Transcript Document

Rare decays at B factories
Peter Križan
University of Ljubljana and J. Stefan Institute
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Fundamental Questions in Flavor Physics
Are there new sources of CP violation?
Experiments: bs CPV, compare CPV angles from tree and loops
Are there new operators with quarks enhanced by
New Physics ?
Experiments: AFB(BK*l l), BK  rates and asymmetries
Are there right-handed currents ?
Experiments: bs  CPV, BV V triple-product asymmetries
Are there new flavor changing neutral currents ?
Experiments: bs   bar, D-Dbar mixing+CPV+rare, 
Data sample of ∼50ab−1@Y(4S) needed to address these questions
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Contents
FCNC bs decays
•bs : inclusive rate, CP violation
•bd penguins: B  r, w decays
•Measurement of Afb vs q2 in B  K* l+ l- decays
Decays with >1 neutrino
•Purely leptonic decays: B-  t- nt , B0  t+ t•B-  K- n n
•Semileptonic decay: B-  D(*) t- nt
July 24, 2006
...ITEP
Only
a limited selection
of topics.
Meeting
Peter Križan,
Ljubljana
Why FCNC decays?
Flavour changing neutral current (FCNC) processes (like
bs, bd) are fobidden at the tree level in the Standard
Model. Proceed only at low rate via higher-order loop
diagrams.
Ideal place to search for new physics.
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Radiative Decays
•
•
•
•
•
Inclusive Br(bs)
BK* isospin asymmetry (D+-)
Mixing induced CPV
Direct CPV in BXs
BXd 
|C7|, SF for |Vub|
sign of C7
red: discussed in this talk
July 24, 2006
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Inclusive Br(bs)
Motivation: measure |C7| and shape function parameters (from
E spectrum for |Vub| extraction)
Inclusive and semi-inclusive 
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38 Peter
modes,
55%
rate
Križan,
Ljubljana
Inclusive Br(bs)
BF(B  Xs , E>1.6 GeV )=(3.55±0.24
+0.09
-0.10
±0.03) x 10-4
 consistent with SM expectations (3.57±0.30) x 10-4
However: theory error is expected to get reduced by a factor
of ~2 (NNLL calculations are under way)
interesting for charged Higgs mass limit
need a better measurement of inclusive rate
Also: important to fix the value of Wilson coeff. C7 and to
determine the spectrum shape.
At 5 ab-1 : Emin down to 1.5 GeV and stat. error ~5%
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana

BXs CP Asymmetry
• Sensitive to NP – right handed
currents
• Theoretically clean.
• Standard Model “~Zero”.
–  is polarized, and the final
state is almost flavor
specific.
t
b
mb
ms
b
– Helicity flip of  suppressed
by ~ms/mbS ~ 0.06 sin2f1
b
C7
W-
s L
ms
mb
s R
KS trajectory
+ -

• Time dependent CPV requires
B vertex
vertex reconstruction with
KS+ x  100m,  y  5m,  z  3mm,
Vertex recon. eff. at Belle
51% (SVD2), 40% (SVD1)
July 24, 2006
IP profile


Possible at e+e- B-factory
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Peter Križan, Ljubljana
B0KS0 time dependent CPV
Atwood, Gershon, Hazumi, Soni,
PRD71, 076003 (2005)
M(KS0) < 1.8GeV/c2
– NP effect is independent of the resonance structure.
Example: Belle 386MBB
• Two M(KS0) regions(MR1:0.8-1.0GeV/c2/MR2: <1.8GeV/c2)
• 70+-11 (45+-11) events in MR1(2).
S= +0.08 ±0.41 ±0.10
A= +0.12±0.27±0.10
Good tag (0.5<r<1.0)
July 24, 2006
ITEP Meeting
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B0KS0 time dependent CPV
Results:
Belle
S(BK*, K*KS0)=-0.01 ± 0.52 ± 0.11
S(B KS0)=0.08 ± 0.41 ± 0.10
BaBar
S(BK*, K*KS0)=-0.21±0.40 ±0.05
Prospects:
Present Belle
(stat./syst.)
Acpmix(BK*, K*KS0) 0.41 / 0.10
Acpdir(BXs)
0.051 / 0.038
hep-ex/0507059
PRD 71 (2005) 0501103
5ab-1
50ab-1
0.14
0.04
0.011
0.005
Add more modes: BKSf (with angular analyisis), higher K
resonances, BKSh (recent observation by BaBar),...
July 24, 2006
ITEP Meeting
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Acp(BXs) vs SUSY models
50ab-1
Mixing CPV
5ab-1
U(2)
tanb=30
mSUGRA
tanb=30
Acpmix
Acpdir
Direct CPV
mSUGRA
tanb=30
SU(5)+nR
tanb=30
SU(5)+nR
tanb=30
degenerate
SU(5)+nR
tanb=30
non-degenerate
degenerate
mg (GeV )
July 24, 2006
U(2)
tanb=30
SU(5)+nR
tanb=30
non-degenerate
mg (GeV )
T. Goto, Y.Okada, Y.Shimizu,T.Shindou, M.Tanaka
ITEP Meeting
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Križan, Ljubljana
hep-ph/0306093,
also in SuperKEKB
LoI
bd penguins
Supressed by |Vtd/Vts | 2 vs b  s
Interesting:
•Measurement of |Vtd/Vts|
Addresses the same physics issue as Bs- Bs mixing (from
a different perspective: box vs loop)
Difference in
dynamics
Form factor ratio
•CP violation could be sizeable in SM (order 10%)
•New physics could be quite different from b  s
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Belle: First observation of B  r, w
Ref: PRL 96, 221601 (2006)
Reconstructing rare B meson decays at Y(4s): use two variables,
energy diference DE and beam constrained mass Mbc
DE   Ei - ECM 2
M bc  ( ECM
 2
/ 2) - ( pi )
2
signal
qq
K*
other B
_
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Vtd/Vts from B  r, w
The measured branching fraction
BF(B  r/w)= 1.32
Ref: PRL 96, 221601 (2006)
+0.34
-0.31
(exp.)
+0.10 (theo.)
-0.09
+0.026
-0.025
(exp.)
+0.018
–0.015
Translates to
|Vtd|/|Vts| = 0.199
(theo.)
which is compatible with SM constraints based on fits of
other CKM parameters.
Together with the evidence
of BK0 K decays modes,
this demonstrates the
existence of a new quark
level transition: bd
68%CL
95%CL
Full UT fit
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ITEP Meeting
r
Peter Križan, Ljubljana
Implications of Belle’s observation of bd 
Comparison with the recent observation of Bs mixing at Tevatron:
•green: Belle measurement of |Vtd/Vts| in bd 
•yellow: CDF measurement of |Vtd/Vts| from Bs mixing
The width of the Bs mixing
contour is limited by
theory while Bd γ needs
much more data.
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bd  future prospects
With 1-2 orders of magnitude more statistics (5 ab-1, 50 ab-1):
•Direct CP violation and time-dependent CPV with Bρ0 γ and
B  ωγ
•Measurements of inclusive b  d γ
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ITEP Meeting
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B  K* l+ l-
b  s l+l- was first measured in B  K l+l- by Belle (2001).
Important for further searches for the physics beyond SM
d  b  s
dsˆ
+ -
  
2
2
F
5
b
2
*
ts tb
2
 G m VV
ˆ
1
s




48 3
 4 
2
2
2


 2
 1 + 2sˆ  C9eff + C10eff + 4 1 +  C7eff + 12 Re  C7eff C9eff *  
 sˆ 


em


Ci: Wilson coefficients
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Particularly sensitive: forward-backward asymmetry in K* l+l
l-
l+
B
B
q
K*
K*
q
l+
lBackward event
Forward event
[γ* and Z* contributions in BK* l l interfere and give
rise to forward-backward asymmetries c.f. e+e- + - ]


1
AFB ( K l l )  C10 (q )ReC9 F1 + 2 C7 F2 
q


* + -
July 24, 2006
2
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Peter Križan, Ljubljana
Sample used for AFB(BK*ll)(q2)
Ref: PRL 96, 251801 (2006)
Treat q2, cos(θ)
dependence of bkgs.
Sample for BK* l l:
113±13 events
Unbinned fit to the variables q2 (di-lepton invariant
mass) and cos(θ) for the BK* l l data.
Fit parameters A9/A7 and A10/A7 (Ai = leading term in Ci)
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ITEP Meeting
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Control sample BKll
BK l l control sample:
96±12 events
Consistent with flat
Integrated asymmetry:
+ - +
AFB ( B  K l l ) 
0.10  0.14  0.01
July 24, 2006
ITEP Meeting
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Constraints on Wilson coefficients from
AFB(BK* l l)(q2)
Projections of the full fit to q2, cos(θ)
Integrated FB
asymmetry
*
AFB ( B  K +l -l + ) 
0.50  0.12  0.02;(3.4 )
J/y
y’
Observed integrated AFB rules out some radical New Physics
Models with incorrect signs/magnitudes of C9 and C10 (red and
pink curves)
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Results of the unbinned fit to q2 and cos(θ)
distributions for ratios of Wilson coefficients.
SM
A10/A7
A10/A7
ＳＭ
A9/A7
Best fit
|A7| constrained from
bs  to be close to SM
A9/A7
Ref: PRL 96, 251801 (2006)
at 95% C.L.
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AFB(BK* l l)(q2), BaBar
BaBar: 229 M BB
PRD 73 (2006) 092001
Integrated FB asymmetry
AFB >0.55 (@ 95% CL)
First bin excludes SM (blue) at 2 level?
July 24, 2006
ITEP Meeting
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AFB(BK* l+ l-)[q2] at Super B Factory
q02
Precision with 5ab-1
dC9 ~ 11%
dC10 ~14%
d q02/q02 ~11%
July 24, 2006
4AFB zero-crossing q02 will be
determined with 5% error with 50ab-1
ITEP Meeting
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Purely leptonic decay Bt n
• Proceed via W annihilation in the SM.
• Branching fraction
• Provide information of fB|Vub|
– |Vub| from BXu l n
fB
– Br(Btn)/Dmd
|Vub| / |Vtd|
cf) Lattice
• Expected branching fraction
|Vub| = (4.39 ± 0.33)×10-3 (HFAG)
fB = (216 ± 22) MeV (lattice)
July 24, 2006
BF(B  t nt) = (1.59 ± 0.40)×10-4
ITEP Meeting
Peter Križan, Ljubljana
Charged Higgs contribution to Bt n
mb tan b + mu cot b
mt tan b
b
u
H+/W+
t+
~
e0 = SUSY corrections to b
Yukawa coupling
Br(SM) ~ 1.59 x 10-4
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ITEP Meeting
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Full Reconstruction Method
• Fully reconstruct one of the B’s to
– Tag B flavor/charge
– Determine B momentum
– Exclude decay products of one B from further analysis
B
e(8GeV)
e+(3.5GeV)
Υ(4S)
Decays of interest
BXu l n,
BK n n
BDtn, tn

full reconstruction
BD etc. (0.1~0.3%)
B
Offline B meson beam!
Powerful tool for B decays with neutrinos
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Fully reconstructed sample
Belle (447M BB)  4.12x105 B0B0
+ 6.80x105 B+B-
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Event candidate B-  t- nt
July 24, 2006
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Bt n (Belle)
• NBB (produced) = 447M
• NB+B- (full recon.)
= 6.80 x 105 (purity 0.57)
• t decay
modes
t   nn , e-nn
t -   -n ,  - 0n ,  - + -n
hep-ex/0604018 - preliminary
Obtained Eresidual
– Cover 81% of t decays
• Event selection
– Main discriminant: residual
ECL energy
Fit to Eresidual  21.2+6.7
-5.7
signal events.
4.2σ significance including
systematics
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Impact of B-  t- nt
•From BF(B  t nt) Product of B meson decay constant fB
and CKM matrix element |Vub|use |Vub| from HFAG  fB
•Use BF(B  t nt) with Dmd  constraint in the r,h plane
The common
uncertainty from fB
cancels in this ratio.
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Charged Higgs limits from B-  t- nt
If the theoretical prediction is taken for fB  limit on
charged Higgs mass vs. tanb
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Bt n prospects
• Expected precision
at Super-B
– 13% at 5 ab-1
– 7% at 50 ab-1
• Search with D(*) l n tag will help.
 BaBar 232M BB
PRD 73 (2006) 057101
– Tag eff ~ 1.75 x 10-3
– Signal selection eff. ~31%
– Similar S/N to Belle (full recon. sample)
Br ( B  tn )  2.8 10-4 (90%CL)
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Future Prospects: Btn
95.5%C.L. exclusion boundaries
DfB(LQCD) = 5%
Extrapolations (T.Iijima)
Lum.
DB(Btn)
exp
(for BFobs = BFSM)
D|Vub|
414 fb-1
36%
7.5%
5 ab-1
10%
5.8%
50 ab-1
3%
4.4%
tan b / mH
50ab
If D|Vub| = 0 & DfB = 0
-1
rH
July 24, 2006
tan b / mH
Peter Križan, Ljubljana
B  t +t BaBar (232M BB)
PRL 96 (2006) 241802
Challenging measurement: 2-4 neutrinos per event!
•Fully reconstruct one B (D(*)X, X=combination of up to 5
pions and kaons), 280k events
• t decay modes: lnn, -n, r-n (51% of tt decays)
•Reject events with KL, KS, K± and employ neural network
(kinematics of charged track momenta and ECL residual energy)
263±19 events (expect 281±40 from sidebands, MC)
BF(B  t+t-) < 4.1 x 10-3 (90%CL)
SM prediction: 0.12 x 10-6
 First ever limit on this channel
Constrains
leptoquark couplings
and tanb enhancements
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
B-  K- n n
BK(*)νν is a particularly interesting and challenging mode
(with B  τν as a small background), theoretically clean
Experimental signature: B  K + nothing
The “nothing” can also be light dark matter with mass of order
1 GeV. Direct dark-matter searches cannot see the M<10 GeV
region.
-6
SM prediction: (3.8+1.2
-0.6) x 10
B  τν analysis is a proof that such a one prong decay can be
studied at a B factory
Present limits:
•BaBar (89M BB): BF(B+K+νν) < 52 x 10-6 PRL 94
(2005)101801
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
B-  K- n n prospects
MC extrapolation to 50 ab-1
5
Observation of B±  K± n n
SM prediction:
G.Buchalla, G.Hiller, G.Isidori
(PRD 63 014015)
Extra EM calorimeter energy
Fig. From SuperKEKB LoI
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Charged Higgs search in BD t n
Charged Higgs contribution
mb tan b + mc cot b
b
c
B
mt tan b
H+ /
( B  Dt vt )
( B  Dv )
t+
nt
W+
Decay amplitude  mb mt tan 2 b
Br(SM) ~ 8 x 10-3
Tauonic decay is the most sensitive
•Analysis: reject events with p, K, reject D*tn contamination, no
remaining charged or 0 tracks, cut on the ECL residual energy,
angle between two n’s and missing mass.
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
BD t n (MC studies)

Signal selection efficiency
D 0t + (e +n tn e )n t
D 0t + (  +n tn e )n t

10.2%
2.6%
D 0t + ( +n t )n t
26.1%
13.3%
D 0t + ( r +n t )n t
Expectation at 5 / 50 ab-1 for B+ decay
5ab-1
Mode
Nsig
Nbkg
D0t + ( +ntn )nt
280
550
D t (h nt )nt
620
3600
0 +
+
50ab-1
S
12.7
dB/B
7.9%
Nsig
Nbkg
2800
5500
6200
36000
S
dB/B
40.3
2.5%
5 observation possible at 1ab-1
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
BD t n constraint on charged Higgs
Once branching fraction is measured, we can determine R.
MW
R
tan b
MH
Reach in R
M.Tanaka, Z.Phys. C67 (1995) 321
BF error
Form factor error
 Reach in R: 11
July 24, 2006
ITEP Meeting
at 5ab-1
Peter Križan, Ljubljana
BD t n  charged Higgs
Constraint
From bs
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Super-B and LHCb: complementary
Clean environment  measurements that no other experiment can
perform. Examples: CPV in B g fK0, B g h’K0 for new phases, B g
KS0 for right-handed currents.
“B-meson beam” technique  access
to new decay modes; proof B gtn
Example: discover B g Knn.
Measure new types of asymmetries.
Example: forward-backward
asymmetry in b g s, see
Rich, broad physics program
including B, t and charm physics.
Examples: searches for t g  and
D-D mixing with unprecedented
sensitivity.
LHCb
LHCb
LHCb
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Summary
• Radiative, electroweak and tauonic B decays are of great
importance to probe new physics.
• We are starting to measure Btn, Dtn, AFB(K*ll), ACP(K0)
etc. at the current B factories.
Hot topics in the coming years !
Watch out for updates (including this week)...
• For precise measurements, we need a Super-B factory!
Observe K(*) nn, zero crossing in AFB, D(*)tn
Expected precision (5ab-150ab-1);
– Br(tn):
13%7%
– Br(D(*)tn):
7.9%2.5%
– q02 of AFB(K*ll):
11%5%
– ACP(K0) tCPV:
0.140.04
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Additional slides
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Charged Higgs from Br(bs)
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
Radiative decays: prospects
Summary by M. Nakao 1st Super-B workshop at Hawaii (2004)
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
B-  e- ne, - n
Helicity supressed with respect to B  τν
B-  -n
SM prediction: 0.4 x 10-6
(Possibly better for charged Higgs limits than tn at high stat)
Present limits:
•Belle (152M BB): BF(B-  -n) < 2 x 10-6
hep-ex/0408132
•BaBar (89M BB): BF(B-  -n) < 6.6 x 10-6 PRL 92 (2005)221803
B -  e- n e
SM prediction: ~0.00001 x 10-6
Present limit:
•Belle (65M BB): BF(B-  e- ne) < 5.4 x 10-6 BELLE-CONF-0247
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
B -  e+ e- , +No new results from B factories...
•BaBar (120M BB): BF(B  e+e-) < 0.083 x 10-6
BF(B  +-) < 0.061 x 10-6 PRL94(2005)221803
•Belle (85M BB): BF(B  e+e-) < 0.19 x 10-6
BF(B  +-) < 0.16 x 10-6
PRD 68 (2003)111101
.... With present statistics we could be competitive with Tevatron
Limits from Tevatron:
hep-ex/0508058
BF(Bd  +-) < 0.032 x 10-6
SM prediction: 0.0001 x 10-6
BF(Bs  +-) < 0.12 x 10-6
SM prediction: 0.0035 x 10-6
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana
BD t n (MC studies)
• Use fully reconstructed
samples.
• t decay modes
t -   -nn , e-nn ,  -n , r -n
• Analysis cuts;
– Reject events with p, KL
– Reject D* t n contamination
Signal
mD*0 - mD0 - 142  10 MeV/c 2
– No remaining charged or 0 tracks
– ECL residual energy
Eresidual  100MeV
– Angle between two n’s
-1.0  cosqnn  0.8
BG
– Missing mass
pB - pD - p
July 24, 2006
2
 1.2 (GeV / c 2 ) 2
ITEP Meeting
Peter Križan, Ljubljana
B  t nt
BF(B  t nt)=(1.06
+0.34
-0.28
(stat.)
hep-ex/0604018 - preliminary
+0.18
-0.16
(syst.)) x 10-4
 Product of B meson decay constant fB and CKM
matrix element |Vub|
fB |Vub| = (7.73
+1.24 (stat.) +0.66 (syst.))
-1.02
-0.58
10-4 GeV
Using |Vub| = (4.39 ± 0.33)×10-3 from HFAG
fB = (176
+28
-23
(stat.)
+20
-18
(syst.)) MeV
First measurement of fB!
fB = (216 ± 22) MeV (an unquenched lattice calc.)
[HPQCD, Phys. Rev. Lett. 95, 212001 (2005) ]
July 24, 2006
ITEP Meeting
Peter Križan, Ljubljana