Supriya Das SQM 2006, 26th March 2006, UCLA 1 Event By Event Fluctuation in K/  ratio atRHIC Supriya Das § VECC, Kolkata (for STAR Collaboration) § Present address: GSI, Darmstadt

Supriya Das SQM 2006, 26th March 2006, UCLA 2 Statistical fluctuations: Statistical fluctuations: Arise due to the measurement process itself such as finite number statistics Arise due to the measurement process itself such as finite number statistics Dynamical fluctuations : Reflect the dynamics and responses of the system (density fluctuations etc.) (density fluctuations etc.)Motivation Why K/  ? K/  ratio shows interesting behavior as function of collision energy. It would be interesting to see what happens to the fluctuation of the ratio.

Supriya Das SQM 2006, 26th March 2006, UCLA 3 Search for QCD Phase Transition The production of strangeness may be related to the onset of deconfinement Excitation function of / shows structure around s NN 1/2 = 7 GeV The excitation function of / is smooth C. Blume (NA49), hep-ph/

Supriya Das SQM 2006, 26th March 2006, UCLA 4 Fluctuations in / Fluctuations in / Event-by-event fluctuations in / may give insight into the production mechanism of K’s NA49 measured dynamical fluctuation in K/  ratio by comparing the width of distributions from data and mixed events Pb+Pb at 158 A GeV (top 5% central) S. V. Afanasiev et al. for NA 49 Collaboration PRL 86 (2001)  mixed  width of K/  distribution for mixed events  data  width of K/  distribution for data K  number of K   K  per event   number of      per event

Supriya Das SQM 2006, 26th March 2006, UCLA 5 Fluctuations in / Fluctuations in / NA49 has also measured the fluctuation of / as a function of incident energy for central Pb+Pb collisions from 6 to 17 GeV using the observable  dyn C. Roland QM 2004

Supriya Das SQM 2006, 26th March 2006, UCLA 6 RHIC BRAHMS PHOBOS PHENIX STAR AGS TANDEMS 1 km v =  c = 186,000 miles/sec Relativistic Heavy Ion Collider

Supriya Das SQM 2006, 26th March 2006, UCLA 7 Tracking Detectors: TPC, FTPC, SVT Calorimeters: BEMC, EEMC, ZDC Trigger Detectors: CTB, BBC, MWPC Photon Detector: PMD Others: TOF, FPD Goal : to track all the hadrons (and photons) in each collision Solenoidal Tracker At RHIC

Supriya Das SQM 2006, 26th March 2006, UCLA 8  Large acceptance detector ( 2 units of  with full  symmetry)  Good K to  separation (for a wide momentum range) from Time Projection Chamber M. Anderson et al. for STAR Collaboration, NIMA499 (2003) Potential at STAR

Supriya Das SQM 2006, 26th March 2006, UCLA 9 Analysis MethodI Analysis Method I  dyn  Kaons and Pions are counted event by event and the ratio is plotted for a large number of events.  Same ratio is calculated from mixed events and distribution of that is obtained.  Width of the distribution (  ) is the measure of fluctuation  Dynamical fluctuation,  dyn is calculated as  dyn =  (  data 2 –  mixed 2 ) Statistical fluctuation

Supriya Das SQM 2006, 26th March 2006, UCLA 10 Phase space distributions of identified K and 

Supriya Das SQM 2006, 26th March 2006, UCLA 11 Analysis Method I (contd…) Mixed Event : To get the measure of the statistical fluctuation from  Finite number statistics  Experimental resolution  Correlations if any  Mixed track pool constructed by randomly picking up one track from each event.  Same cuts applied on the mixed tracks before applying the particle identification.

Supriya Das SQM 2006, 26th March 2006, UCLA 12  dyn K  for different center of momentum energies [ Data not corrected for efficiency]

Supriya Das SQM 2006, 26th March 2006, UCLA 13 Excitation Function for  dyn We extracted  dyn for Au+Au, 0 - 5% most central, for 20, 62, 130, and 200 GeV and compared the results with the NA49-SPS results Possibilities  Related to K + /  + horn  Increase of resonances decaying into K +  with increasing incident energy  Dilution of correlations as multiplicity increases with energy Statistical errors only

Supriya Das SQM 2006, 26th March 2006, UCLA 14 Better Measure The use of  dyn is problematic because it involves event-by- event fluctuations of a ratio A better measure is dyn,K   Insensitive to efficiency  Properly deals with small multiplicities  Centrality studies We will use dyn,K  for our systematic studies of K/  fluctuations First proposed by Pruneau, Gavin and Voloshin PRC 66 (2002) Used in STAR Net Charge fluctuation paper – PRC 68 (2003)

Supriya Das SQM 2006, 26th March 2006, UCLA 15 Based on multiplicity of charged particles in the STAR TPC (|  |<0.5) Determination of collision centrality

Supriya Das SQM 2006, 26th March 2006, UCLA 16 Centrality dependence of dynamical fluctuation for different collision energies

Supriya DasSQM 2006, 26th March 2006, UCLA17 ConclusionsConclusions  Excitation function of  dyn remains flat at RHIC energies.  Study of the excitation function and centrality dependence of K/  fluctuations requires a robust variable like dyn,K .  dyn,K  is positive and it decreases with increasing centrality of collisions for 62 and 200 GeV centre of mass energies.

Supriya Das SQM 2006, 26th March 2006, UCLA 18 STAR ~500 Collaborators STAR Collaboration