Electroproduction of hadrons in nuclei

Transcription

1 Electroproduction o hadrons in nuclei Nicola Bianchi Bianchi@ln.inn.it Fragmentation Function modiications in the nuclear medium HERMES recent and new results Expectations rom CLAS Interpretations Workshop on on In-Medium Hadron Hadron Physics. Giessen, November

2 DF on Nucleon & Nuclear Medium h dσ h ( z ) q ( x) dσ D ( z) Inclusive DIS on nuclei: EMC eect Medium modiications o Distribution Functions : interpretation at both hadronic (nucleon s binding, Fermi motion, pions) and partonic levels (rescaling, multi-quark system)

3 Fragmentation Functions on Nucleon h z D d x q z ) ( ) ( ) ( d h σ σ FFs are measured with precision in e+e- FFs ollow pqcd Q -evolution like DFs FFs scale with z=e h /< like DFs with x FFs probabilistic interpretation like DFs SIDIS multiplicities are also good measurements o FFs: = h h DIS x q e z D x q e dz z x dn N ) ( ) ( ) ( ), ( 1

4 SIDIS multiplicities on Nucleon (HERMES: EPJ C1(001) 599). What happens in a nuclear medium?

5 Nuclear Attenuation Observation: reduction o multiplicity o ast hadrons due to both hard partonic and sot hadron interaction. Production and Formation Times + FF modiications are crucial or the understanding o the space-time evolution o the hadron ormation process

6 Hadron multiplicity ratio Experimental observable: hadron multiplicity ratio in nuclei and deuterium Nh ( z, ν) N DIS DIS A R M (z, υ) = = = N h ( z, ν) 1 d σh N DIS 1 σ σ DIS Determine R M versus: d σh dzdν dzdν Leptonic variables : ν (or x) and Q Hadronic variables : zand P t Dierent nuclei : size and density D h Σe q (x)d (z) Σe q (x) h Σe q (x)d (z) Σe q (x) A D Dierent hadrons : lavors and mixing o FFs

7 Experiments SLAC: 0 GeV e - -beam on Be, C, Cu Sn PRL 40 (1978) 164 EMC: GeV µ-beam on Cu Z.Phys. C5 (1991) 1. WA1/59: 4-64 GeV ν(ν)-beam on Ne Z.Phys. C70 (1996) 47. HERMES: 7.6 or 1 GeV e + -beam on He, N, Ne, Kr, Xe. EPJ C0 (001) 479. PLB 577 (003) ATTENUATION CLAS: 5.4 GeV e - -beam on C, Fe, Pb E-0-104

8 The energy range (ν 3-5 GeV) is well suited to study medium eects. Measurements over the ull z range Possibility to use several dierent gas targets PId: π +, π -, π 0, K +, K -, p, p -

9 HERA It is an experiment which studies the spin structure o the nucleon and not only E=7.5 1 GeV e + (e - ) I ~ 30 ma p beam o 90 GeV, not used by HERMES Last part o the ill dedicated to high-density unpolarised target runs:

10 The Spectrometer (NIM A417 (1998) 30) e+ identiication: 99% eiciency and < 1% o contamination PID: RICH, TRD, Preshower, e.m. Calorimeter For N target: by Cerenkov π ID 4<p<14 GeV For He, Ne, Kr targets: by RICH π, K, p ID.5<p<15 GeV π 0 ID by e.m. Calorimeter.

11 Particle Identiication Positrons hadrons separation: Double radiator RICH: Aerogel + C 4 F 10. Cerenkov photons detected by ~4000 PMTs. Detection eiciency: 99% (π), 90% (K), 85-95% (p)

12 Hadron multiplicity ratio vs transer energy ν HERMES, PLB 577 (003) 37 EMC Coll. Z.Phys. C5 (1991) 1. SLAC PRL 40 (1978) 164 Clear nuclear attenuation eect or charged hadrons. Increase with ν consistent with EMC data at higher energy Discrepancy with SLAC due to the EMC eect, not taken into account at that time HERMES kinematics is well suited to study quark propagation and hadronization

13 Hadron Multiplicity Ratio vs z=e h /ν EMC SLAC WA1/WA59 HERMES

14 Multiplicity ratio or identiied hadrons vs ν HERMES, PLB 577 (003) 37 Experimental indings: π + = π - = π 0 ~ K - K + > K - p > -p, p > π, p > K

15 Multiplicity ratio or identiied hadrons vs z HERMES, PLB 577 (003) 37 Dierent FF modiication or quark and anti-quark Dierent τ p and τ h or mesons and baryons Dierent σ h : σ π+ = σ π- 0 mb σ Κ+ 17 mb, σ Κ- 3 mb σ p 40 mb, σ p- 60 mb

16 Multiplicity ratio on He, Ne, Kr nuclear attenuation: 1-R h = A α Data suggest α~/3

17 Multiplicity ratio on He, Ne, Kr

18 Multiplicity ratio vs Q Q Dependence: indication o FF evolution modiication Stronger at small ν (large x); weaker at high ν (small x)

19 Hadrons and E beam =1 & 7 GeV Extension o the ν range down to GeV Measurements are still in progress at HERMES <ν<3 GeV Q <10 GeV

20 Multiplicity Ratio vs p t In pa and AA collisions hadrons gains extra transverse momentum due to the multiple scattering o projectile partons propagating through the nucleus (Cronin eect.) CERN SIDIS show a p t enhancement similar to that observed in AA scattering. The enhancement in AA is typically explained at p t ~1- GeV assuming ISI. In SIDIS Cronin only rom FSI : no multiple scattering o the incident particle nor interaction o its consituents.

21 P t dependence or identiied hadrons Nucl-ex/ Dependence o the Cronin eect on the hadron species. Cronin eect or protons larger than or pions.

22 Experiments with CLAS and CLAS++ (NIM A503 (003) 513) 5.4 GeV exp. in 003 Q 4 GeV, ν 5 GeV 11 GeV in with Jlab upgrade Q 9 GeV, ν 9 GeV Charged particle angles Neutral particle angles 8-70 Momentum resolution ~0.5% (charged) Angular resolution ~0.5 mr (charged) Identiication o p, π + /π -, K + /K -, e - /e +

23 Factorization issues at Jlab Given the relatively low energy o Jlab (max 6 GeV) the actorization o SIDIS into DF and FF maybe questionable Semi-inclusive asymmetry A 1p (π + ) agrees with HERMES alls on the same curve as inclusivea 1p ; no z-dependence observed Cross section reproduced by Monte- Carlo based on LO x-z actorization (Hall C). LO x-z actorization is not (much) violated at 6 GeV

24 Anticipated CLAS Data Can measure π +,,0, η, ω, η, φ, Κ +,,0, p, Λ, Σ +,0, Ξ 0,

25 CLAS EG, very preliminary, 5% o total data set DIS kinematics, Q >1, all ν Ask this plot to Will Brooks brooksw@jlab.org Carbon Iron Lead No acceptance correction (small, two targets in the beam) Not inal calibrations (should be nearly irrelevant, bins are huge) No iducial cuts (probably ok, two targets in beam) No radiative correction (eect primarily cancels in ratios) No correction or pi+ rom rho (need ull statistics to correct or this)*** Few-percent kaon contamination in region -.7 GeV No isospin correction or heavy targets(~5%?) No x F cuts

26 Expectations rom Hall-A E04-00 For ixed kinematics a high precision meas. at large z

27 Expectations rom CLAS++ upgrade

28 Models based on pre-hadronic interaction B. Kopeliovich et al.: hep-ph/951114, NPA 740, 11 (004). T. Falter et al.: nucl-th/040603, PRC in print. A. Accardi et al.: NPA 70, 131 (003). Important role o the pre-hadron ormation and interaction : Which time and cross section? Absorption or rescattering? Hadron ormation mainly outside the nucleus. Induced radiation is a smaller contribution compared to absorption or rescattering. Models based on partonic energy loss X.N. Wang et al.: PRL 89, (00). F. Arleo et al.: EPJ C 30, 13 (003). Energy loss mechanism or the hadron suppression, parton rescattering or the enhancenment at large p T

29 Gluon Bremsstrahlung B.Kopeliovich et al., hep-ph/ Nucl.Phys. A740 (004) 11 FF modiication: Nuclear Suppression + Induced Radiation Nuclear suppression: interaction o the qq in the medium. Energy loss: induced gluon radiation by multiple parton scattering in the medium _ Nuclear Suppression Nuclear Suppression + Induced Radiation

30 Pre-hadron FSI and ormation times T.Falter et al., PLB 594 (004) 61 and PRC in print, nucl-th/ τ p = 0 ; τ >0.5 m/c compatible with data R M is very sensitive to the σ pre-h ; (σ pre-h =0.33 σ h )

31 Nice agreement or p+, p-, K+ with Q -rescaling + nuclear absorption (lower curves). Rescaling + Absorption Model ) )Q (Q (z, D ) (z,q D ) )Q (Q (x, q ) (x,q q ) (Q ; A h h A A A ) ( ) ( A N A N A s A s ξ ξ µ µ ξ λ λ α µ α = = = > Q A.Accardi et al., NPA70(003)131

32 FF modiication X.N.Wang et al., NPA696(001)788 PRL89(00)16301 multiple parton scattering and induced parton energy loss (without hadron rescattering) pqcd approach: LPM intererence eect A /3 dependence Consistency with the quadratic nuclear size dependence [A /3 ] th 1 ree parameter C quark-gluon correlation strength in nuclei. From 14 N data C= GeV : E = n < z > Cα m R g s N A

33 de/dl and Gluon density at RHIC de/dl PHENIX Au predictions determined by using C= GeV rom HERMES data. <de/dl> 0.5 GeV/m or 10-GeV quark in Au. PHENIX: hot, expanding system. HERMES: cold, static system. E sta αρ 0 R A ; ρ 0 gluon density and R A 6 m Ε exp E sta (τ 0 /R A ); τ 0 initial ormation time o dense medium Gluon density in hot matter much higher than in cold matter

34 FF modiication + transport coe. F.Arleo et al., NPA715(003)899 With ormation time eect Without ormation time eect Sot gluons radiated in the dense QCD medium (gluon transport coeicient rom DY) Energy loss Í 0.6 GeV/m in agreement with X-N Wang Nice agreement with both HERMES and old EMC data

35 Disentangling hadronic and partonic eects R h (z ) = d d N(z1,z dn(z ) 1 N(z1,z dn(z ) 1 ) ) A D Number o events with at least hadrons (z leading =z 1 >0.5) Number o events with at least 1 hadron (z 1 >0.5) I only hadronic eect: double-hadron over single hadron ratio is expected to be much smaller in nucleus compared to deuterium. I only partonic eect: double-hadron over single hadron ratio in nucleus and deuterium is expected to be close to unity.

36 Two hadron production (prelim.) Small eect in R h compared to single hadron multiplicity Small A-dependence (also conirmed by irst Xe data) Curves rom Falter et al. with per-hadronic FSI described with a transport code Curve rom Majumder et al. (hep-ph/ ) with partonic energy loss

37 Two hadron production Rank-1 Rank-3 Rank- All h rank 1,,3 No +- and -+ no rank, only 1,3 Small additional reduction or higher rank (produced beore, more inside the nucleus)

38 Summary and outlook HERMES is providing new results on hadron production in e-nucleus interaction: Nuclear attenuation in a wide kinematical range, vs ν, z, Q, p t or 4 He, 14 N, 0 Ne, 84 Kr ( 131 Xe is coming) First measurement with identiied hadrons : π +, π -, π 0, K +, K -, p, - p. First observation o hadron-type attenuation. First clear observation o the Cronin eect in SIDIS. Eect in Ratio o double/single hadron production in A over D is small and with almost no A-dependence. Measurements are also in progress at Jlab! Nuclear modiication o the quark Fragmentation Functions Pre-hadronization and inal hadronization times Partonic energy loss and scattering