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Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration

Detailed study of parton energy loss via measurement of fractional momentum loss of high p T hadrons in heavy ion collisions. Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration. Hard scattering as densimeter.

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Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration

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  1. Detailed study of parton energy loss via measurement of fractional momentum loss of high pT hadrons in heavy ion collisions Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration

  2. Hard scattering as densimeter Cross section ofA+B collisions  AB  p+p collisions p+p Au+Au 0 without energy loss 0 with energy loss Yield [GeV-1c] Energy loss =Yield suppress pT [GeV/c] X.-N., Wang, PRC 58 (1998)2321 • Parton may change its momentum in the medium. • Energy loss through Gluon radiation, etc.. • Effect is path-length and parton density dependent ~a densimeter~. • Look at leading particles of jet as a measure of jet energy. T. Sakaguchi, HPT2014@Nantes, France

  3. High pThadron RAA Black: Year-2004, Red: Year-2007 MinBias 0-10% Black- 2004 Red - 2007 40-50% 20-30% MinBias, Black: p0, Blue: h 60-70% 80-93% PRC82, 011902(R) (2010) PRC87, 034911 (2013) • Measured in 200GeV Au+Au collisions. • p0 and h are very consistent. • Results have been solid over years. T. Sakaguchi, HPT2014@Nantes, France

  4. Collision energy dependence of RAA PRL 101, 162301(2008) PRL109, 152301 (2012) • p0 in Cu+Cu @ 200, 62.4, 22.4GeV (RHIC Year-5) • 200GeV and 62GeV show suppression, and 22.4GeV shows enhancement (Cronin) • p0 in Au+Au @ 200, 62.4, 39GeV (RHIC Year-4, 7, 10) • Similar suppression at higher pT T. Sakaguchi, HPT2014@Nantes, France

  5. Centrality dependence of RAA PRL 101, 162301(2008) PRL109, 152301 (2012) • Centrality dependence of integrated p0 RAA was investigated in Cu+Cu and Au+Au collisions • As a function of cms energy • Top: Cu+Cu: • 2.5<pT<3.5GeV/c • Bottom: Au+Au • pT>6GeV/c • Indication of a switch of suppression and enhancement below 39GeV? T. Sakaguchi, HPT2014@Nantes, France

  6. Similar suppression for RHIC and LHC? PRC87, 034911 (2013) • RHIC data from PHENIX publication • p0 in Au+Au @ 0.2TeV • LHC data from ALICE publication • Charged hadrons in Pb+Pb @ 2.76TeV • Center-of-mass energies differ by a factor of 14! • Similar RAA doesn’t mean similar energy loss • RAA is not a good quantity? • Power of the spectra is different  energy loss will be different T. Sakaguchi, HPT2014@Nantes, France

  7. Looking at suppressions from a different angle T. Sakaguchi, HPT2014@Nantes, France

  8. New quantity ~momentum loss~ dpT (p+p) denotes p+p yield scaled by number of binary nucleon-nucleon collisions (Ncoll). pT • Coming back to the original idea: measuring energy loss of partons • Statistically measure the fractional momentum loss (dpT/pT) of high pT hadrons instead of RAA. T. Sakaguchi, HPT2014@Nantes, France

  9. In 2005, statistics was not enough, so.. Note pT is pT in Au+Au PHENIX, PRC76, 034904 (2007) • We assumed that the spectra at high pT follows power-law function • With this assumption, we wrote a formula to obtain dpT/pT from RAA • Fractional momentum shift: S(pT)/pT=S0 T. Sakaguchi, HPT2014@Nantes, France

  10. Sloss in 200GeV Au+Au collisions PHENIX, PRC76, 034904 (2007) • Sloss (dpT/pT), where pT is pT at a Au+Au point • Lines: Sloss Npart2/3 • Sloss increases approximately like Npart2/3 • GLV and PQM model suggested 2/3 T. Sakaguchi, HPT2014@Nantes, France

  11. Path-length dependence of RAA cyan, 60–70% mauve, 50–60% blue, 40–50% green, 30–40% red, 20–30% black, 0–10% PHENIX, PRC76, 034904 (2007) • PHENIX measured the RAA as a function of emission angle with respect to event planes for several centralities • Gives handle of path-length that partons traverse • Le is path from the center of ellipse to the edge T. Sakaguchi, HPT2014@Nantes, France

  12. Path-length dependence of Sloss cyan, 60–70% mauve, 50–60% blue, 40–50% green, 30–40% red, 20–30% black, 0–10% PHENIX, PRC76, 034904 (2007) • Converted RAA to Sloss and plotted against Le • Data points nicely aligned for 5<pT<8GeV/c T. Sakaguchi, HPT2014@Nantes, France

  13. ALICE recently performed similar study P. Christiansen, K. Tywoniuk, and V. Vislavicius, PRC 89, 034912 (2014) • Using Pb+Pb 2.76TeV data (ALICE). L should be equivalent to the Le in the previous slide • L is not very good at higher pT? T. Sakaguchi, HPT2014@Nantes, France

  14. With better statistics.. T. Sakaguchi, HPT2014@Nantes, France

  15. Direct calculation is possible dpT pT • Direct calculation of fractional momentum loss (dpT/pT) became possible. • One doesn’t need to assume the function form of the spectra. T. Sakaguchi, HPT2014@Nantes, France

  16. Direct calculation is possible p+pp0 spectra Au+Aup0 spectra • Direct calculation of fractional momentum loss (dpT/pT) became possible. • One doesn’t need to assume the function form of the spectra. T. Sakaguchi, HPT2014@Nantes, France

  17. Fractional momentum loss (dpT/pT) of p0 0-10% MinBias dpT/pT 20-30% 40-50% 60-70% 80-93% PRC87, 034911 (2013) • Measured fractional momentum loss (dpT/pT) instead of RAA • In Au+Au collisions • dpT/pT=0.2 in 0-10% centrality, =0.02 in 70-80% centrality T. Sakaguchi, HPT2014@Nantes, France

  18. Energy dependence of dpT/pT(I) RAA PRL109, 152301 (2012) • dpT/pT decreases significantly going from 200 to 62, 39GeV. • Significantly different dpT/pT while the RAA is similar. T. Sakaguchi, HPT2014@Nantes, France

  19. Energy dependence of dpT/pT (II) LHC RHIC PRC87, 034911 (2013) • dpT/pT increase by a factor of 1.5 from 200GeV to 2.76TeV. • ~0.2 for RHIC and ~0.3 for LHC T. Sakaguchi, HPT2014@Nantes, France

  20. Energy dependence of dpT/pT (III) LHC RHIC PRC87, 034911 (2013) PRL109, 152301 (2012) dpT/pT from 62GeV to 2.76TeV: by a factor of 6 change! T. Sakaguchi, HPT2014@Nantes, France

  21. Systematic studies across systems We tried to plot dpT/pT against universal variables Number of participant nucleons (Npart) Number of quark participants (Nqp) Charged multiplicity (dNch/dh), as a measure of the energy density T. Sakaguchi, HPT2014@Nantes, France

  22. Number of quark participants (Nqp)? Ratios of Nqp/Npart as a function of Npart for 62, 130 and 200GeV Au+Au collisions PHENIX, PRC89, 044905 (2014) • Number of quark participants, Nqp, is estimated using a Glauber model. • Nucleons are distributed using a Woods-Saxon distribution. • Quarks are distributed around the nucleon centers following:r(r)= r0proton e-ar, where a = 4.27 fm-1. • Quarks interact when their distance, d, satisfies the condition of: • Quark-quark inelastic cross section (sqqinel) is estimated by reproducing the n-n inelastic cross section of: T. Sakaguchi, HPT2014@Nantes, France

  23. Is Nqp a good scaling variable? dET/dh/(0.5 Npart) dET/dh/(0.5 Nqp) PHENIX, PRC89, 044905 (2014) • Recently, PHENIX found that the dET/dh scales better with Nqp than Npart • dET/dh affects the energy loss of partons T. Sakaguchi, HPT2014@Nantes, France

  24. dpT/pT over collision systems (vsNpart) • Plotting against Npart • Npart are obtained in given centrality at given cms energy. • dpT/pT‘s at pT=7GeV/c of p+p are plotted. T. Sakaguchi, HPT2014@Nantes, France

  25. dpT/pT over collision systems (vsNqp) • Plotting against Nqp • Nqp are obtained in given centrality at given cms energy. • dpT/pT‘s at pT=7GeV/c of p+p are plotted. T. Sakaguchi, HPT2014@Nantes, France

  26. dpT/pT over collision systems (vsdNch/dh) • Plotting against dNch/dh (as a measure of energy density) • dNch/dh are obtained in given centrality at given cms energy. • dpT/pT‘s at pT=7GeV/c of p+p are plotted. T. Sakaguchi, HPT2014@Nantes, France

  27. Consistency with previous studies PRL101, 232301 (2008) • PHENIX studied fractional momentum loss in two publications • PRC76, 034904 (2007), PRL101, 232301 (2008) • Assuming the spectra shape is power-law with the power “n”, we can write: • If we assume dNch/dh Npart1.16, found in PRC71, 034908(2005), we can write the relationship as follows: T. Sakaguchi, HPT2014@Nantes, France

  28. dpT/pT over collision systems (vsdNch/dh) k=0.35, b=2.510-2 k=0.55, b=6.010-3 • Plotting against dNch/dh (as a measure of energy density) • dNch/dh are obtained in given centrality at given cms energy. • dpT/pT‘s at pT=7GeV/c of p+p are plotted. T. Sakaguchi, HPT2014@Nantes, France

  29. Review the money plot T. Sakaguchi, HPT2014@Nantes, France

  30. Summary • Looking at fractional momentum loss gives more insight on actual energy loss of partons • Similar RAA does not give similar energy loss • Centrality, system, and energy dependence of fractional momentum loss is studied. • A trend is seen from 200GeV Au+Au to 2.76TeV Pb+Pb • dpT/pTvsdNch/dh for 200GeV Au+Au and Cu+Cu collisions tend to merge into the one for 2.76TeV Pb+Pb collisions at larger dNch/dh, independent of √sNN. • Within same √sNN, both Npart and Nqp scaling work very well. T. Sakaguchi, HPT2014@Nantes, France

  31. Backup T. Sakaguchi, HPT2014@Nantes, France

  32. Hard scattering as densimeter 0 without energy loss 0 with energy loss Yield [GeV-1c] Energy loss =Yield suppress pT [GeV/c] PHENIX, p0 in Au+Au, PRL. 91, 072301 (2003) X.-N., Wang, PRC 58 (1998)2321 • Parton may change its momentum in the medium. • Energy loss through Gluon radiation, etc.. • Effect is path-length and system dependent ~a densimeter~. • Look at leading particles of jet as a measure of jet energy. T. Sakaguchi, HPT2014@Nantes, France

  33. dpT/pT over collision systems (vsdNch/dh) a=0.35, b=2.510-2 a=0.55, b=6.010-3 • Plotting against dNch/dh (as a measure of energy density) • dNch/dh are obtained in given centrality at given cms energy. • dpT/pT‘s at pT=7GeV/c of p+p are plotted. T. Sakaguchi, HPT2014@Nantes, France

  34. Consistency with previous studies PRL101, 232301 (2008) • PHENIX studied fractional momentum loss in two publications • PRC76, 034904 (2007), PRL101, 232301 (2008) • Assuming the spectra shape is power-law with the power “n”, we can write: • In this study, if we assume dNch/dh Npart, we can write the relationship as follows: T. Sakaguchi, HPT2014@Nantes, France

  35. d+Au and Au+Au system similarity? arXiv:1304.3410 • Au+Au 60-92% and d+Au 0-20% have similar Npart, Ncoll • Ratios of all ID’edhadron spectra are on the same curve • Common production mechanism? • If all CNM scales with Npart, ratios may mean Eloss in the medium in peripheral Au+Au • Low pT increase may rise from rapidity shift in d+Au T. Sakaguchi, HPT2014@Nantes, France

  36. Setup for measurement View From Beam p0 EMCal View From Side h Results presented here are obtained from 0.813 nb-1Au+Au 200GeV events recorded by PHENIX in 2007. • Event triggered by a coincidence of BBC South and BBC North. • Sitting in 3.1<|h|<3.9 • p0 and h measurement • EMCal(PbSc, PbGl): Energy measurement and identification of real photons. • Tracking(DC, PC): Veto to Charged particles. T. Sakaguchi, HPT2014@Nantes, France

  37. How we measure p0, h? p0 PRC87, 034911 (2013) PRC82, 011902(R) (2010) p0 h h • Reconstruct hadrons via 2g invariant mass in EMCal (example is in Au+Au) • Subtract Combinatorial background • Compute Mass using gs from different events. (mixed-event technique) T. Sakaguchi, HPT2014@Nantes, France

  38. p0, h spectra in Au+Au h p0 T. Sakaguchi, HPT2014@Nantes, France Spectra reached to ~20GeV/c for p0 and ~22GeV/c for h

  39. Systematic errors p0 systematic errors h systematic errors Type A: point-by-point fluctuating errors Type B: pT-correlated errors Type C: overall normalization errors T. Sakaguchi, HPT2014@Nantes, France

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