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

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

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

HERMES experiment Tracking: dP/P = (0.7-1.3)%, dq < 0.6 mrad Particle ID: Target: dP/P = (0.7-1.3)%, dq < 0.6 mrad detector eff. 99% (e+), RICH eff. 95% (p), 85% (K), 73% (p) r ~ 1015-1016 nucl/cm-2 , gas: 2H, 3He, 14N, 20Ne, 84Kr DIS2002 Erika Garutti

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

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

Parton Energy Loss Calculated from DIS data: Compared to hadron yield (X.N. Wang, hep-ph/0111404) 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

Gluon Bremsstrahlung Model (B.Kopeliovich et al., hep-ph/9511214) 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

Hadron Separation vs n Observations: Ratt|p+/p- ~ Ratt|K+/K-  tfp+/p- ~ tfp+/p- R att|p < Ratt|p : s(pd) @ 3s(pd) @ E = 1 GeV (?) R att|p < Ratt|p/K  tfp > tfp/K (?) Average kinematics DIS2002 Erika Garutti

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

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/0104031)  Transition at pt ~ 1-2 GeV/c Similar pt2-enhancement Clean information on quark transport in cold nuclear matter DIS2002 Erika Garutti

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

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