Transcript Radiative Penguin Decays - Santa Cruz Institute for

Lake Louise Winter Institute
Chateau Lake Louise
20-26 February 2011
Summary of Recent Results on
Rare Decays of B Mesons from
BaBar
Searching for New Physics via Effective
Flavor-Changing Neutral Currents
Bruce A. Schumm
Santa Cruz Institute for Particle Physics
University of California, Santa Cruz
for the BaBar Collaboration
Outline
Recent (past year) results are in three areas:
B  K l+ l- with Missing Energy
B  K 
B  K + -
B
(limit)
(limit)
(limit)
b  (s,d)  Penguins
CP Violation in Penguin Decays
(measurement)
B → Xd and the Status of |Vtd/Vts| (measurement)
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The BaBar Dataset
426 fb-1
54 fb-1
BaBar collected 468 M BB pairs between 2000-2007
and 54 fb-1 off-resonance data
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Flavor-Changing Neutral Currents and New Physics
For example:
The Basic Story:
B+  K+ 
• FCNC process in SM require
loops  suppressed rates
• New physics can enter at
same order
• Modification of BF (x10 or
greater!)
Standard Model
• Large CP-violating effects
But always a battle against
backgrounds…
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Contribution from
Extended Higgs Sector
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B  K,K Approach
Mitigate backgrounds by
tagging recoil B meson
Tagging
B Meson
Signal
B Meson
B  K
K Boosted Decision Tree
• Missing energy
• Whole-event properties
• Signal kinematics
• Reconstruction quality
K Selection: Multivariate Algorithm
(Boosted Decision Tree)
Tag with reconstructed
exclusive SL decay;   1%
B  K
Tag with fully reconstructed
Hadronic decay;   0.2%
K Selection: Cut-Based
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B  K,K Results
Comparison of results, B+  K+
K Result:
B( B  K  )  1.3105 (90% CL)
B( B0  K 0 )  5.6 105 (90% CL)
Phys. Rev D82, 112002 (2010)
SM Expectation  4x10-6
SM Expectation
W. Altmannshofer et al., JHEP 04, 022 (2009)
G. Buchalla et al., PRD63, 014015 (2000)
K Result (Preliminary):
PRELIMINARY
B( B0  K 0   )  3.3103 (90% CL)
SM Expectation  2x10-7
J.L. Hewett, Phys. Rev. D53, 4964 (1996)
Momentum Transfer to
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Bruce Schumm
+-
System
(But New Physics effects coupling to
m2f could approach measured limit)
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B  
Form B candidates from photon pairs
after likelihood-based 0 rejection
arXiv:1010.2229; to appear
in Phys. Rev. D
B(B) = (1.7  1.1(stat.)  0.2(syst.)) x 10-7
(1.9 significance)
B(B) < 3.2 x 10-7 (90% CL)
SM Expectation (Bosch & Buchalla, JHEP 0208:054, 2002)
B (B   )  (3.1 16..64 )  108
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Radiative Penguins I: ACP in b  (s,d) 
• Reconstruct single high-energy photon
2.1 < E* < 2.8 GeV
• Reduce backgrounds by requiring
lepton on tagging side
• Charge of lepton tags flavor on signal
side
Inclusive Radiative Penguin
Reconstruction
Tagging
B Meson
High Energy
Photon
ACP 
( B  X )  ( B  X )

( B  X )  ( B  X )
PRELIMINARY
 0.057 0.063 (stat. syst.)
Standard model expectation:
(Lepton from
SL decay)
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X
ACP  106
Any signal would be an unambiguous
signature of new physics.
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Radiative Penguins II: b  d (“Xd”) and Vtd/Vts
Motivation and Interpretation
• (bs) leading indirect constraint on new physics (SUSY, extended
Higgs, extra dimension…)
• (bd)/(bs)  0.03  Precise measurements of (bd) even
more constraining?
Vts(d)
(d)
Vt(s,d)
(d)
(d)
Practicalities:
(d)
Vts(d)
• Rate depends on hadronic effects  Normalize to Vts by measuring
corresponding s-quark process
• Rate depends on poorly constrained CKM parameter Vtd  Play off
against B mixing, which also measures Vtd sensitively
 Compare effective values of |Vtd/Vts| from B mixing and radiative
penguins decays (different diagrams!); discrepancy implies new physics
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Radiative Penguins II: b  d (“Xd”) and Vtd/Vts
Initial approach:
Reconstruct B  (,)  and B  K* ;
|Vtd/Vts| from [B(,)]/[BK*]
More current (“Xd” Analysis) :
Reconstruct “semi-inclusively” via
sum of seven exclusive decay modes;
|Vtd/Vts| directly from [bs]/[bd]
Use two independent hadronic system
mass ranges
• 0.6 < MX < 1.0 (, “resonant” region)
• 1.0 < MX < 2.0
Together, comprise ~2/3 of total width
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B  Xd  Results
Result of fit to seven B Xd
modes in high mass region
1.0 < MX < 2.0 GeV/c2
First observation of b  d
transition above resonance
(,) region
Phys. Rev. D 82, 051101(R) (2010)
No evidence for new physics
in bd transition
Theory Error
Relative accuracy of bd
constraint approaching that
for bs transition
Has impact of this constraint
been fully examined?
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Summary
New limits on B  K and B  K
B(B  K+) < 1.3 x 10-5 approaching SM expectation of
B(B  K+)  4 x 10-6
B(B  ) < 3.2 x 10-7; consistent with expected
B(B) = ( 3.16.16.4 )  108
b  (s,d)  Penguins
No observed CP violation in b (s,d); -0.05 < ACP < 0.16
at 90% CL
First observations of bd in non-resonant region;
|Vtd/Vts| from b → d consistent with that from B mixing;
relative accuracy of constraint approaching that of bs.
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Backup
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Measured Regions for B  Xd(s) 
XS
K*
Region
# 0
UNMEASURED
MEASURED
# bodies
1.0 < Mhad < 2.0
0.6 < Mhad < 1.0
2.0 < Mhad
# bodies
UNMEASURED
X d
 and Xd
analyses
# 0
MEASURED
Xd analysis
only
Mhad (MXd)
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B  s and SUSY Parameter Space (cont’d)
… on some of our favorite scenarios …
Fate of “Snowmass” MSSM study points
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B  s and SUSY Parameter Space (cont’d)
… and just in general.
C.F. Berger, J.S. Gainer, J.L. Hewett, T.G. Rizzo,
“Supersymmetry Without Prejudice”, arXiv:0812.0980v1 [hep-ph]
Explore 107 points over 19dimensional parameter space of
CP-conserving MSSM
b  s most effective constraint
(72% of models surviving prior
constraints are eliminated;
better than direct searches for
SUSY partners)
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The BaBar Detector
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