1. Hadron Attenuation by (pre-)hadronic FSI at HERMES
T. Falter, K. Gallmeister, U. Mosel Univ. Giessen, Germany
Duality 05, Frascati June 2005

2. space-time picture of hadronization
Motivation
elementary reactions (eN, gN)
reaction products hadronize long before they reach the detector
confinement ?
estimation of
formation time via hadronic radius
(rh = 0.5 – 0.8 fm) r h t
> f c
time dilatation: t = g t f f
nuclear reactions (eA, JLAB, HERMES or EMC energies)
space-time picture of hadronization
interactions with nuclear medium during tf

3. Motivation Connection with heavy ion physics Au+Au
jet supression at SPS and RHIC (partly due) to hadronic FSI ?
W. Cassing, K. Gallmeister, C. Greiner, NPA 735, 277 (2004).
K. Gallmeister, W. Cassing, NPA 748, 241 (2005).
Au+Au

4. Model eA, gA reactions splitted into 2 parts
g*N ® X using PYTHIA & FRITIOF
additional consideration of
binding energies
Fermi motion
Pauli blocking
coherence length effects
propagation of final state X within
BUU transport model
consideration of
elastic and inelastic scattering (coupled channels)
→ absorption, particle production
kinematical cuts, detector acceptance

5. Hard Interactions eg. direct g*N excitation of hadronic strings
fragmentation according LUND-model
eg. direct g*N
= production point of
color neutral prehadron

6. Hadronic Structure of Photon
HERMES:
VMD, GVMD present
shadowing plays minor role (few percent effect)

7. „Default“ Approach in Transport
string fragments very fast into
color-neutral prehadrons tp = 0
prehadrons need formation time tf = ghtf
to build up hadronic wave function
prehadronic cross section s*
determined by constituent quark model
“leading” prehadrons
(= target-, beam remnants)
can undergo FSI directly
after g*N interaction
hadrons that solely contain quarks
from string fragmentation start to
interact after tf
„Default“ Approach in Transport
s*m = #qini/2 sh
s*b = #qini/3 sh

8. Hadron Attenuation in DIS
Multiplicity Ratio
Experiments
EMC: GeV m-beam on 64Cu
HERMES: GeV e-beam on 14N, 20Ne, 84Kr
Jefferson Lab: 5.4 GeV e-beam on 12C, 56Fe, 208Pb
Attenuation due to
partonic energy loss
X.N.Wang et al., F.Arleo
(pre)hadronic absorption
A.Accardi et al. + rescaling of fragmentation function
B.Kopeliovich et al., T.Falter et al. E h z = h n

9. DIS off Proton HERMES = 2.5 – 24 GeV, Q2 > 1 GeV2, W > 2 GeV
red curves: calculation w/o cuts on hadron kinematics
and assuming 4p-detector
= 2.5 – 24 GeV, Q2 > 1 GeV2, W > 2 GeV

10. Cuts, Acceptance, Averages
charged hadron production in DIS off 84Kr at HERMES
including all experimental cuts
accounting for angular acceptance
of HERMES detector
average kinematic variables from simulation:

11. Without prehadronic FSI
charged hadrons
prehadronic interactions needed

12. tf > 0.5 fm/c compatible with pA data at AGS energies
With prehadronic FSI
charged hadrons
tf > 0.5 fm/c compatible with pA data at AGS energies

13. Influence of Detector charged hadrons (tf = 0.5 fm/c)
needs to be accounted for at zh < 0.4
important for integrated spectra

14. from calculations: <kT>A = <kT>N , ie. not Cronin!
pT Spectra
Cronin ???
from calculations: <kT>A = <kT>N , ie. not Cronin!

15. Attenuation Identified Hadrons
20Ne
84Kr

16. 4D production-/formation points
Extract all information from PYTHIA
for every individual particle
respect finite mass of string
n=14 GeV
Q2=2.5 GeV2
Bialas et al.

17. Attenuation Charged Hadrons
t<tProd2: s=0
t>tProd2: s=sh
Attenuation „Identified hadrons“ will follow soon!
Other cross-section scenarios will be considered.

18. Summary model for g and e induced reactions at GeV energies combines:
QM coherence in entrance channel
coupled channel transport description of FSI
detector acceptance, kinematical cuts
can decribe
coherence length effects in exclusive r0 production
most features observed in hadron attenuation
works also for:
g and e reactions in resonance region
pA, pA and AA reactions
4D Points from PYTHIA:
consistent description of LUND-Fragmentation in MC
at HERMES energies
same parameter set

19. Future Plans HERMES: better description of detector (“loss function”)
PYTHIA: partonic energy loss
side feeding in photo- and electroproduction of charm …

20. Particle origin
HERMES kinematics

21. Effective XS of nucleus debris
comparison with gluon bremsstrahlung model
C. Ciofi degli Atti and B. Z. Kopeliovich, Eur. Phys. J. A 17, 133 (2003).

22. Double hadron attenuation
(tf = 0.5 fm/c)
leading hadron
z1 > 0.5
subleading hadron
z2 < z1