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Quarkonium results:lessons from LHC run-1
E. Scomparin (INFN-Torino)
Trento, March 16-20 2015
Introduction, pre-LHC summary LHC run-1 substantial progress on charmonium/bottomonium studies! Open points and prospects for run-2 Conclusions
A lively topic
2
Quarkonium suppression as a “QGP thermometer”
My own “thermometer” of the interest of the community in quarkonium studies
Number of citations of the seminal Matsui’s and Satz’s paper
09/11/09 1279
06/12/10 1344
22/11/11 1447
09/11/12 1644
17/11/14 2041
14/03/07 1176
Citations doubled in the last ~8 yearsStill a very “hot” topic!
Tc
~30 years of experiments
3
(peripheral) (central)
From the ‘80s…
…until today!
SPS (NA38-NA50-NA60)
RHIC (PHENIX-STAR)
LHC (ALICE-CMS)
C. Baglin et al. (NA38), Phys. Lett. B220(1989) 471
CMS Coll., PRL 109(2011) 222301
HI studies: reference processes
4
Choice of “suitable” reference process for the modification of the quarkonium yields proved to be crucial (and much debated!)
SPS energy Drell-Yan process Cancellation of syst. uncertainties No initial/final state effects in the explored kinematic region Small statistics
RHIC, LHC energy RAA
Limited cancellation of uncertainties Does not account for initial/final state effects not related to the medium Precise reference data can be collected
Ideal reference Normalization to open charm Most “natural” reference initial state effects cancel out Differential comparisons not straightforward
Charm energy loss shifts D-meson pT
J/ suppression removes yield Open charm data have non-negligible uncertainties (especially at low pT)
q
q
+
-
HI studies: role of CNM
5
Considered as a crucial step for the understanding of A-A results However
Description of pA data in terms of various CNM effects is difficult Extrapolation pA AA can be effect-dependent and/or model dependent
At SPS Use of effective quantity abs (break-up cross section) tuned on pA data and then directly extrapolated to A-A (via L-variable)
At RHIC Combination of shadowing (factorized out using nuclear PDFs parameterizations) and break-up Centrality dependence exhibits surprising (understood?) effects
At LHC Break-up cross section negligible (Coherent) energy loss effects become important First attempts (see later) at an extrapolation pA AA
5
p
c
cg
J/, c, ...
6
Low energy results: J/ from SPS & RHICSPS (NA38, NA50, NA60)
sNN = 17 GeV
First evidence of anomalous suppression (i.e. beyond CNM expectations) in Pb-Pb collisions
~30% suppression compatible with (2S) and c decays
RHIC (PHENIX, STAR)sNN = 39, 62.4, 200 GeV
suppression, with strong rapidity dependence, in Au-Au at s= 200 GeV
R.Arnaldi et al.(NA60) NPA830 (2009) 345c A. Adare et al. (PHENIX) PRC84(2011) 054912
7
Low energy results: J/ from SPS & RHICComparison of SPS and RHIC results
Good agreement between SPS and RHIC patterns if cold nuclear matter effects are taken into account
N.Brambilla et al. (QWG) EPJC71 (2011) 1534
Understanding cold nuclear matter effects and feed-downis essential for a quantitative assessment of charmonium physics
Compensation of suppression/recombination effects? Suppression of c and (2S) w/o recombination?
8
Low energy results: (2S) from SPS & RHIC
SPS (NA50) pA, AA @ sNN = 17 GeV RHIC (PHENIX)d-Au @sNN = 200 GeVNA50 Coll., Eur. Phys. J. C 49, 559 (2007)
(2S) is more suppressed than J/ already in pA collisions and the suppression increases in Pb-Pb
PHENIX Coll., PRL 111, 202301 (2013)
unexpected (2S) suppression (forms outside nucleus) stronger than the J/ one in central d-Au
Pb-Pb
p-A
S-U
9
Low energy results: from SPS & RHIC
SPS (NA50) pA, sNN=29 GeV
First measurement at SPS energies. Hint for no strong medium effects on (1S+2S+3S) in pA
RHIC (PHENIX, STAR)dAu, Au-Au sNN = 200 GeV
B. Alessandro (NA50 Coll), PLB 635(2006) 260
RAA compatible with suppression of excited states, with large uncertainties
A. Adare (PHENIX Coll.), 1404.2246L. Adamczyk (STAR Coll.) PLB 735 (2014) 127
Lessons from low-energy A-A…
10
Suppression effect on J/ beyond CNM undisputable at both SPS and RHIC Common interpretation: mainly related to screening/dissociation
in hot (deconfined) matter
Role of J/ regeneration tiny (if any) at SPS energy Quantitatively much debated at RHIC energy
Energy scan very interesting in principle (onset of suppression), but only top energy was explored at the SPS (new NA60+ experiment?) Results at s=39 and 62.4 GeV suffer from large uncertainties (absence of proper reference data)
(2S) largely suppressed in A-A compared to J/ at SPS energy Commonly seen as an effect of its weak binding
resonances out of SPS reach Intriguing results at RHIC, first recent attempt to separate 1S (STAR)
Suppression compatible with complete 2S+3S melting, 1S suppression only for central events
…and questions for LHC
1111
1) Evidence for charmonia (re)combination: now or never!
(3S) b(2P)(2S)
b(1P)
(1S)
2) A detailed study of bottomonium suppression
Do we see enhancement vs centrality ?Do we see J/ flow?Do we see softer pT distributions?
Do we see sequential suppression ?(as recombination does not play a role)
12
The main actors
CMS (high pT)
ALICE (low pT )
CMS Excellent mass resolution for muons(35 MeV for J/) Prompt vs non-prompt Cut low-pT charmonia
ALICE Access mid- and forward-
rapidity (e+e- and + respectively)
Good mass resolution for J/ (~70 MeV for muons, ~30 MeV for electrons)
Full pT acceptance in the whole y-range
Prompt vs non-prompt at y=0
J/ ATLAS CMS
LHCb
ALICEALICE
13
The low pT region: ALICE
B. Abelev et al., ALICEPhys. Lett. B 734 (2014) 314
Centrality dependence of the nuclear modification factor studied at both central and forward rapidities
Inclusive J/ RAA
Small effect of non-prompt contribution
on the inclusive RAA
At forward y, RAA flattens for Npart 100 Central and forward rapidity suppressions compatible within uncertainties
Global syst: 13% e+e- 15% +-
Forward y:No B suppressionRAA
prompt~0.94RAAincl
Full B suppressionRAA
prompt~1.07RAAincl
Central y:No B suppressionRAA
prompt~0.91RAAincl
Full B suppressionRAA
prompt~1.17RAAincl
14
Low pT: comparison ALICE vs PHENIX
Comparison with PHENIX
Stronger centrality dependence at lower energy Systematically larger RAA values for central events in ALICE
Behaviour qualitatively expected in a (re)generation scenario Look at the pT dependence of the suppression
15
Comparison to theory calculations:
Models including a large fraction (> 50% in central collisions) of J/ produced from (re)combination or models with all J/ produced at hadronization provide a reasonable description of ALICE results
Still rather large theory uncertainties: models will benefit from a precise measurement of cc and from cold nuclear matter evaluation
J/ RAA vs centrality: theory comparison
16
A (re)generation “signature”:the pT dependence of RAA
At low pT, for central events, the suppression is up to 4 times larger at PHENIX, compared to ALICE Strong indication for (re)generation
Global syst: 8% ALICE10% PHENIX
17
Moving to higher pT:CMS vs ALICE
Complementary y-coverage: 2.5<y<4 (ALICE) vs 1) 1.6<|y|<2.4 (CMS, left)2) |y|<2.4 (CMS, right)
Qualitative agreement in the common pT range
B. Abelev et al., ALICEPhys. Lett. B 734 (2014) 314
18
CMS results: prompt J/ at high pT
CMS PAS HIN-2012-014CMS-PAS HIN-12-2014
Striking difference with respect to ALICE No saturation of the suppression vs centrality High-pT RHIC results show weaker suppression
No significant pT dependence from 6.5 GeV/c onwards (Re)generation processes expected to be negligible
19
CMS results: prompt J/ at high pT
Striking difference with respect to ALICE No saturation of the suppression vs centrality High-pT RHIC results show weaker suppression
No significant pT dependence from 6.5 GeV/c onwards (Re)generation processes expected to be negligible
CMS PAS HIN-2012-014CMS-PAS HIN-12-2014
20
The contribution of J/ from (re)combination should lead to a significant elliptic flow signal at LHC energy
J/ flow
CMS measures a significant v2 in a region where (re)combination should be negligible due to path-length dependence of J/ suppression
STAR found v2 consistent with 0
ALICE measures v2 (with a significance up to 3 for chosen kinematic/centrality selections) in agreement with transport models including (re)combination
b diffusion
ALICE Coll., Phys. Rev. Lett. 111 (2013) 162301
Moving to p-Pb J/ results: RpPb vs y
21
ALICE and LHCb results in good agreement Strong suppression at forward and mid-y: no suppression at backward y Data are consistent with models including shadowing and/or energy loss Color Glass Condensates (CGC) inspired models underestimate data Dissociation cross section abs<2 mb cannot be excluded
LHCb Coll., JHEP 02 (2014) 072
ALICE Coll., JHEP 02 (2014) 073
RpPb vs pT
22 22
The pT dependence of J/ RpPb has been studied in the three y ranges
backward-y mid-y forward-y
backward-y: negligible pT dependence, RpA compatible with unity mid-y: small pT dependence, RpA compatible with unity for pT>3GeV/c forward-y: strong RpA increase with pT
Comparison with theory: Data consistent with pure shadowing calculations and with coherent
energy loss models (overestimating J/ suppression at low pT, forward-y) CGC calculation overestimate suppression at forward-y
Event activity dependence: QpPb
23 23
/
/
JpppA
JpAJ
pAT
YQ
At forward-y, strong J/ QpA decrease from low to high event activity At backward-y, QpA consistent with unity, event activity dependence
not very significant
CNM effects: from p-Pb to Pb-Pb
24
x-values in Pb-Pb sNN=2.76 TeV, 2.5<ycms<4
x-values in p-Pb sNN=5.02 TeV, 2.03 < ycms < 3.53 210-5 < x < 810-5
x-values in p-Pb sNN=5.02 TeV, -4.46 < ycms < -2.96 110-2 < x < 510-2
Partial compensation between sNN shift and y-shift
If CNM effects are dominated by shadowing RPbPb
CNM = RpPb RPbp = 0.75 ± 0.10 ± 0.12 RPbPb
meas = 0.57 ± 0.01 ± 0.09“compatible” within 1-
210-5 < x < 910-5
110-2 < x < 610-2
Same kind of “agreement” in the energy loss approach
…which does not exclude hotmatter effects which partlycompensate each other
F. Arleo and S. Peigne, arXiv:1407.5054
25
pT-dependence
pA
AAPb-Pb
p-Pb
Pb-Pb
p-Pb
Perform the extrapolation as a function of pT
No more “agreement” between Pb-Pb and CNM extrapolations High-pT suppression is not related to CNM effects At low pT CNM suppression is of the same size of the effects observed in Pb-Pb: recombination ?
Comparing charmonia and open charm: p-Pb
26
ALICE p-Pb results, mid-rapidity, pT integrated
RpPbJ/ = 0.73 0.08 0.15RpPb
D = 0.85 0.05 0.11(weighted average of pT differential points using FONLL cross section (no FONLL unc.)and RpPb(0-1)=RpPb(1-2) )
Assuming RpPb(0-1) = 0.4
RpPbD = 0.82 0.05 0.11
Within uncertainties (and with reasonableextrapolations to pT=0), CNM effects onintegrated J/ and D-mesons production
have the same size
ALICE Coll., PRL 113 (2014) 232301
Comparing charmonia and open charm: p-Pb
ALICE p-Pb results, mid-rapidity, pT differential
Bin-to-bin comparison less straightforward
g
g
D
D
g
g
J/At fixed pT, gluon kinematicscan be (very) different for
single D and J/
ALICE Coll., PRL 113 (2014) 232301
Comparing charmonia and open charm: p-Pb
28
Single muon results available for pT > 2 GeV/c (More) difficult to extract an integrated RpPb
Bin-to-bin comparison not straightforward
p-going direction
Comparing charmonia and open charm: p-Pb
29
Single muon results available for pT > 2 GeV/c (More) difficult to extract an integrated RpPb
Bin-to-bin comparison not straightforward
Pb-going direction
Comparing charmonia and open charm: Pb-Pb
30
RPbPbD = 0.51 0.08 0.09
(weighted average of pT differential points using FONLL cross section (no FONLL unc.)and RpPb(0-1)=RpPb(1-2) )
Assuming RpPb(0-1) = 1
RPbPbD = 0.63 0.08 0.10
RPbPbJ/ = 0.73 ± 0.09 ± 0.06 ± 0.09
0-10%
Good compatibility (especially assuming RpPb(0-1) = 1) between D and J/ Suppression and regeneration balance Warning: DS, c (not included) may be enhanced in Pb-Pb
ALICE, PLB 734 (2014) 314
Comparing charmonia and open charm: Pb-Pb
31
0-10%
RPbPbJ/ = 0.56 ± 0.02 ± 0.02 ± 0.08
Forward rapidity: results for muons with pT >4 GeV/c Extrapolation to all pT problematic
ALICE, PLB 734 (2014) 314
J/ in Pb-Pb: run-1 summary
32
Evidence for smaller suppression compared to RHIC Occurrence of recombination is at present the only explanation
pT-dependence of RPbPb also compatible with recombination
Although qualitative interpretation looks unambiguous, the quantitative assessment of the effects at play needs refinement Values for dcc/dy evolved. At present, in the forw.-y ALICE domain:
SHM 0.15 – 0.25 mb (y=4 and y=2.5) – no shadowing Zhao and Rapp 0.5 mb – “empirical” shad. vs no shad. Zhuang et al. 0.4 – 0.5 mb – EKS98 shadowing Ferreiro et al. 0.4 – 0.6 mb + Glauber-Gribov shad. ~ nDSG(min.) > EKS98
LHC run-2 (almost) a factor 2 gain in s would it be possible to extract dcc/dy which gives the best fit to run-1 results, extrapolate to run-2 energy (FONLL?) and give predictions ?
Suppression persists up to the largest investigated pT
Higher pT reach in run-2 increase of RPbPb ? Predictions ?
Interesting indication for azimuthal anisotropies. Run-2 needs Experiment (much) larger statistics Theory solid predictions
J/ in p-Pb: run-1 summary
33
p-Pb data: characterization of CNM effects in terms of shadowing plus coherent energy loss (no break-up) looks satisfactory
Effects are strong, RpPb~ 0.6 at low pT and central to forward rapidity Strong influence of CNM effects in Pb-Pb in the corresponding
kinematic region
Uncertainties on shadowing calculations are large, could one use the LHC data to better constrain shadowing ?
The simple estimate RPbPbCNM=RpPbRPbp (inspired to a shadowing
scenario) leads, once this effect is factorized out, to an even steeper pT-dependence of RPbPb
Also for p-Pb, run-2 energy predictions (s~8 TeV), with parameters TUNED on run-1 results, would allow a crucial test of our understanding of the involved mechanisms
34
The (2S) yield is compared to the J/ one in Pb-Pb and in pp
Improved agreement between ALICE and CMS data (wrt preliminary)
(2S)/J/ in Pb-Pb
CMS (central events)pT>3 GeV/c & 1.6<|y|<2.4 (2S) less suppressed than J/pT>6.5 GeV/c & |y|<1.6 (2S) more suppressed than J/
35
(2S) RpPb vs ycms
Spp
Jpp
JpA
SpAJ
pAS
pA RR2
22
(2S) suppression is
stronger than the J/ one and reaches a factor ~2 wrt pp
Same initial state CNM effects (shadowing and coherent energy loss) expected for both J/ and (2S)
Theoretical predictions in disagreement with (2S) result
Other mechanisms needed to explain (2S) behaviour?
Final state effects related to the (hadronic) medium created in the p-Pb collisions?N.B.: crossing times smaller than formation time, no nuclear break-up (Forward-y: c~10-4 fm/c, backward-y: c~710-2 fm/c)
ALICE Coll., JHEP12(2014)073
36
(2S) QpPb vs event activity The (2S) QpA is evaluated as a function of the event activity
Rather similar (2S) suppression, increasing with Ncoll, for both ALICE and PHENIX results
Spp
Jpp
JpA
SpAJ
pAS
pA QQ2
22
with
QpA instead of RpA due to potential bias from the centrality estimator, which are not related to nuclear effects
Jpp
multpA
JpAJ
pA T
YQ
J/ and (2S) QpPb vs event activity J/ and (2S) QpA are compared vs event activity
forward-y: J/ and (2S) show a similar decreasing pattern vs event activity
backward-y: the J/ and (2S) behaviour is different, with the (2S) significantly more suppressed for largest event activity classes
Another hint for (2S) suppression in the (hadronic) medium?37
(2S): run-1 summary
38
In Pb-Pb collisions the CMS results show an enhancement of the (2S) yield, compared to J/, at intermediate pT, and a suppression at low pT
A convincing explanation of the Pb-Pb results is still lacking
The ALICE preliminary results are marginally compatible with this observation (large uncertainties, low S/B)
In p-Pb collisions a significant suppression, compared to J/, is observed
The effect becomes very strong at backward rapidity, and implies sizeable final-state effects on the (2S)
Formation-time vs crossing-time arguments imply that the suppression may be related to the (hadronic?) medium created in p-Pb collision First theory calculations support this interpretation
Run-2 is expected to yield large luminosity, mandatory for a meaningful study of (2S) in Pb-Pb
39
suppression in Pb-Pb collisions
LHC is the machine for studying bottomonium in AA collisions
Main features of bottomonium production wrt charmonia:
• no B hadron feed-down• gluon shadowing effect
are smaller• (re)combination expected
to be smaller• theoretical predictions
more robust due to the higher mass of b quark
with a drawback…smaller production cross-section
Clear suppression of states in PbPb with respect to pp collisions
CMS Coll., PRL 109, 222301 (2012)
pp
PbPb
40
suppression in Pb-Pb collisions
Strong suppression of (2S)
(1S) suppression compatible with suppression of excited states (50% feed-down)
Sequential suppression of the three states according to their binding energy:
Suppression at LHC is stronger than at RHIC
RAA((1S)) = 0.56 ± 0.08 (stat) ± 0.07 (syst)
RAA((2S)) = 0.12 ± 0.04 (stat) ± 0.02 (syst)
RAA((3S)) <0.1 (at 95% C.L)
CMS Coll., PRL 109, 222301 (2012)
41
Comparison of ALICE vs CMS results
Stronger suppression at forward rapidity than at mid-rapidity, in particular for central collisions
Comparison of ALICE (forward-y) and CMS (mid-y) results
CMS Coll., PRL 109 (2012) 222301 ALICE Coll., PLB 738 (2014) 361
ALICE
CMS
ALICE
CMS
42
Comparison with theory
• Evolving QGP described via a dynamical model including suppression of bottomonium states, but not CNM nor recombination
• 2 different initial temperature y profiles: boost invariant or Gaussian (3 tested shear viscosity)
MO
DEL
The model underestimates the measured (1S) suppression at forward-y, while it is in fair agreement with mid-y data
43
Comparison with theory
• Transport model accounting for both regeneration and suppression
• CNM effects included via an effective absorption cross section (0-2 mb)
MO
DEL
The measured RAA vs centrality is slightly overestimated by the model at forward-y, while it reproduces CMS resultsConstant RAA behavior vs y is not supported by the data
(1S) measured at forward-y by both ALICE and LHCb
Compatible RpA results within uncertainties (but LHCb systematically higher)
Hint for stronger suppression at forward-y (similarly to J/)
Theoretical calculations based on initial state effects seem not to describe simultaneously forward and backward y
44ALICE Coll., PLB 740 (2015) 105-117LHCb Coll., JHEP 07(2014)094
(1S) Production in p-Pb
45
CMS Coll., JHEP 04 (2014) 103 CMS Coll., PRL 109 (2012)
(2S)/(1S) (ALICE)2.03<y<3.53: 0.27±0.08±0.04-4.46<y<-2.96: 0.26±0.09±0.04
Compatible with pp results 0.26±0.08 (ALICE, pp@7TeV)
Initial state effects similar for the three states
p-Pb vs pp @mid-y: final states effects in p-Pb affecting the excited states
p-Pb vs PbPb @mid-y : even stronger suppression of excited states in PbPb
ALICE (and LHCb) observes: CMS analyses the double ratio [(2S)/(1S)]/[(nS)/(1S)]pp
and finds
p-Pb
Pb-Pb
0.83±0.05±0.05
(nS)/(1S) Production in p-Pb
46
(nS)/(1S) vs event activity
Strong decrease with increasing charged particle multiplicity both in pp and p-Pb
production affects multiplicity?
or multiplicity affects the ?
activity around the breaks the state
(1S) produced with more particles than excited states
Weaker dependence when the activity estimator is in a different kinematic region with respect to the
CMS Coll., JHEP 04 (2014) 103
: run-1 summary
47
First detailed study of bottomonia in HI collisions
Suppression of 1S, 2S, 3S states clearly observed More weakly bound states are more suppressed Evidence for sequential suppression
Suppression of 1S state at mid-rapidity consistent with feed-down effects
Rapidity dependence of 1S suppression exhibits surprising features Still not satisfactorily reproduced by models
p-Pb results, still significant uncertainties at forward-y, no sharp conclusions
At central rapidity, evidence for final-state effects on 2S and 3S states
CMS RpPb results still to be delivered
Intriguing features on yields vs event activity
Conclusions (1)
48
LHC run-1 has led to a very significant advance of our understanding of charmonia/bottomonia in hot matter
Charmonium highlight evidence for a new mechanism which enhances the J/ yield, in particular at low pT, with respect to low-energy experiments
In addition Indications for J/ azimuthal anisotropy (non-zero v2) Significant final state effects on (2S) in p-Pb, likely related to the
(hadronic) medium created in the collision
Bottomonium highlight evidence for a stronger suppression of 2S and 3S states compared to 1S. Effect not related to CNM and compatible with sequential suppression of “bottomonium” states
In addition 1S is also suppressed (~50%). Feed-down effect only? y-dependence of 1S suppression to be understood
49
Conclusions (2) Prospects for run-2
Collect a ~1 order of magnitude larger integrated luminosity
High-statistics J/ sample Comparison with run-1 AND with theoretical predictions crucial
to confirm/quantify our understanding in terms of regeneration
Significant (2S) sample Crucial: run-1 results “exploratory” (and interpretation not clear)
High-statistics (1S) sample A significant increase in 1S suppression with respect to run-1 might imply that a high-T QGP is formed (“threshold” scenario)
Differential (2S) and (3S) results from run-1 are limited by statistics Centrality and pT-dependent studies important to assess details of
sequential suppression
Backup
50
51
52
53
RHIC: suppression vs recombination Did we reach a consensus on the role played by recombination at RHIC ?
J/ pT distribution should be softer (<pT
2>) wrt pp
J/ elliptic flow J/ should inherit the heavy quark flow
One should in principleobserve
Evidence not compelling Could weaker suppression at y=0 be due to other effects (CNM, for example)?
CMS, focus on high pT
Muons need to overcome the magnetic field and energy loss in the absorber
Minimum total momentum p~3-5 GeV/c to reach the muon stations
Limits J/ acceptance Midrapidity: pT>6.5 GeV/c Forward rapidity: pT>3 GeV/c
..but not the one (pT > 0 everywhere)
56
Non-zero v2 for J/ at the LHCCMS HIN-2012-001
E.Abbas et al. (ALICE),PRL111(2013) 162301
The contribution of J/ from (re)combination should lead
to a significant elliptic flow signal at LHC energy
A significant v2 signal is observed by BOTH ALICE and CMS The signal remains visible even in the region where the contribution of (re)generation should be negligible Due to path length dependence of energy loss ? Expected for J/ ? In contrast to these observations STAR measures v2=0
Finally, the
57
LHC is really the machine for studying bottomonium in AA collisions (and CMS the best suited experiment to do that!)
First accurate determination of suppression
58
Suppression increases with centrality
First determination of (2S) RAA: already suppressed in peripheral collisions
(1S) (see also ALICE) compatible with only feed-down suppression ?
Probably yes, also taking into account the normalization uncertainty
Compatible with STAR (1S+2S+3S)(but large uncorrelated errors): expected ?Is (1S) dissoc. threshold still beyond LHC reach ? Full energy
(1S) vs y and pT from CMS+ALICE
59
Start to investigate the kinematic dependence of the suppression Suppression concentrated at low pT (opposite than for J/, no recombination here!) Suppression extends to large rapidity (puzzling y-dependence?)
Do not forget CNM…
60
Also in the sector, the influence of CNM is not negligible
With respect to 1S, the 2S and 3S states are more suppressed than in pp… but less than in Pb-Pb confirm Pb-Pb suppression as hot matter effect As a function of event activity, loosely related to centrality in pPb (and surely not in pp!) “smooth” behaviour: to be understood!
RHIC: energy scan
61
System size and energy dependence of RAA
No appreciable dependence on both energy and system size
Not trivial! Requires counterbalancing of suppression+regeneration effects over
a large s-region (note however large global systematics) Warning: CNM effects (shadowing) expected to vary with s
Quarkonia – where are we ?
62
Two main mechanisms at play1) Suppression in a deconfined medium2) Re-generation (for charmonium only!) at high s
can qualitatively explain the main features of the results
ALICE is fully exploiting the physics potential in the charmonium sector (optimal coverage at low pT and reaching 8-10 GeV/c)
RAA weak centrality dependence at all y, larger than at RHIC Less suppression at low pT with respect to high pT
CNM effects non-negligible but cannot explain Pb-Pb observations
CMS is fully exploiting the physics potential in the bottomonium sector (excellent resolution, all pT coverage)
Clear ordering of the suppression of the three states with their binding energy as expected from sequential melting (1S) suppression consistent with excited state suppression (50% feed-down)
Conclusions
63
LHC: first round of observations EXTREMELY fruitful
Many (most) of the heavy-quark/quarkonia related observables were investigated, no showstoppers, first physics extracted
Many (most) of the heavy-quark/quarkonia related observables would benefit from more data to sharpen the conclusions full energy run, 2015-2017 upgrades, 2018 onwards
RHIC: still a main actor, with upgraded detectors
Lower energies: SPS, FAIR
Serious experimental challenge High-B region of the phase diagram unexplored for what concerns heavy quark/quarkonia below 158 GeV/c
From RpAincl to RpA
prompt
64
Assume RpAnon-prompt = 1
The value of RpAprompt can differ significantly from RpA
prompt at large fb
Is the difference significant for ALICE?
65
Exercise
1) Assume RpPbnon-prompt=1
2) Plot RpPbprompt vs fb for the values
of RpPbinclusive measured by ALICE
3) Plot the ALICE point at the fB
value corresponding to the pT
where the measurement is performed
Result
For ALL the pT range accessibleto ALICE, the difference betweenRpPb
inclusive and the calculatedRpPb
prompt is smaller than theuncertainties
PHENIX – new systems/energies
66
Old system (Au-Au) at new energy: still a balancing of suppression and regeneration ? Theory seems to say so….
New system (Cu-Au) at old energy: Cu-going finally different! (probably not a CNM effect) A challenge to theory SPS went the other way round (from S-U to Pb-Pb…)
PHENIX – CNM
67
First study of a charmonium excited state at collider energy
Seems contradicting our previous knowledge
pT dependence of RdAu
Increase vs pT at central/forward y Reminds SPS observation
But different behaviour at backward rapidity Not easy to reproduce in models!
Overall picture still not clear !
STAR -
68
Bottomonium: the “clean” probe 3 states with very different binding energies No complications from recombination
But not that easyat RHIC!
…and this has been split into3 centrality bins…. Compatible with 3S melting
and 2S partial melting
Hints from theory
69
Theory is on the data ! Fair agreement, but…. … one model has no CNM, no regeneration …the other one has both CNM and regeneration (which would be responsible for all (2S) in central events)
Still too early to claim a satisfactory understanding ?
70
(2S) RpPb vs ycms
Can the stronger suppression of the weakly bound (2S) be due to break-up of the fully formed resonance in CNM?
possible if formation time (f ~0.05-0.15fm/c) < crossing time (c)
forward-y: c~10-4 fm/cbackward-y: c~710-2 fm/c
break-up effects excluded at forward-y
at backward-y, since f ~c , break-up in CNM can hardly explain the very strong difference between J/ and (2S) suppressions
Final state effects related to the (hadronic) medium created in the p-Pb collisions?
The (2S) suppression with respect to binary scaled pp yield can be quantified with the nuclear modification factor
zc
L
D. McGlinchey, A. Frawley and R.Vogt, PRC 87,054910 (2013)
arXiv:1405.3796
Charmonia – data samples
71
ALICE Lint (2011) = ~70 b-1 (2.5<y<4), ~28 b-1 (|y|<0.9) Trigger: MB + 2 tracks in the muon trigger chambers (pT> 1 GeV/c)
Background subtraction via like-sign or mixed-event techniques
B. Abelev et al., ALICEarXiv:1311.0214.
Charmonia – data samples
72
CMS PAS HIN-2012-014
CMS Lint (2011) = ~150 b-1 (|y|<2.4) Trigger: dimuon events at L1 (no constraints on muon momentum)
Use pseudo-proper decay lengthto estimate the b-hadron decay length
N.B.: discuss only prompt production in this talk