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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
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
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