1. Motivation2. DIS kinematic variables 3. and particle production4. Bose-Einstein correlations between and5. Charged particle momentum distributions6. Azimuthal asymmetry of particle production
through the energy flow7. Summary
Fragmentation and correlation of hadrons in ep collisions
Artur Ukleja (Warsaw University)
on behalf of H1 and ZEUS Collaborations
XXXVI International Symposium on Multiparticle Dynamics
September 02–08, 2006, Paraty, Rio de Janeiro, Brazil
, 0SK KKKK SS 00
2Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Motivation
HA
DR
ON
ISA
TIO
N
1. Produce partons (Matrix Element)
2. Fragmentation (Parton Shower)
3. Hadronisation
Measuring hadrons would contain information on:
• Fragmentation properties ( production, BEC, charged particle momentum)
• Matrix Element (charged particle momentum, azimuthal asymmetry)
, , 0SK
3Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
DIS kinematic variables
)(ke
)(Pp
)'(' ke
xP
222 'kkqQ
ehXep
h
X
The photon virtuality Q2 and Bjorken variables are defined as:
2QqP
Qx
2
2
kP
qPy
collisions at HERA give information about soft and hard processes
ehXepHERA:
The CMS energy squared of the ep system:
2Pks
GeV 318300 s1994-97
1998-06
4Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
and particle production , 0SK
0.950.02 GeV 255
95.002.0 GeV 2522
22
yQ
yQ
DIS
PHP
0.950.2 GeV 1 22 yQ
particle fragmentation
5Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
OBS
2
:PHP
:DIS
xp
Qxp
T
T
resolved 75.0
direct 75.0
2
OBS
OBS
jets
jets
OBS
jets
x
x
yE
eE
xe
T
direct resolved
• Baryon-antibaryon asymmetry
• Baryon to meson ratio
)()(
)()(
NN
NNA
)(
)()(0SKN
NNR
6Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Baryon-antibaryon asymmetry
PHPin % 0.10.6 predictionPYTHIA % 6.007.0
lowat % 0.21.0 prediction ARIADNE % 6.12.1
high at % 0.20.4 prediction ARIADNE % 3.13.0
0.10.1
27.01.2
25.08.0
A
QA
QA
• No evidence of baryon numbers propagated to central rapidity
• Baryon and antibaryon are produced according to the same mechanism
ARIADNE: with a strangeness factor of S=0.3 and 0.22
Q2>25 GeV2
0.02<y<0.95
7Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Baryon to meson ratio
• ARIADNE (S=0.3) follows the shape of the data
• Baryon to meson ratio increases at low xOBS up to 0.7, not
predicted by PYTHIA (is flat at about 0.4)
• For high xOBS same baryon to meson ratio as in DIS and e+e-
8Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Baryon to meson ratio (R) in PHP
• R is bigger, most significantly at high pT
LAB for the fireball enriched
• PYTHIA predicts almost the same R for both sample
• PYTHIA prediction approximately follows the measured values of R for the fireball depleted
Fireball depleted
Fireball enrichedJet of the highest ET
contributed at most 30% to the total hadronic ET
9Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
BEC have been observed in DIS at HERA.
(gives information about hadronisation process)
The two-particle correlation
function is studied as:
M – invariant mass of the pair
BE correlations between and KKKK SS 00
2bosons
222112 4)( mMppQ
Two bosons with momenta p1 , p2 produced at points r1 and r2
1 2 – bosons
BEC as the method of determination of the size of the particle emission source
10Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Bose-Einstein correlation function
)(
)()(
12ref
1212 QP
QPQR
Standard parametrisation of R(Q12)
is Goldhaber-like parametrisation
) 1)(1()( 1212
2212 QeQR rQ
r – radius of the particle emission source – coherence strength factor
=0 since linear behavior in the high Q12 region
P(Q12) – the two-particle distribution for identical kaon pairs
Pref(Q12) – the reference distribution in the absence of BEC
11Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
BEC function for 00SSKK
22112 )( ppQ
231B583(2004)Phys.Lett. (ZEUS)
0.0220.036-
00
fm syst)()0.009(stat0.666r
similar to is for r value
SSKK
fm syst)(0.08(stat)0.61r 0.070.08-
12Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
BEC function for KK
22112 )( ppQ
(ZEUS) 00
0.070.08-
231B583(2004)Phys.Lett. (ZEUS)
0.0220.036-
00
fm syst)(0.08(stat)0.61r
fm syst)()0.009(stat0.666r
and
similar to is for r value
SKSK
SSKK
KK
fm syst)(0.09(stat)0.57r 0.150.06-
13Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
BEC comparison with LEP
A good agreement with LEP for radius
ZEUS r=0.57±0.09(stat) fm
ZEUS r=0.61±0.08(stat) fm
14Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Charged particle momentum distributions
Qp
phx 2
Scaled momentum distribution is defined in the Breit Frame as:
ph – momentum of charged track in the current region of Breit FrameQ – virtuality of the exchange boson
Parton splitting in pQCD causes scaling violations in structure functions. Also seen in fragmentation functions. Test pQCD.
15Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Scaling violations
• Number of hadrons:
increase at small xp with ↗Q
100<Q2<20000 GeV2
0.05<y<0.6
16Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Charged particle momentum distributionsCompared with e+e- experiments
100<Q2<20000 GeV2 0.05<y<0.6
• Number of hadrons:
increase at small xp with ↗Q
decrease at large xp with ↗Q
The cause of the scaling violations is the same as for the scaling violations observed for the deep inelastic structure functions.
• e+e- data show the same behavior as ep data
17Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Charged particle momentum distributionsCompared with LO MC predictions
100<Q2<20000 GeV2 0.05<y<0.6
• CDM and PS models provide general reasonable description of the data
• At high xp HERWIG predictions even fail to show scaling behavior producing a flat spectrum
18Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
2sinsin2coscos)(
EDCBAd
d hXeep
Azimuthal asymmetry
2
2sin 2
sin
2
cos2 2
cos
A
E
A
DA
C
A
B
Azimuthal asymmetry comes from:• two-body processes (BGF and QCDC)• photon polarisation• longitudinally polarized electron beam• final hadron polarisation• intrinsic parton momentum in the proton
2cos BGF
cos QCDC
qqg
qgq
19Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
2sinsin2coscos)(
EDCBAd
d hXeep
Azimuthal asymmetry
In the Born approximation
for purely electromagnetic interactions
with unpolarised initial electron beam
the terms containing sin and sin2 vanish
as a consequence of a time-reversal invariance
X X
The coefficients D and E arise
from parity violating weak interactions
or polarisation of the initial electron beam
20Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Energy flow method
Each particle is weighted with its energy
Multiplicity methodPhys.Lett.B481(2000)199-212
Jet analysisPhys.Lett.B551(2003)226-240
i i
i i
E
EHCM
,T
HCMHCM,THCM
coscos
21Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Asymmetry as a function of HCMNC DIS: 100<Q2<8000 GeV2 0.01<x<0.1 0.2<y<0.8
tsignifican is cos HCM
Energy flow method
22Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Cut ET>2 GeV is sufficient to removed non perturbative effectsProposed by Chay et al. Phys.Lett.B269(1991)175-182
Asymmetry as a function of HCMminT,E
spredictionby described good is 2cos
sprediction above cos 01at
sprediction below cos 5.25at
HCM
HCMHCM
HCMHCM
23Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Summary and conclusionsMeasurements: and production BEC charge particle momentum
• have been made at HERA• ep data show the similar behavior as e+e- data
Detailes, for example:• The baryon to meson ratio increases at low x
OBS up to 0.7, not predicted by PYTHIA (is flat at about 0.4)
Azimuthal asymmetry is investigated for cos , cos2 , sin , sin2as a function of and ET,min
• cos and cos2 is significant• sin and sin2 consistent with null• NLO better describe ZEUS data then LO MC predictions
, 0SK
24Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
BACK UP
25Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Fireball enriched and fireball depleted
Line represents the cut used to separate fireball enriched and fireball depleted
Fraction of the total ET carried by two jets of highest transverse energy
Fireball depleted events are dominated by dijet events carrying most of the total ET
Fireball enriched and fireball depleted has about the same number of events
26Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
• good agreement with LEP for radius
• higher value then for ALEPH, DELPHI
• the f0 (980) resonance is expected in the same low Q12 region where BEC are measured
• small contribution of f0 (980) in data can significantly change value
• the estimation of f0 (980) in data is 10 %
• the ALEPH, DELPHI removed f0 resonance
BE correlations between 00SSKK
231B583(2004)Phys.Lett.
(ZEUS) 0.022
0.036-
0.0110.003-
00
fm syst)()0.009(stat0.666r
syst)(stat)(007.0475.0
similar to is for r value
SSKK
27Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
BE correlations between KK
• good agreement with LEP for radius
• smaller value then for e+e-
• different fragmentation processes in e±p and e+e-
• proton influence is expected – ZEUS data populate mostly proton fragmentation region
• K+K- can be production from 0 (1020) resonance dacay – strong signal of 0 (1020) in ZEUS data
(ZEUS) 00
0.070.08-
0.280.08-
231B583(2004)Phys.Lett.
(ZEUS) 0.022
0.036-
0.0110.003-
00
fm syst)(0.08(stat)0.61r
syst)(stat)(29.016.1
fm syst)()0.009(stat0.666r
syst)(stat)(007.0475.0
and similar to is for r value
SKSK
SSKKKK
28Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Charge particle momentum distributionsCompared with NLO QCD predictions
100<Q2<20000 GeV2 0.05<y<0.6
The data show a clear sensitivity to the fragmentation function used in the NLO QCD predictions
29Artur Ukleja, Warsaw University (on behalf of H1 and ZEUS Collaborations)
XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil
Summary and conclusions• Measurements of and production have been made at HERA
• No evidence of baryon numbers propagated to central rapidity• The baryon to meson ratio increases at low x
OBS up to 0.7, not predicted by PYTHIA (is flat at about 0.4)
• BEC have been measured in DIS at HERA• The radius value for KS
0KS0 is consistent with K±K± and with ±±
• The radius value is compatible with LEP results
• Scaled charge particle momentum is investigated at high Q2
• e+e- data show the same behavior as ep data• MC tuned from LEP data can successfully described ep data over
large region of Q
Azimuthal asymmetry is investigated for cos , cos2 , sin , sin2as a function of and ET,min
• cos and cos2 is significant• sin and sin2 consistent with null• NLO better describe ZEUS data then LO MC predictions
, 0SK