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Detailed study of parton energy loss via measurement of fractional momentum loss of high p T hadrons in heavy ion collisions Takao Sakaguchi Brookhaven.

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Presentation on theme: "Detailed study of parton energy loss via measurement of fractional momentum loss of high p T hadrons in heavy ion collisions Takao Sakaguchi Brookhaven."— Presentation transcript:

1 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

2 Hard scattering as densimeter 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. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 2 X.-N., Wang, PRC 58 (1998)2321 Energy loss =Yield suppress  0 without energy loss  0 with energy loss Yield [GeV -1 c] p T [GeV/c] p+pAu+Au Cross section of A+B collisions  AB  p+p collisions

3 High p T hadron R AA Measured in 200GeV Au+Au collisions.  0 and  are very consistent. Results have been solid over years. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 3 PRC82, 011902(R) (2010) MinBias, Black:  0, Blue:  Black: Year-2004, Red: Year-2007 PRC87, 034911 (2013) MinBias Black- 2004 Red - 2007 0-10% 20-30% 40-50% 60-70%80-93%

4 Collision energy dependence of R AA  0 in Cu+Cu @ 200, 62.4, 22.4GeV (RHIC Year-5) – 200GeV and 62GeV show suppression, and 22.4GeV shows enhancement (Cronin)  0 in Au+Au @ 200, 62.4, 39GeV (RHIC Year-4, 7, 10) – Similar suppression at higher p T 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 4 PRL 101, 162301(2008) PRL109, 152301 (2012)

5 Centrality dependence of R AA Centrality dependence of integrated  0 R AA was investigated in Cu+Cu and Au+Au collisions – As a function of cms energy Top: Cu+Cu: – 2.5<p T <3.5GeV/c Bottom: Au+Au – p T >6GeV/c Indication of a switch of suppression and enhancement below 39GeV? 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 5 PRL 101, 162301(2008) PRL109, 152301 (2012)

6 Similar suppression for RHIC and LHC? RHIC data from PHENIX publication –  0 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 R AA doesn’t mean similar energy loss – R AA is not a good quantity? – Power of the spectra is different  energy loss will be different 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 6 PRC87, 034911 (2013)

7 Looking at suppressions from a different angle 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 7

8 New quantity ~momentum loss~ Coming back to the original idea: measuring energy loss of partons Statistically measure the fractional momentum loss (  p T /p T ) of high p T hadrons instead of R AA. 2014-09-12 8 T. Sakaguchi, HPT2014@Nantes, France pTpT pTpT (p+p) denotes p+p yield scaled by number of binary nucleon- nucleon collisions (N coll ).

9 In 2005, statistics was not enough, so.. We assumed that the spectra at high p T follows power-law function With this assumption, we wrote a formula to obtain  p T /p T from R AA – Fractional momentum shift: S(p T )/p T =S 0 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 9 Note p T is p T in Au+Au PHENIX, PRC76, 034904 (2007)

10 S loss in 200GeV Au+Au collisions S loss (  p T /p T ), where p T is p T at a Au+Au point Lines: S loss  N part 2/3 – S loss increases approximately like N part 2/3 – GLV and PQM model suggested 2/3 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 10 PHENIX, PRC76, 034904 (2007)

11 Path-length dependence of R AA PHENIX measured the R AA as a function of emission angle with respect to event planes for several centralities – Gives handle of path-length that partons traverse L  is path from the center of ellipse to the edge 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 11 PHENIX, PRC76, 034904 (2007) cyan, 60–70% mauve, 50–60% blue, 40–50% green, 30–40% red, 20–30% black, 0–10%

12 Path-length dependence of S loss Converted R AA to S loss and plotted against L  Data points nicely aligned for 5<p T <8GeV/c 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 12 PHENIX, PRC76, 034904 (2007) cyan, 60–70% mauve, 50–60% blue, 40–50% green, 30–40% red, 20–30% black, 0–10%

13 ALICE recently performed similar study Using Pb+Pb 2.76TeV data (ALICE). L should be equivalent to the L  in the previous slide L is not very good at higher p T ? 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 13 P. Christiansen, K. Tywoniuk, and V. Vislavicius, PRC 89, 034912 (2014)

14 With better statistics.. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 14

15 Direct calculation is possible Direct calculation of fractional momentum loss (  p T /p T ) became possible. One doesn’t need to assume the function form of the spectra. 2014-09-12 15 T. Sakaguchi, HPT2014@Nantes, France pTpT pTpT

16 Direct calculation is possible Direct calculation of fractional momentum loss (  p T /p T ) became possible. One doesn’t need to assume the function form of the spectra. 2014-09-12 16 T. Sakaguchi, HPT2014@Nantes, France p+p  0 spectraAu+Au  0 spectra

17 Fractional momentum loss (  p T /p T ) of  0 Measured fractional momentum loss (  p T /p T ) instead of R AA – In Au+Au collisions  p T /p T =0.2 in 0-10% centrality, =0.02 in 70-80% centrality 2014-09-12 17 T. Sakaguchi, HPT2014@Nantes, France  p T /p T PRC87, 034911 (2013) MinBias 0-10% 20-30%40-50% 60-70%80-93%

18 Energy dependence of  p T /p T (I)  p T /p T decreases significantly going from 200 to 62, 39GeV. Significantly different  p T /p T while the R AA is similar. 2014-09-12 18 T. Sakaguchi, HPT2014@Nantes, France R AA PRL109, 152301 (2012)

19 Energy dependence of  p T /p T (II)  p T /p T increase by a factor of 1.5 from 200GeV to 2.76TeV. ~0.2 for RHIC and ~0.3 for LHC 2014-09-12 19 T. Sakaguchi, HPT2014@Nantes, France LHC RHIC PRC87, 034911 (2013)

20 Energy dependence of  p T /p T (III)  p T /p T from 62GeV to 2.76TeV: by a factor of 6 change! 2014-09-12 20 T. Sakaguchi, HPT2014@Nantes, France PRL109, 152301 (2012) LHC RHIC PRC87, 034911 (2013)

21 Systematic studies across systems We tried to plot  p T /p T against universal variables Number of participant nucleons (N part ) Number of quark participants (N qp ) Charged multiplicity (dN ch /d  ), as a measure of the energy density 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 21

22 Number of quark participants (Nqp)? Number of quark participants, N qp, is estimated using a Glauber model. – Nucleons are distributed using a Woods- Saxon distribution. – Quarks are distributed around the nucleon centers following:  (r)=  0 proton e - ar, where a = 4.27 fm -1. Quarks interact when their distance, d, satisfies the condition of: Quark-quark inelastic cross section (  qq inel ) is estimated by reproducing the n-n inelastic cross section of: 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 22 Ratios of N qp /N part as a function of N part for 62, 130 and 200GeV Au+Au collisions PHENIX, PRC89, 044905 (2014)

23 Is N qp a good scaling variable? Recently, PHENIX found that the dE T /d  scales better with N qp than N part dE T /d  affects the energy loss of partons 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 23 dE T /d  /(0.5 N part )dE T /d  /(0.5 N qp ) PHENIX, PRC89, 044905 (2014)

24  p T /p T over collision systems (vs N part ) Plotting against N part – N part are obtained in given centrality at given cms energy. –  p T /p T ‘s at p T =7GeV/c of p+p are plotted. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 24

25  p T /p T over collision systems (vs N qp ) Plotting against N qp – N qp are obtained in given centrality at given cms energy. –  p T /p T ‘s at p T =7GeV/c of p+p are plotted. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 25

26  p T /p T over collision systems (vs dN ch /d  ) Plotting against dN ch /d  (as a measure of energy density) – dN ch /d  are obtained in given centrality at given cms energy. –  p T /p T ‘s at p T =7GeV/c of p+p are plotted. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 26

27 Consistency with previous studies 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 dN ch /d   N part 1.16, found in PRC71, 034908(2005), we can write the relationship as follows: 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 27 PRL101, 232301 (2008)

28  p T /p T over collision systems (vs dN ch /d  ) Plotting against dN ch /d  (as a measure of energy density) – dN ch /d  are obtained in given centrality at given cms energy. –  p T /p T ‘s at p T =7GeV/c of p+p are plotted. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 28 k=0.55,  =6.0  10 -3 k=0.35,  =2.5  10 -2

29 Review the money plot 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 29

30 Summary Looking at fractional momentum loss gives more insight on actual energy loss of partons – Similar R AA 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  p T /p T vs dN ch /d  for 200GeV Au+Au and Cu+Cu collisions tend to merge into the one for 2.76TeV Pb+Pb collisions at larger dN ch /d , independent of √s NN. Within same √s NN, both N part and N qp scaling work very well. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 30

31 Backup 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 31

32 Hard scattering as densimeter 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. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 32 X.-N., Wang, PRC 58 (1998)2321 Energy loss =Yield suppress  0 without energy loss  0 with energy loss Yield [GeV -1 c] p T [GeV/c] PHENIX,  0 in Au+Au, PRL. 91, 072301 (2003)

33  p T /p T over collision systems (vs dN ch /d  ) Plotting against dN ch /d  (as a measure of energy density) – dN ch /d  are obtained in given centrality at given cms energy. –  p T /p T ‘s at p T =7GeV/c of p+p are plotted. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 33  =0.55,  =6.0  10 -3  =0.35,  =2.5  10 -2

34 Consistency with previous studies 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 dN ch /d   N part, we can write the relationship as follows: 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 34 PRL101, 232301 (2008)

35 d+Au and Au+Au system similarity? Au+Au 60-92% and d+Au 0- 20% have similar N part, N coll Ratios of all ID’ed hadron spectra are on the same curve Common production mechanism? If all CNM scales with N part, ratios may mean E loss in the medium in peripheral Au+Au Low p T increase may rise from rapidity shift in d+Au 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 35 arXiv:1304.3410

36 Setup for measurement Event triggered by a coincidence of BBC South and BBC North. – Sitting in 3.1<|  |<3.9  0 and  measurement – EMCal(PbSc, PbGl): Energy measurement and identification of real photons. – Tracking(DC, PC): Veto to Charged particles. 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 36 View From Beam View From Side Results presented here are obtained from 0.813 nb -1 Au+Au 200GeV events recorded by PHENIX in 2007. 00  EMCal

37 How we measure  0,  ? Reconstruct hadrons via 2  invariant mass in EMCal (example is in Au+Au) Subtract Combinatorial background – Compute Mass using  s from different events. (mixed-event technique) 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 37 PRC87, 034911 (2013) PRC82, 011902(R) (2010)   00 

38  0,  spectra in Au+Au 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 38 00  Spectra reached to ~20GeV/c for  0 and ~22GeV/c for 

39 Systematic errors Type A: point- by-point fluctuating errors Type B: p T - correlated errors Type C: overall normalization errors 2014-09-12T. Sakaguchi, HPT2014@Nantes, France 39 sourcetype5GeV10GeV15GeV20GeV peak extractionB2222 acceptanceC2.5 PID efficiencyB788.59 energy scaleB7.5888 photon conversionC2222 cluster mergingB00818 total 11121522 sourcetype5GeV10GeV15GeV peak extractionB43.53 acceptanceC2.5 PID efficiencyB788.5 energy scaleB1112 photon conversionC222 total 1215  0 systematic errors  systematic errors

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