1. Recent Results from BABAR
P.-Fabrizio Salvatore
Royal Holloway College, University of London
For the BABAR Collaboration
Measurement of sin2b
Measurement of sin2aeff
Future: g and sin (2b + g )
Hadron Structure 2002, Herl’any
22-27 September 2002

2. Fabrizio Salvatore, Royal Holloway College
Outline
The search for CP violation with asymmetric e+e- collider
PEPII and the BaBar Experiment
sin2b measurement:
The golden modes: b -> ccs
The Cabibbo-suppressed modes: b -> ccd
The pure penguin modes: b -> sss
sin2aeff measurement:
CP asymmetries in p+p- and K+p-
p+p0 and p0p0 decay rates
CP asymmetries in r+p- and r+K-
Future: g and sin(2b +g )
Asymmetry in B ->D0(CP)K decay
B0 ->D* (n)p decays
Conclusions - -
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

3. Physics principles: CP violation in the SM
The only source of CP violation in the SM is the KM phase that appears in the CKM matrix
Unitarity Triangle comes from the unitarity of the matrix f1 f2 f3
a, b and g constrained by CP asymmetries in B decays
CP from complex component of Vub and Vtd
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

4. Time-dependent CP violation from B0-B0 mixing
fCP b d
u,c,t
top quark box introduces: Vtb Vtd*
Dmd = mH - mL W
Direct CP violation if multiple amplitudes with different phases
Purely CP violation in interference of decays with and without mixing
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

5. Fabrizio Salvatore, Royal Holloway College
PEPII performances
Peak luminosity: 4.60 x 1033cm-2s (exceeded design goal 3.0 x 1033)
PEP-II delivered 99 fb-1
BaBar recorded 94 fb-1
For sin2b and sin2a used:
On peak 81 fb-1
88M BB pairs
Off peak 10 fb-1
Run on peak
2a 9.0
2b 26.7
2c 25.0
81.4
800 bunches
E mA
E mA
IP 147 micron x 5 micron
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

6. Fabrizio Salvatore, Royal Holloway College
BABAR Detector
Svt 5 layer double sided strips
DCH 40 stereo layers
DIRC: 144 quart bars, PMTS
EMC 6580 crystals
IFR: 19 layers
SVT: 5 double side layers. 97% efficiency, 15 mm z hit resolution (inner layers, perp. tracks)
Momentum resolution (SVT+DCH): (pT)/pT = 0.13 %  pT %
DIRC: 144 quartz bars. Provide K- separation GeV/c  GeV/c
EMC: 6580 CsI(Tl) crystals. Energy resolution: E/E = 2.3 %E-1/4  1.9 %
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

7. B0-B0 events at the (4S) resonanceZ m- K-
Flavour tag and vertex reconstruction
Boost: bg = 0.55
(4S)
Btag
Brec m-
Exclusive B meson and vertex reconstruction p+ p- KS m+
Coherent BB pair B0
Start the Clock
Compute f+ (Dt)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

8. Vertexing and tagging algorithms
Beam spot
Interaction Point
BREC Vertex
BREC daughters
BREC direction
BTAG direction
TAG Vertex
TAG tracks, V0s z
Brec vertex from charged Brec daughters
BTag vertex from:
All charged tracks not in Brec, constrain with Brec vertex, beam spot, and (4S) momentum
High efficiency: 95%
Average Dz resolution ~ 180 mm
(measured from data)
New tagging algorithm based on neural networks:
inputs: leptons, K, slow p (D* decay) and high-momentum tracks
5 mutually exclusive categories:
Lepton - isolated high-momentum leptons;
kaon I – high quality K, correlated K and slow p;
kaon II – low quality K or slow p;
Inclusive – unidentified leptons, low quality K, high-momentum tracks;
Untagged
Use per-event estimate sigma_delta_Z
Empirical model to correct it
Q = % (~7% improvement)
PRL87 (Aug01)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

9. sin2b from charmonium states (b  ccs)
Tree level dominates and CP only from B 0-B 0 mixing B0 K0
lf = hf e-i2b, hf=±1
B0 -> J/Y Ks
B0 -> Y(2S) Ks
B0 -> cc1 Ks
B0 -> hc Ks
hf = -1
hf = 1 B0 -> J/Y KL
hf = 1- 2RT B0 -> J/Y K*0 (K*0 -> Ks p0)
RT = % (PRL87)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

10. Event yields and purity
Event Sample
Ntag
Purity
J/y Ks(p+p-)
974
97%
J/y Ks(p0p0)
170
89%
y(2S) Ks
150
c1 Ks 80
95%
hc Ks
132
73%
Total (hf = -1)
1506
92%
J/y KL
988
55%
J/y K*0 (Ks p0)
147
81%
All CP modes
2641
78%
Eta_c KS has more peaking background than other modes
15% Psi KS
13% Peaking background
Recent addition:
B0 hc Ks
where hc  K+K-p0 or
K+Ks p-
Energy-substituted mass:
Energy difference:
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

11. Fabrizio Salvatore, Royal Holloway College
sin2b result
Unbinned maximum likelihood fit:
34 parameters: sin2b, mistag fract. (8), Dt resolution funct. (8), bkgnd (17)
tB = ps, Dmd = ps-1 fixed (PDG 2002)
hf =-1
hf =+1
sin2b =  0.074
sin2b =  0.158
sin2b =  (stat)  (sys)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College
(hep-ex/ )

12. Asymmetry in b  ccs modes with lepton tag
Golden mode (cc) Ks with lepton tag only
Ntagged = 220
Purity = 98%
Mistag fraction 3.3%
sDt 20% better than other tag categories
sin2b = 0.79  0.11
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

13. sin2b fit results by decay mode
Consistency of CP Channels: P(c2) = 57%
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

14. Constraints in the (r,h) plane
Method as in Höcker et al, Eur.Phys.J.C21: ,2001
One solution for b is in excellent agreement with measurements of unitarity triangle apex
2 sigma errors
r = r (1-l2/2)
h = h (1-l2/2)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

15. Search for new physics in (cc)KS events
In the measurement of sin2b we have assumed |lf | = 1 (SM expectation)
Sf  - hf sin2b Cf  0
If another amplitude that contributes with a different phase:
| lf | =  (stat)  (syst)
Sf =  (stat)  (syst)
Fit |lf | and Sf using the
clean (cc)Ks modes
(hf =-1, Ntagged = 1506,
Purity = 92%):
Consistent with the Standard Model expectation of |lf |=1 and nominal fit sin2b =  for (cc)Ks modes alone.
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

16. The Cabibbo-suppressed modes (b  ccd ) (I)
B0  D*+D*-: same weak phase as b  ccs (tree level);
small penguin contribution (<0.1 Tree);
not CP eigenstate (needs angular analysis) B0
D* -
D* +
Vcd
RT = +
Ntagged= 102
Purity = 82%
Parameterize l in terms of CP-odd (l) and CP-even (l+) components and use:
|l |= 1, Im(l ) =
|l+| = 0.98  0.25 (stat)  0.09 (syst)
Im(l+) = 0.31  0.43 (stat)  0.10 (syst)
(hep-ex/ )
Im(l+) measurement ~2.7s from BaBar sin2b in charmonium, assuming no penguins.
If penguins are negligible, then
Im(l+) = - sin2b
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

17. The Cabibbo-suppressed modes (b  ccd) (II)
B0  J/y p0 : also color-suppressed
Vcd
Tree: ~VcbVcd*
Penguin:~VcbVcd* + VubVud*
Comparable tree and penguin contribution ~ O(l3)
Ntagged = 49
Purity = 59%
hf = + 1
(hep-ex/ )
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

18. sin2b from penguin mode B0  f KS
Dominated by b  sss gluonic penguins
Same Weak phase as b  ccs, but sensitive to new physics in loops
Small branching fraction O(10-5)
Significant background from qq continuum
Using only f  K+K-
Ntagged = 66
Purity = 50%
hf = - 1
(hep-ex/ )
|lfK| = 1 fixed
SfK = (stat)  0.09 (syst)
+0.52
- 0.50
Cross check on B+  f K +: SfK = 0.26  0.27
Analysis of B0  h’ KS in progress
If no new physics, SfK = sin2b
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

19. Summary of sin2b results
New measurement of sin2b from charmonium modes (88 x106 BB)
Submitted to PRL July 17, 2002
(hep-ex/ )
Results have been improving by more than just luminosity gain
sin2b = ± (stat) ± (syst)
July 00
Feb 01
July 01
Mar 02
July 02
Interesting new measurements are being obtained on the open charm modes:
B 0D*+D*- (hep-ex/ )
and b penguin modes:
B 0J/ p 0 (hep-ex/ )
B 0f K0S (hep-ex/ )
Million BB pairs
No hints of physics beyond the Standard Model yet, but lots of opportunities to challenge the theory with the increasing event statistics in BaBar
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

20. sin2a from charmless B decays
Penguin contribution is non-negligible
measure sin2aeff
mixing
decay +
Tree (T)
Penguin (P)
B0  p+p-
need BF from B -> p+p-, p+p0 and p0p0 and isospin analysis to obtain a from aeff
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

21. needs excellent particle ID (DIRC)
sin2a : B → pp, Kp, KK modes
Small branching ratios ( )
lots of data needed
Data sample: 88M BB events
Large background from continuum (qq) events
use kinematic and topology of events to separate signal from light-quark bg
Fisher discriminant: q* p+ p- p*
Ambiguity between p and K
needs excellent particle ID (DIRC)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

22. K/p separation using the DIRC
Identification of h+h’- tracks as p or K using the angle qc measured in the DIRC
Double-gaussian PDFs built from the difference (qc – qcexp)/s(qc)
p hypothesis
K hypothesis
K/p separation and PDF parameters measured using fully reconstructed data
For e=85%:
P(K->p) = 1.7%
P(p->K) = 2.7 %
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

23. Event yields and Kp asymmetry
Preliminary
no tagging or vertexing needed
Time-independent maximum likelihood fit to extract event yields and Kp asymmetry
Direct CP
Submitted to Phys Rev (hep-ex/ )
Mode
Yield
BR (10-6)
ACP(Kp)
B0 → p+p-
B0 → K+p-
B0 → K+K-
1 + 8
< 0.6 (90% C.L.)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

24. mES and DE distributions
Preliminary
Signal events are selected in the (mES,DE) plane
same as for sin2b measurement
Bo -> pp
Bo -> pp Kp
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

25. Spp and Cpp measurement
Time-dependent unbinned maximum likelihood fit
Same tagging and vertexing procedure as for sin2b
1 ps
Projection in sample of pp-selected events
qq+ Kp
Spp =
Cpp =
Preliminary
Submitted to Phys Rev (hep-ex/ )
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

26. Extraction of a from aeff
B ->p+p-, p+p0 and p0p0 decays related by isospin
(gluonic) penguins contribute only to I=0
p+p0 has I=2 only tree amplitude only
(|A+0| = |A-0|)
2aeff = 2a + kpp
Need to measure:
B+ ->p+p0, B0 ->p0p0, B0 ->p0p0
Isospin analysis
Gronau and London, Phys.Rev.Lett 65, 3381 (1991)
Otherwise, put limit on BR(B0 ->p0p0):
Grossman-Quinn bound
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

27. B+->p+p0 and B+->K+p0 branching ratio
Preliminary
B+->p+p0 has pure tree amplitude and
no CP expected
Fit region
e+e- → qq
r+p-
Usual charmless two-body analysis
B0-> r+p- bg reduced by a
tight cut on DE
Simultaneous fit to pp0/Kp0
Mode
Yield
BR (10-6)
ACP
B+ →p+p0
B+ →K+p0
hep-ex/
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

28. B0->p0p0 branching ratio
Preliminary
Small signal expected
Flavour tagging and event topology used to reduce qq bg
B+->r+p0 bg reduced using a cut on m(p+p0) and DE
B0->p0p0 yield determined by unbinned ML fit:
@ 90% CL
|a – aeff| < 510
hep-ex/
Central value for BR:
If BR as high as its central value, Grossman-Quinn bound not adequate isospin analysis is necessary
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

29. B0->rh: direct and indirect CP measurement CP
NOT CP eigenstate
BR = ( )x10-6
insensitive to CP
rK self tagging
Direct CP ACP and C = 0
Indirect CP S = 0
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

30. Event yields and charge asymmetry
B0/B0->r-p+
B0/B0->r+p-
Clear B0->rp signal
Maximum likelihood fit to extract yields and charge asymmetry:
Preliminary
hep-ex/
Validation test: fit tB and Dmd using data
tB = ( ) ps
Dmd = ( ) ps-1
World Average
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

31. Time-dependent asymmetry
hep-ex/
Preliminary
expected ~0.4 (from naïve factorization)
sensitive to strong phase differences
dominated by uncertainties on B background components
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

32. Using previous results and their correlations:
Direct CP violation
Direct CP can be expressed using the asymmetries:
r meson from spectator quark
p meson from spectator quark
Using previous results and their correlations:
A+- = (stat)+0.16(syst)
A-+ = (stat)+0.09(syst)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

33. Summary of sin2a and direct CP violation results
Charmless two-body decays:
branching ratios and CP asymmetries in B0->p+p-, K+p- and K+K- (hep-ex/ )
no evidence for large direct or indirect CP violation in p+p-
branching fractions needed to extract a from aeff computed:
upper limit on BR(B0->p0p0) (hep-ex/ )
B+->p+p0 and K+p0 branching ratios (hep-ex/ )
still too early for significant constraint:
Charmless three-body decays:
first CP asymmetry measurement for B0->rp and B0->rK (hep-ex/ )
|a – aeff| < 510
A+- = (stat)+0.16(syst)
A-+ = (stat)+0.09(syst)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

34. Future: g and sin(2b+g) (I)
Preliminary
g with B ->D0(CP)K W+ B+ b u s c K+ D0
Vus
Vcb *
Colour allowed
Vcs
Vub
Colour suppressed
hep-ex/
data sample 75 fb-1
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

35. Future: g and sin(2b+g) (II)
Preliminary
B ->D*p/r/a1 h+ W+ B0 b d u c
D*-
Vud
Vcb *
Cabibbo allowed W+ B0 b d c u h-
Vcd
Vub *
Cabibbo suppressed
D*+
Time evolution of B0->D*-h+ and B0->D*+h- related to sin(2b +g )
For precise measurement, need many events
D*a1 mode has the largest BR (~1.3%)
use partial reconstruction:
Only the slow p from D*->D0p decay and the p/r/a1 (a1->r0p) are reconstructed
If only the D0 is missing, in the (4S) frame the B direction lies on the surface of a cone
Averaging over this surface, the missing mass mmiss can be defined
P*(p,r,a1)
P*p
P*D0
P*B
Signal: mmiss peaks to D0 mass
Bg events: broader distribution
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

36. First steps: B0 lifetime using D*p and D*r decays
Validation for the partial reconstruction technique
tB extracted using an unbinned maximum likelihood fit
B ->D* r
Nsig =
B ->D* p
Dt(ps)
Continuum
Comb. BB
Peak. BB
Signal
Nsig =
data sample 20.7 fb-1
tB = (stat)+0.075(syst) ps
hep-ex/
tB = ( ) ps
World Average
tB = (stat)+0.038(syst) ps
hep-ex/
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

37. D*a1 branching fraction measurement
B ->D*a1
data sample 20.7 fb-1
Continuum background rejected using a neural network technique
exploit the different topologies between qq events (jet structure) and B events (spherical)
mmiss distribution obtained from off-reso data subtracted from that obtained on on-reso
result fitted with a combination of:
BB Monte Carlo events
signal Monte Carlo events
data on-reso (off-reso subtr.)
signal+BB bg MC
BB bg MC only
PDG: ( )%
BF = ( )%
Signal yield:
Preliminary
hep-ex/
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

38. Summary: B ->D0(CP)K and B0 ->D*(n)p
B -> D0(CP)K mode:
ratio of branching fraction for B->D0K and B->D0p modes
first measurement of CP asymmetry in B->D0 (CP) K (hep-ex/ )
B -> D*(n)p mode :
B0 lifetime using D*p and D*r decays (hep-ex/ , hep-ex/ )
branching fraction of B0 -> D*a1 decay channel (hep-ex/ )
R= ( )%
ACP= ( )
+0.09
-0.07
BF = ( )%
tB = ( ) ps
Combined measurement:
Analyses just begun, still lot of work to do !
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

39. Conclusions (I)
New measurement of sin2b from charmonium modes
Submitted to PRL July 17, 2002
(hep-ex/ )
sin2b = ± (stat) ± (syst)
BaBar and Belle’s sin2b results have convinced the physics community that CKM is the dominant source of CP violation
First steps to analyze decay modes related to g and sin(2b +g )
first measurement of CP asymmetry in B->D0K (hep-ex/ )
B0 lifetime with D*p and D*r decays (hep-ex/ , hep-ex/ )
branching fraction of B0->D*a1 decay (hep-ex/ )
No evidence for large direct or indirect CP violation in B0->p+p-
Measurement of the branching ratios for B+-> p+p0,K+p (hep-ex/ )
Upper limit on BR(B0-> p0p0) and constraint on |a -aeff|
(hep-ex/ )
CP asymmetry in B0/B0->r+p+ decay (hep-ex/ )
(hep-ex/ )
Extremely productive time for B physics with BaBar !
More still to come !
BUT
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

40. More exciting physics results are on their way !
Conclusions (II)
A lot more to do with the 100 fb-1 of data already recorded and those still to come in the next run starting this fall
higher precision in the sin2b measurement
measurement of a and g
better knowledge of |Vub| and |Vcb|
rare decays (possibility to probe
new physics)
Charm physics (D0 mixing, CP, ….)
tau results
other very interesting
physics results:
More exciting physics results are on their way !
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

41. Fabrizio Salvatore, Royal Holloway College
Tagging performance
Category
Efficiency (e)
Mistag Fr. (w)
d Mistag
Q=e(1-2w)2
Lepton
9.1  0.2
3.3  0.6
-1.4  1.1
7.9  0.3
KPiorK
16.7  0.2
9.9  0.7
-1.1  1.1
10.7  0.4
KorPi
19.8  0.3
20.9  0.8
-4.2  1.1
6.7  0.4
Inclusive
20.0  0.3
31.6  0.9
-2.0  1.2
2.7  0.3
Total
65.6  0.5
28.1  0.7
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

42. Sources of Systematic Error
s(sin2b)
Description of background events
CP content of background components
Background shape uncertainties
Composition and content of J/y KL background 0.015
Dt resolution and detector effects
Silicon detector alignment uncertainty
Dt resolution model
Mistag differences between BCP and Bflav samples 0.012
Fit bias correction
Fixed lifetime and oscillation frequency
TOTAL
CP content of argus background taken to be -1 to 1!
Resolution model (3 gaussians or 2?gaussians plus exponential)
Error reduction
Switched PDG2002 from 2000
Split peaking background per mode
Increased MC stastics by factor of 7
Steadily reducing systematic error: July 2002 = 0.033
July 2001 = 0.05
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

43. Fabrizio Salvatore, Royal Holloway College
sin2b in subsamples
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

44. Cross-check on data control samples
Observed no asymmetry as expected
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

45. CP composition of B0  D*+D*-
We measure CP odd fraction (corrected for acceptance) to be small:
R = 0.07  0.06 (stat)  0.03 (syst)
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

46. The Cabibbo-suppressed modes (b  ccd)
B0  D*+D- :
D* _ D+ B0
D*+
D _ CP
conjugation
strong
phase
Not a CP eigenstate
possible strong phase contributions;
different decay time distributions for :
B0  D- D*+
B0  D*- D+
D*D 56 fb-1
Ntagged= 85
Purity = 52%
S+- =  1.41  0.20
C+- =  0.74  0.13
S-+ =  0.88  0.05
C-+ =  0.50  0.08
Update to full data set in progress
September 26, 2002
Fabrizio Salvatore, Royal Holloway College

47. Validation of tagging, vertexing and fit procedure
Projection in sample of K-selected events
Use B0 ->Kp events:
T=tag charge, Q=K charge
same sample as for CP asymmetries
tB and Dmd floating in the fit
tB = ( ) ps
Dmd = ( ) ps-1
tB = ( ) ps
Dmd = ( ) ps-1
World Average
September 26, 2002
Fabrizio Salvatore, Royal Holloway College