Andrea Dainese

1
Preparazione per lamisura di produzione di D0
2 Convegno Italiano sulla Fisica di ALICE Vietri
sul Mare (SA), 30/5-1/6, 2006
misura del beauty nel canale semi-elettronico

• Andrea Dainese
• INFN Legnaro

2
Contents

• Charm and beauty in ALICE motivations
• D0 ? Kp reconstruction
• D0 cross section measurement in pp, pPb, Pb-Pb
• A.D. R.Grosso PhD theses,
  PPR v2
• Beauty measurement via displaced electrons in pp
  and Pb-Pb
• Antinori, A.D., Bombonati, Lunardon,
  Turrisi, Internal Notes to appear, PPR v2
• Sensitivity in comparison to predictions, in pp
  (pQCD) and Pb-Pb (energy loss)

3
c and b production at the LHC

• Important test of pQCD in a new energy domain
• remember the 15-years saga of b production at
  the Tevatron
• and c production not yet fully reconciled
• LHC NLO predictions (ALICE baseline for charm /
  beauty)

CDF, PRL91 (2003) 241804 FONLL Cacciari, Nason
Cacciari, Frixione, Mangano, Nason and Ridolfi,
JHEP0407 (2004) 033
system ?s 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
M.Mangano
4
HQs as a probe of small-x gluons

• Probe unexplored small-x region with HQs at low
  pt and/or forward y
• down to x10-4 with charm already at y0

• Window on the rich phenomenology of high-density
  PDFs
• gluon saturation / recombination effects
• non-linear terms in PDFs evolution
• Possible effect enhancement of charm production
  at low pt w.r.t. to standard DGLAP-based
  predictions

Eskola, Kolhinen, Vogt, PLB582 (2004)
157 Gotsmann, Levin, Maor, Naftali, hep-ph/0504040
5
Pb-Pb collisions Parton Energy Loss

• Partons travel 4 fm in the high colour-density
  medium
• Energy loss (gluon radiation collisional?)

(BDMPS)
Medium transport coefficient ? gluon
density
Casimir coupling factor 4/3 for quarks 3 for
gluons
Probe the medium
? Carlos
Baier, Dokshitzer, Mueller, Peigne, Schiff,
(BDMPS), NPB483 (1997) 291
6
Lower E loss for heavy quarks?

• In vacuum, gluon radiation suppressed at q lt
  mQ/EQ
  
• ? dead cone effect
• Dead cone implies lower energy loss
  (Dokshitzer-Kharzeev, 2001)
• Detailed calculation confirms this qualitative
  feature, although effect is small and
  uncertainties significant (Armesto-Salgado-Wiedema
  nn, 2003)
• Exploit abundant massive probes at LHC
  study the effect by measuring the nuclear
  modification factor for D and B

Dokshitzer, Kharzeev, PLB519 (2001) 199 Armesto,
Salgado, Wiedemann, PRD69 (2004) 114003
7
News from RHIC heavy-flv decay electrons
suppressed!

• Indirect measurement non-photonic electrons
  (Dalitz and conversions subtracted) charm /
  beauty inclusive (uncertainty on pp baseline)

Radiative
Radiative Collisional
Energy loss calculations tend to underpredict
suppression
Djordjevic, Gyulassy, Wicks, nucl-th/0512076
Armesto, Cacciari, Dainese, Salgado, Wiedemann,
hep-ph/0511257
8
Color-charge and mass dep. of E loss with
Heavy-to-Light ratios at LHC
Heavy-to-light ratios Compare g ? h , c ? D
and b ? B
For 10 lt pt lt 20 GeV, charm behaves like a m0
quark, light-flv hadrons come mainly from
gluons RD/h enhancement probes color-charge dep.
of E loss RB/h enhancement probes mass dep. of E
loss
Armesto, Dainese, Salgado, Wiedemann, PRD71
(2005) 054027
9
Beauty-to-Charm ratio RB/D

• Compare c and b ? same colour charge
• Mass effect ? Enhancement of factor 2,
  independent of (for
  )

Adapted from Armesto, Dainese, Salgado,
Wiedemann, PRD71 (2005) 054027
10
D0? K-p in ALICE

• Exclusive reconstruction
• direct measurement of the
  pt distribution
• Weak decay with mean proper length ct 124 mm
• Large combinatorial background ? (dNch/dy)2
• STRATEGY invariant-mass analysis of
  fully-reconstructed topologies originating from
  (displaced) secondary vertices
• Measurement of Impact Parameters (ITSTPC)
• Measurement of Momenta (ITSTPC)
• Particle identification (TOF) to tag the two
  decay products

11
Vertexing track d0 resolution
Resolution mainly provided by the 2 layers of
silicon pixels
? 9.8 M
12
Interaction vertex reconstruction in pp collisions

• Vertex diamond stable for few hours if beam
  focused, precise vertex position from average
  over many events
• Nominal size of the beam
• s 15 mm in Pb-Pb
• s 15 mm in pp (L 1032 cm-2 s-1)
• s ? 150 mm in pp (if L is reduced at ALICE IP to
  1030 cm-2 s-1)
• In pp the E-by-E vertex position has to be
  reconstructed in 3D using tracks
• Finding/fitting algorithm developed and optimized
  

A.D. and M.Masera, ALICE-INT-2003-027.
13
Selection of D0 candidates
increase S/B by factor 103!
14
Time-of-flight PID
TOF
Pb-Pb, dNch/dy6000
Optimization for hadronic charm decays was
studied minimize probability to tag K as p
K id. required for D0 pt lt 2 GeV/c
15
Results
S/B initial (M?3s) S/B final (M?1s) Significance S/?SB (M?1s)
Pb-Pb central 5 ? 10-6 10 35 (for 107 evts, 1 month)
pPb min. bias 2 ? 10-3 5 30 (for 108 evts, 1 month)
pp 2 ? 10-3 10 40 (for 109 evts, 7 months)
central Pb-Pb
Note with dNch/dy 3000 in Pb-Pb, S/B larger by
? 4 and significance larger by ? 2
16
Statistical Errors
(R.Grosso)
17
Feed-down from Beauty

• At LHC energies
• Fraction of D0 from chain b ? B0/B ? D0 not
  negligible
• Standard NLO pQCD Pythia fragmentation BR
• Selections increase this ratio to 10-15
• Results have to be eventually corrected for
  feed-down
• systematic error from
• uncertainty on b cross section
• Possibility to have direct
• estimate by D0 d0 (à la CDF)

18
D0 cross section measurement
19
B ? e X Detection strategy

1. Electron PID reject most of the hadrons
2. d0 cut reduce charm and bkg electrons (Dalitz, g
   conv.)
3. Subtract (small) residual background (ALICE data
   MC)

20
Electron identification

• Combined info from TRD (trans. rad.) and TPC
  (dE/dx)
• TRD rejects 99 of the p? and ALL heavier hadrons
  (pt gt 1 GeV/c)
• TPC further rejects residual pions (up to 99 at
  low p)
• About 20 of electrons rejected

21
Effect of electron identification (pp)
22
Errors Summary

• d0 cut tuned vs pt to find best compromise
  between statistical and systematic errors from
  charm and bkg subtractions

23
Cross section of electrons from B
inner bars stat. errors outer bars stat. ?
pt-dep. syst. errors not shown norm. error (5
pp, 9 Pb-Pb)
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
24
Comparison to pQCD predictions perspectives for
1st month
D0 ? Kp
pp, ?s 14 TeV

• Expectations for first pp run
• Scaling of stat. errors according to ?Nevts
• No dedicated cuts study

Detector configuration ITS TPC TOF
25
Comparison to pQCD predictions perspectives for
1st month
B ? e X
pp, ?s 14 TeV

• Expectations for first pp run
• Scaling of stat. errors according to ?Nevts
• No dedicated cuts study

Detector configuration ITS TPC TRD (1/5 at
end 07)
26
Charm and Beauty E Loss RAA
D0 ? Kp
B ? e X
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
27
Interpretation of RAAThe role of hadronisation

• Lowish pt D and B mesons may hadronise inside the
  medium via coalescence ? no clean study of parton
  E loss
• Up to which pt is this relevant?
• ? Study particle type-dependence of RCP

RHIC

• ALICE _at_ LHC
• kaons and hyperons
• D meson RCP sensitivity under study

E loss only
28
Heavy-to-light ratios RD/h
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
29
Heavy-to-light ratios RB/D
1 year at nominal luminosity (107 central Pb-Pb
events, 109 pp events)
30
Summary

• Feasibility studies for D0 and B measurements in
  pp, Pb-Pb (and pPb,only D0) carried out
• many critical items identified and partially
  addressed PID, d0 primary vertex measurement,
  feed-down from beauty to charm
• Results are very promising
• pt coverage in the range 1--18 GeV/c for D0 and
  electrons from B
• some physics applications identified and
  studied
• First measurements in pp already after first
  month (107 evts)
• D0 coverage up to pt 7 GeV/c
• B total cross section not much on pt dependence
• Getting ready for first collisions
• Long to-do list presented at May PWG3
• Analyses to be performed / tuned on 2006 pp
  production (PDC06)