Post on 16-Jan-2016
description
Overview of CMS heavy-ion resultsRaphaël Granier de Cassagnac
for the CMS collaborationLLR – École polytechnique / IN2P3
ERC grant “QuarkGluonPlasmaCMS”
LHC days, October 2nd 2012, Split
A wealth of results• Multiplicity and transverse energy
– dNch/dη ≈ 1600 and dET/dη ≈ 2 TeV !
• Particle correlations– Elliptic flow (incl. π0) and higher harmonics– Di-hadron correlations (the “ridge”)
• Candles: Electro+weak bosons– Z and W bosons – Isolated photons
• Jet quenching– Photon+Jet– Fully reconstructed jets – Jet fragmentation & shape
• Quarkonium suppression – Five states disappearing 02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 2
Affordable in a 20’ talk?
A wealth of results• Multiplicity and transverse energy
– dNch/dη ≈ 1600 and dET/dη ≈ 2 TeV !
• Particle correlations– Elliptic flow and higher harmonics– Di-hadron correlations (the “ridge”)
• Candles: Electro+weak bosons– Z and W bosons – Isolated photons
• Jet quenching– Photon+Jet– Fully reconstructed jets – Jet fragmentation & shape
• Quarkonium suppression – Five states disappearing 02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 3
Affordable in a 20’ talk?
All results available at https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHINOr google search “CMS heavy ions”18 submitted PbPb papers (as many as ALICE)+ 10 documented preliminary analysis (PAS)
Particule detection |η|<2.4
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 5
Silicium: pixels (3) and strips (10) |η|<2.4
EMCalPbWO4 |η|<3
HCal: Scintillators |η|<5
Muon: drift tubes + RPC |η|<2.4
+ high rapidity extension
Muons 1-2% resolutionup to 100 GeV/c
Photons 10% resolutionin central events at 20 GeV
PB-PBCOLLISION
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 6
From the key concept: centrality…
• Collision centrality related to energy deposit in (forward) calorimeters
• Then to geometrical quantities:– Ncoll = number of
elementary NN collisions– or TAA = Ncoll / σpp
• Hard probes are supposed to scale with Ncoll, in the absence of medium effect, RAA = 1 02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 7
… to the nuclear modification factor RAA
• Collision centrality related to energy deposit in (forward) calorimeters
• Then to geometrical quantities:– Ncoll = number of
elementary NN collisions– or TAA = Ncoll / σpp
• Hard probes are supposed to scale with Ncoll, in the absence of medium effect, RAA = 1 02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 8
RAA = =dNAA
dNPP Ncollx dσPP TAAx
dNAA
PbPb collisions @ √sNN = 2.76 TeV
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 9
Dec. 2010: ≈ 7 μb–1 PbPb
Dec. 2011: ≈ 150 μb–1 PbPb
x 20
+ Mar. 2011 ≈ 230 nb–1 pp @ 2.76 TeV
Binary-scaledequivalent as manyZ, W, photons…
NEW CANDLES
Electro+Weak bosons should go through the colored medium without feeling it
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 10
Z boson centrality independence (150 μb–1)
11
RAA =dNAA
dσPP TAAx
• Very low pp statistics available at 2.76 TeV≈ 20 times less Z than PbPb
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 11
Z boson centrality independence (150 μb–1)
12
dNAA / TAA = dσpp x RAA
• Very low pp statistics available at 2.76 TeV≈ 20 times less Z than PbPb
(PRL 106 (2011) 212301)CMS-PAS-HIN-12-008
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 12
Z boson centrality independence (150 μb–1)
• Very low pp statistics available at 2.76 TeV≈ 20 times less Z than PbPb
• Compare to POWHEG (NLO generator) instead– Well tested at Tevatron (2
TeV) and LHC (7 TeV)– 5% uncertainty from
NNLO, pdfs, etc.
13
dNAA / TAA = dσpp x RAA
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
(PRL 106 (2011) 212301)CMS-PAS-HIN-12-008
13
Z boson centrality independence (150 μb–1)
• Very low pp statistics available at 2.76 TeV≈ 20 times less Z than PbPb
• Compare to POWHEG (NLO generator) instead– Well tested at Tevatron (2
TeV) and LHC (7 TeV)– 5% uncertainty from
NNLO, pdfs, etc.
14
dNAA / TAA = dσpp x RAA
RAA = 0.95 ± 0.03 ± 0.13
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
(PRL 106 (2011) 212301)CMS-PAS-HIN-12-008
14
W boson centrality independence (7.2 μb–1)
15
dNAA / TAA = dσpp x RAA
W
W+
W–
PLB 715 (2012) 66
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 15
W boson centrality independence (7.2 μb–1)
16
dNAA / TAA = dσpp x RAA
PLB 715 (2012) 66
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 16
W boson centrality independence (7.2 μb–1)
17
dNAA / TAA = dσpp x RAA2010 PbPb ≈ pp data
RAA(W) = 1.04 ± 0.07 ± 0.12
RAA(W+) = 0.82 ± 0.07 ± 0.09
RAA(W–) = 1.46 ± 0.14 ± 0.16
Consistent with pure isospin
PLB 715 (2012) 66
More d quarks in Pb make more W+ than in pp
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 17
Photon centrality independence (7.2 μb–1)
18
PLB 710 (2012) 256( isolated photons, after large background subtraction )
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 18
Unmodified electro+weak bosons
• Within uncertainties, electro+weak bosons are not modified1. Confirm the validity of
Ncoll scaling
2. More precision may reveal nuclear PDF modifications
3. But let’s first use these calibrated probes…
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 19
JET QUENCHING
Photon+jet (150 μb–1)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 21
Pythia+Hydjet
Area normalized to unity
Photon-jet momentum balance
arXiv:1205.0206
Photon+jet (150 μb–1)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 22
PbPb Pythia+Hydjet
0-10%
Area normalized to unity
Photon-jet momentum balance
arXiv:1205.0206
Photon+jet (150 μb–1)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 23
PbPb Pythia+Hydjet
0-10%
Area normalized to unity
Photon-jet momentum balance
20% lose jet partner
PbPb
PbPb
Pythia+Hydjet
pp
pp
Pythia+Hydjet
Jet-photon pT balance 14% drop
arXiv:1205.0206
Modified jet RAA (150 μb–1)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 24
CMS-PAS-HIN-12-004
Jet RAA
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 25
CMS-PAS-HIN-12-004 Cone size R = 0.3, but does not vary a lot for R = 0.2 or 0.4
Where does the energy go?
• To large angle & low pT
– Qualitative idea in the first 2010 (di)jet paper
• Quantitatively– Low pT, fragmentation
functions– Large angle, jet shape
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 26
100 GeV inclusive jetAnti-kT R=0.3 jet in PYTHIA
95% of jet energy in r < 0.2
PRC 84 (2011) 024906 G. Roland at QM’12
95% of jet energy in pT > 4 GeV particles
Jet fragmentation
• At first sight (QM’11, run 1, pT(track) > 4 GeV & pT(jet) > 100 GeV), surviving jets are not modified
• Looking closer (QM’12, run 2, pT(track) > 1 GeV & more energetic jets), modifications appear
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 27
ξ = ln(1/z) & z=pT(track)/pT(jet)where pT(jet) is quenched already
( < pT(parton) )
arXiv:1205.5872 accepted by JHEPvs CMS-PAS-HIN-12-013
ξ
Jet fragmentation and shapes
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 28
No change at small r, high pT
Narrowing/depletion at intermediate pT
Broadening/excess at large r, low pT
CMS-PAS-HIN-12-013
PbPb/ppdistributions
Back to RAA of jets (and b-jet)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 29
Note: first b-jet identificationin heavy-ion collisions
CMS-PAS-HIN-12-003
Back to RAA of jets, and hadrons
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 30
Charged particles with pT = 50-100 GeV/c
z = pT(track)/pT(jet) = 0.4-0.6 x < 1
Looking at the same parton pT range
PbPb fragmentation function = pp for ξ <1
Jets: CMS-PAS-HIN-12-004Hadrons: EPJC 72 (2012) 1945
G. Roland at QM’12
QUARKONIA
Quarkonium suppression
• Old predicted signature of the QGP– Quarkonia should melt one after the
other, depending on their binding energy– Recent example of melting temperatures
• @ SPS / RHIC, no / marginal access to the (yet unresolved) Upsilon family
• @ SPS, J/ψ and ψ’ studied in detail• @ RHIC, J/ψ brought up surprises…
– Though they are suppressed, the balance of various effects is not clear…
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 32
Matsui & Satz,PLB168 (1986) 415
Mocsy, EPJC61 (2009) 705BNL workshop in June
ϒ(1S)
χb
J/ψ, ϒ(2S)
χc, χ’b, ψ', ϒ(3S)
Prompt J/ψ suppression
• CMS J/ψ pT > 6.5 GeV/c– Material and B-field– Feed down from B J/ψ is
subtracted• More suppression than at RHIC
– CMS < STAR (pT > 5 GeV/c)
• More suppression than at low pT
– CMS < ALICE (all pT)
• Popular explanation: regeneration from uncorrelated and – Stronger at low pT
> 100 pairs in a central event
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 33
centrality
JHEP05 (2012) 176 & CMS-HIN-PAS-12-014
Prompt J/ψ suppression
• CMS J/ψ pT > 6.5 GeV/c– Material and B-field– Feed down from B J/ψ is
subtracted• More suppression than at
RHIC (at high pT)– CMS < STAR (pT > 5 GeV/c)
• Less suppression at low pT
– CMS < ALICE (inclusive, all pT)
• Popular explanation: regeneration from uncorrelated and – Stronger at low pT
> 100 pairs in a central event02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 34
centrality
JHEP05 (2012) 176 & CMS-HIN-PAS-12-014
First look at ψ(2S)
• Relatively less ψ(2S) than J/ψ, as expected@ midrapidity |y|< 1.6, thus high pT > 6.5 GeV
• (a hint of an opposite behaviour at lower pT, but less than 2σ)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 35
CMS-PAS-HIN-12-007
Upsilon (1S), (2S) and (3S)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 36
(PRL107 (2011) 052302)arXiv:1208.2826
Upsilons (1S), (2S) and (3S)
Upsilon(1S) and (2S) at LHC
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 37
Sequential disappearance of the 3 states
For minimum biasRAA (Y(1S)) = 0.56 ± 0.08 ± 0.07RAA (Y(2S)) = 0.12 ± 0.04 ± 0.02RAA (Y(3S)) < 0.10 @ 95% CL
(Remember a large part of Y(2S)comes from higher state decays,
in particular the χb)
(PRL107 (2011) 052302)arXiv:1208.2826
Five states to bind them all
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 38
Mironov at QM’12
Forgetting low pT J/ψ(regeneration)for a while…
RAA(MB) vs binding energylooks ordered…
TBD with more data vs centrality and unfolding
cold effects (pA) & feeddowncould start acting as a
thermometer?
To conclude
• Three unmodified control probes (photon, Z and W)• Detailed studies of jet quenching • Five quarkonium suppressions• And more!
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 39
1/ Being interpreted in terms of Quark-GluonPlasma properties…2/ Once we have checked what happens in pPb (2013…)
Back up
W boson production
Less W+ and more W– in PbPb than in pp (isospin effect)
– Cancels for W+ + W–
• W boosted towards the valence quark (higher rapidity)
• Spin conservation μ+ (μ–) boosted back to (away from) midrapidity
Different muon rapidity distributions (not heavy-ion specific) between W+ and W–
41
p p
u d
W+
μ+
ν
@ LO : &
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
Muon charge asymmetry• Less up quarks make less W+ in PbPb than in pp
• Isospin effect bringing down asymmetry by 0.2 to 0.4• (EPS09 modifications are 0.03 at most)
42
N+ – N– N+ + N–
PLB 715 (2012) 66
|ημ|
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
How to find photons?• Trigger on ECAL clusters
– Uncorrected ET > 15 GeV, fully efficient for ET > 20 GeV
• Subtract underlying event– From same pseudorapidity
strip, event by event• Look for isolated cluster
– Remove photons from bremsstrahlung and jet fragmentation…
• Look at shower shape in the highly segmented ECAL – Further remove isolated π0, η
43
photon-like π,η 2γ
Δϕ
Δη
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
Photon spectrum (2010)
44
PLB 710 (2012) 256
Consistent with JETPHOXWith unmodified pdf (CT10)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
Unmodified photons
45
PLB 710 (2012) 256
• Normalised by pp!• Consistent with unity!• Uncertainties still larger than modifiedpdf uncertainties…
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split
Jet reconstruction performances
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 46
Resolution
Responce
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 47
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 48
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 49
Modified hadrons (150 μb–1)
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 50
EPJC 72 (2012) 1945
b-jet
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 51
J/ψ at RHIC (all pT)
• Two surprises:– At midrapidity, same
suppression at RHIC and at SPS, while density must be higher
– More suppression at forward rapidity at RHIC, while density must be lower
• Two popular answers:– Cold: shadowing / saturation
brings forward yields down– Hot: recombination of
uncorrelated cc brings midrapidity yield up
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 52
PHENIX, PRL98 (2007) 232301, also 1103.6269SPS from Scomparin @ QM06
J/ψ at RHIC (all pT)
• Two surprises:– At midrapidity, same
suppression at RHIC and at SPS, while density must be higher
– More suppression at forward rapidity at RHIC, while density must be lower
• Two popular answers:– Cold: shadowing / saturation
brings forward yields down– Hot: recombination of
uncorrelated cc brings midrapidity yield up
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 53
PHENIX, PRL98 (2007) 232301, also 1103.6269SPS from Scomparin @ QM06
First look at ψ(2S)
• More forward 1.6 < |y| < 2.4, down to pT = 3 GeV• Relatively more ψ(2S) than J/ψ ?
02/10/2012 raphael@in2p3.fr - Heavy ions in CMS - Split 54
CMS-PAS-HIN-12-007
(ψ’/ψ)PbPb / (ψ’/ψ)pp
• ψ(2S) more suppressed than J/ψ @ high pT
• ψ(2S) less suppressed than J/ψ @ low pT ? (<2σ)2012, May 29th Heavy Ions in CMS - raphael@in2p3.fr 55
HIN-12-007CMS-PAS-HIN-12-007