Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos...
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Transcript of Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos...
Quarkonium suppression at the SPS
International Workshop on Heavy Quarkonium, DESY, Oct. 2007Carlos Lourenço
or
Are the SPS J/ and ’ suppression patterns“smoothy” or “steppy” ?
The QCD phase transition
QCD calculations indicate that, at a critical temperature around 170 MeV, strongly interacting matter undergoes a phase transition to a new state where the quarks and gluons are no longer confined in hadrons
quarks and gluons
hadrons
The phase diagram of QCD
Tem
per
atu
re
net baryon density
Ear
ly u
nive
rse
nucleinucleon gas
hadron gas
quark-gluon plasmaTc
0
N. Cabibbo and G. Parisi, Phys. Lett. B59 (1975) 67
The first QCD Phase Diagram
So Dark the Confinement of Man
For details, see:
“The Da Vinci colour Code”
The really first QCD Phase Diagram
Not easy to see...unless you know what you are looking for
How do we study bulk QCD matter?
We heat and compress a large number of hadrons, in the lab, by colliding heavy nuclei at very high energies
Pb208
Pb208 +
p
One Pb-Pb collision seen by NA49at the CERN SPS
A very large volume of compressed QCD matter
QGP ?
We study the 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
vacuum
QGP
hadronicmatter
The good QCD matter probes should be:
Well understood in “pp collisions”
Only slightly affected by the hadronic matter, in a very well understood way, which can be “accounted for”
Strongly affected by the deconfined QCD medium...
Heavy quarkonia (J/, ’, c, , ’, etc) are good QCD matter probes !
Challenge: find the good probes of QCD matter
Challenge: creating and calibrating the probes
The “probes” must be produced together with the system they probe (!)and very early, to be there before the matter to be probed: quarkonia
We need “trivial” (reference) probes,not affected by the dense QCD matter: photons, Drell-Yan dimuons
We need “trivial” collision systems,to understand how the probes are affectedin the absence of “new physics”: pp, p-nucleus, light ions
Tomography in medical imaging:Uses a calibrated probe and a well understood interaction to derive the 3-D density profile of the medium from the absorption profile of the probe.
“Tomography” in heavy-ion collisions:- Jet suppression gives the density profile of the matter- Quarkonia suppression gives the confinement state (hadronic or partonic) of the matter
“Tomography” of the produced QCD matter
The suppression of the J/ production yield in nuclear collisions should be a clear signal of the QCD phase transition from confined hadronic matterto a deconfined plasma of quarks and gluons
In the beginning was the Verb, and the Verb was…
“... colour screening prevents c-cbar binding ...”
In the deconfined phase the QCD potential is screened and the heavy quarkonia states are “dissolved” into open charm or beauty mesons.
Different heavy quarkonium states have different binding energies and, hence, are dissolved at successive thresholds in energy density or temperature of the medium; their suppression pattern woks as a “thermometer” of the produced QCD matter.
Latti
ce Q
Qba
r fr
ee e
nerg
y
T
The “melting” of the heavy-quarkonia states
The feed-down from higher states leads to a “step-wise” J/ suppression pattern
state J/ c'
Mass [GeV} 3.096 3.415 3.686B.E. [GeV] 0.64 0.2 0.05
Td/Tc --- 0.74 0.15 1.10 0.74 0.15
’
c
A “smoking gun” signature of QGP formation: steps
“Well known” J/ cocktail:60% direct J/30% from c decays10% from ’ decays
HERA-B J/ cocktail:72% direct J/21% from c decays 7% from ’ decays
Drell-Yan dimuons are not affected by the dense medium they cross
reference process
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 (our probe) are “anomalously dissolved” by the deconfined medium created in central Pb-Pb collisions at SPS energies
p-Be
p-Pb
centralPb-Pb
J/ normal nuclear
absorption curve
reference data
J/ suppression: from theory predictions to SPS data
2/ndf = 0.7 2/ndf = 1.4
The J/ and ’ “normal nuclear absorption” in p-A collisions
’
J/
NA50 p-A 400 GeV
The Glauber model describes the J/ and ’ “normal nuclear absorption”, in p-A collisions, in terms of the average path length, L, which they traverse in the target nucleus, from the production point to the nuclear “surface”
NA50
normal nuclearabsorption
NA60 collected less J/ events in In-In than NA50 in Pb-Pb but they are directly compared to the normal nuclear absorption curve, calculated with “Glauber”, without using the “statistically challenged” Drell-Yan yield
~ 29 000 J/ dimuons
The calculation of Npart for each EZDC bin uses the Glauber model,
which reproduces distributions collected with minimum bias triggers (no dimuons)
NA60: a third generation J/ experiment at the SPS
There is a good agreement between the Pb-Pb and In-In suppression patterns when plotted as a function of the Npart variable, determined from the (same) ZDC detector.
The statistical accuracy of the In-In points is, however, much better...
The pink box represents the ±6% global systematic uncertainty in the relative normalization between the In-In and the Pb-Pb data points.
J/ suppression at the SPS: In-In vs. Pb-Pb patterns
Now there isn’t...Now there is
Question: Is there a “step” in the SPS J/ suppression pattern measured at the SPS ?
Answer:
Capella and Ferreirohep-ph/0505032
Digal, Fortunato and SatzEPJ C32 (2004) 547
Grandchamp and RappNP A715 (2003) 545PRL 92 (2004) 212301
Pb-Pb @ 158 GeVCF: suppression by “comovers”
DFS: percolation phase transition
GR: dissociation and regeneration in QGP and hadron gas, inc. in-medium properties of open charm and charmonium states
J/ suppression at the SPS: model tuning on the Pb data
None of these predictions describes the measured suppression pattern...
Homework exercise:calculate the 2/ndf for eachof these curves (ndf = 8)
Note: the In-In data set was taken at the same energy as the Pb-Pb data...to minimise the “freedom” of the theoretical calculations
Note: by moving up or down all the data points, within the 6% uncertainty on their global normalisation, we can get better (and worse) agreements...but even in the best cases, the 2/ndf remains very high...
S. Digal et al. EPJ C32 (2004) 547
A. Capella, E. Ferreiro EPJ C42 (2005) 419
R. Rapp EPJ C43 (2005) 91centrality dependent 0
R. Rapp EPJ C43 (2005) 91fixed termalization time 0
In-In 158 A GeV
Data vs. theoretical predictions: the results
Capella & Ferreiro = 49Digal et al. = 21
Rapp (fixed 0) = 14
Rapp (variable 0) = 9
Solutions:
Nuclear plus hadron gas absorptionL. Maiani et al., NP A748 (2005) 209F. Becattini et al., PL B632 (2006) 233
Nuclear absorption only...
plus largest possible absorption in a hadron gas(T = 180 MeV)
This figure
Data vs. theoretical post-dictions...
2/ndf = 7.42/ndf = 16
ndf = 8
The probability that the measurements should really be on any of these two curves and “statistically fluctuated” to where they were in fact observed is... zero
In-In 158 A GeV
HSD
Charmonium dynamics in heavy ion collisionsO. Linnyk et al., SQM 2007, June 28, 2007and Nucl. Phys. A 786 (2007) 183.
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
In-In data vs. a step function in Npart
Npart is convenient to compare the measured In-In and Pb-Pb data, since it is derived from the same EZDC variable (measured by the same detector) using the same Glauber formalism (except for different nuclear density functions).
Also, the derivation of Npart from EZDC is trivial and essentially model independent.
Maybe the “real variable” driving charmonia suppression is not Npart. Then, the measured smearing is the convolution of the detector resolution with the “physics smearing”, due to the conversion from the “real variable” to Npart
But the Npart “detector resolution” is 20 and the “total resolution” from fitting the
measured pattern is 19 (!) indicating that the “physics smearing” is negligible with respect to the detector resolution...
In summary, the In-In pattern indicates that: 1) there is a step and2) the “physics variable” is Npart
A step function in Npart or in another “physics variable” ?
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 !..
In summary, the Pb-Pb pattern 1) rules out the single-step function and2) indicates the existence of a second step...
What about the Pb-Pb pattern? Another step?
The ’ suppression pattern also shows a significantly stronger dropthan expected from the “normal extrapolation” of the p-A data
abs ~ 20 mb
’
The “change of slope” at L ~ 4 fm is very significant and looks very abrupt...The third step of the day ! Starts to look like a “stairway to heaven”...
’
’ suppression in heavy-ion collisions at the SPS
We made measurements, to rule out one of these two scenarios (or both)
normal nuclearabsorption
suppressionby QGP
J/
sur
viva
l pr
obab
ility
Back to the ideal world
The predicted patterns, before any data points were available,were quite different from each other We thought it was going to be very easy to discriminate between the two theories...
Energy densityc
Can any of the models describe the experimental data points?
Observations made at CERN
All kept data points agree with the expected normal nuclear absorption pattern!
“outlier” point;to be rejected
normal nuclearabsorption
Data versus the “no new physics” model
calibrationerror
anomaloussuppression
All kept data points agree with the expected QGP suppression pattern!
Data versus the “new physics” model
New and improved data points are needed
B decays
direct J/suppression
’, c
suppression
gluonanti-shadowing
recombinationof uncorrelated
ccbar pairs
J/
sur
viva
l pr
obab
ility
A more detailed theoretical frameworkJ/
sur
viva
l pr
obab
ility
Energy density
Once again, the model prediction agrees with the measurements...
Improved model versus new experimental data
1) There is a BIG difference between “the measurements are compatible with the model expectations...”and“the measurements show beyond reasonable doubt that the model is good”
2) “Nature never tells you when you are right, only when you are wrong” You only learn something when the theory fails to describe the data... [Bacon, Popper, Bo Andersson]
Be happy if your model is shown to be wrong…
3) Today, none of the “fancy theories” describes the In-In suppression pattern
All the “fancy theorists” should be happy
4) The very simple step function gives a perfect description of the In-In pattern; a second step is needed to describe the Pb-Pb pattern
We found what we were told to look for, as a “smoking gun QGP signal” the experimentalists should be happy
Take-home messages...