Post on 16-Jan-2016
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Luca Stanco - Padova Heavy Quarkonium, Fermilab 1
Charmonium Production at HERALuca Stanco – INFN Padova
Outline:• Introduction• J/ Production Mechanisms• Inelastic J/ and ’ photoproduction • Inelastic J/ electroproduction• Polarization Measurements• Conclusions and Outlook
International Workshop on Heavy QuarkoniumFERMILAB, September 20-22, 2003
H1 and ZEUS collaborations
Luca Stanco - Padova Heavy Quarkonium, Fermilab 2
Introduction - I
• photoproduction (Q2 < 1 GeV2) scattered e not seen in the main detector• electroproduction (2 < Q2 < 100 GeV2) scattered e detected in calorimeter • J/ detected through: +- , e+e- decay modes
Kinematic variables:
frame rest proton in
EE
PqPpz
qPW
kPs
kkqQ
p
/
/
)(
)(
)'(
2
2
222
Luca Stanco - Padova Heavy Quarkonium, Fermilab 3
Introduction - II
charmonium production ?
Color Singlet Model (CSM)
(orders of magnitude too low)
Non-Relativistic QCD (NRQCD)
Luca Stanco - Padova Heavy Quarkonium, Fermilab 4
Production Mechanisms - I
Direct photon gluon fusion: 2.0z
Color Singlet Modelcc must have J/ quantum numbersOnly one free parameter given by
ll
Non-Relativistic QCDcc also in colour octet stateAdditional free parameters
Long distance matrix elements (LDMEs)LDMEs not calculablefrom experiments
CSM CS+CO
Luca Stanco - Padova Heavy Quarkonium, Fermilab 5
Production Mechanisms - II
Resolved photon processes (gg fusion): 2.0z
Color Singlet Model Non-Relativistic QCD
suppressed with increasing Q2
CSM CS+CO
Luca Stanco - Padova Heavy Quarkonium, Fermilab 6
Production Mechanisms – III (background)
1. .Diffraction (subracted in ZEUS: 15%, not subtracted in H1: 2%)
2. Decay of diffractively or inelastically produced ’ mesons: ’ J/ not subtracted in data !
3. Decay of c mesons: ’ J/ (low z) not subtracted in data !4. Decay of B mesons: B J/ X (low z, high pt,) not subtracted in
data !
Suppressed by cuts z<0.9, p*t, (pt, in p), additional activity in the detector
ELASTIC diffraction: z = 1 Proton dissociation: z 1Proton dissociation: z 1ELASTIC diffraction: z = 1 Proton dissociation: z 1
Luca Stanco - Padova Heavy Quarkonium, Fermilab 7
Production Mechanisms and DATA
z > 0.450 < W < 180
From MC: 44% of diffractive proton-dissociation,(17% for z < 0.9)
J/ variables
27%17%
Luca Stanco - Padova Heavy Quarkonium, Fermilab 8
Photoproduction: DATA and CSM NLO
H1: 96-00, +-
ZEUS: 96-97, +-
(scaled to H1 phase space)
1. Good agreement between H1 and ZEUS
2. full NLO of the direct -g fusion (M.Krämer)
3. theory in agreement with data both in shape and normalization, within the large theoretical uncertainties
Luca Stanco - Padova Heavy Quarkonium, Fermilab 9
Photoproduction: DATA and NRQCD LOThe measurements explore the low z region: z=0.05 (H1), z=0.1 (ZEUS)
1. Large uncertainties in calculation due to LDMEs from CDF
2. Large values of LDME are here excluded
3. .NRQCD LO calculation including direct and resolved photon (M.Krämer and M.Cacciari) provide a good description of whole z range with small LDMEs
Luca Stanco - Padova Heavy Quarkonium, Fermilab 10
Photoproduction: DATA and NRQCD LOCut on low pT to exclude low z (and to increase hard scale)
1. NRQCD LO calculation resumming soft contributions at high z (M.Beneke, G.A.Schuler and S.Wolf)
2. : energy loss of J/ due to soft gluon radiation
Resummation reduces discrepancies at high z
Luca Stanco - Padova Heavy Quarkonium, Fermilab 11
’ Photoproduction: DATA and CSM
1. Underlying production mechanisms for J/and’ are the same !
2. Integrated on DATA: 0.33±0.10+0.01
-0.02
3. .LO-CSM prediction : 24%
0.55 < z < 0.950 < W < 180
Luca Stanco - Padova Heavy Quarkonium, Fermilab 12
Electroproduction: Q2 and p*T, dependence
1. Comparisons with CS and NRQCD LO contributions (B.A.Kniehl and L.Zwirner)
2. . CS contribution too low by 2.7 and too step in (p*
T,)2 missing higher orders ?
3. .CS+CO too high at low Q2 and (p*
T,)2 ( 2) CS+CO desription improves at high Q2 and (p*
T,)2 (smaller theoretical errors)
H1: 97-00, e+e- and +-
Luca Stanco - Padova Heavy Quarkonium, Fermilab 13
ZEUS: 99-00, +-
(not easyly scalable to H1 phase space)
Electroproduction: z and rapidity dependence
z: missing resummation of soft terms for CS+CO comparisons
CS below data but shape consistent
CS+CO above the data
Luca Stanco - Padova Heavy Quarkonium, Fermilab 14
Polarization Measurements
Polarization of J/ provides information on production processes independent of normalization uncertainties
Polarization is measured in decay angular distributions in J/ rest frame system:
* : angle + to z’ axis (opposite direction to that of the proton)* : angle + to plane determined by incoming photon and proton
**
*2*
2cos33
11
cos1cos
1
d
d
λd
d
=+1: transverse polarization, =-1: longitudinal polarization
Luca Stanco - Padova Heavy Quarkonium, Fermilab 15
H1: 96-00, +-
ZEUS: 96-00, +-
Polarization Measurements: photoproduction
1. variable more promising to disentangle
2. more data needed to decide on production mechanism(s)
Luca Stanco - Padova Heavy Quarkonium, Fermilab 16
Conclusions and Outlook
Photoproduction: • medium z: good agreement with CSM NLO calculations• low z: resolved photon contributions improve agreement• NRQCD with small LDMEs gives reasonable description• ’ in line with expectations (but still large exper. errors)
Electroproduction: • CS (LO) alone too low, wrong (p*
T,)2 dependence• NRQCD with small LDMEs gives reasonable description
DATA: • major improvements in data statistics needed for conclusions from polarization measurements only possible with HERA II data
Theory: • NLO calculation in NRQCD is needed ! (both for photo- and electro-production)