1. Hadronic Charm: Introduction & D0Kp
Andrea Dainese
(INFN LNL)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

2. 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
Physics (& comp. with theory)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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.
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

4. 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

5. 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
Physics (& comp. with theory)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

6. Event reconstruction (RAW  ESD  AOD)
Reconstruction in the barrel  tracks
Standard AOD (Analysis Object Data), extracted from ESD (Event Summary Data):
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

7. The key issue for HF reco: track impact parameter
Primary
Vertex B e X d0
rec. track
Distance of closest approach to the primary vertex
At “high” pt: d0  ct  HF decay tracks displaced by ~100 mm
 ALICE ITS with SPD
< 60 mm (rf)
for pT > 1 GeV/c
BA, CT, LNL, PD
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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:
s of d0 distribution for primaries
s [mm]
bias!
bias!
s 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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+
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

10. 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
Physics (& comp. with theory)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

11. Analysis scheme (ESD/AOD ➔ AOD)
Standard AOD
ESD or
Standard AOD
+ HF vertices
(15-20% in size)
2-prong HF
3-prong HF
...
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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 J/y
store D0
store D*+
store D+, Ds+, Lc
store D0
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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 x
pull
resolution [mm]
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

14. Set of classes for storage and analysis of candidates
AliVParticle
AliAODRecoDecay
PWG2
PWG3
AliAODRecoDecayHF
AliAODv0
AliAODRecoDecayHF2Prong
AliAODRecoDecayHF3Prong
D0,J/y from B,...
D+,Ds,Lc,...
AliAODRecoDecayHF4Prong D0
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

15. 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

16. Selection Variables & PID
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)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

17. Extraction of signal raw yield: Invariant mass analysis
Here, 5 million pp events (1/200 of 1-year’s statistics)
pt > 0
“PPR cuts”
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

18. Extraction of signal raw yield: Invariant mass analysis
RS/TS~0.30
RS/TS~0.25
RS/TS~0.20
RS/TS~0.15
PID: (p,p), (K,K) rejected
Beware of reflections:
no PID
Reflections
Combinatorial
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

19. Extraction of signal raw yield: Invariant mass analysis
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 (+- 3s) =
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)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

20. Significance maximization
Optimize cut values in pt bins: maximize significance in cut-variables space (e.g. 4D space)
Example:
3<pt<5 GeV/c
0<pt<1 GeV/c
2<pt<3 GeV/c
5<pt<8 GeV/c
A.Rossi
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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?)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

22. 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
Physics (& comp. with theory)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

23. Corrections & Errors: Beauty 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

24. Corrections & Errors: Acceptance, 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

25. Effect of misalignment on S/B and significance (S/S+B)
Residual misalignment: negligible effect
“Full” misalignment: 15-20% worsening of statistical errors
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

26. 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

27. Evaluation of d0 res. from data
pt  0.4 GeV/c
pt  1.1 GeV/c
pt  4.5 GeV/c
primaries
all
A.Rossi
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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
sd0=12mm: OK!
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

29. 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
Physics (& comp. with theory)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

30. Calibrating the probe (pp, s = 14 TeV)
measured at 14 TeV, then
scaled by pQCD to 5.5 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)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

31. Charm E Loss : RAA 1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
E loss calc.:
Armesto, Dainese, Salgado, Wiedemann
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

32. Heavy-to-light ratios
probes colour-charge dep.
of QCD energy loss
probes mass dep.
of QCD energy loss
E loss calc.:
Armesto, Dainese, Salgado, Wiedemann
1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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 (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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

34. EXTRA SLIDES
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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/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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

36. Candidate cuts (1)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

37. 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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)
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

40. TPC parametrization TPC param / full tracking full tracking TPC param
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese

42. 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
Terzo Convegno sulla Fisica di ALICE, LNF, Andrea Dainese