Andrea Dainese

1
Hadronic CharmIntroduction D0?Kp

• Andrea Dainese
• (INFN LNL)

2
Analysis Scheme
Event reconstruction (RAW ? ESD ? AOD)
Charm production (ESD/AOD ? AOD for Ds)
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
Physics ( comp. with theory)
3
Heavy-quark production at the LHC

• Baseline 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 --
Theoretical uncertainty of a
factor 2-3
MNR code Mangano, Nason, Ridolfi, NPB373 (1992)
295.
4
MC Sample for Tools Development

• 5106 pp events at 14 TeV (PYTHIA PhysicsRun
  cocktail)
• 85 pp min. bias w/o heavy quarks
• 14 pp (MSEL1) with charm, pthard-binned
• 1 pp (MSEL1) with beauty, pthard-binned
• Fast production full ITS, TPC param, no TOF, no
  TRD
• Generated via LCG in Legnaro, Torino, CNAF in
  April06

5
Analysis Scheme
Event reconstruction (RAW ? ESD ? AOD)
Charm production (ESD/AOD ? AOD for Ds)
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
Physics ( comp. with theory)
6
Event reconstruction (RAW ? ESD ? AOD)

• Reconstruction in the barrel ? tracks
• Standard AOD (Analysis Object Data), extracted
  from ESD (Event Summary Data)

7
The key issue for HF reco track impact parameter

• Distance of closest approach to the primary
  vertex
• At high pt d0 ? ct ? HF decay tracks displaced
  by 100 mm
• ? ALICE ITS with SPD

8
Track impact parameter measurement in pp
collisions

• Track impact parameter resolution sd0 svtx ?
  strack
• Vertex reconstructed from tracks (LNL, To)
• Bias (underestimate of d0) if the considered
  track is used for vertex fit

9
Effect of ITS misalignment on d0 resolution

• Impact parameter resol
• strack 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)

null residual full full
10
Analysis Scheme
Event reconstruction (RAW ? ESD ? AOD)
Charm production (ESD/AOD ? AOD for Ds)
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
Physics ( comp. with theory)
11
Analysis scheme (ESD/AOD ? AOD)
Standard AOD
ESD
or
Standard AOD HF vertices (15-20 in size)
2-prong HF
3-prong HF
...
12
AliAnalysisVertexingHF
Bari, Legnaro, Torino
single-track cuts on quality, pt (d0?) common
cuts for all analyses
build all (,-) pairs and compute secondary vtx
for D,Ds,Lc,D
for D0?Kp, J/y (from B)?ee
loop on all tracks ( -) build triplets,
create AliAODRecoDecayHF3Prong, apply reco cuts
(common for the 3 particles?)
create AliAODRecoDecayHF2Prong apply reco cuts
tight D0 mass cut loop on all tracks for D
candidates
for D0?Kppp
loop on all tracks ( -) create
AliAODRecoDecayHF
store D0
store D0
store D, Ds, Lc
store J/y
store D
13
Secondary vertex reconstruction

• Two 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

14
Set of classes for storage and analysis of
candidates
AliVParticle
AliAODRecoDecay
PWG3
PWG2
AliAODRecoDecayHF
AliAODv0
AliAODRecoDecayHF2Prong
AliAODRecoDecayHF3Prong
D,Ds,Lc,...
D0,J/y from B,...
AliAODRecoDecayHF4Prong
D0
15
Analysis Scheme
Event reconstruction (RAW ? ESD ? AOD)
Charm production (ESD/AOD ? AOD for Ds)
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
16
Selection Variables PID

• Variables
• 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 (TOF)
• keep all pairs (no PID)
• keep only pairs with a K
• reject only (p,p), (K,K)

17
Extraction of signal raw yieldInvariant mass
analysis

• Here, 5 million pp events (1/200 of 1-years
  statistics)

pt gt 0 PPR cuts
18
Extraction of signal raw yieldInvariant mass
analysis

• Beware of reflections

no PID
Reflections
Combinatorial
19
Extraction of signal raw yieldInvariant mass
analysis

• Two possible approaches
• direct fit w/o bkg subtraction (only if large
  S/B, gt 50?)
• 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/?SB (- 3s) 4.3 ----------
From Simulation ------------ Total S integral
(- 3s) 39.5 S/B (- 3s) 90 SGNC as S/?SB
(- 3s) 4.3 (59 for 109 evts)
20
Significance maximization

• Optimize cut values in pt bins maximize
  significance in cut-variables space (e.g. 4D
  space)
• Example

A.Rossi
21
Results
pp (109 evts)
pp (109 evts)
PPR

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

22
Analysis Scheme
Event reconstruction (RAW ? ESD ? AOD)
Charm production (ESD/AOD ? AOD for Ds)
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
Physics ( comp. with theory)
23
Corrections ErrorsBeauty feed-down (10)

• Methods
• 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 NLO
  pQCD

24
Corrections ErrorsAcceptance, Reco
Selection Efficiency

• Method
• 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, 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

25
Effect of misalignment on S/B and significance
(S/?SB)

• Residual misalignment negligible effect
• Full misalignment 15-20 worsening of
  statistical errors

26
Evaluation of d0 res. from data

• Evaluation of d0 resolution
• d0 distribution is dominated
• by primary particles for
• d0ltd0MAX
• Fit in this range provides
• the resolution, to be then
• compared with that in AliRoot

27
Evaluation of d0 res. from data
pt ? 4.5 GeV/c
pt ? 0.4 GeV/c
pt ? 1.1 GeV/c
primaries all
A.Rossi
28
Evaluation of d0 res. from data

• 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
• ? 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

no misal.
ITS
sd012mm OK!
29
Analysis Scheme
Event reconstruction (RAW ? ESD ? AOD)
Charm production (ESD/AOD ? AOD for Ds)
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
Physics ( comp. with theory)
30
Calibrating the probe (pp, ?s 14 TeV)
Expected sensitivity in comparison to pQCD
D0 ? Kp
stat. err. vs events
1 month
Detector configuration ITS TPC TOF
1 year at nominal luminosity (109 pp events)
31
Charm E Loss RAA
E loss calc. Armesto, Dainese, Salgado, Wiedemann
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
32
Heavy-to-light ratios
E loss calc. Armesto, Dainese, Salgado, Wiedemann
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
33
Summary

• Prepared software tools for reconstruction of
  (most) hadronic charm decays (J/y) 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...)
• D0?Kp
• run a realistic analysis (sgnbkg 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

34
EXTRA SLIDES
35
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/?250 mm, long.
  svertex 5.3 cm
• Luminosity (?1/s2vertex) 1030 cm-2s-1 (70 kHz
  for spp 70 mb)
• Revols scenario 20x10h 5-10x107 min. bias
  events
• Subsystems directly used for D0 analysis ITS,
  TPC, TOF
• Assumption TPC, full ITS, half TOF (-0.9lthlt0.9,
  Dfp ?)

First pp data detector scenario
36
Candidate cuts (1)
37
Corrections ErrorsAcceptance, 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 y0

central Pb-Pb
central Pb-Pb
38
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

39
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)

40
TPC parametrization
TPC param / full tracking
full tracking TPC param
full tracking TPC param
full tracking TPC param
41
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
42
Corrections Errors TO-DOs

• TO DO for beauty feed-down
• - define procedure to generate MC with B -gt 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