alice physics week, muenster, 13.02.2007 andrea dainese 1 andrea dainese, infn legnaro work with...

ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 1

Andrea Dainese, INFN LegnaroAndrea Dainese, INFN Legnarowork with Andrea Rossi, Padova Universitywork with Andrea Rossi, Padova University

Preparation for DPreparation for D00KK analysis analysis


Invariant mass analysis and significance maximization (in bins of pt, y, RP…)

Analysis SchemeEvent reconstruction (RAW ESD AOD)

Charm “production” (ESD/AOD AOD for D’s)

D0 signal selection (using PID and geom/kinem cuts)

Correction for efficiencies, acceptance, BR

KDselectedN 0

1||

0

yt

Dproduced

dydp

dN

Cross section normalisation1||

0

yt

D

dydp

d


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

11.2 mb

0.16

0.5 mb

0.007

ccevN cc /bbevN bb /

mb 70inelpp







KDselectedN 0

1||

0

yt

Dproduced

dydp

dN


0

yt

D

dydp

d


Event reconstruction (RAW ESD AOD)

Reconstruction in the barreltrack parameters with and without primary vertex constraint

Alignment correction performedITS: expected residual misalignment per module (talk by A.Jacholkowski)

SPD: 10 m (r, r), 20 m (z) + rotations/tilts

SDD: 20 m (r, r, z) + rotations/tilts

SSD: 13 m (r, r), 10 m (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 ESDAliAODEvent

- Part of the event Meta Data- Global event information

chargedtracks

vertices(V0,...)


Primary vertex from tracks

warning: 90% of tracks from D decay used to find primary vertex

(talk on Friday)

primary K,-decay

D-decay B-decay


Track impact parameter measurement in pp collisions

Track impact parameter resolution: d0 = vtx track

Vertex reconstructed from tracks

Bias (underestimate of d0) if the considered track is used for vertex fit: of d0 distribution for primaries

m

bias!

bias!

of d0/error(d0) distr. for primaries

➔ primary vertex has to be reconstructedfor each D candidateexcluding its daughters:time-consuming!


Effect of ITS misalignment on d0 resolution

Impact parameter resol:

track = ascatter/pt bmeas cmisalign

Use ITS toy modelno 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







KDselectedN 0

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yt

Dproduced

dydp

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0

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dydp

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Production of D0 K-+ 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 AliD0toKpi and AliD0toKpiAnalysis classes

being adapted to AOD / AliAnalysisTask scheme


CharmAOD: Classes Layout

AliAODVirtualParticle

AliAODRecoDecay

AliAODRecoDecayHFAliAODv0

AliAODRecoDecayHF2Prong

AliAODRecoDecayHF3Prong

(already exists; PWG2agreed to adapt it to this scheme)

doneto be done


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

create AliAODRecoDecayHF2Prong apply D0 reco cuts on d0d0, cospointing and mass

store

loop on all tracks (+ & -): 1) build triplets, create AliAODRecoDecayHF3Prong,apply reco cuts (common for the 3 particles?)

2) if pair has D0 mass, attach trackand create a D*+ candidate

loop on all tracks (+ & -) …create AliAODRecoDecayHF…

store store

for D+,Ds+,c

+, D*+

for D0K

for D0K







KDselectedN 0

1||

0

yt

Dproduced

dydp

dN


0

yt

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dydp

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Selection Variables & PID

Variables:(pt of decay tracks)

DCA: distance of closest approach between the two tracks

cos*: cosine of decay angle

d0xd0: product of the two tracks r impact parameters

cospointing: cosine of pointing angle

3 PID “modes” considered:no PID

K id required

(,), (K,K) pairs rejected


Extraction of signal raw yield:Invariant mass analysis

Here, 5 million pp events (1/200 of 1-year’s statistics)

pt > 0“PPR cuts”



Beware of reflections:

Reflections

Combinatorial

no PIDRS/TS~0.30 RS/TS~0.25 RS/TS~0.25

RS/TS~0.20 RS/TS~0.15

work by C.Ivan

PID: (,), (K,K) rejected



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

• fit side-bands with expo: initial expo parameters• fit everything with expo + gauss with constraint on total integral

------------ From Fit ---------------------- Total S integral (+- 3) = 39.7 +- 9.3 S/B (+- 3) = 85% SGNC as S/S (+- 3) = 4.3 (58 for 109 evts) SGNC as S/S+B (+- 3) = 4.3 ---------- From Simulation ------------ Total S integral (+- 3) = 39.5 S/B (+- 3) = 90% SGNC as S/S+B (+- 3) = 4.3 (59 for 109 evts)


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):

2<pt<3 GeV/c3<pt<5 GeV/c5<pt<8 GeV/c


Results (scaled to 109 events)

Checked performance w/o PID: not much worsening, but have to tighten cuts (larger systematic errors?)

PPR

S/S=1/SGNC







KDselectedN 0

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Dproduced

dydp

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0

yt

D

dydp

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Corrections & Errors:Beauty feed-down (~10%)

HOW?

1. Monte Carlo with state-of-the-art pQCD input

2. use measurements from ALICE (from single , 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


Corrections & Errors:Acceptance, Reco & Selection EfficiencyHOW?

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, , 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


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


A.Rossi

pt 0.4 GeV/c

primariesall


A.Rossi

pt 1.1 GeV/c

primariesall


A.Rossi

pt 4.5 GeV/c

primariesall


A.Rossi

limited statistics!d0MAX /

Fit range for evaluation of resolution

Conclusions:• a fit of all tracks’ d0 distr. in the range ~ (-3, +3) allows to extract the d0 resolution• resolution is a convolution of track position resolution, primary vertex resolution, misalignment effectsOpen points:• devise method to separate track and vertex contributions• study other methods (e.g. using cosmic crossing all detector)


Summary

Performed realistic D0 analysis on 5 million pp events (PDC06-like sample)First version of invariant mass fitDeveloped multi-dimensional SGNC maximization methodResults (signal SGNC) compatible with PPR onesTo be repeated asap on PDC06 events

Long TO-DO listport analysis to AOD/AliAnalysisTask frameworkeffect of misalignmentprocedure for corrections...


EXTRA SLIDES


First pp data: machine scenario

* ~ 10 m (will be 0.5 m for Pb-Pb)

Bunch spread:

transverse bunch (*) ~ 70 m, long. bunch ~ 7.5 cm

Vertex spread:

transverse vertex =bunch/2~50 m, long. vertex = 5.3 cm

Luminosity: (1/vertex) ~1030 cm-2s-1 (70 kHz for pp = 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<<0.9, =)

First pp data: detector scenario


Candidate cuts (1)


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


Beauty feed-down

Feed-down can be up to 15% after selection

Can use upper cut on |d0| to control it

To subtract it:1) use simulation with state-

of-the-art pQCD c and b predictions for LHC

2) later, use b cross section measured at LHC

3) later, use d0 of D0 to estimate feed-down


Simulation & Reconstruction

Detectors: full transport in ITS, track references at TPC Rin

Primary Vertex: * = 10 m x = y = 50 m, 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)


TPC parametrization

full trackingTPC param



TPC param / full tracking


Reco & Sele TO-DOsTO 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 2 (as done for primary)

TO DO for inv. mass analysis: prepare fit procedure/code; take into account reflections in fit; background subtraction

IN PROGRESS

IN PROGRESS, talk on Friday


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 db/dpt

- define procedure to use ALICE single 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 dataIN PROGRESS

alice physics week, muenster, 13.02.2007 andrea dainese 1 andrea dainese, infn legnaro work with...

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