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Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/ and ’ suppression patterns “smoothy” or “steppy” ?
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Page 1: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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” ?

Page 2: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 3: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 4: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

N. Cabibbo and G. Parisi, Phys. Lett. B59 (1975) 67

The first QCD Phase Diagram

Page 5: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 6: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 7: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

One Pb-Pb collision seen by NA49at the CERN SPS

Page 8: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

A very large volume of compressed QCD matter

Page 9: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 10: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 11: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 12: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 13: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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 ...”

Page 14: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 15: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 16: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 17: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 18: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 19: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 20: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

Now there isn’t...Now there is

Question: Is there a “step” in the SPS J/ suppression pattern measured at the SPS ?

Answer:

Page 21: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 22: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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:

Page 23: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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...

Page 24: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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.

Page 25: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 26: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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” ?

Page 27: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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?

Page 28: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 29: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 30: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

Can any of the models describe the experimental data points?

Observations made at CERN

Page 31: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 32: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

calibrationerror

anomaloussuppression

All kept data points agree with the expected QGP suppression pattern!

Data versus the “new physics” model

Page 33: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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

Page 34: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

Once again, the model prediction agrees with the measurements...

Improved model versus new experimental data

Page 35: Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns.

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...


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