Open Heavy Flavour Measurement using Leptonic Final States at the ALICE Experiment

Transcription

1 Open Heavy Flavour Measurement using Leptonic Final States at the ALICE Experiment MinJung Kweon for the ALICE Collaboration Physikalisches Institut, Universität Heidelberg December 03 rd 20, December LHC Physics day for LPCC, CERN

2 Open heavy flavour measurement via lepton channels Theoretical uncertainty of a factor 2-3 system: snn: σ QQ NN [mb] QQ N total p+p 14 TeV charm/beauty p+p 7 TeV charm/beauty 11.2/ /0.23 MNR code (NLO): Mangano, Nason, Ridolfi, NPB373 (1992) / /0.003 Measurement at lower energy GeV, p+p σ cc = 567 ± 57(stat) ± 193(sys)µb σ bb = (stat) (sys)µb Cross sections cc(bb) at LHC x(x0) larger than at RHIC PRL 3, (2009) PRL 97, (2006) Branching Ratios: c l + X 9.6 % b l + X 11 % b c l + X % High rate of lepton production from semi-leptonic decay Complementary to heavy flavor hadronic decays(andrea s talk) Proton-proton collisions - Measurement of heavy flavour production(charm and beauty) in p+p will provide important test of pqcd in a new energy domain and heavy ion reference Heavy-ion collisions - Heavy quark energy loss in the medium 03 December 20, December LHC Physics day for LPCC, CERN 2

3 Leptons in ALICE Electrons at Mid Rapidity ( η <0.9) Muons at Forward Rapidity(-4<η<-2.5) Inner Tracking System Time Projection Chamber Transition Radiation Detector Time Of Flight ElectroMagnetic Calorimeter ZDC ~116m from I.P. FMD V0 ITS ACORDE EMCAL TRD TPC ABSORBER TRACKING CHAMBERS MUON FILTER Muon Spectrometer TRIGGER CHAMBER TOF DIPOLE MAGNET ZDC ~116m from I.P. PHOS capable from ~ 0 MeV to above 50 GeV Collaboration: 31 countries, 9 institutes, > 00 people 03 December 20, December LHC Physics day for LPCC, CERN 3

4 Trigger and Data Sample for p+p at 7 TeV Trigger Minimum bias, based on interaction trigger: SPD( η <2) or V0-A(2.8< η <5.1) or V0-C(-3.7< η <-1.7) at least one charged particle in 8 η units ~95% of σinel Single-muon trigger: Muon trigger chamber and MinBias Trigger detectors forward muon in coincidence with Min Bias Data Since March 31st 20 until PbPb collision started, collected ~8.5x 8 minimum bias triggers ~1.3x 8 muon triggers Analysis shown here is based on 1.6 nb -1 for electrons 3.49 nb -1 for muons Activated in coincidence with the BPTX beam pickups 03 December 20, December LHC Physics day for LPCC, CERN 4

5 Analysis Approach via Electrons (1) Measure inclusive electron transverse momentum spectrum Electron Cocktail π 0 Dalitz decay sources: the π 0 measured spectrum (Fit with Hagedorn function and use PYTHIA electron decay kinematics) (2) Build background contributions spectrum described with an electron cocktail (photonic, Dalitz/dielectron decays of mesons, weak kaon decay, direct radiation, J/ψ and Υ) (3) Measure heavy flavor semielectronic decays by subtracting (2) from (1) Heavier meson sources(η, η', ρ, ω, φ): implemented via mt scaling(verified for ƞ) Photon conversion sources: - Calculate photon conversion in the beam pipe and 1/3 of the first pixel layer (0.5 % X0) - Use the ratio of conversion to Dalitz electrons to estimate the e ± contributions 03 December 20, December LHC Physics day for LPCC, CERN Conv. Dalitz = BR γγ 2 1 e 7 9 X X 0 BR Dalitz 2 2 5

6 Electron Identification Currently up to 4 GeV/c based on the Time Projection Chamber and the Time of Flight detector (TOF resolves TPC crossings) de/dx in TPC (a.u.) Soon extend to higher momentum with the Transition Radiation Detector and the ElectroMagnetic Calorimeter K p d 900 GeV ALICE performance work in progress 1 momentum p (GeV/c) K p TPC e ALICE Performance p+p at TOF s = 900 GeV (2009 data) 2 I Vitev, A Adil and H van Hees, 0.4 [J. Phys. G: Nucl. Part. Phys. 34 (2007) S769 S773] [Phys.Lett.B666:533 (2008)] momentum p (GeV/c) 1 03 December 20, December LHC Physics day for LPCC, CERN 6

7 Electron Identification in Steps e π Kaon & Proton Rejection with TOF(3 from the electron line in TOF) Current ToF resolution: 130 ps clean rejection of K (for p < 1.5 GeV/c) p (for p < 3 GeV/c) Further hadron rejection with TPC Momentum dependent cut on number of sigmas from the electron line in TPC Subtract remaining hadron background Gaussian fits of TPC de/dx distributions in momentum slices hadron contamination as function of momentum p (< 4 GeV/c) 03 December 20, December LHC Physics day for LPCC, CERN 7

8 Uncorrected Inclusive Electron Spectrum Corrections to the raw electron spectrum for - geometrical acceptance - reconstruction efficiency - detector resolution with PYTHIA+PHOJET 03 December 20, December LHC Physics day for LPCC, CERN 8

9 Cocktail and Corrected Inclusive Electron Spectrum Data & Cocktail Ratio Data/Cocktail Excess from open heavy flavors (including J/ψ, direct radiation) Systematic errors on input π 0 spectrum (+20% 40%) is propagated to the cocktail (Will be reduced in near future!) No systematic errors are shown yet on the corrected inclusive electron spectrum 03 December 20, December LHC Physics day for LPCC, CERN 9

10 Perspectives 37)89#'="A:)9>8%2"7'#>B)9)# Extend good electron identification at higher momentum with TRD and EMCal Transition Radiation Detector TPC de/dx slice w/o and with TRD 6'#%)7)89#':%8":$>$"9)*%CD&2% $3E$FG.%3=2/0%87H*9)#*%"**>A:)$I ElectroMagnetic Calorimeter!"#$%&'()&*+(&,-' E/p distributions Counts 4 p = 2GeV/c without TRD with TRD 3 Pion Rejection Factor: 90 Electron Efficiency: ALICE Performance 24/09/ TPC de/dx - <de/dx> [ ] electron Provide good e/π separation from 1 to ~15 GeV/c Provide possibility to trigger (L1) on high pt identified particles ;<="*8>'88?>@A*><$)%%%%%%%%%%!"#$%&#'()*%+,-,.%/0123%!)"45%67"4'#%37)89#':* December 20, December LHC Physics day for LPCC, CERN

11 Separation of beauty contributions <",#*#-"& 8"#5-% Select electrons from heavy flavour decays via minimum distance of closest approach cuts increase S/B B jet tagging by selecting jets containing secondary vertex primary vertex r secondary vertex p quasi secondary particle Jet Axis Excellent vertex capabilities, impact parameter resolution (~ 75 μm at 1 GeV/c) IP Analysis is ongoing in both directions 03 December 20, December LHC Physics day for LPCC, CERN 11

12 Analysis Approach via Muons Muon sources(mc) Analysis approach (1) Remove hadrons and low pt secondary muons by requiring a muon trigger signal (2) Remove decay muons by subtracting MC dn/dpt normalized to data at low pt alternative method: use muon distance of closest approach to primary vertex (3) What is left are muons from charm and beauty (4) Apply efficiency corrections Absorber Tracking Chambers B Magnet Filter Trigger Chambers 03 December 20, December LHC Physics day for LPCC, CERN 12

13 Background subtraction and Efficiency Estimation Most delicate analysis step: subtraction of residual secondary and decay muons from π, K pt > 2 GeV/c: secondary contribution small(~ 3 %) use different PYTHIA tunes (Perugia-0 and ATLAS-CSC), vary secondary yields to evaluate systematics Resulting systematic error on HF muons: 30 % 20 % from low to high pt Efficiency > 87 % for pt > 2.5 GeV/c 03 December 20, December LHC Physics day for LPCC, CERN 13

14 Combined Charm and Beauty Cross Section The pqcd (FONLL) calculation reproduces the shape and is in agreement with data within errors. Int. Lumi: 3.49 nb -1 Next steps: muon DCA method will allow to reduce systematics due to background subtraction improved spectrometer alignment already deployed extend pt reach(up to 20 GeV/c) by increasing the statistics Extract beauty cross section (dominates muon spectrum above few GeV/c) prepare reference for Pb-Pb RAA 03 December 20, December LHC Physics day for LPCC, CERN 14

15 -9 Min-Bias 3 Min-Bias 2 0-% 2 0-% Min-Bias 1-20% 0 0-% % -20% % % 20-40% % % 1 Summary % 20-40% % p+p p+p An inclusive -2 /42mb % -2 /42mbAu+Au electron spectrum is compared to cocktails describing electrons s@ NN = s NN 200 = 200 GeV GeV -14 from meson p+p decays -2 /42mb s = 200 GeV and photon NN conversions An excess is observed at high p p T T [GeV/c] pt coming from heavy flavor, J/ψ decays and and andthe thedata clearly favor larger v direct radiation HF Invariant Invariant yields yields of electrons of electrons from fromheavy- heavy- this thiseffect effectalone. FIG. Analysis 1 (color online). based Invariant on yields impact of electrons parameter from heavyflavor decays for different Au Au centrality classes and for is ongoing to separate the beauty contribution FIG. FIG. 1 (color 1 (color online). online). flavor flavor decays decays for different for different Au Au Au Au centrality centrality classes classes and and for for p p collisions, scaled by powers of for clarity. The solid p collisions, p p collisions, scaled by scaled powers by powers of for of clarity. for clarity. The solid lines are the result of a FONLL calculation normalizedthe to the solid lines are the lines result are the of result a FONLL of a FONLL calculation calculation normalized normalized to the p p data [18] and scaled with ht to the p data p [18] p data and [18] scaled and with scaledht with AA i AA i for each Au Au centrality class. The inset shows the ratio ht for AA of ieach for heavy-flavor each Au Au Au toau centrality background class. The electrons insetfor shows minimum the ratio biasofauheavy-flavor collisions. to background Error bars electrons (boxes) for depict minimum statistical bias (systematic) Au Auuncertainties. collisions. Error bars (boxes) depict statistical (systematic) uncertainties. 1.6 centrality The differential class. The inset shows production the ratio of cross heavy-flavor section to as 1.4 a function of pt of muons from 1.4 HF background have electrons been measured for minimum bias in 2 AuGeV/c collisions. < pt < GeV/c, 4 < η < 2.5 Error bars (boxes) depict statistical (systematic) uncertainties. 3/(2πT) 12/(2π 1.2 The results are in agreement with the FONLL predictions within errors 3/(2πT) T) 1 12/(2πT) Figure 3 shows the measured R AA and v HF Figure 3 shows the measured R AA and v HF 2 of heavyflavor electrons in 0% % central and 2minimum of heavyflavor collisions, electronsand in 0% % our corresponding central and 0 minimum data [6,29]. bias The bias collisions, data indicate and our strong corresponding coupling of heavy 0 data quarks [6,29]. to the The medium. indicate While strong at low coupling p T the suppression of heavy quarks is smaller to the than me- that data dium. ofwhile 0, R AA at low of heavy-flavor p T the suppression decay electrons is smaller approaches than that the of 0, 0 Rvalue AA offor heavy-flavor p T > 4 GeV=c decayalthough electrons a significant approachescontri- butionfor from p T > bottom 4 GeV=c decays although is expected a significant at high contri- p T. The the 0 value bution large from v HF 2 bottom indicates decays that the is charm expected relaxation at high time p T. is The comparable large v HF to the short time scale of flow development in the 2 indicates that the charm relaxation time is comparable produced medium. It should be noted that much reduced uncertainties to the short and time the scale of flow development in the produced medium. It energy extended should be loss p T range noted at that LHC! of the present data permit the comparisons of R much reduced AA and v 2 of the heavy and uncertainties light flavors. and the extended p T range of the present data permitmore the comparisons quantitative of statements R AA andrequire v 2 of theoretical heavy and guidance. flavors. Figure Kweon, University 3 compares of Heidelberg the R AA and v 2 of lightminjung heavy-flavor Analysis on the Pb+Pb data is ongoing! We got surprise by the result of heavy quark energy loss at RHIC! Exciting to see the result of heavy quark AA above 0.3 and 3 GeV=c and of 0 T with T GeV=c as above 0.3 and 3 GeV=c and of function of centrality given by part 0 with p Error bars T > 4 GeV=c as function of centrality given by N (boxes) depict part. Error bars (boxes) depict statistical statistical (point-by-point (point-by-point systematic) uncertainties. The The right right (left) (left) box boxatatrr AA AA 1 shows the relative uncertainty from fromthe the p p p p reference commonto to all points for p T > 0:3 3 GeV=c. suppression. This value of ^q would imply a strongly coupled medium. In this model the azimuthal anisotropy is isonly onlydue duetoto the path length dependence of energy loss, 2 than predicted from R R AA AA HF v (a) 0-% central s 1.4 NN = 200 GeV s 1.2 NN = 200 GeV (b) minimum bias R AA v HF minimum bias F (a) (a) (b) 0-% central 0-% central s NN = 200 GeV Armesto et al. (I) Armesto et al. (I) van Hees et al. (II) van Hees et al. (II) Moore & Teaney Moore &(III) Teaney (III) Armesto et al. (I) van Hees et al. (II) Moore & 3/(2πT) 12/(2ππT) 0 RTeaney AA (III) π 0 v 2, p > 2 GeV/c π 0 R T AA e π ± 0 R v AA 2, p T HF, e ± v > 2 GeV/c HF e ± R, e ± AA v p p T [GeV/c] T [GeV/c] December 20, December LHC Physics day for LPCC, CERN 15

16 BACKUP SLIDES 03 December 20, December LHC Physics day for LPCC, CERN 16

17 6)2(3*7$2(/-*8$)#,-/"* /()-2$$*)00'#')"#39 03 December 20, December LHC Physics day for LPCC, CERN 17

18 Cocktail Ingredient(input π 0 spectrum)!!"#"$%"&'()%*+,-./+0%%1 2 %-3+45/.* #)8':*9#F89)$%M>9?%E?'9':%8':4)#*>':*%%%%%%%%%%%%%N%O<%O'8?%P=':$"5%--Q 7A! 6&7%3/ :%;9/%1 2 % R<S"A)#.%/<%;8?")T)#.%=<%;9#"9H"::.%U<%V'A)7*":A &?5*<%W)4<%JBX%P+,,YQ%,Z[,,Z <3+45/,%,/+%;85%=85>% 5>+%?,@+09/:% ;.:4589:$ ;<="*8>'88?>@A*><$)%%%%%%%%%%!"#$%&#'()*%+,-,.%/0123%!)"45%67"4'#%37)89#':* 03 December 20, December LHC Physics day for LPCC, CERN 18

19 Cocktail Ingredient(Other mesons and Conversion electrons)!"#$%"&'(")*+),! 1:87D$)$E%-.'-/.'0.'1.'2! 1FG7)F):9)$%4>"%( 3 ')4#5%+6 X)#>J>)$%J'#%Y%>:%/0123%Z 75"48&*+)'9&*(':;*8*+'4*+$"&)%*+)! H'9%#)I)89)$E%9?'*)%J#'F%9?)%()"F%G>G)% ":$%K-LM%'J%J>#*9%G>N)7%7"5)#%%OP,<Q%R%S, T! U"9>'%'J%8':4)#*>':*%9'%V"7>9W% )7)89#':*E <'=>?@A ;<="*8>'88?>@A*><$)%%%%%%%%%%!"#$%&#'()*%+,-,.%/0123%!)"45%67"4'#%37)89#':* 03 December 20, December LHC Physics day for LPCC, CERN 19

20 µ Primary K/π Subtraction: Vertex Unfolding Fitting d 2 N µ dp t dv z 1 ρ(v z ) = d 2 Nµ c/b + d 2 N primary K /π µ dp t dv z dp t dv z d 2 N µ dp t dv z d 2 Nµ c/b +(L + v z ) ( dp t dv z + d 2 N secondary K/π µ dp t dv z 1 L+ < v z > (neglected) d 2 primary K /π Nµ ) dp t dv z Method has been already successfully tested on simulations; expected linear increase of muon yield w/ the vertex position evidenced with data; high statistics is needed. X. M. Zhang (LPC, IOPP & QLPL) measure µ LHC/ALICE RQW 20, October 20 9 / December 20, December LHC Physics day for LPCC, CERN 20

21 Systematic Error background subtraction: from 20% to 7% with p t ; alignment: 2% p t ; detector response: 5%; model bias: 20%; min-bias cross section: % (not included); total: from 29% to 24.4% with p t ; X. M. Zhang (LPC, IOPP & QLPL) measure µ LHC/ALICE RQW 20, October / December 20, December LHC Physics day for LPCC, CERN 21

22 Charm and Beauty Separation D and B separation by fitting with pqcd shapes Simulated results in 14 TeV via (di)muons PYTHIA PYTHIA Input distributions are well reconstructed; nice agreement between single muon and dimuon channels Systematic errors are 20% for B and D in the single muon channel and, 15% for B and 20% for D in the dimuon channel This analysis procedure is currently applied to p+p data at 7 TeV 03 December 20, December LHC Physics day for LPCC, CERN 22