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

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

RHIC – Exotic Particle Factory RHIC – Dense Partonic Matter and Rapid Hadronization  Unique Collision Environment for Possible Exotic Particles Formation  Exotic Mesons, Pentaquarks, Di-baryons [  and Strangelets

Formation of Dense Matter at RHIC 1)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

Empirical Quark Scaling in R AA and v 2 STAR PHENIX Baryon Meson Constituent (n) Quark Scaling -- Meson n=2 and Baryon n=3 grouping Saturation of v 2 at Intermediate p T Very different from fragmentation formation scheme !!

Hadronization of Bulk Partonic Matter PRL 92 (2004) ; PRL 91 (2003) At hadron formation time there is a collective v 2 among constituent quarks Recombination/coalescence provides a hadronization scheme (not necessarily related to partonic matter, works for d+Au) Possible geometrical nature of v 2 saturation – surface emission

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

Au + Au Collisions at RHICSTAR Central Event (real-time Level 3)

STAR Pentaquark Searches  +  p + K S  ++  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)

Particle identification Particle Identification: dE/dx from TPC

dAu results M (GeV/c 2 ) pK + and pK - from 18.4 M d+Au at 200 GeV Background – Combinatorial and Correlated Pairs

dAu results Understand the Background! PeaK?!

dAu results The invariant mass distribution is fitted to a Gaussian plus a linear function. A sigma signal is seen Measured mass is about 1.53 GeV/c 2. Full width is about 15 MeV

Possible Sources of Background Double Conversion of  0 photons  0    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  K +  p     These background sources contribute to the residuals in the event-mixing. But they do not produce a narrow peak !

 ++   +p and using  as K       K

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

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

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

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

Spectrum? Spectrum includes  ++ and  -- Mt-exponential fit yields: dN/dy = T = MeV Yields for some particles in dAu Ks: L+Lbar: Xi+Xibar: Phi: After acceptance and efficiency correction Assuming 100% branching ratio  ++ /  ~ 2%

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

A Stringent Limit from HERA-B HERA-B hep-ex/ sqrt(s)42 GeV pA (C,Ti,W)200 M inelastic events  + /  <0.92%; 95%CL  + /  (1520)<2.7%; 95% CL Our Estimate in STAR d+Ausqrt(s) 200 GeV   /  ~ 0.35% Does this imply  (1520)/  ~ 34%? STAR  (1520)/  ~ 10% !

The Puzzle Continues 1)If pK + peak at 1530 MeV/c 2 is a real pentaquark, then I = 1 likely, there must be a  +. But the recent JLab null result on  + casts serious doubt on the observation of  +. 2)The STAR observed yield is so small such that many experiments would not have the sensitivity to see it. 3)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)?

STAR – Exciting Physics Program A full TOF and Heavy Flavor Tracker upgrade will greatly enhance STAR’s capability !! RHIC – Exotic Particle Factory 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

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

The End