1. Federico Antinori (INFN, Padova & CERN, Ginevra)
Introduzione alla fisica degli heavy flavour nelle collisioni nucleari ultrarelativistiche
Federico Antinori
(INFN, Padova & CERN, Ginevra)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

2. LHC is a Heavy Flavour Machine!
cc and bb rates
ALICE PPR (NTLO + shadowing)
115 / 4.6
0.65 / 0.85
6.6 / 0.2
Pb-Pb 5.5 TeV (5% cent)
0.16 /
1 / 1
11.2 / 0.5
pp 14 TeV
shadowing
system
NN x-sect (mb)
total multiplicity cc
PbPb/pp bb
PbPb/pp
PbPb
PbPb pp pp
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

3. Probing the medium with heavy flavours
c, b produced in early stages of collision, then conserved (neglecting annihilation)
production quantitatively under control in pQCD
 ideal probes of bulk, strongly interacting phase
energy loss?
thermal production?
no extra production at hadronization
 ideal probes of fragmentation
independent string fragmentation vs recombination
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

4. Corso in due parti Parte prima: Parte seconda: introduzione
heavy flavour in collisioni elementari
Parte seconda:
heavy flavour in collisioni nucleo-nucleo
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

5. Parte prima : introduzione, heavy flavour in collisioni elementari
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

6. Heavy Flavour Decays
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

7. Some zoology... Lower mass heavy flavour hadrons decay weakly
t ~ ps
ct ~ 100’s µm
weakly decaying states from PDG 2006 summary tables:
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

8. Impact parameter ~ ct in projection: so:
In UR limit b ~ Lorentz invariant:
... so b ~ independent of g
if cos qCM distribution is flat:
so, in space,
primary vertex
decay vertex
decay length = L
impact parameter = b q
in projection:
so: y x d j b
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

9. Weak decays of charm typically: large branching ratio to kaons:
D+  K-+X BR ~ 28 %
“golden” channel: D+  K-p+p+ BR ~ 9%
D0:
D0  K-+X BR ~ 50%
“golden” channels: D0  K-p+ BR ~ 4% ; D0  K-p+p+p- BR ~ 7%
W± branchings:
large semileptonic branching ratio, varies with heavy flavour particle, typical ~ 10%
~ 10% heavy flavour hadrons give in final state an e± (and ~ 10% a µ±)
(and with a respectable pT...)
C = “Cabibbo angle” c s’ W+ u d’ e+ ne µ+ nµ b c W-
(similarly: )
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

10. Standard experimental tools
WA92:
Si µstrips
[Adamovich et al.: NIM A 379 (1996) 252]
Silicon vertex detectors:
so: tracks from heavy flavour weak decays typically “miss” primary vertex by ct ~ 100’s µm
impact parameter resolutions of typical heavy flavour apparatus ~ 10’s µm
e± and/or µ ± identification
charged kaon identification
primary vertex
decay vertex
decay length = L
impact parameter = b q
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

11. Heavy Flavour Production in QCD
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

12. Heavy Flavour hadro-production in pQCD
Factorization:
(at sufficiently large Q2)
hadron
hadron
charmed
hadron
parton distribution functions
xa = momentum fraction of
parton a in hadron A
cross-section at parton level
e.g.:
fragmentation
z = fraction of
c momentum
to hadron D
cross-section
at hadron level
a=q
b=q Q
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

13. factorization implies:
PDFs can be measured with one reaction...
say: Drell-Yan: A+B  e+e- + X
... and used to calculate a different one
say: heavy-flavour production
fragmentation independent of the reaction (e.g.: same in pp, e+e-)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

14. Parton Distribution Functions
PDFs vary depending on momentum transfer scale Q2
Intuitively:
higher Q2 -> higher resolution
high-x parton -> lower-x partons
The Q2 evolution of the PDFs can be calculated in pQCD
Altarelli-Parisi evolution
(DGLAP)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

15. Leading-order (LO) Relevant diagrams: pair creation
qq  QQ (quark-antiquark annihilation)
gg  QQ (gluon-gluon fusion) q Q Q g Q g Q g
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

16. A few results the partonic cross-section decreases with energy
faster for qq than for gg (which therefore is expected to dominate, except near threshold)
the parton luminosities near threshold increase with energy,
the cross section increases with the energy of the hadron-hadron collision
the pair cross section is proportional to:
y (y): rapidity of Q (Q)
Q and Q therefore expected to be close in y
Experimentally: EHS, 360 GeV p-p  DDX
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009
[EHS: PLB 123 (1983) 98]

17. Next-To-Leading-Order (NTLO)
in absolute value, LO cross sections are typically underestimated by factor (“K factor”)
at NTLO: additional diagrams, such as: Q
higher order corrections to pair creation Q
flavour excitation Q
gluon splitting
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

18. the agreement with experiment for the total cross-section is good (within large bands...)
e.g.: charm cross section at fixed target:
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009
[Mangano: hep-ph/ ]

19. results depend on the values of:
mc, µR (renormalization scale), µF (factorization scale)
the result of an exact calculation would be independent of the choice of the scale parameters µR, µF
the residual scale dependence is a measure of the accuracy of the calculation
e.g.: for b production at Tevatron (µR=µF=µ):
[Mangano: hep-ph/ ]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

20. it is important to match the PDFs with the order of the calculation.
e.g. one must avoid double counting:
at LO:
at NTLO: Q
“intrinsic flavour” Q
“flavour excitation”
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

21. Heavy Flavour in p/p-A
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

22. Nuclear shadowing
PDFs in the nucleus different from PDFs in free proton
R = ratio of nuclear to nucleon PDFs
from Deep Inelastic Scattering (e-+p; e-+A), Drell-Yan (p+p, p+A -> l +l -+X)
e.g.:
R for gluons vs
gluon momentum fraction x
from EKS parametrization
[Eskola et al.: EPJ C9 (1999) 61]
shadowing
antishadowing
SPS
RHIC
LHC
typical x for cc production (y  0)
x  SPS
x  RHIC
x  a few LHC
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

23. Nuclear dependence
From pQCD one expects the cross section for production off nuclei to increase like number of nucleon-nucleon collisions
(“binary collision scaling”)
proportional to number of nucleons (for min. bias collisions):
modulo shadowing effects, expected to be small
Experimentally: not far... e.g. WA82:
D production in p-+W/Si at SPS (340 GeV beam momentum)
(relatively) central production
with a =1
“Feynman’s x”
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

24. Caveats... i) a = 1 does not work down to pp!
e.g.: MacDermott & Reucroft [PLB 184 (1987) 108] compare pA results with earlier hydrogen data from NA27, good agreement using:
note: similar situation for light flavours!
systematic study by Barton et al. [PRD 27 (1983) 2580], for various reactions at 100 GeV FT
e.g.: central for production of p, K, p from p on nuclear targets:
with
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

25. note: a is known to decrease with xF for light hadrons
ii) lower a at large xF?
early beam dump experiments, sensitive at large xF (max acceptance for xF  0.5)
(in tracking experiments, typically max. acceptance for xF  0.2)
e.g. WA78 [Cobbaert et al.: PLB 191 (1987) 456]
a for muons escaping dump (p-A at 320 GeV FT ):
note: a is known to decrease
with xF for light hadrons
[Barton et al.: PRD 27 (1983) 2580]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

26. Heavy Flavour Fragmentation
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

27. Fragmentation k  1 GeV/fm String fragmentation model:
(e.g. [PYTHIA hep-ph/ ])
as coloured quarks fly away, energy is stored in the field:
above a certain distance it is cheaper to break the string by creating a new qq pair than to keep increasing the distance
the string snaps, e.g.: the heavy quark ends up “hadronising” together with a light antiquark
the newly created quarks are of course light
estimated ratios:
u : d : s : c  1 : 1 : 0.3 : 10-11
no heavy flavour production in string breaking!
k  1 GeV/fm
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

28. Fragmentation function
c  D, D takes fraction z of c momentum
fragmentation function: DD/c(z)
depends only on fraction z
e.g.:
Peterson (e = 0.015)
Colangelo-Nason
(a = 0.9, b=6.4)
Peterson
Colangelo-Nason
e.g.:
(parameters from
fits to charm
production at LEP)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

29. How to measure the fragmentation function?
we don’t measure the original Q momentum ...
but in e+e- we do know the Q momentum (by energy conservation!)
e.g.:
fragmentation functions are usually extracted from e+e- measurements and then used for other collisions e- Q e+ Z0
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

30. e.g.: fits to charm x = 2E/s distributions in e+e-:
[Cacciari & Greco: PRD55 (1997) 7134]
very similar parameters at the two energies (as expected)
Peterson fragmentation
s = 10.6 GeV (ARGUS)
s = 91.2 GeV (OPAL)
e = (OPAL)
e = (ARGUS)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

31. e.g. at NTLO a Q can radiate:
like for the PDFs, the fragmentation function has to be matched to order of pQCD calculation
e.g. at NTLO a Q can radiate:
so final energy before
non-perturbative part of
fragmentation lower than at LO
harder fragmentation at NTLO
at NTLO: e  0.015
at LO: e  0.06
(e.g.: [Cacciari & Greco: PRD55 (1997) 7134]) Q
Peterson fragmentation
e = (NTLO)
e = 0.06 (LO)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

32. D* decays, D0(cu) / D+(cd) ratio
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

33. D* decays
Most of the D mesons (from spin counting, ~ 75%) are not directly produced at hadronization, but in D* decays
D±, D0 J=0
D*±, D*0 J=1
Due to fine tuning of the values of the masses:
m(D±) + m(p0) < m(D*±)
m(D0) + m(p±) < m(D*±)
m(D0) + m(p0) < m(D*0)
but...
m(D±) + m(p±) > m(D*0)
... the light quark content of charged D is preserved also in case of resonance decays:
a D0(cu) can originate from either D*0(cu) or D*+(cd)
a D+(cd) can only originate from a D*+(cd)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

34. D0/D+ ratio at LEP D*0 and D*+ both decay strongly into D’s, but:
D*+ can decay to both D0 and D+
D*0 can only decay to D0
From spin degeneracy one expects:
D0 : D+ : D*0 : D*+ = 1 : 1 : 3 : 3
... and therefore a large D0/D+ ratio
using the experimental branching ratios:
but experimentally, at LEP:
[ALEPH: EPJ C16 (2000) 597]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

35. Heavy Flavour at Tevatron
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

36. Beauty at Tevatron Run 0 Run II
Discrepancy between pQCD and data seems to have disappeared...
from...
a factor 5.5 (but only 1.6 s ...)
to...
Run 0
[CDF: PRL 68 (1992) 3403]
Spectrum of J/y from secondary B decays
Run II
[Cacciari et al: JHEP 0407 (2004)]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

37. From run I on, important improvements in accuracy:
experiment (vertex detectors, high statistics)
prediction (post-HERA PDF sets)
Levels of stability over time:
no large room for new physics any more...
for more see, e.g.:
[Cacciari et al: JHEP 0407 (2004) 033, Cacciari: hep-ph/ , Mangano: hep-ph/ ]
Data
Predictions
from [Cacciari et al: JHEP 0407 (2004) 033]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

38. What about charm? Nice data from CDF run II
roughly in agreement with full pQCD calculation
(though prediction somewhat low)
[CDF: Phys.Rev.Lett. 91 (2003) ]
A curiosity (?):
good agreement between data and prediction for bare quark
[Vogt: talk at SQM 2004]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

39. Parte seconda : heavy flavour in collisioni nucleo-nucleo
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

40. Charm and beauty: ideal probes
study medium with probes of known colour charge and mass
e.g.: energy loss by gluon radiation expected to be:
parton-specific: stronger for gluons than quarks (colour charge)
flavour-specific: stronger for lighter than for heavier quarks (dead-cone effect)
study effect of medium on fragmentation (no extra production of c, b at hadronization)
independent string fragmentation vs recombination
e.g.: D+s/D+
+ measurement important for quarkonium physics
open QQ production natural normalization for quarkonium studies
B meson decays non negligible source of non-prompt J/y
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

41. Heavy flavour production in AA
binary scaling:
can be broken by:
initial state effects (modified PDFs)
shadowing
kT broadening
gluon saturation (colour glass)
(concentrated at lower pT)
final state effects (modified fragmentation)
parton energy loss
violations of independent fragmentation (e.g. quark recombination)
(at higher pT)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

42. What do we know from the SPS?
Intermediate mass dimuon excess in central Pb-Pb at SPS (NA50)
Main known sources in that region: Drell-Yan and charm pairs
M (GeV/c2)
central collisions
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

43. Study of the I.M. excess in NA60
Fit weighted impact parameter distribution
prompt from J/ψ dimuons, charm from PYTHIA
requires > 2 x expected D-Y to fit data
NA60
H.Woehri and C.Lourenco, Phys.Rep. 433 (2006)
6500 A, 2match < 3
sensitivity to assumption on cc pT, Δφ
extracted value of cc cross section ~ 2 – 3 larger than extrap.
but compatible with extrapolation from NA50 p-A
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

44. Heavy Flavour @ RHIC: experimental techniques
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

45. Non-photonic electrons
Identified electron spectra
STAR: dE/dx in TPC + TOF at low pT, EMC at high pT
PHENIX: combined RICH and E/p (with E from EM cal)
Rejection of non-heavy-flavour electrons
Main source of electrons: “photonic”
g  e+e- conversions
Dalitz decays p0  e+e-g
Dalitz decays h  e+e-g
STAR:
rejected by full invariant mass analysis of e+e- combinations
PHENIX:
estimated by simulation and subtracted (“cocktail method”)
measured by “converter method” and subtracted
Other sources of non-charm electrons:
w, r, j, K decays
estimated by sim. and subtracted (in both STAR and PHENIX)
(“internal conversions”)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

46. Reconstructed decays (STAR)
D0  K-p+
tracks from TPC
K, p identification from dE/dx
no separation of D decay vertex
large combinatiorial background evaluated by event mixing and subtracted
residual background, subtracted with linear fit
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

47. Low pT muons (STAR) m/p in TPC (dE/dx) m/p in TOF
[C Zhang (STAR) QM06]
m/p in TPC (dE/dx)
m/p in TOF
fit to impact parameter distribution
charm m should ~ point to primary...
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

48. Experimental status
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

49. PHENIX pp D0 Excess wrt FONLL: Similar situation also in CDF: Ratio:
1.72  0.02 (stat)  0.19 (sys)
(0.3 < pT < 9.0 GeV/c) D0
[A. Adare et al. (PHENIX) Phys.Rev.Lett. 97 (2006) ]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009
[D. Acosta et al. (CDF) PRL 91 (2003) ]

50. STAR v PHENIX pp ~ a factor 2 discrepancy [J. Lajoie (PHENIX) QM06]
hep-ex/
[J. Lajoie (PHENIX) QM06]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

51. STAR dAu, AuAu Internal consistency [M. Calderon (STAR) QM06]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

52. STAR v PHENIX dAu, AuAu
Discrepancy pretty “stable” v collision system, channel, pT
looks like something very basic...
of course then RAA not too different...
[A. Suaide QM06]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

53. STAR v PHENIX: RAA RAA of non-photonic electrons
[A. Suaide QM06]
similar picture from STAR and PHENIX
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

54. Interpretations
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

55. Theoretically...
Energy loss for heavy flavours is expected to be reduced:
i) Casimir factor
light hadrons originate from a mixture of gluon and quark jets, heavy flavoured hadrons originate from quark jets
CR is 4/3 for quarks, 3 for gluons
ii) dead-cone effect
gluon radiation expected to be suppressed for q < MQ/EQ
[Dokshitzer & Karzeev, Phys. Lett. B519 (2001) 199]
[Armesto et al., Phys. Rev. D69 (2004) ]
average energy loss
distance travelled in the medium
Casimir coupling factor
transport coefficient of the medium
 R.Baier et al., Nucl. Phys. B483 (1997) 291 (“BDMPS”)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

56. Experimentally... non ph. el. ~ as suppressed as light hadrons
use of high density (qhat), introduction of elastic (in addition to radiative) energy loss... not enough
high qhat and no beauty electrons does better
[B.I. Abelev et al (STAR): nucl-ex/ ]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

57. How much beauty? high pT region expected to be beauty-dominated
[M. Cacciari et al.: PRL 95 (2005) ]
high pT region expected to be beauty-dominated
but how “high”?
[A. Suaide QM06]
not easy to disentangle c/b contributions to RHIC non ph. el. samples (no heavy flavour vertex detectors in RHIC experiments)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

58. E loss being understood?
DongJo Kim (PHENIX)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

59. another sobering caveat…
Relative abundances in charm sector also important:
e.g.: Λc/D may change from pp to AA D0 D
Ds+
c+
BR (Xe) in %
17.2  1.9
6.71  0.29
8 +6-5
4.5  1.7
c/D
(e  c)/(e  D)
and what about Ds?
s enhancement!
Sebastien Gadrat
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009
(see also P Sorensen & X Dong, PRC 74 (2006) )

60. Vertex Detectors! need less indirect measurement
full reconstruction of charm decays!
get rid of b/c ambiguities
study relative abundances in charm sector
Silicon Pixels in ALICE (+ ATLAS, CMS)
Silicon Vertex upgrades in STAR, PHENIX
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

61. Track Impact Parameter
track impact parameter (d0): separation of secondary tracks from HF decays from primary vtx
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

62. Impact parameter measurement in ALICE
ALICE Silicon Pixels
PIXEL CELL
z: 425 mm
rf: 50 mm
Two layers:
r = 4 cm
r = 7 cm
 9.8 M
expected d0 resolution (s)
e.g.: D0  K-p+
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

63. LHC is a Heavy Flavour Machine!
cc and bb rates
ALICE PPR (NTLO + shadowing)
115 / 4.6
0.65 / 0.85
6.6 / 0.2
Pb-Pb 5.5 TeV (5% cent)
0.16 /
1 / 1
11.2 / 0.5
pp 14 TeV
shadowing
system
NN x-sect (mb)
total multiplicity cc
PbPb/pp bb
PbPb/pp
PbPb
PbPb pp pp
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

64. low-x (a field on its own!)
large cross-sections
low-x (a field on its own!)
 accessible x1, x2 regions in the ALICE experiment
muon
arm
central
detector
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

65. Heavy Flavour Quenching?
some prediction ...
charm
beauty
[Armesto et al.: Phys.Rev. D71 (2005) ]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

66. D0  K-p+ expected ALICE performance  similar performance in pp
S/B ≈ 10 %
S/(S+B) ≈ (1 month Pb-Pb running)
statistical.
systematic.
 similar performance in pp
(wider primary vertex spread)
pT - differential
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

67. Beauty to electrons Expected ALICE performance (1 month Pb-Pb)
e± identification from TRD and dE/dx in TPC
impact parameter from ITS
S/(S+B)
S per 107 central Pb-Pb events
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

68. Electrons (from b) pt spectrum
stat  syst error
Error composition
stat error
11% from overall
normalization not included
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

69. Beauty to single muons expected in the muon arm
 very high statistics and heavy flavour purity expected
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

70. Beauty to dimuons Two main sources: B µ+ + D + X µ- + X B µ- + X
“BDSAME”
“BBDIFF”
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

71. Beauty to dimuons Consistency check!
low mass mm
high mass mm
low mass: µ+ and µ- from decay of same B or B
high mass: µ+ and µ- from decay of B and B
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

72. Expected ALICE performance on D, B RAA
mass dependence
colour charge dependence
mb = 4.8 GeV
D0  K-p+
B  e + X
1 year at nominal luminosity
(107 central Pb-Pb events, 109 pp events)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

73. Charm v2 at LHC? Full reconstruction of D decays at LHC
qualitatively different measurement from non-photonic electrons!
b vs c
better correlation with original heavy-quark momentum
First indications from preliminary studies in ALICE: expected error ~ few % (D v2)
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

74. Ds+ Ds+ as probe of hadronization?
from string fragmentation: cs / cd ~ 1/3
after decays: Ds+ (cs) / D+ (cd) ~ 0.6
from recombination: cs / cd ~ N(s) / N(d)
 how large at LHC?
experimentally accessible?
D+ (ct ~ 310 µm)  K-p+p+ with BR ~ 9.2 %
in Alice: similar performance as for D0  K-p+
Ds+ (ct ~ 150 µm)  K-K+p+ with BR ~ 4.4 %
but mostly resonant decays: Fp+ or K0*K+ (non resonant only 20 %)
 favours bkgnd rejection (for D+  K-p+p+, non-resonant ~ 96 %)
may be well visible (expecially if Ds+/D+ is large!)
Ds v2 would be particularly interesting!
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

75. At LHC: real jets! 2 GeV 20 GeV 100 GeV 200 GeV
Mini-Jets 100/event /event k/month
Well visible event-by-event! e.g. 100 GeV jet + underlying event:
e.g.: study quenching with b-tagged jets!

76. b tagging ATLAS u rejection (Ru) performance in Pb-Pb
H  bb, uu with MH = 400 GeV
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

77. Away side cone? Collective behaviour opposite to jet?
PHENIX Preliminary
Dq*=p
Df*=0
Collective behaviour opposite to jet?
eg: Mach cone
John QM2006
[Casalderrey-Solana, et al.: hep-ph/ ]
[Stocker: Nucl.Phys. A750 (2005) 121])
Assume effect is real:
What happens with big-fat-heavy quark jets?
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

78. Modified Mach cone?
Heavy quarks at moderate pT move with substantially lower speed
e.g.: for beauty, taking:
cS2 = 0.2
m(b) = 4.5 GeV
b quark is “subsonic”
for p < 2.25 GeV
for p ~ 3-4 GeV,
shock wave angle ~ 40O
[FA, E Shuryak: J.Phys. G31 (2005) 19]
shock wave angle [degrees]
Now:
observing THAT
would be something!
p(b) [GeV]
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009

79. Conclusioni
Con gli heavy flavour, la Natura ci mette gentilmente a disposizione un meraviglioso strumento per studiare le proprietà del mezzo prodotto nelle collisioni nucleari ultrarelativistiche
LHC è una macchina da heavy flavour
alte rese di produzione molto
gamma in pT estesa
jet ben sviluppati
L’esperimento ALICE è ben attrezzato per questa fisica
FA - Quark Matter Italia - Roma Sanità - 24 aprile 2009