Terzo Convegno sulla Fisica di ALICE, LNF, 13.11.2007 Andrea Dainese 1 Andrea Dainese (INFN LNL)...

Terzo Convegno sulla Fisica di ALICE, LNF, 13.11.2007 Andrea Dainese 1

Andrea Dainese Andrea Dainese (INFN LNL)(INFN LNL)

Hadronic Charm:Hadronic Charm:Introduction & DIntroduction & D00KK


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

Physics (& comp. with theory)


Heavy-quark production at the LHCBaseline predictions: NLO (MNR code) in pp + binary scaling (shadowing included for PDFs in the Pb)

ALICE baseline (PPR) for charm / beauty:

system :

sNN :Pb-Pb (0-5% centr.)

5.5 TeV

p-Pb (min. bias)

8.8 TeV

pp

14 TeV

4.3 / 0.2 7.2 / 0.3 11.2 / 0.5

115 / 4.6 0.8 / 0.03 0.16 / 0.007

0.65 / 0.80 0.84 / 0.90 --

[mb] QQNNQQ

totN

Theoretical uncertainty of a factor 2-3

MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.

98EKSshadowingC


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

Fast production: full ITS, TPC param, no TOF, no TRD

Generated via LCG in Legnaro, Torino, CNAF in April06







KDselectedN 0

1||

0

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Dproduced

dydp

dN


0

yt

D

dydp

d



Event reconstruction (RAW ESD AOD)

Reconstruction in the barrel tracksStandard AOD (Analysis Object Data), extracted from ESD (Event Summary Data):

Set of TLists:

AliAODHeaderPart of the event Meta Data, e.g.:• run #, event #, field, trigger, event tags

Global event information, e.g.:• centrality, multiplicity

chargedtracks

V0

(K0S,)

jets & 0

Set of TLists:



chargedtracks

V0

(K0S,)

jets & 0


PrimaryVertex B

e

Xd0

rec. track

The key issue for HF reco: track impact parameter

Distance of closest approach to the primary vertex

At “high” pt: d0 c HF decay tracks displaced by ~100 m

ALICE ITS with SPD

< 60 m (r)for pT > 1 GeV/c

BA, CT, LNL, PD


Track impact parameter measurement in pp collisions

Track impact parameter resolution: d0 = vtx track

Vertex reconstructed from tracks (LNL, To)

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

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

primary vertex has to be reconstructed for each D candidate excluding its daughters

D-decay


Effect of ITS misalignment on d0 resolution

Impact parameter resol:

track = ascatter/pt bmeas cmisalign

Effect studied with full simulation of exptected initial (full+) and residual (after realignment) misalignments

See talk tomorrow

Effect on D0 measurement studied (see later)

nullresidualfullfull+







KDselectedN 0

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Analysis scheme (ESD/AOD ➔ AOD)

Set of TLists:



chargedtracks

V0

(K0S,)

jets & 0

Set of TLists:



chargedtracks

V0

(K0S,)

jets & 0

Standard AOD

Standard AOD+ HF vertices (15-20% in size)

Set of TLists:



chargedtracks

V0

(K0S,)

jets & 0

Set of TLists:



chargedtracks

V0

(K0S,)

jets & 02-prong

HF3-prong

HF...

ESDor


AliAnalysisVertexingHFsingle-track cuts on quality, pt (d0?)

[common cuts for all analyses]

build all (+,-) pairs and compute secondary vtx

create AliAODRecoDecayHF2Prong apply reco cuts

store D0

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

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

store D+, Ds+, c store D0

for D+,Ds+,c

+,D*+

for D0K

for D0K, J/ (from B)ee

store J/

tight D0 mass cutloop on all tracks for D*+ candidates

store D*+

Bari, Legnaro, Torino


x

pull

x

reso

lutio

n [

m]

Secondary vertex reconstructionTwo different vertexers available

classical vertexer (used also for primary vertex reco): finder + fast fitting algorithm (LNL-To)

Kalman-filter vertexer, with possibility to apply topological & mass constraints (GSI), under test

Possibility to remove D0 decay tracks from primary vertex unbiased (or less biased) estimate of impact parameters


Set of classes for storage and analysis of candidates

AliVParticle

AliAODRecoDecay

AliAODRecoDecayHFAliAODv0

AliAODRecoDecayHF2Prong AliAODRecoDecayHF3ProngD+,Ds,c,...D0,J/ from B,...

AliAODRecoDecayHF4ProngD0

PWG3PWG2







KDselectedN 0

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Dproduced

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Selection Variables & PID

Variables: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 (TOF):keep all pairs (no PID)

keep only pairs with a K

reject only (,), (K,K)


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



Two possible approaches:direct fit w/o bkg subtraction (only if large S/B, > 50%?)

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:

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

A.Rossi


Results

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

pp (109 evts)

PPR

pp (109 evts)







KDselectedN 0

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

Methods:

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 NLO pQCD


Corrections & Errors:Acceptance, Reco & Selection EfficiencyMethod:

Embedding of MC signal in real events, and calculate all corrections in one go (selected in-acceptance). Average correction in {pt, y} grid use ALICE common correction framework (A.Mastroserio)

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


Effect of misalignment on S/B and significance (S/S+B)

Residual misalignment: negligible effect

“Full” misalignment: 15-20% worsening of statistical errors


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


pt 0.4 GeV/c

primariesall

Evaluation of d0 res. from datapt 1.1 GeV/c pt 4.5 GeV/c

A.Rossi


Evaluation of d0 res. from data

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 effects devise method to separate track and vertex contributions

Study other (complementary) methods e.g. using cosmic muons crossing all ITS d0 resolution at high pt

d0=12m: OK!

no misal.

ITS







KDselectedN 0

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Dproduced

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Calibrating the probe (pp, s = 14 TeV)

D0 K

tpp

tAA

colltAA pN

pN

NpR

d/d

d/d1)( measured at 14 TeV, then

scaled by pQCD to 5.5 TeV

Expected sensitivity in comparison to pQCD:

1 year at nominal luminosity(109 pp events)

Detector configuration:ITS + TPC + TOF

~1 month

stat. err. vs # events


Charm E Loss : RAA

1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)

E loss calc.:Armesto, Dainese, Salgado, Wiedemann


Heavy-to-light ratios

1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)

)()()(/ thAAt

DAAthD pRpRpR probes colour-charge dep.

of QCD energy loss

)()()( D from eB from e/ tAAtAAtDB pRpRpR

probes mass dep.of QCD energy loss

E loss calc.:Armesto, Dainese, Salgado, Wiedemann


Summary

Prepared software tools for reconstruction of (most) hadronic charm decays (+J/) in one go (Ba - LNL/Pd - To)

will (soon) run on ESD and on AOD

will (soon) allow to choose between two vertexers

to be tested on the Grid

Track impact parameter measurement is crucial for hadronic charm (esp. in Pb-Pb)

studied possible systematics on this quantity (primary vtx, misalignment...)

D0K:run a realistic analysis (sgn+bkg together) on 5M pp events

tried a first version of invariant mass fit to extract raw yield warning: signal reflection

developed multi-dimensional SGNC maximization method

results (signal SGNC) compatible with PPR ones

set up procedure to apply 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

Terzo Convegno sulla Fisica di ALICE, LNF, 13.11.2007 Andrea Dainese 1 Andrea Dainese (INFN LNL)...

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