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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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 2
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 3
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 4
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 5
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,...)
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 6
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 7
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!
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 8
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 9
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 10
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 11
CharmAOD: Classes Layout
AliAODVirtualParticle
AliAODRecoDecay
AliAODRecoDecayHFAliAODv0
AliAODRecoDecayHF2Prong
AliAODRecoDecayHF3Prong
(already exists; PWG2agreed to adapt it to this scheme)
doneto be done
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 12
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 13
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 14
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 15
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 16
Extraction of signal raw yield:Invariant mass analysis
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 17
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
• 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)
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 18
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 19
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 20
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 21
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 22
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 23
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 27
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)
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 28
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...
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 30
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 32
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 33
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 34
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)
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 35
TPC parametrization
full trackingTPC param
full trackingTPC param
full trackingTPC param
TPC param / full tracking
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 36
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
ALICE Physics Week, Muenster, 13.02.2007 Andrea Dainese 37
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