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

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

3. 3 Forward di-Hadron Production in d+Au

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

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

6. 6 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) R dAu in 2 forward rapidity Bins Guzey, Strikman, Vogelsang, PLB603, 173

7. 7 CNM effects: dynamical shadowing, Energy Loss, Cronin R dA Past, di-Hadron Future Kharzeev, NPA 748, 727 (2005) 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) Kharzeev, Levin, McLerran Nucl. Phys. A748 (2005) 627 Color Glass Condensate (Qiu, Vitev PLB632:507,2006)

8. 8 di-Hadron Signal  Peripheral d+Au Correlation Function CORRELATED N pair “Di-Hadron Nuclear Modification factor” Possible indicators of nuclear effects J dA < 1, R dA < 1 Angular decorrelation of widths “Sgl-Hadron Nuclear Modification factor” “Conditional Yield” Number of di-jet particle pairs per trigger particle after corrections for efficiencies, combinatoric background, and subtracting off pedestal Caveats: 1. Low p T (but back-to-back peak is selected) 2.Pedestal Determination (Assumed up to twice the width as a systematic). 3.Di-Hadrons instead of di-jets (but ok if fragmentation unmodified)

9. 9  0 (trigger,central)/  0 (associate,forward)  =0.55 GeV/c p+p Correlation Function d+Au 0-20% d+Au 60-88% =0.77 GeV/c =1.00 GeV/c 3.0 < p T t < 5.0 GeV/c for all plots p T t,  0 p T a,  0 PHENIX Preliminary

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

11. 11 J dA vs N coll, p T mid, p T fwd MPC  0 pT Suppression of di-hadron correlation (relative to p+p binary scaling hypothesis) with Increasing Centrality Decreasing p T mid Decreasing p T fwd p T t,  0 p T a,  0

12. 12 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 p T t,  0 p T a,  0

13. 13 Fwd-Fwd: p+p vs d+Au Central “Monojet” in central d+Au collisions Beam view of d+Au peripheral collision p T t,  0 p T a,  0

14. 14 JdA for Fwd-Fwd MPC  0 pT (assuming LO) Better way to plot: Suppression of JdA gets larger in fwd-fwd correlations Trend with p T, centrality also consistent with mid-fwd correlations

15. 15 x Au frag Dependence Note: points for mid-fwd JdA are offset for visual clarity Statistical and systematic errors are added in quadrature 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)? 60-88% (Peripheral) 0-20% (Central)

16. 16 Extending the LO picture b=0-100% Q 2 = 4 GeV 2 x Au EPS09 NLO gluons Eskola, Paukkunen, Salgado, JHP04 (2009)065 Low x, mostly gluons  J dA  ~ R G Au High x, mostly quarks Weak effects expected

17. 17 Where is the Saturation Scale if we are actually seeing the CGC? Iancu and Venugopalan, hep-ph/0303204 Extended scaling? H. Kowalski and D. Teaney. Phys. Rev.D, 68:114005, 2003 We evaluated in PYTHIA the ~ coverage for Q 2 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 Q s from the data? Nuclear Scaling: Look at impact parameter dependence by varying centrality Fwd-Cnt? Fwd-Fwd?

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

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

20. 20 Can we determine Q s ? 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???? xfrag ~ 1.5x10 -2 xfrag ~ 6x10 -3 xfrag ~ 6x10 -4

21. 21 J/  Production in d+Au

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

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

24. 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) 62 GeV 39 GeV SPS PHENIX forward PHENIX y=0 CMS: 0 <|y|< 2.4 p T > 6.5 (more on LHC in a minute) N part R AA

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

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

27. 27 Rapidity or x Coverage

28. 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 Q 2 Real way to do this is to try to extract G(x) from di-hadron data, and then predict J/ 

29. 29 Ultraperipheral J/ 

30. 30 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 )=10 29 cm -2 s -1 2<E  <300GeV AuAu --> Au+Au* 92 barns X+neutrons AuAu --> Au*+Au* 3.67  0.26 barns X+neutrons Y+neutrons “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 Ultra-Peripheral Interaction

31. 31  Au  J/  Au* measurement in PHENIX e+e+ ee   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 & PC tracking detectors –RICH & EmCal electron identification devices –Muon Tracker n l+l-l+l- |  |<0.35

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

33. 33 Impact Parameter Dependence Horowitz, INT-PUB-11-005 (arxiv:1102.5058) UPC J/ψ p T 2 distribution (Theoretical) Coherent( γAu ): low pt peak Incoherent( γn ): wider pt distribution (Incoherent + neutron tagged : Yellow shadow ) Strikman et al, PLB 626 p. 72-79 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. 34 P T dependence of UPC J/ψ+Xn(N)+Xn(S) UPC J/  p T (~t 1/2 ) 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. 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 x 10 -3 10 -2 10 -1 EPS09: A New Generation of NLO and LO Nuclear PDF’s, Eskola,Paukannen,Salgado JHEP 0904:065 2009 Direct measurement of G(x) at from photoproduction (  ~g 2 (x)) Possibly study dynamics of J/  propagation through nuclear matter Feature or Bug? Test of QED in strong-coupling regime?:  =Z  EM ~0.6 Nucleus-Nucleus Interactions

36. 36  + ,  +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 x 10 -3 10 -2 10 -1 EPS09: A New Generation of NLO and LO Nuclear PDF’s, Eskola,Paukannen,Salgado JHEP 0904:065 2009 Direct measurement of G(x) at from photoproduction (  ~g 2 (x)) PHENIX UPC J/Psi Possibly study dynamics of J/  propagation through nuclear matter Feature or Bug? Test of QED in strong-coupling regime?:  =Z  EM ~0.6 Nucleus-Nucleus Interactions

37. 37  + ,  +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 x 10 -3 10 -2 10 -1 EPS09: A New Generation of NLO and LO Nuclear PDF’s, Eskola,Paukannen,Salgado JHEP 0904:065 2009 Direct measurement of G(x) at from photoproduction (  ~g 2 (x)) PHENIX UPC J/Psi Possibly study dynamics of J/  propagation through nuclear matter Feature or Bug? Test of QED in strong-coupling regime?:  =Z  EM ~0.6 Nucleus-Nucleus Interactions

38. 38 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 Are these enough to see the elephant in the room?

39. 39 Backup Slides

40. 40 I dA vs J dA : Can we decouple effects? I dA is the per trigger comparison of d+Au jet associated counts relative to p+p J dA 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 I dA ~ 0.5, and R dA ~ 1.1 J dA ~ 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. 41 J dA, R dA vs N coll MPC  0 pT Qiu-Vitev Shadowing + Energy Loss (private communication)

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

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

44. 44 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 UPC Comparison with HERA data [ZEUS, Eur.Phys.J. C24 (2002) 345] [H1, Eur.Phys.J. C46 (2006) 585]