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Rapidity dependence of azimuthal correlations for pp and dAu

Rapidity dependence of azimuthal correlations for pp and dAu. Xuan Li (Shandong Uni. &BNL) For the STAR Collaboration WWND 2011 (Winter Park). Outline. Motivation Background STAR forward-mid rapidity, forward-forward rapidity correlations.

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Rapidity dependence of azimuthal correlations for pp and dAu

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  1. Rapidity dependence of azimuthal correlations for pp and dAu Xuan Li (Shandong Uni. &BNL) For the STAR Collaboration WWND 2011 (Winter Park)

  2. Outline • Motivation • Background • STAR forward-mid rapidity, forward-forward rapidity correlations. • New results in pseudo-rapidity interval between 1 and 2. • Cluster finder introduction. • π0 candidates searching. • Preliminary correlation results. • Jet-like event correlations. • Conclusions & Outlook Xuan Li

  3. Motivation lepton quark • The nucleon gluon density at low x. Nucleon γ* gluon Proton gluon density Can’t increase indefinitely. Saturation? Rapid rise of the gluon density at low-x evident from F2(x)/lnQ2 at fixed x (Prytz relation) arxiv:hep-ph/0201195 The nucleon gluon density is known in the 0.0001<x<0.3. Rizvi E. Talk presented at the “International Euro Physics Conference on High Energy Physics”, July 2003 Xuan Li Fixed Target Experiments

  4. Gluon saturation is expected at low x How sharp is the transition? • Parton gas approach saturation through evolution. Parton saturation is expected at low x and low Q2. At a given x, nuclei (mass number A) gluon density ≈ A1/3 × nucleon gluon density, leading to the expectation Qs2≈A1/3 xβ. [hep-ph/0304189] Current fixed target data provides 0.02<x<0.3 range for nuclear gluon density. Xuan Li

  5. How to access low x gluon • Large rapidity inclusive p production (hp~4) • probes asymmetric partonic collisions. Mostly high-x valence quark + low-x gluon. • Forward inclusive production. Phys. Rev. Lett. 97.152302 pp data is in agreement with perturbative QCD. Suppression of forward inclusive particle in dAu data is better described in Color Glass Condensate (CGC) predictions . Xuan Li

  6. How to access low x gluon Inclusive production measures integral of broad x range. If we measure π0-π0, we can probe limited x range for gluon. • Inclusive π0 to correlated π0-π0. From inclusive π0 to π0-π0 Phys. Lett. B603 (2004) 173 Forward π0-forward π0 are more sensitive to low x gluon than inclusive production. Xuan Li

  7. How to measure the sensitivity • Effects on the azimuthal correlations from different parton distribution for 2->2. scattering. Near side peak Away side peak arXiv:hep-ex/1005.2378 The away side peak height is correlated with the parton density distribution. Xuan Li

  8. Back to back correlations • pQCD 22 process =back-to-back di-jet (Works well for p+p) • With high gluon density, 21 (or 2many) process = Mono-jet ? Kharzeev, Levin, McLerran  Nucl. Phys. A748 (2005) 627 CGC predicts suppression of back-to-back correlation. Xuan Li

  9. Color Glass Condensate (CGC) prediction • Test the phase boundary at fixed Q2. Fix PT , look through different x region K. Golec-Biernat, M. Wustoff, Phys. Rev. D 59, 014017 Fix Pt for π0 at forward rapidity, and vary the rapidity of the associated π0. Vary the Pt to study the boundary. Xuan Li

  10. STAR Detectors Proton (Deuteron) Proton (Gold) • The full view of STAR Forward Meson Spectrometer (FMS) East Beam Beam Counter (BBC) Endcap electro-magnetic calorimeter (EEMC) Barrel electro-magetic calorimeter (BEMC) Xuan Li

  11. STAR Detectors EEMC measuring range 1<η<2 Tower range Δϕ=0.1, Δη=0.057-0.099 • The detectors of STAR used for correlations. Front view of north half of FMS FMS measuring range 2.3<η<4. Δϕ=0.058, Δη=0.1 for large cells. BEMC measuring range -1<η<1. Tower range Δϕ=0.05, Δη=0.05. Nearly hermetic electro-magnetic calorimeters cover -1<η<4. Xuan Li

  12. Forward-mid rapidity correlation • Probe nuclei gluon density at 0.008 < x < 0.07 . PYTHIA simulation FMS-BEMC(TPC) correlation Triggering on the forward rapidity π0, the rapidity of the associated π0 is correlated with the xbj of the soft parton involved in the partonic scattering. Arxiv:hep-ex/0502040 Xuan Li

  13. Forward-mid rapidity correlation • FMS-BEMC(TPC) azimuthal correlation. • Back to back azimuthal correlation peak looks similar in pp and dAu data. • There is no dramatic broadening from pp to dAu. • Forward-mid rapidity correlations are not near the saturation region. PT(FMS)>2.5GeV/c 1.5GeV/c<PT(BEMC/TPC)<PT(FMS) arXiv: hep-ex/0907.3473 Xuan Li

  14. Forward-forward rapidity correlation • Probe gluon density at 0.0009 < x < 0.005. FMS-FMS correlation PYTHIA simulation • Look at forward-forward correlation to access lowest x region. Xuan Li

  15. Forward-forward rapidity correlation • FMS-FMS azimuthal correlation. • Similarity of near side peak in pp and dAu data. • There is significant broadening from pp to dAu in forward-forward rapidity azimuthal correlations in the away side peak. PP data dAu data arXiv:hep-ex/1005.2378 Xuan Li

  16. Forward-forward rapidity correlation PP data • Centrality cut on the dAu data. dAu centrality averaged • The suppression of the height of the away side peak in • the central dAu collisions suggests forward-forward correlations • at low x are consistent with gluon saturation in nuclei. • (2) The degree of broadening is consistent with multi-parton • scattering in central dAu collisions associated with saturation. dAu central dAu peripheral J.L. Albacete, C. Marquet arXiv:1005.4065 Xuan Li

  17. Forward-near forward rapidity correlation • Probe gluon density at intermediate region which is 0.003<x<0.02 . PYTHIA simulation FMS-EEMC correlation ? Xuan Li

  18. FMS π0 triggered event • Within the FMS high tower triggered data, selecting events where FMS di-photon invariant mass is less than 0.2GeV/c2 and Pt is larger than 2.5 GeV/c . pp data For example, the invariant mass of photon pair in the FMS. Arbitrary unit Xuan Li

  19. Introduction to cluster finder • BEMC (EEMC) geometry EEMC η range [1.08,2.0], BEMC η range [-1,1]. Use minimum bias cluster finder instead of constrained cluster finder to reproduce FMS-BEMC correlations. Then apply the same method to approach FMS-EEMC correlations. X(Y) Y Z X EEMC BEMC ϕ ϕ η η Xuan Li

  20. Event display • Run 8 pp FMS triggered data. Cluster is energy threshold bounded group of towers. The threshold for the BEMC tower is 70MeV, and for EEMC is 100MeV. Sorting the tower energy, then add the towers near the high tower to construct cluster. cluster cluster EEMC BEMC Xuan Li

  21. BEMC invariant mass with di-cluster • Take one cluster as photon candidate, then pair two clusters with energy ratio cuts. In addition to π0 selection cuts, we apply Pt cuts for example 1.5GeV/c<Pt<2.5GeV/c. π0 candidates Arbitrary unit Arbitrary unit There are π0 candidates in pp and dAu data. Xuan Li

  22. π0-π0 azimuthal correlation with new cluster finder (FMS-BEMC) • FMS photon pair Pt > 2.5GeV/c and mass<0.2 GeV/c2. BEMC di-cluster 1.5GeV/c < Pt < 2.5GeV/c and mass<0.2GeV/c2. The FMS-BEMC results with this cluster finder are consistent with preliminary results shown in arXiv: hep-ex/0907.3473 . Uncorrected Coincidence Probability (radian-1) Width 0.709± 0.019(stat.) Width 0.754 ± 0.024(stat.) FMS triggered pp data FMS triggered dAu data Xuan Li

  23. New Rapidity (1<η<2)EEMC di-cluster invariant mass • Take one cluster as photon candidate, then pair two clusters with energy ratio cuts. In addition to π0 selection cuts, we apply Pt cuts for example 1.5GeV/c<Pt<2.5GeV/c. π0 candidates Arbitrary unit Arbitrary unit There are π0 candidates in pp and dAu data. Xuan Li

  24. π0-π0 azimuthal correlation (FMS-EEMC) • FMS photon pair Pt > 2.5GeV/c and mass<0.2 GeV/c2. EEMC di-cluster 1.5GeV/c < Pt < 2.5GeV/c and mass<0.2GeV/c2. The π0 in EEMC require 2 clusters. Uncorrected Coincidence Probability (radian-1) Width 0.967 ± 0.120(stat.) Width 0.897 ± 0.060(stat.) FMS triggered pp data FMS triggered dAu data Xuan Li

  25. π0-π0 azimuthal correlation (FMS-EEMC) with lower pt cuts • FMS photon pair Pt > 2.0GeV/cand mass<0.2 GeV/c2. EEMC di-cluster 1.0GeV/c < Pt < 2.0GeV/c and mass<0.2GeV/c2. Uncorrected Coincidence Probability (radian-1) Width 1.032 ± 0.179(stat.) Width 0.833 ± 0.048(stat.) FMS triggered pp data(10%) FMS triggered dAu data(10%) Xuan Li

  26. Initial look at Jet-like events (super-cluster) in BEMC • How to get jet-like event • Use single cluster as seed, then find a cone with R ( )<0.5. • Require mass of ‘jet’ >0.2GeV/c2 to emphasize ‘jetty events’ . • Distance between jet center and seed less than 3cm to reduce bias effects . • The mass of the jet-like event with 1.5GeV/c<Pt<2.5GeV/c. Arbitrary unit pp Arbitrary unit dAu Xuan Li

  27. π0+jet-like azimuthal correlation (FMS-BEMC) • FMS photon pair Pt > 2.5GeV/c. BEMC jet-like candidate 1.5GeV/c < Pt < 2.5GeV/c. Uncorrected Coincidence Probability (radian-1) Width 0.761 ± 0.061(stat.) Width 0.832 ± 0.008(stat.) FMS triggered pp data FMS triggered dAu data No significant broadening in FMS-BEMC π0+jet-like correlations. Xuan Li

  28. Initial look at Jet-like events (super-cluster) in EEMC • How to get jet-like event • Use single cluster as seed, then find a cone with R ( )<0.5. • Require mass of ‘jet’ >0.2GeV/c2 to emphasize ‘jetty events’ . • Distance between jet center and seed less than 3cm to reduce bias effects . • The mass of the jet-like event with 1.5GeV/c<Pt<2.5GeV/c. Arbitrary unit Arbitrary unit pp dAu Xuan Li

  29. π0+jet-like azimuthal correlation (FMS-EEMC) • FMS photon pair Pt > 2.5GeV/c. EEMC jet-like candidate 1.5GeV/c < Pt < 2.5GeV/c. Uncorrected Coincidence Probability (radian-1) Width 0.903 ± 0.014(stat.) Width 0.751 ± 0.042(stat.) FMS triggered pp data FMS triggered dAu data Significant broadening in FMS-EEMC π0+jet-like correlations. Xuan Li

  30. Conclusions • There are π0 and jet-like candidates in the EEMC tower clusters. • There are hints of broadening in the away side peak for FMS-EEMC π0+jet-like azimuthal correlation. • The transition from parton gas to CGC saturation state is not sharp. Outlook • To add ESMD information for π0 reconstruction. • Use self consistent jet finder for jet-like events. • Get corrected normalized azimuthal correlation. Xuan Li

  31. Introduction to EEMC shower maximum detector • The SMD helps distinguish photon from charged hadrons. The electro-magnetic shower passing through EEMC Pre-shower1 Pre-shower2 Tower Shower Maximum Detector ( SMD ) Post-shower Front view of SMD U/V plane EM shower

  32. Event display of π0 in the EEMC EEMC tower E (GeV) ESMD strips E (MeV) • EEMC has shower maximum detector (ESMD). Photon 1 SMD will help define the photon position and the energy sharing between two photons . Photon 2 Xuan Li

  33. Backup Xuan Li

  34. Current measured nuclei gluon density at low x. Current fixed target data provide 0.02<x<0.3 range for nuclei gluon density [Phys. Rev. C70 (2004)044905]. Xuan Li

  35. The nuclei gluon density prediction The distribution of nucleons in the nucleus, • Transverse density of nuclei definition. • At a given x, nuclei (mass number A) gluon density ≈ A1/3 × nucleon gluon density, leading to the expectation Qs2≈A1/3 xβ. • Current fixed target data provides 0.02<x<0.3 range for nuclear gluon density. Transverse density of light nuclei The transverse distribution is defined as [hep-ph/0304189] Xuan Li

  36. <z> <xq> <xg> Partonic scattering for forward π0 production NLO pQCD Jaeger,Stratmann,Vogelsang,Kretzer Xuan Li

  37. FMS coverage Xuan Li

  38. STAR Detectors • In η , ϕ space Nearly hermetic electro-magnetic calorimeter cover -1<η<4. Xuan Li

  39. Forward-forward rapidity correlation The impact parameter is related with the charge sum in the east BBC by a model. • Centrality determination in dAu . • Multiplicity in dAu measured by the east beam beam counter (BBC) at STAR reflects the centrality. HIJING impact parameter cm) arXiv:hep-ex/1005.2378 dAu data PP data Peripheral Central Xuan Li

  40. Centrality cuts in dAu Xuan Li

  41. Motivation • Provide direct sensitivity to nuclei gluon density at 0.001< x < 0.02. FMS-FMS correlation FMS-EEMC correlation FMS-BEMC(TPC) correlation Triggering on the forward rapidity π0, the rapidity of the associated π0 is correlated with the soft parton involved in the partonic scattering. Xuan Li

  42. Energy threshold studies • For example, BEMC tower energy deposited (GeV) in pp data. With energy threshold 35MeV With energy threshold 70MeV Energy threshold is selected to suppress noise. Xuan Li

  43. Event display • Run 8 dAu fms triggered data. EEMC BEMC Xuan Li

  44. BEMC dAu number of raw tower hits • P MB data MB simulation

  45. Cluster width definition • BEMC • Unfold the barrel, and put in the Rϕ, Z plane. X(Y) Z Rϕ Small width R ϕ Large width Z Xuan Li

  46. Cluster width definition • EEMC • In xy plane. Y Y X Small width Large width X Xuan Li

  47. Simulated π0 decay kinematics • Projection on the EEMC, with the π0 Pt in [1.25GeV/c, 2.5GeV/c] and Zγγ<0.7 cuts. • For FMS π0 events, • Cuts on the single cluster is • 1.25GeV/c<Pt<2.5GeV/c • Zγγ < 0.7 Dγγ VS η of π0 Most of the π0 events are in EEMC single clusters. Xuan Li

  48. dAu FMS triggered data • FMS di-photon invariant mass. With FMS photon pair which has mass less than 0.2GeV/c2 and Pt larger than 2.5 GeV/c. Xuan Li

  49. π0 jet-like azimuthal correlation (FMS-BEMC) • FMS photon pair Pt > 2.5GeV/c. BEMC jet-like candidate 1.5GeV/c < Pt < 2.5GeV/c and mass<0.3GeV/c2. Uncorrected Coincidence Probability (radian-1) Width 0.722 ± 0.048 Width 0.728 ± 0.028 FMS triggered pp data (60%) FMS triggered dAu data(30%) No significant broadening in FMS-BEMC π0 jet-like correlations. Xuan Li

  50. BEMC efficiency studies • π0 efficiency in the BEMC Ermes Braidot thesis Fig 5.18 Xuan Li

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