1. Hadron Formation in Nuclei in Deep-inelastic Scattering
Erika Garutti (NIKHEF)
On behalf of the HERMES collaboration
Nuclear Attenuation on 14N and 84Kr
Kinematics Dependences
Attenuation for Different hadron types
Hadron Formation Times
Conclusion and Outlook
DIS2002
Erika Garutti

2. Hadron Production in DIS 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
Fragmentation functions from SIDIS multiplicities
DF FF
DIS2002
Erika Garutti

3. 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 160 GeV) depend on tpf
mT = transverse mass
A = collision area of two nuclei
dN/dy = rapidity density
DIS2002
Erika Garutti

4. HERMES experiment Tracking: dP/P = (0.7-1.3)%, dq < 0.6 mrad
Particle ID:
Target:
dP/P = ( )%, dq < 0.6 mrad
detector eff. 99% (e+), RICH eff. 95% (p), 85% (K), 73% (p)
r ~ nucl/cm-2 , gas: 2H, 3He, 14N, 20Ne, 84Kr
DIS2002
Erika Garutti

5. Hadron Attenuation Data Selection Kr: p, K, (p) from RICH 14N
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 Cerenkov
Ph < 1.4, 4 < Pp < 13.5 GeV
DIS2002
Erika Garutti

6. 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
Dhf(z) modification scales with A2/3
DIS2002
Erika Garutti

7. Parton Energy Loss Calculated from DIS data: Compared to hadron yield
(X.N. Wang, hep-ph/ )
Calculated from DIS data:
cold matter
Compared to hadron yield
in Au-Au collisions:
expanding system (QGP)
 dE/dx ~ 0.25 GeV/fm
 dE/dx ~ 0.3 GeV/fm
DIS2002
Erika Garutti

8. Gluon Bremsstrahlung Model
(B.Kopeliovich et al., hep-ph/ )
pQCD based model for high-z mesons:
Highly virtual quark looses energy via gluon
emission till final meson is formed
nuclear suppression +
induced radiation 
Suppression of high-z mesons
high-z: quarks emit only few gluons
correspond to small tf
long time for hadron-Nucleus interaction:
 Strong Suppression
DIS2002
Erika Garutti

9. Hadron Separation vs n Observations: Ratt|p+/p- ~ Ratt|K+/K-
 tfp+/p- ~ tfp+/p-
R att|p < Ratt|p :
E = 1 GeV (?)
R att|p < Ratt|p/K
 tfp > tfp/K (?)
Average kinematics
DIS2002
Erika Garutti

10. Hadron Separation vs z R att(z)|p ~ Ratt (z)|K 
R att|p >1 for low z:
rescattering (?)
R att|p at high z:
information on Dpq(z)
(Guo & Wang , PRL 85 (2000) 3592)
DIS2002
Erika Garutti

11. Cronin Effect In Heavy Ion Collisions: In DIS on nuclei:
Enhancement at high pt in AA
collisions relative to pp collisions.
In DIS on nuclei:
Agreement with multiple parton
scattering model
(E.Wang and X.N.Wang nucl-th/ )
 Transition at pt ~ 1-2 GeV/c
Similar pt2-enhancement
Clean information on quark
transport in cold nuclear matter
DIS2002
Erika Garutti

12. Conclusions & Outlook Strong nuclear attenuation at high z
Similar attenuation for p and K
Observed: R att|p < Ratt|p/K
Interpretation: tfp > tfp/K (?)
Gluon bremsstrahlumg model describes n and z
dependence of nuclear attenuation for pions.
Comparison between 14N and 84Kr in agreement
with Dhf(z) modification model.
Observed Cronin effect with a transition between
hard and soft processes around pt = 1 GeV.
more to come:
additional HERMES data on 4He and 20Ne
comparison to theory for separate hadron type
DIS2002
Erika Garutti

13. Formation Time Extraction
Model used:
one time scale with
sq = 0, sh = 25 mb
i.e. n = 14 GeV, z = 0.5
 tpf = 3 10–23 sec
DIS2002
Erika Garutti