New results fromNew results from

Delia Hasch

DPG Spring Meeting 2004 – Nuclear PhysicsCologne (Germany) March, 8-12 2004

(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

decaydecay

( < 0.6cm)

( < 1.0cm)

( > 7cm)

[PLB 585(2004),213]

Eve

nts

/ (8

MeV

)

XpKXDe 0S

Exotic baryonic states Exotic baryonic states

The signal and the backgroundThe 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 backgroundexcited * hyperons (not included in Pythia6)

M = 1528 MeV = 8 MeV

[PLB 585(2004),213]

W. Pauli

N. Bohr

SPIN: even they were puzzledSPIN: even they were puzzled

f

fff zDdxqz )()()(d hqh

distributionfunction

Semi-inclusive deep inelasting Semi-inclusive deep inelasting scatteringscattering

fragmentationfunction

;2

sin4EE'Q 2lab

2

E'Eνlab

2Mν

Qx

2lab

ν

Ez h

lab

relevant kinematic variables

HERMES @ DESYHERMES @ 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 slideHERMES in 1 slide

polarisation by Sokolov-Ternov effect:

HERMES in 1 slideHERMES in 1 slide•HERA e+/e- beam of 27.6 GeV, I~40 mA, beam-pol~55%

•pure polarised gas targets: 3He, H, D ~1015 n/cm2

•pure UNpolar. gas targets: H, D, He, N, Ne, Kr ~1017 n/cm2

polarised targets: spin reversal every 120 sec

HERMES in 1 slideHERMES in 1 slide•HERA e+/e- beam of 27.6 GeV, I~40 mA, beam-pol~55%

•pure polarised gas targets: 3He, H, D ~1015 n/cm2

•pure UNpolar. gas targets: H, D, He, N, Ne, Kr ~1017 n/cm2

•forward spectrometer: p/p~2%, <0.6 mrad, 40-220 mrad•kinematics: 0.02<x<0.6, 1.0<Q2<15 GeV2

hadron separationdouble radiator RICH for , K, p ID

hadron/positron separationcombining signals from: TRD, calorimeter, preshower, RICHTRD, calorimeter, preshower, RICH

Particle identificationParticle identification

Lg11f

The quark contents of the nucleonThe quark contents of the nucleon

TLTwCorr SxhxgSxfx 51511

2 )()()(2

1)(

Lg11f

The quark contents of the nucleon The quark contents of the nucleon

TLTwCorr SxhxgSxfx 51511

2 )()()(2

1)(

1h

The quark contents of the nucleon The quark contents of the nucleon

TLTwCorr SxhxgSxfx 51511

2 )()()(2

1)(

single helicity flip

CHIRAL ODD NOT ALLOWED IN

E.M. INTERACTIONS

1h

The quark contents of the nucleonThe quark contents of the nucleon

TLTwCorr SxhxgSxfx 51511

2 )()()(2

1)(

single helicity flip

double helicity flip

chiral odd FF:

Collins FF

)(H1 z

peculiarity of transversityrelativistic nature of quark:

in absence of relativistic effects h1(x)=g1(x)Q2 –evolution: unlike for g1

p(x), the gluon doesn’t mix with quark in h1

p (x)

high sensitivity to the valence quark polarisation q and q have opposite sign.

_

tensor charge: first moment of h1 calculations from lattice QCD

Azimuthal angles and asymmetries Azimuthal angles and asymmetries

)( S angle of hadron relative to initial quark spin (Sivers)

)( S angle of hadron relative to final quark spin (Collins)

1T1 Df (Sivers) •chiral-even naïve T-odd DF

•related to parton orbital momentum

•violates naïve universality of PDF

- different sign of in DY

t1f

t1fpeculiarity of

11 Hh (Collins)

Azimuthal angles and Azimuthal angles and asymmetriesasymmetries

)sin(A)sin(A

),(N),(N

),(N),(N

||

1),(A

SSiversUTS

CollinsUT

ShSh

ShSh

TS

hUT

S

fit amplitudes simultanously (prevents mixing effects of acceptance)

Azimuthal angles and Azimuthal angles and asymmetriesasymmetries

)sin(A)sin(A

),(N),(N

),(N),(N

||

1),(A

SSiversUTS

CollinsUT

ShSh

ShSh

TS

hUT

S

)(Dfe

H h e|S|

1

)sin(A

q

hq1

q1

2q

q

hq),1(1

q1

2q

T

UU

UTShhCollinsUT yf

q

hq1

q1

2q

q

hq1

qT1

2q

T

UU

UTSphSiversUT Dfe

De|S|

1

)sin(/M|P|A

f

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 Transverse asymmetry for ++, , --, , 00

)( s )( s

kind of brainstorm is under way for modelinterpretation

FF on nucleon:

DF and FF on nucleon & nuclear DF and FF on nucleon & nuclear medium medium

f

hfff zDdxqz )()()(d h

What happens in a nuclear medium ?

Nuclear attenuationNuclear attenuationobservation: reduction of multiplicity of fast hadrons due to both hard partonic and soft hadron interaction

Nuclear attenuationNuclear attenuationobservation: reduction of multiplicity of fast hadrons due to both hard partonic and soft hadron interaction

significant attenuation of fast forward hadrons

[PLB577(2003),37]

Df2f

hff

2f

Af2f

hff

2f

D

h2

DIS

A

h2

DISM

(x)qΣe(z)(x)DqΣe

(x)qΣe(z)(x)DqΣe

dzdνσd

σ1

dzdνσd

σ1

υ)(z,R

Hadron separation vs Hadron separation vs

Experimental findings:

~ K-

K + > K-

p > p, p > , p > K -

[PLB577(2003), 37]

Fragmentation function Fragmentation function modification modification

(parton energy loss)(parton energy loss)

•1 free parameter tuned on 14N (quark-gluon correlation strength inside nuclei)

•dE/dx for HERMES dE/dx for PHENIX (Au) @RHIC

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

fixed by HERMES data

Gluon density 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 & Conclusion & outlookoutlook

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 & Conclusion & outlookoutlook

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 transverselypolarised target

Conclusion & Conclusion & outlookoutlook

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 interpretationnuclear matter

significant hadron suppression in a wide kinematic regionfirst observation of hadron-type dependence of attenuation GOAL: obtain unambiguous information on hadron

formation and transport in cold nuclear matter

Conclusion & Conclusion & outlookoutlook

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 interpretationnuclear matter

significant hadron suppression in a wide kinematic regionfirst observation of hadron-type dependence of attenuation

Stay tuned …New exiting results will come soon !

Uncertainty from diffractive VM Uncertainty from diffractive VM contributioncontribution

desired process: SIDIS ep X

different physics: diffractive 00 production