High Density Matter and

Searches for Exotics @RHIC

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 andRapid 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 pTjet correlations and the energy dissipation

in soft particle production

Empirical Quark Scaling in RAA and v2

STAR

PHENIX

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 !!

Hadronization of Bulk Partonic Matter

PR

L 92

(20

04

) 05

23

02

; PR

L 91

(20

03

) 18

23

01

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

Clustering and Surface Emission

Volcanic mediate pT – Spatter (clumps)

Enhancement of Clustersat intermediate pT !(baryons and hyperons)

Search for Multi-quark (>3) Cluster State at RHIC !

Au + Au Collisions at RHIC

STARSTAR

Central Event

(real-time Level 3)

STAR Pentaquark Searches

+ p + KS

++ 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/c2)

pK+ and pK- from 18.4 M d+Au at 200 GeVBackground – 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 3.5-5.0 sigma signal is seen Measured mass is about 1.53 GeV/c2. 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 = 0.0012 +- 0.0006T = 315 +- 30 MeV

Yields for some particles in dAuKs: 0.321 +- 0.006 +- 0.03L+Lbar: 0.339 +- 0.007Xi+Xibar: 0.0251 +- 0.0006Phi: 0.0642

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 --/++ = 0.47 +- 0.2

++ --

++ plus --

A Stringent Limit from HERA-B

HERA-B hep-ex/0408048sqrt(s) 42 GeVpA (C,Ti,W) 200 M inelastic events+/ <0.92%; 95%CL+/(1520) <2.7%; 95% CL

Our Estimate in STARd+Au sqrt(s) 200 GeV/ ~ 0.35%

Does this imply (1520)/ ~ 34%?

STAR(1520)/ ~ 10% !

The Puzzle Continues1) If pK+ peak at 1530 MeV/c2 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 significantpeak 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 TrackerUsing 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

pppA

AA

Exotic

RHIC – Dedicated QCD Machine & Beyond

(spin) (CGC,EMC)

(Deconfinement Phase Transition)

The End