BaBar:%20Risultati%20recenti%20e%20prospettive

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BaBar Risultati recenti e prospettive

• Fernando Ferroni
• Universita di Roma La Sapienza I.N.F.N.
  Roma1

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BABAR Collaboration
China 1/5 Inst. of High Energy Physics,
Beijing Germany 3/23 Ruhr U Bochum TU Dresden U
Rostock France 5/51 LAPP, Annecy LAL
Orsay LPNHE des Universités Paris 6/7 Ecole
Polytechnique CEA, DAPNIA, CE-Saclay United
Kingdom 10/71 U of Birmingham U of
Bristol Brunel University U of Edinburgh U of
Liverpool Imperial College Queen Mary Westfield
College Royal Holloway, University of London U of
Manchester Rutherford Appleton Laboratory
Italy 12/89 INFN Bari INFN Ferrara INFN
Frascati INFN Genova INFN Milano INFN Napoli
USA 36/253 Caltech, Pasadena UC, Irvine UC, Los
Angeles UC, San Diego UC, Santa Barbara UC, Santa
Cruz U of Cincinnati U of Colorado Colorado
State Elon College Florida AM U of Iowa Iowa
State U LBNL LLNL U of Louisville U of Maryland U
of Massachusets MIT U of Mississippi Mount
Holyoke College Northern Kentucky U U of Notre
Dame ORNL/Y-12 U of Oregon U of
Pennsylvania Prairie View AM Princeton SLAC U of
South Carolina Stanford U U of Tennessee U of
Texas at Dallas Vanderbilt U of Wisconsin Yale U
INFN Padova INFN Pavia INFN Pisa INFN Roma INFN
Torino INFN Trieste
Canada 4/15 U of British Columbia McGill U U de
Montréal U of Victoria
Norway 1/2 U of Bergen Russia 1/7 Budker
Inst., Novosibirsk
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PEPII
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BaBar
SVT z resolution 70 microns Tracking
?(pT)/pT 0.13 ? pT ? 0.45 DIRC K-?
separation gt 3.4? for Plt3.5GeV EMC ?E/E
1.33?E-1/4 ? 2.1
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Outline

• PEPII BaBar
• Physics Motivation CP in B
• Results
• Mixing Lifetimes
• sin 2b
• Rare decays
• Perspectives

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Particle physics in new millennium

• Origin of masses
• Remote energy scale (Gravity)
• CP Violation and our universe

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Why CP violation ?

• Needed for matter-antimatter asymmetry
• Standard Model CP-Violation (CKM)
• thought to be insufficient to explain
• universe asymmetry
• 37 years of intense experimental and
• theoretical effort of background

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CP Violation in SM
SM with three generation accommodates CP
violation through phase in CKM matrix
SM predicts a variety of CP violating asymmetries
in the B-system, some of which can be cleanly
interpreted in terms of CKM matrix elements
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The Triangle
CP
Bd ? Dp , Kp
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The Unitarity Triangle
The sides are determined by measurements of the
magnitudes of CKM elements
CP asymmetries to fCP measures angles
of triangle, in some cases with little or no
theoretical ambiguities
Goal of the B-physics program is to overconstrain
triangle, critically test CKM structure of SM
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CP measurement

• Reconstruct a CP eigenstate
• Flavour tag with other B
• Measure Dz ---gt Dt tCP - ttag
• Fit time evolution

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B decay topology
Reconstruction of the CP eigenstate
Tag of the other B
B0
B0
Measurement of Dz
Lifetime, Mixing, CP
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Smearing of an asimmetry
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PEPII-BaBar Operations
Design 3.0 nb-1/s 135 pb-1/d 0.80
fb-1/w 3.3 fb-1/m Achieved 3.28
184 1.03 3.8

• Data from 1999-2000 run
• 20.7 fb-1 on-resonance
• N(?(4S)) 22.74 0.36 million
• 2.6 fb-1 off-resonance

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PEPII-BaBar Operations
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Interaction region

• Permanent magnets inside the support tube

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J/Y Ks Event at BaBar
B0?J/Y Ks J/Y-gtmm- Ks -gt pp-
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DIRC Detection of Internally Reflected
Cherenkov light
New design for a Cherenkov detector

• 144 quartz bars (1.7 cm thick)
• 10752 PMT in 6 m3 of
• purified water
• Total space 8 cm (0.14 X0)

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K/p separation
Pion-Kaon separation at high momenta
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Mixing and sin2b
Common wrong tag fractions and resolution
function parameters can be determined by a large
Bflav sample
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Bflav sample
B0 ? D() -p, D() -r, D() -a1, J/YK0 B-
? D()0 p- , J/YK-, Y(2S)K-
DEEB - ?s /2 s15 MeV mES ?(s/4 -
pB2) s3MeV
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B reconstruction

• Y(4S) -gt BB

energy difference
energy substituted (constrained) mass
DE sideband
DE
mES sideband
signal
mES
one more pion...
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Bflav sample
6368 evts Purity 84
7645 evts Purity 86
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Run I Data Set
23M BB pairs recorded 3 fb-1 of continuum
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CP sample (Ks modes)
J/ Y Ks (??-)259 (purity 98)
J/Y ? l l
J/ Y Ks (?0?0)50 (84)
Y(2s)Ks (??-)55 (97)
Y(2S) ? l l ? J/Ypp
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Final CP sample of K0s modes
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CP sample (KL modes)
Neutral clusters not consistent with noise, g
or p0 are considered as KL candidates B mass
constraint is imposed
92 signal Purity 40
108 signal Purity 51
Reconstructed with EMC
Reconstructed with IFR
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Tagging
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Vertexing
DtDz/lt bg cgt
Use per event error and parametrize the
resolution function with scaling factors
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Lifetimes
PDG 1.550.03 1.650.03 1.060.03
?B0 1.546 ? 0.032 ? 0.022 ps ?B 1.673 ?
0.032 ? 0.022 ps ?B/ ?B0 1.082 ? 0.026 ? 0.011
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Mixing adronico/leptonico
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Mixing compilation
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Fitting procedure
Mixing and sin2b measurements are done with the
same strategy do a global fit to all the events
that can carry information Mixing
tagged flavour eigenstates sin2b
tagged flavour and CP eigenstates Extract as many
parameters as possible from data
Biggest correlation with sin2b 7.6
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Log Likelihood vs sin 2 ?
Total
KS
KL
?
sin 2 ? 0.34 ? 0.20(stat) ? 0.05(sys)
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Systematics
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Asymmetries
sin2b0.25 ? 0.22 (stat)
J/Y KS
sin2b0.87 ? 0.51 (stat)
J/Y KL
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Asymmetries
Total CP tagged sample 529 events 164 of
background mainly in J/Y KL
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sin2b by decay mode
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sin2b by tagging category (Ks only)
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Compilation of all known results
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Comparison to predictions of non-CP
sin 2b
eK
Vub/Vcb, DMd,DMs
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New fuel for sin2b (B ? DD-)
The Standard Model predicts time-dependent
CP-violating asymmetries in the decays B0 ?
D()D()- proportional to sin2b
D Reconstruction D ? D0p, Dp0
D0 ? K-p, K-pp0, K-pp-p, KSpp- D ? K-pp,
KSp, K-Kp
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New fuel for sin2b
Beware of this one (non flying birds !)
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B ? DD-, Signal
Nsignal 31.8 Events NBkg 6.2 Events Estimated
from sideband in DE and MES
Br(B0?DD-) (8.0 1.6 (stat) 1.2 (syst)) ?
10-4
(But angular analysis to do CP)
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Charmless two-body B decays
Direct CP search Time-dependent CP
asymmetry pp- ? sin(2a), fK0 ?
sin(2b) Theoretical model validation
u
Vud,s
p, K
d,s
W
Vub
b
u
p-
B0
d
d
Cabibbo-suppressed tree diagrams
Vtd,s
Vtb
d,s
b
W
p, K
u
B0
t
u
p-
d
d
penguin diagrams
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Charmless decays
pp-, Kp-, KK- (hh-) p0 p, p0 K (p0
h) K0 p, K0 K (K0 h) K0p0 fK fK,fp fK0
K0 as KS to pp- f ? KK- K ? Kp0,KS p
Fully reconstructed decays Efficiency (with
daughter BF) K0p0,hp0,hK0,hh 10-45
fK,fK0,fK 3-20
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Composite particles
lt E gt 3 GeV
s 8.5 MeV
s 4.3 MeV
p0 mass
f mass
KS mass
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Background suppression
p0
Jet-like topology
background
Background dominated by continuum
qqbar production (u,d,s,c)
cos qS
signal
cos(qS) cosine of angle between sphericity axes
of B and rest of the event
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Background suppression
Fisher discriminant
Linear combination of event-shape variables
(cones)
hh- DE sideband (dots) continuum hh- MC(his)
(dots) B- ? D0p- (his) hh- MC
background
signal
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Likelihood analysis
Use an extended global likelihood fit to extract
different signal yields (NS) in each topology
mES, DE, Fisher(cosqTh), (f mass), qC
Independent control sample to study Probability
Density Function for both BKG and SIG
hh- DE sideband
B- ? Dop-
ARGUS function
Gaussian s ? 2.6 MeV
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More PDFs
DE with pion hypothesis
signal MC
KK- Kp- pp-
Background udsc
-0.15
0.15 GeV
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More PDFs (Cherenkov)
Control sample D ? D0p ? K-p
qC qC(K)
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Results
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Systematics

• Vary PDF parameters
• alternative PDF

Variation in
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Results
Likelihood visualization onto mES
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Predicting g or disproving models
B.Beneke et al.
input SM g
CLEO/Belle/BaBar (my) average 0.26 /- 0.06
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Radiative decays (B ? K0g)
CKM matrix elements Vtd, Vts
No considerable CP asymmetry expected in
Standard Model (lt 1)
Sensitive to New Physics (SUSY,W- ?H-)
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B0? K0g, Signal and Backgrounds
B0? K0g
ee- ? qqg
ee- ? qq ? Xp0
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B ? K0g, Signal Estimation
MES Distribution -200 MeV lt DE lt 100 MeV
Yield Nsignal 139.2 13.1 events Br(B0 ?
K0g)(4.39 0.41 (stat) 0.27(syst)) ? 10-5
ACP -0.035 ? 0.094 (stat)? 0.022 (syst)
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The near future
Expect to have 40fb-1 more by the end of the run
II
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The near future recoil physics

• In 20 fb-1 (present stat 5 times more by end of
  2002)
• 12 K fully reconstructed hadronic B mesons
• 40 K semi-exclusive B (maybe one/two missing
  particles)
• 20 K semi-leptonic B (one n missing)
• Will be able to reconstruct single B in modes
  with BF 10-4 - 10-5

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The immediate future
The usual painful start-up
however better than last year
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while the competitor..
Belle is doing very well
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The near future for sin2b
BaBar will collect 0.5 ab-1
We will know sin2b at the 0.02 level by 2005
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The far future
It could be a new machine at slightly higher
energy Y(5S) and asymmetry and considerably
higher luminosity (10 36 cm -2 s -1)
Youre all invited !