Measurement of Electrons from Beauty-Hadron Decays in p-pb Collision at snn = 5.02 TeV with ALICE at the LHC

Measurement of Electrons from Beauty-Hadron Decays in p-pb Collision at snn = 5.02 ev with ALICE at the LHC Minjung Kim, Inha University Advised by: Prof. MinJung Kweon, Prof. Jin-Hee Yoon Dec 5 th 2014, Heavy Ion Meeting

Motivation Heavy Flavour in Heavy-Ion Collisions Heavy quarks (charm and beauty) are produced in the initial hard scattering processes, experience the full evolution of the system Natural probe of the hot and dense medium created in heavy-ion collisions 2

Motivation Heavy quark Energy Loss in Medium Collisions with medium constituents Medium-induced gluon radiation depends on : Casimir colour factor (CR) Mass - In vacuum, gluon radiation is suppressed at angles smaller than M Q /E Q - In medium, this implies lower energy loss for massive partons Prediction for ΔE: ΔEg > ΔElight quark > ΔEc > ΔEb measurement of b quark and c quark separately is needed 3

Motivation Nuclear Modification Factor R AA = dn AA / dp N coll dn pp / dp = RAA>1, medium enhancement RAA=1, no medium effect RAA<1, medium suppression Measurement in p-pb collisions Control experiment for the Pb-Pb measurement Address cold nuclear matter effects 4

Electron Analysis in ALICE Measurement of b quark production via electron from semi-leptonic decays of beauty-hadron(b) Substantial branching ratio :~11% [B e], ~% [B D e] Excellent vertex and impact parameter resolution of IS and eid capability in ALICE ime Projection Chamber Inner racking System d0 rφ resolution (µm) 300 250 09/07/2013 200 pp s = 7 ev p-pb snn = 5.02 ev 150 Pb-Pb snn = 2.76 ev 0 50 [includes primary vertex resolution] 0-1 1 ALI PERF 53023 Data Sample ime Of Flight Rapidity Coverage (this analysis) -0.60 < ylab < 0.60-1.06 < ycms < 0.14 5 p (GeV/c)

Electron Identification at low p OF(ime Of Flight) PID : Symmetric 3σ cut around electron hypothesis Reject kaons for p<1.5 GeV/c Reject protons for p<3 GeV/c PC(ime Projection Chamber) PID : Select tracks in the upper half of the electrons Bethe-Bloch band( 0.5σ < de/dx -<de/dx>e < 3σ) for further hadron(mostly pion) rejection electron efficiency of 69% π K P K P p-pb e e p-pb π 6

Analysis Approach for Electrons from B Hadron Decay After Electron Identification : 1.Minimum impact parameter cut to increase S/B ratio 2. Subtract remaining background(non-heavy flavour electrons & charm hadron decay electrons) based on ALICE measurement 3. Correct subtracted electron spectra for acceptance and efficiency 7 normalized counts 1-1 -2-4 -5 s NN = 5.02 ev -1.06< y <0.14 CMS 1<p <6 GeV/c ALICE Preliminary PYHIA b ( c) e c e DPMJE Conversions Dalitz decays -0.08-0.06-0.04-0.02 0 0.02 0.04 0.06 0.08 d charge (cm) 0

Impact Parameter Distributions for p Normalized Entries -1 1.0 < p <1.3 < 1.3(GeV/c) 1.3 < Impact Parameter Distribution in 1.0 < p Impact Parameter Distribution in 1.3 < p < 1.5(GeV/c) p <1.5 1.0 < p < 1.3(GeV/c) -2 c->e b->e, b->c->e conversion elec. Dalitz elec. Normalized Entries -1 1.3 < p < 1.5(GeV/c) -2 c->e b->e, b->c->e conversion elec. Dalitz elec. c e b e (+b c e) Dalitz conversion -4-4 -5-5 -0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter (cm) -0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter (cm) 1.5 < p < 2.0 Impact Parameter Distribution in 1.5 < p < 2.0(GeV/c) 2.0 < Impact Parameter Distribution in 2.0 < p < 6.0(GeV/c) p < 6.0 Normalized Entries -1 1.5 < p < 2.0(GeV/c) -2 c->e b->e, b->c->e conversion elec. Dalitz elec. Normalized Entries -1 2.0 < p < 6.0(GeV/c) -2 c->e b->e, b->c->e conversion elec. Dalitz elec. -4-4 -5-5 -0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter (cm) -0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter (cm) Each source is characterised by a distinctive impact parameter distribution for various p range 8

p Dependent Minimum Impact Parameter Cut p dependent 0.0054+0.078*Math::Exp(-0.56*x) impact parameter cut Impact parameter cut efficiency minimum ip cut (cm) 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 1 2 3 4 5 6 7 8 (GeV/c) p Minimum impact parameter cut optimised by Monte Carlo

Estimation of Electron Backgrounds Backgrounds are estimated by weighting relevant electron source yields in MC simulations (PYHIA, DPMJE) using ALICE measured spectra Electrons from charm-hadron decays via the D- meson cross section measured with ALICE ALICE measured D 0 e PYHIA decay kinematics he contributions of light meson decays : Pion Dalitz decay (π 0 e + e γ) Conversion electrons: π 0 γγ(br 98%), γ + X e + e ) charged pions Based on measured in ALICE light meson spectra, estimate light meson decay electron backgrounds with PYHIA decay kinematics 11

Raw Yield after Impact Parameter Cut Applied ) -1 ((GeV/ c) Raw d N/dp 5 ALICE Preliminary 4 3 2 p-pb, s NN = 5.02 ev Raw yield b ( c) e c e Conversions Dalitz decays Yield of background sources measured inclusive electrons signal : b( c) e backgrounds S/B 1 5 4 3 2 1 0 1 2 3 4 5 6 7 (GeV/c) Correct for efficiency and acceptance p spectrum p 12

b e ransverse Momentum Distributions in p-pb Collisions 13

Beauty Decay Electron RpPb RpPb of electrons from beauty-hadron decays is consistent with unity in given p range Cold nuclear matter effect is not seen with current uncertainty 15

Summary & Outlook Beauty production was studied via the measurement of electrons from beauty-hadron decays. RpPb of electrons from beauty-hadron decays is compatible with unity within uncertainties between 1.2 GeV/c < p < 7 GeV/c." At low p(below 1.2 GeV/c), there is some remaining contamination, mostly proton.

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Analysis Approach for Electrons from B Hadron Decay 1.Charged particle tracks selected fulfilling track quality and eid cuts (composed by electrons from photon conversion, Dalitz, charm hadron decays, beauty hadron decays) Impact Parameter : rack s transverse distance closest approach to the primary vertex Beauty hadron has cτ 500 μm and hard momentum spectrum, which leads to larger impact parameter of decay electrons than those from background. Electron tracks from beauty hadron decays features broader IP distribution compared to that from background 2.Minimum impact parameter cut to increase S/B ratio 3. Subtract remaining background(non-heavy flavour electrons & charm hadron decay electrons) based on ALICE measurement 4. Correct subtracted electron spectra for acceptance and efficiency 21

pp Reference Cross section of beauty decay electrons in pp collisions at s = 7 ev is consistent with FONLL pqcd calculations. Extrapolation of the data from pp collisions at 7 ev to 5.02 ev based on the s dependence of FONLL calculation FONLL scaling uncertainty is included 22

NN Normalized Entries Positive Charge 1 < p < 6 GeV/c Data MC Normalized Entries Negative Charge 1 < p < 6 GeV/c Data MC -1 Normalised Entriees -2 positive charge htestpmc_t Entries 115432 Mean 2.967 RMS 0.6897-1 Normalised Entriees -2 negative charg 1 < p < 6GeV DAA MC ruth MC recon -4-4 -0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter(cm) -5-5 Charge * IP distributio 0 5 15 20 25 30 0 5 15 2 Production Vertex(cm) Prod Impact parameter cut efficiency Charge * IP distribution Fig. 13: Comparison of distribution of the radial distance of the production vertex of V reconstructed Impact MC (red), parameter and MC truth (blue) cut with efficiency minimum bias sample (generated by -0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter(cm) pixel are required. Data/MC 3 2.5 2 1.5 1 1 < p Positive Charge < 6 GeV/c Data/MC 3 2.5 2 1.5 1 1 < p Negative Charge < 6 GeV/c Flat minimum ip cut (cm) 0.08 0.07 0.06 0.05 0.04 0.5 IP Step beauty IPEfficiencyForCh e Impact paramete beauty e(esd pt) 0.5 charm e IP Step Efficiency conversion e(esd pt) 0.0054+0.078*Math::Exp(-0.56*x) 0.4 beauty e beauty Dalitz e(esd e(esd pt) pt) Fine for pions charm e conversion e(esd pt) 0.0054+0.078*Math::Exp(-0.56*x) 0.4 Dalitz e(esd pt) 0.3 from K0s decays 0.3 p dependent impact parameter cut applied p dependent impact parameter cut applied minimum ip cut (cm) 0.08 0.07 0.06 0.05 IP cut efficiency IP cut efficiency 0.2 0.2 IPEfficiencyFo Impact para 0.5 0-0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter(cm) 0.5 0.03 0.02 0.01 0.04 0.03 0.02 0.01 0 21 23 3 4 4 5 5 6 6 7 7 88 p p (GeV/c) 0 0 1 1 2 2 3 3 4 4 0-0.2-0.15-0.1-0.05 0 0.05 0.1 0.15 0.2 Charge*Impact Parameter(cm) MinJung MinJung Kweon, Kweon, Inha University Inha University March 17 17 th th, 2014, 2014 Fig. 14: p -dependent impact parameter requirement on absolute impact parameter (left) selection criterion for different electron sources. 0.1 0.1 Fig. 12: Comparison of the impact parameter distributions of pions from V0 pions in data and MC for positive charge and negative charge for 1 < p < 6 GeV/c).

Understanding of unphysical low pt excess (II) Impact parameter significance Impact parameter (cm) -1 Normalised Entriees -2 1.0 < p < 2.0 GeV/c Data MC 0 < Production Radius <3-1 Normalised Entriees -2 1.0 < p < 6.0 GeV/c Data MC counts 3 PYHIA, s = 7 ev, y < 0.8 1<p <6 GeV/c t c e b e conversion elec. Dalitz elec. 0.5 < pt < 1 (GeV/c) 0.5 < pt < 1 (GeV/c) 2-4 Data/MC -0.1-0.05 0 0.05 0.1 Data/MC ImpactParamter(cm)*Charge 4 3.5 3 1.0 < p < 2.0 GeV/c 1 < pt < 1.5 (GeV/c) -4 Data/MC -0.1-0.05 Data/MC 0 0.05 0.1 ImpactParamter(cm)*Charge 4 3.5 3 1.0 < p < 6.0 GeV/c 1 < pt < 1.5 (GeV/c) Data/MC Data/MC 3 2.5 2 1.5 3 2.5 2 1.5 Conversion Conversion electrons electrons pp at 7 ev Data/MC Data/MC 1<p 1<p <2 GeV/c <2 GeV/c t t Data/MC Data/MC 2<p 2<p <6 GeV/c <6 GeV/c (p shifted) (p shifted) t t t t 2.5 2.5 1 1 2 1.5 2 1.5 0.5 0.5 0 0-0.06-0.06-0.04-0.04-0.02-0.02 0 0 0.02 0.02 0.04 0.04 0.06 d (r ) d (cm) (r ) (c 0 0 1 1 0.5 0.5 0-0.06-0.04-0.02 0 0.02 0.04 0.06 ImpactParamter(cm)*Charge 0-0.06-0.04-0.02 0 0.02 0.04 0.06 ImpactParamter(cm)*Charge