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Rencontres QGP France Etretat , France Septembre 22, 2010. Cold nuclear matter effects on quarkonium. Elena G. Ferreiro Universidade de Santiago de Compostela, Spain. Work done in collaboration with F. Fleuret , J-P. Lansberg , N. Matagne and A. Rakotozafindrabe - PowerPoint PPT Presentation
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Cold nuclear matter effects on quarkonium
Rencontres QGP FranceEtretat, France Septembre 22, 2010
Elena G. FerreiroUniversidade de Santiago de Compostela, Spain
Work done in collaboration with F. Fleuret, J-P. Lansberg , N. Matagne and A. Rakotozafindrabe
arXiv:0912.4498 PRC81 (2010)
Introduction and motivation
• A lot of work trying to understand A+A data (since J/ y QGP signal)
• Here we focalise on p+A data (where no QGP is possible) only cold nuclear matter (CNM) effects are in play here:
shadowing and nuclear absorption
• In fact, the question is even more fundamental: p+p data we do not know the specific production kinematics at a partonic level:
CS (2→2) vs CO (2→1)
Quakonium as a hint of deconfinement
Quakonium as a hint of coherence
Quakonium as a hint of QCD
QGP hint
nPDF hint
QCD hint
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Introduction and motivation
Our goal:
To investigate the CNM effects and the impact of the specific partonic production kinematics
• Results on J/ y production
• Extend our study to ϒ CNM effects
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
QGP recombinationsequential suppression
•cold effects:
•hot effects:
gluon shadowing
nuclear structure functions in nuclei ≠ superposition of constituents nucleons
NI@SPS, IMP@RHIC
nuclear absorptionmultiple scattering of a pre-resonance c-cbar pair within the nucleons of the nucleus
IMP@SPS, RHIC?
CGC
parton saturationpercolation
non-lineal effects favoured by the high density of partons become important and lead to eventual saturation of the parton densities non thermal colour connection
hadronic comovers
partonic comovers
dissociation of the c-cbar pair with the dense medium produced in the collision partonic or hadronicsuppression by a dense
medium, not thermalized
wo thermalisation NO QGP
w thermalisation QGP
COLD and HOT effects
Others: Cronin effect energy loss
hint of coherence
hint of deconfinement
hint of QCD
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Abigail Bickley, August 9, 2007 5
• Color Singlet Model:– perturbative creation of the ccbar pair in color singlet state with
subsequent binding to J/y with same quantum numbers– hard gluon emission– underpredicts J/ production cross section– predicts no polarization
J/y production mechanisms
• NRQCD Color Octet Model:– uses NRQCD formalism to describe the non-perturbative hadronization of the ccbar color
octet to the color singlet state via soft gluon emission– factorizes the charmonium production into a short distance hard part and a long distance
matrix element which is claimed to be universal– predicts large transverse polarization at high pT (not seen by data)
• Color Evaporation Model:– phenomenological approach– perturbative creation of the ccbar pair in the color octet state
with subsequent non-perturbative hadronization to color singlet via unsuppressed soft gluon emission
– predicts no polarizationp
p
J/y
soft g
cc
p
p
J/y
hard g
cc
2→1 g+g → J/y
2→2g+g → J/ +y g hard g
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Nuclear shadowing is an initial-state effect on the partons distributions
• Gluon distribution functions are modified by the nuclear environment
• PDFs in nuclei different from the superposition of PDFs of their nucleons
Shadowing: an initial cold nuclear matter effect
Shadowing effects increases with energy (1/x) and decrease with Q2 (mT)
shadowing
antishadowing
The shadowing corrections strongly depend on the partonic process producing the J/Y
since it affects kinematics (x,Q2)
nPDF hint
QCD hint
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Particle spectrum altered by interactions with the nuclear matter they traverse=> J/Y suppression due to final state interactions with spectator nucleons
• At low energy: the heavy system undergoes successive interactions with nucleons in its path and has to survive all of them => Strong nuclear absorption• At high energy: the coherence length is large and the projectile interacts with the nucleus as a whole => Smaller nuclear absorption
sabs @ mid y < sabs @ forward y?Rapidity dependence of nuclear absorption?
• Usual parameterisation:(Glauber model)
Nuclear absorption: a final cold nuclear matter effect
coherence hint
Energy dependence
In terms of formation time:
Sabs = exp(- r sabs L )nuclear matter density break-up cross section path length
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
On the kinematics of J/y production: two approaches
Investigating two production mechanisms (including pT for the J/ )y :
g+g → J/y• intrinsic scheme: the pT of the J/ y comes from initial partons
g+g → J/y+g• extrinsic scheme: the pT of the J/y is balanced by the outgoing gluon
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• CNM -shadowing- effects depends completly on J/y kinematics (x,Q2)
• J/y kinematics depends on the production mechanism =>
2→2
2→1
Intrinsic J/y production kinematics
• Intrinsic scheme: 2 → 1 process CEM @ LO
• y, pT can be determined using PHENIX p+p data Phys. Rev. Lett. 98, 232002 (2007)
• Easy to handle : yJ/y and pT
J/y directly give x1,2
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Straightforward evaluation of the gluon PDF shadowed in the nucleus at x2 (and x1 in AA)
Q2=(2mc)2+(pT)2=mT
• We deal with a 2 → 2 partonic process with collinear initial gluons
• The quadri-momentum conservation results in a complex expression of x2 as a function of (x1, y, pT)
• Information from the data alone – the y and pT spectra– is not sufficient to determine x1 and x2: the presence of a final-state gluon authorizes much more freedom to choose (x1, x2) for a given set (y, PT)
• Models are mandatory to compute the proper weighting of each kinematically allowed (x1, x2)
•We use s—channel cut mechanism Extension of CSM Haberzettl and Lansberg, Phys.Rev.Lett.100,032006 (2008) Also 2 -> 2: CSM @ LO, CEM @NLO
Extrinsic J/y production kinematics
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Good results at low pT
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
shadowing
nuclear absorption
partonic cross section
fit to data s-channel cut modelkinematic variables
On the kinematics of J/y production: equations
Extrinsic vs intrinsic kinematics IIntrinsic scheme Extrinsic scheme
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
both implemented in a Monte Carlo code: JINE.G. Ferreiro, F. Fleuret, and A. Rakotozafindrabe ,Eur. Phys. J. C61, 859 (2009)
E.G. Ferreiro, F. Fleuret, J-P. Lansberg and A. Rakotozafindrabe, Phys.Lett.B680, 50 (2009)
Extrinsic vs intrinsic kinematics II
For a given set (y, pT): extrinsic scheme: more freedom for x for a given y => larger x in extrinsic scheme
We expect different shadowing effects in both cases
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
2 → 1 2 → 2
• antishadowing peak shifted toward larger y in the extrinsic case• in order to reproduce data: nuclear absorption
sabs extrinsic > sabs intrinsic
for a given yx larger in extrinsic
2→2
g+g
→ J/
+y
g2→
1 g
+g →
J/y
• shadowing depends on the partonic process: 2→1 or 2→2
arXiv:0912.4498 PRC
Results for d+Au: J/ y rapidity dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
EKS98: compatible with intrinsic & extrinsic
EPS08: extrinsic scheme is favorized
nDSg: neither extrinsic nor intrinsic…
Fit of sabs with EKS, EPS and nDS(g) from RdAu
nPDF hint
QCD hint
Results for d+Au: J/ y rapidity dependence of RCP
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Data dependence on y: • Suppression for the most forward points in the three centrality ranges • In the negative rapidity region, dominated by large x, no nuclear effects
Data at back and mid-y can be described with a σabs of 2–4 mb, while the most forward points seem to decrease more than our evaluation
Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models
sabs(y)?
sabs and c2from RdAu EKS EPS nDS(g) LO
intrinsic 3.20 0.9 2.11 1.1 2.21 1.6
extrinsic 3.90 1.1 3.60 0.5 3.00 1.4
Fit of sabs with EKS, EPS and nDS(g) from RdAu and RCP
sabs int < sabs ext
sabs from RCP Intrinsic: increase of σabs with y Extrinsic: softer increase of σabsa constant behavior cannot be ruled out (see EPS08)
EKS98 EPS08 nDSg sabs (y)
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Results for d+Au: J/ y centrality dependenceExtrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• in the backward region: antishadowing=>progressive increase of RdAu vs Ncoll
• in the forward region: shadowing => progressive decrease of RdAu vs Ncoll
EKS98 EPS08 nDSg
Results for d+Au: J/ y transverse momentum dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models
Growth of RdAu not related to Cronin effect: it comes from the increase of x for increasing PT
• in the mid and forward-y region: x goes through the antishadowing region => enhancement in RdAu
• In the backward region: x sits in an antishadowing region=> decrease in RdAu
EKS98 EPS08 nDSg
Results for Au+Au: J/ y centrality dependenceIntrinsic scheme: Same CNM suppression atforward and central rapidity
Extrinsic scheme: More CNM suppression atforward than central rapidity
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Extrinsic scheme : RAA @ forward y < RAA @ mid y Hot Nuclear matter effects still needed, but…
Less need for recombination effects
Results for Au+Au: J/ y rapidity dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Intrinsic: flat behaviour
• Extrinsic: maximun at y=0
Again, this indicates that less recombination would be required in the extrinsic case
Results for A+A: J/ y transverse momentum dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models
RAA increases with PT partially matching the trend of PHENIX and STAR data
Nuclear modification factor larger than one for PT ≈ 8GeV (STAR results)?
J/ψ behavior closer to the one of photons than to the one of other hadrons?
Hypothesis: energy losss + Landau-Pomeranchuk-Migdal effect ?
The energy loss of a colored object in CNM is limited to be constant
However, by the LPM effect , its magnitude will be larger for a CO than for a CS
Rather a colorless state than a colored one which propagates in the NM?
On the kinematics of ϒ production
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Results at 1.8 TeV:
• CSM describes well ds/dpT at NNLO
• LO CSM is sufficient to describe low pT data
Results at 200 GeV:
LO upper line: mb = 4.5 GeV, μR = MT , μF = 2MTLO lower line: mb = 5.0 GeV, μR = 2MT , μF = MT
We take the parameters of the upper curve in the following.
2 → 2 process
Results for d+Au: ϒ rapidity dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Intrinsic vs extrinsic scheme
• Antishadowing peak shifted toward larger y in the extrinsic case
• Different shadowing effects in the 2 approaches
Results for d+Au: ϒ rapidity dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Extrinsic scheme: sabs= 0, 0.5, 1 mb in 3 shadowing models
• backward: ok within uncertainties• central: reasonable job • forward : clearly too high (for any σabs)
Physical interpretation• backward: EMC effect• central: antishadowing • forward : shadowing≈1 energy loss is needed
E loss tool
Work in progress: EMC effect
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
antishadowingEMC
Let us try to increase the suppression of g(x) in the EMC region, keeping momentum conservation : ʃxg(x) dx = Cte
Works better for backward region
Conclusions
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• for J/y
d+Au collisions: RdAu vs y 0 => sabs extrinsic > sabs intrinsic RCP vs y => sabs(y)
Au+Au collisions: RAA vs y RAA vs Npart => less need for recombination in 2 →2
• We have studied the influence of specific partonic kinematics
within 2 schemes: intrinsic (2→ 1) and extrinsic (2→2) pT
for different shadowings: EKS98, EPS08, nDGg including nuclear absorption
• for ϒ
antishadowing and EMC region need of energy loss
http://phenix-france.in2p3.fr/software/jin/index.html
2→2 process
Brain storming: can we distinguish shadowing vs nuclear absorption?
• p+A measurements for different species? J/ y vs y’ (or DY….) Assumption: shadowing J/ y ≈ shadowing y’ => sabs J/ / y sabs y’
• p+A measurements for different A @ fixed energy? Assumption: sabs = sabs (s,y) => check of sabs J/ / y sabs y’
• p+A measurements for fixed A @ different energies? => sabs J/ / y sabs y’ = sabs J/ / y sabs y’ (s)
• Other possibilities: ϒ vs continuum
Even better: UPCNo nuclear absorption => Only shadowing!
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Backup slides
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• On the kinematics of J/y production: detail equations
• s-chanel cut model
• The Glauber Monte Carlo code
• Shadowing models
• Nuclear absorption
• Comparation with Vogt’s results (CEM @ LO without pT) Fit procedure
• J/y production mechanisms
• Work in progress: RdAu vs Ncoll and RdAu vs pT for EKS98,EPS08, nDSg
• Some other results
Results for A+A: J/ y centrality dependenceExtrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
RAA systematically smaller in the forward region than in the mid-y regionThe difference increases for more central collisionsThis difference matches well the one of the data when σabs = 0 One needs a larger σabs if one wanted to reproduce the normalisation of the AuAu data, disregarding any effects of hot nuclear matter (HNM)However, for such large σabs, surviving J/ψ from inner production points would be so rare that the difference between shadowing effects at mid and forward rapidities would nearly vanishNote that for a σabs in the range of 2–4 mb, a difference remains
Results for A+A: J/ y rapidity dependenceExtrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
RAA peaks at y = 0, reducing the need for recombination which concentrates at mid y This effect is present in the three shadowing parametrizations we have usedThis effect reduces with the increase of sabs
Results for d+Au: ϒ centrality dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Extrinsic scheme: sabs=0 mb, sabs= 0.5mb , sabs= 1 mb in 3 shadowing models
EKS EPS nDSg
Results for d+Au:ϒ transvese momentum dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Extrinsic scheme: sabs=0 mb, sabs= 0.5mb , sabs= 1 mb in 3 shadowing models
EKS EPS nDSg
Extrinsic vs intrinsic kinematics II
For a given couple(y, pT), x2 is larger inthe extrinsic scheme
We expect different shadowing effectsin both cases
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Much more freedom to choose (x1, x2) for a given set (y, PT)
Work in progress: EKS98 centrality dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Extrinsic sheme• Intrinsic sheme
EKS98
EKS98
EKS98
Work in progress: EPS08 centrality dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Extrinsic sheme• Intrinsic sheme
EPS08
EPS08
Work in progress: nDSg centrality dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Extrinsic sheme• Intrinsic sheme
nDGg
nDSg
Work in progress: EKS98 pT dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Extrinsic sheme• Intrinsic sheme
EKS98 EKS98
Work in progress: EPS08 pT dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Extrinsic sheme• Intrinsic sheme
EPS08 EPS08
Work in progress: nDSg pT dependence
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Extrinsic sheme• Intrinsic sheme
nDSg nDSg
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
On the kinematics of J/y production: equations I
shadowing
nuclear absorption
partonic cross section
fit to data s-channel cut modelkinematic variables
On the kinematics of J/y production: equations II
Concerning
it can be factorized in the nuclear density distribution, the shadowing modification factor and the usual gluon PDFs:
where we have included the centrality dependence of the shadowing:
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
On the kinematics of J/y production: equations III
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
s-channel cut model: motivation
a suitable production model for low pT J/y
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
s-channel cut contributions
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
s-channel cut contributions
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
s-channel cut contributions to the basic CSM:
• take into account the dynamics of the ccbar in the bound state• need for 4-point coupling ccbar-J/y-g
• new degrees of freedom constrained by fits• so far the best description of low-pT data
s-channel cut contributions: first evaluations
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
s-channel cut model vs. other models in the market
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Various models for the y spectra in p+p
[NRQCD calculation] Cooper, Liu & Nayak, Phys. Rev. Lett. 93, 171801 (2004)[g(gg)s + Feed-down] Khoze, Martin, Ryskin Stirling, Eur. Phys. J. C39, 163 (2005)
The Glauber Monte Carlo code
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
E.G. Ferreiro, F. Fleuret, A. Rakotozandrabe. arXiv :0801.4949 [hep-ph]
• Nuclear shadowing is an initial-state effect on the partons distributions
• Gluon distribution functions are modified by the nuclear environment
• PDFs in nuclei different from the superposition of PDFs of their nucleons
Shadowing: a cold nuclear matter effect
E. G. Ferreiro USC CNM effects on J/y production: intrinsic and extrinsic ECT Trento 25 May 09
EKS and EPS shadowing model• Introduce an initial parameterisation for nuclear parton distributions RA(x,Q2
0) based on a fit to DIS data at Q2
0 = 2.25 GeV2
• The further evolution in Q2 is predicted by the DGLAP equations at LO
• RHIC high-pT forward-rapidity hadron data suggest a stronger gluon shadowing than obtained in previous global analyses
fiA(x,Q2) Ri
A(x,Q2) fi(x,Q2) GRV-LO, CTEQ4L
GRV-LO, CTEQ6L1high pT RHIC data at Q20 = 1.69 GeV2
E. G. Ferreiro USC CNM effects on quarkonium Palaiseau 5 March 09
EKS shadowing model 1. Introduce an initial parameterisation for
nuclear parton distributions RA(x,Q20) based
on the DIS data at Q20 = 2.25 GeV2
2. Once the nuclear parton distributions are given at an initial scale Q2
0>>Λ2QCD the further
evolution in Q2 is predicted by the DGLAP eqs:
DGLAP eqs: relation between the logarithmic Q2-evolution of the structure functions and the gluon distribution, giving the possibility to calculate the value of ratios at any Q2 if an initial value is known• It is assume that
• at Q2 >Q20 the scale evolution of the nuclear parton densities is purely perturbative
• the initial conditions at Q20 contain the nonperturbative input
• the evolution is made at leading order (LO)
3. The slope of the nuclear parton distributions in Q2 is obtained in this way
No centrality dependence is included in the modelE. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
GRV-LO, CTEQ4L
EPS shadowing model• Global fit to DIS, DY and high pT RHIC data
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• LO, Q20 = 1.69 GeV2
• RHIC high-pT forward-rapidity hadron data suggest a stronger gluon shadowing than obtained in previous global analyses
nDSg shadowing model• Define nPDF using a convolution approach: the free nucleon parton densities are convoluted with very simple weight functions that parameterize nuclear effects
Instead of:LO
• LO and NLO evolution
Differences with other parameterizations:
• ESK98: less small x shadowing and very little antishadowing at intermediate x in gluon densities
•HKM: low x shadowing in the valence distribution (none in HKM), ratios for sea and gluon densities approach 1 as x grows while they strongly rise within HKM
they use:
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• Approach based on multiple collisions • It takes into account triple pomeron interactions -equivalente to interaction among gluon-• It leads to a shadowing due to coherence effects
• Shadowing increases with s (~1/x) and decreases with pT (~ mT)
Pomeron shadowing model
• Shadowing corrections: integral of the triple P cross section over the single P one
• Reduction of multiplicity from shadowing corrections
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
• The primordial spectrum of particles is altered by interactions with the nuclear matter they traverse on the way out to the detector
• Rapidity dependence of the nuclear absorption: sabs at mid y < sabs at forward y
• Usual parameterisation:
Nuclear absorption: a cold nuclear matter effect
• Nuclear absorption: interaction of the preresonant c-cbar pair with spectator nucleons
Sabs = exp(- r sabs L )
nuclear matter density path lengthbreak-up cross section
• Note: some authors consider
• At high energy: the coherence length is large and the projectile interacts with the nucleus as a whole => Smaller nuclear absorption with growing energies
E. G. Ferreiro USC CNM effects on quarkonium Palaiseau 5 March 09
EKS shadowing model: intrinsic vs. Vogt’s
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
EKS shadowing model: intrinsic & extrinsic vs. Vogt’s
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
EPS shadowing model: intrinsic vs. Vogt’s
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
EPS shadowing model: intrinsic & extrinsic vs. Vogt’s
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
nDSg shadowing model: intrinsic vs. Vogt’s
NLO
LO
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
nDSg shadowing model: intrinsic & extrinsic vs. Vogt’s
NLO
LO
Vogt’s: LOOurs: NLO
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Fit procedure
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Fit procedure: results I
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Fit procedure: results II
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Abigail Bickley, August 9, 2007 67
• Color Singlet Model:– Color singlet cc pair created in same quantum state as J/– Underpredicts J/ production cross section by a x10– Predicts no polarization
p
p
J/y
hard g
c
c
Lansberg, Int. J. Mod. Phys. A21 (2006)
J/y production mechanisms: CSM
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Abigail Bickley, August 9, 2007 68
• NRQCD Color Octet Model:– Includes octet state cc pairs that radiate soft gluons during
hadronization– Color octet matrix elements derived from experimental data were
expected to be universal, but are not – Predicts large transverse polarization (>0) at high pT that is not seen
in experimental data
p
p
J/y
soft g
c
c
Reisert, Beauty 2006
J/y production mechanisms: COM
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Abigail Bickley, August 9, 2007 69
• Color Evaporation Model:– Phenomenological approach– Charmonium states formed in proportions determined by
experimental data for any cc pair that has a mass below the DD threshold
– Uses emission of soft gluons to form J/– Predicts no polarization
Reisert, Beauty 2006
J/y production mechanisms: CEM
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10
Abigail Bickley, August 9, 2007 70
• pQCD involving 3-gluons:– Hadronization mechanism includes channel involving the fusion of
a symmetric color octet state with an additional gluon– Successfully reproduces experimental cross section and
polarization measurements– Fails to reproduce experimental rapidity distribution => New
result!
Khoze et al Eur.Phys.J. C39 (2005)
J/y production mechanisms: pQCD involving 3-gluons
E. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10