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RHIC As an Exotic Particle Factory -- Recent Result on Pentaquark Searches

RHIC As an Exotic Particle Factory -- Recent Result on Pentaquark Searches. Huan Z. Huang Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University. QCD Structure of Hadrons.

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RHIC As an Exotic Particle Factory -- Recent Result on Pentaquark Searches

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  1. RHIC As an Exotic Particle Factory -- Recent Result on Pentaquark Searches Huan Z. Huang Department of Physics and Astronomy University of California, Los Angeles Department of Engineering Physics Tsinghua University

  2. QCD Structure of Hadrons Confinement – Hadrons must be color singlet ! Existing Hadrons: meson – quark and anti-quark pair Baryon – three quark system q q q q q Color Configuration

  3. ggg – Glue Ball • qqQQ – Tetra-quark • qqqqQ – Penta-quark • qqqqqq – Di-baryons: H(uuddss), di-W (ssssss) • Strange Quark Matter QCD Allowed State

  4. Artist’s View of Proton and Glueball proton glueball

  5. Not Easy to Identify Glueball • We do not know the mass precisely • probably ~ 1.5-2.5 GeV/c2 • 2) The width is probably wide • Buried in many normal quark resonance states • in the same mass region !

  6. H0(uuddss) Detection H0  pS- p n p-

  7. Strange Quark Matter Stability Stable SQM -- Ground State of QCD > 1116 MeV unstable Stability M/Baryon [940,1116] MeV Weak <940 MeV Stable { Witten, Phys. Rev. D30, 272 (1984) E. Farhi and R.L. Jaffe, Phys. Rev. D30, 2379. Theoretical Prediction of Stable Particles Often not Reliable -- Particle Mass ~ a few 1000 MeV -- Binding Energy a few MeV (deuteron) No QCD or Phenomenological calculation has better than 1% accuracy !

  8. Stable (ct>50 ns) strange quark matter has not been detected at the level ~10-9 per central Au+Pb collisions ! E886 E878 E864 Final

  9. Q+ Exotic Baryon D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305. • Exotic: S=+1 • Low mass: 1530 MeV • Narrow width: ~ 15 MeV • Jp=1/2+ Isospin = 0 M = [1890-180*Y] MeV

  10. Q+ Spring-8 Result M = 1.540.01 GeV G < 25 MeV Gaussian significance 4.6s Q+ • + d  K- K+ n p Cuts: no fK+K- no recoil p (gn only) Missing mass for n PRL 91, 012002 (2003)

  11. CLAS/JLAB Results g d → p K+ K-n g p → n K+ K- p+ • M = 15425 MeV • < 21 MeV 5.2 s • M = 155510 MeV • < 26 MeV 7.8 s Phys. Rev. Lett. 92, (2004) 032001 Phys.Rev.Lett.91, (2003) 252001

  12. Many Experiments Confirm Q+

  13. CDF p + p Very High Energy HERA-B p + A sqrt(s) 42 GeV BES BaBar e+ + e- collisions ALEPH DELPHI Many Experiments with Null Results Noticeably (biased list)

  14. Q+ Possible Q+ Photo-Production Reactions CLAS/JLAB LEPS/SPring-8 Q+ Exclusive Channels ! Not Solid Physical Picture!

  15. CLAS Recent Null Results on Pentaquark Searches gdLnK+ gppK+K- Pentaquark production in these EXCLUSIVE channels at JLab Kinematics is NOT favored !!

  16. Evidence for + Is Disappearing LEPS-d2 CLAS-d2 CLAS-d1 LEPS-d LEPS-C CLAS g11 SAPHIR CLAS-p BELLE DIANA BaBar ZEUS nBC Hermes SPHINX JINR SVD2 HyperCP SVD2 ALEPH, Z COSY-TOF HERA-B BES J,Y CDF FOCUS WA89 2002200320042005 • Over ten experiments reported positive evidence initially • Since the mid of 2003, null results dominate • Two dedicated high statistic experiments reported null results, and contradicts with previous positive observations from the same collaboration (CLAS@JLab) • NA49 X-- has never been confirmed by any experiment

  17. K－p missing mass spectrum – New LEPS ResultsT. Nakano @ SQM2006 Excesses are seen at 1.53 GeV and at 1.6 GeV above the background level. Q+ Counts/5 MeVC 1.53-GeV peak: ~ (in the 5 bin = 25 MeV) preliminary No visible signal in sidebands. preliminary Counts/5 MeV MMd(γ,K－p) GeV/c2 sideband L* MMd(γ,K－p) GeV/c2 sum Normalization of L* is obtained by fit in the region of MMd < 1.52 GeV.

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

  19. STAR Pentaquark Searches Q+  p + KS Q++  p + K+ Data Set: Au + Au 200 GeV run 2 (~1.7 M, 30-80%) p + p data 200 GeV run 2 (~6.5 M) 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%)

  20. Particle identification Particle Identification: dE/dx from TPC

  21. pK+ and pK- from 18.6 M d+Au at 200 GeV Background – Combinatorial and Correlated Pairs dAu results M (GeV/c2)

  22. dAu results PeaK?! Understand the Background!

  23. dAu results ? D++ 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

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

  25. 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

  26. 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 !

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

  28. D/N*(1535)decay and pK does not make the peak Kp Delta++ Mass Delta++ Mass N*(1535)pp wrong charge for q++!

  29. Other PID Cuts Kaon 0.2<p&pt<0.7, Proton 0.3<p&pt<1.0, no opening angle cut

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

  31. Can the Peak Be Real ??

  32. 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)

  33. 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)

  34. 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)

  35. Is There an Obvious Contradiction ? The signal is not significant in Au+Au systems ! d+Au is indeed a favored system: signal strength and combinatorial background !! RHIC should have another long d+Au run !!

  36. +KsP • dAu data, Ks was identified by topological method • The +is probably there, several reasons may be responsible for the less significant signal: • Smaller branching ratios • Half of the Ks will become KL • Efficiency for finding Ks at low pt is low • This year’s AuAu data may give us an answer?

  37. 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) !

  38. The Puzzle Continues • If pK+ peak at 1530 MeV/c2 is a real pentaquark, then • I = 1 likely, there must be a q+. But the recent JLab • null result on q+ casts serious doubt on the observation • of q+. • The STAR observed yield is so small such that many • experiments would not have the sensitivity to see it. • Within the STAR data we have not seen any significant • peak signal in p+p data and Au+Au at • 200 GeV and Cu+Cu 62 GeV. • What do these null observations mean? • Production dynamics or data set bias unknown to us? • What is so special about d+Au 200 GeV (18.6 M events)? • 4) Can the formation is such that photo-production is not favored?

  39. An Intriguing Production Mechanism • pK+ Interaction – Repulsive • DK+ Interaction – Attractive !! • DK Coalescence  Q  pK+ • (NpK = 1575 MeV; DK>NpK; but D is very wide !) • lifetime ~ 1 fm  not easy for the coalescence process • in e+e, photo-production and p+p collisions. • spin 3/2, parity -1; pK d-wave decay  narrow width p+A collisions favored !

  40. RHIC – Exotic Particle Factory • RHIC – Very Dense Partonic Matter and • Rapid Hadronization • -- Hadron Formation Through Parton • Clustering (coalescence/recomb.) • Unique Collision Environment for Possible Exotic Particles Formation • Exotic Mesons, Pentaquarks, Di-baryons [WW] and Strangelets

  41. Volcanic mediate pT – Spatter (clumps) Clustering and Surface Emission Enhancement of Clusters at intermediate pT ! (baryons and hyperons) Search for Multi-quark (>3) Cluster State at RHIC !

  42. RHIC – Exotic Particle Factory STAR – Exciting Physics Program A full TOF and Heavy Flavor Tracker upgrade will greatly enhance STAR’s capability !! Heavy Flavor Tracker Using Active Pixel Sensor two layers of thin silicon detector 1.5 cm and 4 cm radius Charmed Exotics?! Full Barrel TOF Using MRPC

  43. Exotic Particles Hadrons with internal structure beyond existing QCD qqq and q-qbar framework !! RHIC – Dedicated QCD Machine & Beyond Exotic (Deconfinement Phase Transition) AA AA pp pA pp pA (CGC,EMC) (spin)

  44. Potential exotic particles/phenomena: penta-quark states (uudds, uudds!) di-baryons H – (L-L, uuddss) [W-W] (ssssss) strange quark matter meta-stable Parity/CP odd vacuum bubbles disoriented chiral condensate …… Discoveries from Unexpected Areas?! RHIC -- Frontier for bulk partonic matter formation (quark clustering and rapid hadronization) -- Factory for exotic particles/phenomena

  45. The End

  46. Other PID Cuts Kaon 0.2<p&pt<0.8, Proton 0.3<p&pt<1.5, no opening angle cut

  47. Other PID Cuts Kaon 0.2<p&pt<0.8, Proton 0.3<p&pt<1.0, no opening angle cut

  48. Q++ L(1520) Is There an Obvious Contradiction ? The signal is not significant in Au+Au systems ! L(1520)pK- branching ratio ~ 22%, corrected for the ratio. d+Au is indeed a favored system: signal strength and combinatorial background !! RHIC should have another long d+Au run !!

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