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Hadron Formation in Nuclei in Deep-inelastic Scattering

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

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Hadron Formation in Nuclei in Deep-inelastic Scattering

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

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

  5. Hadron Attenuation 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 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 Erika Garutti

  7. Parton Energy Loss (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 ~ 0.25GeV/fm  dE/dx ~ 0.3GeV/fm Erika Garutti

  8. 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 Erika Garutti

  9. Hadron Separation vsn • 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 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) Erika Garutti

  11. Cronin Effect In Heavy Ion Collisions: 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 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 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 Erika Garutti

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