Hadronization in DIS at

Valeria Muccifora (on behalf of the HERMES collaboration)

SQM2003 Atlantic Beach 12-17/03/03

•Medium modification: Parton Distributions and Fragmentation Functions.•Models for hadronization in DIS.•Nuclear attenuation measurements.

•Conclusions and outlook

Medium Modification of Parton Distributions

Inclusive DIS on nucleons -> Parton DistributionsInclusive DIS on nuclei -> EMC effect: Reduction of the structure function of a nucleus in the valence quark region (Bjorken variable x>0.4) compared to that of free nucleon.

G.A.Miller and J.R.Smith P.R.C 65 (2002)015211:…the depletion of DIS structure function observed in the valence quark is due to some interesting effect involving dynamics beyond the conventional nucleon-meson treatment of nuclear physics.

V.Muccifora SQM2003

Parton Fragmentation Semi-Inclusive DIS (SIDIS) of high energy leptons on

nucleons:=E-E’ x= Q2/2M

Z=Eh/dh(z) f

qf(x)·df·Dfh(z)

DF FFFFs are measured in e+e- and follow pQCD evolution like DFs.SIDIS multiplicities are also good measurements of FFs:

f ff

fhfff

h

DIS xqe

zDxqe

dzzxdN

N )(

)()(),(12

2

V.Muccifora SQM2003

Multiplicities vs FFsHERMES Eur. Phys. J. C21 (2001) 599

Factorization holds in the HERMES kinematics.

Isospin invariance in the production of charged and neutral pionsAgreement with NLO QCD evolution of FFs measured at LEP.

V.Muccifora SQM2003

Medium Modification of Fragmentation

Nucleus acts as an ensemble of targets: reduction of multiplicity of fast hadrons due to both hard partonic and soft hadronic interactions. Nuclear Attenuation:

Df ff

fhfff

Af ff

fhfff

De

h

Ae

h

A

xqe

zDxqe

xqe

zDxqe

NzN

NzN

zR

|)(

)()(

|)(

)()(

|)(),(

|)(),(

),(

2

2

2

2

• Medium modification of FF Dfh(z)

•Hadron formation time (f=lf/c)

=E-E’ x= Q2/2MZ=Eh/

V.Muccifora SQM2003

Formation times

dependence of the dilepton mass spectrum produced in heavy ion collision at GSI.P.L.B 411 (1997) 187.E.P.J. C5 (1998) 349.

p dependence of antiproton yield produced in p+A reaction at AGS.Nucl. Phys. A707 (2002) 224.

V.Muccifora SQM2003

Models for nuclear attenuationDirect production: One-time scale f.Bialas Chmaj, P.L.B 133 (1983) 241String model: Two-time scale model c , f.f - c=cEh/k=cz/k.(string constant k1 GeV/fm).Bialas Chmaj, P.L.B 291 (1987) 793

1),(),(2

A

AA lbPlbdlbdbR

lfh

lf

lcs

lc

l

A lbdllbdllbdlP )',(')',(')',('1 *

V.Muccifora SQM2003

FF Modification ModelGuo, Wang PRL 85 (2000) 3591

FF and their QCD evolution are described in the framework of multiple parton scattering and induced radiation.

• The emitted g and the leading q propagate coherently Landau-Pomeranchuk-Midgal interference effects. • Different modification of quark and antiquark FF.

Rescattering without g-radiation:pt-broadening.Rescattering with another q : mix of q and g FF.

g-rescattering including g-radiation: dominant contribution in QCD evolution of FF.

FF Modification ModelDq h(zh,Q2,A)´ =Dq h(zh,Q2)+ Dq h(zh,Q2)

Dq h(zh,Q2)' CA s2/Nc C/Q2x2A dq h(zh,xB,xA,Q2).

EEzD

EE /1/11

Equivalent to rescale the FF for the fraction of the parton energy loss E/E: D(z)

Wang, Guo N.P. A 696 (2001) 788

Arleo JHEP 11 (2002) 44.

Quark energy loss shift its energy:and leads to a z shift:

hh

qq

EzEz

EE

*

)*,(*),(),,( 22 QzDzDdAQzzD hf

Eh

o

hf

V.Muccifora SQM2003

Rescaling Model

In the nucleus: A>N Q2 rescalingqf

A(x,Q2)=qf(x,A(Q2)Q2)Df

h|A(z,Q2)=Dfh(x,A(Q2)Q2)

Scale factor related to deconfinement scale:

Q2 appears scaled either by (mass scale parameter) or by 2 (low momentum cutoff): 1/ 2 2

Accardi, Muccifora, Pirner, nucl-th 0211011, NPA in print.

Multiplicity appears with rescaled DF and rescaled FF:),(),(11 222 QzD

dxddQxqedxd

dzdN

N Ahf

q

f AffA

hA

e

(Supplemented by nuclear absorption in terms of string model)

)(2)(

)(2

0

2

2

QQ

Q sA

N

A

HERMES at DESYHERMES studies the spin structure of the nucleon … and

not only..

V.Muccifora SQM2003

E=27.5 GeV e+ (e-)I ~ 30 mA

p beam of 920 GeV, not used by HERMES

Internal target polarized and unpolarized gas.Last part of the fill:high-density unpolarized runs.

HERMES Spectrometer

•e+ identification: 99% efficiency and <1% of contamination.•Particle identification: Cerenkov (RICH ’98), TRD, Preshower, e.m. Calorimeter.•14N: Cerenkov 4< P<14 GeV.•84Kr: RICH , K, p, p separation 2.5<P<15 GeV.

-

V.Muccifora SQM2003

Hadron attenuation vs transfer energy

•HERMES kinematics optimal to study medium effect in FF.•Increase with consistent with the EMC data at higher

energy.•Discrepancy with SLAC mainlydue to the EMC effect

HERMES, EPJ C 20 (2001) 479.HERMES, hep-ex/0012049.EMC Coll. Z.Phys. C52 (1991) 1.SLAC PRL 40 (1978) 1624.

V.Muccifora SQM2003

Hadron attenuation vs z=Eh /

•HERMES data provide information in the unexplored region z>0.8.

V.Muccifora SQM2003

EMC SLAC

Charged hadron/pion on 14N

No difference between + and -

Difference between h+

(+,K+,p) and h- (- ,K-,p-).different th for different hadrons

RICH to clarify the differences for different h

V.Muccifora SQM2003

different FF modification for different hadrons

Attenuation on 84Kr vs with hadron IDRICH ID: /K (2.5-15 GeV),p/p (4-15 GeV).-

• ++- and K-

• K+ > K-

• p> p and p> /K-

V.Muccifora SQM2003

Attenuation on 84Kr vs z with hadron ID

Possible interpretation:

•Different FF modification for q and q.

-

•Different tf for mesons and baryons.•Different hadronic cross sections: += - 20 mb.+ 17 mb - 23 mb.p

40 mb p 60 mb

-

V.Muccifora SQM2003

Hadron attenuation vs FF modification(parton scattering and induced radiation without hadron-

rescattering)E.Wang , X.N. Wang PRL 89 (2002)

162301.

• First evidence of the quadratic nuclear size dependence [A2/3] th due to QCD radiation spectrum and LPM interference.•1 free parameter Cquark-gluon correlation strength

in nuclei.•From 14N data C=0.0060 GeV2:

22ANsg RmCznE

V.Muccifora SQM2003

Gluon density by dE/dLE.Wang , X.N. Wang PRL 89 (2002)

162301.

• Esta 0RA2 ; 0 gluon density and RA6 fm

• exp Esta (20/RA); 0 initial formation time of dense medium

PHENIX: hot, expanding system.HERMES: cold, static system.

V.Muccifora SQM2003

dE/dLPHENIXAu predictions determined by using C=0.0060 GeV2 from HERMES data.<dE/dL>0.5 GeV/fm for 10-GeV quark in Au.

Gluon density in the initial hot stage of Au+Au is 15 times higher than in cold nuclear matter.

F. Arleo JHEP 11 (2002) 044.<> s Q L2

Transport coefficient Q=0.75 GeV/fm2 derived from Drell-Yan

Hadron attenuation vs FF modification

• dE/dL=<>/L dE/dL=0.62 GeV/fm for L 5 fm. V.Muccifora SQM2003

Q2-rescaling + nuclear absorptioncharge and flavor dependence

•Different cross sections for different hadrons (isospin averaged) Q2-rescaling: upper curves Q2-rescaling + Nuclear absorption (LUND string model for hadron formation and interaction): lower curves

Nice agreement for +, - and K+. • K- data show higher absorption. V.Muccifora SQM2003

Q2-rescaling + nuclear absorptioncharge and flavor dependence

• Discrepancy between data and predictions for K-

suggests a stronger absorption mechanism for particles that do not contain any valence quark.

V.Muccifora SQM2003

• Shorter hadron formation length since rank 1 hadrons would not partecipate in the K-

formation in the model:

K- and K+ (p and p) data can provide new insightabout formation length

-

In the lepton-nucleon scattering neither multiple scattering of the incident particle nor interaction of its constituents complicate the

interpretation.

Clean and reliable information on quark transport in ‘cold’ nuclear matter.

Attenuation vs pt2 (Cronin effect)

•The hard component of the incoherent parton scattering becomes dominant at pt 1-2 GeV.•The higher pt enhancement in Kr suggest A-dependence for Cronin in DIS.

EMC

HERMES

V.Muccifora SQM2003

Direct measurements of multiparton correlation functions

<pt> broadening depends on multiparton correlation function TqF

A and on nuclear size A1/3:

pt -broadening in SIDIS

),(

),()(

22

1222

22 min

Qxqe

dzQxTzDzepp A

q

z

AqFq

eN

t

eA

t

•HERMES data, on 5 nuclei and for , K, p and p, will provide infos on the A- and flavor-dependence of <pt> .

-

V.Muccifora SQM2003

-•RHIC: different <pt>

for , K, p and p.

Conclusions & Outlook

First observation of hadron-type dependence of the attenuation. Cronin effect has been observed.

The HERMES measurements are providing information on:

• Nuclear modification of the quark Fragmentation Functions,

• Hadronization times,• Partonic energy loss and Cronin effect. GOAL:

To obtain unambiguos informations on hadron and quark transport in

Cold Nuclear Matter

Near Future:pt-broadening for , K, p and p.Collected data on 4He, 20Ne New insights on the A-dependence.

-

Nuclear attenuation in a new region of kinematic plane for 14N and 84Kr and for the first time for identified +, -, K+, K-, p, p .

-

Falter et al. nucl-th/0303011FSI by means of a BUU transport model. Input parameter f

Hadron FSI and formation times

RMh very sensitive

to the interaction cross section of thepropagating leading hadrons.

Average f >0.3 fm/c compatible with the values extracted fromp+A reactions at AGS.V.Muccifora SQM2003