Measurement of D-meson nuclear modification factor and flow in Pb-Pb collisions with ALICE at the LHC Fabrizio Grosa on behalf of the ALICE Collaboration Politecnico and INFN Torino Hard Probes, Aix-Les-Bains 01-05/10/2018 Outline Physics motivation The ALICE experiment D0, D+, D*+, Ds+ meson nuclear modification factor and elliptic flow Event-shape engineering applied to the D-meson elliptic flow and pT-differential yields First measurement of charge-dependent D 0 ( D 0 ) directed flow at LHC energies Conclusions 02/10/2018 Hard Probes - Fabrizio Grosa 1/19 HF as a probe of the quark-gluon plasma Heavy flavours (charm and beauty quarks) because of their large masses are mainly produced in hard-scattering processes ➡ Production time of cc(bb) pair at rest tprod ≃ ℎ/4mc(b) ≃ 0.05(0.01) fm/c ➡ QGP formation time tQGP ≃ 0.1-1 fm/c HF probe the entire space-time evolution of the system, interacting with the medium constituents via ➡ elastic scatterings ➡ gluon radiation Observables: 1 dNAA /dpT ➡ Nuclear modification factor RAA = ⟨TAA⟩ dσpp/dpT (I) Density and path-length dependence of energy loss (II) Colour-charge and quark-mass dependence of energy loss (III) Modification in the hadronisation mechanism in presence of a medium (quark coalescence) ➡Azimuthal anisotropies 02/10/2018 Hard Probes - Fabrizio Grosa 2/19 Elliptic flow and event-shape engineering d3N 1 d2N ∞ E = 1 + v cos[n(φ − Ψ )] { ∑ n n } dpT 2π pTdpTdy i=1 second harmonic v = ⟨cos[2(φ − Ψ )]⟩ 2 2 coefficient, elliptic flow y � A A z x Reaction plane Ψ2 Asymmetry between the in-plane (parallel to Ψ2) and out-of plane (orthogonal to Ψ2) regions At low pT: participation in the collective motion and thermalisation of heavy quarks in the medium At high pT: path-length dependence of energy loss 02/10/2018 Hard Probes - Fabrizio Grosa 3/19 Elliptic flow and event-shape engineering d3N 1 d2N ∞ E = 1 + v cos[n(φ − Ψ )] { ∑ n n } Event-shape engineering dpT 2π pTdpTdy i=1 technique that allows us to second harmonic v2 = ⟨cos[2(φ − Ψ2)]⟩ study various observables in coefficient, classes of events corresponding elliptic flow to the same centrality, but y different eccentricity � 0.3 ALICE A |>1} η 30-40% Pb-Pb sNN = 2.76 TeV A z x ∆ 0.2 0.5<|η|<0.8 {SP, | 2 0.1 v Reaction plane Ψ2 0 1.5 Unbiased Asymmetry between the in-plane (parallel to 10% large-qV0C 10% small-qV0C 2 2 (unbiased) 1 (ESE-selected) >1} 35% large-qTPC 55% small-qTPC Ψ2) and out-of plane (orthogonal to Ψ2) η 2 2 >1} ∆ η ∆ qTPC (70% rej.) qTPC (70% rej.) 0.5 2 2 regions {SP, 2 {SP, v 2 0 5 10 At low pT: participation in the collective v p (GeV/c) T motion and thermalisation of heavy quarks in ALI−PUB−95339 the medium PRC 93, 034916 (2016) At high pT: path-length dependence of energy loss 02/10/2018 Hard Probes - Fabrizio Grosa 3/19 Charge-dependent directed flow d3N 1 d2N ∞ E = 1 + ∑ vn cos[n(φ − Ψn)] Originated by two competing dpT 2π pTdpTdy { } i=1 effects: first harmonic v1 = ⟨cos(φ − Ψ1)⟩ coefficient, B ⃗ directed flow F ⃗ x z ➡ y Faraday effect Electric field � induced by A A z x decreasing B ⃗ F ⃗ Reaction plane Ψ1 B ⃗ x Asymmetry between the same and opposite z ➡ Hall effect impact-parameter direction v ⃗ Lorentz force Charge-dependent v1 can be used to study F ⃗ F ⃗ induced by the magnetic field created in heavy-ion moving charges collisions F ⃗ = q v ⃗ × B ⃗ 02/10/2018 Hard Probes - Fabrizio Grosa 4/19 Charge-dependent directed flow d3N 1 d2N ∞ E = 1 + v cos[n(φ − Ψ )] Charm quark is an ideal probe { ∑ n n } dpT 2π pTdpTdy i=1 ➡ formation time is comparable to first harmonic the time scale when the magnetic v1 = ⟨cos(φ − Ψ1)⟩ coefficient, field reaches its maximum value directed flow ➡ relaxation time is similar to the y QGP lifetime ➡ expected larger effect compared � to light hadrons A A z x Reaction plane Ψ1 Asymmetry between the same and opposite impact-parameter direction Charge-dependent v1 can be used to study the magnetic field created in heavy-ion collisions K. Das et all, PLB 768 (2017) 260-264 02/10/2018 Hard Probes - Fabrizio Grosa 4/19 The ALICE experiment Time Projection Inner Tracking Chamber System Track reconstruction Track Particle identification reconstruction via specific energy loss Primary and decay vertices reconstruction Time of Flight detector Particle identification via the time- of-flight measurement 02/10/2018 Hard Probes - Fabrizio Grosa 5/19 The ALICE experiment Time Projection Inner Tracking Chamber System Track reconstruction Track Particle identification reconstruction via specific energy loss ZDC detectors Primary and Spectator-plane estimation decay vertices reconstruction Time of Flight detector Particle identification V0 detectors via the time- Trigger of-flight Centrality estimation measurement Event-plane estimation 02/10/2018 Hard Probes - Fabrizio Grosa 5/19 The ALICE experiment Time Projection Inner Tracking Chamber System Track reconstruction Track Particle identification reconstruction via specific energy loss ZDC detectors Primary and Spectator-plane estimation decay vertices reconstruction Data sample ~108 Pb-Pb MB collisions √s = 5.02 TeV Time of Flight NN ℒ -1 detector int ≈ 13 �b Particle identification V0 detectors via the time- Trigger of-flight Centrality estimation measurement Event-plane estimation 02/10/2018 Hard Probes - Fabrizio Grosa 5/19 D-meson reconstruction Meson Mass (GeV/c2) decay channel c� (µm) BR (%)[1] [1] �+ K+ D0 (cu)- 1.865 K-�+ 123 3.93 SV p - �p D D+ (cd) 1.870 K-�+�+ 312 9.46 - + D*+ (cd) 2.010 D0 (→ K-�+) �+ strong decay 2.66 Ds PV K- Ds+ (cs)- 1.968 φ (→ K-K+) �+ 150 2.27 ×106 ×103 ) 0.8 ) 2 2 6 0 - + 2 c ALICE c D → K π µ = 1868 ± 2 MeV/c 0.7 5 and charge conj. σ = 12 MeV/c2 0-10% Pb−Pb, sNN = 5.02 TeV Full reconstruction of decay topologies 4 1 < p < 2 GeV/c S = 14044 ± 1939 0.6 µ = 1868 ± 2 MeV/c2 T 3 σ = 12 MeV/c2 displaced few hundred microns from the 0.5 S = 14044 ± 1939 2 0 - + 1 Counts / (8 MeV/ 0.4 D → K π interaction vertex and charge conj. 0 0.3 1 < p < 2 GeV/c −1 T 1.75 1.8 1.85 1.9 1.95 2 −2 1.75 1.8 1.85 1.9 1.95 2 Counts - bkg fct. / (8 MeV/ Reduction of the combinatorial M(Kπ) (GeV/c 2) M(Kπ) (GeV/c 2) ×103 ) ) 2 + - + + 2 2 *+ 0 + - + + 2 background achieved applying: c 1.4 D → K π π µ = 1871 ± 1 MeV/c c 70 D → D π → K π π µ = 145.6 ± 0.2 MeV/c 2 2 and charge conj. σ = 17 ± 1 MeV/c 60 and charge conj. σ = 0.9 ± 0.2 MeV/c ➡ 1.2 8 < p < 10 GeV/c S = 1158 ± 89 24 < p < 36 GeV/c S = 73 ± 17 geometrical selection of T 50 T 1 40 displaced decay-vertex topology 0.8 30 20 Counts / (14 MeV/ 0.6 Counts / (0.8 MeV/ ➡ particle identification (PID) of 10 0.4 0 1.75 1.8 1.85 1.9 1.95 2 0.14 0.142 0.144 0.146 0.148 0.15 0.152 0.154 decay tracks M(K ππ ) (GeV/c 2) M(K ππ ) - M(Kπ) (GeV/c 2) ) 350 ) 30 2 + + - + + 2 2 + + - + + 2 c Ds → πφ → K K π µ = 1968 ± 3 MeV/c c Ds → πφ → K K π µ = 1969 ± 3 MeV/c 2 2 Signal extracted from invariant-mass 300 and charge conj. σ = 11 ± 2 MeV/c 25 and charge conj. σ = 17 ± 3 MeV/c 4 < p < 6 GeV/c S = 161 ± 34 12 < p < 16 GeV/c S = 44 ± 9 T 20 T 250 D+ D+ analysis s 15 + + Ds 200 D 10 Feed-down from b-hadrons subtracted Counts / (10 MeV/ Counts / (14 MeV/ 150 5 100 0 with a FONLL-based method [2] 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 ALI−PUB−145151 M(KKπ) (GeV/c 2) M(KKπ) (GeV/c 2) [1] PDG, Chin. Phys. C40 (2016) 100001 [2] Cacciari et al., JHEP 1210 (2012) 137 arXiv:1804.09083 02/10/2018 Hard Probes - Fabrizio Grosa 6/19 D-meson RAA 2.2 AA ALICE R 2 − Pb Pb, sNN = 5.02 TeV 1.8 Average D0, D+, D*+, |y|<0.5 1.6 − 1.4 0 10% 30−50% 1.2 60−80% 1 0.8 0.6 0.4 0.2 Filled markers: pp rescaled reference Open markers: pp p -extrapolated reference T 0 0 5 10 15 20 25 30 35 40 45 50 p (GeV/c) ALI−DER−147453 T arXiv:1804.09083 Increasing suppression from peripheral (60-80%) to central (0-10%) Pb-Pb collisions 02/10/2018 Hard Probes - Fabrizio Grosa 7/19 D-meson RAA 2.76 TeV 5.02 TeV 2.2 2.2 AA ALICE AA ALICE Pb-Pb 0-10% R 2 R 2 Pb−Pb, s = 5.02 TeV NN 0 + + 1.8 Average D0, D+, D*+, |y|<0.5 1.8 Average D , D , D* , |y |<0.5 sNN = 5.02 TeV 1.6 1.6 sNN = 2.76 TeV, JHEP 03 (2016) 081 0−10% Djordjevic 1.4 1.4 s =5.02 TeV 30−50% NN s =2.76 TeV 1.2 60−80% 1.2 NN 1 1 Filled markers: pp rescaled reference Open markers: pp p -extrapolated reference 0.8 0.8 T 0.6 0.6 0.4 0.4 0.2 Filled markers: pp rescaled reference 0.2 Open markers: pp p -extrapolated reference T 0 0 0 5 10 15 20 25 30 35 40 45 50 0 5 10 15 20 25 30 35 40 45 50 p (GeV/c) p (GeV/c) ALI−DER−147453 T ALI−PUB−145244 T arXiv:1804.09083 Increasing suppression from Similar suppression at √sNN = 5.02 TeV compared peripheral (60-80%) to central to 2.76 TeV can be explained by a counterbalance (0-10%) Pb-Pb collisions between an increased medium temperature/ density and harder D-meson spectra [1] [1] Djordevic: PRC 92, 024918 (2015) 02/10/2018 Hard Probes - Fabrizio Grosa 7/19 D-meson RAA vs.