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Nuclear effects in DIS at HERMES. Erika Garutti (NIKHEF) On behalf of the HERMES collaboration. Inclusive DIS on nuclei ( 14 N and 84 Kr) Semi-inclusive DIS on nuclei Nuclear Attenuation  Hadron Formation Times Link to heavy-ion physics Conclusion and Outlook.

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nuclear effects in dis at hermes

Nuclear effects in DISat HERMES

Erika Garutti (NIKHEF)

On behalf of the HERMES collaboration

  • Inclusive DIS on nuclei (14N and 84Kr)
  • Semi-inclusive DIS on nuclei
  • Nuclear Attenuation  Hadron Formation Times
  • Link to heavy-ion physics
  • Conclusion and Outlook

Antwerpen, 16-19 Sep. 2002

medium modification of parton distributions
Medium modification of Parton Distributions

Late ’60s:Inclusive high energy DIS of leptons on nucleons

Parton Distributions

’80s:Inclusive lepton DIS on nuclei

Medium effects

(shadowing,EMC effect)

Antwerpen, 16-19 Sep. 2002

the q 2 dependence
… the Q2 dependence

Antwerpen, 16-19 Sep. 2002

medium modification of parton fragmentation
Medium modification ofParton Fragmentation

DF FF

Semi-Inclusive DIS of leptons on nucleons

(LO)

Fragmentation functions from SIDIS multiplicities

Semi-Inclusive DIS of leptons on nuclei

  • Nuclear Attenuation:
  • Reduction of multiplicity of the
  • fast forward hadrons due to:
  • Hard partonic interactions
  • Soft hadron interactions.
  • Formation time:

tf = lf / c

Antwerpen, 16-19 Sep. 2002

motivation
Motivation
  • Why is formation time of interest?
  • Dependence on hadron type
  • Comparison to model predictions
  • Link to Heavy Ion physics
  • Formation time in Heavy Ion physics:
  • Initial energy density in Quark Gluon Plasma

plasma formation time  Estimate t0 ~ tf (?)

  • Impact of tpf in dilepton spectrum

(P.Filip,J.Pisut Phys. Lett. B 411 (1997) 187)

Predictions for in Pb-Pb (LHC, @ 160 GeV) depend on tpf

mT = transverse mass

A = collision area of two nuclei

dN/dy = rapidity density

Antwerpen, 16-19 Sep. 2002

hadron attenuation
Hadron Attenuation

14N

Multiplicity ratio for A/D

Multiplicity ratio for A/D

z > 0.8

Unexplored

region

  • Data Selection
  • Kr: p, K, (p) from RICH
  • 2.5 (4) < Ph < 15 GeV
  • x > 0.06 , y < 0.85
  • Q2 > 1 GeV2 , W2 > 4 GeV2

N: h, p from Cherenkov

  • Ph < 1.4, 4 < Pp < 13.5 GeV

Antwerpen, 16-19 Sep. 2002

gluon bremsstrahlung model
Gluon Bremsstrahlung Model
  • (B.Kopeliovich et al., hep-ph/9511214)
  • pQCD based model for high-z mesons:
  • Highly virtual quark looses energy via gluon
  • emission till final meson is formed
  • induced radiation +
  • nuclear suppression
  • (dominant)
  •  cp = 1.35 [fm/GeV c]
  • Suppression of high-z mesons
  • high-z: quarks emit only few gluons
  • correspond to small tf
  • long time for hadron-Nucleus interaction

tf = ch n(1-z)

Antwerpen, 16-19 Sep. 2002

direct production on 14 n
Direct Production on 14N

(HERMES Coll., EPJ C20 (2001) 479)

  • Phenomenological inter-nuclear
  • reinteraction model:
  • DIRECT PRODUCTION
  • (1-time scale model)
  • (Bialas & Chmaj, PLB 133(1983) 241)
  • tf = ch n(1-z)
  • s*= 0
  • sh fixed for diff. h-type

Multiplicity ratio for 14N/D

Antwerpen, 16-19 Sep. 2002

hadron separation vs z
Hadron Separation vs z

1-time scale model fit:

  • leading hadrons (z > 0.5)

cp consistent with 14N

  • 14N: 1.37+/-0.18 fm/Gev
  • 84Kr: 1.49+/-0.10 fm/GeV
  • cp consistent with gluon brems. model
  • Th: 1.35fm/GeV
  • cp > cp/K
  • att(z)|p ~ att(z)|K
  • att|p >1 for low z:
  • rescattering
  • att|p at high z:
  • information on Dpq(z)
  • (Guo & Wang , PRL 85 (2000) 3592)

Antwerpen, 16-19 Sep. 2002

hadron separation vs n
Hadron Separation vsn
  • Observations:
  • att|p+/p- ~ att|K+/K-
  •  tfp+/p- ~ tfK+/K-
  • att|p> att|p :
  • s(pd) @ 3s(pd) @ E = 1 GeV (?)
  • att|p< att|p/K
  •  tfp> tfp/K (?)
  • Average kinematics

Antwerpen, 16-19 Sep. 2002

hadron separation vs n1
Hadron Separation vsn

Enhancement at high n due to

rescattering of produced hadron

on target protons

Leading protons have Ratt < 1

Antwerpen, 16-19 Sep. 2002

fragmentation function modification model
Fragmentation Function Modification Model

(Guo & Wang , PRL 85 (2000) 3592)

Modification of Dhf(z) in medium due to

multiple parton scattering (in QCD)

 Dhf(z) modification increases for small n

 DDhf(z) scales with A2/3 due to LPM interference

Antwerpen, 16-19 Sep. 2002

parton energy loss
Parton Energy Loss

(X.N. Wang, hep-ph/0111404, X.N. Wang, hep-ph/0202105)

Compared to hadron yield

in Au-Au collisions:

average over expanding system (QGP)

Dhf(z) Modificationequivalent

toDhf(z) Rescaling by parton

Energy loss (DE/E):

 dE/dx ~ 0.25GeV/fm

  • expansion corr.  hot,dens system
  • dE/dx|stat~dE/dx|exp(RA/2t0) = 4.5 GeV/fm
  • RA ~ 6fm, t0 ~ 0.2 fm
  • Gluon density in initial stage of Au-Au QGP is ~ 15 times that of cold nuclear matter

Calculated from DIS data:

cold, static system

 dE/dx ~ 0.3GeV/fm

Antwerpen, 16-19 Sep. 2002

cronin effect
Cronin Effect

In Heavy Ion Collisions:

Enhancement at high pt in AA

collisions relative to pp collisions.

In DIS on nuclei:

Multiplicity ratio for A/D

Agreement with multiple parton

scattering model

(E.Wang and X.N.Wang nucl-th/0104031)

 Transition at pt ~ 1-2 GeV/c

  • Similar pt2-enhancement
  • Clean information on quark
  • transport in cold nuclear matter

Antwerpen, 16-19 Sep. 2002

conclusions outlook
Conclusions & Outlook
  • Strong nuclear attenuation at high z and low n
  • Similar attenuation for p and K
  • Observed: att|p< att|p/K
  • Interpretation: tfp> tfp/K (?)
  • Nuclear modification of Dhf(z) unambiguous info
  • Hadronization times on quark transport
  • Parton energy loss and Cronin effect in cold matter

more to come:

  • additional HERMES data on 4He and 20Ne
  • pt broadening for p, K, p
  • comparison to theory for separate hadron type

Antwerpen, 16-19 Sep. 2002

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