Masanori HIRAI 2006, Nov 9, Tokyo-u Observation on dA scattering at forward rapidities V. Guzey, M. Strikman, and W. Vogelsang Phys. Lett. B603 (2004) 173-183 Masanori HIRAI 2006, Nov 9,　Tokyo-u

Introduction BRAHMS at RHIC ? PRL93,24303 (2004) Deuteron-Au collision RdAu , Rcp Forward rapidity h=2.2, 3.2 for negatively charged hadron Suppression of RdAu increasing hadron rapidity Nuclear effect of initial condition in target nucleus Shadowing effect ? ? Expectation of enhancement of h- in dAu experiment, However.. Isospin considerations [p: up(x)>dp (x), d:ud(x)=dd(x)] NLO pQCD calculation Parton moment fraction x for hadron production at BRAHMS Effect of leading-twist nuclear shadowing

NLO pQCD calculation Success for RHIC experiment pp  0 X at s=200 GeV PHENIX collaboration, PRL91, 241083 (2003) dAu for central rapidity h=0 D. de Florian, R. Sassot, PRD69, 074028 (2004) Prediction for hadron production High precision Ambiguity of initial and final distributions PDF and FF obtained by global analysis Forward region ? STAR collaboration, PRL92, 171801 (2004) 3.4<h<4.0, h=3.8: good agreement BRAHMS ?

Kinematics and x ranges probed in forward scattering Cross section by pQCD Theoretical uncertainty mR,F=pT (pT/2..2pT) Non-perturbative part Parton distribution function f(x) Fragmentation function D(z) Perturbative part Partonic cross section 22 process gggg, ggqq,qgqg qqqq, qq’qq’ qqqq, qqgg, qqq’q’

Kinematics and x ranges probed in forward scattering Kinematics for hadron production

Kinematics and x ranges probed in forward scattering Cross section for 22 process Integration of phase space for the parton d

Kinematics and x ranges probed in forward scattering Another integration for zc 23 process in NLO

Kinematics and x ranges probed in forward scattering Central rapidity: h=0 Symmetric x1 and x2, pT/s Forward scattering h>0 Asymmetric x1 covering the large-x region, x2 at small-x How small x2 in forward region x2 > 0.01, pT=1.5 GeV The shape depends on the PDF sets Increasing x2 with pT One of estimation for average <x2> CTEQ6M GRV98

Influence of leading-twist nuclear shadowing Nuclear target d & Au Nuclear effect on PDFs Shadowing effect, x<0.1 Antishadowing, 0.1<x<0.2 EMC effect, 0.2<x<0.8 Fermi motion, x>0.8 BRAHMS kinematics Averaged x2=0.01: shadowing effect ? Leading-twist NPDF Diffractive L. Frankfurt, V. Guzey, M. Strikman, PRD71, 054001 (2005) Global fit with nuclear DIS and DY data M.H, S. Kumano, N. Nagai, PRC70, 044905 (2004) D. de Florian, R. Sassot, PRD69, 074028 (2004)

Leading-twist nuclear shadowing Gribov’s theorem:Sov. Phys. JETP29, 483 (1969) Relation between nuclear shadowing and diffraction Factorization of diffraction process: J. C. Collins,PRD57, 3051 (1998) Diffractive PDF fD(b,Q2,xp,t) obtained by HERA measurement NPDF taking account of shadowing effect Neglected nuclear effect of deuteron: d=(p+n)/2 A few % correction Q2 evolution given by DGLAP equation NPDF at initial scale Q2=2 GeV Large effect of gluon shadowing Diffractive constitute, 10%(quark), 30%(gluon) Satisfying conservation low Baryon number, momentum conservation Antishadowing effect from momentum cons Enhancement: x=0.1(quark), x=0.03(gluon)

Other nuclear PDFs Pb/D valence antiquark gluon Ca/D

Nuclear PDFs by DS Valence- and anti-quark distributions Ca/D Valence- and anti-quark distributions are very similar. Gluon shadowing is fairly small, but it is within the HKN uncertainties.

Nuclear effect on p0 production D(x1)-Au(x2)  p0 + X Suppression at small-x Shadowing effect Enhancement at x=0.1 Antishadowing effect pT increasing Decreasing shadowing effect Shad.1 & shad.2 Enhancement at x, #1:x=0.03, #2:x=0.1 Suppression RdAu due to shadowing Forward rapidity  small value of x2 Low pT

Isospin consideration for the ratio of dA and pp cross section BRAHMS data h=0, 1: (h++h-)/2 h=2.2, 3.2: h- Charged hadron Assuming pion dominant qg process d:f(x1), Au:g(x2) Enhancement of RdAu of negative hadron p: p+>p-, u-quark dominates d: p+=p-, ud(x1)= dd(x1)=[dp (x1) +up (x1)]/2 Valence quark distribution in d and p Important role in forward h- production

Ration RdAu(pT) Charged hadron Negative charged hadron Moderate pT dependence Negative charged hadron h=2.2, 3.2 Increasing RdAu with pT Difference of dv quark contribution Suppression in low-pT Shadowing effect Positive charged hadron s(dAu h+X)> s(dAu h-X) Factor 3 at pT=3 GeV ? Challenging to understanding it in terms of a non-perturbative effect

Conclusion and outlook Intrinsic enhancement of RdAu for negative hadron Different nature of the “projectile” (deuteron vs. proton) Suppression of RdAu for summed charged hadron Impossible to explain RdAu suppression at forward rapidity NLO pQCD+ Leading-Twist NPDF(shadowing& antishadowing) Suppression of 15% due to shadowing effect Positive charged hadron vs. negative charged hadron Enhancement of proton production ? Experimental data is quite challenging to understanding Energy loss effect Initial state only: 10% Initial & final state: 3%