Preparation for D 0  K p analysis

Preparation for D0Kp analysis Andrea Dainese, INFN Legnaro work with Andrea Rossi, Padova University ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Analysis Scheme Event reconstruction (RAW  ESD  AOD) Charm “production” (ESD/AOD  AOD for D’s) D0 signal selection (using PID and geom/kinem cuts) Invariant mass analysis and significance maximization (in bins of pt, y, f  FRP…) Correction for efficiencies, acceptance, BR Cross section normalisation ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

MC Sample for Tools Development • 5×106 pp events at 14 TeV (PYTHIA “PhysicsRun” cocktail): • 85% pp min. bias w/o heavy quarks • ~14% pp (MSEL=1) with charm, pthard-binned • ~1% pp (MSEL=1) with beauty, pthard-binned • ALICE baseline: cross sections from NLO pQCD with “best guess” set of parameters • Fast production: TPC param + full ITS, no TOF, no TRD • Generated in Legnaro, Torino, CNAF in April06 ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Event reconstruction (RAW  ESD  AOD) • Reconstruction in the barrel • track parameters with and without primary vertex constraint • Alignment correction performed • ITS: expected residual misalignment per module (talk by A.Jacholkowski) • SPD: 10 mm (r, rf), 20 mm (z) + rotations/tilts • SDD: 20 mm (r, rf, z) + rotations/tilts • SSD: 13 mm (r, rf), 10 mm (z) + rotations/tilts • different alignment parameters to be used in MC for syst. error evaluation • Primary vertex reco (crucial for heavy flavour analyses!) • Standard AOD (talk by M.Oldenburg), extracted from ESD AliAODEvent - Part of the event Meta Data - Global event information charged tracks vertices (V0,...) ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Primary vertex from tracks (talk on Friday) K,L-decay primary D-decay B-decay warning: 90% of tracks from D decay used to find primary vertex ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

s of d0 distribution for primaries s of d0/error(d0) distr. for primaries s [mm] bias! bias! Track impact parameter measurement in pp collisions • Track impact parameter resolution: sd0 = svtxstrack • Vertex reconstructed from tracks • Bias (underestimate of d0) if the considered track is used for vertex fit: ➔primary vertex has to be reconstructed for each D candidate excluding its daughters: time-consuming! ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Effect of ITS misalignment on d0 resolution • Impact parameter resol: strack = ascatter/pt  bmeas  cmisalign • Use ITS toy model • no geometry • just gaussian smearings • Determine the cmisalign parameter for different misalign. scenarios • Estimate being repeated with full AliRoot simu/reco chain • Effect on D0 significance being studied ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Production of D0 K-p+ candidates Analysis with opposite-charge track pairs • all tracks with 6 ITS points (possibly) • two selection steps: • single-track cuts, to reduce combinatorics (CPU time & disk space) --- secondary vertex reconstruction (talk on Friday) --- • candidate cuts • implemented in AliD0toKpiandAliD0toKpiAnalysisclasses • being adapted to AOD / AliAnalysisTask scheme ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

CharmAOD: Classes Layout done to be done AliAODVirtualParticle AliAODRecoDecay AliAODRecoDecayHF AliAODv0 (already exists; PWG2 agreed to adapt it to this scheme) AliAODRecoDecayHF2Prong AliAODRecoDecayHF3Prong ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

CharmAOD scheme (with F.Prino) single-track cuts on pt and d0(pt) need common cuts for all analyses (to be studied) build all (+,-) pairs and compute secondary vtx for D+,Ds+,Lc+, D*+ for D0Kp loop on all tracks (+ & -): 1) build triplets, create AliAODRecoDecayHF3Prong, apply reco cuts (common for the 3 particles?) 2) if pair has D0 mass, attach track and create a D*+ candidate create AliAODRecoDecayHF2Prong apply D0 reco cuts on d0d0, cosqpointing and mass for D0Kppp store loop on all tracks (+ & -) … create AliAODRecoDecayHF … store store ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Selection Variables & PID • Variables: • (pt of decay tracks) • DCA: distance of closest approach between the two tracks • cosq*: cosine of decay angle • d0xd0: product of the two tracks rf impact parameters • cosqpointing: cosine of pointing angle • 3 PID “modes” considered: • no PID • K id required • (p,p), (K,K) pairs rejected ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Extraction of signal raw yield:Invariant mass analysis • Here, 5 million pp events (1/200 of 1-year’s statistics) pt > 0 “PPR cuts” ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

RS/TS~0.25 RS/TS~0.25 RS/TS~0.30 RS/TS~0.20 RS/TS~0.15 PID: (p,p), (K,K) rejected work by C.Ivan Extraction of signal raw yield:Invariant mass analysis • Beware of reflections: no PID Reflections Combinatorial ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

fit side-bands with expo: initial expo parameters • fit everything with expo + gauss with constraint on total integral Extraction of signal raw yield:Invariant mass analysis • Two possible approaches: • direct fit w/o bkg subtraction (only if large S/B, > 5-10%?) • background subtraction with event mixing + fit • Direct fit tried: exponential + gaussian ------------ From Fit ---------------------- Total S integral (+- 3s) = 39.7 +- 9.3 S/B (+- 3s) = 85% SGNC as S/sS (+- 3s) = 4.3 (58 for 109 evts) SGNC as S/S+B (+- 3s) = 4.3 ---------- From Simulation ------------ Total S integral (+- 3s) = 39.5 S/B (+- 3s) = 90% SGNC as S/S+B (+- 3s) = 4.3 (59 for 109 evts) ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

2<pt<3 GeV/c 5<pt<8 GeV/c 3<pt<5 GeV/c 0<pt<1 GeV/c Significance maximization • Optimize cut values in pt bins: maximize significance in cut-variables space (e.g. 4D space) • Example (work by A.Rossi): ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

PPR sS/S=1/SGNC Results (scaled to 109 events) • Checked performance w/o PID: not much worsening, but have to tighten cuts (larger systematic errors?) ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Corrections & Errors:Beauty feed-down (~10%) • HOW? • Monte Carlo with state-of-the-art pQCD input • use measurements from ALICE (from single m, then e) • SYSTEMATIC ERROR: uncertainty on b-bbar cross section from theory (1) or data (2). For (1), the syst. error estimated to be ~8-10% according MNR; should be smaller according FONLL ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Corrections & Errors:Acceptance, Reco & Selection Efficiency • HOW? • Embedding of MC signal in real events, and calculate all corrections in one go (selected  in-acceptance). Average correction in {pt, y} grid • NEEDED: tuned MC (good descr. of tracking effs and resols). d0 resol. is crucial, must be evaluated from data vs pt, q, PID, NITSclusters • SYSTEMATIC ERROR: - compare weights in different runs, and with the two field orientations (+z and -z) - check stability of extracted yield VS variation of cuts - repeat weights calculations (MC) with different sets for alignment corrections ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Evaluation of d0 res. from data Evaluation of d0 resolution: d0 distribution is dominated by primary particles for |d0|<d0MAX Fit in this range provides the resolution, to be then compared with that in AliRoot ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

pt 0.4 GeV/c primaries all A.Rossi ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Fit range for evaluation of resolution limited statistics! d0MAX / s • Conclusions: • a fit of all tracks’ d0 distr. in the range ~ (-3s, +3s) allows to extract the d0 resolution • resolution is a convolution of track position resolution, primary vertex resolution, misalignment effects • Open points: • devise method to separate track and vertex contributions • study other methods (e.g. using cosmic m crossing all detector) A.Rossi ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Summary • Performed realistic D0 analysis on 5 million pp events (PDC06-like sample) • First version of invariant mass fit • Developed multi-dimensional SGNC maximization method • Results (signal SGNC) compatible with PPR ones • To be repeated asap on PDC06 events • Long TO-DO list • port analysis to AOD/AliAnalysisTask framework • effect of misalignment • procedure for corrections • ... ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

EXTRA SLIDES ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

First pp data: machine scenario • b* ~ 10 m (will be 0.5 m for Pb-Pb) • Bunch spread: • transverse sbunch (b*) ~ 70 mm, long. sbunch ~ 7.5 cm • Vertex spread: • transverse svertex =sbunch/2~50 mm, long. svertex = 5.3 cm • Luminosity: (1/s2vertex) ~1030 cm-2s-1(70 kHz for spp = 70 mb) • Revol’s scenario: 20x10h ~5-10x107 min. bias events • Subsystems directly used for D0 analysis: ITS, TPC, TOF • Assumption: TPC, full ITS, half TOF (-0.9<h<0.9, Df=p ?) First pp data: detector scenario ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Candidate cuts (1) ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Corrections & Errors:Acceptance, Reco & Selection Efficiency Selection efficiency: from selected to reconstructed signal Reconstruction eff.: from reconstructed to in-acceptance Acceptance: from in-acceptance to dN/dy at y=0 central Pb-Pb central Pb-Pb ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Beauty feed-down • Feed-down can be up to 15% after selection • Can use upper cut on |d0| to control it • To subtract it: • use simulation with state-of-the-art pQCD c and b predictions for LHC • later, use b cross section measured at LHC • later, use d0 of D0 to estimate feed-down ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Simulation & Reconstruction • Detectors: full transport in ITS, track references at TPC Rin • Primary Vertex: b* = 10 m sx = sy = 50 mm, as expected for the 2007 run • Reconstruction: • TPC tracking response parametrized (old parametrization from 2002  conservative efficiencies and resolutions) • Slow Points in ITS • z of vertex from SPD • Kalman in ITS with AliITStrackerV2 • full vertex reco with tracks NOT INCLUDED (to be done before analysis) ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

TPC parametrization TPC param / full tracking full tracking TPC param full tracking TPC param full tracking TPC param ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Reco & Sele TO-DOs TO DO for single-track cuts (pt and d0): - estimate CPU time, signal and background efficiency vs cut values - estimate cut values compatible with “final” candidate cuts TO DO for secondary vertex: implement vertex fitting with errors and c2 (as done for primary) TO DO for inv. mass analysis: prepare fit procedure/code; take into account reflections in fit; background subtraction IN PROGRESS, talk on Friday IN PROGRESS ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Corrections & Errors TO-DOs TO DO for beauty feed-down: - define procedure to generate MC with B -> D0, and reweight results according to a given pQCD dsb/dpt - define procedure to use ALICE single m measurement to infer B production in the barrel TO DO for systematic errors: - define procedure for embedding (how many {pt,y} bins? needed MC stats? which real events? vs dNch/dy? vs zvertex?) - define procedure to evaluate d0 resol. from data IN PROGRESS ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese

Preparation for D 0  K p analysis