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Probing the Low-x Structure of the Nucleus with the PHENIX Detector

Probing the Low-x Structure of the Nucleus with the PHENIX Detector. Mickey Chiu. INT, Seattle, 20 October 2011. PRL 107.172301. 1. 2. PRL 107.142301. Low-x nucleon/nuclear structure is a very difficult business! We’ll want to test it with as many probes as we can. 3.

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Probing the Low-x Structure of the Nucleus with the PHENIX Detector

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  1. Probing the Low-x Structure of the Nucleus with the PHENIX Detector Mickey Chiu INT, Seattle, 20 October 2011

  2. PRL 107.172301 1 2 PRL 107.142301 Low-x nucleon/nuclear structure is a very difficult business! We’ll want to test it with as many probes as we can. 3 • Di-hadron correlations in d+Au • J/ Production in d+Au • UPC (diffractive) J/ in Au+Au PLB 679 (2009) 321-329

  3. Forward di-Hadron Production in d+Au

  4. PHENIX Muon Piston Calorimeter SOUTH North PbWO4 d(forward) Au(backward) • Fwd-Fwd, x~(0.001,0.005) • Mid-Fwd, x~(0.008,0.040) • Mid-Bwd, x~(0.050,0.100) Small cylindrical holes in Muon Magnet Pistons, Radius 22.5 cm and Depth 43.1 cm 4

  5. MPC Performance Jet1 Jet2 “Trigger” Near North MPC Far Decay photon impact positions for lowand high energy p0s. The decay photons from highenergy p0s merge into a single cluster Sometimes use (EM) clusters, but always corrected to 0 energy Clusters  80% 0 (PYTHIA)

  6. RdAu in 2 forward rapidity Bins Guzey, Strikman, Vogelsang, PL B603, 173 • Large suppression in RdA • That increases with centrality • And increases with larger rapidity • Consistent with previous measurements • However, x covered by single inclusive measurement is over wide range • Includes shadowing, anti-shadowing, (EMC effect) Guzey, Strikman, Vogelsang, PLB603, 173

  7. RdA Past, di-Hadron Future CNM effects: dynamical shadowing, Energy Loss, Cronin Color Glass Condensate Kharzeev, NPA 748, 727 (2005) (Qiu, Vitev PLB632:507,2006) Kharzeev, Levin, McLerran  Nucl. Phys. A748 (2005) 627 • Di-Hadron Correlations allow one to select out the di-jet from the underlying event • Constrains x range (probe one region at a time) • Probe predicted angular decorrelation of di-jets (width broadening)

  8. di-Hadron Signal Peripheral d+Au Correlation Function “ConditionalYield” • Number of di-jet particle pairsper trigger particle after corrections for efficiencies, combinatoric background, and subtracting off pedestal CORRELATED Npair Df “Di-Hadron Nuclear Modification factor” “Sgl-Hadron Nuclear Modification factor” • Possible indicators of nuclear effects • JdA < 1, RdA < 1 • Angular decorrelation of widths • Caveats: • 1. Low pT (but back-to-back peak is selected) • Pedestal Determination (Assumed up to twice the width as a systematic). • Di-Hadrons instead of di-jets (but ok if fragmentation unmodified)

  9. p0 (trigger,central)/p0 (associate,forward) <pTa>=0.55 GeV/c <pTa>=0.77 GeV/c <pTa>=1.00 GeV/c 3.0 < pTt < 5.0 GeV/c for all plots p+p Correlation Function d+Au 60-88% d+Au 0-20% pTt, p0 Df PHENIX Preliminary pTa, p0

  10. Correlation Widths, d+Au and p+p Trigger p0: |h| < 0.35, 3.0 < pT < 5.0 GeV Trigger p0: |h| < 0.35, 2.0 < pT < 3.0 GeV dAu 0-20% pp dAu 40-88% • Widths are consistent between p+p and d+Au (all centralities) within large statistical and systematic errors • No broadening seen (within errors) No significant broadening between p+p and d+Au within large experimental uncertainties 10

  11. JdA vs Ncoll, pTmid, pTfwd MPC p0 pT • Suppression of di-hadron correlation (relative to p+p binary scaling hypothesis) with Increasing Centrality Decreasing pTmid Decreasing pTfwd pTt, p0 pTa, p0

  12. pTt, p0 pTa, p0 Fwd-Fwd: p+p vs d+Au Peripheral Peripheral d+Au collisions are similar to p+p collisions Beam view of d+Au peripheral collision

  13. pTt, p0 pTa, p0 Fwd-Fwd: p+p vs d+Au Central “Monojet” in central d+Au collisions Beam view of d+Au peripheral collision

  14. JdA for Fwd-Fwd MPC p0 pT • Suppression of JdA gets larger in fwd-fwd correlations • Trend with pT, centrality also consistent with mid-fwd correlations (assuming LO) • Better way to plot:

  15. xAufrag Dependence 60-88% (Peripheral) 0-20% (Central) • Plotting vs suggests that the effect is due to something happening in the nucleus as one probes to lower x • Does it prove CGC? • Shadowing? Initial state energy loss? Multi-Parton Interactions (MPI)? Note: points for mid-fwd JdA are offset for visual clarity Statistical and systematic errors are added in quadrature

  16.  JdA ~ RGAu Low x, mostly gluons Extending the LO picture Eskola , Paukkunen, Salgado, JHP04 (2009)065 EPS09 NLO gluons b=0-100% Q2 = 4 GeV2 xAu High x, mostly quarks Weak effects expected

  17. Extended scaling? Fwd-Cnt? Fwd-Fwd? Where is the Saturation Scale if we are actually seeing the CGC? H. Kowalski and D. Teaney. Phys. Rev.D, 68:114005, 2003 Iancu and Venugopalan, hep-ph/0303204 • We evaluated in PYTHIA the ~ coverage for Q2 and x for the fwd-fwd and cnt-fwd correlations • No nuclear modifications evaluated yet • Not clear that we are in the saturation region – possibly in extended region? • Can we explore Qs from the data? • Nuclear Scaling: Look at impact parameter dependence by varying centrality

  18. d+Au MC Glauber d Au Centrality 0-20% 20-40% 40-60% 60-88% bnucleon bnucleon • From Glauber Monte Carlo we can determine the number of nucleons in the path of each nucleon in the deuteron

  19. JdA Centrality Dependence • Fit using EPS09 parametric function: • Evaluate JdA at xfrag = 6x10-4, 6x10-3, 1.5x10-2

  20. Can we determine Qs? xfrag ~ 1.5x10-2 xfrag ~ 6x10-3 xfrag ~ 6x10-4 • If we are measuring gluons w/ JdA, then we can perhaps extract length and x dep of Qs, as well as possibly extracting the value of Qs at RHIC???? • Eg, are we seeing an approx linear dependence on length????

  21. J/ Production in d+Au

  22. low x Energy loss of incident gluon shifts effective xF and produces nuclear suppression which increases with xF high x R(A/p) R=1 xF What are the CNM effects that are so strong in Quarkonia production? Traditional shadowing from fits to DIS or from coherence models anti-shadowing RG in Au shadowing Absorption (or dissociation) of into two D mesons by nucleus or co-movers p A Gluon saturation from non-linear gluon interactions for the high density at small x - Amplified in a nucleus.

  23. What are the CNM effects that are so strong in Quarkonia production? J/ψ in d+Au – learning about CNM thickness dependence Reasonable agreement with EPS09 nPDF + br=4 mb for central collisions but not peripheral PHENIX arXiv:1010.1246v1 EPS09 with linear thickness dependence fails to describe centrality dependence of forward rapidity region.

  24. Quarkonia Suppression in A+A Collisions – key observations and questions • Overall suppression of J/ψ is very similar between: • SPS (17.2 GeV) • RHIC (200,62,39 GeV) • and LHC (2.76 TeV) RAA SPS RAA PHENIX y=0 PHENIX forward Npart CMS: 0 <|y|< 2.4 pT > 6.5 39 GeV 62 GeV Npart (more on LHC in a minute) Npart Npart

  25. Quarkonia Suppression in A+A Collisions – comparing RHIC & LHC caution caution Mid Rapidity all pT • LHC suppressed more than RHIC at y~0 • (but CMS is pT> 6.5 GeV/c) • LHC suppressed less than RHIC at forward y • (here ALICE is pT> 0) • Features expected from regeneration, which is concentrated at small pT CMS pT > 6.5 GeV/c Forward Rapidity High-pT suppressed more than low pT (but ALICE y~3; ATLAS y~0) However suppression roughly flat with rapidity for pT>6.5 So may also be consistent with regeneration at small pT ALICE ATLAS ALICE, all pT Rcp CMS Npart Missing LHC data – y~0, pT> 0 RAA? (where regeneration may be rather large) 25 y

  26. What are the CNM effects that are so strong in Quarkonia production? J/ψ in d+Au – learning about CNM thickness dependence Vary the strength of suppression (a) & see what relationship between RdAu and RCP is given strictly by Glauber geometry for different dependences on density-weighted thickness Woods-Saxon PHENIX arXiv:1010.1246v1 • Break-up has exponential dependence • EPS09 & initial-state dE/dx have unknown dependences The forward rapidity points suggests a quadratic or higher geometrical dependence

  27. Rapidity or x Coverage

  28. Does di-hadron data match J/Psi? • Comparison not so bad, considering many other uncertainties (production model, energy loss, breakup cross-section). Also J/ is generally at higher Q2 • Real way to do this is to try to extract G(x) from di-hadron data, and then predict J/

  29. Ultraperipheral J/

  30. “Hadronic” Collider Processes • You’re probably familiar with the “Hadronic Interactions” • But there are a lot more processes going on at a hadron collider Hadronic Interaction: Au-Au --> X ~7 barns -: AuAu --> AuAu + e+e- ~33 kbarns AuAu --> AuAu + 2(e+e-) ~680 barns AuAu --> AuAu + 3(e+e-) ~50 barns -N: L(-N )=1029 cm-2s-1 2<E<300GeV AuAu --> Au+Au* 92 barns X+neutrons AuAu --> Au*+Au* 3.670.26 barns X+neutrons Y+neutrons Hadronic Interaction Ultra-Peripheral Interaction

  31. n l+ l- p e+ g e-  Au  J/ Au* measurement in PHENIX • UPC dedicated trigger • Rapidity gap 3<||<4  MB interaction veto (BBC veto) • Large probability to exchange additional photons by GDR  1 or 2 ZDC trigger • EmCal trigger (E>0.8GeV) • DiMuon Trigger •  Au  J/ ( l+l-) Au* • DC & PCtracking detectors • RICH & EmCal electron identification devices • Muon Tracker ||<0.35

  32. [ 1) ] [ 2) ] [ 3) ] [ 4) ] coherent incoherent [ 1) P.R.L.89 012301 (2002)…] [ 2) P.L.B626 (2005) 72 ] [ 3) arXiv0706.2810 [hep-ph] ] [ 4) arXiv:0706.1532 [hep-ph] ] J/ cross section vs theoretical calculations  d/dy |y=0 = 76  31 (stat) 15 (syst) b • Compatible with coherent predictions, • With more statistics, sensitive to the shadowing parameterizations, coherent [Filho et al, PRC78 044904 (2008)]

  33. UPC J/ψ pT2 distribution (Theoretical) Coherent(γAu): low pt peak Incoherent(γn): wider pt distribution (Incoherent + neutron tagged : Yellow shadow ) Impact Parameter Dependence Strikman et al, PLB 626 p. 72-79 Horowitz, INT-PUB-11-005 (arxiv:1102.5058) EIC Workshop, INT, Seattle 2010 • Fourier transform of t distribution can distinguish the density of the nucleus vs b • However, incoherent contribution is a potentially large source of background

  34. PT dependence ofUPC J/ψ+Xn(N)+Xn(S) • UPC J/ pT (~t1/2) also confirms existence of incoherent contribution • Strategy: measure at forward rapidities to get incoherent, subtract from total to get remainder • Major challenges: momentum resolution of 3 MeV! (technical driver for EIC detector) • Statistics (EIC is good, RHIC/LHC is poor)

  35. +, +p, +A “Applications” • Higgs as well as many SUSY ptcls should be produced at the LHC in + and +p (+A) • High energy photon interactions at the LHC, de Jeneret et al, arXiv:0908.2020 • FP220, FP420 • Observation of exclusive charmonium production and gamma+gamma to mu+mu- in p+pbar collisions at sqrt{s} = 1.96 TeV, CDF, PRL102:242001,2009 Nucleus-Nucleus Interactions • Direct measurement of G(x) at from photoproduction (~g2(x)) 10-3 10-2 10-1 10-3 10-2 10-1 10-3 10-2 10-1 x EPS09: A New Generation of NLO and LO Nuclear PDF’s, Eskola,Paukannen,Salgado JHEP 0904:065 2009 • Possibly study dynamics of J/ propagation through nuclear matter • Feature or Bug? • Test of QED in strong-coupling regime?: =ZEM~0.6

  36. PHENIX UPC J/Psi +, +p, +A “Applications” • Higgs as well as many SUSY ptcls should be produced at the LHC in + and +p (+A) • High energy photon interactions at the LHC, de Jeneret et al, arXiv:0908.2020 • FP220, FP420 • Observation of exclusive charmonium production and gamma+gamma to mu+mu- in p+pbar collisions at sqrt{s} = 1.96 TeV, CDF, PRL102:242001,2009 Nucleus-Nucleus Interactions • Direct measurement of G(x) at from photoproduction (~g2(x)) 10-3 10-2 10-1 10-3 10-2 10-1 10-3 10-2 10-1 x EPS09: A New Generation of NLO and LO Nuclear PDF’s, Eskola,Paukannen,Salgado JHEP 0904:065 2009 • Possibly study dynamics of J/ propagation through nuclear matter • Feature or Bug? • Test of QED in strong-coupling regime?: =ZEM~0.6

  37. PHENIX UPC J/Psi +, +p, +A “Applications” • Higgs as well as many SUSY ptcls should be produced at the LHC in + and +p (+A) • High energy photon interactions at the LHC, de Jeneret et al, arXiv:0908.2020 • FP220, FP420 • Observation of exclusive charmonium production and gamma+gamma to mu+mu- in p+pbar collisions at sqrt{s} = 1.96 TeV, CDF, PRL102:242001,2009 Nucleus-Nucleus Interactions • Direct measurement of G(x) at from photoproduction (~g2(x)) 10-3 10-2 10-1 10-3 10-2 10-1 10-3 10-2 10-1 x EPS09: A New Generation of NLO and LO Nuclear PDF’s, Eskola,Paukannen,Salgado JHEP 0904:065 2009 • Possibly study dynamics of J/ propagation through nuclear matter • Feature or Bug? • Test of QED in strong-coupling regime?: =ZEM~0.6

  38. Are these enough to see the elephant in the room? Summary • Three Tests of Saturation in PHENIX (or probes of g(x)) • FWD-FWD di-hadron yields in d+Au relative to p+p (JdA) • Suppression depends strongly on centrality • And gets stronger as both particles go toward more forward rapidities • Nuclear Shadowing? We see extreme Shadowing in most central. • Gluon Saturation/Color Glass Condensate? • If so, we can extract a wealth of information on Qs from our measurements • Initial State Energy Loss? MPI? • Angular Broadening of Away Side Jet? • Mid-Fwd, no increase seen within errors • Mid-MidFwd, also no increase • Fwd-Fwd, currently inconclusive • J/ Production in d+Au not well understood • Forward rapidities not well described – something extra going on? • Highly important to understand CNM effects for HI interpretation • Ultraperipheral J/ is a third, very different probe of gluon distribution • Can get a ~10% measurement of G(x) at x~10-2 • Statistics and detector challenged for G(x,b) impact parameter dep measurement

  39. Backup Slides

  40. IdA vs JdA: Can we decouple effects? • IdA is the per trigger comparison of d+Au jet associated counts relative to p+p • JdA is the rate of the associated pairs from a jet (per minbias event) • Can we use this to tell if the jets are modified, or do they disappear? • From the CNT-MPC corrrelations, we get IdA ~ 0.5, and RdA ~ 1.1 • JdA ~ 0.5 • The rate of correlated pairs is about half of p+p • Does this imply that the missing jets have disappeared, and not that they are modified, since IdA ~ JdA? • But not true for STAR FMS triggered-central barrel, where IdA ~ 1 and JdA ~ 0.5

  41. JdA, RdA vs Ncoll MPC p0 pT Qiu-Vitev Shadowing + Energy Loss (private communication)

  42. Muon-Central IdA & Widths, 2003 d+Au d Au Phys.Rev.Lett.96:222301,2006

  43. Nuclear Modification in d+Au at Forward(Backward) Rapidity • Forward η suppression • No backward η suppression • Gluon Saturation? • Cronin, Shadowing, E-loss? • Look at 2 particle correlations … Punch through hadrons & Hadron decay muons 43 Phys. Rev. Lett. 94, 082302 (2005)

  44. UPC Comparison with HERA data • Rough comparison with HERA e-p data, if coherent incoherent ratio is 50% - 50% • HERA (H1 & ZEUS) input • Result: • coh= 1.01  0.07 • incoh= 0.92  0.08 •  ~ 1, good agreement with HERA data hard probes scaling [ZEUS, Eur.Phys.J. C24 (2002) 345] [H1, Eur.Phys.J. C46 (2006) 585]

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