Quarkonium production in heavyion collisions fixed target RHIC

Quarkonium production in heavy-ion collisions: fixed target, RHIC and LHC Roberta Arnaldi INFN Torino (Italy) Joint meeting IPNO-LAL LUA 9 -AFTER Orsay, 18 -20 Novembre 2013 1

History of heavy-ion quarkonium studies Quarkonium suppression is, since 25 years, one of the most striking signatures for QGP formation in AA collisions LHC p. A s Ge. V/c 5020 LHC AA 2760 RHIC 200 SPS 17 1986 1990 ~2000 2013 Year 2

From suppression…to (re)combination Differences in the binding energies of the quarkonium states lead to a sequential melting of the states with increasing temperature (Digal, Petrecki, Satz PRD 64(2001) 0940150) thermometer of the initial QGP temperature (2 S) J/ c Tc ϒ(1 S) T~T T~3 T T<T T>>T c cc Increasing the energy of the collision the cc pair multiplicity increases In most central AA collisions SPS 20 Ge. V RHIC 200 Ge. V LHC 2. 76 Te. V Nccbar/event ~0. 2 ~10 ~60 An enhancement via (re)combination of cc pairs producing quarkonia can take place at hadronization or during QGP stage P. Braun-Muzinger and J. Stachel, Phys. Lett. B 490(2000) 196, R. Thews et al, Phys. Re. V. C 63: 054905(2001) 3

How can we measure medium effects? Nuclear modification factor RAA: compare quarkonium yield in AA with the pp one, scaled by a geometrical factor (from Glauber model) If yield scales with the number of binary collisions RAA = 1 If there are medium effects RAA 1 Cold Nuclear Matter effects (CNM): • • • Nuclear parton shadowing Parton energy loss cc in medium dissociation Hot Medium effects: • • quarkonium suppression enhancement due to recombination knowledge of CNM effects fundamental to disentangle genuine QGP induced suppression in AA need infos on quarkonium production in p. A collisions! 4

From “low energy” experiments… Charmonium production deeply investigated at SPS (NA 50, NA 60) s. NN = 17 Ge. V RHIC (PHENIX, STAR) s. NN =39, 62. 4, 200 Ge. V Eur. Phys. J. C 71: 1534, 2011 Observation of J/ suppression Puzzles from SPS and RHIC • • RHIC: stronger suppression at forward rapidities SPS vs. RHIC: similar RAA pattern versus centrality Hint for (re)combination at RHIC? No final theoretical explanation Decisive inputs expected from LHC results, having access to: • higher energy • • larger cc multiplicity other quarkonium states (bottomonium) 5

… to LHC data! Currently available AA and p. A results: ALICE J/ , (2 S), + - 2. 5<y<4 J/ e+e|y|<0. 9 p. T coverage down to p. T~0 ATLAS J/ + - CMS |y|<2. 4 p. T J/ >6. 5 Ge. V/c J/ , (2 S) + - |y|<2. 4 p. T >6. 5 Ge. V/c + - p. T >0 |y|<2. 4 (J/ p. T coverage depends on y) LHCb J/ + - 2<y<4. 5 p. T coverage down to p. T~0 (no heavy ion physics program) Complementary quarkonium results from LHC experiments 6

ALICE: low p. T J/ ALICE 2. 5<y. J/ <4 PHENIX 1. 2<|y. J/ |<2. 2 ALICE |y. J/ |<0. 9 PHENIX |y. J/ |<0. 35 ALICE Coll. ar. Xiv: 1311. 0214 Clear J/ suppression with almost no centrality dependence above Npart~100 Less J/ suppression at mid-rapidity wrt forward y for central events Comparison with PHENIX: ALICE results show weaker centrality dependence and smaller suppression for central events Is this the expected signature for (re)combination ? 7

ALICE RAA vs p. T J/ production via (re)combination should be more important p. T region accessible by ALICE at low transverse momentum Different suppression for low and high p. T J/ primordial Smaller RAA for high p. T J/ recombination Models: ~50% of low-p. T J/ are produced via (re)combination, 8 while at high p. T the contribution is negligible

CMS: high p. T J/ The high p. T region can be investigated by CMS! Good agreement with ALICE (at high p. T) in spite of the different rapidity range High p. T: stronger J/ suppression at LHC wrt to RHIC (re-combination should not play a role) 9

J/ flow The contribution of J/ from (re)combination should lead to a significant elliptic flow signal at LHC energy D. Moon, HP 2013 ALICE PRL 111, 162301 (2013) STAR Hint for J/ flow in heavy-ion collisions (LHC), contrary to v 2~0 observed at RHIC! ALICE: qualitative agreement with transport models including regeneration CMS: path-length dependence? ar. Xiv: 1212. 3304 10

(2 S) in Pb-Pb Study of other charmonium states can help constraining theoretical models (2 S) much less bound than J/ (2 S) studied by both CMS and ALICE (different kinematics) comparing the (2 S) yield to the J/ one in Pb-Pb and in pp At SPS, (2 S) is more suppressed than J/ and the suppression increases with centrality ALICE excludes a large enhancement Difference trend in ALICE and CMS: large statistics and systematic errors prevent a firm conclusion on the (2 S) enhancement or suppression versus centrality Nucl. Phys. A 19 (2013), pp. 595 -598 CMS PAS HIN-12 -007 11

The family LHC is the machine for studying bottomonium in AA collisions Main features of bottomonium production: • no B hadron feed-down • gluon shadowing effect are smaller • (re)combination is less important Clear suppression of (n. S) in Pb. Pb wrt pp PRL 109, 222301 (2012) 12

(n. S) RAA (n. S) suppression increases with centrality Clear (2 S) suppression even in peripheral collisions Sequential suppression of states? (1 S) suppression might be compatible with excited state suppression (~50% feed-down)? Compatible with STAR (1 S+2 S+3 S) (within large errors)(ar. Xiv: 1109. 3891) STAR RAA( (1 S+2 S+3 S)) = 0. 56 0. 21+0. 08 -0. 16 CMS RAA( (1 S+2 S+3 S)) ~0. 32 13

Comparison and J/ Similar RAA for low p. T inclusive J/ and (1 S) Sequential suppression observed for prompt J/ and (n. S) at high p. T interplay of the competing mechanisms for J/ and can be different and dependent on kinematics! 14

Where are we? 27 years after first suppression prediction, this is finally observed also in the sector with very good accuracy! Two main mechanisms at play: 1. Suppression in a deconfined medium 2. Re-combination (for charmonium) at high s can qualitatively explain the main features of the results RAA vs binding energy: looser bound states more suppressed than the tighter ones however hot and cold effects not yet disentangled…need p. A results! Nucl. Phys. A 904 -905 (2013) 194 c-201 c 15

What can we learn from p. A? New results from p-Pb data at s. NN = 5. 02 Te. V investigate initial/final state Cold Nuclear Matter effects on J/ : shadowing, energy loss, parton saturation effects, cc dissociation in the medium… provide a reference for AA collisions to disentangle genuine QGP effects 16

J/ nuclear modification factor Rp. A vs y Rp. A decreases towards forward y • • Theoretical predictions: reasonable agreement with shadowing EPS 09 NLO calculations (R. Vogt) or EPS 09 LO (E. Ferreiro et al) models including coherent parton energy loss contribution (F. Arleo et al) CGC description (H. Fujii et al) seems not to be favoured Very good agreement between ALICE vs LHCb results 17

J/ nuclear modification factor Rp. A vs p. T Forward rapidity Mid-rapidity Backward rapidity Forward y: Rp. A increases towards high p. T Mid-rapidity: Rp. A tends to increase vs p. T Backward y: Rp. A is rather flat and close to unity Theoretical predictions: reasonable agreement with • • shadowing EPS 09 NLO calculations (R. Vogt) models including coherent parton energy loss contribution (F. Arleo et al) CGC description (H. Fujii et al) seems not to be favoured 18

J/ Rp. Pb(p. T) vs RPb. Pb(p. T) Hypothesis: 2 1 kinematics for J/ production similar xg in spite of different s and y factorization of shadowing effects in p-Pb and Pb-Pb: Mid-rapidity Forward rapidity RPb. Pb enhanced when corrected by this shadowing evaluation 19

(1 S) measurements in p-A Hint for (1 S) Rp. Pb suppression at forward rapidity. Smaller effect at backward y Rp. Pb comparable for J/ and (1 S) EPS 09 shadowing models, CGC and coherent energy loss in fair agreement with (1 S) Rp. A result 20

(2 S) measurements in p-A Forward rapidity (2 S) is clearly suppressed in p-A wrt pp (at s=7 Te. V) (2 S)/J/ suppression is observed also in d-Au at s=200 Ge. V Shadowing and/or coherent energy loss don’t explain the stronger (2 S) suppression. Hot medium effects? 21

(2 S) & (3 S) measurements in p-A p-Pb vs Pb. Pb: additional final-state effects in Pb-Pb affecting the excited states more than the ground state p-Pb vs pp: excited states more suppressed than the ground states. Suppression increases with increase of charged particle multiplicity L. Benhabib, HP 2013 22

Conclusions Quarkonia study in heavy ion collisions is already a 25 years long story! LHC charmonium and bottomonium results are now complementing the large wealth of data from SPS, RHIC! the picture is quite complicated because of the interplay of many mechanisms! SPS CNM l entia sequ ing melt feed RHIC n io ress p p u s down n ratio e n e reg …but, hopefully, putting together all the pieces of the puzzle, the quarkonium production in AA collisions will be clarified! from / J B L LH HC C 23

Backup 24

Quarkonium production can proceed: • • directly in the interaction of the initial partons via the decay of heavier hadrons (feed-down) Displaced Prompt For J/ (at CDF/LHC energies) the contributing mechanisms are: Direct production Feed-down from higher charmonium states: ~ 8% from (2 S), ~25% from c Feed Down 30% Direct 60% B decay 10% B decay contribution is p. T dependent ~10% at p. T~1. 5 Ge. V/c Feed down and J/ from B, if not properly taken into account, may affect physics conclusions 25

ALICE and ATLAS J/ 26

(2 S)/ 27

CMS: theoretical comparison 28

ALICE: theoretical comparison 29

CMS: high p. T J/ The high p. T region can be investigated by CMS! Small hint of p. T dependent suppression even in the CMS p. T range Good agreement with ALICE (high p. T) in spite of the different rapidity range High p. T: stronger J/ suppression at LHC wrt to RHIC (re-combination should not play a role) 30

J/ RAA vs rapidity tog lier RAA y pattern depends on the J/ p. T At high p. T (CMS) almost no y dependence in the range |y|<2. 4 At low p. T (ALICE) RAA decreases by 40% from y=2. 5 to y=4 Suppression beyond the current shadowing estimates. Important to quantify cold nuclear matter effects in p-A collisions JHEP 05 (2012) 063, CMS PAS HIN-12 -014 PRL 109 (2012) 072301, ar. Xiv: 1311. 0214 31

(1 S) ALICE vs CMS tog lier e ALICE has measured the inclusive (1 S) RAA in the forward y region Centrality dependence of CMS and ALICE (1 S) RAA is comparable Suppression factor is rather constant in the y range covered by ALICE and CMS 32

Ratio forward to backward yields: RFB: free from uncertainties on the pp reference The RFB ratio shows a rather flat y dependence and a p. T dependence with stronger forward to backward suppression at low p. T Less stringent comparison to theory wrt Rp. A: however theoretical predictions including energy loss show strong nuclear effects at low p. T, in fair agreement with the data 33

(2 S) in Pb-Pb Study of other charmonium resonances can help constraining theoretical models (2 S) much less bound than J/ Results from the SPS showed a suppression larger than the J/ one (2 S) studied by both CMS and ALICE, different kinematics 34

(2 S) in Pb-Pb The (2 S) yield is compared to the J/ one in Pb-Pb and in pp At SPS, the (2 S)/J/ suppression increased with centrality Overall interpretation is challenging ALICE excludes a large enhancement Difference trend in ALICE and CMS: large statistics and systematic errors prevent a firm conclusion on the (2 S) enhancement or suppression versus centrality Nucl. Phys. A 19 (2013), pp. 595 -598 CMS PAS HIN-12 -007 35

Excited quarkonia states in p-A Excited states suppressed relative to ground states (2 S) & (3 S) L. Benhabib, HP 2013 (2 S) is clearly suppressed in p-A wrt pp (at s=7 Te. V) Similar suppression observed also in d-Au at s=200 Ge. V Shadowing and/or coherent energy loss don’t explain the stronger (2 S) suppression. Hot medium effects? p-Pb vs Pb-Pb: additional final state effects in Pb-Pb affecting the excited states more than the ground state p-Pb vs pp: suppression increases with increase of charged particle multiplicity 36