First LHCb results from pa and Pb-Pb collisions

Transcription

1 First LHCb results from pa and Pb-Pb collisions L. Massacrier on behalf of the LHCb collaboration Laboratoire de l Accélérateur Linéaire, Orsay Institut de Physique Nucléaire d Orsay LHCP th 18th June Lund, Sweden

2 Outline q The LHCb detector q LHCb running modes and phase space coverage q Physics motivation for heavy-ion studies q The Fixed Target data taking q Results from p-pb and Pb-p data taking - J/ψ production - ψ(s) production - ϒ(nS) production - Z production - Prompt D 0 production q First look at Pb-Pb data q Conclusions and prospects L. Massacrier LHCb results from pa and PbPb collisions LHCP 016

3 L. Massacrier LHCb results from pa and PbPb collisions LHCP The LHCb detector q Single arm spectrometer in the forward region q Fully instrumented in its angular acceptance ( < η < 5) q Designed initially for b-physics but general purpose detector (fixed target, heavy-ion ) Vertex detector IP resolution ~ 0µm Decay time resolution ~ 45 fs RICH: K/π/p separation ε(kàk) ~ 95% Mis-ID: ε(πàk) ~ 5% Muon system µ identification: ε(µàµ) ~ 97% Mis-ID: ε(πàµ) ~1-3% Dipole magnet Bending power 4 Tm Tracking system Δp/p = 0.4% - 0.8% (5 GeV/c 0 GeV/c) Electromagnetic + hadronic calorimeters JINST 3 (008) S08005 IJMPA 30 (015) 15300

4 LHCb running modes and phase space coverage q LHCb can operate in parralel collider mode or fixed target mode snn = 8. TeV snn = 5.0 TeV Collider mode p Pb Pb snn = 69 GeV snn = 1 GeV Fixed target mode q Kinematic acceptance p Gas (He,Ne, Ar ) Pb Pb Gas (Ne, Ar) pp and p-gas ppb and Pbp PbPb and Pb-Gas Collider mode: forward/backward coverage Fixed target mode: Central and backward coverage Energy between SPS and RHIC Bridge the gap from SPS to LHC with a single experiment L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 4

5 Physics motivation for heavy ion studies Nucleus-Nucleus collisions Probe Quark Gluon Plasma formation, study the phase transition ü Study sequential suppression of quarkonia, charmonia recombination, heavy quark energy loss In LHCb: * At the GeV (Fixed target) and TeV scale (collider) * Measurement of all quarkonia states (χ c ) / Disentangle prompt & from-b * Forward measurement of both open HF & quarkonia down to zero p T Study the dynamics of the hadronization process ü Measurement of total cross-sections, energy flow measurements, particle multiplicities, Bose- Einstein of Fermi-Dirac correlations Probe gluon shadowing in the nuclei at low-x with exclusive vector meson photoproduction in Ultra-Peripheral Collisions Proton-Nucleus collisions Interesting by themselves but also reference for heavy ion studies ü Study Cold Nuclear Matter (CNM) effects in absence of QGP formation * Heavy Flavour and quarkonia to study gluon shadowing, coherent parton energy loss, ü Study Parton Distribution Functions of free and bound nucleons with electroweak bosons, quarkonia, Drell-Yan * LHCb probes low-x (forward ppb) and large-x region (backward p-pb & fixed target) ü Two-particle correlations to probe collective effects in the dense environment of high energy collisions ü Input for cosmic ray studies (dark matter searches)àlow energy phe collisions (fixed target) 5

6 The Fixed Target data taking (SMOG) à SMOG: System for Measuring Overlap with Gas: - Main use so far for precise luminosity determination - Low density noble gas injected in the VELO, in the interaction region - Only local temporary degradation of LHC vacuum q q q q q q q q pne pilot run at snn = 87 GeV (01) ~ 30 min PbNe pilot run at snn = 54 GeV (013) ~ 30min pne run at snn = 1 GeV (015) ~ 1h phe run at snn = 1 GeV (015) ~ 8h par run at snn = 1 GeV (015) ~ 3 days par run at snn = 69 GeV (015) ~ few hours PbAr run at snn = 69 GeV (015) ~ 1.5 week phe run at snn = 1 GeV (016) ~ days L. Massacrier SMOG system Preferred target Gas A He Ne Ar Kr Xe LHCb results from pa and PbPb collisions LHCP 016 6

7 Fixed Target Interaction Properties L. Massacrier LHCb results from pa and PbPb collisions LHCP LHCb-CONF entries/0 mm 5 4 LHCb preliminary pa - without SMOG entries/0 mm pa - with SMOG LHCb preliminary 3 4 Beam 1 3 Beam Beam 1 Beam z PV [mm] z PV [mm] Beam 1 only Beam only Weighted sum All collisions q Beam-Beam / Beam-Gas interactions can be separated from the filling scheme à Fixed target collisions can be isolated from regular collisions in collider mode No need for dedicated physics runs! q SMOG increases the beam gas rate by two order of magnitudes à Gas pressure (~ 1.5x -7 mbar) ~ order of magnitude larger than vacuum pressure

8 Results from Pb-Ne and p-ne collisions q Pb-Ne collisions at s NN = 54 GeV, about 30 min of data taking (013) Events / 16 MeV/c 14 LHCb Preliminary Pb-Ne Collisions 1 8 J/ψ σ = 5.0 ± 1.9 MeV/c = 8 ± N signal dimuon invariant mass (MeV/c ) q p-ne collisions at s NN = 1 GeV, about 1h of data taking (015) entries / 8 MeV/c LHCb preliminary 015 pne data D 0 entries / 16 MeV/c LHCb preliminary 015 pne data J/ψ NEW µ + µ invariant mass (MeV/c ) π K invariant mass (MeV/c ) L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 8

9 The p-pb and Pb-p data taking (013) q p-pb and Pb-p data collected at a nucleon-nucleon center of mass energy s NN = 5 TeV q Asymmetric beams: nucleon-nucleon center-of-mass system shifted by Δy = 0.47 in the direction of the p beam E p = 4 TeV E Pb = 1.58 A Pb TeV p + Pb collisions (forward) Rapidity coverage: 1.5 < y CMS < data sample: L int = 1.1 nb -1 à Applies to all analyses unless specified p Pb Pb + p collisions (backward) Rapidity coverage: -5.5 < y CMS < data sample: L int = 0.5 nb -1 à Applies to all analyses unless specified E Pb = 1.58 A Pb TeV Pb E p = 4 TeV p Common rapidity range :.5 < y CMS < 4 L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 9

10 L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 J/ψ production in p-pb and Pb-p JHEP 0 (014) 07 q J/ψ are reconstructed from two well identified muons q Disentangle prompt J/ψ from J/ψ from b using pseudo-proper time: t Z = (Z J/Ψ Z PV ) M J/Ψ p z q Yields of prompt J/ψ and J/ψ from b extracted from simultaneous fit of mass and pseudo-proper time ) Candidates / (5 MeV/c (a) LHCb ppb(fwd) = 5 TeV s NN forward.5 < y < m µµ p T Mass distribution: - Signal: Crystal-Ball function - Background: Exponential < 14 GeV/c [MeV/c ] Candidates / (0. ps) (c) LHCb ppb(fwd) = 5 TeV s NN forward.5 < y < 3.0 < 14 GeV/c t z [ps] t Z distribution: - Signal: - δ(t z ) for prompts J/ψ (blue curve) - Exponential for J/ψ from b (black line) - Background: Empirical function from sideband (green hatched) p T

11 J/ψ nuclear modification factor (R ppb ) JHEP 0 (014) 07 q R ppb (y) = (1/ A) (dσ pa / dy) / (dσ pp / dy) in common range.5 < y CMS < 4.0 R ppb (b) LHCb ppb s NN = 5 TeV p T LHCb, J/ψ from b < 14 GeV/c EPS09 LO ndsg LO y Prompt J/ψ: strong suppression at forward y (strong CNM effect) à Data well described by coherent energy loss models (w and w/o shadowing) J/ψ from b: small suppression in the forward region à first indication of suppression of b hadron production Models: EPS09LO (CSM): PRC88 (013) ; NPA 96 (014) 36 EPS09NLO (shadowing + CEM): IJMP E (013) Energy Loss: JHEP 03 (013) 1; JHEP 05 (013) 155 ndsg LO: PRC88 (013) L. Massacrier LHCb results from pa and PbPb collisions LHCP

12 L. Massacrier LHCb results from pa and PbPb collisions LHCP J/ψ forward to backward ratio (R FB ) JHEP 0 (014) 07 R FB (y) = (dσ pa / dy) / (dσ Ap / dy) q in common range.5 < y CMS < 4.0 q No need for pp refence cross section, part of experimental and theoretical uncertainties cancel out R FB (b) LHCb ppb s NN = 5 TeV p T LHCb, J/ψ from b < 14 GeV/c EPS09 LO ndsg LO y q Rapidity dependence: Prompt J/ψ: Clear forward-backward asymmetry à More statistics needed to distinguish between models J/ψ from b: Small forward-backward asymmetry

13 L. Massacrier LHCb results from pa and PbPb collisions LHCP Ψ(S) forward to backward ratio LHCb-CONF q Similar signal extraction stragegy as for the J/ψ q R FB as a function of p T and rapidity in common range.5 < y CMS < 4.0 q No need for pp refence cross section, part of experimental and theoretical uncertainties cancel out Large experimental uncertainties à more statistics needed to get a trend R FB of inclusive ψ(s) compatible both with unity and with suppression of inclusive J/ψ

14 Ψ(S) nuclear modification factor LHCb-CONF q Ψ(S) nuclear modification factor is calculated from J/Ψ nuclear modification factor Prompt R Ψ(S) ppb R J/Ψ ppb R Assuming σ J/Ψ pp (5 TeV) Ψ(S) (5 TeV) σ J/Ψ (7 TeV) pp Ψ(S) (7 TeV) σ pp with σ pp From b R = R ψ (S) ppb J/Ψ R ppb = σ ψ (S) ppb (5TeV) J/Ψ (5 TeV) σ ppb σ J/Ψ pp (5 TeV) Ψ(S) (5 TeV) σ pp Inclusive Prompt ψ(s) more suppressed than prompt J/ψ Eloss + shadowing don t explain the ψ(s) suppression in the backward region (other mechanism at play?) Suppression of ψ(s) from b consistent with that of J/ψ from b Suppresion of inclusive ψ(s) consistent with ALICE results L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 ALICE: JHEP 1 (014)

15 L. Massacrier LHCb results from pa and PbPb collisions LHCP ϒ(1S) R pa and R FB JHEP 07 (014) 094 q In common rapidity range.5 < y CMS < 4.0 q Measurement of ϒ(1S) R ppb and R FB is complementary to the one of J/ψ Probing different x A R ppb LHCb ppb s NN = 5 TeV R FB 1. 1 LHCb ppb s NN = 5 TeV E.loss+EPS09 NLO in Ref.[3] Υ(1S) Prompt J/ψ y ϒ(1S) is also sensitive to CNM effets R ppb versus rapidity: Suppression in forward region is smaller than for J/ψ Central value in forward region close to that of J/ψ from b à CNM effects on b hadrons Indication of enhancement in the backward region à could be attributed to anti-shadowing R FB versus rapidity: Ratio in agreement with predictions of energy loss + shadowing (EPSO9 NLO) E.loss+EPS09 NLO in Ref.[3] Υ(1S) Prompt J/ψ y

16 L. Massacrier LHCb results from pa and PbPb collisions LHCP Z production in p-pb and Pb-p JHEP 09 (014) 030 Muon selection: p T > 0 GeV/c,.0 < η < 4.5, 60 < M(µ + µ - ) < GeV/c Backgrounds: very small, purity > 99% determined from data Clean signal: 11 forward candidates, 4 backward candidates [nb] σ Z µ + µ syst. syst. stat. LHCb ppb s NN = 5 TeV FEWZ NNLO + MSTW08 FEWZ NNLO + MSTW08 + EPS09 (NLO) 0 backward forward Cross sections in agreement with predictions, although the production of Z in the backward region appears slightly higher than prediction R FB calculated in the common rapidity range is lower than expectations à deviation of.σ from R FB = 1 Statistical precision of measured cross sections prevents conclusions on the presence of CNM Looking forward to take more data during run II

17 L. Massacrier LHCb results from pa and PbPb collisions LHCP Prompt D 0 production in p-pb/pb-p LHCB-CONF NEW q D 0 reconstructed in D 0 à K - π + decay channel q L int = 0.11 nb -1 (forward), L int = 0.05 nb -1 (backward) q Prompt D 0 yields obtained from D fit of D 0 invariant mass and χ of Impact Parameter q D 0 pp reference cross section at s = 5 TeV obtained from extrapolation of LHCb measurements at s = 7 TeV and s = 13 TeV à LHCb unique to measure prompt D 0 down to zero p T in the forward region q No strong p T dependence of the D 0 R ppb at forward and backward rapidities q Nuclear modification factor smaller at forward rapidity q Measurement consistent with theoretical predictions from NLO MNR with CTEQ6M + EPS09NLO à Nucl. Phys. B.373 (199) 95, JHEP (003) 046, JHEP 04 (009) 065

18 L. Massacrier LHCb results from pa and PbPb collisions LHCP Prompt D 0 production in p-pb/pb-p LHCB-CONF q D 0 forward to backward ratio q Cancellation of pp reference cross section and of part of the uncertainties NEW q Clear forward-backward asymmetry à CNM effect q No strong p T dependence of the R FB q Asymmetry more important at larger rapidity q Measurement consistent with theoretical predictions from NLO MNR with CTEQ6M + EPS09NLO à Nucl. Phys. B.373 (199) 95, JHEP (003) 046, JHEP 04 (009) 065

19 First LHCb Pb-Pb data taking (december 015) L. Massacrier LHCb results from pa and PbPb collisions LHCP q 4 colliding bunches in LHCb NEW q Estimate of the collected integrated luminosity ~ 3-5 µb -1 q Pb-Pb data taken without any global event cut à Important for future determination of the collision centrality à Track reconstruction performed for events with number of clusters in the Velo < 000 Energy deposition in the electromagnetic (Ecal) / hadronic (Hcal) calorimeters could be a good centrality estimator Entries [a.u.] 5 LHCb preliminary 4 s NN = 5 TeV % 30-40% 0-30% -0% 0-% Ecal Energy [TeV] Entries [a.u.] LHCb preliminary = 5 TeV s NN % Number of Velo Clusters 3 Number of Velo Clusters LHCb preliminary = 5 TeV s NN Ecal Energy [TeV]

20 First LHCb Pb-Pb data taking (december 015) J/ψ and D 0 signals in bins of Ecal event activity (full statistics) NEW Candidates per 8.0 MeV/c LHCb preliminary s NN = 5 TeV 70%<Event Activity<90% Candidates per 8.0 MeV/c 5 LHCb preliminary 50%<Event Activity<70% s NN = 5 TeV Candidates per 8.0 MeV/c M(µµ) [MeV/c LHCb preliminary 70%<Event Activity<90% s NN = 5 TeV ] Candidates per 8.0 MeV/c M(µµ) [MeV/c LHCb preliminary 50%<Event Activity<70% s NN = 5 TeV ] M(Kπ) [MeV/c ] M(Kπ) [MeV/c ] Nice K 0 s and Λ signal also observed (not shown) L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 0

21 First LHCb Pb-Pb data taking (december 015) L. Massacrier LHCb results from pa and PbPb collisions LHCP Coherent photoproduction of J/ψ in Pb-Pb UPC ü Events containing only Long Tracks and only VELO tracks ü Number of hits in SPD* < 0 ü No Upstream, Downstream and T tracks Candidates per 8.0 MeV/c LHCb preliminary = 5 TeV s NN M(µµ) [MeV/c ] Candidates per (GeV/c) 1 LHCb preliminary = 5 TeV s NN p ( µ + µ - ) [GeV/c) ] T p (µµ) [(GeV/c) T * SPD: Scintillating Pad Detector à identifies charged particles, allows e - /γ separation. Located before Ecal + Hcal 1 ] q New HERSHEL detector installed in LHCb: - Forward detector 5 < η < 8 - Possibility to define rapidity gaps - Was running during 015 data taking

22 Conclusions and prospects q LHCb is in the unique position to do fixed target physics q Exploit SMOG system with different noble gases (p-ne, p-he, p-ar, Pb-Ne, Pb-Ar) q Bridge the gap from SPS to LHC physics with a single experiment q LHCb succesfully participated in the proton-pb data taking in 013 q Measurement of J/ψ, ψ(s) and ϒ production à Cold nuclear matter effects visible in J/ψ, ψ(s) and ϒ(1S) production q First observation of forward Z production in proton-nucleus collisions à Analysis will benefit from larger statistics data sample in Run q LHCb plans to participate in the 016 ppb data taking ( s NN = 5 and 8. TeV) q Fixed target study during lowest energy run q Expecting L int ~ 0nb -1 at s NN = 8. TeV à Improved precision on ψ(s), Z production measurements à New measurements at reach: ϒ(3S), associated HF production, Drell-Yan q LHCb detector has also collect PbPb data for the first time at the end of 015 q Rich program in heavy flavour physics, EW, (soft) QCD and QGP studied foreseen q Results soon to come! LHCb is more than a pp heavy flavour experiment, it is a truly general purpose detector in the forward region L. Massacrier LHCb results from pa and PbPb collisions LHCP 016

23 L. Massacrier LHCb results from pa collisions ISMD Back up

24 L. Massacrier LHCb results from pa and PbPb collisions LHCP J/ψ forward to backward ratio (R FB ) JHEP 0 (014) 07 R FB (y) = (dσ pa / dy) / (dσ Ap / dy) q in common range.5 < y CMS < 4.0 q No need of pp refence cross section, part of experimental and theoretical uncertainties cancel p T dependence: Prompt J/ψ : forward backward asymmetry agrees best with eloss + shadowing (except at low p T ) J/ψ from b: R FB close to 1

25 L. Massacrier LHCb results from pa and PbPb collisions LHCP Ψ(S) production in p-pb and Pb-p LHCb-CONF q Similar analysis strategy as for the J/ψ q Yields of prompt ψ(s) and ψ(s) from b extracted from simultaneous fit of mass and pseudo-proper time forward forward Mass distribution: - Signal: Crystal-Ball function - Background: Exponential t Z distribution: - Signal: - δ(t z ) for prompts ψ(s) (blue curve) - Exponential for ψ(s) from b (black line) - Background: Empirical function from sideband (green hatched)

26 L. Massacrier LHCb results from pa and PbPb collisions LHCP Ψ(S) relative suppression wrt J/ψ LHCb-CONF q Relative suppression is calculated as: R = R ψ (S) ppb J/Ψ R ppb = σ ψ (S) ppb (5TeV) J/Ψ (5 TeV) σ ppb σ J/Ψ pp (5 TeV) Ψ(S) (5 TeV) σ ψ (S) ppb (5TeV) J/Ψ (5 TeV) σ pp σ ppb σ J/Ψ pp (7 TeV) Ψ(S) (7 TeV) σ pp ALICE: JHEP 1 (014) 073 PHENIX: Phys. Rev. Lett. 111 (013), no. 0 (0301) Intriguing stronger suppression of prompt ψ(s) than that of prompt J/ψ Similar suppression for ψ(s) from b and J/ψ from b à R compatible with 1 within large uncertainties Results for inclusive ψ(s) compatible with ALICE measurement

27 L. Massacrier LHCb results from pa and PbPb collisions LHCP ϒ(nS) production in p-pb and Pb-p JHEP 07 (014) 094 q ϒ states in the dimuon decay channel q Forward: 1.5 < y CMS < 4.0, backward: -5.0 < y CMS < -.5; p T < 15 GeV/c q Fit performed with 3 Crystal Balls for signal and an exponential for background Limited statistics do not permit to do a differential measurement Forward production Backward production Candidates per 60 MeV/c LHCb ppb s NN = 5 TeV 1.5 < y < 4.0 p < 15 GeV/c T Candidates per 60 MeV/c LHCb ppb s NN = 5 TeV 5.0 < y <.5 p < 15 GeV/c T m µ + µ - [MeV/c ] m µ + µ - [MeV/c ]

28 L. Massacrier LHCb results from pa and PbPb collisions LHCP Prompt D 0 production in p-pb/pb-p LHCB-CONF q D 0 reconstructed in D 0 à K - π + decay channel NEW q Lint = 0.11 nb -1 (forward), Lint = 0.05 nb -1 (backward) q Prompt D 0 yields obtained from D fit of D 0 invariant mass and χ of Impact Parameter à LHCb unique to measure prompt D 0 down to zero p T

29 L. Massacrier LHCb results from pa and PbPb collisions LHCP Two particle correlations in p-pb and Pb-p LHCB-CONF q Measurement of angular (Δη,Δϕ)-correlations of prompt charged particles q Both beam configurations analyzed separately: L int = 0.46nb -1 (p+pb), L int = 0.30nb -1 (Pb-p) q Rapidity range 1.5 < y CMS < 4.4 (forward), -5.4 < y < -.5 (backward) q Correlation function is decribed as a per-trigger particle associated yield: 1 N trig d N pair S(Δη, Δϕ) = B(0, 0) dδηdδϕ B(Δη, Δϕ) p-pb configuration Δϕ=0 near-side ridge clearly visible in high event activity class (however not very pronounced) Pb-p configuration Δϕ=0 very pronounced near-side ridge in Pb-p in high activity event class

30 Two particle correlations in p-pb and Pb-p q To study the evolution of the long-range correlations on the near and away sides in more details, correlation function on Δϕ are calculated: Δη b Y(Δφ) 1 dn pair N trig dδφ = 1 1 Δη b Δη a Δηa N trig d N pair dδηdδφ dδη q D-yield averaged in the range.0 < η <.9 to exclude short range correlations (jet peak) q Subtraction of the zero yield at minimum (ZYAM) Correlation yield increases with event activity Away-side ridge decreases towards higher p T On the near side the ridge emerges (from -30% event activity class in Pb-p, from 0-% event activity class in p-pb) with a maximum in 1 < p T < GeV/c Near-side ridge is more pronounce in Pb-p than in p-pb Y( φ)-czyam Y( φ)-czyam Y( φ)-czyam Y( φ)-czyam Y( φ)-czyam LHCB-CONF < p < 1.0 GeV/c 1.0 < p <.0 GeV/c.0 < p < 3.0 GeV/c T T T C ZYAM =1.61 (p+pb) C ZYAM =.06 (Pb+p) C ZYAM =.83 (p+pb) C ZYAM =4.01 (Pb+p) C ZYAM =3.74 (p+pb) C ZYAM =5.78 (Pb+p) C ZYAM =4.9 (p+pb) C ZYAM =7.38 (Pb+p) C ZYAM =5.58 (p+pb) C ZYAM =8. (Pb+p) 0 4 φ φ φ L. Massacrier LHCb results from pa and PbPb collisions LHCP 016 C ZYAM =0.3 (p+pb) C ZYAM =0.37 (Pb+p) C ZYAM =0.56 (p+pb) C ZYAM =0.70 (Pb+p) C ZYAM =0.81 (p+pb) C ZYAM =1.14 (Pb+p) C ZYAM =1.0 (p+pb) C ZYAM =1.75 (Pb+p) C ZYAM =1.4 (p+pb) C ZYAM =.03 (Pb+p) 0 φ φ 4 LHCb s NN = 5 TeV p+pb data Pb+p data C ZYAM =0.18 (p+pb) C ZYAM =0.1 (Pb+p) φ C ZYAM =0.3 (p+pb) C ZYAM =0.6 (Pb+p) C ZYAM =0.9 (p+pb) C ZYAM =0.35 (Pb+p) C ZYAM =0.33 (p+pb) C ZYAM =0.40 (Pb+p) 0 φ φ % 30-50% -30% 0-% 0-3% Event activity 30