Heavy-Ion results from LHCb Michael Winn on behalf of the LHCb collaboration Laboratoire de l’Accélérateur Linéaire, Orsay 56th International Winter Meeting on Nuclear Physics, Bormio, 26.01.2018
Outline ◮ nucleus-nucleus collisions in collider mode ◮ proton-nucleus collisions in collider mode ◮ proton-nucleus collisions in fixed-target mode ◮ Conclusions Bormio 2018 Michael Winn, LHCb Collaboration 1/26
Nucleus-nucleus collisions in collider mode nucleus–nucleus (PbPb) event display with a J /ψ candidate average multiplicity about 40 × average pp multiplicity most central about 200 × average pp multiplicity: about ATLAS/CMS phase 2 for number of tracks per crossing LHCb PbPb performance figures: https://twiki.cern.ch/twiki/bin/view/LHCb/LHCbPlots2015 Bormio 2018 Michael Winn, LHCb Collaboration 2/26
PbPb collisions at the LHC as a probe of QCD matter p/T 4 : pressure over temperature 4 HRG: Hadron Resonance Gas HTL: Hard thermal loop SB: Stefan-Boltzmann limit of non-interacting quarks and gluons PLB 370 (2014), T-range from PRC 89, 044910 (2014) The QCD many-body system in the lab: nucleus-nucleus collisions ◮ measure equilibrium properties: deconfinement, chiral restoration, thermodynamic&transport properties ◮ quantify QCD properties: QCD radiation, hadronisation, phase transition characteristics ◮ understand non-equilibrium dynamics and relation to equilibrium → What can LHCb contribute in PbPb collisions? Bormio 2018 Michael Winn, LHCb Collaboration 3/26
LHCb in PbPb collisions at √ s NN = 5 TeV Experiment 2015 PbPb 150 mio MB evts. (0.02 nb − 1 ) ALICE central 0.225 nb − 1 analysed ALICE muon 0.464 nb − 1 analysed CMS 0.515 nb − 1 analysed ATLAS LHCb 50 mio MB evts., 50-100% tracking modified version in arXiv:1609.01135, references therein. ◮ first LHCb data in 2015: competitive for soft probes and charm in terms of event statistics in unique acceptance ◮ soft trigger requirement: → combined with LHCb PID capability: unique sample at the LHC including exclusive production studies from γ -induced processes ◮ envisage a factor 10 larger integrated PbPb-luminosity in 2018 should be possible with change in β ∗ & doubling number of bunches ◮ 2017 0.4 ≈ µ b − 1 Xe-Xe collisions by LHCb Bormio 2018 Michael Winn, LHCb Collaboration 4/26
LHCb in PbPb collisions: centrality reach PbPb performance figures: https://twiki.cern.ch/twiki/bin/view/LHCb/LHCbPlots2015 ◮ designed for low "pile-up" pp collisions: running in pp at average number of visible collisions of 1.0 ◮ occupancy limitation in PbPb collisions: current tracking algorithms up to 50% in centrality Bormio 2018 Michael Winn, LHCb Collaboration 5/26
LHCb in PbPb collisions: J /ψ signal PbPb performance figures: https://twiki.cern.ch/twiki/bin/view/LHCb/LHCbPlots2015, "event-activity" corresponds to centrality percentiles. ◮ clear signal up to edge of occupancy limit thanks to similar resolutions as in pp collisions ◮ data-driven efficiency determinations challenging ◮ prompt J /ψ pilot analysis knowledge will be combined with other analyses for publication Bormio 2018 Michael Winn, LHCb Collaboration 6/26
p –nucleus collisions in collider mode 2016 p –nucleus ( p Pb) event display mean charged particle multiplicity per collision: about 3-4 × pp Bormio 2018 Michael Winn, LHCb Collaboration 7/26
p –nucleus: control & limits of collinear factorisation left: taken from arXiv:1612.05741; right: modified version of graphic in “QCD and collider physics”, Ellis, Stirling, Webber ◮ no HERA equivalent for lepton-nuclei : parton flux unconstrained for LHC heavy-ion low- p heavy-quark production total charm, beauty production in p -nucleus vital input for AA s ∝ A 1 / 3 ◮ saturation scale Q 2 nucleus → linear parton evolution break-down? ◮ Which framework if collinear factorisation no longer valid? color glass condensate arXiv:1002.0333 ? ◮ Are there further effects? like energy loss by enhanced small-angle gluon radiation arXiv:1212.0434 Bormio 2018 Michael Winn, LHCb Collaboration 8/26
p -nucleus/ pp high multiplicity events: interesting questions Left: taken from arXiv:1404.7327 Kn = L micro / L macro , already dN/d η =270! Right: taken from arXiv:1611.00329. ◮ correlations & bulk production@low- p T & large multiplicity: ’same’ patterns as in PbPb , where sign for locally thermalised system ◮ hydro in large multiplicity p Pb: set-up as in PbPb describing data despite precondition doubts arXiv:1705.03177 ◮ colour glass condensate & color reconnections explanations not ruled out arXiv:1607.02496, arXiv:1705.00745 ◮ alternative explanations via interference of multi-parton scatterings arXiv:1708.08241 , string interactions arxiv:1710.09725 Bormio 2018 Michael Winn, LHCb Collaboration 9/26
D 0 in p Pb at √ s NN =5 TeV arXiv:1707.02750, JHEP 1710 (2017) 090. ◮ sensitive to gluons down to x = 10 − 6 ◮ consistency between colour glass condensate and nuclear PDF predictions: to be investigated ◮ assuming no other effect, constraining nPDFs in unexplored area: first fit and consistency with prompt and non-prompt J /ψ -data from LHCb at 8 TeV, see arxiv:1712.07024 Bormio 2018 Michael Winn, LHCb Collaboration 10/26
Λ C in p Pb at √ s NN =5 TeV LHCb-CONF-2017–05. ◮ test of charm fragmentation in p Pb: crucial input for hadronisation phenomenology Bormio 2018 Michael Winn, LHCb Collaboration 11/26
LHCb di-hadron correlations in p Pb collisions LHCb p+Pb s = 5 TeV LHCb Pb+p s = 5 TeV NN NN 1.0 < p < 2.0 GeV/c 1.0 < p < 2.0 GeV/c T T Event class 0-3% Event class 0-3% φ φ 2.2 ∆ ∆ N N d d 1.45 2.15 2 2 η η d d ∆ ∆ 2.1 1.4 d d trig trig 2.05 1 1.35 1 N N 4 4 3 3 2 2 2 2 ∆ ∆ φ φ 1 0 1 0 η η ∆ ∆ 0 0 -2 -2 -1 -1 PLB 762 (2016) 473. ◮ unique forward acceptance with full tracking compared to other experiments ◮ qualitative agreement with mid-rapidity findings by ALICE, ATLAS and CMS in high multiplicity events ◮ significant difference between lead and proton fragmentation side, when comparing same fraction of events based on multiplicity in experimental acceptance 2 . 0 < η < 4 . 9 Bormio 2018 Michael Winn, LHCb Collaboration 12/26
LHCb di-hadron correlations in p Pb collisions 1.0 < p < 2.0 GeV/c LHCb s = 5 TeV NN T Activity bin I Activity bin II Activity bin III Activity bin IV Activity bin V ZYAM 0.15 0.15 0.15 0.15 0.15 0.15 C =1.21 ( p+Pb ) C =1.32 ( p+Pb ) C =1.42 ( p+Pb ) C =1.51 ( p+Pb ) C =1.64 ( p+Pb ) ZYAM ZYAM ZYAM ZYAM ZYAM 0.15 < p < 1.0 GeV/c 1.0 < p < 2.0 GeV/c 2.0 < p < 3.0 GeV/c T T T C =1.04 ( Pb+p ) C =1.16 ( Pb+p ) C =1.27 ( Pb+p ) C =1.38 ( Pb+p ) C =1.54 ( Pb+p ) )-C ZYAM ZYAM ZYAM ZYAM ZYAM ZYAM 0.15 0.10 0.10 0.10 0.10 0.10 0.10 C =1.61 (p+Pb) C =0.32 (p+Pb) ZYAM ZYAM LHCb φ C =2.06 (Pb+p) C =0.37 (Pb+p) ∆ )-C ZYAM ZYAM 0.10 s = 5 TeV 50-100% Y( NN 0.05 0.05 0.05 0.05 0.05 0.05 φ p+Pb data ∆ Y( 0.05 Pb+p data 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0 0 2 2 4 4 0 2 4 0 2 4 0 2 4 0 2 4 ∆ φ ∆ φ ∆ φ ∆ φ ∆ φ ∆ φ ZYAM 0.15 C =2.83 (p+Pb) C =0.56 (p+Pb) C =0.18 (p+Pb) ZYAM ZYAM ZYAM PLB 762 (2016) 473. C =4.01 (Pb+p) C =0.70 (Pb+p) C =0.21 (Pb+p) )-C ZYAM ZYAM ZYAM 30-50% 0.10 φ ∆ ∆ φ Y( 0.05 0.00 ◮ increase of near-side correlation towards larger ZYAM 0.15 C =3.74 (p+Pb) C =0.81 (p+Pb) C =0.23 (p+Pb) ZYAM ZYAM ZYAM C =5.78 (Pb+p) C =1.14 (Pb+p) C =0.26 (Pb+p) multiplicities and lower p T after pedestal )-C 0.10 ZYAM ZYAM ZYAM 10-30% φ ∆ Y( subtraction 0.05 0.00 ◮ results at forward and backward rapidity at ZYAM 0.15 C =5.03 (p+Pb) C =1.19 (p+Pb) C =0.29 (p+Pb) ZYAM ZYAM ZYAM C =7.81 (Pb+p) C =1.78 (Pb+p) C =0.36 (Pb+p) )-C ZYAM ZYAM ZYAM 0.10 0-10% same estimated absolute multiplicity in φ ∆ Y( 0.05 acceptance: similar results of correlation 0.00 ZYAM 0.15 strength after pedestal subtraction C =5.67 (p+Pb) C =1.39 (p+Pb) C =0.32 (p+Pb) ZYAM ZYAM ZYAM C =8.63 (Pb+p) C =2.07 (Pb+p) C =0.40 (Pb+p) )-C ZYAM ZYAM ZYAM 0.10 0-3% φ ◮ looking forward to model comparison: ∆ Y( 0.05 kinematics favourable for application of 0.00 0 2 4 0 2 4 0 2 4 ∆ φ ∆ φ ∆ φ ∆ φ ∆ φ ∆ φ ∆ φ saturation-based models Bormio 2018 Michael Winn, LHCb Collaboration 13/26
LHCb p Pb collisions: 2016 run about 30 nb − 1 at 8.16 TeV with Hadron PID and precision tracking/vertexing down to low- p T : a factor 20 more than at 5 TeV in 2013 → unique opportunity to constrain nuclear effects in highly asymmetric system bridging between pp and pPb ◮ ψ (2S) precision close to the one of J /ψ in 2013: confirm factorisation breaking, measure χ c ◮ open charm and J /ψ : comparison with Drell-Yan ◮ double charm production and c ¯ c ( c )- correlations ◮ fully reconstructed open beauty and Υ family 13.6 ± 0.3 nb − 1 in p Pb 20.8 ± 0.5 nb − 1 in Pb p ≈ 10 9 minimum events in both configurations Bormio 2018 Michael Winn, LHCb Collaboration 14/26
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