New results from BABAR, MarieHlne Schune, BNL, May 20th 20021

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New results from BABAR
Brookhaven National Laboratory Particle Physics
Seminar May 20, 2002
Marie-Hélène Schune Laboratoire de lAccélérateur
Linéaire Orsay, France
All numbers are preliminary
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New results from BABAR
56 fb-1

• I will not talk about
• sin2b in charmonium modes
• BABAR and PEPII
• Charmless B decays
• B0???, K? or KK
• B0??0?0
• The B recoil physics
• semileptonic branching fractions
• of B and B0
• D meson production in B decays

sin2b 0.75 ?0.09 ?0.04
Winter 2002 conferences
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CKM matrix for 3 generations

• CKM matrix has 4 real parameters (one phase
  included)
• 2 are well known
• lVussin(qCabbibo)0.2205?0.0018
• A Vcb/l2 0.83 ?0.06
• unitarity of the CKM matrix leads to constraints
  that can be tested

h
Unitarity Triangle
r
4
The BABAR detector
1.5T solenoid
CsI(Tl) EMC
e (3.1GeV)
DIRC (PID)
Drift Chamber
Silicon Vertex Tracker
e- (9GeV)
Instrumented Flux Return

• SVT 97 efficiency, 15mm z resol. (inner layers,
  perpendicular tracks)
• Tracking s(pT)/pT 0.13 PT ? 0.45
• DIRC K-p separation gt3 s for Plt3.5GeV/c
• EMC ?E/E 1.33 E-1/4 ? 2.1

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(No Transcript)
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PEP-II asymmetric B Factory

• 9GeV e- on 3.1GeV e
• ?s10.58 GeV
• for B0 coherent neutral B pair production and
  decay (p-wave)
• boost of ?(4S) in lab frame bg0.55

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Running at the ?(4S)
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B factory performances

• May 2nd
• PEPII delivered 87 fb-1
• BABAR recorded 83 fb-1 (including 9 fb-1 off
  peak )
• results for 55 fb-1

daily integrated luminosity
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2 - Charmless B decays

• Study of penguins diagrams
• Possible direct CP violation
• a
• g
• B0???, K? or KK
• Branching fractions (aeff ?a, g)
• CP violations measurements (aeff , a )
• B0??0?0 (aeff ?a)

h
(r,h)
a
b
g
r
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B0??? and CP violation (1)
BF(B0???) ltlt BF(B0?K?) penguins contributions may
be large
mixing e-2ib
Tree only lhfe2ia (a p-b -g) Cpp0
Sppsin(2a)
TreePeng. Cpp? 0 Sppsin(2aeff)
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B0??? and CP violation (2)
f B0 tag
Spp0.7 and Cpp0.
perfect flavour tagging time resolution
realistic mis-tagging finite time resolution
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B0???, K? or KK kinematics

• Main variables
• cosqS angle between the B0 sphericity axis
  and the sphericity axis of the rest of the event
• F Fisher discriminant based on energy flow
  cones (CLEO)

Axis of Rest Event
Jets
Candidate
cosqS
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B0???, K? or KK mES and DE

• Energy substituted mass
• dominated by the
• beam energy knowledge
• DE assume pp mass
• dominated by the
• tracking resolution
• s(DE)26 MeV

325 MeV
mES
pp
Kp
KK
background
45 MeV
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B0???, K? or KK the PID (1)

• The DIRC

Quartz bar
Active Detector Surface

• Measure Angle of Cherenkov Cone in quartz
• Transmitted by internal reflection
• Detected by PMTs

Particle
Cherenkov light
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DIRC PMT light catchers
DIRC stand-off box, magnetic shielding and
electronic crates 
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B0???, K? or KK the PID (2)

• DIRC performances measured on data using D?D0p
  and D0 ?Kp

s(qc) ? 2.2 mrad
K/p separation
2.5s
p range of 2-body B decays at BABAR
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B0???, K? or KK analysis strategy

• Start with a B0?hh- (no PID)

unbinned max L with DE, mES, F, q1c, q2c
measure Npp NKp NKK and
17600 events for 56 fb-1
add Dt and tagging information (as for sin2b ),
fix the yields extract Spp and Cpp
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B0???, K? or KK branching fractions results
Likelihood projections remove one 1 variable
from fit cut on L proba
small cross-feed
83 B0???
small cross-feed
356 B0?K?
mES DE
mES
DE
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B0???, K? or KK BF comparison
BF(B0???) ltlt BF(B0?K?)
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B0???, K? or KK CP analyses Dt

• Time information Dt
• resolution dominated by Btag vtx (s(Dz) 180 mm)
• extracted from data Breco sample
  (D()p,D()r,D()a1)
• Background shape side bands

Similar to sin(2b) analyses
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B Flavour tagging methods
Hierarchical, mutually exclusive, tagging
categories
For electrons, muons and kaons use the charge
correlation
l-
W
n
W-
b
c
s
W-
b
c
K0
D, D
Lepton Tag
Kaon Tag
Neural Network
Multivariate analysis exploiting the other
kinematic information of the event, e.g.,

• Momentum spectrum of the charged particles
• Information from non-identified leptons and
  kaons
• Soft p from D decay

Each category is characterized by the probability
of giving the wrong answer (mistag fraction w)
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B0???, K? or KK CP analyses tagging

• Split the events into 4 tagging categories
• leptons
• kaons
• NT1
• NT2
• Performances obtained
• on data (Breco sample)

mES
leptons
NN type tagging
kaons
Similar to sin(2b) analyses
NT1
NT2
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B0???, K? or KK CP analyses validation

• Validation measure tB on pp/Kp sample
• Validation measure Dmd

tB1.66 ?0.09 ps
Select the Kp events and plot Amix
Dmd0.517 ?0.062 ps-1
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B0???, K? or KK CP analyses results

• Spp -0.01?0.37?0.07 Spp? -0.66,0.62 at 90
  CL
• Cpp -0.02?0.29?0.07 Cpp? -0.54,0.48 at 90
  CL

27 B0???
Select the B0??? events Plot the asymmetry
between B0 tag and B0tag events
9 Background
25 B0???
9 Background
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(r,h) constraints from Spp and Cpp
BBNS QCD FACTORISATION APPROACH M. Beneke,
G. Buchalla, M. Neubert and C.T. Sachrajda
Nucl.Phys.B606 (2001) 245
CKM Fitter H. Höcker, H. Lacker, S. Laplace and
F. Le Diberder Eur. Phys. J. C21 225-259
(2001) http//ckmfitter.in2p3.fr/
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B0???, K? or KK CP comparisons

• Belle (K Trabelsi Moriond)

-Cpp (BABAR)
App
c2(Spp,Cpp)9 (2.5 s)
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Search for B0??0?0

• BF(B0??0?0)
• measured ? isospin analysis to get a from
  B0???-
• (M. Gronau, D. London Phys Rev Lett. 65
  3381-3384 (1990))
• upper bound ? still a useful constraint
• (Y. Grossman, H. Quinn Phys Rev D 58 017504
  (1998))
• Experimentally challenging
• low BF expected (th. predictions 10-7 - few
  10-6)
• purely neutral final state
• Recent results

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Search for B0??0?0 analysis (1)

• Main variables
• cosqS angle between the B0 sphericity axis
  and the sphericity axis of the rest of the event
• F Fisher discriminant based on the energy flow
  cones
• mEC energy constrained mass
• DE EB ?s/2 in the CMS

Axis of Rest Event
Jets
Candidate
F
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Search for B0??0?0 analysis (2)

• The B? ?r?p0 background
• event shape similar to the signal one
• mEC only slightly wider (small p? missing)
• DE is the only discriminating variable
• in the fit fix BF(B? ?r?p0)2.410-5 (from CLEO
  upper limit)

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Search for B0??0?0 results

• Unbinned maximum L fit using F PDF and (mEC , DE
  ) PDF
• Compare with an optimized cut and count analysis
  
• Fit yield

• Main systematics
• neutral efficiency
• continuum mEC param.
• F param.
• B? ?r?p0 yield

BF(B0??0?0) lt 3.4 10-6 at 90 CL
54 fb-1
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3 - The B recoil physics
generic B decay B type known ?should allow (in
principle !) to measure all B BF Will show
leptonic studies D0 and D? production
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The B recoil physics

• B factories the worlds largest sample of
  reconstructed B mesons

56 fb-1
Nsignal13743?125
Reconstruct the Cabibbo-favored hadronic decays
B0 sample
Nsignal12909?120
B sample
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Inclusive semileptonic B decays

• Inclusive rate is large
• Sides of the unitarity triangle Vcb and Vub
• B?Xcen is large
• B?Xuen is an experimental challenge

(r,h)
a
g
b
(1,0)
(0,0)
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Inclusive semileptonic B decays

• Compare b/b0 with t(B)/t(B0)
• Extract the prompt and cascade lepton spectrum
  from the charge correlation with the Breco
• B-?Xce-n
• B?Xcen
• B0 correct for mixing
• CLEO results (2.4 fb-1) using B0 tagged sample
  and ?(4S) ?l
• b0 (10.78 ?0.60?0.69)
• b (10.25 ?0.57?0.65)
• b/b0

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Electron identification

• Variables
• E/p
• Shower shapes
• DCH and DIRC
• Performances measured on data

90

• Backgrounds
• ? conversions
• p0 dalitz decays
• J/? decays

10-3
p (GeV)
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Background subtracted electrons spectra

• Right sign Wrong sign

B? N right sign Np
results on 21 fb-1
B0 Nright signN0p(1-cd)N0ccd Nwrong
signN0pcdN0c(1-cd)
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b0 and b results

• BF results ratio

B
B0
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D production in B decays

• Inclusive branching fractions of B0 and B to
  charmed hadrons
• Enters in the nc ( mean charm per B decay )
  computation
• For each B specie two measurements are performed
  
• The absolute BF BF(B?DX) with D D0 or D
• large statistics
• Need e(D) from MC
• The wrong D ratio
• Wrong D sample statistically limited
• Need to correct for mixing for the B0
• More MC independant

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D production in B decays reconstruction

• Hadronic
• B0 ?Dp, Dr, Da1

• Semileptonic B0 ? D l n
• fit to cosqB-Dl variable

50 fb-1
mES
cosqB-Dl

• D reconstruction D0 ?Kp and D? ?Kpp

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BF(B?DX)

• Fit N(D) and correct for Brec background ?
  BF(B?DX)

Brec B0 ?Dln
M(Kp)
M(Kpp)
Brec B0 ?Dp, Dr, Da1
() Correlated syst. () Uncorrelated syst.
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w(D) for neutral B mesons

• Correlate the D and the B flavours
• For B0 should correct for mixing
• done on an optimized time interval (Dtlt2.5 ps)
  ? reduced statistical uncertainty, Dmd dependance

Mix
cobs
cd w (1 - 2 cd)
MixUnmix
w( B0 ? D 0X ) () Semilept. 15.9 ? 3.5 ? 2.4
Hadronic 9.6 ? 4.7 ? 1.1
Combined 13.1 ? 2.8 ? 1.5 ? 0.6
Brec B0 ?Dln
Brec B0 ?Dp, Dr, Da1
Unmix
w( B0 ? D? X) () Semilept. 7.3 ? 3.7 ?
1.9 Hadronic 8.9 ? 7.1 ? 1.8 Combined 7.7 ? 3.3
? 1.4 ? 0.8
Mix
M(Kp)
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D production in B decays

• Results suggest B0 spectator quark effect
  negligible in wrong D production
• Results consistent with world data (B
  admixture)
• In the future
• Add the B? sample
• 100 fb-1
• start to look for Ds and Lc (looser Breco
  selection ?)

30 or 51 fb-1
Compare BF( B0 ? D0 D X) (83.1 ? 6.4)
with world data BF( Badmixt ? D0 D X)
(78.5 ? 3.4)
Better understanding of the overall picture of
the B decays
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Summary

• A true factory of B mesons
• BF(B0 ???-) (5.4?0.7?0.4) 10-6
• BF(B0 ?K?-) (17.8?1.1?0.8) 10-6
• Unfortunately not enough to get B0??0?0
• BF(B0??0?0) lt 3.4 10-6 at 90 CL
• CP violation results
• Spp -0.01?0.37?0.07
• Cpp -0.02?0.29?0.07
• B recoil physics is starting
• Semi leptonic measurements
• D mesons production in B
• decays