now there isn’t

1/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007

Now there isn’t...Now there is

Outline:

• Heavy quarkonia : a hard probe of dense QCD matter

• Reminder of some NA38, NA50 and NA60 results

• Quarkonia studies with the CMS detector

• Bonus track; previously unreleased:

Is there a “step” in the SPS J/ suppression pattern ?

Heavy Quarkonia as Probes of High Density QCD Physics:

from pp to Pb-Pb collisions, from NA38/NA50/NA60 to CMS

Early Time Dynamics in HI Collisions, Montréal, July 16-19, 2007Carlos Lourenço, CERN


QGP ?

We study the QCD matter produced in HI collisions by seeing how it affects well understood probes,as a function of the temperature of the system (centrality of the nuclear collisions)

Calibrated“probe source”

Matter under study

Calibrated“probe meter”

Calibratedheat source

Probe

Probing the QCD matter produced in HI 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 particularly good QCD matter probes !

Challenge: find good probes of QCD matter


The “probes” must be produced together with the system they probe !

They must be created very early in the collision evolution, so that they are there before the matter to be probed: hard probes (jets, quarkonia, ...)

We must have “trivial” probes,not affected by the dense QCD matter,to serve as baseline reference: photons, Drell-Yan dimuons

We must have “trivial” collision systems,to understand how the probes are affectedin the absence of “new physics”: pp, p-nucleus, d-Au, light ions

Creating and calibrating the probes


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 matterQuarkonia suppression gives the state(hadronic or partonic) of the matter

“Tomography” of the produced QCD matter


In a deconfined phase the QCD binding potential is Debye screened and the heavy quarkonia states are “dissolved”. In other words, the free hard gluons are energetic enough to break the bound QQ states into open charm and 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 is a thermometer of the produced QCD matter.

Latti

ce Q

Qba

r fr

ee e

nerg

y

T

Why is quarkonia suppression interesting?

H. Satz, hep-ph/0512217


Feed-down from higher states leads to “step-wise” J/ and suppression patterns.The suppression of bottomonium states is a very important component of the LHC HI physics program.

state J/ c

' (1s) b

(2s) b' (3s)

Mass [GeV} 3.096 3.415 3.686 9.46 9.859 10.023 10.232 10.355B.E. [GeV] 0.64 0.2 0.05 1.1 0.67 0.54 0.31 0.2

Td/Tc --- 0.74 0.15 --- --- 0.93 0.83 0.74 1.10 0.74 0.15 2.31 1.13 0.93 0.83 0.74

A “smoking gun” signature of QGP formation

’

c

H. Satz, hep-ph/0512217


Charmonia studies made by NA50

J/

Pb-Pb 158 GeVp-Pb 400 GeV

p-Pb @ 400 GeV

J/ ~ 105 MeV

Studies of J/ and ’ production, in p-nucleus and Pb-Pb collisions, have been published in the last few years by the NA50 collaboration.

Charmonia production yields have been presented either in relative terms, with respect to the yield of high-mass Drell-Yan dimuons, or as absolute production cross-sections per target nucleon. With rather good charmonia statistics...

real data !


The J/ and ’ are absorbed in p-A collisions

2/ndf = 0.7 2/ndf = 1.4

The lines are the result of Glauber calculations, assuming that the reduction of the production cross section per target nucleon is exclusively due to final state absorption of the charmonia states in the cold nuclear matter it crosses.

From a global fit to the 400 and 450 GeV p-A data (16 independent measurements), NA50 determined the following absorption cross-sections:abs(J/ = 4.2 ± 0.5 mb ; abs(’) = 7.7 ± 0.9 mb


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 ccbar 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/ suppression at the CERN SPS: NA38 / NA50

J/ normal nuclear

absorption curve

reference data


J/ suppression at the CERN SPS: NA60

Nuclearabsorption

Rescaled to 158 GeV

NA60 In-In 158 A GeV

1) There is a remarkable agreement between the NA60 p-A data point at 158 GeV and the 400–450 GeV points rescaled to 158 GeV...2) There is a remarkable 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...


Data vs. theoretical predictions: the model tuning

The In-In NA60 data can be compared with theoretical predictions based on models tuned on the J/ suppression pattern defined by the Pb-Pb NA50 data

Capella and Ferreirohep-ph/0505032

Digal, Fortunato and SatzEPJ C32 (2004) 547

Grandchamp and RappNP A715 (2003) 545PRL 92 (2004) 212301

Pb-Pb @ 158 GeV

CF: suppression by “comovers”DFS: percolation phase transitionGR: dissociation and regeneration in QGP and hadron gas, inc. in-medium properties of open charm and charmonium states


Data vs. theoretical predictions: the results

None of these predictions describes the measured suppression pattern...

Homework exercise:calculate the 2/ndf for eachof these curves (ndf = 8)

Note: the In data was taken at the same energy as the Pb data to minimise the “freedom” of the theoretical calculations

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 post-dictions...

Nuclear plus hadron gas absorptionL. Maiani et al., NP A748 (2005) 209F. Becattini et al., PL B632 (2006) 233

Nuclear absorption...

plus largest possible absorption in a hadron gas (T=180 MeV)

This figure


0.6

0.8

1.0

1.2 NA60, In+In, 158 A GeV QGP threshold melting NA50, Pb+Pb, 158 A GeV QGP threshold melting

0 50 100 150 200 250 300 3500.4

0.6

0.8

1.0

1.2

HSD

NA60, In+In, 158 A GeV Comover absorption NA50, Pb+Pb, 158 A GeV Comover absorption

Npart

0 50 100 150 200 250 300 3500.4

0.6

0.8

1.0

1.2

( (J

/ ) /(

DY

))

/ (

(J/

) /(

DY

)) G

laub

er

Npart

QGP threshold melting

Comover absorption

In+In, 158 A GeV

HSD

Data vs. theoretical post-dictions... (cont.)

Charmonium dynamics in heavy ion collisionsO. Linnyk et al., SQM 2007, June 28, 2007and Nucl. Phys. A 786 (2007) 183.

It looks really strange that the curve“QGP threshold melting” is very smooth... and the “comover absorption” has a step !


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...

Data vs. theoretical post-dictions... (the end)

zero

In-In 158 A GeV

HSD


Step at Npart = 86 ± 8

A1 = 0.98 ± 0.02

A2 = 0.84 ± 0.01

2/ndf = 0.75 (ndf = 5)

In-In data vs. a sharp step function in Npart

Taking into account the EZDC resolution, the measured pattern is perfectly

compatible with a step function in Npart...

The real function can have the step in a different variable (energy density, etc) if the smearing induced when converting that variable to Npart is not larger than the ZDC

resolution (around 20 in Npart whatever the centrality)

Npart

Mea

sure

d /

Ex

pec

ted

1

Step position

A1A2


What about the Pb-Pb pattern? Another step?

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 = 11)

Npart

Mea

sure

d /

Ex

pec

ted

1

Step positions

A1A2

A3

If we try fitting the In and Pb data with one single step we get 2/ndf = 5 !... The Pb data points rule out the single-step function... and strongly indicate the presence of a second step...


The ’ suppression pattern also shows a significantly stronger drop than expected from the “normal extrapolation” of the p-A data

abs ~ 20 mb

’

The “change of slope” at L ~ 4 fm is quite significant and looks very abrupt...

’

’ suppression in heavy-ion collisions at the SPS


Hard Probes at LHC energies

• Very large cross sections at the LHC

• Pb-Pb instant. luminosity: 1027 cm-2s-1

• ∫ Lumi = 0.5 nb-1 (1 month, 50% run eff.)

• Hard cross sections: Pb-Pb = A2 x pp

pp-equivalent ∫ Lumi = 20 pb-1

1 event limit at 0.05 pb (pp equiv.)

jet

Z0+jet+jet

prompt

h/h

pp s = 5.5 TeV

1 event

J

1 b

1 nb

1 pb

M. Ballitjin, C. Loizides, G. Roland, CMS note AN-2006/099


Phase space coverage of the CMS detector

CMS (with HF, CASTOR, ZDC) + TOTEM: almost full η acceptance at the LHC ! charged tracks and muons: |η| < 2.5, full φ electrons and photons: |η| < 3, full φ jets, energy flow: |η| < 6.7 (plus η > 8.3 for neutrals), full φ excellent granularity and resolution very powerful and flexible High-Level-Trigger

CA

ST

OR

TOTEM

HFHF

= -8 -6 -4 -2 0 2 4 6 8

ZDC

5.2 < |η| < 6.6

η > 8.3 neutrals

T1/T2 CASTOR ZDC RP RP


h±, e±, , ± measurement in the barrel (|| < 2.5)

Si Tracker + ECAL + muon-chambers

Si TrackerSilicon micro-stripsand pixels

CalorimetersECAL PbWO4

HCAL Plastic Sci/Steel sandwich

Muon BarrelDrift Tube Chambers (DT)Resistive Plate Chambers (RPC)


So far, only the dimuon decay channel has been considered.The physics performance has been evaluated with the 4 T field (2 T in return yoke) and requiring a good track in the muon chambers. The good momentum resolution results from the matching of the muon tracks to the tracks in the silicon tracker.

Quarkonia studies in CMS


Pb-Pb → + X event in CMS

dNch

/d = 3500

Pb-Pb event simulated using the CMS software framework developed for pp


→ : acceptances and mass resolutions

CMS has a very good acceptance for dimuons in the Upsilon mass region(21% total acceptance, barrel + endcaps)

The dimuon mass resolution allows usto separate the three Upsilon states:~ 54 MeV within the barrel and~ 86 MeV when including the endcaps

Barrel: both muons in || < 0.8

Barrel + endcaps: muons in || < 2.4

pT (GeV/c)

Acc

epta

nce

O. Kodolova, M. Bedjidian, CMS note 2006/089


J/ → : acceptances and mass resolutions

barrel +endcaps


barrel

• The material between the silicon tracker and the muon chambers (ECAL, HCAL, magnet’s iron) prevents hadrons from giving a muon tag but impose a minimum muon momentum of 3.5–4.0 GeV/c. This is no problem for the Upsilons, given their

high mass, but sets a relatively high threshold on the pT of the detected J/’s.

• The low pT J/ acceptance is better at forward rapidities; total acceptance ~1%.

• The dimuon mass resolution is 35 MeV, in the full region.

barrel +endcaps

pT (GeV/c)

J/

Acc

epta

nce

p T (G

eV

/c)


The CMS High Level Trigger

ET reach x2

x35

x35

jets

Pb-Pb at 5.5 TeVdesign luminosity

• CMS High Level Trigger: 12 000 CPUs of 1.8 GHz ~ 50 Tflops !• Processes full events with fast versions of the offline algorithms

• pp L1 trigger rate (design L): 100 kHz• Pb-Pb collision rate: less than 8 kHz

pp L1 trigger rate Pb-Pb collision rate the HLT can process all Pb-Pb events

• Pb-Pb event size: ~2.5 MB (up to ~9 MB)• Data storage bandwidth: 225 MB/s 10–100 Pb-Pb events/s• HLT reduction factor: 3000 Hz → 100 Hz• Average HLT time budget per event: ~10 s

• The event samples of hard processes are statistically enhanced by very large factors

M. Ballitjin, C. Loizides, G. Roland, CMS note AN-2006/099


Reach of quarkonia measurements (for 0.5 nb-1)


J/

● produced in 0.5 nb-1

■ rec. if dN/d ~ 2500○ rec. if dN/d ~ 5000

Expected rec. quarkonia yields:J/ : ~ 180 000

: ~ 26 000’ : ~ 7 300; ’’ : ~ 4 400

Good statistical accuracy (with HLT) of the expected ’ / ratio versus pT

Pb-Pb

Similar low pT yields

for J/ and


Summary

The J/ is “anomalously” suppressed in Pb-Pb and In-In collisions at the SPS with respect to the “normal nuclear absorption curve” derived from the p-nucleus data

No theoretical model gives a good description of the measured data, until now further work is needed, including studies of pT distributions, ’ yields, etc

The In-In pattern indicates a step-like suppression function with a drop of ~ 15% for collisions of Npart higher than around 86

“La science donne du monde des images crédibles, non parce qu’elles sont vraies mais parce qu’elles sont les meilleures que l’on trouve à un moment donné”

The existence of step-wise patterns might be an incorrect interpretation of the SPS suppression data, but it is, today, the only good description of the measurements

Next goal: measure the suppression patterns of the states at LHC energies, as a function of centrality and pT

The CMS experiment is particularly well suited for such studies first physics data taking periods expected in 2008 (protons) and 2009 (Pb-Pb)


Before the measurements are made, theorists often tell us that the interpretation of the data will be easy

However, theorists are often wrong...especially before the measurements are made...

The good news is that nowwe have clear instructions...

Bonus slide: a lesson from the SPS to the LHC

now there isn’t

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