# Presentation: 841421

## Hadron Suppression in DIS @HERMES

- Hadron Suppression in DIS @HERMES

- Pasquale Di Nezza
- (on behalf of the HERMES Collaboration)

- DF and FF modification in a nuclear medium
- Nuclear attenuation measurements at HERMES
- Comparison with theory
- Hadron re-interaction vs partonic energy loss

- Quark and Matter, Oakland Jan 11-17, 2004

## DF and FF on Nucleon & Nuclear Medium

- Interpretation at both hadronic (nucleon’s binding, Fermi motion, pions) and partonic levels (rescaling, multi-quark system)

## DF and FF on Nucleon & Nuclear Medium

- FFs are measured with good precision and follow pQCD evolution like DFs (HERMES: EPJ C21(2001) 599). What happens in a nuclear medium ?

## Nuclear Attenuation

- _Observation_: reduction of multiplicity of fast hadrons due to both *hard partonic* and *soft hadron interaction*.

## Nuclear Attenuation

- Production and Formation Time measurements + FFs are crucial for the understanding of the space-time evolution of the hadron formation process

- _Observation_: reduction of multiplicity of fast hadrons due to both *hard partonic* and *soft hadron interaction*.

## The energy range is well suited to study quark propagation and hadronization

- Measurements over the full z range

- Possibility to use several different gas targets

## HERMES @ DESY

## The Internal Target

- (NIM A343 (1994) 334)

- Internal storage cell
- Pure gas target, no dilution factor
- Nuclear targets: (H, D), 3He, 4He, 14N, 20Ne, 40Ar, 84Kr, 131Xe
- Densities: ~1015 – 1017 nucl*cm-2

## The Spectrometer

- e+ identification: 99% efficiency and <1% of contamination
- PID: RICH, TRD, Preshower, e.m. Calorimeter
- For N target: by Cerenkov pion ID in the range 4<p<14 GeV
- For He, Ne, Kr target: by RICH , K, p ID in the range 2.5<p<15 GeV

- (NIM A417 (1998) 230)

## Particle Identification

- _Double radiator RICH_: Aerogel + C4F10. Cerenkov photons detected by ~4000 PMTs._Detection efficiency_: 99% (), 90% (K), 85-95% (p)

## Hadron Attenuation

## Hadron Attenuation

## Hadron separation vs 

- Hadron separation vs 

- HERMES, PLB 577 (2003) 37

## Hadron separation vs 

- HERMES, PLB 577 (2003) 37

- Hadron separation vs 

## Hadron separation vs 

- HERMES, PLB 577 (2003) 37

- Hadron separation vs 

## Hadron separation vs z

- Different FF modification for *quark* and *anti-quark*
- Different h for mesons and baryons
- Different h:
- + = -  20 mb
- +  17 mb, - 23 mb
- p  40 mb, p-  60 mb

- HERMES, PLB 577 (2003) 37

## Nuclear Attenuation on He, Ne, Kr

- Assuming the dependence:
- A = 1-Rhatt

- Data suggest ~2/3

## Nuclear Attenuation on He, Ne, Kr

## Nuclear Attenuation vs Q2

## Pt dependence

- In pA collisions the p gains extra transverse momentum due to random soft collisions. Partons enter the final hard process with extra kt (Cronin eff.)

## Pt dependence

- Pt dependence

- In DIS neither multiple scattering of the incident particle nor interaction of its constituents complicate the interpretation

- Clean and reliable information on quark transport in ‘cold’ nuclear matter

## Comparison with Theory

## Gluon Bremsstrahlung 

- Gluon Bremsstrahlung

- B.Kopeliovich et al., hep-ph/9511214
- hep-ph/0311220

- FF modification: Nuclear Suppression + Induced Radiation

- _Vacuum energy loss:_ *q****gq’*.  (dE/dz ~2.5 GeV/fm by E772/E866 for DY on nuclei)

- _Energy loss induced by multiple interactions in the medium_    (rising in pt)

- _Color Transparency of the qq_ (~1/Q2)

## Gluon Bremsstrahlung

- B.Kopeliovich et al., hep-ph/9511214
- hep-ph/0311220

- Fast pions are consistent with GB model (production length lp(1-zh)/Q2 vanish at zh 1)

## Gluon Bremsstrahlung

- B.Kopeliovich et al., hep-ph/9511214
- hep-ph/0311220

- Only prediction for h containing target valence quark.
- Good agreement also for K+

## Gluon Bremsstrahlung

- B.Kopeliovich et al., hep-ph/9511214
- hep-ph/0311220

- Combined effects:
- pre-hadron shrinks at large Q2
- larger nuclear transparency
- production lengths contracts

- Good description;
- Faster rise at high Pt ?

## FF modification 

- FF modification

- X.N.Wang et al.,
- NPA696(2001)788
- PRL89(2002)162301

## FF modification (parton energy loss)

- FF modification (parton energy loss)

- 1 free parameter tuned on 14N (quark-gluon correlation strength inside nuclei)
- dE/dx for HERMES  dE/dx for PHENIX (Au)

- X.N.Wang et al.,
- NPA696(2001)788
- PRL89(2002)162301

## Gluon Density

- Cold <--> Hot nuclear matter correlation
- Gluon density in Au+Au~15 times higher than in cold matter

- X.N.Wang et al.,
- NPA696(2001)788
- PRL89(2002)162301

## Rescaling + Absorption Model

- A.Accardi et al.,
- NPA720(2003)131

## (Pre-)Hadron FSI and formation times

- RM is very sensitive to the pre-h ; (pre-h=0.33 h)
- f>0.5 fm/c compatible with data

- T.Falter et al., nucl-th/0303011

## FF modification + transport coef.

- F.Arleo et al.,
- NPA715(2003)899

## Disentangling absorption and induced energy loss

- Could it be too naïve ?
- R2 depends on:
- hadron production length
- local nuclear density
- absorption cross section
- Pt, z1, z2, ...

## Disentangling absorption and induced energy loss

- _Preliminary_ R2 calculated for Kr/D and N/D:
-  >7 GeV, Eh>1.4 GeV, zleading>0.5
-  opposite charges neglected (rank-2)

- Results from STAR show jet suppression is due to FSI (energy loss). No contribution from absorption ...

## Disentangling absorption and induced energy loss

- _Preliminary_ R2 calculated for Kr/D and N/D:
-  >7 GeV, Eh>1.4 GeV, zleading>0.5
-  opposite charges neglected (rank-2)

- Results from STAR show jet suppression is due to FSI (energy loss). No contribution from absorption ... high Pt events, different zh distributions. It’s difficult to compare HERMES-RHIC ... for the moment.

## Conclusions

**Pasquale Di Nezza**

- _Outlook_: Disentangle between  and z dependence
- 	    P**t** broadening for different hadrons
- 	    Double/Single-hadron ratio

## Hadrons and Pions @ Ebeam=12 & 27 GeV

- Hadrons and Pions @ Ebeam=12 & 27 GeV

- Extension of the  range down to 2 GeV

## Slide 38

## Slide 39