1. Measurement of heavy-flavour production down to low pT with ALICE
Andrea Dainese
INFN – Legnaro
for the ALICE Collaboration
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

2. Layout Heavy-flavour production at LHC
baseline predictions (pQCD)
Heavy quarks as probes of the initial state
importance of low pT measurements
Why ALICE is well-suited for these measurements
Strategies and expected performance for:
D0  K-p+
B  e + X
Summary
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

3. c and b production in pp at the LHC: testing QCD at s = 14 TeV
Important test of pQCD in a new energy domain (7sTEVATRON)
remember the “15-years saga of b production at the Tevatron”*…
…and D production not yet fully reconciled 
Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033
CDF, PRL91 (2003)
FONLL: Cacciari, Nason
* M.Mangano
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

4. pQCD predictions for the LHC
Compare predictions by several different models (HERA-LHC Workshop)
CERN/LHCC
hep-ph/
charm
beauty
Good agreement between collinear fact.-based calculations:
FO NLO (Mangano, Nason, Risolfi) and FONLL (Cacciari, Nason)
kT fact. CASCADE (Jung) higher at large pT
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

5. Theoretical Uncertainties
Evaluation of theoretical uncertainties (HERA-LHC Workshop)
CERN/LHCC
hep-ph/
charm
beauty
MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295.
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

6. ALICE baseline yields Cross sections: NLO (MNR code)
mc=1.2 GeV, mF=mR=2mc; mb=4.75 GeV, mF=mR=mb
Yields: assuming sppinel = 70 mb at 14 TeV
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

7. c and b production at the LHC: a probe of small-x gluons
Probe unexplored small-x region with HQs at low pT and/or forward y
down to x~10-4 with charm already at y=0
Cartoon
charm
beauty
Window on the rich phenomenology of high-density PDFs
gluon saturation / recombination effects
breakdown of factorization ?
increasing s
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

8. (A.D., K.Eskola, V.Kolhinen, K.Kutak, H.Jung, K.Peters, R.Vogt)
Deviations from pQCD baseline due to small-x effects? maybe already in pp ... “Small-x effects in heavy-quark production in pp” in HERA-LHC workshop proceedings
CERN/LHCC
hep-ph/
(A.D., K.Eskola, V.Kolhinen, K.Kutak, H.Jung, K.Peters, R.Vogt)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

9. GLR-MQ non-linear term in DGLAP eq.
Eskola, Honkanen, Kolhinen, Qiu, Salgado, NPB660 (2003) 211 R
non-linear (quadratic)
correction has “–” sign
Q2 evolution is slower
Refit HERA F2 data, reduces F2 at
low x and moderate Q2
xg(x,Q2) at
low Q2 (<10 GeV2) and x (<10-3)
is larger than in DGLAP
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

10. Non-linear effects in BK equation×
Kutak, Kwiecinski, Martin, Stasto
Non-linear part has no impact in the kinematical region of HERA
H.Jung et al., CASCADE MC with CCFM uPDFs
and KKMS nonlinear term
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

11. GLR-MQ vs BK: gluons R = 5 GeV-1 = 1 fm R = 4 GeV-1 = 0.8 fm
Caveat: LO!
Linear (dashed) vs non-linear (solid) in BK with R = 4 GeV-1
Linear (blue) vs non-linear (red) in
DGLAP
Kutak, Kwiecinski, Martin, Stasto
Eskola, Honkanen, Kolhinen, Qiu, Salgado, NPB660 (2003) 211
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

12. Charm at s = 14 TeV: x,Q2 range (1)
Simple estimate: c
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

13. Charm at s = 14 TeV: x,Q2 range (2)
PYTHIA simulation (LO):
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

14. Charm at s = 14 TeV: x,Q2 range (3)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

15. Non-linear effects on charm in pp
14 TeV
R = 0.6 fm
R = 0.3 fm
|y| < 1
R = 1 fm
Charm enhancement due to non-linear effects in GLR-MQ
Charm suppression due to non-linear effects in BK
Dainese, Bondila, Eskola, Kolhinen, Vogt, JPG30 (2004) 1787
H.Jung et al., CASCADE MC with CCFM uPDFs
and KKMS nonlinear term
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

16. Probing nuclear initial state with HQs
Shadowing in pA (AA)
CGC in pA (AA)
Double parton scattering in pA
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

17. Probing nuclear initial state with HQs
Shadowing in pA (AA)
CGC in pA (AA)
Double parton scattering in pA
Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

18. Probing nuclear initial state with HQs
Shadowing in pA (AA)
CGC in pA (AA)
Double parton scattering in pA
Saturation scale Qs2(x) ~ xg(x)A/RA2 ~ xg(x)A1/3
At LHC for x~10-4, Qs~2-2.5 GeV > mc
For mT,c~Qs, charm prod. CGC-dominated:
suppression: scales with Npart in pA (not Ncoll)
harder pT spectra, since typical kT~Qs~2 GeV, while
in standard factorization kT~LQCD~0.2 GeV
Kharzeev, Tuchin, NPA 735 (2004) 248
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

19. Probing nuclear initial state with HQs
Shadowing in pA (AA)
CGC in pA (AA)
Double parton scattering in pA
probe “many-body” PDFs
normal and anomalous: different A dep.
signature: events with “tagged” DD (can use D0+e+ or e+e+) and ch. conj.
NB: there is a “background” from normal bb events, but it can be estimated from measured single inclusive b cross section
predicted rate: cccc/cc ~ 10% (Treleani et al.)
Cattaruzza, Del Fabbro, Treleani, PRD 70 (2004)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

20. The ALICE Detector |h| < 0.9, B = 0.5 T TPC + silicon tracker
g, e, p, K, p identification
-4 < h < -2.5
muons
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

21. ALICE heavy-flavour potential
HERA-LHC Workshop
CERN/LHCC
hep-ph/
ALICE combines electronic (|h|<0.9), muonic (-4<h<-2.5), hadronic (|h|<0.9) channels
ALICE covers low-pT region
ALICE covers central and forward regions
Precise vertexing in the central region to identify D (ct ~ mm) and B (ct ~ 500 mm) decays
A.Dainese (ALICE)
M.Smizanska (ATLAS)
C.Weiser (CMS)
U.Uwer (LHCb)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

22. Heavy-flavour analyses
Hadronic decays:
D0K-p+, D*+D0p+, D+K-p+p+, Ds+K+K0*/fp+…
Leptonic decays:
B e/m + X
Invariant mass analysis of lepton pairs: BB, DD, BDsame, J/y, y’,  family, B J/Y + X
BB m m m (J/y m)
e-m correlations
talks by M.Gagliardi, D.Stocco
central rapidity (this talk)
In red, channels studied for the
PPR Volume 2
CERN/LHCC
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

23. Vertexing: track d0 resolution
Resolution mainly provided by the 2 layers of silicon pixels
< 60 mm (rf)
for pT > 1 GeV/c
Primary
Vertex B e X d0
rec. track
PIXEL CELL
z: 425 mm
rf: 50 mm
Two layers:
r = 4 cm
r = 7 cm
 9.8 M
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

24. D0 K-p+: Invariant mass analysis
Example (extrapolated to expectation for 109 pp events):
0.5-1 GeV/c GeV/c GeV/c
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

25. D0 K-p+: Results Down to pT ~ 0 in pp and p-Pb (1 GeV/c in Pb-Pb)
inner bars: stat. errors
outer bars: stat.  pt-dep. syst.
not shown: 9% (Pb-Pb), 5% (pp, p-Pb)
normalization errors
1 year at nominal luminosity
(107 central Pb-Pb events,
109 pp events)
+ 1 year with 1month of p-Pb running
(108 p-Pb events)
Down to pT ~ 0 in pp and p-Pb (1 GeV/c in Pb-Pb)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

26. B  e + X: Detection strategy
Electron PID: reject most of the hadrons
d0 cut: reduce charm and bkg electrons (Dalitz, g conv.)
Subtract (small) residual background (ALICE data + MC)
Primary
Vertex B e X d0
rec. track
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

27. B  e + X: Results inner bars: stat. errors
outer bars: stat.  pT-dep. syst. errors
not shown: 5% normalization error
Using electrons in
2 < pT < 20 GeV/c
obtain B meson
2 < pTmin < 30 GeV/c
MC-based
procedure
à la UA1
1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

28. Comparison to pQCD predictions
pp, s = 14 TeV
charm (D0  Kp)
beauty (B  e+X)
1 year at nominal luminosity
(109 pp events)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

29. How to detect the enhancement due to nonlinear effects?
The idea is that the effect (enh. only at very low pt) cannot be mimicked by NLO pQCD
In practice: consider ratio “Data/Theory” for all reasonable choices of theory parameters
Data:
mc = 1.2 GeV, Q2 = 4mT2
and enhancement
mc = 1.3 GeV, Q2 = mT2
Dainese, Bondila, Eskola, Kolhinen, Vogt,
JPG30 (2004) 1787
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

30. Sensitivity to D0 RpA at |y|<1
p-Pb pp
Example with shadowing
R.Grosso, PhD thesis (2004)
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

31. Summary Charm and beauty production study at the LHC:
test of QCD in a new energy domain
at low pT: access to small-x gluon dynamics; saturation?
ALICE is well-equiped for heavy-flavour studies
using several different channels / strategies
acceptance down low pT at central and forward rapidity
small extrapolation for total cross section
sensitivity to small-x QCD
Predictions are welcome!
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

32. EXTRA SLIDES
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

33. LHC running conditions
Pb-PB nominal run
pp nominal run
Ldt = cm-2 s-1 x 106 s
cm-2 PbPb run, 5.5 TeV
NPbPb collisions = collisions
Ldt dt = cm-2 s-1 x 107 s
cm-2 for pp run, 14 TeV
Npp collisions = collisions


Muon triggers:
~ 100% efficiency, < 1kHz
Muon triggers:
~ 100% efficiency, ~ 1kHz
Electron triggers:
Bandwidth limitation
NPbPb central = collisions
Electron triggers:
~ 50% efficiency of TRD L1
20 physics events per event
Hadron triggers:
Npp minb = collisions
Hadron triggers:
NPbPb central = collisions


High Energy QCD Workshop, ECT* Trento, Andrea Dainese

34. Electron ID D and B mesons have 10% B.R. to electrons
Combined info from TRD (trans. rad.) and TPC (dE/dx)
TRD rejects 99% of the p and ALL heavier hadrons (pT > 1 GeV/c)
TPC further rejects residual pions (up to 99% at low p)
About 20% of electrons rejected
fraction of misidentified pions
High Energy QCD Workshop, ECT* Trento, Andrea Dainese

35. Effect of electron identification
residual charm contribution subtracted using D0 measurement
 3-5% syst. error
High Energy QCD Workshop, ECT* Trento, Andrea Dainese