now there isn’t
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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
2/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
3/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
4/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
5/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
6/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
7/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
8/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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 !
9/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
10/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
11/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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...
12/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
13/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
14/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
15/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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 !
16/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
17/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
18/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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...
19/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
20/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
21/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
22/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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)
23/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
24/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
Pb-Pb → + X event in CMS
dNch
/d = 3500
Pb-Pb event simulated using the CMS software framework developed for pp
25/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
→ : 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
26/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
J/ → : acceptances and mass resolutions
barrel +endcaps
O. Kodolova, M. Bedjidian, CMS note 2006/089
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)
27/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
28/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
Reach of quarkonia measurements (for 0.5 nb-1)
O. Kodolova, M. Bedjidian, CMS note 2006/089
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
29/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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)
30/29Carlos Lourenço, ETD HIC, Montreal, Canada, July 2007
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
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