Transcript BABAR risultati di Fisica con i primi 100 fb-1

BABAR
Risultati di Fisica
-1
con i primi 100 fb
Stefano Passaggio
INFN – Sezione di Genova
Gruppo I
16-21 Settembre 2002
PEP-II performance
 Highest inst. luminosity reached so far: 4.602x1033 cm-2 sec-1
 Design: 3x1033 cm-2 sec-1
~88 million BB pairs
Daily luminosity
Integrated luminosity
design
recorded
Off-peak
Gruppo I, Settembre 2002
S.Passaggio
2
Selection of BaBar
experimental results
“Io non posso ritrar di tutti a pieno
però che sì mi caccia il lungo tema
che molte volte al fatto il dir vien meno.”
un poeta del ’300…

Choice criteria



recent results (summer conferences)
future perspectives
Organization




time dependent CP asymmetries (sin2, sin2)
time independent (direct) CP asymmetries (charmless 2-body, DK)
other excerpts from BaBar @ ICHEP 2002
(older) non-CP B physics (BR’s, lifetimes, oscillations)
Gruppo I, Settembre 2002
S.Passaggio
3
Time dependent CP asymmetries

 t   f     B  t   f 
A  t  
  B  t   f     B  t   f 
 B
f CP
0
0
phys
CP
2 Im
1 
f cp
2
CP
0
0
phys

phys
phys
CP
sin  m t  
d
f cp
1 
1 
CP
2
f cp
2
cos  m t 
d
f cp
Cf
Sf
Interference between
mixing and decay.
(,,g) measurement
J/
 4S
e
Coherent B-antiB pair
Direct CP violation. Need
more than one amplitude
with different weak and
strong phases.
e
0
BCP


K S0


Exclusive
B Meson
Reconstruction
0
Btag
z
K

Δ t  Δ z/  βγ  c
Gruppo I, Settembre 2002
S.Passaggio
B Flavor Tagging
4
sin2
 Golden modes: b  ccs
Mode
SM 
Ntag
Purity (%)
J/Ks (-)
974
96.5
J/Ks (00)
170
88.5
(2s)Ks
150
96.9
cKs
80
94.5
cKs
132
63.4
(cc)Ks
1506
92.2
J/KL
988
55.2
CP = +1
J/K*0(Ks 0)
147
81.2
CP = 0.65
2641
78.2
23618
84.2
1757
95.8
25375
84.5
All CP
Brec (had.)
J/K*0(K+-)
Bflav
R.Faccini
  CP e 2i 

 ACP (t )  CP sin 2  sin(md t )
all amplitudes have the same weak phase
CP = -1
CP odd fraction (L=1) measured: R  (16.0  3.5)%
CP  1  2 R
c has been added to the sample (c  KsK+ and c  K+K-0)
Gruppo I, Settembre 2002
S.Passaggio
5
sin2 golden modes (contd)
88 106 BB pairs
CP=-1
Winter02
was 0.09
sin2 = 0.755  0.074
CP=+1
sin2 = 0.723  0.158
sin2 = 0.741  0.067 (stat)  0.033 (syst)
Submitted to PRL, hep-ex/0207042
Gruppo I, Settembre 2002
S.Passaggio
Winter02 was 0.04
6
sin2 golden modes (contd)
Constraining ,
Look for direct CP (BSM)



No direct CP violation in these
modes within SM
Leave  free and fit for || and
Sf
Use only (cc ) K S0
|| = 0.948  0.051(stat)  0.029 (syst)
sin2 measurement is now
really constraining
the apex position!
Gruppo I, Settembre 2002
Sf = 0.759  0.074 (stat)
No direct CP observed
S.Passaggio
7
Analysis improvements


s(sin2)
ICHEP00
Still improving faster
than statistics
Winter 01
LP01
Improved track efficiency and
vertex resolution
Winter 02
Re-optimized selection criteria
0
Gruppo I, Settembre 2002
S.Passaggio
Improved effective tagging
efficiency (Q: 26.0 28.1)
New channel added (cKS)
8
sin2 with

D*+D*-
Trieste
b  ccd
 Theoretically uncertain penguin contributions (predicted to be small)
 D*+D*- is a mixture of different CP eigenstates (L=0,1,2)
 Transversity analysis to determine the CP odd fraction
R  = 0.07  0.06  0.03
 Measure the CP even parameters:  , Im
88 106 BB pairs
Im(+) = 0.31  0.43 (stat)  0.13 (syst)
|| = 0.98  0.25 (stat)  0.09 (syst)
ICHEP 02 contributed paper, preliminary
If no penguin contribution: Im   sin 2 
Fixing Im  0.741 and   1 and refitting
the change in likelihood corresponds to 2.7 s
Needs more statistics to conclude
Gruppo I, Settembre 2002
S.Passaggio
9
Other sin2 results
 B0  J/ 0
 Again:
b  ccd
 If no penguin measures sin2
 Tree and penguin should have the same order of magnitude
 BR(B0  J/ 0) = (2.0  0.6  0.2) 10-5
 S(J/ 0) = 0.05  0.49(stat)  0.16(syst)
ICHEP 02,preliminary
 C(J/ 0) = 0.38  0.41(stat)  0.09(syst)
 B0   KS

b  sss
 Pure penguin (tree highly suppressed)
 Within SM measures sin2
 New physics may show up through loop diagrams
 BR(B0 KS) = (8.1+3.1-2.5  0.8) 10-6
 sin2 = -0.19+0.52-0.50(stat)  0.09(syst) (assuming ||=1)
Still statistically limited…
adding also Belle: 2.7 s
Gruppo I, Settembre 2002
ICHEP 02,prelim.
S.Passaggio
10
Roma
sin2: B0+ Experimentally, one measures eff  , due to non negligible
penguin contributions
P
T
+
  e
i ig
2 i 1 P / T e e
1 P / T e i e  ig
C  sin( )
Effect of penguin contributions
S  1  C sin( 2 eff )
2
6
 BR( B     0 )  (5.51.0
0.9stat  0.6syst ) 10

0
 
6
 BR( B    )  (4.7  0.6stat  0.6syst ) 10

0
0 0
6
 BR( B    )  3.6 10  90 % CL 
Gruppo I, Settembre 2002
Need BR’s for +-, 0, 00
to get  from eff
Roma, Torino
S.Passaggio
Isospin analysis
11
B0+-: time dependent analysis
 88 106 BB pairs
 mES and E
S, C
unbinned max likelihood fit
B0   
K
qq + K
S   0.02  0.34( stat )  0.05( syst )
C   0.30  0.25( stat )  0.04( syst )
Gruppo I, Settembre 2002
S.Passaggio
12
Direct CP violation
Roma, Torino
Milano
Interference between diagrams with different strong (i) and weak phases(i)
Large asymmetries possible in B+/0 decays
ACP 
Br ( B  f )  Br ( B  f )
Br ( B  f )  Br ( B  f )
Diagrams from New Physics can contribute
(but hard to extract CKM phases)
At the edge of discovery in some channels
More statistics needed
ACP ( B   J /   )  0.01  0.22stat  0.006syst
ACP ( B   J / K  )  0.003  0.030stat  0.004syst
Gruppo I, Settembre 2002
S.Passaggio
Napoli
13
B-D0
K
(CP)
 B-  D0K-
B  D0CPK
(direct CP)
Pisa
key ingredients for theoretically clean methods
of measuring the angle g
 Measurement of B-  D0K-,
D0  K-+, K-++-, K-+0 (non-CP eigenstates)
BR( B   D 0 K  )
R
 (8.31  0.35stat  0.20syst )%

0 
BR ( B  D  )
 Measurement of B  D0CP K,
D0CP  K+K- (CP-even)
ACP
0
0
BR( B   DCP
K  )  BR( B   DCP
K)

 0.17  0.23stat

0


0

BR( B  DCP K )  BR( B  DCP K )
0.09
0.07
No evidence of direct CP violation yet
Gruppo I, Settembre 2002
S.Passaggio
14
Other excerpts of
BaBar @ ICHEP 2002
Vub
 Inclusive Electron Spectrum in Charmless Semileptonic B Decays
near endpoint
BR
BR( B  X u e e )  (0.152  0.014stat  0.014syst ) 103
preliminary
Vub  (4.43  0.29exp  0.25OPE  0.50 fu  0.35sg ) 103
 Charmless Exclusive Semileptonic B Decays
( B  (  , , ) e e )
BABAR inclusive
BR( B0   e e )  (3.39  0.44stat  0.52syst  0.60th ) 104
preliminary
0.40
Vub  (3.69  0.23stat  0.27syst 0.59th
) 103
Gruppo I, Settembre 2002
S.Passaggio
15
BaBar @ ICHEP 2002
Vcb
 Measurement of BR for Inclusive Semileptonic B Decays
BB events tagged by the presence of a high momentum electron
(p* = 1.4  2.3 GeV/c)
A second electron in the event is taken as the signal lepton
(require p*  0.6 GeV/c to avoid large backgrounds)
Opposite sign: primary B decays
Same sign: predominantly secondary charm decays
BR( B  Xe )  (10.87  0.18stat  0.30syst ) %
Vcb  0.0423  0.0007exp  0.0020theory
Gruppo I, Settembre 2002
S.Passaggio
16
BaBar @ ICHEP 2002
b  sg




 Determination of BR for Inclusive Decays
 b  sg NLO prediction within SM (10%)
BSM contributions to loop  observable deviations
quark-hadron duality: ( B  X sg )  (b  sg )
fully inclusive approach to reduce model
dependence to access the parton level process
bkg reduced by looking at other B
BR( B  X sg )  (3.88  0.36stat  0.37syst
B  X sg
Pisa
consistent with SM
0.43
4
0.23model) 10
 b  sg Using a Sum of Exclusive modes



fully reconstruct 12 exclusive decay modes
use MX to measure the Eg spectrum
1st moment of Eg spectrum
HQET  0.37  0.09stat  0.07syst  0.10model GeV/c2

fit of MX spectrum
BR(b  sg )  (4.3  0.5stat  0.8syst  1.3model ) 104

also constrain 1 (HQET)
Gruppo I, Settembre 2002
S.Passaggio
17
BaBar @ ICHEP 2002
The study of the time evolution of:
D 
B   ()  
 Ds K
0
() 
s
Roma



B0  D()   (~A2)
B0  D()   (~A4: CKM suppressed)
provides a theoretically clean measurement of sin(2   g )
 This measurement requires a knowledge of the ratio D between the
decay amplitudes of these two processes

A( B 0  D ()   ) cannot be obtained from a direct measurement (large
0
()  
background from the CKM allowed B  D  process)
 SU(3) symmetry (in naïve factorization model & if annihilations are
negligible)
BF
(B0 
Ds
 )

BF (B0  D )
tg2qC
fDs2
fD2
 2D
need to measure these BR
BF (B0  Ds K): allows to check that the annihilation is small
Gruppo I, Settembre 2002
S.Passaggio
18
()  
D


s
0
B   ()  
 Ds K
BaBar @ ICHEP 2002
Roma
Results on 84 Million B Pairs:
D S + 
(B0  DS+ -) =
[3.2  0.9  1.0]  10-5
3.3s significance
DS*+
(B0  DS-K+) =
[3.2  1.0  1.0]  10-5
3.5s significance
(B0  DS*+  -) < 4.1  10-5
(B0  DS*-K+) < 2.5  10-5
DS-K
DS*-K
@90% C.L.
||~0.020±0.004(stat.+sys.)
(theoretical error due to SU(3) breaking ~30%)
Gruppo I, Settembre 2002
S.Passaggio
19
B  c0 K



BaBar @ ICHEP 2002
Genova
In the framework of naïve factorization, the decay B  c0 K is forbidden when
the assumption is made that the process occurs through the production of a
“color singlet” cc pair. If a “color-octet” term is included, then the BR is
expected to be of the same order of magnitude as
BR(B±  c1 K±) = (6.5 ± 1.1)  10–4.
c0  +–



The c0 is reconstructed in the two
decay modes
c0  +–
c0  K+K–
The signal yield is separated from
combinatorial and “peaking”
background (i.e. from other B
decays with the same final state)
by means of an UML fit to the +–
(K+K–) invariant mass distribution.
c0  K+K–
Combined result for ∫L = 70 fb–1:
B(B±  c0 K±) = (2.4 ± 0.7)  10–4
Gruppo I, Settembre 2002
S.Passaggio
20
BaBar @ ICHEP 2002
Charm physics: D0 decays
Bari
D 0  K 0 K  
Dalitz plot analysis of 3-body D0 decays
Look for intermediate resonances that contribute
to the 3-body final states
Extract fractions and relative phases
of intermediate resonant states
D 0  K 0 K  
BR( D 0  K 0 K   )
 (8.32  0.29stat  0.56syst ) 102
0
0  
BR( D  K   )
D0  K 0 K  K 
BR( D 0  K 0 K   )
 (5.68  0.25stat  0.41syst ) 102
0
0  
BR( D  K   )
BR( D 0  K 0 K  K  )
 (16.30  0.37stat  0.27syst ) 102
0
0  
BR( D  K   )
Gruppo I, Settembre 2002
S.Passaggio
21
B0/B± lifetime
BaBar has published two measurements of the B meson lifetimes
 Using one fully reconstructed B meson hadronic decay
(PRL 87(2001)202803) 23 106 BB pairs
 B  1.546  0.032(stat)  0.022(syst) ps
0
 B  1.673  0.032(stat)  0.023(syst) ps

 B  B  1.082  0.026(stat)  0.012(syst)

0
Padova
0
 
 Using partially reconstructed B  D l  l (l  e,  )
(PRL 89(2002)011802) 23 106 BB pairs

0 
 Use only the slow ± from D  D  (low Q  s gives D* flight dir)

Brec  Oppositely charged l  pairs give signal, same sign pairs give bkg
 M2  ( Ebeam  E *  El )2  ( p2 *  pl2 )
(low Q  neglect B momentum)
D
D
 Other B decay position from a selection of remaining tracks
Gruppo I, Settembre 2002
S.Passaggio
22
B0
lifetime (contd)
Padova
sig
91700
evts
Crucial: modeling of
t resolution function
for signal and background
fi(B+), fi(cont), fi(BB)
 B  1.529  0.012(stat)  0.029(syst) ps
0
most precise measurement of (B0)
Gruppo I, Settembre 2002
S.Passaggio
23
Measurement of md
Ferrara, Roma
 Select events containing 2 leptons from semileptonic B decays
 B0 flavor at decay tagged by sign of lepton charge
 l+l-  unmixed events (+); ll  mixed events (-)  t
 B B in a coherent P-wave state  S (t; md ) 
 time dependent asymmetry:
0
0
S (t )  S (t )
 cos md t
S (t )  S (t )
md=0.493±0.012±0.009
ps-1
e
4

(1  cos md t )
opposite
sign
same
sign
Mixing measurements validate
time-dependent asymmetry
measurement techniques.
asymmetry
Gruppo I, Settembre 2002
S.Passaggio
24
The next future…
Ferrara, Napoli, Roma
 Physics on the recoil
The high luminosity and the high number of fully
reconstructed B’s opens a brand new world in B physics
In 80 fb-1 :


300 K fully reco B
40 K semileptonic B (one 
missing)
Able to reconstruct single B in
modes with BF ~10-4 - 10-5
Gruppo I, Settembre 2002
S.Passaggio
25
Physics on the recoil: 100 fb-1
BR
Nevents
Goal
bcl
~10-1
~3•104
Vcb
BR(B0,B+ Xl)
bul
~3•10-3
~1000
Vub
bsg
~3•10-4
~100
BR(bsg)
B
10-5 ~10-4
3~30
BR(B)
Gruppo I, Settembre 2002
S.Passaggio
26
Physics on the recoil
 Vcb
Inclusive Semileptonic spectrum
 Vub
Ferrara, Roma
Analysis on the recoil (with full reconstruction of the hadronic
system) will yield a statistical error of 10% and a comparable
systematic error by end of the year
 b  sg
Pisa, Roma
 B  
Napoli
(Inclusive)
(Measure fB)
results expected for the winter conferences
Gruppo I, Settembre 2002
S.Passaggio
27
Other ongoing analyses
 Vcb
Ferrara, Napoli, Trieste
D(*)l (D(*)fully reconstructed), dN/dy differential distribution
results expected by winter conferences
 CP/CPT
Pisa
measurement of the lifetime difference and test of CPT and T
violation in the B0d meson system
 Hadronic charmonium decays
Genova
search for unconfirmed charmonium states (hc)
 ISR to excl. final states
 BR(DS)
Gruppo I, Settembre 2002
(2n, KK, …)
Frascati
Frascati, Perugia
S.Passaggio
28
Conclusions
CP violation in B physics
is now an established fact
 sin2 (golden) = 0.741  0.067 (stat)  0.033 (syst)
 D*+ D*-: Im(+) = 0.31  0.43 (stat)  0.13 (syst)
  KS:
(2.7 s: penguin?)
sin2 = -0.19+0.52-0.50(stat)  0.09(syst) (BaBar+Belle: 2.7 s)
 S = 0.02  0.34stat  0.05syst Isospin analysis
C = -0.30  0.25stat  0.04syst
has started…
New physics?
(will see…)
 Time is ripe for observing smaller effects
(direct CP, …)
 Exploit high luminosity to attack the systematics
physics on recoil
Gruppo I, Settembre 2002
S.Passaggio
29
Backup slides
PEP-II @ SLAC
High luminosity asymmetric B factory @ (4S)
9 GeV e- on 3.1 GeV e+
(4S) boost:
Gruppo I, Settembre 2002
<g>  0.55
S.Passaggio
31
The BaBar detector
1.5T solenoid
DIRC (PID)
CsI(Tl) EMC
e ID
g reconstruction
Bremsstrahlung recovery
sE/E = 2.3% E-1/4  1.9%
e+ (3.1GeV)
Drift Chamber
e- (9GeV)
High quality tracking
(fiducial volume: 041 < q < 2.54)
s(pT)/pT = 0.13% PT  0.45%
Instrumented Flux Return
Silicon Vertex Tracker
 ID
z hit resolution ~ 15 m
Gruppo I, Settembre 2002
S.Passaggio
32
CP violation with B mesons
BH , L  p B 0  q B 0
 A  A( B  f )

 A  A( B  f )
q A
(independent from phase conventions)

p A
Three observable interference effects:
q
1
p
 CP violation in decay (direct):
A
1
A
 CP violation from mixing/decay interference:
Gruppo I, Settembre 2002
S.Passaggio
mixing
 CP violation in mixing:
B0
B
0
Af
CP
f
Af
t
 =1, Im   0
33
Generalities on reconstruction
 Kinematic variables used for signal and background
estimates (fully reconstructed B’s)
 E  EB* 
 mES 
s
2
s
 pB* 2
4
(s
15  80 MeV, larger with neutrals)
EB* ( pB* )  reconstructed B energy (momentum) in (4S ) rest frame
(s
3MeV)
 From z to t: t  z g c
nominal Y(4S) boost in lab frame
proper time difference between the 2 B decays
 Lepton ID: e  EEMC/pDCH; lateral shower shape (EMC); dE/dx (DCH)
  EEMC; penetr. depth, strip mult., track continuity (IFR)
 /K separation: (when applied) based on dE/dx (DCH), Čerenkov ring
opening (DIRC)
 Continuum rejection: typically based on upper cut on normalized
Gruppo I, Settembre 2002
Fox-Wolfram 2nd moment (H2/H0  0.4  0.95)
S.Passaggio
34
-K
separation
K sample

hypothesis
K
hypothesis
D*+ D0+  (K-+)+
For e85%
P(K)=1.7%
P( K)=2.7%
Gruppo I, Settembre 2002
S.Passaggio
35
 asymmetry
[Belle – BaBar]
Gruppo I, Settembre 2002
S.Passaggio
36