1. Open heavy flavor analysis with the ALICE experiment at LHC
Serhiy Senyukov
Università del Piemonte Orientale, INFN Torino
On behalf of ALICE Collaboration

2. Outline of the talk Physics motivation for HF analyses
Probing the QGP medium
Testing pQCD in pp-collisions
ALICE detector and its performance
Tracking and vertexing
Particle identification (PID)
Expected physics performance
Present results
D mesons via hadronic decays
Single electrons
Single muons
5th workshop on High pt Physics at LHC

3. Physics motivation: HF and QGP
Heavy flavor particles can be used as a penetrating probe of the medium created in a Heavy Ion collision
HF quarks are produced early in the collisions (large Q2)
They travel through the created medium interacting with its constituents
Radiative energy loss should play dominant role and is described by the following formula: K- K+ π+ π-
QGP A c
Ds- D0 c̄ s
Primary production
Interaction with QGP
Formation and decay of D mesons
Detection of products
The energy loss depends on: color charge (quark vs. gluon), parton mass (dead cone effect) and energy density of the medium.
5th workshop on High pt Physics at LHC

4. Physics motivation: energy loss
Experimental variable used to measure parton energy loss is the nuclear modification factor (RAA):
Energy loss should appear as a suppression of the RAA . This effect has been seen at RHIC via non-photonic electrons coming from c and b quarks. However the present models fail to reproduce the experimental results.
PRL, 98, (2007)
Physics motivation: HF and pp
Heavy flavor should be measured in pp collisions:
Gives necessary normalization for heavy-ion data. (See above)
Allows to test pQCD predictions in a new energy scale
5th workshop on High pt Physics at LHC

5. Charm production at LHC
SPS
RHIC
LHC
s (GeV)
17.2
200
5500
Ncc
≈ 0.2
≈10
≈100
x (at y=0)
≈ 10-1
≈ 10-2
≈ 10-4
Large cross-section
Much more abundant production with respect to SPS and RHIC
central y
Forward y
Small x
unexplored small-x region can be probed with charm at low pT and/or forward rapidity
down to x~10-4 at y=0 and x~10-6 in the muon arm
5th workshop on High pt Physics at LHC

6. ALICE detector ITS, TPC, TRD, ToF (||<0.9)
(di-)electrons: J/, ’, , ’,’’, open charm, open bottom, W±, Z0
muon spectrometer (-4<<-2.5)
(di-)muons: J/, ’, , ’,’’, open charm, open bottom, W±, Z0
electron-muon coincidences: open charm & bottom
ITS, TPC, ToF (||<0.9)
hadrons: D0, D±,…
5th workshop on High pt Physics at LHC

7. Detector performance: Tracking/Vertexing
Actual performance is very close to that expected from MC simulations
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8. Detector performance: PID
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9. Expected physics performance: pT spectra
pp, s = 14 TeV
charm (D0  Kp)
beauty (B  e+X)
1 year at nominal luminosity (31030 cm-2s-1)
(109 pp events)
5th workshop on High pt Physics at LHC

10. Expected performance: RAA etc.
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)
5th workshop on High pt Physics at LHC

11. Statistics collected by ALICE
Two trigger classes:
Minimum bias interaction trigger (INT1B): ≥ 1 charged particle in 8 η units
Single-muon trigger (MUS1B): forward muon in coincidence with MB trigger
By the 1st September ALICE collected:
~ 694 M of INT1B events
~ 50M of MUS1B events
Data reconstruction and analysis is on the way. Thus results presented here are obtained using the fraction of data:
140 M INT1B events for hadronic branch and 160M for single electrons analysis
4.7 M MUS1B events for single muon analysis
5th workshop on High pt Physics at LHC

12. Three ways to see open heavy flavor:
Charged hadrons (K and π) – D mesons at central rapidity
Single electrons – D and B mesons at central rapidity
Single muons – D and B mesons at forward rapidity
5th workshop on High pt Physics at LHC

13. Reconstruction via charged hadrons: analysis strategy
General idea: invariant mass analysis of track combinations (pairs, triplets, quadruplets) with correct signs
Single track selection
Particle identification using TPC and TOF
Topological cuts: impact parameter, distance between secondary and primary vertex, pointing angle
Estimation of the feed-down from beauty
Efficiency and acceptance correction
5th workshop on High pt Physics at LHC

14. Results: D0K-π+ Signal pT -integrated >2 GeV/c
Position: 1867±1 MeV/c2
Width: 14±1 MeV/c2
Hint of the signal down to 1 GeV/c
5th workshop on High pt Physics at LHC

15. Results: D+K-π+π+ Signal pT -integrated >2 GeV/c
Position: 1870±1 MeV/c2
Width: 13±1 MeV/c2
Hint of the signal down to 1 GeV/c
5th workshop on High pt Physics at LHC

16. Results: D*±D0πs±
Signal pT -integrated >2 GeV/c seen as ΔM(Kππ-Kπ)
Position: ±0.03 MeV/c2
Width: 0.62±0.03 MeV/c2
Hint of the signal down to 1 GeV/c
5th workshop on High pt Physics at LHC

17. More results coming: D0K+π+π-π+
Signal pT -integrated for 3<pT<5 GeV/c
Position: 1864±2 MeV/c2
Width: 15±2MeV/c2
5th workshop on High pt Physics at LHC

18. More results coming: Ds+K+K-π+
Signal pT -integrated for 3<pT<5 GeV/c
Position: ±1.1 MeV/c2
Width: 4.4±1.4 MeV/c2
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19. Reconstruction via single electrons: analysis strategy
Single track selection
Identification as electron by TPC, TRD and TOF
Subtraction of the photonic component using the cocktail
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20. Results: B,D  e + X
Only TPC and TOF are used for electrons identification.
TRD calibration is ongoing
Possibility to use EmCAL is considered
5th workshop on High pt Physics at LHC

21. Reconstruction via single muons: analysis strategy
remove hadrons & low pt  secondary /K: tracking-trigger matching
remove  secondary /K: DCA cut (only if pt < 1.5 GeV/c studied)
remove   primary /K: vertex displacement method, high pt data, models
correct  dN/dpt for efficiency/acceptance
convert to  differential cross section
unravel charm & beauty  dN/dpt components via a combined fit
from  cross sections to B (D)-hadron cross sections
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22. B,D  μ + X: Subtraction of   primary /K using high pT data:
Subtraction hadrons & low pt  secondary /K:
This particles are absorbed by the iron absorber placed between tracker and trigger chambers.
Effect is seen on DCA distribution  DCA – Distance of Closest Approach (distance between extrapolated track & interaction vertex in the plane perpendicular to the beam direction and containing the vertex)
Subtraction of   primary /K using high pT data:
Fit high pT range (i.e. charm & beauty) & extrapolate at low pT
Subtraction from the total pT distribution gives an estimate of the muon yield from primary /K and allows to extract the muon yield from HF decays
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23. Results: B,D  μ + X
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24. Conclusions
Open heavy flavor is an important tool for studying Quark Gluon Plasma and QCD:
Measure of medium properties via energy loss
Test of pQCD in a new energy domain
ALICE is well equipped for heavy flavor:
Two rapidity regions coverage
Good tracking and vertexing
Good PID capabilities
First promising results:
D+, D0, D* and Ds signal seen in a range 1<pT<12 GeV/c
Uncorrected pT-spectra for single electrons and muons are obtained.
Pb-Pb collisions to come
5th workshop on High pt Physics at LHC