Rencontres QGP France 2019 Production of the D s± meson in proton-proton collisions at 13 TeV as a function of multiplicity Arthur Gal University of Strasbourg Institut Pluridisciplinaire Hubert Curien
Outline Part I : Physics motivations → Small systems versus heavy ion → What are the interests in proton-proton at high multiplicity ? → Heavy fm avour production as a function of multiplicity in proton-proton collisions Part II : Presentation of my current analysis work → ALICE detector → Extraction of the D s production yield → Production yield as a function of the event multiplicity in pp collisions
Three main collision systems : pp, p-Pb and Pb-Pb → small systems : pp, p-Pb At LHC, three main collision systems available → heavy ion : Pb-Pb Proton-proton Pb-Pb 0 Pre- equilibrium 0.5 - 1 → quasi-perfect fm uid QGP phase → hydrodynamic description → kinematically and chemically 7 equilibrated → interplay between hard and soft QCD processes → statistical physics principles - hard scattering - multi parton interaction 10 - fragmentation of beam remnants chemical freeze-out - initial and fj nal state radiation kinetic → relative contributions of these processes freeze-out 20 spatial distributions of hard partons ( x ≥ 10 -3 ) Hadronic gaz fm/ c 3 (10 -24 s)
<latexit sha1_base64="YPk8F2Pi3q3ysyEHF0vKbajTjA=">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</latexit> Proton-proton collision system Why studying proton-proton ? •Historically pp is a reference system → test of the QCD → no QGP in pp ⇒ reference for p-A and AA systems •Recently typical e fg ect of heavy-ion phenomenology has been observed in pp high multiplicity → two-particle angular correlations ⇒ ridge observed ( ∆ 휙 ≃ 0, | ∆ 휂 | > 2 ) 10.1007/JHEP09(2010)091 10.1016/j.physletb.2016.12.009 → azimuthal anisotropy harmonics ⇒ “elliptic fm ow” harmonic v 2 1 dN pair X Expansion in Fourier series : 1 + 2 V n ∆ cos ( n ∆ φ ) α N trig d ∆ φ n 4
Proton-proton collision system → strangeness enhancement ⇒ originally proposed as a QGP signature ) − π + p+ p ( × 6) + π Ratio of yields to ( 0 2K S − 1 10 Λ + Λ 2 φ ( × 2) + − Ξ + Ξ ( × 3) − 2 + 10 − Ω + Ω ( × 12) ALICE Preliminary ALICE pp, s = 13 TeV pp, s = 7 TeV Pb-Pb, s = 5.02 TeV NN p-Pb, s = 5.02 TeV Xe-Xe, s = 5.44 TeV NN NN − 3 10 2 3 4 10 10 10 10 10.1038/nphys4111 ALI-PUB-106886 〈 d N /d η 〉 ch | η |< 0.5 ALI − PREL − 159147 훺 (s s s) m ≃ 1.7 GeV/ c 2 → continuity between 훯 (d s s) m ≃ 1.3 GeV/ c 2 strangeness pp, pPb and PbPb content 훬 (u d s) m ≃ 1.1 GeV/ c 2 K 0s (d s) m ≃ 0.5 GeV/ c 2 → enhancement increases with strangeness content rather than with mass or baryon number → similar to the patterns seen in p–Pb and Pb–Pb collisions at the LHC → behaviour not reproduced by any of the MC models commonly used 5
Heavy fm avour quarks to heavy fm avour hadrons H eavy fm avour quarks : m c ≃ 1.3 GeV/ c 2 , m b ≃ 4.2 GeV/ c 2 >> Λ QCD ≃ 0.2 GeV •Produced in hard scattering processes (high Q 2 ) → possible perturbative QCD calculation of the production cross section down to low p T → di fg erent heavy quarks ⇒ di fg erent Q 2 probed •Fragmentation process in “PYTHIA”-like Monte Carlo models → non perturbative process → fragmentation model (Lund string model) → colour rope : string close in space can interact and form ropes → colour reconnection : colour connections between partons in the fj nal state coming from di fg erent hard scattering processes ⇒ hadron production is a fg ected by the whole system evolution H eavy fm avour hadrons open heavy fm avours : c → D 0 , D ± , D s ± , D * ± , Λ c ± … b → B 0 , B ± , B s ± … hidden heavy fm avours : c → J/ Ψ , Ψ (2S) … b → γ (1S, 2S, 3S) … 6
Heavy fm avour as a function of multiplicity in proton-proton collision ALICE paper pp 7 TeV (10.1007/JHEP09(2015)148) 25 25 〉 〉 〉 T T T 20 20 ALICE, pp s = 7 TeV ALICE, pp s = 7 TeV ALICE p p p Percolation, p >0 d d d T 0 + + 0 + + pp s = 7 TeV Average D , D , D* meson | y |<0.5, 2< p <4 GeV/ c Average D , D , D* meson | y |<0.5, 2< p <4 GeV/ c 18 18 EPOS 3.099 y y y T T - - D meson /d + /d + Prompt J/ ψ → e e , | y |<0.9, p >0 Non-prompt J/ ψ → e e , | y |<0.9, p >0 /d 20 20 EPOS 3.099 + Hydro T T 16 16 N N N B feed-down and normalization PYTHIA 8.157 2 2 uncertainties not shown 2 d d 14 14 d 〈 〈 〈 ) / ) / 15 15 ) / 12 12 T T T p p 10 10 p d d d y y 10 10 y 8 8 /d /d /d N N 6 6 N 2 2 (d (d 2 (d 4 4 5 5 2 2 1 < p < 2 GeV/ c 2 < p < 4 GeV/ c +6%/-3% normalization unc. not shown +6%/-3% normalization unc. not shown T T ± 6% unc. on (d N /d η ) / 〈 d N /d η 〉 not shown ± 6% unc. on (d N /d η ) / 〈 d N /d η 〉 not shown 〉 B feed-down unc. B feed-down unc. T 20 20 0.4 0.4 B fraction hypothesis: × 1/2 (2) at low (high) multiplicity B fraction hypothesis: × 1/2 (2) at low (high) multiplicity p d 0.2 0.2 18 18 y 0 0 /d 16 16 0.2 0.2 − − N 14 14 − 0.4 − 0.4 2 d 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 〈 12 12 ) / (d N /d η ) / 〈 d N /d η 〉 (d N /d η ) / 〈 d N /d η 〉 ch ch ch ch ALI − PUB − 95849 ALI − PUB − 92971 10 10 T p d 8 8 y /d 6 6 N 4 4 2 → open vs hidden heavy fm avour production (d 2 2 4 < p < 8 GeV/ c 8 < p < 12 GeV/ c T T ⇒ the behaviour is most likely related to cc and bb production 0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 (d N /d η ) / 〈 d N /d η 〉 (d N /d η ) / 〈 d N /d η 〉 ⇒ not signi fj cantly in fm uenced by hadronisation ch ch ch ch ALI − PUB − 92985 → heavy- fm avour relative yield enhancement qualitatively described by : - PYTHIA 8.157 calculations including the MPI contributions to particle production - percolation model (exchange of colour sources between the projectiles) - EPOS 3 event generator 7
D s meson Motivation D s meson measurement → D s composed by a charm and a strange quark ⇒ study strangeness enhancement in conjunction with charm production → reach the overlap between pp and pPb, PbPb on the heavy fm avour side + + + / D / D / D 6 < < 8 GeV/ 2 < p < 4 GeV/ c 4 < p < 6 GeV/ c p c T T T + s + s + s D D D 1 1 1 0.5 0.5 0.5 → within uncertainties, di ffj cult to argue for a + yield ratios modi fj cation of the D s /D + 3 + 3 3 2 2 2 10 10 10 in pp and p–Pb collisions / D 10 10 10 / D 10 10 10 8 < p < 12 GeV/ c 12 < p < 16 GeV/ c 〈 d N /d η 〉 〈 d N /d η 〉 〈 d N /d η 〉 T T + ch + | η |<0.5 ch | η |<0.5 ch | η |<0.5 s s D D 1 1 ALICE Preliminary pp Minimum Bias, s = 5.02 TeV p − Pb, s = 5.02 TeV NN SPD multiplicity classes 0.5 0.5 Pb − Pb, s = 5.02 TeV NN arXiv:1804.09083 V0 multiplicity classes 4.3% BR uncertainty not shown ± 3 3 2 2 10 10 10 10 10 10 〈 d N /d η 〉 〈 d N /d η 〉 ALI − PREL − 149859 ch | η |<0.5 ch | η |<0.5 Goal of my current work ALICE paper pPb 5.02 TeV (arXiv:1906.03425) ⇒ complete the picture ⇒ D s analysis as a function of multiplicity in pp ⇒ using the high statistics available in pp at √ s = 13 TeV 8
Outline Part I : Physics motivations → Small systems versus heavy ion → What is are the interests in proton-proton at high multiplicity ? → Heavy fm avour production as a function of multiplicity in proton-proton collisions Part II : Presentation of my current analysis work → ALICE detector → Extraction of the D s production yield → Production yield as a function of the event multiplicity in pp collisions
ALICE detector Inner Tracking System 26 x 16m Time Projection 10 000 tons Chamber Time Of Flight V0 (trigger, centrality, multiplicity) Key roles •Particle trajectories reconstruction 0.1 < p T < 50 - 80 GeV/ c Particularities •Momentum measurement •“low” material budget (12-13% X 0 , ITS+TPC) •Vertex reconstruction •“low” B fj eld ( ∼ 0.5 T) •Particle identi fj cation •identi fj ed particles down to p T ∼ 100 MeV/c 10
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