Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 1 Probing deconfinement with quarkonia : new answers to old questions Carlos Lourenço, CERN Workshop on Hot and Dense Matter, Mumbai, Feb. 2008 Outline: What are the “cold nuclear matter effects” in charmonium absorption ? How do they affect the SPS J/and ’ suppression patterns ? [ work being done in collaboration w Ramona Vogt and Hermine K. Wöhri What gets you into trouble is not what you don’t kn but what you think you know Mark Twain (Larry at QM08)
Transcript
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 1
Probing deconfinement with quarkonia :
new answers to old questions
Carlos Lourenço, CERNWorkshop on Hot and Dense Matter, Mumbai, Feb. 2008
Outline:
What are the “cold nuclear matter effects” in charmonium absorption ?
How do they affect the SPS J/ and ’ suppression patterns ?
[ work being done in collaboration withRamona Vogt and Hermine K. Wöhri ]
What gets you into trouble is not what you don’t knowbut what you think you know
Mark Twain(Larry at QM08)
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 2
QGP ?
We study the bulk QCD matter produced in HI collisions by seeing how it affectswell understood probesas a function of the temperature of the system (centrality of the collisions)
Calibrated“probe source”
Matter under study
Calibrated“probe meter”
Calibratedheat source
Probe
“Seeing” the QCD matter formed in heavy-ion collisions
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 3
Challenge: find the good probes of QCD matter
vacuum
QGP
hadronicmatter
The good QCD matter probes should be:
Heavy quarkonia (J/, ’, , ’, etc) are very good QCD matter probes !
Well understood in “pp collisions”
Slightly affected by the hadronic matter, in a well understood way, which can be accounted for
Strongly affected by the deconfined QCD medium...
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 4
reference process
Drell-Yan dimuons are not affected by the dense medium they cross
The yield of J/ mesons (per DY dimuon) is “slightly smaller” in p-Pb collisions than inp-Be collisions; and is strongly suppressedin central Pb-Pb collisions
Interpretation: strongly bound c-cbar pairs are “dissolved” by the QCD medium created in central Pb-Pb collisions at SPS energies
p-Be
p-Pb
centralPb-Pb
reference data
J/ normal nuclear
absorption curve
S-U
Pb-Pbp-A
NA38 / NA51 / NA50
J/ suppression: the NA38/50/51 picture
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 5
We must have a robust and well understood reference baseline, in A-A collisions, with respect to which we can clearly and unambiguously identify patterns specific to the high-density medium produced in high-energy nuclear collisions
What should we really expect in the absence of a deconfined QCD medium but accounting for all the other “standard” aspects of nuclear collisions?
This requires :
→ Understanding the basic properties of quarkonium production in pp and p-A→ A robust model to turn the p-A patterns into reliable A-A expectations
Quarkonium studies in proton-nucleus collisions: why?
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 6
Charmonium absorption in p-nucleus collisions
The J/ and ’ production cross sections scale less than linearly with the number of target nucleons (unlike high-mass Drell-Yan dimuons)
’
J/
NA50 p-A 400 GeV
p-Pb @ 400 GeV
J/ ~ 105 MeV
The Glauber model describes the J/ and ’ “normal nuclear absorption” with a single parameter: the absorption cross section
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 7
From a global fit to the 400 and 450 GeV p-A data (16 independent measurements), NA50 determined the following absorption cross sections (with GRV94LO PDFs):abs(J/ = 4.5 ± 0.5 mb ; abs(’) = 8.3 ± 0.9 mb from production cross sections
These calculations assume that the reduction of the production cross section per target nucleon is exclusively due to charmonium final-state absorption
abs = 4.5 ± 0.5 mb
abs = 8.3 ± 0.9 mb
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 8
It seems that the J/ absorption, at mid-rapidity, becomes weaker with increasing
collision energy, at least between SPS and RHIC energies
The 158 GeV p-A data of NA60 will clarify if the trend continues to lower energies
J/
0 mb
3 mb
Low x2 ~ 0.003(shadowing region)
PHENIX
J/ absorption in p-A collisions vs. collision energy
Slid
e sh
own
at H
P06
Without nuclear effects on the PDFs With nuclear effects on the PDFs
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 9
J/
The increase of with pT is identical at 400, 800 and 920 GeV (at mid-rapidity)
Maybe the increase of from NA50 to E866 to HERA-B to PHENIX
is due to the increase of the average pT of the J/ when s increases...
And strongly decreases at high xF where the J/ and ’ have similar absorptions
J/ absorption in p-A collisions vs. pT and xF
NA50
E866
Slid
e sh
own
at H
P06
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 10
Vogt: final state absorptionVogt: final state absorption
Slid
e sh
own
at H
P06
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 11
Nuclear effects on the PDFs
The EKS 98 model gives significant anti-shadowing for charm production at the SPS
Similar for p-Pb at 450 GeV and Pb-Pb at 158 GeV… but ~6% more J/ mesons are produced, per nucleon, in Pb-Pb than in p-Pb, if both are taken at 158 GeV
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 12
Initial state nuclear effects vs. final state absorption
At SPS energies, the gluon anti-shadowing makes the J/ production cross section per nucleon increase from pp to p-Pb, if we would ignore final state absorption
abs = 0 mb
abs = 4 mb
abs = 7 mbEKS980<y*<1
pp p-Pb
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 13
p-PbJ/
EKS98
FGSo
FGSh
FGSl
nDS
nDSg DeFlorian and Sassot
Eskola, Kolhinen and Salgado
Frankfurt, Guzey and Strikman
EKS98 is not the only available model of nuclear effects on the parton densities
DeFlorian and Sassot predict no anti-shadowing for J/production at SPS energies while the FGSo parameterization predicts stronger anti-shadowing than EKS98…
The new EPS08 model gives more anti-shadowing at the SPS than EKS98…
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 14
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 15
Feed down influence on J/ absorption
We can redo the Glauber calculations assuming 60% / 30% / 10% as the fractions of direct J/ production and feed downs from c and ’ decays...
And fixing the abs of each of the three states to their geometrical values
The result is perfectly equivalent to a fit with a free effective abs(J/)
2/ndf = 1.0
coincidence?
[Figure made by G. Borges]
(no nuclear effects considered here)
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 16
Let’s express the abs values of the three charmonium states in terms of the value of the directly produced 1S state, called “J” to distinguish it from the observed “J/” (affected by feed down), assuming that they scale with the square of their radii:
with r(c) / r(J) = 1.44 ; r(’) / r(J) = 1.8 [values from H. Satz]
This is a guess… but it is better to assume an answer based on an educated guess than to ignore the existence of the question…
The generic survival probability for the state J (or ’, or c) is then given by:
And assuming 60% J, 30% c feed down and 10% ’ feed down, the survival probability to be compared with the J/ data is:
Now we can fit the existing J/ and ’ data with a single free parameter:
From qualitative hints to more detailed calculations
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 17
The charmonium production cross section in p-A collisions
fraction of charm-anticharm cross section below 2mD
K factor to match the magnitude of the LO and NLO cross sectionssurvival probability for nuclear absorptionparton density in the proton; j = g, q, qbarparton density in the nucleus
nucleon density in the nucleusmodification of the parton densities in the nucleusparton momentum fractions
FJ
Kth
SAabs
fjp(x1,Q2)
FjA(x2,Q2,b,z’)
A(b,z’)Rj(A,x2,Q2)
x1, x2
The calculations were done with several PDF sets and nuclear effects models: GRV LO 94, GRV LO 98, CTEQ6L, MRST2001LO; non-modified and modified by EKS98, nDS, nDSg, etc
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 18
From the measurements of NA3, E866 and HERA-B, respectively at 200, 800 and 920 GeV, we calculated the mid-rapidity ratios between the heavy and light targets of J/ (and ’) “per nucleon cross sections”
200 GeV : p-Pt / pp = 0.737 0.026 for the J/800 GeV : p-W / p-Be = 0.8713 0.0263 for the J/
and 0.8032 0.0274 for the ’
920 GeV : p-W / p-C = 0.903 0.031 for the J/
Existing J/ and ’ cross sections in p-A collisions
From the NA50 measurements, at 400 and 450 GeV, we calculated the J/ and ’ cross section ratios, between the heavy targets (Al, Cu, Ag, W, Pb) and Be
400 J/ ’
Al/Be 0.9360.029 1.0150.071
Cu/Be 0.9070.028 0.8290.063
Ag/Be 0.8470.026 0.7760.060
W/Be 0.8040.025 0.6550.052
Pb/Be 0.7880.024 0.6600.049
450 J/ ’
Al/Be 0.9650.041 0.9670.051
Cu/Be 0.9340.037 0.8930.044
Ag/Be 0.8660.034 0.7990.038
W/Be 0.7920.036 0.7060.039
2 data points
1 data point
1 data point
10 data points8 data points
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 19
Extraction of the absorption cross section
For each energy and target, the calculations were made with several N-PDFs and for abs values between 0.0 and 8.0 mb, in steps of 0.5 mb
Comparing the calculations with the data we derive the “best” abs and its error
abs (mb)
4.880.29 EKS983.750.27 nDSg3.390.26 none
200 GeV
abs : insensitive to the PDF set but very dependent on the nuclear effects model
EKS98
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 20
Using GRV LO 94 and no nuclear effects, we get abs(J) 3.34 0.25 mb
Conclusion: if we use the same inputs as NA50, we get the same values
(with a smaller error because we make a global fit of the J/ and ’ data pointswith one single free parameter, while NA50 made two independent fits)
Our calculations vs. the NA50 values
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 21
(open circles)
(closed circles)
Significant drop of abs with collision energy
The J/ and ’ absorption, at mid-rapidity, weakens with increasing collision energy
Exp.Elab
(GeV)
NA3 200
NA50 400
NA50 450
E866 800
E920 920 (maximum c.m.s. energyof the J/ – N collision)
Assuming a power law function, we can extrapolateabs to lower
and higher energies
158 GeV
abs at 158 GeV is ~50–60%
higher than at 400–450 GeV !
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 22
R
dA
u
Mid-rapidity data point : R(dAu) = 0.84 0.20 (stat. and syst. errors added in quadrature)
Cold nuclear matter effects at RHIC energies
PHENIX
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 23
Extraction of abs from the PHENIX mid-rapidity d-Au data
The calculations were redone with several N-PDFs and for abs values between 0.0
and 8.0 mb, in steps of 0.5 mb
None / nDSg
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 24
abs extrapolated to RHIC energies
PHENIX(EKS98)
The extrapolation from fixed-target energies matches well the PHENIX d-Au data
Much more accurate RHIC data needed to verify the functional form of the energy dependence
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 25
The ’ suppression pattern shows a significant and abrupt drop between the “normal extrapolation” of the 450 GeV p-A data and the S-U / Pb-Pb patterns
But this “step” happens between data sets collected at very different energies…and will disappear if the ’ abs increases significantly from 450 to 158 GeV !NA60 p-A data at 158 GeV will soon address (and hopefully answer) this question
’
Preliminary
’
Effect on the ’ “suppression”: magnitude and shape
abs = 8.3 ± 0.9 mb
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 26
The relative comparison between the In-In and Pb-Pb J/ suppression patterns will not change, because they were both taken at the same energy, 158 GeV, preciselyto minimise the number of “free parameters” in their comparison
But there will be a common decrease of the magnitude and of the slope’s steepness
Effect on the J/ “suppression”: magnitude and shape
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 27
In the QGP phase the heavy quarkonium states are “dissolved”, at successive temperature thresholds
The feed-down from higher states leads to a “step-wise” J/ suppression pattern
Quarkonium melting by QGP : thresholds steps
’
c
J/ cocktail (in pp):
~ 60–65% direct J/~ 25–30% from c decays
~ 10% from ’ decays
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 28
Step at Npart = 86 ± 8
A1 = 0.98 ± 0.02
A2 = 0.84 ± 0.01
2/ndf = 0.75 (ndf = 83 = 5)
Taking into account the EZDC resolution,
the measured pattern is perfectly compatible with a step function in Npart
Npart
Mea
sure
d /
Ex
pec
ted
1
Step position
A1A2
Maybe there is even a hint of charm “coalescence” in the most central collisions
The In-In J/ suppression pattern versus a step function
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 29
Npart is convenient to compare In-In and Pb-Pb data: derived from the same EZDC using the same Glauber formalism (except for the nuclear density functions)
If the “real variable” driving charmonium suppression is not Npart the measured smearing is the convolution of the detector resolution with the “physics smearing”
The detector resolution is 20 (in Npart), while a fit to the measured pattern gives 19:
the “physics smearing” is negligible with respect to the ZDC resolution…
Is the step in Npart or in another variable?
The In-In data indicates a step in the J/ suppression pattern and suggests that “the physics variable” is Npart or a variable very strongly correlated to Npart
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 30
Steps: Npart = 90 ± 5 and 247 ± 19
A1 = 0.96 ± 0.02
A2 = 0.84 ± 0.01
A3 = 0.63 ± 0.03
2/ndf = 0.72 (ndf = 165 = 11)
Npart
Mea
sure
d /
Ex
pec
ted
1
Step positions
A1A2
A3
If we try fitting the In-In and Pb-Pb data with one single step we get 2/ndf = 5 !
the Pb-Pb points rule out the single-step function and indicate a second step
What about the Pb-Pb suppression pattern?
-12% : ’ ?
-21% : c ?
We urgently need a much more accurate Pb-Pb pattern
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 31
Summary and outlook
The J/ and ’ final state “normal nuclear absorption”, determined by p-A data, is insensitive to the PDF set used but is significantly affected by the nuclear effects model assumed: none, EKS98, nDSg, etc
The latest PDF sets are mature, constrained by a wealth of data (DIS, DY, etc), while the nuclear effects on the gluon densities have not yet been measured…
We must measure the open charm nuclear dependence, versus pT and y
All existing J/ and ’ p-A data can be described by Glauber calculations using one single abs parameter, with the c and ’ values fixed by geometrical scaling and the “observed J/” value fixed from the feed down fractions
The fitted abs values show a significant decrease from 200 to 920 GeV ;the value extrapolated to 158 GeV is 50–60% larger than previously assumed…
We must re-evaluate the SPS J/ and ’ suppression patterns, with N-PDFs and the increased abs : the “anomalous suppression” will decrease in magnitude and will become less steep
Carlos Lourenço — Hot and Dense Matter — Mumbai Feb. 2008 32
Acknowledgements:
This work started after discussions withHelmut Satz and Bob Thews, in May 2006
Previous related work:
- Hard Probes 2006 talk, by CL- Quark Matter 2006 talk, by RV
References of the data points:
NA3, NA50, E866 : published papersHERA-B : values reported at HP06PHENIX : preprint arXiv: 0711.3917
