Shadowing Effects on Open and Hidden Heavy Flavor Production at the - PowerPoint PPT Presentation

Shadowing Effects on Open and Hidden Heavy Flavor Production at the LHC R. Vogt Lawrence Livermore National Laboratory, Livermore, CA 94551, USA Physics Department, University of California, Davis, CA 95616, USA

Cold Nuclear Matter Effects in Hadroproduction In heavy-ion collisions, one has to fold in cold matter effects, typically studied in pA or d A interactions from fixed-target energies to colliders Important cold nuclear matter effects in hadroproduction include: • Initial-state nuclear effects on the parton densities (nPDFs) • Initial- (or final-) state energy loss • k T broadening from multiple scattering • Final-state absorption on nucleons • Final-state break up by comovers (hadrons or partons) • Intrinsic QQ pairs After some very brief discussion of each, I will concentrate on nuclear parton densities (shadowing) Open heavy flavor not affected by absorption or comover interactions

Cold Matter Effects Quantified by A Dependence Open charm appears to be independent of A ( N bin ) but quarkonium has a definite A dependence The A dependence includes some or all of the aforementioned nuclear effects E772, p + A −> µ + µ − S = 200 GeV Sys. error Integrated Cross Section Ratios NN 1.2 400 d+Au FONLL err. 0 (D +e) NLO err. 1.1 b) C Ca Fe W p+p 300 1 µ 0 ( (D +D*) 0 Au+Au (D ) y=0 0.9 0−80% /dy| 2 H) .96 A 200 0.8 R(A/ NN c DY c σ J/ Ψ d 0.7 .92 A 50−80% 20−50% 0−20% Ψ ’ 100 0.6 FONLL in p+p Υ 1S Υ 2S+3S 0.5 STAR Preliminary 0 2 3 1 10 10 10 0.4 10 100 number of binary collisions N Mass Number bin Figure 1: (Left) The dependence of the open charm cross section on the number of binary collisions measured by the STAR Collaboration at central rapidity. (Right) The A dependence of quarkonium and Drell-Yan production measured by E772.

E866 Measured Open Charm and J/ψ vs x F E866 also measured open charm pA dependence using single muons with p µ T > 1 GeV/ c (unpublished) Different from J/ψ for y < 0 . 7 but similar for higher y , suggests that dominant effects are in the initial state Open Charm - E866/NuSea (Preliminary) J/ Ψ - E866/NuSea 1.1 0 - E789 D α 1 0.9 2 α (x F ) = 0.960 ( 1-0.0519 x F - 0.338 x F ) 0.8 0 0.5 1 1.5 2 y c.m. Figure 2: The J/ψ and open charm A dependence as a function of x F (Mike Leitch).

Quick Tour of Cold Matter Effects

Parton Densities Modified in Nuclei Nuclear deep-inelastic scattering measures quark modifications directly More uncertainty in nuclear gluon distribution, only indirectly constrained by Q 2 evolution of parton densities 1.1 1.1 1.05 NMC EPS09NLO 1.05 1.05 1.0 1.0 =4 0.95 0.95 ) 0.9 0.9 2 1.0 0.85 0.85 2 ( , =0.0125 =0.0175 =0.025 0.8 0.8 1.1 1.1 0.95 1.05 1.05 1.0 1.0 0.95 0.95 0.9 0.9 0.9 0.85 0.85 1.05 =0.035 =0.045 =0.055 0.8 0.8 =12 2 ) 1.1 1.1 1.0 1.05 1.05 C ( , ) 2 1.0 1.0 2 2 ( , 0.95 0.95 0.95 2 )/ 0.9 0.9 Sn ( , 0.85 0.85 0.9 =0.070 =0.090 =0.125 0.8 0.8 2 1.1 1.1 0.85 1.05 1.05 1.0 1.0 1.05 0.95 0.95 =40 0.9 0.9 1.0 0.85 0.85 =0.175 =0.25 =0.35 ) 0.8 0.8 2 0.95 1.1 1.1 2 ( , 0.9 1.05 1.05 1.0 1.0 NMC 0.85 0.95 0.95 SLAC 0.9 0.9 0.8 0.85 0.85 0.75 =0.45 =0.55 =0.70 0.8 0.8 10 -3 10 -2 10 -1 0.75 0.75 1 1 10 100 1 10 100 1 10 100 2 [GeV 2 ] Figure 3: (Left) Ratios of charged parton densities in He, C, and Ca to D as a function of x . (Right) Evolution of gluon distributions in Sn relative to C targets with Q 2 for several fixed values of x . [From K.J. Eskola.]

Why Shadowing Is Not All There Is Effective α dissimilar as a function of x 2 , closer to scaling for y cm At negative x F , the HERA-B result suggests a negligible effective J/ψ absorption cross section Argument for more physics at forward x F than accounted for by nuclear shadowing 20 [mb] s targets Experiment NA60 17 Al,Cu,In,W,Pb,U / Be PHENIX - PRL 107, 142301 (2011) 18 NA3 19 Pt / p ψ abs 1.1 J/ NA60 27 Cu,In,W,Pb,U / Be σ E866 39 W / Be (a) (b) J/ ψ 16 E866 39 Fe / Be HERA-B 42 W / C 14 1.0 12 0.9 10 α 8 0.8 6 4 0.7 NA3 (19 GeV) 2 E866 (39 GeV) EKS98 PHENIX (200 GeV) 0 0.6 0 0.5 -2 -1 -2 -1 0 1 2 3 10 10 x 2 y cm x F Figure 4: (Left) Comparison of effective α for NA3, E866 and PHENIX. (Mike Leitch) (Right) Comparison of effective σ abs for J/ψ (from QWG report, 2010).

Parton Energy Loss Can Describe Trends Energy loss by multiple scattering in the initial (gluon) or final ( cc ) state results in a backward shift in the longitudinal dependence Same mechanism is responsible for k T broadening – what’s lost to longitudinal kicks increases the average p T of the final state Arleo et al. used a power law model of pp collisions to implement final-state energy loss on J/ψ , results shown below agree for fixed target interactions, when shadowing is stronger there is a separation Figure 5: (Left) Shift in x F distribution caused by energy loss. (Mike Leitch) (Right) The LHC J/ψ R p Pb ( y ) data from ALICE and LHCb compared to energy loss model of Arleo et al. .

Quarkonium Absorption Woods-Saxon nuclear density profiles typically used � ∞ d 2 b −∞ dz ρ A ( b, z ) S abs � σ pA = σ pN A ( b ) � ∞ � ∞ dz ′ ρ A ( b, z ′ ) σ abs ( z ′ − z ) � d 2 b � � = σ pN −∞ dz ρ A ( b, z ) exp − z Note that if ρ A = ρ 0 , α = 1 − 9 σ abs / (16 πr 2 0 ) The value of σ abs depends on the whether geometry is taken into account and how realistic that geometry is – hard sphere, A α etc. Effective σ abs also depends on whether or not shadowing is taken into account Feed down to J/ψ from χ c and ψ ′ decays included � d 2 b [0 . 6 S abs A ψ, dir ( b ) + 0 . 3 S abs A χ cJ ( b ) + 0 . 1 S abs σ pA = σ pN A ψ ′ ( b )] Generally assume that each charmonium state interacts with a different, constant asymptotic absorption cross section but, with color singlets, the state grows until it reaches its asymptotic size, NRQCD approach would have different absorption cross sections with different dependence on rapidity, √ s for all states The χ c A dependence remains unknown (PHENIX measured R dAu similar to J/ψ but with large uncertainties, no y dependence

A Dependence of J/ψ and ψ ′ Not Identical Fixed-target data sets (NA50 at SPS, E866 at FNAL) show clear difference at low x F (midrapidity) At RHIC, J/ψ production almost independent of centrality in d+Au collisions while ψ ′ shows a very strong dependence. Comovers? Figure 6: (Left) The A dependence for J/ψ and ψ ′ production as a function of x F from E866 at FNAL ( √ s = 38 . 8 GeV). (Right) The J/ψ and ψ ′ nuclear modification as a function of collision centrality in d+Au collisions at √ s = 200 GeV at RHIC.

Effective Absorption Cross Section Energy Dependent Data corrected for shadowing effects here, dependence of effective absorption cross section on center of mass energy is clear, similar but weaker trend is seen even without shadowing At the LHC, the absorption cross section is negligible (also, formation time stretched so that charmonium states fully formed outside the nucleus), comovers would be only possible effect = 0) [mb] NA3 NA50-400 NA50-450 E866 cms 10 HERA-B (y PHENIX ψ abs J/ σ ψ J/ 1 EKS98 2 10 s [GeV] NN Figure 7: At midrapidity, the effective absorption cross section decreases as a function of energy. (Modified from Lourenco, Wohri and RV.)

Intrinsic Charm Intrinsic charm long predicted (since 1980’s) but difficult to confirm Several groups have included an intrinsic component in global PDF analyses, Pumplin result from 2007 shown here, latest results from this group similar IC allowed within each scenario characterized by � x � c + c at µ 0 = 1 . 3 GeV, � 1 � x � c + c = 0 dx x [ c ( x ) + c ( x )] Observable consequences on the rapidity distribution at large y , different A depen- dence (surface relative to volume) causes drop at large x F ( x 1 ) Figure 8: (Left) Goodness of fit for global analyses including IC as a function of � x � C + c for the light-cone formalism of Brodsky et al. (solid), the meson-cloud model (dashed); and sea-like (dotted). The lower dots correspond to candidate fits, 0.057% for Brodsky et al. , 0.96% for the meson cloud and 1.1% for sea-like IC. The upper dots are the most marginal fits in the different scenarios, 2% for Brodsky et al. , 1.9% for the meson cloud and 2.4% for sea-like. [From Pumplin et al. ] (Right) Fraction of J/ψ produced in association with a single c -quark ( gc → J/ψc ) relative to the direct yield (NLO + ) as a function of y ψ and for no IC, sea-like and Brodsky et al. (BHPS). [From Brodsky and Lansberg.]

Shadowing Effects at the LHC

Shadowing Parameterizations Fixed by Global Fits Most fits (HKN, nDS, DSSZ, EKS, EPS) use available nDIS and Drell-Yan data, along with momentum sum rule and DGLAP evolution to fit a set of parameters modifying the proton PDFs Example shown is by Eskola and collaborators Details of fitting and data employed vary but trends are similar Most fits now available up to NLO, FGS and EPS09s also include impact parameter dependence but other centrality parameterizations also available 1.5 Fermi- antishadowing motion y a 1.0 EMC- y e 0.6 effect y 0 shadowing 0.2 x a x e -3 -2 -1 10 10 10 1 Figure 9: An illustration of the fit function R A i ( x ) for fits by Eskola et al. .