening angle cut  very effective Associated production LK+ pp- + K+ These background sources contribute to the residuals in the event-mixing. But they do not produce a narrow peak !

  42. STAR theta_ --> K0s p searches in p+p, d+Au and Au+Au collisions at 200 GeV Sevil Salur Yale University Talk given in the APS meeting, Denver, 05/01/2004 and Poster presented in this meeting

  43. Sevil Salur, Yale Univ. APS Meeting 05/01/2004 Simulation Studies II Reconstruction OUTPUT Monte Carlo INPUT Signal Mixed Event Background Signal after Background Subtraction STAR Preliminary One MC Q+ (Tinv slope =250 MeV ) is embedded in each real p+p event. Only 3% of these Q+’s were reconstructed after cuts. The width and the mass remain consistent with the MC input after the reconstruction. (10 MeV ) (1.54 GeV/c2 )

  44. Simulation Studies Sevil Salur, Yale Univ. APS Meeting 05/01/2004 Q can be reconstructed in this PT and y range NEntries Momentum Distributions from Monte Carlo Q+ Identified from real events. NEntries Proton K0s Cuts to optimize signal over background PT [GeV/c] PT [GeV/c]

  45. Sevil Salur, Yale Univ. APS Meeting 05/01/2004 FeasibilityStudies with current Au+Au data W. Liu, C.M. Ko Phys.Rev.C68:045203,2003J.Letessier, G.Torrieri, S.Steinke and J.Rafelski hep-ph/0310188 Jorgen Randrup nucl-th/0307042 ~0.5-1.5  per event for AuAu • 0.5-1.5 X 1.5 Million  0.8-2.3 Million • Efficiency 3%  25-70 K • Branching Ratio 50%  10-35 K • BR 50% from K0 s  5-17K • Background pairs per event in the mass range of  is 2. • 2 X 1.5 Million  3 Million • Significance  = Signal/√(2 X Background+Signal) •  2-7

  46. Q++ and L(1520) Using the Same Analysis Procedure L(1520) Same charge Sign (SS) and Opposite Sign (OS) background different

  47. Background Shape Depends on Cuts M (GeV/c2) M (GeV/c2) K [0.2-0.6] GeV/c P [0.3-1.5] GeV/c K [0.2-0.6] GeV/c P [0.3-1.0] GeV/c

  48. Monte Carlo 1733   K0s STAR preliminary Momentum of K0s is lower than of  Suggests cut : mom(K0s) < ~1 GeV 1733  K0s generated (inv. Slope(mt)= 500 MeV) 1730  K0s in detector acceptance. Generated with: y=-1.5 to 1.5, inv. Slope(mt) = 250 MeV, width=1 MeV K0s 

  49. Can the Peak Be Real ??

  50. Other PID Cuts Kaon 0.2<p&pt<1.0, Proton 0.3<p&pt<1.5, no opening angle cut

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