Sevil Salur for STAR Collaboration, Yale University

WHAT IS A PENTAQUARK?WHAT IS A PENTAQUARK?

STAR at RHIC, BNL measures charged particles via Time Projection Chamber . Due to the very short lifetime of pentaquarks, topological analysis, which is used to analyze long lived particles such as s

and cannot be used. An alternative method is use a mixing technique which we use to identify resonances in STAR. In this technique, s

‘s are identified with topological analysis. The identifieds

are mixed with a p to get . The background is achieved by mixing p’s from one event with the s

candidates from another event.

Charged particles are identified by p and dE/dx information obtained by the TPC.

can be reconstructed in

this PT and y range

FEASIBILITY STUDIES WITH THE CURRENT DATAFEASIBILITY STUDIES WITH THE CURRENT DATA

THE ANALYSIS AND TECHNIQUESTHE ANALYSIS AND TECHNIQUESpreliminary

SUMMARY AND FUTURE PLANSSUMMARY AND FUTURE PLANS

•Pentaquarks are observed in 6 different experiments.

•Preliminary acceptance and efficiency studies show that we should be able to find pentaquarks at the few % level. Resonances can be clearly reconstructed via event mixing techniques in p-p, d-Au and Au-Au central collisions. Optimization of cuts to improve the signal over background is in progress.

•Possibility of measuring the anti pentaquarks at RHIC (antibaryon/baryon~1).

•Much more data from Run 4 which has just started !!!

Au+Au at √sNN=200 GeV 100 Million Events planned (70 times the Current Data). The significance will increase to 20-84 with the above estimations.

preliminary p+p

DpK

e

s’s are identified by the decay

topology technique due to their relatively long lifetime.

• Preliminary dN/dy in p+p of (1520) 0.004 per event • 8 Million X 0.004 32 K(1520)• 0.1-1 X 32 K 3-32 K 0.5-1.5 X 1.5 Million 0.8-

2.3M• Efficiency 3% 90-960 25-70K• Branching Ratio 50% 45-480 10-25K• B R 50% from K0

s 22-240 5-18K

Background pairs per event in the mass range of is 0.0004 2• 0.0004 X 8 Million 3200 2 X 1.5 Million 3MSignificance = Signal/√(2 X Background+Signal)

0.25-3 2-7

WHICH PENTAQUARKS WE ARE LOOKING FORWHICH PENTAQUARKS WE ARE LOOKING FOR

STAR Time Projection Chamber (TPC)

+n+K+ No No id for n

++p+Kp+K00 YesYes

YesYes

No No id for n

No No id for 0

No No id for pGood opportunity to observe anti pentaquarks (antibaryon/baryon ~ 1 at RHIC)

pp YesYes

n No No id for n or

pp YesYes

YesYes

YesYes

pp YesYes

~0.5-1.5 per event for AuAu from theoretical prediction (1,2,3)

(1520)

p+p √s=200GeV

SIMULATION STUDIESSIMULATION STUDIES

Monte Carlo INPUT

One Monte Carlo Pentaquark with a full TPC simulation per event with a distribution of Tinv slope =250 MeV is embedded in real p+p events. Only 3% of these ’s could be reconstructed. The width and the mass remains consistent with the Monte Carlo input after the reconstruction. A similar Monte Carlo study yields a 5 acceptance of 2% for STAR.

Reconstruction OUTPUT

preliminary

Signal

Mixed Event Background

Signal after Background Subtraction

STAR Preliminary

p-p at s =200GeV

*± +*±

Significance =15±2

*± +*±

d-Au at sNN =200GeV

STAR PreliminarySignificance =60±4

*±

STAR Preliminary

Au-Au at sNN =200GeV

Significance =20±3

±

NE

ntri

es

Mixing Technique Works.Mixing Technique Works.

This technique has been successfully used in STAR to identify resonances such as K*, (1385), (1520), and (1530), etc… (See talk by Christina Markert (Friday Parallel 2: Strangeness Spectra) “Strange Baryon Resonance Production in p+p, d+Au and Au+Au Collisions at RHIC energies” and below …) (1385)as in the case of’s are identified by decay topology similarly to due to their long life time and ’s are identified by dE/dx information

Optimizing Momentum Cuts via Monte Carlo Tracks Optimizing Momentum Cuts via Monte Carlo Tracks

Upper and lower momentum cuts are applied in agreement with the momentum distributions of the decay particles of the Monte Carlo to maximize the signal over background.

Momentum distribution of the protons and kaons

decayed from Monte Carlo and in real events

Cou

nts

It is a five-quark system.

Chiral Soliton Model: Chiral dynamics generated narrow K+n resonance (partial motivation of experiments). Uncorrelated Quark Model: Q 4Q in the lowest orbital of a mean field. Bag, NRQM… Correlated Diquark Description: Quarks are correlated in an antisymmetric color, flavor and spin state.

C→(nK+) K−X

K+Xe→(pK0) X p→(nK+) K−d

p→(nK+) K0

d,Ne→(pK0) K0

e+d→(pK0) X

p+p→() XYZ…

d→(nK+) K−p

First Look at the Invariant Mass Spectrum of First Look at the Invariant Mass Spectrum of K K00+ p :+ p :

More studies needed. No strong signal yet. Signal to background depends highly on the selection of events and applied cuts. To improve cuts and understand the decay mechanism we can do simulation studies.

Clear signals of and(1385) have been observed in all three systems. shares the same decay channel with (1385) so does one of the non exotic members of the antidecuplet.

M inv (p+K0) [GeV/c2]M inv (p+K0) [GeV/c2]

Antidecuplet from

Chiral Soliton Model

Nen

trie

s

Nen

trie

sN

entr

ies

Cou

nts

p [GeV/c]

preliminaryp+p

Cou

nts

p [GeV/c]

Describing Pentaquarks with Describing Pentaquarks with Models:Models:

Minv [GeV/c2]Minv [GeV/c2]Minv [GeV/c2]

Star Preliminary d+Au Star Preliminary Au+AuStar Preliminary p+p

Cou

nts

?

Signal

Mixing Background

After Background Subtraction5) R. Jaffe and F.Wilczek, hep-ph/03073416) T. Nakano et al., AAPPS Bull.13:2-6,2003 7) V.V. Barmin et al, hep-ex/0304040

REFERENCESREFERENCES1) W. Liu, C.M. Ko, Phys. Rev. C68, 045203 (2003) 2) J.Letessier, G.Torrieri, S.Steinke and J.Rafelski, hep-ph/0310188 3) Jorgen Randrup, nucl-th/0307042 4) D. Diakonov, V. Petrov, and M. Ployakov, Z. Phys. A 359, 305 (1997)

We can repeat the same study for the d+Au collisions. To estimate the yield we assume Npart scaling. The number of participants in d+Au is 8 while in p+p it is 2 and in Au+Au it is 350 for most central collisions. The lower limit is obtained from p+p scaling while the upper limit is from Au+Au yield estimates.

Rapidity vs PT AcceptanceRapidity vs PT AcceptanceLeft plot shows the TPC acceptance which is defined as the ratio of that are possible to reconstruct compared to simulated input. Right plot shows the phase space population of the after reconstruction.

• 0.0016-0.034 X 10M • Efficiency 3 % 600-10000• Branching Ratio 50% 300-5000

• B R 50 % from K0s 150-2500

Background pairs per event in the mass range of is 0.001 • 0.001 X 10 Million 10000• Signal/ √(2X Background +Signal) 1-16

?