New results from Delia Hasch DPG Spring Meeting 2004 – Nuclear Physics Cologne (Germany) March, (on behalf of the HERMES Collaboration) Exotic baryons: the HERMES pentaquark Spin: first measurement of Transversity Nuclear matter: production and transport of hadrons

direct reconstruction: detection of each decay particle, invariant mass reconstuction deca y ( < 0.6cm) ( < 1.0cm) ( > 7cm) [PLB 585(2004),213] Events / (8 MeV) Exotic baryonic states

The signal and the background  Monte Carlo + gen: M=1450 MeV,  =2 MeV reco: M=1450 MeV,  =7 MeV Pythia6 + mixed event background Pythia6 mixed event background excited  * hyperons (not included in Pythia6) M = 1528 MeV  = 8 MeV [PLB 585(2004),213]

W. Pauli N. Bohr  SPIN: even they were puzzled

distribution function Semi-inclusive deep inelasting scattering fragmentation function relevant kinematic variables

DESY Collaboration of 180 phys., 33 Inst., 12 Countries

HERA e+/e- beam of 27.6 GeV, I~40 mA, beam-pol~55 % HERMES in 1 slide polarisation by Sokolov-Ternov effect:

HERMES in 1 slide HERA e+/e- beam of 27.6 GeV, I~40 mA, beam-pol~55 % pure polarised gas targets: 3 He, H, D ~10 15 n/cm 2 pure UNpolar. gas targets: H, D, He, N, Ne, Kr ~10 17 n/cm 2 polarised targets: spin reversal every 120 sec

HERMES in 1 slide HERA e+/e- beam of 27.6 GeV, I~40 mA, beam-pol~55 % pure polarised gas targets: 3 He, H, D ~10 15 n/cm 2 pure UNpolar. gas targets: H, D, He, N, Ne, Kr ~10 17 n/cm 2 forward spectrometer:  p/p~2%,  <0.6 mrad, mrad kinematics: 0.02<x<0.6, 1.0<Q 2 <15 GeV 2

hadron separation double radiator RICH for , K, p ID hadron/positron separation combining signals from: TRD, calorimeter, preshower, RICH Particle identification

The quark contents of the nucleon

single helicity flip CHIRAL ODD NOT ALLOWED IN E.M. INTERACTIONS

The quark contents of the nucleon single helicity flip double helicity flip chiral odd FF: Collins FF peculiarity of transversity relativistic nature of quark: in absence of relativistic effects h 1 (x)=g 1 (x) Q 2 –evolution: unlike for g 1 p (x), the gluon doesn’t mix with quark in h 1 p (x) high sensitivity to the valence quark polarisation q and q have opposite sign. _ tensor charge: first moment of h 1 calculations from lattice QCD

Azimuthal angles and asymmetries Azimuthal angles and asymmetries angle of hadron relative to initial quark spin (Sivers) angle of hadron relative to final quark spin (Collins) (Sivers) chiral-even naïve T-odd DF related to parton orbital momentum violates naïve universality of PDF - different sign of in DY peculiarity of (Collins)

Azimuthal angles and asymmetries Azimuthal angles and asymmetries fit amplitudes simultanously (prevents mixing effects of acceptance)

Azimuthal angles and asymmetries Azimuthal angles and asymmetries

Sivers moments first measurement of naïve T-odd DF in DIS (orbital momentum) opposite sign from DY (RHIC…)? Collins moments large  + expected puzzle (?) surprisingly large disfavoured  - Transverse asymmetry for  +,  -,  0 kind of brainstorm is under way for model interpretation

FF on nucleon : DF and FF on nucleon & nuclear medium DF and FF on nucleon & nuclear medium 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 observation: reduction of multiplicity of fast hadrons due to both hard partonic and soft hadron interaction significant attenuation of fast forward hadrons [PLB577(2003),37]

Hadron separation vs Hadron separation vs Experimental findings:         ~ K - K + > K - p > p, p > , p > K - [PLB577(2003), 37]

Fragmentation function modification (parton energy loss) 1 free parameter tuned on 14 N (quark-gluon correlation strength inside nuclei) dE/dx for HERMES  dE/dx for PHENIX [X.N.Wang et al., NPA696(2001)788, PRL89(2002)162301]

fixed by HERMES data Gluon density [X.N.Wang et al., NPA696(2001)788, PRL89(2002)162301] cold hot nuclear matter correlation gluon density in Au+Au~15 times higher than in cold matter

Conclusion & outlook Delia Hasch ongoing data taking with 3 tracks trigger for exotics search exotics narrow exotic baryon resonance has been directly reconstructed { M= 1528 ± 2.6 ± 2.1 MeV  = 8 ± 2 MeV precise determination of the mass background description by Monte Carlo simulation

Conclusion & outlook Delia Hasch exotics narrow exotic baryon resonance has been directly reconstructed { M= 1528 ± 2.6 ± 2.1 MeV  = 8 ± 2 MeV precise determination of the mass background description by Monte Carlo simulation first observation of non-zero Sivers effect sizeable Collins asymmetries measured for  0 and  - ;  + puzzle spin: transversity a kind of brain storm is underway for model interpretation ongoing data taking with transversely polarised target

Conclusion & outlook Delia Hasch exotics narrow exotic baryon resonance has been directly reconstructed { M= 1528 ± 2.6 ± 2.1 MeV  = 8 ± 2 MeV precise determination of the mass background description by Monte Carlo simulation first observation of non-zero Sivers effect sizeable Collins asymmetries measured for  0 and  - ;  + puzzle spin: transversity a kind of brain storm is underway for model interpretation nuclear matter significant hadron suppression in a wide kinematic region first observation of hadron-type dependence of attenuation GOAL: obtain unambiguous information on hadron formation and transport in cold nuclear matter

Conclusion & outlook Delia Hasch exotics narrow exotic baryon resonance has been directly reconstructed { M= 1528 ± 2.6 ± 2.1 MeV  = 8 ± 2 MeV precise determination of the mass background description by Monte Carlo simulation first observation of non-zero Sivers effect sizeable Collins asymmetries measured for  0 and  - ;  + puzzle spin: transversity a kind of brain storm is underway for model interpretation nuclear matter significant hadron suppression in a wide kinematic region first observation of hadron-type dependence of attenuation Stay tuned … New exiting results will come soon !

Uncertainty from diffractive VM contribution desired process: SIDIS ep  X different physics: diffractive  0  0 production