D + s production at central rapidity with the ALICE detector

Transcription

1 D s production at central rapidity with the ALICE detector Graduate School in Physics and Astrophysics XXVI Cycle Gian Michele Innocenti Supervisors: Prof. M. Masera, Dott. F. Prino Gian Michele Innocenti - urin University 1

2 Overview of the talk Introduction to the physics of Quark Gluon Plasma ALICE detector D s meson reconstruction strategy in ALICE proton-proton analysis at 7 ev Pb-Pb analysis at 2.76 ev Prospects in view of the ALICE upgrade Conclusions Gian Michele Innocenti - urin University 2

3 Why Heavy-Ions? Under extreme conditions of density and temperature nuclear matter is expected to undergo a phase transition towards the Quark Gluon Plasma. C 17 MeV QGP is a soup of deconfined quarks and gluons Ultra-relativistic heavy-ion collisions used to reproduce these conditions: emperature of the fireball of 1 12 K Similar to at the very early stages of Universe (1-5 s) after Big Bang! Gian Michele Innocenti - urin University 3

4 Space-ime evolution of the collision Pre-equilibrium: large number of hard scatterings between partons of the two nuclei re-scattering between low momentum partons in the medium which lead to thermal equilibrium QGP: >C. At this stage, partons strongly interact with the medium and can lose energy via radiative mechanisms Hadronization: As fireball expands, temperature decreases and <C Chemical freeze-out: particle composition is fixed hermal freeze-out: momentum spectra are fixed Gian Michele Innocenti - urin University 4

5 Charm production as a probe of QGP Charm quarks produced in hard scatterings (described by pqcd) in the early stages of the collisions: Experience the full evolution of the medium Interact strongly with the medium energy loss <ΔE> Radiative component of Eloss modeled as: < E>/ s C R ˆqL 2 s is the QCD coupling constant L is the distance in the medium CR is the Casimir factor ˆq is the trasport coefficient which is proportional to the density of the medium hrough the study of the energy loss we gather information on the properties of the medium created in the collisions Gian Michele Innocenti - urin University 5

6 Phenomenology of heavy-ion collisions A heavy-ion collisions can be described as a simple superposition of independent nucleon-nucleon collisions (Glauber model). Peripheral collisions: Small overlap region, large impact parameters b Small number of nucleon-nucleon collisions <Ncoll> Central collisions: Large overlap region, small impact parameters b Large number of nucleon-nucleon collisions <Ncoll> Gian Michele Innocenti - urin University 6

7 How to estimate the energy loss? he effect of charm energy loss can be estimated via the nuclear modification factor RAA of charmed mesons (D mesons) dn/dp is the distribution of reconstructed D meson as a function of the transverse momentum p In absence of in-medium effect RAA=1 In presence of in-medium energy loss p spectra in Pb-Pb shifted at low p RAA<1 At low p effects due to the modification of the PDF are expected Gian Michele Innocenti - urin University 7

8 Strange charmed mesons and recombination Mechanism of hadronization Recombination: Low p partons in the mediums combined to form a higher p hadron. Fragmentation: high p partons fragment in hadrons with lower p he medium created in heavy-ion collisions presents an enhanced number of strange quark More strange quarks means more D s mesons if recombination plays a role in charm hadronization RAA of D s larger than the RAA of nonstrange D mesons Gian Michele Innocenti - urin University 8

9 Why proton-proton physics is interesting by itself? Measurement of D meson cross section in pp is a fundamental test for the theoretical models which describe hard processes using the factorization approach σhh Hx = PDF(xa,Q 2 ) PDF(xb,Q 2 ) σab Hx Dq H(zq,Q 2 ) Cross section in hadronic collisions Parton distribution function: xi fraction of the momentum of the hadron carried by the parton i partonic cross section Fragmentation function of the quark q in the hadron H he partonic cross-section can be calculated using pqcd PDFs and fragmentation functions are extrapolated from data since related to non perturbative processes Gian Michele Innocenti - urin University 9

10 Heavy-ion collisions: A huge mess! In Pb-Pb collision, a huge amount of particles is created! Let s try to understand what we want to do! Reconstruct the trajectories of all the particles created in the collisions and their species (Pions, Kaons..) Identify the position of the interaction (primary vertex) Reconstruct the topologies of the decays of particles: Ex. Ds K K - π We need an accurate vertex and track reconstruction to separate the primary vertex from the decay vertices (separation between the two vertices few hundreds μm) Precise measurement of particle yield, invariant mass, energy... Gian Michele Innocenti - urin University 1

11 A Large Ion Collider Experiment at the LHC ALICE is the only LHC experiment designed specifically to study heavy-ion collisions: Excellent tracking performances in a very high multiplicity environment Accurate Particle Identification (PID) Precise vertex reconstruction Gian Michele Innocenti - urin University 11

12 Some more details Inner racking System: 6 layers of Silicon Detectors close to the beam: Interaction point determination (vertex) Reconstruction trajectory of particles (tracks) ime Projection Chamber (PC) Cylindrical chamber filled with gas mixture Main tracking detector Particle identification of pion, kaon, proton via energy loss ime-of-flight (OF): Particle identification of pion, kaon, proton via the measurement of the time of fight Gian Michele Innocenti - urin University 12

13 A key word in ALICE: Particle identification PID is a crucial feature of ALICE It allows to identify the particle species using: - momentum of particle provided by tracking detectors - PID detectors which give e.g. the energy deposit of a particle in a material (Bethe-Bloch) or ime of Flight Why is it useful? In our analysis, it allows to reject Ds which do not present the expect particle species in the final state Huge reduction of the background Gian Michele Innocenti - urin University 13

14 How to build a D s candidate? D s decay length point p (D ) s cτ = 15 μm BR = 2.28% K - K Identification of all the possible triplets of tracks that can be decay products of Ds Φπ K K - π Some of them are signal events= products of a real Ds decay Some of them are background events = due å to the combination of tracks not coming from a Ds decay o reject background events: PID selection selection on the topology of the decay (decay length, invariant mass of the decay resonance Φ,etc.) E.g. signal events characterized by larger values of decay length w.r.t to backgroud events Gian Michele Innocenti - urin University 14

15 How to extract the signal? We fill histograms with the invariant mass of the D s candidates Histogram is fitted with a sum of: - a gaussian shape for the signal S - an exponential shape for the background B he signal yield is the integral of the gaussian shape GOAL is to tune the topological selection to enlarge the statistical significance of the peak S/ SB Why? High significance means small uncertainties in the extracted yield! Gian Michele Innocenti - urin University 15

16 Cut optimization Cut tuning performed varying the parameters of the topological selection to enlarge the statistical significance Significance wrt coshetapoint vs inv. mass (Mphi-MKK) [GeV] (Ptbin2 6.<pt<8.) With some caveats... Selection efficiency not too small to avoid too big correction Signal stable w.r.t cut variation inv. mass (Mphi-MKK) [GeV] Mean of the signal shape compatible with the PDG values Width of the signal shape compatible with Monte Carlo simulations coshetapoint Gian Michele Innocenti - urin University 16

17 How to correct the yield? Acceptance and selection efficiency: Not possible to reconstruct all the D s A large fraction of D s mesons not reconstructed because: Out of the detector acceptance Rejected by the topological PID selection How to correct? Acceptance Efficiency Physics Letters B 718 (212) pp, s = 7 ev Prompt Ds D meson selection acceptance efficiencies estimated with Monte Carlo simulations which include a realistic description of our detector 1-3 Prompt D (GeV/c) s p, No PID Gian Michele Innocenti - urin University 17

18 How to correct the yield? GOAL: measure the production of D s originated from the hadronization of a charm quark (called prompt) c quark D meson KKπ But some of our D s come from a b-quark decays b quark B meson D meson KKπ We have to correct our yield for this contribution... and finally! Gian Michele Innocenti - urin University 18

19 How to correct the yield? GOAL: measure the production of D s originated from the hadronization of a charm quark (called prompt) c quark D meson KKπ But some of our D s come from a b-quark decays b quark B meson D meson KKπ We have to correct our yield for this contribution... and finally! Gian Michele Innocenti - urin University 18

20 pp results at 7 ev Gian Michele Innocenti - urin University 19

21 Ds ± signal in pp collisions Analysis performed on the 21 pp sample at 7 ev 3 x1 8 minimum bias events corresponding to an integrated luminosity of 4.8 nb -1 Entries / 8 MeV/c 2 Entries / 8 MeV/c 2 25 pp, s=7 ev 2 < p < 4 GeV/c D s K K and charge conj. µ = ±.3 GeV/c 2 =.8 ±.2 GeV/c S (3 ) 125 ± Invariant Mass KK (GeV/c 2 ) Entries / 1 MeV/c 2 Physics Letters B 718 (212) 6 < p < 8 GeV/c µ = ±.2 GeV/c 2 =.1 ±.3 GeV/c S (3 ) 79 ± 19 2 Entries / 8 MeV/c < p < 6 GeV/c µ = ±.2 GeV/c 2 =.12 ±.2 GeV/c S (3 ) 189 ± Invariant Mass KK (GeV/c 8 < p 2 < 12 GeV/c µ = ±.3 GeV/c 2 =.14 ±.3 GeV/c S (3 ) 85 ± 16 2 ) ALI PUB Invariant Mass KK (GeV/c ) Invariant Mass KK (GeV/c Invariant mass distributions of Ds ± candidates in 4 p intervals from 2 to 12 GeV/c fitted with a Gaussian function (signal) exponential (background) Gian Michele Innocenti - urin University ) 2

22 D s p-differential cross section in pp at 7 ev p-differential cross section for prompt Ds mesons Integrated luminosity of 4.8 nb -1 Compared to two theoretical models based on the factorization approach Physics Letters B 718 (212) Gian Michele Innocenti - urin University 21

23 D s p-differential cross section in pp at 7 ev c ) -1 ( µb GeV y < ALICE, pp D s, D = 7 ev, D D s * JHEP 1 (212) 128 arxiv D D D D * s (L (L (L (L int int int int -1 = 5. nb ) ( -1 = 5. nb ) -1 = 5. nb ) -1 = 4.8 nb ) 5) p-differential cross section for prompt Ds mesons Integrated luminosity of 4.8 nb -1 Compared D, D and to D * two p-differential theoretical cross models section based also on the measured factorization at approach the same energy d / dp I DER 4253 syst. unc. ± 3.5 % global norm. unc. (not shown) p (GeV/c) Physics Letters B 718 (212) Gian Michele Innocenti - urin University 21

24 D meson ratios in proton-proton collisions at 7 ev /D D ALICE Syst. unc. /D * D FONLL GM-VFNS PYHIA 6.4, Perugia p (GeV/c) p (GeV/c) D s /D.6.5 /D D s p (GeV/c) p (GeV/c) Ratios between the p-differential cross section of D mesons measured by ALICE compared with the predictions of pqcd calculations Gian Michele Innocenti - urin University 22

25 Pb-Pb results at 2.76 ev Gian Michele Innocenti - urin University 23

26 Ds ± signal in central Pb-Pb collisions Analysis performed on the 211 Pb-Pb sample at 2.76 ev 1.6 x1 7 events in the -7.5 % centrality range corresponding to an integrated luminosity of 28 μb -1 REMINDER: -7.5 % means very central events, high overlap within the two nuclei 2 Entries / 8 MeV/c Pb-Pb D 6 s NN = 2.76 ev, 16 x 1 s - φ π K K π Centrality -7.5 % 4 < p events (D s ) < 6 GeV/c 2 Entries / 8 MeV/c < p (D s ) < 8 GeV/c 2 Entries / 1 MeV/c < p (D s ) < 12 GeV/c 24/7/ Significance (3σ) 4. ± 1. S (3σ) 483 ± 123 B (3σ) ± 32 S/B (3σ).35 Mean = ±.2 Sigma =.7 ± Invariant mass KKπ (GeV/c ALI PERF ) Significance (3σ) 3.3 ±.9 S (3σ) 19 ± 32 B (3σ) 971 ± 9 S/B (3σ).1128 Mean = ±.3 Sigma =.8 ± Invariant mass KKπ (GeV/c 2 ) Significance (3σ) 4.2 ±.9 Mean = ±.4 S (3σ) 86 ± 22 1 B (3σ) 342 ± 7 Sigma =.16 ±.4 S/B (3σ) Invariant mass KKπ (GeV/c ) Invariant mass distributions of Ds ± candidates in 3 p intervals from 4 to 12 GeV/c Gian Michele Innocenti - urin University 24

27 Non-strange D meson, RAA D Let s start with the RAA of a non-strange D meson (D also measured in ALICE) not sensitive to the recombination of charm with the strange quarks. What can we learn? REMINDER: RAA=1 in absence of interaction with medium We observe a RAA=.25 at high p. his can be explained with a strong energy loss of the charm! Very interesting indication of a strongly interacting medium! Gian Michele Innocenti - urin University 25

28 Let s add the D s! What do we see? At high p the suppression is also strong RAA.25 D s RAA seems to be larger at lower pt but not possible to conclude within the present uncertainties o conclude on a possible enhancement due to charm recombination we need more pp and Pb-Pb LHC runs! Gian Michele Innocenti - urin University 26

29 Comparison with models prompt D R AA Pb-Pb, s NN = 2.76 ev *, D, D -7.5%, y <.5 Average D D s -7.5%, y <.5 Filled markers : pp rescaled reference Open markers: pp p -extrapolated reference AMU, arxiv: D D s RAA of Ds and average of non-strange D meson compared to the predictions of a theoretical model which includes: - in-medium energy loss - recombination of charm quark in the medium D s RAA measured by ALICE is well described by the theoretical models within the (large) uncertainties p (GeV/c) Gian Michele Innocenti - urin University 27

30 ALICE upgrade ALICE collaboration is working on a challenging plan to improve the capability of our detector (scheduled for LHC long shut down ) New pixel technologies are under study to build an upgraded IS with reduced material budget and improved read-out rate Upgraded PC will be equipped with a new readout electronics and new gas mixture Improved resolution Possibility to enlarge the ALICE read-out rate by a factor > 1! Gian Michele Innocenti - urin University 28

31 Studies of D s for the ALICE upgrade RAA of Ds considered a promising physics case in view of the ALICE upgrade Effect of the increased luminosity In the highest luminosity scenario the statistical significance will be 5-7 with p bins of 1 GeV/c statistical uncertainties < 2 %! Gian Michele Innocenti - urin University 29

32 fhistoinvmasscurrent Studies of D s for the ALICE upgrade RAA of Ds considered a promising physics case in view of the ALICE upgrade Effect of the increased luminosity Effect of the improved IS resolution hmass Entries 3461 Mean RMS Entries / 6 MeV/c HIJING Pb-Pb at s NN =5.5 ev 5 ± 2 x 1 events enriched with Ds signals - D K K s Current IS Significance (3 ) = 6.6 ± 1. S/B (3 ) =.65 In the highest luminosity scenario the statistical significance will be 5-7 with p bins of 1 GeV/c Upgraded IS Significance (3 ) = 16.2 ± S/B (3 ) = < p t < 3 GeV/c Invariant Mass KK (GeV/c ) statistical uncertainties < 2 %! Strong reduction of the background at low p Gian Michele Innocenti - urin University 29

33 fhistoinvmasscurrent Studies of D s for the ALICE upgrade RAA of Ds considered a promising physics case in view of the ALICE upgrade Effect of the increased luminosity Effect of the improved IS resolution hmass Entries 3461 Mean RMS.644 In the highest luminosity scenario the statistical significance will be 5-7 with p bins of 1 GeV/c statistical uncertainties < 2 %! 2 Ratio Upgraded Entries / Current / 6 MeV/c IS HIJING Pb-Pb at s NN =5.5 ev HIJING 5 ± 2 x 1 Pb-Pb events at enriched s - NN =5.5 with ev, D centrality s signals -1 % D - s K K s Upgraded IS Significance (3 ) = 16.2 ± S/B (3 ) =.435 Current IS Significance (3 ) = 6.6 ± 1. S/B S/B (3 ) =.65 Significance / Invariant Mass KK 2 p (GeV/c) (GeV/c ) Strong Relevant reduction improvement of the of background significance at and low S/B p at low p.9 2 < p t < 3 GeV/c t N ev Gian Michele Innocenti - urin University 29

34 fhistoinvmasscurrent Studies of D s for the ALICE upgrade RAA of Ds considered a promising physics case in view of the ALICE upgrade Effect of the increased luminosity Effect of the improved IS resolution hmass Entries 3461 Mean RMS.644 In the highest luminosity scenario the statistical significance will be 5-7 with p bins of 1 GeV/c statistical uncertainties < 2 %! Invariant Mass KK 2 p (GeV/c) (GeV/c ) Strong Relevant reduction improvement of the of background significance at and low S/B p at low p Possibility to reduce strongly the uncertainties on the RAA measurement and to extend the measurement in the low p region 2 Ratio Upgraded Entries / Current / 6 MeV/c IS HIJING Pb-Pb at s NN =5.5 ev HIJING 5 ± 2 x 1 Pb-Pb events at enriched s - NN =5.5 with ev, D centrality s signals -1 % D - s K K s Upgraded IS Significance (3 ) = 16.2 ± S/B (3 ) =.435 Current IS Significance (3 ) = 6.6 ± 1. S/B S/B (3 ) =.65 Significance /.9 2 < p t < 3 GeV/c t N ev Gian Michele Innocenti - urin University 29

35 Summary and Conclusions Ds meson reconstruction in ALICE Strategy for yield extraction, efficiency correction and subtraction of the contribution of D s from B meson decay Measurement of p-differential cross section in pp collisions at 7 ev First measurement of D s RAA in heavy-ion collisions with Pb-Pb at 2.76 ev Prospect for the D s analysis in view of the ALICE upgrade Gian Michele Innocenti - urin University 3

36 Summary and Conclusions Ds meson reconstruction in ALICE Strategy for yield extraction, efficiency correction and subtraction of the contribution of D s from B meson decay Measurement of p-differential cross section in pp collisions at 7 ev First measurement of D s RAA in heavy-ion collisions with Pb-Pb at 2.76 ev Prospect for the D s analysis in view of the ALICE upgrade HANK YOU FOR YOUR AENION! Gian Michele Innocenti - urin University 3

37 Other tasks I am currently INFN fellow at CERN (From July 212-July 213) Detector I was involved as On call expert in the maintenance of the Silicon Drift Detector from July 212 to present during the pp runs at 8 ev and the pa runs at 5 ev. I will continue my contribution in the SDD project during the LHC Shut Down Contribution to other analyses I worked in the Pb-Pb task force in the centrality determination of Pb-Pb events I am actually involved in the group which defines the centrality determination strategy for pa collisions collected in January-February 213 Gian Michele Innocenti - urin University 31

38 PCs and alks Paper Committees: D s meson production at central rapidity in proton-proton collisions at s = 7 ev, Physics Letters B 718 (212), pp alks in conferences with proceedings: D meson production at central rapidity in pp collisions at 7 ev with the ALICE detector Strangeness in Quark Matter 211, Cracow (Poland) D s production at central rapidity in Pb-Pb collisions at snn = 2.76 ev with the ALICE detector Quark Matter 212, Washington DC (USA) D s production in pp and Pb-Pb collisions at snn = 2.76 ev with ALICE Hot Quarks 212, Puerto Rico (USA) Gian Michele Innocenti - urin University 32

39 Posters Posters in conferences with proceedings: D s production at central rapidity in pp collisions at s = 7 ev with the ALICE experiment Hadron Collider Physics Symposium 211, Paris France D s and D production in pp collisions at 7 ev with the ALICE experiment Physics at the LHC 211, Perugia Italy Other posters in conferences: D s production in pp collisions at 7 ev with ALICE Quark Matter 211, Annecy (France) D s production in pp collisions at 7 ev with ALICE Hard Probes 212 Cagliari (Italy) Gian Michele Innocenti - urin University 33

40 List of publications Gian Michele Innocenti - urin University 34

41 List of publications Gian Michele Innocenti - urin University 35

42 List of publications Gian Michele Innocenti - urin University 36

43 List of publications Gian Michele Innocenti - urin University 37

44 List of publications Gian Michele Innocenti - urin University 38

45 List of publications Gian Michele Innocenti - urin University 39

46 List of publications Schools Quark Gluon Plasma and Heavy-ion collisions: present,past and future Villa Gualino, orino 7-12 March 211 Gian Michele Innocenti - urin University 4

47 Gian Michele Innocenti - urin University 41

48 Backup Slides Gian Michele Innocenti - urin University 41

49 Inner racking System 6 cilindrical layers of silicon detectors with radii from 3.9 to 43. cm two innermost layer are equipped with Silicon Pixel Detectors with radii 3.9 and 7.6 cm IS has coverage η <.9 (1.98 for SPD ) Main goals: primary and secondary vertex reconstruction with high resolution required for the detection of open charm and beauty measurement with resolution better than 1 μm of the impact parameter of the tracks reconstruction and identification of the low momentum tracks with p < 2 MeV/c Gian Michele Innocenti - urin University 42

50 ime Projection Chamber and ime of Flight Detector PC 51 cm long cylindrical chamber filled with 9 m 3 of drift volume filled with a gas mixture PC has coverage η <.9 for tracks with full radial length main tracking detector of the ALICE central barrel (from.2 to 1 GeV/c) particle identification via specific energy deposit OF large array area of MRPC that covers the full azimuthal angle and η <.9 in pseudorapidity at radii from cm particle identification in the intermediate momentum range via time of flight measurement p< 2.5 GeV/c for pions and kaons p< 4 GeV/c for protons. Gian Michele Innocenti - urin University 43

51 Resonant decay channels Efficiency Acceptance pp, s = 7 ev he Ds decays to the same KKπ final state via various resonant channels. he two with larger BRs are: Ds Φπ K K - π Ds K * π K K - π Prompt D s D s D s, No PID D s K D s K * * K K, No PID p (GeV/c) he possible contribution of the K * channel has been studied by evaluating the acceptance x efficiency factor for the two channels after topological and PID selections ALI PUB 4188 arxiv: he K * channel is strongly suppressed by the requirement on the ϕ mass and by the PID selection Gian Michele Innocenti - urin University 44

52 B feed down subtraction in pp analysis Same approach used for the four D mesons measured in ALICE D s,d, D and D * Fraction of prompt D mesons fprompt estimated as: s s where s s beauty production cross section from FONLL[1] calculations Alternative approach used to estimated the systematic uncertainty from B feed-down s s [1] M. Cacciari, M. Greco, P. Nason, JHEP 985 (1998) 7 Gian Michele Innocenti - urin University 45

53 B feed down subtraction in Pb-Pb analysis Same approach used for the four D mesons measured in ALICE D s,d, D and D * Fraction of prompt D mesons fprompt estimated as : s average nuclear overlap function in the centrality class considered beauty production cross section from FONLL[1] calculations Hypothesis on the RAA of Ds from B: central value assuming RAA (Ds from B)=RAA (prompt Ds ) Alternative approach used to estimated the systematic uncertainty from B feed-down [1] M. Cacciari, M. Greco, P. Nason, JHEP 985 (1998) 7 Gian Michele Innocenti - urin University 46

54 p-integrated ratios at 7 ev Measured cross sections extrapolated to full p range with FONLL Ratio 1.4 ALICE, p >, y <.5 SHM LHCb Prelim., p >, 2<y<4.5 - e e, p > ZEUS, p >3.8 GeV/c mid-y H1, p >2.5 GeV/c, mid-y PYHIA6, Perugia- y <.5, p > ALICE p > ALAS (prelim) p > ZEUS ( p) p >3.8 GeV/c.4 H1 (DIS) p >2.5 GeV/c SHM.2 D D D D * Ratios of D meson cross sections compatible within uncertainties with results at different energies and collision systems D s D D s D Combined e e p > - PYHIA6, Perugia- y <.5, p > s strangeness suppression factor γs Gian Michele Innocenti - urin University 47

55 p-integrated ratios at 7 ev Measured cross sections extrapolated to full p range with FONLL Ratio 1.4 ALICE, p >, y <.5 SHM LHCb Prelim., p >, 2<y<4.5 - e e, p > ZEUS, p >3.8 GeV/c mid-y H1, p >2.5 GeV/c, mid-y PYHIA6, Perugia- y <.5, p > ALICE p > ALAS (prelim) p > ZEUS ( p) p >3.8 GeV/c.4 H1 (DIS) p >2.5 GeV/c SHM.2 D D D D * Ratios of D meson cross sections compatible within uncertainties with results at different energies and collision systems D s D D s D Combined e e p > s strangeness suppression factor γs Results compared to predictions from PYHIA [1] and Statistical Hadronization Model (SHM) with V=3 fm 3, =164 MeV, fugacity =.6 [2] - PYHIA6, Perugia- y <.5, p > Gian Michele Innocenti - urin University 47

56 p-integrated ratios at 7 ev Measured cross sections extrapolated to full p range with FONLL Ratio 1.4 ALICE, p >, y <.5 SHM LHCb Prelim., p >, 2<y<4.5 - e e, p > ZEUS, p >3.8 GeV/c mid-y H1, p >2.5 GeV/c, mid-y PYHIA6, Perugia- y <.5, p > ALICE p > ALAS (prelim) p > ZEUS ( p) p >3.8 GeV/c.4 H1 (DIS) p >2.5 GeV/c SHM.2 D D D D * Ratios of D meson cross sections compatible within uncertainties with results at different energies and collision systems D s D D s D Combined e e p > s strangeness suppression factor γs Results compared to predictions from PYHIA [1] and Statistical Hadronization Model (SHM) with V=3 fm 3, =164 MeV, fugacity =.6 [2] [1]. Sjostrand, S. Mrenna, P. Skands, JHEP 5 (26) 26 [2] A. Andronic, F. Beutler, P. Braun-Munzinger, K. Redlich and J. Stachel, Phys. Lett. B 678 (29) 35 - PYHIA6, Perugia- y <.5, p > Gian Michele Innocenti - urin University 47

57 Systematic uncertainties feed-down (%) AA Systematic uncertainty from R ALI PERF meson 4 < p < 6 GeV/c Pb-Pb 3/8/212 D s s NN =2.76 ev Centrality -7.5% Hypothesis on (R feed-down)/(r prompt) AA AA 6 < p 8 < p < 8 GeV/c < 12 GeV/c Summary plot of systematic uncertainty contributions (feed-down from B excluded) Systematic uncertainties from B feeddown on RAA as a function of the hyphotesis on the RAA feeddown in the range considered (1/3 < RAA (D from B)/RAA (prompt D)<3) Gian Michele Innocenti - urin University 48

58 dn/dp in Pb-Pb and pp c) -1 (GeV y < D s meson s NN =2.76 ev Systematic uncertainties dn/dp in Pb-Pb collisions at 2.76 ev compared to the pp reference dn/dp -2 1 from Data from B feed-down subtr. ± 4.8% norm. unc. on pp ref. not shown BR syst. unc. not shown pp reference obtained from the measured cross section at 7 ev by: Centrality -7.5% Pb-Pb pp rescaled reference yield in Pb-Pb pp reference - scaling to 2.76 ev using FONLL - multiplying by the nuclear overlap function <AA> (arxiv: ) ALI PREL p (GeV/c) Gian Michele Innocenti - urin University 49

59 Ds /D and Ds /D ratios in Pb-Pb and pp collisions Ds ratios calculated with the Pb-Pb yields compared to the results obtained in pp at 7 ev / D D s D : Pb-Pb Preliminary, pp JHEP 1 (212) 128 Ds: Pb-Pb Preliminary, pp arxiv: Pb-Pb at s NN = 2.76 ev stat. unc. syst. unc. pp at s = 7 ev stat. unc. syst. unc. ± 5.4% BR unc. (not shown) / D D s D : Pb-Pb Preliminary, pp JHEP 1 (212) 128 Ds: Pb-Pb Preliminary, pp arxiv: Pb-Pb at s NN = 2.76 ev stat. unc. syst. unc. pp at s = 7 ev stat. unc. syst. unc. ± 5.7% BR unc. (not shown) p (GeV/c) p (GeV/c) Partial cancellation in the ratio of the systematic uncertainties due to tracking efficiency and to the contribution to B feed down uncertainty of the variation of the FONLL parameters Contribution of the hypothesis on the RAA from B considered completed uncorrelated pp and Pb-Pb ratios still compatible within the uncertainties Gian Michele Innocenti - urin University 5

60 Ds meson reconstruction strategy in the ALICE central barrel D s mesons production is measured in ALICE via the reconstruction the weak decay channel: Ds Φπ K K - π which presents a cτ = 15 μm and a BR of 2.28% Invariant mass analysis of decays topologies originated from displaced vertices Each candidate triplet selected according to topological cuts (e.g. decay length) to reduce the large combinatorial background D s decay length point p (D ) s K - K A particle identification strategy is also used to enlarge the S/B ratio he invariant mass distributions of selected candidates are then fit to extract the signal and the background yields Gian Michele Innocenti - urin University 51

61 Particle identification selection (PID) PC: identification based on de/dx: - N*σ compatibility with Bethe-Bloch curves OF: identification based on difference between the measured time-of-flight (tmeas = tof - t) and the one expected for a given particle species Gian Michele Innocenti - urin University 52

62 Particle identification selection (PID) PC: identification based on de/dx: - N*σ compatibility with Bethe-Bloch curves OF: identification based on difference between the measured time-of-flight (tmeas = tof - t) and the one expected for a given particle species Factor > 2 of background reduction in p range 4-6 GeV/c in Pb-Pb Gian Michele Innocenti - urin University 52

63 From raw yield to cross section Efficiency 1 pp, s = 7 ev Acceptance LI PUB Prompt D Prompt D, No PID (GeV/c) Acceptance x efficiency for prompt Ds and Ds from B meson decay (feed down) Higher efficiencies for Ds from B feed-down due to larger displacement from the primary vertex s Feed-down Ds s p Gian Michele Innocenti - urin University 53

64 From raw yield to cross section Efficiency 1 pp, s = 7 ev Acceptance LI PUB Prompt D Prompt D, No PID (GeV/c) Acceptance x efficiency for prompt Ds and Ds from B meson decay (feed down) Higher efficiencies for Ds from B feed-down due to larger displacement from the primary vertex s Feed-down Ds s p Feed down subtraction Fraction of prompt Ds mesons fprompt estimated using: - beauty production cross section from pqcd calculations (FONLL) - MC efficiency for feed-down Ds [1] M. Cacciari, M. Greco, P. Nason, JHEP 985 (1998) 7 Gian Michele Innocenti - urin University 53