M. Calvi 1

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Fisica del B ai collider adronici presente e
futuro
Marta Calvi Università di Milano Bicocca and INFN
IFAE 2005 Catania
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B Physics now and in the LHC era
Outstanding results from B-Factories provide a
successful test the CKM paradigm of flavour
structure and CP violation. However present
knowledge is still incomplete.
(from CKM-fitter )
New Physics could still be hidden in box and in
penguin diagrams, realm of indirect discoveries.
If NP will be found in direct searches, B
Physics measurements will have to sort out how
the flavour problem is really solved in these
theories.
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B Physics at Hadron Colliders
The reason for going at hadron colliders

• Huge bb cross section sbb500 mb _at_14 TeV
  (1nb _at_Y(4S) )
• Access to all b-hadrons Bd,Bu, Bs, b-baryons
  and Bc

The challenge

• Presence of underlying event. High particle
  multiplicity.
• High rate of background events (sbb/sinel10-3).

Experimental requirements

• Trigger (also on fully hadronic decays)
• Excellent tracking and vertexing (mass
  resolution, proper time resol.)
• Excellent PID (exclusive selections, flavour
  tagging)

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The present CDF/D0
Excellent mass resol. PID dE/dx,TOF
Silicon vetex trigger
Excellent m and track coverage
Results from CDF and D0 at Tevatron have
demonstrated that precision B physics is possible
at hadron machines.
Lb?J/y L
An example b-baryons
Data on tape ?600 pb-1/experiment.
Used for present results ?220-450 pb-1
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The future ATLAS-CMS
pT vs h for detected B hadrons

• B physics mainly in the first two years with
  L 1-2x1033 cm2s-1 ? 10-20 fb-1 /year.
• At high luminosity ( gt20 piled-up interaction)
  pursue very rare B decays.

B-physics program will depend on trigger
strategy and allocated bandwidth.
Classical scenario B events triggered by
high-pT m or mm.
CMS also exploit online tracking for
exclusive B events selection at HLT. Good
results from studies on some benchmark channels.
ATLAS maximize B-physics capabilities with
reduced detector at start-up with a flexible
trigger strategy (start with a mm trigger, add
further triggers in the beam-coast and for
low-luminosity fills.)
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The future LHCb
10-300 mrad
Forward peaked production of b hadrons
at LHC
pp interactions/crossing
Luminosity locally tuned (by defocusing beams) to
limit pile up of pp interaction per bunch
crossing
L 2x1032 cm2s-1 1012 bb produced per year
(taking 1 year107 s)
Should be available from day one
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LHCb trigger
detector
40 MHz
L0, L1, L0L1 efficiency
high pT (m,e,g,h) hardware, 4 ms latency
1 MHz
high IP, high pT tracks software,1 ms
40 kHz
HLT software using complete event 10 ms
2 kHz
storage
Systematics from data
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B Flavour Tagging
Several algorithms used to determine the flavour
of the signal B meson at production.
Tagging power ?D2 ?(1-2w)2 (in )
Kaon tagging most powerful for LHCb.LHCb
combined power for Bs6. Lower for B0 (4) due
to reduced same-side tagging power (p).Recent
Neural-Net based studies achieved 9 for Bs (not
used here).
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A complete program on B Physics would include

• Precise measurement of B0s-B0s mixing Dms, DGs
  and phase fs.

• Precise determinations of angle g including from
  processes only at tree-level, in order to
  disentangle possible NP contributions.
• Several other measurements of CP phases in
  different channels for over-constraining the
  Unitarity Triangles.

• Search for effects of NP appearing in rare
  exclusive and inclusive B decays.

• Studies on b-baryons and Bc physics, studies of
  bb production

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B0s-B0s mixing
DGs GL - G H
Dms MH -M L

• Precise constraint from Dmq ratio

From CKM fits Dms20.53.2 ps-1.
If Dmsgt30 ps-1 ? NP at 3s.

• Large decay width difference in SM

(cf DGd / Gd O(1) )
DGs / Gs O(10)

• Small mixing phase in SM

fs -2 arg (VtsVtb) -2 l2 h ? -0.04
Contributions from new particles can affect both
the amplitude and the phase of mixing.
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CDF Bs mixing in Semileptonics
Opposite side flavour tags (e,m,jet charge)
eD2(1.430.09)
Limit Dmsgt7.7 ps-1 _at_95CL
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CDF Bs mixing in Bs? Dsp
Opposite side flavour tags (e, m, jet charge)
eD2(1.120.18)
s(t)?100 ps
Low sensitivity for hadronic only.
Combined limit Dmsgt7.9
ps-1 _at_95 CL
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Bs mixing, Tevatron perspectives
DO limit, semileptonics
Dmsgt5.0 ps-1 _at_95 CL

• Improve statistics from
• Better flavour tagging (same side K tag) Add more
  channels More
  integrated luminosity
• Improve proper time resolution.

DO projections
Semileptonics dominate now, hadronic modes matter
more for large Dms Scans dominated by statistics
now, at large Dms proper time resolution is the
limiting effect.
CDF expects sensitivity ?15-16 ps-1 from
improvements, on same data set.
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Bs mixing at LHC
Best mode Bs0?Ds-p
LHCb 1 year 80k events, S/B?3
Control of mistag rate,resolution,
backgroundand acceptance is important.
Plot made for Dms20 ps-1
st 40 fs
proper time resolution (fs)
LHCb 5? observation of Bs oscillation for Dmslt68
ps-1 (1 year)
Once observed, precision to measure Dms 0.01ps-1
ATLAS 5 s observation for Dms lt 22 ps-1 (10
fb-1 ). Most recent CMS sensitivity is
lower due to trigger restriction.
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?Gs from Bs?J/?f
D0 Preliminary
Use untagged Bs?J/?f events. VV decay mixture
of CP-even and CP-odd components.
Fit distributions of mass, proper decay length
and transversity angle to measure relative
contribution of CP states,
D0 Preliminary
D0 Preliminary
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?Gs from Bs?J/?f
DG/G 0.21 1/Gt(ps) 1.39
R? 0.170.10
0.33 0.45
0.25 0.33
0.65 1.40
0.15 0.16
0.15 0.13
0.130.08
CP-odd fraction at t0
Including constraint from w.a. Bs lifetime to
flavour specific decay channels
tfs1.430.05 ps
DG/G 0.23
0.16 0.17
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fs and ?Gs with Bs?J/?f (h)
Bs?J/?f is the Bs counterpart of the golden mode
B0 ?J/yKS, measuring fd.
Fit angular distributions of tagged events, as a
function of proper time, to measure DGs and the
phase fs of Bs oscillation.
LHCb 100k Bs?J/?(mm)f events/year, S/Bgt3
fs
Similar sensitivity on fs reached also using
Bs?J/y(??)h, with 7k events per year, pure CP
state.
ATLAS/CMS achieve similar sensitivieties for 20
fb-1
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? from Bs?DsK

• Exploit Interference between two tree diagrams
  via Bs mixing Bs?Ds?K? and Bs?Ds?K?
• Time-dependent CP asymmetries measure g fs
  (and strong phase D) ? extract g taking fs from
  Bs?J/?f.
• Very little theoretical uncertainty, insensitive
  to NP.

Bs?DsK
Bs?Ds?
Need excellent PID for K/p separ.
5400 events/ yr S/Bgt1.0 at 90CL
?(?) 14º (1 year)
5 yrs of data, ?ms 20 ps -1

• New analysis combination of Bs?Ds()K and
  B0?D()p using U-spin symmetry. Expected
  sensitivity 5º in 5 years.

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? from B?? D?K?

• Measure 6 time integrated decay rates B0?D0K0,
  D0K0 and DCPK0 ( CP conjugates), where DCP
  ?KK- (or pp-).
• Decays are self-tagging through K0 ? Kp-.

Appropriate construction of amplitudes allows
both g and strong phase D to be extracted
(Gronau Wyler, Dunietz)
Similar to B? D0K but here two colour
suppressed diagrams and A(B??D0K?) /
A(B??D0K?) 0.4
LHCb annual yields for g 65?, D 0)

• s(g) 8?

(55?ltglt105?, -20?ltDlt20?)
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CDF B?h?h?
Kinematics and dE/dx to separate contributions
?1.4 s for K/p separation
???? hypothesis
BR(Bd?pp) / BR(Bd?Kp) 0.240.060.05
BABAR 0.26 0.036 0.015
Direct ACP(Bd?Kp) -0.040.080.01
BABAR -0.1330.030.009
fsBR(Bs?KK) / fdBR(Bd?Kp) 0.500.08(stat)0.07
(syst)
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? from B?????? and Bs?K?K?
Large penguins contributions in both decays
Measure time-dependent CP asymmetry for B??????
and Bs?K?K?.
Exploit U-spin symmetry for P/T ratio
(Fleischer).
Use RICH detectors for K/p separ.
Bd???-
without RICH
Knowing fs, fd ? can solve for g .
B?????? (95CL)
d
sM17 MeV
Bs?K?K? (95CL)
B?????? 26 k events/yr B??K?? 135 k
Bs?K?K? 37 k
?(?) ? 5º (1 year)
g (º)
?(U-spin)
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a from B?? r? ? ?p-??
Quinn Snyder Time dependent analysis of Dalitz
distribution allows a clean determination of a
independently from penguin contributions
M(p0p-)
M(p0p)
po reconstr. eff.
11-parameters fit to a, T and P amplitudes,
strong phases, resonant and non-resonant
background
Merged po
Resolved po
LHCb 14k events/yr S/Bgt1.3
sa lt 10o (1 year)
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b?sss penguin decays
B-Factories measure 3.7s between sin2b from
charmonium and from b?sss penguin
modes(fKs,hKs). If related to NP it is important
to examine also other channels involving b?sss
penguins.
BR(Bs?ff)(146stat6syst)x10-6
ACP(B?fK)-0.070.17stat0.03syst
Large samples of Bs ? ff, Bs ? KK ..., will be
reconstructed at LHC, and also Bs ? fg , B?Kg
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B0 ? K0 ??-
BR(B0?K??-)SM(1.2?0.4)x10-6
BR(s)
AFB(s)
Forward-backward asymmetry sensitive to NP via
non-standard values of Wilson coeff. C7,C9,C10.
Zero point known in SM at 5.
sM(??-)2 GeV2
AFB(s)

LHCb 4400 evts/year S/Bgt0.4
?(BR) 2-3
?(BR) 2-3 ?(ACP) 2-3
AFB(s) reconstructed using toy MC (two years
data, background subtracted).Zero point located
to 0.04 .
ATLAS 2000 events, S/B7 (30 fb-1).
s (mmm/mB)2

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Bs ? ??- at Tevatron
BR(Bs0???-)SM (3.5?0.1)x10-9 ? Good
sensitivity to NP. Can be strongly enhanced in
SUSY BR(Bs???-)(tanb)6, for large tanb.
2005 D0 limit (300 pb-1)
2004 CDF limit (171 pb-1)
SUSY SO(10) (Dermisek, Rabi et al.)
Excluded by Bs?mm-
4 events observed, expected bg 4.31.2
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Bs ? ??- at LHC
LHCb 17 events Bs0???- in 1 year at
2x1032cm-2s-1 Background study requires
additional MC statistics, no events selected from
full background sample, but only corresponds to
S/?B gt 2 ?(MBs)18 MeV/c2
ATLAS/CMS can exploit also high luminosity runs
(clear signature)
yields for 100 fb-1 (1 year at 1034 cm-2s-1)
Background estimates (from 1999)
differ significantly, update awaited.
Significant BR measurement, even for SM value!
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Bc at Tevatron
Original observation Bc?J/yln (CDF'98)
New CDF first observation in fully
recon-structed hadronic decays Bc?J/yp
M(Bc) 6287.04.8stat1.1syst MeV/c2
D0 observation in inclusive semileptonic decays
Bc?J/y mX
t(Bc)0.448 0.121 ps
0.123 0.096
M(Bc) 5.95 0.14 0.34 GeV/c2
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Bc at LHC
LHCb 14k events/year S/Bgt1.3
Bc?J/y(mm)p reconstructed
109- 5x1010 Bc produced per year at
2x1032 -1034 cm-2s-1
Precision measurements of mass and lifetime
M( J/y p )
Quarkonium-like Bc mesons allow to study the
interplay of strong and weak interactions
Heavy-Quark Expansions, Non-Relativistic QCD,
Factorization
Fleisher,Wiler g measurements with Bc? DsD0
using triangle relations
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Conclusions
Extensive program on B-Physics being developed by
CDF/D0 at Tevatron.
Experiments at the LHC expect to take B-Physics a
significant step further than the B factories
access to other b hadron species and high
statistics.
LHCb combines excellent vertexing and particle ID
with flexible trigger, dedicated to B
physics. ATLAS and CMS will also contribute
significantly. Competitive for modes with
muons and small BR.
Performances at LHC have been studied on several
benchmark channels. Suggestion from
theory on new channels are also important in
order to fully exploit the opportunities of Bs
system, b-baryons and Bc mesons.
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sin(2b) from B0?J/y Ks

• Gold plated channel for b, used at B-Factories.

ACP(t)
direct CPV0 in SM
sin (2b)

• LHC will bring high statistics which can be used
  to measure also Adir

LHCb B0?J/y(??)Ks 216k evts/yr, B/Slt0.8
?(sin2b)0.022 1 year
ATLAS 3 years at 1033 cm-2s-1