Measurement of forward-rapidity heavy-flavour muons in proton-proton collisions at s = 7 TeV with ALICE

Transcription

1 Measuremen of forward-rapidiy heavy-flavour muons in proon-proon collisions a s = 7 TeV wih ALICE D. Socco for he ALICE Collaboraion Ecole des Mines, CNRS-IN2P3, Universié de Nanes Nanes, France Ocober 11, 20

2 Ouline 1 Inroducion Moivaions Feaures a LHC The ALICE experimen and is Muon Specromeer 2 Heavy-flavour analysis Background subracion Correcions Resuls 3 Conclusions D. Socco Hard Probes 20 - Eila 11 Oc / 19

3 Ouline 1 Inroducion Moivaions Feaures a LHC The ALICE experimen and is Muon Specromeer 2 Heavy-flavour analysis Background subracion Correcions Resuls 3 Conclusions D. Socco Hard Probes 20 - Eila 11 Oc / 19

4 Moivaions Charm and beauy: hard probes of he ho and dense maer formed in heavy-ion collisions: produced a he beginning of he collision (large Q 2 ) experience he evoluion of he fireball (large cτ) inerac srongly wih he medium (paron energy-loss) Charm/beauy flavoured hadrons measured in boh heavy-ion and proon-proon collisions (as reference) Furher oucomes: Tes of pqcd in proon-proon collisions Reference for quarkonia measuremens in heavy-ion collisions D. Socco Hard Probes 20 - Eila 11 Oc / 19

5 Heavy-flavours a he LHC LHC PbPb@5.5TeV RHIC AuAu@200GeV σ c σ c σ b 0 σ b σ W σ Υ σ Z σ Υ Big sep in energy: abundan producion probe unexplored small-x region P.Giubellino, arxiv: [nucl-ex] D. Socco Hard Probes 20 - Eila 11 Oc / 19

6 Energy-loss sudies New medium-blind references available: W is affeced by shadowing only. Observables: Shif in he crossing-poin of from c/b and W. R AA reduced by a facor 2-5 in 2 GeV/c < p < 20 GeV/c Z.Conesa e al., Phys.Le. B 663 (2008) 202 D. Socco Hard Probes 20 - Eila 11 Oc / 19

7 The ALICE experimen D. Socco Hard Probes 20 - Eila 11 Oc / 19

8 The ALICE experimen b/c hadrons (plenary alk by A. Dainese) b/c e + X (parallel alk by S. Masciocchi) EmCal TPC ITS V0 TRD TOF D. Socco Hard Probes 20 - Eila 11 Oc / 19

9 The ALICE experimen b/c hadrons (plenary alk by A. Dainese) b/c e + X (parallel alk by S. Masciocchi) b/c + X EmCal Muon Specromeer TPC ITS V0 TRD TOF D. Socco Hard Probes 20 - Eila 11 Oc / 19

10 The ALICE experimen b/c hadrons (plenary alk by A. Dainese) b/c e + X (parallel alk by S. Masciocchi) b/c + X EmCal Tracking chambers Trigger chambers TPC ITS V0 TRD TOF Fron absorber Dipole magne Muon filer Accepance: 4 < η < 2.5 Tracking chamber resoluion: 0 m Trigger sysem wih programmable p cus. Lowes value p 0.5 GeV/c D. Socco Hard Probes 20 - Eila 11 Oc / 19

11 Ouline 1 Inroducion Moivaions Feaures a LHC The ALICE experimen and is Muon Specromeer 2 Heavy-flavour analysis Background subracion Correcions Resuls 3 Conclusions D. Socco Hard Probes 20 - Eila 11 Oc / 19

12 Tracks in he specromeer ( couns / 0.5 GeV/c ) dn/dp All Charm Beauy Decay Secondary Hadrons Unknown Pyhia Perugia0 s = 7 TeV 4 < η < < θ abs < 178 Reconsruced verex c/b π/κ Heavy-flavour c/b Decay π/k 1 π/κ π/k Secondary π/κ p (GeV/c) Remove hadrons and low-p secondary maching racks wih rigger Remove decay verex displacemen, high-p daa, models Correc for accepance/efficiency Esimae he cross-secion D. Socco Hard Probes 20 - Eila 11 Oc / 19

13 Daa selecion Daa analysed in he period LHCc and reprocessed afer alignmen: 31 runs 60 6 Minimum Bias evens (V0 scinillaors pixel deecor ) & beam-beam couners 2 6 Muon rigger evens Inegraed luminosiy: 3.49 nb 1 Specromeer condiions sable in he seleced runs # mu racks # mu rig. even Accepance cu: 4 < η < 2.5 Run number Cu on he angle of he rack a he exi poin of he fron absorber (171 < θ abs < 178 ). Rejecion of beam-gas background evens. Rejec evens wih no reconsruced verex in he wo pixel layers Maching racks wih rigger D. Socco Hard Probes 20 - Eila 11 Oc / 19

14 Momenum resoluion Firs pass alignmen already performed: sensiive improvemens for di-muon sudies bu sill a 12% resoluion expeced a p GeV/c p (GeV/c) p (GeV/c) dn/dp (couns) real align ideal align + dn/dp (couns) p (GeV/c) Curren sysemaics for alignmen: 2% p. Daa disribuion meaningful up o p GeV/c Improved alignmen is ready: ess ongoing Old alignmen New alignmen D. Socco Hard Probes 20 - Eila 11 Oc. 20 / 19

15 Uncorreced muon disribuions (enries/0.5 GeV/c) dn/dp ALICE Performance 06//20 s = 7 TeV 4 < η < < θ abs < 178 Reco. verex w/ rigger maching Muon riggered evens Beam beam Beam gas w/ phys. sel. w/o phys. sel. dn/ddca (enries/ cm) ALICE Performance 06//20 s = 7 TeV 4 < η < < θ < 178 abs Reco. verex w/o phys. sel. w/ rigger maching Muon riggered evens p > 2.0 GeV/c Beam beam Beam gas p (GeV/c) PWG3 MUON DCA (cm) PWG3 MUON 023 Trigger chambers Tracking chambers Small conribuion of beam-gas evens in he period ( 1%) Conribuion furher reduced by he offline rejecion of beam-gas ( physics selecion ) B DCA π Fron absorber Dipole magne Muon filer D. Socco Hard Probes 20 - Eila 11 Oc / 19

16 Background subracion In he analysis we focus on he region p > 2 GeV/c: secondary conribuion is low ( 3%) main source of background: decay muons ( 25%) ( couns / 0.5 GeV/c ) dn/dp All Charm Beauy Decay Secondary Hadrons Unknown Pyhia Perugia0 171 s = 7 TeV 4 < η < 2.5 < θ abs < 178 Reconsruced verex w/ rigger maching Pyhia Perugia-0 w/ realisic sim. of deecor R MC sabiliy vs. run condiion p (GeV/c) Decay conribuion subraced wih simulaions: Disribuion shape from MC Compue he raio: (R HF MC R MC = decay oal in he bin 0.5 < p < 1 GeV/c 20% ; Rsecondary MC 16%) Normalize he MC shape o he daa according o he obained raio Subrac D. Socco Hard Probes 20 - Eila 11 Oc / 19

17 Perspecive: esimae he fracion of decay muons from daa / / z z / 1 / 3 2 The collision akes place in he beam crossing region. The posiion is: almos fixed in he ransverse plane (σ 0 m) disribued as a Gaussian (σ 4 cm) along he beam direcion 90 cm 90 cm π/κ IP region IP region π/κ ) 1 dn dn dn dn MB N MB dv N 1 dv MB z MB dvz dn N 1 dv MB MB dn dv z dvz / ( Probabiliy ha hadron decays before reaching he absorber (i.e. prob. of having a decay bkg. muon) is disance IP - Absorber ALICE Performance 27/06/20 χ / ndf / 12 Prob Line norm 1.405e+04 ± 1.620e+04 Line slope 1303 ± Single muons in (GeV/c) < Vz (cm) Cus: 171 < θ abs p χ / ndf / 12 Prob Line norm 2.703e+04 ± (deg) < 178, 1.0 < p 8.791e+03 Line slope ± 67.5 Mach Trigger, (GeV/c) < Vz (cm) CAVEATS: pp a s = 7 TeV 2 dn MB N MB dv z dn dv z dn MB N MB dv z dn dv z Min. Bias rigger, χ / ndf / 12 Prob Line norm 4.057e+04 ± 0.5 < p 1.657e+04 Line slope ± (GeV/c) < Vz (cm) Evens wih only 1 verex in SPD 1.5 < p χ 2 / ndf / 12 Prob Line norm 8932 ± Line slope ± vz (cm) (GeV/c) < Vz (cm) PWG3 MUON 012 (a.u.) dn /dp Uncorreced single muons in pp a s = 7 TeV Toal mu HF mu + sec. Bkg mu 171 < θ abs (deg) < 178 Mach Trigger Min. Bias rigger Only 1 verex in SPD ALICE Performance 27/06/ p (GeV/c) MB evens wih only 1 reconsruced verex needed (low pileup) large saisical flucuaion; sysemaics under sudy D. Socco Hard Probes 20 - Eila 11 Oc / 19 PWG3 MUON 013

18 Decay background subracion: sysemaics Comparison of decay muons from 2 differen unings of Pyhia: Perugia-0 and ATLAS R MC vs pseudo-rapidiy Change he conribuion of secondary by 0% Resuling uncerainy on heavy-flavour muons decreasing from 20% o 7% wih p Addiional 20% error o accoun for any discrepancies in he descripion of daa (conservaive assumpion) D. Socco Hard Probes 20 - Eila 11 Oc / 19

19 Accepance / efficiency correcions M. L. Mangano, P. Nason and G. Ridolfi, Nucl. Phys. B 373 (1992) 295 Simulaions: shape of p and y disribuions paramerized from MNR NLO charm quark cross secion. Realisic descripion of he deecor Two-dimensional correcion marix used: reduced dependency on inpus higher saisics needed Eff. 87% for p > 2 GeV/c in he full rapidiy range Sysemaic errors from: y (a.u.) uncerainies in he simulaion of he deecor response (racker efficiency, rigger efficiency, residual misalignmen): < 5% 2 realism of he parameerizaion of he MC inpu: Efficiency p 6 (GeV/c) Use disribuions for muons from beauy insead of charm as MC inpu Apply o daa and compare Resuling error: < 1% in 2 < p < 6.5 GeV/c D. Socco Hard Probes 20 - Eila 11 Oc / 19

20 Summary on sysemaics Change of MC inpu for background Deecor response simulaion: 5% Alignmen: 2% p Discrepancies in he descripion of daa: 20% D. Socco Hard Probes 20 - Eila 11 Oc / 19

21 Firs resuls Correced daa are normalized by he he number of MB evens and he pileup (from rigger scalers) and muliplied by he MB cross secion deermined via a Van der Meer scan % error on MB cross-secion no included Small saisical error (hidden by markers) The pqcd FONLL calculaion (c + b ) reproduce well he shape and is in agreemen wih daa wihin errors D. Socco Hard Probes 20 - Eila 11 Oc / 19

22 Ouline 1 Inroducion Moivaions Feaures a LHC The ALICE experimen and is Muon Specromeer 2 Heavy-flavour analysis Background subracion Correcions Resuls 3 Conclusions D. Socco Hard Probes 20 - Eila 11 Oc / 19

23 Conclusions The firs analysis of single muons in he ALICE Muon Secromeer has been presened: abou 2 million evens wih muon rigger analysed, wih an inegraed luminosiy of 3.49 nb 1 heavy-flavour conribuion exraced from ransverse momenum specra firs evaluaion of he sysemaics performed The ransverse momenum differenial cross-secion of heavy-flavour muons in he range 2 < p < 6.5 GeV/c has been measured: pqcd calculaions in agreemen wih daa wihin he sysemaic errors he shape of he disribuion is well reproduced Perspecives: Improve alignmen for sudies wih a higher p reach Tes he sysemaics wih addiional MC producions: improvemen on sysemaic errors esimaion Improve daa-driven mehods o measure he main background conribuion a low-p The improved differenial cross-secion measuremen wih exended p range will provide he baseline for measuremens of heavy-flavour energy-loss in heavy-ion collisions D. Socco Hard Probes 20 - Eila 11 Oc / 19

24 Ouline 4 Backup slides

25 Minimum Bias vs. Muon rigger evens The shape of specra (wih rigger mach) is he same in Minimum Bias (MB) and Muon riggered (MU) evens Using Muon rigger o ge larger saisics MB riggers used for cross-check and normalizaion

26 Normalizaion and pileup Minimum Bias (MB) even normalizaion: d 2 σ dp = σmb 1 dy pileup 1 ɛ(p, y) 1 d2 N MB N MB dp dy Muon rigger (MU) even normalizaion: d 2 σ dp = σmb 1 dy pileup 1 ɛ(p, y) 1 N MB N MB N d2 N MU MU dp dy Pileup correcion facors assuming poisson disribuion of average (): () CF () = () = ln( L0b MB ) 1 e () N b f rev Low luminosiy High luminosiy

27 Trigger selecion dn/ddca ( couns / cm ) All Charm Beauy Decay Secondary Hadrons Unknown Pyhia Perugia0 171 s = 7 TeV 4 < η < 2.5 < θ abs < 178 Reconsruced verex MC dn/ddca ( couns / cm) All Charm Beauy Decay Secondary Hadrons Unknown Pyhia Perugia0 171 s = 7 TeV 4 < η < 2.5 < θ abs < 178 Reconsruced verex w/ rigger maching MC DCA (cm) DCA (cm) Tracking chambers Trigger chambers DCA 171 <θ abs <178 B π Daa Fron absorber Dipole magne Muon filer Hadrons rejeced by requiring he maching of racks wih rigger

28 Furher on sysemaics Sysemaics esimaed wih an independen analysis: Decay disribuion shape from fi o Pyhia Perugia-0. Sysemaic from a % variaion of he he parameers: 20% Change in he normalizaion on he fracion of decay muons (±20% from verex fi) Deecor response simulaion: 5% Alignmen: 2% p Relaive sysemaic error Sum Normalizaion Shape Align Acc./Eff p (GeV/c)

29 Measuring HF: he UA1 mehod 1 Exrac number of muons from heavy flavours Subrac bkg. Combined fi 2 Correc for efficiency, accepance and decay kinemaics dσ H dy (ph L. Manceau, Eur. Phys. J. C 62 (2009) 9 Measured yields > p min ) = N H(Φ ) Ld Inegraed luminosiy Hadron MC disribuion H (ph >pmin ) 1 dσ ɛ dy σ H (Φ ) Lepon deecion efficiency MC cross secions for hadrons wih a lepon in he phase space of analysis

30 Measuring HF: combined fi CAVEAT: assuming perfec combinaorial bkg. subracion. Saisical and sysemaic errors in 1 monh of pp 14 TeV, assuming L = 30. D X + () B X + () Sysemaic error (aking ino accoun combinaorial bkg. subracion): 20% for B and 20% for D L.Manceau e al., Inernal noe submied

31 Decay background subracion (I) The decay probabiliy for primary π/k + X grows almos linearly wih he disance (D) beween verex and absorber: ( P 1 exp γ D ) γ D cτ cos θ cτ cos θ Verex π /K θ Absorpion Origin D z v (0,0,0) 90cm δ z I δz I = λ I 40 cm Hence: d 2 N π/k dp dz v = f (z v) f (p ) P = ρ(z v) A π/k (p ) D The behavior of secondary muons depends on he survival probabiliy (1 P ) of primary π/k: d 2 N sec dp dz v = f (z v) f (p ) (1 P ) = ρ(z v) ( B sec (p ) A sec (p ) D) For heavy-flavour muons: d 2 N c/b dp dz v = f (z v) f (p ) = ρ(z v) B c/b (p )

32 Decay background subracion (II) The oal muon specrum is he sum of he differen muon sources which can be wrien as: d 2 N dp dz v = d 2 N c/b + d2 N π/k + dp dz v dp dz v d 2 N sec dp dz v = ρ(z v)[ B c/b (p ) + D A π/k (p ) + B sec(p ) D A sec(p )] Collecing he erms depending on he disance D: d 2 N dp dz v = ρ(z v)[b c/b (p ) + B sec(p ) + D(A π/k (p ) A sec(p ))] Divide by he verex disribuion and fi wih line: he inercep esimaes he heavy flavour conribuion, wih a bias from secondaries.