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

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, gA @ JLAB, HERMES or EMC energies) space-time picture of hadronization interactions with nuclear medium during tf

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

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

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

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

„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

Hadron Attenuation in DIS Multiplicity Ratio Experiments EMC: 100-200 GeV m-beam on 64Cu HERMES: 27.6 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

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

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:

Without prehadronic FSI charged hadrons prehadronic interactions needed

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

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

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

Attenuation Identified Hadrons 20Ne 84Kr

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.

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

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

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

Particle origin HERMES kinematics

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).

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