Summary of Recent Results on Rare Decays of B Mesons from BaBar for the BaBar Collaboration Lake Louise Winter Institute Chateau Lake Louise 20-26 February

Summary of Recent Results on Rare Decays of B Mesons from

BaBar

for the BaBar Collaboration

Lake Louise Winter Institute

Chateau Lake Louise

20-26 February 2011

Bruce A. SchummSanta Cruz Institute for Particle Physics

University of California, Santa Cruz

Searching for New Physics via Effective Flavor-Changing Neutral Currents

LLWI 2011: Rare Decays at BaBar 2Bruce SchummBaBar

Outline

Recent (past year) results are in three areas:

B K l+ l- with Missing EnergyB K (limit)B K + - (limit)

B (limit)

b (s,d) Penguins CP Violation in Penguin Decays (measurement) B→Xd and the Status of |Vtd/Vts| (measurement)


The BaBar Dataset

54 fb-1

426 fb-1

BaBar collected 468 M BB pairs between 2000-2007 and 54 fb-1 off-resonance data


Flavor-Changing Neutral Currents and New Physics

B+ K+ The Basic Story:

• FCNC process in SM require loops suppressed rates

• New physics can enter at same order

• Modification of BF (x10 or greater!)

• Large CP-violating effects

But always a battle against backgrounds…

For example:

Standard Model

Contribution from Extended Higgs

Sector


B K,K Approach

Mitigate backgrounds bytagging recoil B meson

TaggingB Meson

B K

Tag with reconstructedexclusive SL decay; 1%

B K

Tag with fully reconstructedHadronic decay; 0.2%

SignalB Meson

K Selection: Cut-Based

K Boosted Decision Tree

• Missing energy• Whole-event properties• Signal kinematics• Reconstruction quality

K Selection: Multivariate Algorithm (Boosted Decision

Tree)


B K,K Results

K Result:

Phys. Rev D82, 112002 (2010)

SM Expectation 4x10-6

W. Altmannshofer et al., JHEP 04, 022 (2009)G. Buchalla et al., PRD63, 014015 (2000)

K Result (Preliminary):

SM Expectation 2x10-7

J.L. Hewett, Phys. Rev. D53, 4964 (1996)

(But New Physics effects coupling to m2

f could approach measured limit)Momentum Transfer to +- System

Comparison of results, B+ K+

CL)%90(103.1)( 5 KBB

CL)%90(106.5)( 500 KBB

PRELIMINARYCL)%90(103.3)( 300 KBB

SM Expectation


B

SM Expectation (Bosch & Buchalla, JHEP 0208:054, 2002)

Form B candidates from photon pairs after likelihood-based 0 rejection

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)

arXiv:1010.2229; to appear in Phys. Rev. D

84.66.1 10)1.3()(

BB


Radiative Penguins I: ACP in b (s,d)

TaggingB Meson

610CPAX

High EnergyPhoton

Inclusive Radiative Penguin Reconstruction

• 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

Standard model expectation:

Any signal would be an unambiguous signature of new physics.

PRELIMINARY

(Lepton fromSL decay)

)()(

)()(

XBXB

XBXBACP

syst.) stat.(063.0057.0


Motivation and Interpretation

• (bs) leading indirect constraint on new physics (SUSY, extended Higgs, extra dimension…)

• (bd)/(bs) 0.03 Precise measurements of (bd) even more constraining?

Practicalities:

• 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

Vt(s,d)

Radiative Penguins II: b d (“Xd”) and Vtd/Vts

Vts(d)

Vts(d)

(d)(d)

(d)

(d)


Radiative Penguins II: b d (“Xd”) and Vtd/Vts

Initial approach:

Reconstruct B (,) and B K* ;|Vtd/Vts| from [B(,)]/[BK*]

More current (“Xd” Analysis) :

Reconstruct “semi-inclusively” via sum of seven exclusive decay modes;|Vtd/Vts| directly from [bs]/[bd]

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


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

No evidence for new physics in bd transition

Relative accuracy of bd constraint approaching that for bs transition

Has impact of this constraint been fully examined?

Phys. Rev. D 82, 051101(R) (2010)

Theory Error


Summary

New limits on B K and B KB(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) =

b (s,d) Penguins

No observed CP violation in b (s,d); -0.05 < ACP < 0.16 at 90% CL

First observations of bd in non-resonant region; |Vtd/Vts| from b→ d consistent with that from B mixing; relative accuracy of constraint approaching that of bs.

84.616. 10)1.3(


BackupBackup


Measured Regions for B Measured Regions for B X Xd(s)d(s)

K* Region

1.0 < Mhad < 2.0 2.0 < Mhad

XS

Xd

MEASURED

UNMEASURED

and Xd analyses

Xd analysis only

Mhad (MXd)

# 0

# bodies

# 0

# bodies

MEASURED

UNMEASURED

0.6 < Mhad < 1.0


B B s s and SUSY Parameter Space (cont’d) and SUSY Parameter Space (cont’d)

Fate of “Snowmass” MSSM study points

… on some of our favorite scenarios …


B B s s and SUSY Parameter Space (cont’d) and SUSY Parameter Space (cont’d)

C.F. Berger, J.S. Gainer, J.L. Hewett, T.G. Rizzo,“Supersymmetry Without Prejudice”, arXiv:0812.0980v1 [hep-ph]

Explore 107 points over 19-dimensional 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)

… and just in general.


The BaBar DetectorThe BaBar Detector

Documents

Summary of Recent Results on Rare Decays of B Mesons from BaBar for the BaBar Collaboration Lake Louise Winter Institute Chateau Lake Louise 20-26 February