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
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