Nuclear effects in dis at hermes
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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

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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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