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La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 1
Andrea DaineseAndrea DaineseINFN LegnaroINFN Legnaro
Preparazione per laPreparazione per lamisura di produzione di Dmisura di produzione di D00
22°° Convegno Italiano sulla Fisica di ALICE Convegno Italiano sulla Fisica di ALICEVietri sul Mare (SA), 30/5-1/6, 2006Vietri sul Mare (SA), 30/5-1/6, 2006
+ misura del beauty + misura del beauty nel canale semi-elettroniconel canale semi-elettronico
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 2
Contents
Charm and beauty in ALICE: motivations
D0 K 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)
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 3
c and b production at the LHCImportant 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) 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
[mb] QQNNQQ
totN
LHC: Theoretical uncertainty of a factor 2--3
beauty charm HERA-LHC Workshop Proceedingsusing: Mangano, Nason, Ridolfi, NPB373 (1992) 295
2/5.0
2/5.0
GeV 0.55.4
GeV 8.13.1
,
RF
TRF
b
c
m
m
m
* M.Mangano
CDF, PRL91 (2003) 241804FONLL: Cacciari, Nason
Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 4
increasing s
HQs as 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
Eskola, Kolhinen, Vogt, PLB582 (2004) 157Gotsmann, Levin, Maor, Naftali, hep-ph/0504040
Cartoon
char
mbea
uty
Window on the rich phenomenology of high-density PDFsgluon 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
c(DGLAP+non-linear)c(DGLAP)
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 5
Pb-Pb collisions: Parton Energy Loss
Partons travel ~ 4 fm in the high colour-density medium
Energy loss (gluon radiation +
collisional?)
2 ˆ LqCE Rs
Casimir coupling factor:4/3 for quarks3 for gluons
Medium transport coefficient gluon density
Baier, Dokshitzer, Mueller, Peigne‘, Schiff, (BDMPS), NPB483 (1997) 291
(BDMPS)
Probe the medium
Carlos
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 6
Lower E loss for heavy quarks?In vacuum, gluon radiation suppressed at < 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-Wiedemann, 2003)
Exploit abundant massive probes at LHC & study the effect
by measuring the nuclear modification factor for D and B
Q
Dokshitzer, Kharzeev, PLB519 (2001) 199Armesto, Salgado, Wiedemann, PRD69 (2004) 114003
tBD
pp
tBD
AA
collt
BDAA dpdN
dpdN
NpR
/
/1)(
,
,,
222 ])/([
1
QQ Em
Gluonstrahlung probability
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 7
News from RHIC: heavy-flv decay electrons suppressed!
Armesto, Cacciari, Dainese, Salgado, Wiedemann, hep-ph/0511257 Djordjevic, Gyulassy, Wicks, nucl-th/0512076
Radiative Radiative + Collisional
Energy loss calculations tend to underpredict suppression
Indirect measurement: non-photonic electrons (Dalitz and conversions subtracted); charm / beauty inclusive (uncertainty on pp baseline)
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 8
gq EE mass effect
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
)()()( )(/)( t
hAAt
BDAAthBD pRpRpR
For 10 < pt < 20 GeV, charm behaves like a m=0 quark,light-flv hadrons come mainly from gluonsRD/h enhancement probes color-charge dep. of E lossRB/h enhancement probes mass dep. of E loss
Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 9
Beauty-to-Charm ratio: RB/D
Compare c and b same colour charge
Mass effect Enhancement of factor ~2, independent of (for )
)()()(/ tDAAt
BAAtDB pRpRpR
q̂/fmGeV 20ˆ 2q
Adapted from Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 10
D0 K-+ in ALICEExclusive reconstruction
direct measurement of the pt distribution
Weak decay with mean proper length c = 124 m
Large combinatorial background (dNch/dy)2
STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices
Measurement of Impact Parameters (ITS+TPC)
Measurement of Momenta (ITS+TPC)
Particle identification (TOF) to tag the two decay products
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 11
Vertexing: track d0 resolution
< 60 m (r)for pt > 1 GeV/c
Resolution mainly provided by the 2 layers of silicon pixels
PIXEL CELL
z: 425 m
r: 50 m
Two layers:r = 4 cmr = 7 cm
9.8 M
INFN Legnaro
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 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: = 15 m in Pb-Pb
= 15 m in pp (L ~ 1032 cm-2 s-1)
150 m 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
vertextrackrd )(0
A.D. and M.Masera, ALICE-INT-2003-027.
as in Pb-Pbpp with charmpp min. bias
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 13
Selection of D0 candidates
increase S/Bby factor ~103!
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 14
Time-of-flight PID
TOF
Pb-Pb, dNch/dy=6000
Optimization for hadronic charmdecays was studied:minimize probability to tag K as
K id. required for D0 pt < 2 GeV/c
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 15
S/B
initial
(M3)
S/B
final
(M1)
Significance
S/S+B
(M1)
Pb-Pbcentral
5 10-6 10%~35
(for 107 evts,
~1 month)
pPbmin. bias
2 10-3 5%~30
(for 108 evts,
~1 month)
pp 2 10-3 10%~40
(for 109 evts,
~7 months)
Results
Note: with dNch/dy = 3000 in Pb-Pb, S/B larger by 4 and significance larger by 2
central Pb-Pb
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 17
Feed-down from BeautyAt 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)
%5~/ ccbb
%5.5)(/
)/()/(/
)(/
)(/0
000
0
0
DcdydN
XDBBBRBBbdydN
DcdydN
DbdydN
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 18
D0 cross section measurement
inner bars: stat. errorsouter bars: stat. pt-dep. syst. errorsnormalization error not shown: 9% Pb-Pb and p-Pb, 5% pp
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 19
B e + X: Detection strategy
1) Electron PID: reject most of the hadrons
2) d0 cut: reduce charm and bkg electrons (Dalitz, conv.)
3) Subtract (small) residual background (ALICE data + MC)
PrimaryVertex B
e
Xd0
rec. track
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 20
Electron identificationCombined info from TRD (trans. rad.) and TPC (dE/dx)
TRD rejects 99% of the 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
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 21
Effect of electron identification (pp)
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 22
Errors Summaryd0 cut tuned vs pt to find best compromise between statistical and systematic errors from charm and bkg subtractions
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 23
Cross section of electrons from B
inner bars: stat. errorsouter bars: stat. pt-dep. syst. errorsnot shown: norm. error (5% pp, 9% Pb-Pb)
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 24
pp, s = 14 TeV
Comparison to pQCD predictions &perspectives for 1st month
1 year at nominal luminosity
1 month at ~ end 2007
Detector configuration:ITS + TPC + TOF
Expectations for first pp run:
Scaling of stat. errors according to Nevts
No dedicated cuts study
D0 K
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 25
pp, s = 14 TeV
Comparison to pQCD predictions &perspectives for 1st month
1 year at nominal luminosity
1 month at ~ end 2007
Detector configuration:ITS + TPC + TRD (~1/5 at end ’07)
Expectations for first pp run:
Scaling of stat. errors according to Nevts
No dedicated cuts study
B e + X
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 26
TDpp
TDAA
collT
DAA dpdN
dpdN
NpR
/
/1)(
Tepp
TeAA
collT
eAA dpdN
dpdN
NpR
/
/1)(
Charm and Beauty E Loss : RAA
mb = 4.8 GeV
Low pT (< 6–7 GeV)Also nuclear shadowing (here EKS98), in-medium hadr…
High pT (> 6–7 GeV)Only parton energy loss
D0 K B e + X
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 27
Interpretation of RAA:The 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 @ LHC:• kaons and hyperons• D meson RCP sensitivity under study
E lossonly
Statistical errors for107 min. bias Pb-Pb evts
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 28
Heavy-to-light ratios: RD/h
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
)()()(/ thAAt
DAAthD pRpRpR
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 29
Heavy-to-light ratios: RB/D
1 year at nominal luminosity(107 central Pb-Pb events, 109 pp events)
)()()( D from eB from e/ tAAtAAtDB pRpRpR
La Fisica di ALICE - Vietri sul Mare, 31.05.2006 Andrea Dainese 30
SummaryFeasibility 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 promisingpt 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)