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Cold nuclear matter effect measured with high p T hadrons and jets in 200GeV d+Au collisions in PHENIX Takao Sakaguchi Brookhaven National Laboratory For.

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Presentation on theme: "Cold nuclear matter effect measured with high p T hadrons and jets in 200GeV d+Au collisions in PHENIX Takao Sakaguchi Brookhaven National Laboratory For."— Presentation transcript:

1 Cold nuclear matter effect measured with high p T hadrons and jets in 200GeV d+Au collisions in PHENIX Takao Sakaguchi Brookhaven National Laboratory For the PHENIX Collaboration

2 Why are we interested in d+Au collisions? In order to confirm that the high p T hadron suppression in Au+Au collisions is due to final state effect, and not cold nuclear matter (CNM) effect – Need system without additional effects from a hot medium. CNM effect include: – k T -broadening (Cronin enhancement at moderate p T ) – Shadowing of parton distributions – Cold nuclear matter energy loss – And possibly more… d+Au is more favorable for RHIC operation – p+Au becomes feasible now (M.Bai) 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 2 cartoon PHENIX, Phys. Rev. Lett. 91, 072301 (2003)  0 in Au+Au at 200GeV

3 Nuclear PDFs are centrality dependent? Helenius, Eskola et.al. published centrality dependent nuclear PDFs (arXiv:1205.5359) Compared to PHENIX  0 R dA published in 2003 Theory curves are scaled up/down within systematics New data can help better constraining nPDFs 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 3

4 PHENIX Detector Photon measurement – EMCal(PbSc, PbGl): Energy measurement and identification of real photons – Tracking(DC, PC): Veto to Charged particles Charged particle measurement – Tracking measure momentum – RICH: Identify electrons – EMCal add information on identifying electrons Event triggered by a coincidence of BBC South and BBC North – Sitting in 3.1<|  |<3.9 – Centrality defined by BBC south charge (Gold going direction) 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 4 View From Beam View From Side PHENIX recorded d+Au events of 80 nb -1 in 2008 (2.74 nb -1 in 2003)

5  0 and  reconstruction 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 5

6 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) 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 6 arXiv:1208.2254, accepted for PRC PRC82, 011902(R) (2010)   00 

7 Systematic errors Type A: point- by-point fluctuating errors Type B: p T - correlated errors Type C: overall normalization errors 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 7 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

8  0 and  p T spectra in 200GeV d+Au collisions 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 8 00 

9  0 R dA by centrality 2013-02-07 9 T. Sakaguchi, WWND2013@Squaw Valley New  0 R dA from Run8 Better statistics than Run 3  Extends p T reach by 5 GeV/c  Better constraint for nPDFs Peripheral is most enhanced Central consistent with no modification at p T > 2 GeV/c How do we understand this? Competing nuclear effects?

10  R dA by centrality 2013-02-07 10 T. Sakaguchi, WWND2013@Squaw Valley New  R dA from Run8 Better statistics than Run 3  Extends p T reach by 5 GeV/c  Better constraint for nPDFs Peripheral is most enhanced Central consistent with no modification at p T > 2 GeV/c How do we understand this? Competing nuclear effects?

11 Jet reconstruction 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 11

12 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 12 Reconstruction of jets in p+p Gaussian Filter: Cone-like, but infrared and collinear safe Shape of the filter: – Optimizes the signal-to-background by focusing on the core of the jet – Stabilizes the jet axis in the presence of background Naturally handles isolated particles vs. collective background

13 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 13 Reconstruction of jets in p+p Gaussian Filter: Cone-like, but infrared and collinear safe Shape of the filter: – Optimizes the signal-to-background by focusing on the core of the jet – Stabilizes the jet axis in the presence of background Naturally handles isolated particles vs. collective background

14 Systematic errors Type B: p T -correlated errors Type C: overall normalization errors Bin-by-bin unfolding to correct for p T increase from mild d+Au underlying events (evaluated with embedding analysis) Small residual fake rate ( 9 GeV/c 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 14 sourcetype9-12GeV12-15GeV15-20GeV20+ GeV Trigger efficiencyB5-8 55 UnfoldingB4-10 4-6 Res. Fake rateB5555 AcceptanceC3333 Vertex-dependenceC1111

15 Jet p T spectra in 200GeV d+Au collisions 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 15

16 Jets R dA 2013-02-07 16 T. Sakaguchi, WWND2013@Squaw Valley Higher p T reach than  0 s Enhancement in peripheral, suppression in central. – Similar trend seen in  0 and 

17 Comparison to  0 and  R dA 2013-02-07 17 T. Sakaguchi, WWND2013@Squaw Valley Good agreement within uncertainties, and given the difference in observables.  0,  and jets of same p T sample slightly different parton scales, but let’s overlay them anyways…

18 Comparison to  0 and  R cp 2013-02-07 18 T. Sakaguchi, WWND2013@Squaw Valley Good agreement within uncertainties, and given the difference in observables.  0,  and jets of same p T sample slightly different parton scales, but let’s overlay them anyways…

19 Comparison with models 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 19

20 Comparison to shadowing calculation (I) 2013-02-07 20 T. Sakaguchi, WWND2013@Squaw Valley (Very basic) shadowing calculation uses EPS09 PDF modification* + Glauber MC + PYTHIA (x,Q 2 ) sampling for  0. Shadowing effects match reasonably well within the global scale uncertainties in central events (where modification is weak), but is not compatible with the p T shape in peripheral. * nPDF modification assumed to scale linearly with longitudinal nuclear thickness.  0 R dA

21 Comparison to shadowing calculation (II) 2013-02-07 21 T. Sakaguchi, WWND2013@Squaw Valley ~ 0.3 ~ 0.2 (Very basic) shadowing calculation uses EPS09 PDF modification* + Glauber MC + PYTHIA (x,Q 2 ). Shadowing effects match reasonably well within the global scale uncertainties in central events (where modification is weak), but is not compatible with the p T shape in peripheral. * nPDF modification assumed to scale linearly with longitudinal nuclear thickness. Jets R dA

22 Interpretation of the results Strong centrality dependence of R dA –  0,  and jets R dA are in very nice agreement in spite of completely different systematics – nPDF may be strongly centrality dependent Some thought – Before making the final conclusion, we would like to confirm some global things. 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 22

23 How we define centralities? Use Beam-Beam counter (BBC) installed in 3.1<|  <3.9 – Centrality defined by BBC south charge (Gold going direction) – Participant region Compare with Monte Carlo simulations and determine T AB – Glauber calculation folded with negative binominal distributions (NBD) 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 23 Charge distribution in BBC (South, gold going direction) 0-20% 20-40% 40-60%60-88%

24 Possible dynamics in d+Au collisions We talk about peripheral collision case Soft- and hard-dominated events may produce different hit distributions in BBC In case that hardest jets are produced, less energy will be available for soft-production at high  There could be p T dependent effect? – We use BBC for event triggering as well as centrality definition 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 24 BBC Mid-rapidity Detector

25 PYTHIA simulation Ran PYTHIA and look reconstructed jets in mid-rapidity PYTHIA sees a small anti-correlation effect 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 25 Number of hits in BBC vs reconstructed jet p T Fraction of reconstructed jets when requiring BBC trigger Errors are RMS’s of dists.

26 AMPT p+p simulation AMPT is a HIJING + hadron cascade event generator Plotted as a function of hadron p T in mid-rapidity – Jets are not reconstructed. – AMPT also sees similar effect in single hadrons 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 26 Number of hits in BBC vs hadron p T in mid-rapidity Fraction of hadrons when requiring BBC trigger Errors are RMS’s of dists

27 Conclusion Very solid results from  0,  and jets on R dA that would help constraining nuclear PDF from d+Au collision data – Very consistent each other even though the systematics are very different Huge enhancement in the yield in d+Au peripheral collisions compared to the one expected from p+p collisions We are making several global checks in preparation for publishing the results. 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 27

28 Backup 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 28

29 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 29

30 R dA of Identified Hadrons 2013-02-07 30 T. Sakaguchi, WWND2013@Squaw Valley Mesons follow similar trend w/ p T in all centralities. Cronin enhancement at moderate p T ? Or nPDF moving through antishadowing region into EMC region? Proton enhancement still not explained by Cronin or shadowing models.  R. Hwa, et al. reproduced R CP using recombination of shower + thermal(?) partons (nucl-th/0404066).

31 2013-02-07 T. Sakaguchi, WWND2013@Squaw Valley 31 What is the merging effect? Because of limited granularity of the detector, two  ’s from  0 can not be resolved at very high p T (  ’s merged. mass can not be reconstructed). –Opening angle:  ~ mass/p T We corrected for the inefficiency due to merging, but also introduced a large systematic error. Probability of detecting two  ’s from  0 00 Low p T 00 High p T p T of  0 PbSc PbGl

32 2013-02-07 T. Sakaguchi, WWND2013@Squaw Valley 32 60-88% 0-20% PHENIX Preliminary

33  0 R dA 2013-02-07 33 T. Sakaguchi, WWND2013@Squaw Valley

34 Cronin Enhancement 2013-02-07 34 Enhancement of hadron production in heavy ion collisions Usually modeled as multiple scattering of the incoming parton on the nucleus. Most models don’t have any PID dependence… However, measured enhancement is larger for protons than pions/kaons. Originally thought to be due to steeper p T spectrum of protons and that it would go away at higher energies. But proton enhancement is still much larger at RHIC energies! T. Sakaguchi, WWND2013@Squaw Valley ++ K+K+ p

35 Systematic errors Type A: point-by-point fluctuating errors Type B: p T -correlated errors Type C: overall normalization errors 2013-02-07T. Sakaguchi, WWND2013@Squaw Valley 35

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