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Measurement of Correlation and Fluctuations Between Photons and Charged Particles at RHIC

This study investigates the correlation and fluctuations between photons and charged particles at forward rapidity in AuAu and CuCu collisions at RHIC. The analysis methods include measuring the width and total correlated fluctuations, and the results show approximate 1/Npart scaling and a positive correlation dynamics. There is no abnormal correlation or dependence on charged particle transverse momentum, suggesting no abnormal fluctuations induced by Disoriented Chiral Condensates (DCC).

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Measurement of Correlation and Fluctuations Between Photons and Charged Particles at RHIC

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  1. STAR’s measurement of correlation and fluctuations between photons and charged particles at forward rapidity at RHIC Sunil M. Dogra University of Jammu, India (For the STAR collaboration)‏ Outline Motivation STAR Experiment Analysis Method Results Summary

  2. Motivation • Inclusive photons provide the information of production of  • Chiral symmetry restoration could be reflected via study of Photon-Charged particles Fluctuations. • Formation of Disoriented Chiral Condensates (DCC) generate fluctuations between photons and charged particles. • DCC formationis expected to provide information on the vacuum structure of strong interaction and chiral phase transition. Anti-CENTAURO event of JACEE 36 photons, 1 charged particle

  3. STAR Experiment • Coverage: 2.3< | < 4.0 • Event-by-event number of charged particles • Spatial distribution (,)‏ and pT of charged particles Nucl.Instrum.Meth.A499:624-632,2003 Nucl.Instrum.Meth A 499, 713 (2003) Coverage: | < 1.5

  4. Nucl. Instrum. Meth. A 499, 751 (2003)‏ Photon Multiplicity Detector • Two planes CPV+Preshower • Gas detector of hexagonal cells • Cell cross section : 1.0 cm2 • Cell depth : 0.8 cm • Gas used: Ar+CO2 in 70:30 • Total number of cells : 82,944 • Area of the detector : 4.2 m2 • Distance from vertex : 540 cm • Coverage: -2.3 to -3.8 in with full

  5. Principle of Photon Multiplicity detector • Photons passing through the converter initiate an electro-magnetic shower and produce large signal on several cells of the sensitive volume of the detector. • Hadrons normally affect only one cell and produce a signal representing minimum ionizing particles.

  6. % Efficiency and Purity of Photon sample • Charged hadrons are • rejected by using • thresholds on strengths • and number of cells • on PMD clusters. • Raising thresholds on • cluster ADC increases • purity of photon samples. • This Analysis: • clusters with Ncells > 1 & Cluster ADC > 5*MIP • (Purity ~ 67%)‏

  7. Data Samples AuAu (200GeV) : 1.8 M events CuCu (200 GeV) : 320 K Event cuts: Zvertex <30 cm Photon samples (PMD): cluster ADC > 5 MIP No of cells > 1 Charged tracks (FTPC): dca < 2 cm, nHits > 5, 0.1< pT <3.0 GeV/c

  8. Charged Particles Photons Number of Events Cu+Cu 200 GeV Minbias Distribution -----Top 10% Minbias Distribution -----Top 10% Charged Particles Photons Number of Events Photon and Charged Particle Multiplicities(Uncorrected)‏ Au+Au 200 GeV

  9. Study of photon-charged particles fluctuations (Methods)‏ •  /Meanof ratio (measuring the width)‏ • dynamics(measure of total correlated fluctuations)‏

  10. Fluctuations in N / Nch ....a+1/Npart Measure of Fluctuations = 2 /Mean Error bars are Statistical Error bars are Statistical part 2 /Mean) scaled by Npart : almost constant with Npart (approximate 1/Npart scaling )‏

  11. Robust variable (almost independent of detector efficiency): (confirmed by Monte Carlo Toy Model)‏ • Zero for Poisson-ian fluctuation Photon – Charged Particle Fluctuations by dynamics dynamics = C. Pruneau et al. Phys. Rev. C 66, 044904(2004)‏ Nystrand et at. Phys. Rev. C 68, 034902(2003) Photon fluctuations Correlated fluctuations Charge fluctuations

  12. Three Terms in dynamics Individual fluctuations are larger than correlation making dynamics positive

  13. Effect of purity and efficiency variation Different cuts on photon samples: 3 MIP 4 MIP 5 MIP 6 MIP Independent of MIP cuts

  14. dynamics:Dependence of  Coverage dynamics similar at different  coverage (upstream material effect is small)‏

  15. Scaling of dynamics with Npart Observation: dynamics scaled by Npart : almost constant at lower Npart and increases at higher Npart

  16. B. Mohanty, J Serreau Phys. Reports 414(2005) 263-358 pT dependence of fluctuations • DCC particles are soft • Signals expected to • increase for lower pt • First time access to pT • dependence of charged • particles (absent in WA98)‏ χ

  17. dynamicswith pT cut of Charged Particles ....a+1/Npart Error bars are Statistical No pT dependence on dynamics Small or No DCC signal?

  18. Summary • Photon and Charged particle multiplicity correlations are studied for AuAu & CuCu at 200 GeV Collisions at forward rapidities. • Two Method used:  /Mean and dynamics •  /Mean of N/Nch shows approximate 1/Npart scaling • dynamics is positive (individual fluctuations > than correlated term)‏ • part *dynamics almost constant at lower Npart and increase for higher Npart • No pt dependence -> No abnormal correlations, induced by DCC • An analysis to determine sensitivity of dynamics for DCC is ongoing

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