ALICE results in p Pb collisions at the LHC

ALICE results in p Pb collisions at the LHC Diego Stocco for the ALICE Collaboration (Ecole des Mines, CNRS-INP3, Université de Nantes) Nantes, France

Outline Motivation Goal p Pb collisions Experimental setup 3 A selection of results 4 Summary D. Stocco FFP4 - Marseille 5 8 Jul. 4 / 7

Exploring the QCD matter Strong interaction is: weak at high energies and short distance asymptotic freedom growing with distance between quarks and gluons confinement QCD predicts a phase transition into a deconfined state of quarks and gluons (Quark Gluon Plasma) at extreme conditions of temperature and/or baryon density QGP can be experimentally formed in ultra-relativistic heavy-ion collisions D. Stocco FFP4 - Marseille 5 8 Jul. 4 / 7

Need for multiple colliding systems A A collisions: probing the high density medium Soft probes (charged particle multiplicities, flow, etc.) access global properties of the system and collective effects Hard probes (jets, heavy-flavours, quarkonia, etc.) access medium interaction and transport properties p p collisions Reference to study the effects in A A collisions p A collisions: disentangle the cold nuclear matter effects Modification of parton distributions in nuclei (shadowing) Gluon saturation Eskola, Paukkunen, Salgado, JHEP 94 (9) 65 Recent surprise: hints of collective effects in high multiplicity p Pb collisions reminiscent of Pb Pb D. Stocco FFP4 - Marseille 5 8 Jul. 4 3 / 7

ALICE layout Detector size: Length: 6 m Height: 6 m Weight: ktons D. Stocco FFP4 - Marseille 5 8 Jul. 4 4 / 7

ALICE layout Central barrel: η <.9 racking down to low-p ( MeV/c for pions) (PC+IS) PC de /dx (arb. units) PID (PC de /dx, IS de /dx, OF, RD, EMCal, HMPID) p 7 d t 6 5 4 5/3/3 p-pb snn = 5. ev K 3 e π..3.4 3 4 5 6 7 8 9 OF β ALI PERF 4697 ππ.8 K K p.6 p.4 Detector size: Length: 6 m. Height: 6 m Weight: ktons ALI PERF 46936 D. Stocco p-pb snn snn= =5. 5.eV ev p-pb 5/3/3 p-pb minimum bias 3 4 5 FFP4 - Marseille 5 8 Jul. 4 4 / 7

ALICE layout dn/dm / (5 MeV/c) Muon spectrometer: 4 < η <.5 ψ 4 ω pp s NN = 7 ev pµ > GeV/c φ ψ 3 ϒ Detector size: Length: 6 m Height: 6 m Weight: ktons D. Stocco 4 6 8 M(µ +µ -) (GeV/c) ALI PUB 77 FFP4 - Marseille 5 8 Jul. 4 4 / 7

Prelude: collision centrality In A A collisions Centrality defined by the impact parameter central collisions: large number of participants (N part) peripheral collisions: small N part Experimentally: centrality determined by Glauber model fit of V amplitude Events Phys. Rev. Lett. 6 () 33 Data Glauber fit 7 8% 6 7% 5 5 6% 4 5% 3 4% 3% % 5 % 5% 5 5 ALI PUB 888 VZERO Amplitude (a.u.) Small N part/n coll in p Pb biases in centrality estimation (multiplicity fluctuations, jet-veto bias, geometric bias) Looser correlations between: N part vs impact parameter N part vs multiplicity Event selection based on Pb-going neutron energy released in ZDC minimizes the bias p Pb Pb Pb D. Stocco FFP4 - Marseille 5 8 Jul. 4 5 / 7

A selection of results D. Stocco FFP4 - Marseille 5 8 Jul. 4 6 / 7

Heavy flavours Final goal in A A collisions Nuclear modification factor: Charm and beauty quarks are: produced in the initial hard scattering R AA (p ) = dn AA /dp AA dσ pp/dp experience the full medium evolution lose energy in medium R AA = no nuclear effects (binary scaling) R AA (hot or cold) medium effects ALICE.6 + *+ Average D, D, D.96<y <.4.4. D mesons (arxiv:45.345) p Pb, s NN =5. ev.5 Muons from HF decay p Pb s = 5. ev, µ ± NN c,b decays.5<y <3.54 ALICE Preliminary.8.6.4. ALI PUB 7945 CGC (Fujii Watanabe) pqcd NLO (MNR) with CEQ6M+EPS9 PDF Vitev: power corr. + k broad + CNM Eloss 5 5 5 Shadowing describes the p Pb data.5.5 NLO (MNR) with EPS9 shadowing systematic uncertainty on normalization 4 6 8 4 6 ALI PREL 84 D. Stocco FFP4 - Marseille 5 8 Jul. 4 7 / 7

Heavy flavours Final goal in A A collisions Nuclear modification factor: Charm and beauty quarks are: produced in the initial hard scattering R AA (p ) = dn AA /dp AA dσ pp/dp experience the full medium evolution lose energy in medium R AA = no nuclear effects (binary scaling) R AA (hot or cold) medium effects ALICE.6 + *+ Average D, D, D.96<y <.4.4. D mesons (arxiv:45.345) p Pb, s NN =5. ev.5 Muons from HF decay p Pb s = 5. ev, µ ± NN c,b decays 4<y <.96 ALICE Preliminary.8.6.4. ALI PUB 7945 CGC (Fujii Watanabe) pqcd NLO (MNR) with CEQ6M+EPS9 PDF Vitev: power corr. + k broad + CNM Eloss 5 5 5 Shadowing describes the p Pb data.5.5 NLO (MNR) with EPS9 shadowing systematic uncertainty on normalization 4 6 8 4 6 ALI PREL 8434 D. Stocco FFP4 - Marseille 5 8 Jul. 4 7 / 7

Heavy flavours Final goal in A A collisions Nuclear modification factor: Charm and beauty quarks are: produced in the initial hard scattering R AA (p ) = dn AA /dp AA dσ pp/dp experience the full medium evolution lose energy in medium R AA = no nuclear effects (binary scaling) R AA (hot or cold) medium effects Nuclear modification factor.6.4..8.6 ALICE + *+ Average D, D, D D mesons (arxiv:45.345) p Pb, s NN =5. ev.96<y <.4 Pb Pb, s NN =.76 ev y <.5 centrality % centrality 4 8% Nuclear modification factor.5.5 Muons from HF decay ALICE Preliminary µ ± b,c decays p Pb, s NN =5. ev.5<y <3.54 4<y <.96 Pb Pb, s NN =.76 ev.5<y <4 ( %).4.5. ALI PUB 79458 5 5 5 Shadowing describes the p Pb data Strong effect in Pb Pb collisions hot medium effect 4 6 8 4 6 ALI PREL 846 D. Stocco FFP4 - Marseille 5 8 Jul. 4 7 / 7

Quarkonia Final goal in A A collisions Quarkonium is an HF bound state (cc, bb) binding energy: roughly same order of QGP temperature color screening vary with excited states quarkonia suppression is a thermometer of the medium c b c b p Pb s.4 NN = 5. ev ALICE (JHEP (4) 73): inclusive J/ψ µ + µ, <p <5 GeV/ c. L int ( 4.46<y <.96)= 5.8 nb, L (.3<y <3.53)= 5. nb int + ALICE Preliminary: inclusive J/ψ e e, p > L int (.37<y <.43)= 5 µb global uncertainty = 3.4% x R backw, R Pbp PbPb.4. ALICE inclusive J/ψ µ + µ (.3<y <3.53) x (preliminary) R PbPb (.5<y <4, (arxiv:3.4) ( 4.46<y <.96), s NN =.76 ev, 9%) s NN = 5. ev.8 forw.8.6.6.4. EPS9 NLO (Vogt) CGC (Fujii et al.) ELoss, q =.75 GeV /fm (Arleo et al.) EPS9 NLO + ELoss, q =.55 GeV /fm (Arleo et al.) 4 3 3 4 y ALI PREL 7349.4. hypothesis: factorization of shadowing effects from the two nuclei in Pb Pb and > kinematics for J/ψ production 3 4 5 6 7 8 ALI DER 686 in agreement with shadowing and coherent energy loss models Color Glass Condensate (saturation of low-x gluons) underestimates at forward y Strong effect in Pb Pb collisions hot medium effect D. Stocco FFP4 - Marseille 5 8 Jul. 4 8 / 7

Quarkonia Final goal in A A collisions Quarkonium is an HF bound state (cc, bb) binding energy: roughly same order of QGP temperature color screening vary with excited states quarkonia suppression is a thermometer of the medium c X b c b p Pb s.4 NN = 5. ev ALICE (JHEP (4) 73): inclusive J/ψ µ + µ, <p <5 GeV/ c. L int ( 4.46<y <.96)= 5.8 nb, L (.3<y <3.53)= 5. nb int + ALICE Preliminary: inclusive J/ψ e e, p > L int (.37<y <.43)= 5 µb global uncertainty = 3.4% x R backw, R Pbp PbPb.4. ALICE inclusive J/ψ µ + µ (.3<y <3.53) x (preliminary) R PbPb (.5<y <4, (arxiv:3.4) ( 4.46<y <.96), s NN =.76 ev, 9%) s NN = 5. ev.8 forw.8.6.6.4. EPS9 NLO (Vogt) CGC (Fujii et al.) ELoss, q =.75 GeV /fm (Arleo et al.) EPS9 NLO + ELoss, q =.55 GeV /fm (Arleo et al.) 4 3 3 4 y ALI PREL 7349.4. hypothesis: factorization of shadowing effects from the two nuclei in Pb Pb and > kinematics for J/ψ production 3 4 5 6 7 8 ALI DER 686 in agreement with shadowing and coherent energy loss models Color Glass Condensate (saturation of low-x gluons) underestimates at forward y Strong effect in Pb Pb collisions hot medium effect D. Stocco FFP4 - Marseille 5 8 Jul. 4 8 / 7

Quarkonia Final goal in A A collisions Quarkonium is an HF bound state (cc, bb) binding energy: roughly same order of QGP temperature color screening vary with excited states quarkonia suppression is a thermometer of the medium large cc production at LHC (re)-generation c X c c X b c b p Pb s.4 NN = 5. ev ALICE (JHEP (4) 73): inclusive J/ψ µ + µ, <p <5 GeV/ c. L int ( 4.46<y <.96)= 5.8 nb, L (.3<y <3.53)= 5. nb int + ALICE Preliminary: inclusive J/ψ e e, p > L int (.37<y <.43)= 5 µb global uncertainty = 3.4% x R backw, R Pbp PbPb.4. ALICE inclusive J/ψ µ + µ (.3<y <3.53) x (preliminary) R PbPb (.5<y <4, (arxiv:3.4) ( 4.46<y <.96), s NN =.76 ev, 9%) s NN = 5. ev.8 forw.8.6.6.4. EPS9 NLO (Vogt) CGC (Fujii et al.) ELoss, q =.75 GeV /fm (Arleo et al.) EPS9 NLO + ELoss, q =.55 GeV /fm (Arleo et al.) 4 3 3 4 y ALI PREL 7349.4. hypothesis: factorization of shadowing effects from the two nuclei in Pb Pb and > kinematics for J/ψ production 3 4 5 6 7 8 ALI DER 686 in agreement with shadowing and coherent energy loss models Color Glass Condensate (saturation of low-x gluons) underestimates at forward y Strong effect in Pb Pb collisions hot medium effect D. Stocco FFP4 - Marseille 5 8 Jul. 4 8 / 7

Quarkonia Final goal in A A collisions Quarkonium is an HF bound state (cc, bb) binding energy: roughly same order of QGP temperature color screening vary with excited states quarkonia suppression is a thermometer of the medium large cc production at LHC (re)-generation c c c b c b p Pb s.4 NN = 5. ev ALICE (JHEP (4) 73): inclusive J/ψ µ + µ, <p <5 GeV/ c. L int ( 4.46<y <.96)= 5.8 nb, L (.3<y <3.53)= 5. nb int + ALICE Preliminary: inclusive J/ψ e e, p > L int (.37<y <.43)= 5 µb global uncertainty = 3.4% x R backw, R Pbp PbPb.4. ALICE inclusive J/ψ µ + µ (.3<y <3.53) x (preliminary) R PbPb (.5<y <4, (arxiv:3.4) ( 4.46<y <.96), s NN =.76 ev, 9%) s NN = 5. ev.8 forw.8.6.6.4. EPS9 NLO (Vogt) CGC (Fujii et al.) ELoss, q =.75 GeV /fm (Arleo et al.) EPS9 NLO + ELoss, q =.55 GeV /fm (Arleo et al.) 4 3 3 4 y ALI PREL 7349.4. hypothesis: factorization of shadowing effects from the two nuclei in Pb Pb and > kinematics for J/ψ production 3 4 5 6 7 8 ALI DER 686 in agreement with shadowing and coherent energy loss models Color Glass Condensate (saturation of low-x gluons) underestimates at forward y Strong effect in Pb Pb collisions hot medium effect D. Stocco FFP4 - Marseille 5 8 Jul. 4 8 / 7

W boson Final goal in A A collisions Electroweak boson are not affected by the medium test of binary scaling W (nb) σ µ 5 ALICE Preliminary p Pb = 5. ev µ s NN p > GeV/c 5 5 Open Boxes: Syst. Uncertainty Vertical Bars: Stat. Uncertainty + µ + W Data µ W Data + µ + W POWHEG µ W POWHEG 6 4 4 6 8 µ y ALI PREL 88 Measured cross-sections of muons from W boson decays compared to NLO expectation [S. Alioli, et al., JHEP 87, 6 (8)] (nuclear modifications of PDFs not included) agreement within.5 sigmas. Binary scaling holds D. Stocco FFP4 - Marseille 5 8 Jul. 4 9 / 7

Jets Final goal (for A A collisions) Jet fragmentation is modified by the medium (jet quenching): suppression of jet yields broadening of jet shape di-jet imbalance p Pb at s NN=5. ev Pb Pb at s NN=.76 ev ch. jets.5 ALICE charged jets p Pb 5. ev anti k jets R=.4, η <.5 Reference: Scaled pp jets 7 ev Systematic uncertainty.5 Uncertainty reference + Glauber 4 6 8 ch,jet ALI PREL 538 ALI-PREL-446 In Pb Pb collisions: jet energy moved to low p and large angles Binary scaling for high-p jets in p Pb D. Stocco FFP4 - Marseille 5 8 Jul. 4 / 7

Charged particles Final goal in A A collisions.8.6.4..8.6.4. High p : in-medium energy loss Low p : access to collective effects No nuclear modifications at high-p.4 5 5 5 3 35 4 45 5 Cronin -like peak at intermediate p p ) NSD, p Pb = 5. ev 4 6 8 4 ALI PREL 749 s NN + K +K,.5 < y CMS.3 < y CMS all charged, η <.3 CMS ALICE preliminary < for p <.3 for p <.8 GeV/c >.8 GeV/c.8.6.4..8.6.4. NSD, p Pb + π +π,.5 < y CMS.3 < y CMS p+p,.5 < y CMS.3 < y CMS.4.3...9.8.7.6.5 ALI DER 7555 ALICE preliminary = 5. ev < for p <.3 for p < for p <.3 for p <. GeV/c >. GeV/c < 3. GeV/c > 3. GeV/c 4 6 8 4 ALI PREL 758 s NN ALICE p Pb arxiv:45.737 s NN =5. ev, NSD charged particles, η <.3 K p, π Ξ.8.6.4..8.6.4. (GeV/c ALICE preliminary NSD, p Pb s NN = 5. ev + Ξ +Ξ,.5 < y < CMS all charged, η <.3 CMS 4 6 8 4 ALI PREL 745 Mass dependence of the intermediate-p enhancement collective effect? D. Stocco FFP4 - Marseille 5 8 Jul. 4 / 7

Hadron hadron correlations Final goal in A A collisions wo-particle correlations: explore particle production mechanisms High multiplicity Low multiplicity High - Low < p,trig < p,assoc < 4 GeV/c < GeV/c p Pb s NN = 5. ev % < p,trig < p,assoc < 4 GeV/c < GeV/c p Pb s NN = 5. ev 6 % < p,trig < p,assoc < 4 GeV/c < GeV/c p Pb s NN = 5. ev ( %) (6 %) ) (rad d N assoc d ηd ϕ N trig.4.. ALI PUB 468 η ϕ 3 (rad) 4 ) (rad d N assoc d ηd ϕ N trig.6.4. ALI PUB 464 η ϕ (rad) 3 4 = ) (rad d N assoc d ηd ϕ N trig.85.8.75 ALI PUB 4646 η ϕ (rad) 4 3 ALICE, Phys. Lett. B 79 (3) 9 Double ridge structure in high multiplicity p Pb collision observed Can be explained by Color Glass Condansate (initial state) or hydro calculations (final state) [ALICE, Phys. Lett. B 79 (3) 9] ) dn assoc/d ϕ per η (rad /N trig.88 p Pb s NN = 5. ev Data ( %) (6 %) a + a cos ϕ + a cos 3 ϕ 3.86 < p < 4 GeV/c a + a cos ϕ,trig < p < GeV/c Baseline for yield extraction,assoc.84 HIJING shifted.8.8.78.76 ALI PUB 465 3 4 ϕ (rad) D. Stocco FFP4 - Marseille 5 8 Jul. 4 / 7

Collective flow of QCD matter py px Spatial anisotropy is converted via multiple collisions into an anisotropic momentum distribution Reaction plane (Ψ RP ): defined by the beam axis and the impact parameter vector of the two colliding nuclei Azimuthal distributions of particles measured with respect to the reaction plane can be expanded in a Fourier series: E d3 N d 3 p = d N π p dp dy ( + ) v n cos (n(φ Ψ RP )) n= he elliptic flow is defined as: v = cos((φ Ψ RP )) D. Stocco FFP4 - Marseille 5 8 Jul. 4 3 / 7

v coefficient in p Pb v {PC, sub} Hadron, pion, kaon, proton correlations.5..5..5 p Pb at s NN=5. ev ALICE p Pb s NN = 5. ev ( %) (6 %) h K π p η >.8 (Near side only) v {SP, η >.9}.4.3.. Pb Pb at s NN=.76 ev π ± K ± p+p ALICE 5 6% Pb Pb s NN =.76 ev ALI PUB 56.5.5.5 3 3.5 4 4 6 ALICE, Phys. Lett. B 76 (3) 64 ALI PUB 83874 ALICE, arxiv:45.463 Mass ordering at low-p Intersection with protons at p GeV/c Qualitatively similar to Pb Pb where effects are usually ascribed to hydrodynamics D. Stocco FFP4 - Marseille 5 8 Jul. 4 4 / 7

Summary D. Stocco FFP4 - Marseille 5 8 Jul. 4 5 / 7

Conclusions ALICE studies the properties of QCD matter at the energy densities reached in heavy-ion collisions at the LHC Measurements in p Pb collisions are mandatory to understand the effects of cold nuclear matter Results from p Pb collisions at s NN =5. ev No indication of quenching at high-p (heavy flavours, jets, charged particles) quenching observed in Pb Pb collisions is a genuine final state effect Signature of collective effects (finite v, mass ordering) in most violent p Pb collisions p Pb seems hotter than we thought: lots to be learned ahead D. Stocco FFP4 - Marseille 5 8 Jul. 4 6 / 7

What s next Run II: 5 7 Updated readout, trigger, detectors LHC energy increase (up to 3 ev for pp, 5. ev for Pb Pb) Larger statistics (factor 3 to depending on channel in pp, p Pb and Pb Pb) Run III + IV: starting Increase data taking rate by a factor new detector readout (IS and PC) New forward detectors (under approval) Focus on rare probes (heavy-flavours, quarkonia, jets, etc.) D. Stocco FFP4 - Marseille 5 8 Jul. 4 7 / 7

Backup slides D. Stocco FFP4 - Marseille 5 8 Jul. 4 A.

Centrality in p Pb Event selection based on Pb-going neutron energy released in ZDC minimizes the bias N part/n coll obtained assuming one out of: mid-rapidity dn ch /dη N part forward rapidity dn ch /dη Npart Pb = Npart high-p yields N coll mult Q ppb.8.6.4 p Pb s = 5. ev NN Charged particles η <.3 mult ZN + N coll ALICE PRELIMINARY 5% 5 % % 4% 4 6% 6 8% 8 %..8.6.4. Syst. on pa Syst. on normalization Syst. on dn/dp.5..5.95.9.85 5 5 5 3 ALI PREL 8855 New quantity called Q pa instead of R pa due to possible bias in centrality estimators QpA i = dn pa /dp N coll i dn pp/dp D. Stocco FFP4 - Marseille 5 8 Jul. 4 A.

Charmonia vs multiplicity Pb-going direction (anti-shadowing region) p-going direction (shadowing region) mult Q ppb + Inclusive J/ψ, ψ(s) µ.4 µ ALICE Preliminary p Pb s NN = 5. ev, 4.46 <y <.96 (Pb going direction). mult Q ppb + Inclusive J/ψ, ψ(s) µ.4 µ ALICE Preliminary p Pb s NN = 5. ev,.3 <y < 3.53 (p going direction)..8.8.6.6.4.4. J/ψ ψ(s). J/ψ ψ(s) ALI PREL 7777 8 6 8 4 6 4 5 ZN Energy Event Class (%) ALI PREL 758 8 6 8 4 6 4 5 ZN Energy Event Class (%) J/ψ: consistent with shadowing ψ(s): additional effects at play final state interaction? D. Stocco FFP4 - Marseille 5 8 Jul. 4 A.3

Upsilon.4 p Pb s NN = 5. ev..8.6.4. + Inclusive ϒ(S) µ µ Eloss (Arleo et al., arxiv:.434): ELoss, p ELoss + EPS9 NLO > (preliminary) 4 3 3 4 y ALI DER 58999 Pb Pb at s NN =.76 ev R AA.4..8.6.4. Pb Pb s NN =.76 ev, inclusive ϒ(S), p > ALICE: L int = 69 µb, 9% (open: reflected) CMS: L int = 5 µb, % (PRL 9 () 3) A. Emerick et al., EPJ A48 () 7 otal Primordial Regenerated 4 3 3 4 y ALI PUB 8579 Color Evaporation Model + EPS9 shadowing in fair agreement with data (although slightly overestimates them) Energy loss model show : agreement in the p-going direction when shadowing applied agreement in the Pb-going direction when shadowing not applied Strong effect in Pb Pb collisions D. Stocco FFP4 - Marseille 5 8 Jul. 4 A.4