1. Overview of CMS experimental results from the 2010 PbPb data
Stefano Bianco
Laboratori Nazionali di Frascati dell’INFN
for the CMS Collaboration
Based on talk by Julia Velkovska
at the DNP meeting, East Lansing, 2011

2. OUTLINE Goals CMS Muons Global Observables Hard Probes
Onia Suppression
Conclusions

3. The goals and the tools To produce QGP and characterize its properties
Energy density and T: location on the phase diagram ?
dNch/dη , dET/dη , quarkonium melting (J/ ,  measurements)
Viscosity, speed of sound: Transport of momentum and energy
collective flow and di-hadron correlations
Opacity, diffusion: Transport of particles
Charged hadron RAA
Di-jets colored probes
Heavy flavor
Isolated photons RAA colorless probes
Z-boson RAA
Color screening
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012 3

4. The CMS detector HADRONIC
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012 4

5. Data taking during PbPb run
Very central
Head-on
Days since Nov 1, 2010
Triggering on minimum bias, jets, muons and photons
ALL rare probes written to tape
~half of minimum bias written
Recorded luminosity PbPb 8.7 mb-1 Recorded luminosity TeV 241 nb-1 Total PbPb data volume ~0.89 PetaByte
Note: luminosities will be rescaled by few% after complete analysis of Van der Meer scans
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012 5

6. PERFORMANCE OF MUON DETECTORS
For much more info on the performance of the muon systems in CMS and on the activity of the Frascati group refer to Davide Piccolo’s talk tomorrow at the
LNF Scientific Committeee
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

7. LNF Scientific commettee
MUON DETECTORS
Barrel Region
Overlap Region
Endcap Region
J/ψ + Z events
J/ψ + Z events
J/ψ + Z events
Pt (Gev/c)
Pt (Gev/c)
Pt (Gev/c) η
LNF Scientific commettee 7
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

8. LNF Scientific commettee
RPC
Contribution of RPCs
In specific Eta Regions
LNF Scientific commettee 8
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

9. LNF Scientific commettee
Frascati analysis: Z
Contribution in collaboration with Napoli group in the development of
the tools for data driven methods of Reco/selection/trigger Efficiency
and production yield
Published on 27 October 2011
On JHEP10 (2011) 132
LNF Scientific commettee 9
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

10. Frascati analysis in progress
Single top production xSection
Toward 2012 single top Analysis
Analysis of the differential cross section
in the t channel related to new physics,
and constraints to Vtb vertex
s channel sensible to the exchange of W’.
LNF Scientific commettee 10
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

11. Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 201211

12. The papers from the first PbPb run
HIN (dNch/d): JHEP 08 (2011) 141
HIN (v2 flow): PAS (CDS record )
HIN (Z): PRL 106 (2011)
HIN (dijet inbalance): Phys.Rev. C 84, (2011)
HIN (RAA): PAS (CDS record )
HIN (quarkonia): PAS (CDS record )
HIN (correlations): JHEP 07 (2011) 076
HIN (photons): PAS (CDS record )
HIN (dET/d): PAS (CDS record )
HIN (jet FF’s): PAS (CDS record )
HIN (vn flow): PAS (CDS record )
HIN (correlations): PAS (CDS record )
HIN (Y2s/Y1s ratio): PRL 107 (2011)
Plus a couple more not yet preliminary
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13. Global Observables
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14. Charged particle multiplicity
Uses pixel tracker and two methods
Data : B=0T ; Trigger with 99% efficiency, 1% UltraPeripheralCollisions contamination
Central multiplicity dNch/dh=1610  55 for 05% centrality
dNch/dh/ (0.5 Npart) a factor 2.1 > RHIC ; similar centrality dependence
=participating nucleon pairs
Need a comment about models and scaling /shape compared to RHIC
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15. dET/dη: rapidity and centrality dependence
dET/dη ( η = 0) ≈ 2 TeV - by a factor of 3.4±0.4 higher than RHIC
dET/dη/ (0.5 Npart) : Monotonic increase with Npart
Extrapolate from PHENIX to LHC : ET /Nch value of (0.92±0.06) GeV. It is 200 GeV 0-5%.
The increase for multiplicity is 2.2 +/- 0.1
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012 15

16. dNch/dh and dET/dη: √sNN dependence
dNch/dη/ (0.5 Npart) and dET/dη/ (0.5 Npart) – power law increase with √sNN
dET/dη/ (0.5 Npart) rises faster => More energy per particle than at RHIC
Extrapolate from PHENIX to LHC : ET /Nch value of (0.92±0.06) GeV. It is 200 GeV 0-5%
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17. Charged multiplicity density conclusions
An inclusive look to the phenomenology of PbPb collisions at 2.76TeV
For the most central collisions, charged density is measured, an increase of a factor of 3 compared to RHIC energies.
Multiplicity density distributions show weak dependance
Multiplicity densities follow a power-law function of sqrt(s)
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

18. DIHADRON CORRELATIONS
DATA SIMULATION
Back-to-back jet structure
Jet fragmentation peak
Long-range “ridge” correlations
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

19. DIHADRON CORRELATIONS
Anisotropic hydrodynamic expansion of hot medium is one possible source of long-range azimuthal correlations
For noncentral collisions, they are dominated by 2nd-order Fourier component of distribution, called elliptic flow or v2
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

20. v2(η) : centrality dependence
Multiple methods – give a handle on non-flow and fluctuations
Weak η- dependence, except for most peripheral (EP and v2{2})
may constrain descriptions of the longitudinal dynamics
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21. Elliptic flow at mid-rapidity: LHC and RHIC
Similar pT dependence
CMS: EP , ∆ η > 1
PHENIX: EP
15-30% increase in integral v2
CMS: 20-30%, v2{LYZ}
Extrapolated to pT=0
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22. vn measurements from CMS
PRELIMINARY, IN PROGRESS
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23. Hard probes
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24. Define nuclear modification factor RAA
Study properties of hot and dense medium produced in HI collisions (AA) and compare to proton-proton (pp) collisions.
Compare in the same AA sample the yields of particles that are modified by QGP (jets, onia, etc) to those of unmodified reference particles (photons, Z, etc)
RAA = dN/(TAB dpp)
where TAB is a scaling factor
RAA=1 ………. MEDIUM IS TRANSPARENT
RAA<1 ………………...MEDIUM IS OPAQUE
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012

25. High pT charged hadrons: spectra and RAA
Measuring charged tracks up to pT~100 GeV/c ( jet triggers)
Strong constraints to energy loss models
Centrality 0-5%
Pp ref ?interpolation from 0.9 and 7 TeV data. Measured at 2.76 TeV for the final data
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26. A colorless probe: isolated high pT photons
The final results include a measured pp reference
As expected: no nuclear modifications seen
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27. New colorless probe: Z bosons
How many Z’s ? 39
No significant dependence on centrality
pT dependence consistent with pp
arXiv:
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28. RAA summary
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012
J.Velkovska Overview of CMS experimental results, DNP meeting, East Lansing, Oct , 2011 28

29. Jet quenching Quantify the di-jet energy imbalance by asymmetry ratio
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012
J.Velkovska Overview of CMS experimental results, DNP meeting, East Lansing, Oct , 2011 29

30. Di-jet imbalance Di-jet imbalance increases with centrality
Not reproduced by MC ( PHYTHIA + PbPb data)
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31. Jet angular correlations
Back-to-back even in central collisions
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32. Where does the lost energy go ?
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33. Fragmentation functions
Measured pp reference
of tracks within the jet cone R = 0.3
Tracks are selected with pT > 4GeV/c, which restricts this measurement to the low xsi region of
the fragmentation function. For PbPb analysis, this track selection minimizes the contribution
of the underlying event to the jet fragmentation function. A Monte Carlo derived tracking
efficiency correction is applied to the fragmentation functions.
Leading and sub-leading jets in PbPb fragment like the corresponding energy jet in pp: partons fragment as in vacuum
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34. Jet results summary
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012 34

35. Compact Muon Solenoid: m+m- invariant mass
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36. J/ and  J/ and  observed in m+m- channel
CMS muon acceptance |h|<2.4, pTm>2-4 GeV/c
Excellent mass resolution ~1%, comparable to pp
Use displaced vertices to separate prompt J/ and B-decays
NJ/ =734±54
N =86±12
Y – pp measured ref
J/ 
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37. All quarkonia suppressed: RAA vs. centrality
Non-prompt J/ suppression is a measure of b-quark quenching
High pT J/ is strongly suppressed at the LHC
Inclusive (1S) is suppressed
0-20%
Raa for J/psi :MEASURED in pp reference at 2.76 TeV
Y(nS) states melt at 1.2 Tc (3S), 1.6 Tc (2S), and above 4 Tc (1S), while modern spectral-function approaches with complex potentials [6, 7] favour somewhat lower dissolution temperatures. This sequential melting pattern is generally considered a “smoking-gun” signature of the QCD deconfinement transition. However, a large fraction
of the observed Y(1S) yield is due to decays of heavier states (around 50% for the Y(1S) [8]).
Therefore the melting of the excited states is expected to result in a significant suppression of
the observed Y(1S) yield, even if the medium is not hot enough to directly dissolve it.
Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 2012 37

38. Suppression of excited  states
PbPb
Excited states (2S,3S) relative to (1S) are suppressed
Probability to obtain measured value, or lower, if the real double ratio is unity, has been calculated to be less than 1%
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39. Summary Broad experimental program and excellent detector performance
CMS conducted detailed measurements of global properties of medium in PbPb and pp collisions
CMS has obtained significant statistics of hard probes
Our measurements indicate consistent view of the hot and dense medium
Strong collective effects in the medium
No quenching of weakly and electromagnetically interacting probes
Strong quenching of partons, including b-quarks
Suppression of quarkonia, including excited states of the 
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40. Back-up
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41. The full harmonic spectrum
• vn vs Npart shows different trends:
even harmonics have similar centrality dependence:
decreasing  0 with increasing Npart
• v3 has weak centrality dependence, finite for central collisions
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42. Stefano Bianco - Heavy Ions in CMS - QGP Frascati January 18, 201242

43. v3 (pT): comparison of methods
0-5%
v3f
70-80%
v3{2} and v3f comparable at low trigger pT
Non-flow dominate v3{2} at high pT and in peripheral collisions
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44. Isolated photons Colorless probes Photon selection Check suppression
Nuclear parton distribution function
Initial state
Photon selection
Identify isolated electromagnetic clusters
EHCAL/EECAL <0.2
Energy in cone (R<0.4) less than 5 GeV
Transverse shower shape
Smaller width
Larger width π0
Transverse shower shape using high ECAL granularity
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45. J/: prompt and from B decays
Use separation of primary and m+m- vertices in plane transverse to beam
Long B decay times lead to displaced vertices
Separate:
Prompt J/ production
Non-prompt J/ from B decays
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46. Take home messages from CMS
v2 in wide acceptance
Charged hadron multiplicity
First: ET
First dihadron correlations
pp and PbPb in wide
acceptance
First: h+- RAA pT up to100 GeV/c
A First: Suppression of excited 
First: Jet imbalance and
jet fragmentation function
First: Gauge bosons: Z, W, isolated-g
First: Prompt J/ and
B-hadrons through non-prompt J/
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