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High-Density Matter at RHIC: Pentaquark Searches and Exotic Particles

Explore the unique collision environment at RHIC for exotic particle formation, including pentaquark searches and dense matter hadronization. Investigate empirical quark scaling and constituent quark collectivity. Uncover exotic mesons, di-baryons, and strangelets formation. Analyze multi-quark cluster states and the puzzle of observed null signals. Consider the impact of production dynamics and data set biases on observations. Learn about upcoming upgrades to STAR's capabilities for exciting physics programs.

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High-Density Matter at RHIC: Pentaquark Searches and Exotic Particles

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  1. High Density Matter and Searches for Exotics @RHIC Huan Z. Huang Department of Physics and Astronomy University of California, Los Angeles The STAR Collaboration

  2. Outline • High Density Matter and Its Hadronization at RHIC • Pentaquark Searches in STAR • The Puzzle Continues

  3. 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

  4. Formation of Dense Matter at RHIC • Suppression of high pT hadrons in • central Au+Au collisions • 2) Disappearance of back-to-back high pT • jet correlations and the energy dissipation • in soft particle production

  5. STAR PHENIX Empirical Quark Scaling in RAA and v2 Baryon Meson Constituent (n) Quark Scaling -- Meson n=2 and Baryon n=3 grouping Saturation of v2 at Intermediate pT Very different from fragmentation formation scheme !!

  6. 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

  7. 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 !

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

  9. 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)

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

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

  12. dAu results PeaK?! Understand the Background!

  13. 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

  14. 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 !

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

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

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

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

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

  20. 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%

  21. AuAu 62.4 GeV Results -- ++ ++ plus -- • A nice signal is also seen in AuAu 62.4 GeV data from 20-80% centrality bin, 5.1 M events. • --/++ = 0.47 +- 0.2

  22. 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% !

  23. 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 (8M) data and Au+Au at • 200 GeV (~10M). • What do these null observations mean? • Production dynamics or data set bias unknown to us? • What is so special about d+Au 200 GeV (18.4 M events) • and Au+Au 62.4 GeV (5.1 M events)?

  24. 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

  25. 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)

  26. The End

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