# Presentation: 851314

**Pentaquark Search and**** ************* ****Results from STAR**** **

**What is************+ ****? Why************* ****?**
**How can we search for them at RHIC? **
**What did we learn so far? **
**What else can we do in the near future? **

***Sevil Salur   ***
***  ******Yale University      ***
***STAR Collaboration***

## What is a +? 

- Quark Content: u u d ds

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

**Observed Mass:**** ****~1540 MeV**
**Observed Decay Channels:****  ****p+K****0****  and n+K****+**
**Observed Width:**** ****<10 MeV **

- 

- +

- p

- K0s

- +

**Parity**

- +

- -

**Chiral Soliton Model**
**Correlated Quarks **

**Uncorrelated Quarks **

**K+N Quantum Numbers:**** ****Y = 2  I****3****=0**
**Not Yet Observed:****  ****p+K****+ ****partner ********  I=0**

**R. Jaffe and F.Wilczek, hep-ph/0307341**
**T. Nakano et al., AAPPS Bull.13:2-6,2003 **
**V.V. Barmin et al, hep-ex/0304040**
**C. Alt et al, hep-ex/0310014**** **

**Notes:**
5 hot quarks

## Theoretical Importance of Studying Resonances 

-  Large fraction of the decays occur inside the reaction zone

-  Possible change in the physical properties:
-                    width broadening
-                    mass shift
-                    change in pT spectra

- Due to the very short lifetime ( fireball ) of resonances:

-  Due to its strange quark content and high mass,*(1385) gives us information about strangeness production.

-  Determination of the hadronic expansion time between chemical and thermal freeze-out

## Particle Identification

***Particle Identification***

- NENTRIES

- Charged daughter particles are identified by dE/dx in the TPC.

- 

- Minv GeV/c2

- ’s and K0s are reconstructed by
- standard decay topology technique since they have a long lifetime
- ( c=7.89 cm and cKs=2.7 cm ).

- STAR preliminary

- 

- *(1385)

- momentum p [GeV/c]

**dE/dx**

**p**

**K**

****

******s****NN****=200 GeV p+p**

- K0s

******s****NN****=200 GeV  p+p**

- *-   M=1387±1 [MeV]   =39±2 [MeV]

- e

## Background Subtracted Invariant Mass Spectra

***Background Subtracted Invariant Mass Spectra***

- *±  +*±

- 

- *±  +*±

- 

**** Significance =**15**±**2*

**** Significance =**60**±**4*

**** Significance =**14**±**3*

- *±  +*±

- 

- 0-5%

**Mixed Event Technique  **
**Works for Resonances !**

- 

- *±  +*±

**** Significance =**13**±2*

- STAR Preliminary

- √sNN=62 GeV Au+Au Collisions

## Corrected PT Spectra  

***Corrected P******T ******Spectra****** ****** ***

- Exponential Fit Function :

**<p****T****>=1.21****±0.17 GeV/c T ****inv slope****= 420±84 MeV**

## Particle Mass vs <PT>    

***Particle Mass vs <P******T******>****    *

- Parameterization is from ISR data at  √s=25GeV (Not correct for heavy particles. )

- <pT> values merge for  Au+Au and p+p for heavier particles.

-  Are heavier particles produced in more violent p+p collisions?

## <pT > 

- UrQMD predicts more signal loss at low pT due to more rescattering than regeneration        <pT> is higher.

- There is no increase within the errors in * <pT> from p+p to Au+Au.

***<p******T ******>****** ***

- <pT> for K* shows different behavior than p,K, vs centrality.

- *(1385) measurement in different centralities is on the way...

*********

**p+p**

- K*

- Marcus Bleicher et al.
-  Phys. Lett. B530 (2002) 81-87.  .Phys.G30 (2004) 111.

## * Yields in p+p and Au+Au  

********** Yields in p+p and Au+Au****  *

- No enhancement or suppression within the errors...

- G. Torrieri and J. Rafelski, Phys. Lett. **B509** (2001) 239

- Comparison of two particle ratios without regeneration gives a  ~ 3 fm between chemical and thermal freezeout and T~ 150 MeV in thermal model.

- Thermal Model

## What about+ ?

-    Acceptance and efficiency corrected results are presented for the * pT spectra in p+p and the most central Au+Au collisions.
-      There is no strong increase of <pT> from p+p to 0-5 % Central Au+Au. No radial flow ?  Different production mechanisms (jets in p+p)?   <pT> values merge for  Au+Au and p+p for heavier particles.
- There is no suppression or enhancement in the ratios of */ in p+p and 0-5% Central Au+Au collisions within the errors.

**So far from****************...**

##  + Simulation  Studies 

-                                         Minv [GeV/c2]

- Reconstruction OUTPUT

- STAR Preliminary

- Signal

- Mixed Event Background

- Signal after Background Subtraction

- One MC + (Tinv slope =250 MeV ) is embedded in each real p+p event.
- Only 3% of these +’s were reconstructed after cuts.
- The width and the mass remain consistent with the MC input after the reconstruction.

- Monte Carlo INPUT

********* ******+****** Simulation  Studies ***

- (W=10 MeV )    (M=1.54 GeV/c2 )

- NEntries

## Feasibility Studies for  + with Current p+p Data

***Feasibility*** ***Studies for ************ ******+****** with Current p+p Data***

- Preliminary dN/dy
-              of (1520) in pp 0.004 per event
- 8 Million X 0.004          32 K(1520)
- 0.1-1 X 32 K  in pp     3-32 K
- Efficiency 3%                90-960
- Branching Ratio 50%    45-480
- B R 50 % from K0s         22-240
- Background pairs per event in the mass
- range of  is 0.0004.
- 0.0004 X 8 Million         3200
- = Signal/√(2 X Background+Signal)
-          		             0.25-3

- Assuming ~0.1-1 + per (1520) for p+p

- Minv [GeV/c2]

- Star Preliminary

- Counts

- ?

- Signal
- Mixed Event
- Background

- ?

-  **p+p** **at  ********s =200 GeV**

- 8 Million p+p Events

- Observation is consistent with simulation ! STILL LOOKING INTO OPTIMIZATION

## Outlook - v2  ?

- Nonaka et. al. Phys.Rev. C69 (2004) 031902

***Outlook - v******2******  ?***

- (1385) Flow Measurement with Run 4 !?

- Resonance contribution from
-  QGP hadronization
-  Coalescence in a hadron gas.

- How much final state hadron-hadron recombination ?

- The percentage of each v2  as a function of pT may answer ...
- But we need high statistics at high pT

## Conclusion & Near Future Plans

-  Resonances can be clearly reconstructed via event mixing techniques in all collision environments  with STAR at RHIC. There is no strong increase of <pT> from p+p to 0-5 % Central Au+Au.  No radial flow ?  Different production mechanisms (jets in p+p)?
-  There is no suppression or enhancement in the ratios of */ in p+p and 0-5% Central Au+Au collisions within the errors.
-  Preliminary acceptance and efficiency studies show that we should be  able to find (anti) pentaquarks at the few % level. (antibaryon/baryon~1)
-  No significant signal observed in d+Au and Au+Au Central collisions either.
-                                 Still Optimistically Looking !!!
-  Much more data is available from Run 4 !!!  Better centrality measurement for * and possible v2 measurement.
-  Au+Au at √sNN=200 GeV 50 Million Events taken. (35 times the current data). The significance will increase to  10 - 44 if the is produced with the predicted theoretical yields in RHIC and our acceptance.