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RHIC as an Exotic Particle Factory

RHIC as an Exotic Particle Factory. Huan Z. Huang Department of Physics and Astronomy University of California, Los Angeles. ATHIC-Seoul; June 29-July 1, 2006. Outline. The Evidence for Pentaquarks Is Disappearing Pentaquark Searches in STAR and the Puzzle Continues

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RHIC as an Exotic Particle Factory

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  1. RHIC as an Exotic Particle Factory Huan Z. Huang Department of Physics and Astronomy University of California, Los Angeles ATHIC-Seoul; June 29-July 1, 2006

  2. Outline • The Evidence for Pentaquarks Is Disappearing • Pentaquark Searches in STAR and the Puzzle Continues • RHIC as an Exotic Particle Factory

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

  4. 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

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

  6. 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 T. Nakano –SQM06

  7. K－p missing mass spectrum in g d  L(1520) KN LEPS result -- T. Nakano-SQM06 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.

  8. RHIC – Exotic Particle Factory • RHIC – Dense Partonic Matter and • Rapid Hadronization • Unique Collision Environment for Possible Exotic Particles Formation • Exotic Mesons, Pentaquarks, Di-baryons [WW] and Strangelets

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

  10. 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 (~8 M, Z<75cm) d + Au 200 GeV run 3 (18.4 M) Au + Au 63 GeV run 4 (5.1 M) Cu + Cu 63 GeV run 5 (15.6 M)

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

  12. pK+ and pK- from 18.4 M d+Au at 200 GeV Background – Combinatorial and Correlated Pairs dAu results M (GeV/c2)

  13. dAu results PeaK?! Understand the Background!

  14. 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

  15. D++p+p and using p as K Q p  K Q D D

  16. 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 previous • observations 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 (8M) data and Au+Au at • 200 GeV (~10M). • What do these null observations mean? • Observation of signal depends on a combination of • signal strength and combinatorial background level

  17. A Bold Speculation If STAR observation is true: Quantum Number of the pentaquark state I = 1, s=3/2, parity – Formation cannot be from pK+ coalescence - repulsive interaction ! Possible formation from DK coalescence - attractive interaction - NpK mass ~ 1570 MeV Consequences: Unlikely pentaquarks from e+p scatterings possible e+A through secondary interactions p+A or d+A favored and yield is small

  18. PRL 92 (2004) 052302; PRL 91 (2003) 182301 Hadronization of Bulk Partonic Matter At hadron formation time there is a collective v2 among constituent quarks Recombination/coalescence provides a hadronization scheme (not necessarily related to partonic matter, works for d+Au) Possible geometrical nature of v2 saturation – surface emission

  19. 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 !

  20. The Future is Bright 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

  21. Exotic Particle Factory 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)

  22. The End

  23. 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% !

  24. +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?

  25. Many Experiments Confirm Q+ *Gaussian statistical significance: estimated background fluctuation

  26. 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

  27. How Significant Is the STAR Result? STAR d+Au 2902 211200 6.3 5.0 STAR Au+Au A. Dzierba et al. hep-ex/0412077

  28. D. Diakonov et al. (chiral quark soliton) Naive quark model S. Capstick et al. (isotensor formulation) Fl. Stancu, D.O. Riska (qq with p int.) A. Hosaka (chiral potential) M. Karliner et al.(qq-qqq) R. L. Jaffe et al. (qq-qq-q : 10 + 8) J. Sugiyama et al. (QCD sum rule) F. Csikor et al. (Lattice QCD) S. Sasaki (Lattice QCD) : 1/2+, I=0 : 1/2- : 1/2-, 3/2-, 5/2-, I=2 : 1/2+ : 1/2+ (strong p) : 1/2+, I=0 : 1/2+, I=0 : 1/2-, I=0 : 1/2+->1/2-, I=0 : 1/2-, I=0 Some Theory publications since 2003 ( Mass, width, Spin, Parity, Production mechanism, Partners… Q++implies I=1 and possibly invalids all these models ! Ohashi/Spring-8

  29. Pentaquark or Molecule? If q state has isospin I = 1, there will be q0 n + KS Critical confirmation for I = 1 !! The structure of the q  NpK or DK molecule state cannot be ruled out ! A critical test of experimental sensitivity is the production of deuterons  how many (anti-)deuterons have been seen in CDF and e+e collisions?

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