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Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 11
Event By Event FluctuationEvent By Event Fluctuation in in K/K/ ratio ratio
at at RHICRHIC
Supriya Das §
VECC, Kolkata(for STAR Collaboration)
§ Present address: GSI, Darmstadt
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 22
Statistical fluctuations:Statistical fluctuations: Arise due to the measurement process itself Arise due to the measurement process itself
such as finite number statisticssuch as finite number statistics
Dynamical fluctuationsDynamical fluctuations::
Reflect the dynamics and responses of the system Reflect the dynamics and responses of the system (density fluctuations etc.)(density fluctuations etc.)
MotivationMotivation
Why K/ ?
• K/ ratio shows interestingbehavior as function of collision energy.• It would be interesting tosee what happens to the fluctuation of the ratio.
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 33
Search for QCD Phase TransitionSearch for QCD Phase TransitionSearch for QCD Phase TransitionSearch for QCD Phase Transition
The production of The production of strangeness may be strangeness may be
related to the onset of related to the onset of deconfinementdeconfinement
Excitation function of Excitation function of <K<K++>/<>/<++> shows > shows
structure around sstructure around sNNNN1/21/2
= 7 GeV= 7 GeV
The excitation function of The excitation function of <K<K-->/<>/<--> is smooth> is smooth C. Blume (NA49), hep-ph/0505137
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 44
Fluctuations in <K>/<Fluctuations in <K>/<> > Fluctuations in <K>/<Fluctuations in <K>/<> >
Event-by-event fluctuations in <K>/<Event-by-event fluctuations in <K>/<> > may give insight into the production may give insight into the production
mechanism of K’smechanism of K’s
NA49 measured dynamical fluctuation in NA49 measured dynamical fluctuation in K/K/ ratio by comparing the width of ratio by comparing the width of
distributions from data and mixed eventsdistributions from data and mixed events
σ dyn = σ data2 − σ mixed
2
Pb+Pb at 158 A GeV (top 5% central)
S. V. Afanasiev et al. for NA 49 Collaboration PRL 86 (2001)σmixed width of K / distribution for mixed events
σdata width of K / distribution for data
K number of K K
per event
number of per event
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 55
Fluctuations in <K>/<Fluctuations in <K>/<> > Fluctuations in <K>/<Fluctuations in <K>/<> >
NA49 has also measured theNA49 has also measured thefluctuation of <K>/<fluctuation of <K>/<>>as a function of incidentas a function of incidentenergy for central Pb+Pbenergy for central Pb+Pbcollisions from 6 to 17collisions from 6 to 17GeV using the observable GeV using the observable σσdyndyn
C. Roland QM 2004
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 66
RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
1 km
v = 0.99995c = 186,000 miles/sec
RRelativisticelativistic HHeavyeavy IIonon CColliderollider
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 77
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
SSolenoidalolenoidal TTrackerracker AAtt RRHICHIC SSolenoidalolenoidal TTrackerracker AAtt RRHICHIC
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 88
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 STARPotential at STARPotential at STARPotential at STAR
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 99
Analysis MethodAnalysis Method IIσdyn
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 (σ) is the measure of fluctuation Dynamical fluctuation, σdyn is calculated as
σdyn = (σdata2 –σmixed
2)
Statistical fluctuation
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1010
Phase space distributions of identified K and Phase space distributions of identified K and
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1111
Analysis Method I (contd…)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 DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1212
σσdyndyn KK for different center of for different center of
momentum energiesmomentum energies
[ Data not corrected for efficiency]
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1313
ExcitationExcitation Function for Function for σσdyndynExcitationExcitation Function for Function for σσdyndyn
We extracted We extracted σσdyndyn for Au+Au, 0 - 5% most central, for 20, 62, for Au+Au, 0 - 5% most central, for 20, 62,
130, and 200 GeV and compared the results with the NA49-130, and 200 GeV and compared the results with the NA49-SPS results SPS results
PossibilitiesPossibilities
Related to KRelated to K++//++ horn horn Increase of resonances Increase of resonances
decaying intodecaying intoK + K + with increasing with increasing incident energyincident energy
Dilution of correlations as Dilution of correlations as multiplicity increases with multiplicity increases with
energyenergyStatistical errors only
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1414
Better MeasureBetter MeasureBetter MeasureBetter MeasureThe use of The use of σσdyndyn is problematic because it involves event-by- is problematic because it involves event-by-
event fluctuations of a ratioevent fluctuations of a ratio
A better measure is A better measure is dyn,Kdyn,K
Insensitive to efficiencyInsensitive to efficiency Properly deals with small multiplicitiesProperly deals with small multiplicities Centrality studiesCentrality studies
We will use We will use dyn,Kdyn,K for our systematic studies of K/ for our systematic studies of K/ fluctuations fluctuations
dyn,Kπ =NK NK −1( )
NK
2 +Nπ Nπ −1( )
Nπ
2 − 2NK Nπ
NK Nπ
First proposed by First proposed by Pruneau, Gavin and VoloshinPruneau, Gavin and Voloshin PRC 66 (2002) PRC 66 (2002)Used in Used in STAR Net Charge fluctuation paperSTAR Net Charge fluctuation paper – PRC 68 (2003) – PRC 68 (2003)
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1515
Based on multiplicity of charged particles in the STAR TPC (||<0.5)
Determination of collision centralityDetermination of collision centrality
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1616
Centrality dependence of dynamical Centrality dependence of dynamical fluctuation for different collision energiesfluctuation for different collision energies
Supriya DasSupriya Das SQM 2006 , 26th March 2006, UCLASQM 2006 , 26th March 2006, UCLA 1717
ConclusionsConclusionsConclusionsConclusions
Excitation function of Excitation function of σσdyndyn remains flat at RHIC remains flat at RHIC
energies.energies.
Study of the excitation function and centrality Study of the excitation function and centrality dependence of K/dependence of K/ fluctuations requires a robust fluctuations requires a robust variable like variable like dyn,Kdyn,K . .
dyn,Kdyn,K is positive and it decreases with increasing is positive and it decreases with increasing
centrality of collisions for 62 and 200 GeV centre centrality of collisions for 62 and 200 GeV centre of mass energies.of mass energies.