CIPANP Richard Kass 1 Searches for new physics in B decays at BaBar Outline of Talk Searches for: B...

CIPANPRichard Kass 1

Searches for new physics in B decays at BaBar

Outline of TalkSearches for: B0invisible (γ) Charged Lepton Flavor ViolationMeasurement of BD(*)τν

Richard Kass for the BaBar Collaboration


Search for Binvisible ()

A. Dedes, H. Dreiner, and P. Richardson, Phys. Rev.D65, 015001 (2001)

Search for B decays with neutrinos or other non-interacting (e.g. SUSY)particles in the final state.

In SM B vv is highly suppressed by ~(mv/mb)2

In SM BF(B vvγ) is ~10-9

In SUSY models BF(B invisible) can be enhanced to ~(0.1-1)x10-6

due to neutrino + neutralino production

Previous Babar results with 88.5 fb-1 (B. Aubert et al., Phys.Rev.Lett.93:091802,2004 ): BF(B invisible)<22x10-5, BF(B vvγ) <4.7x10-5


Binvisible (γ) analysis details

Use BaBar data sample: 471x106 BB pairs taken at (4S)Divide the event into a signal B and a tag BUse B0D(*)-l+v as the tag B. l=electron/muon Semi-leptonic B tag has higher efficiency than fully reconstructed B tag B0 → D-lν D- → K+π-π-/KSπ-

B0 → D*-lν D*- → D0π-/D-π0 D0 → K-π+/K-π+π0/K-π+π+π-

Use cosine between B & D(*)l assuming only 1 v is missing common vertex for D(*)l systemSignal side of the event: no charged tracks, require photon with ECM>1.2 GeV for Binvisible γ Use Neural Net to discriminate signal from background (B’s, qq, etc)

B → Invisible Dtag : 9 variables D*tag : 6 variables B → Inv.+γ Dtag : 6 variables D*tag : 4 variables

BaBar Preliminary


Binvisible (γ) analysis details

Extract event yields using unbinned Max. Likelihood fitDiscriminating variable is the extra energy in the EM calorimeter, Eextra

For B → invisible+γ the high energy γ is removed from Eextra.Signal region has Eextra <1.2 GeVSignal efficiencies: B0invisible =17.8x10-4, B0invisible+γ= 16.0x10-4

Signal and background yields determined from ML fit

PreliminaryPreliminary

B0invisible B0invisible+γ


Binv (γ) systematic errors & results

Bayesian approach used to calculate 90% CL upper limits

Use “unphysical”B+inv (γ) asa control sample to check the analysis

00

9.0)(/)( dBBPdBBPUL

P(B) assumes flat priors, systematics modeled as gaussians

BR(B0invisible) <2.4x10-5

BR(B0invisible + γ) <1.7x10-5


Search for Charged Lepton Flavor Violation in B decay

Look for charged B decays B±h±τl with h=π/K and l=e/μLFV highly suppressed in SM ~ (mv/mW)2

Possible to greatly enhance the rate in extensions to SM 2nd & 3rd generations favored if coupling ~ mass

φs is a scalar

Sher & Yuan, Phys.Rev.D44:1461-1472,1991 consider φs and estimate: B±h±τe < 3x10-3

B±h±τ μ < 3x10-4 BaBar: B±K±τ μ < 7.7x10-5 @90% CL, PRL 99, 201801 (2007)

NP SM+v mixing

submitted to PRD arXiv:1204.2852v1


B±h±τl Analysis DetailsUse BaBar data sample: 472x106 BB pairs taken at Y(4S)Divide the event into a signal B and a tag BTag B reconstructed using hadronic decays B±D(*)0X-

X-=combination of s & KsSignal B reconstructed from B±h± l charged tracksh±= π± or K±, l=e or indirectly reconstruct the tau (use 1-prong taus: en): p=-ptag- ph- pl E=Ebeam– Eh- El m2

=E2- |p|2 |m-mPDG|<60 MeV/c2

Use BD(*)0lv, D0Kπ as a control sample for BF normalization NDlv /ND*lv /ND**lv determined from ML fit to data

BD(*)0 μv D0

D*0

D**0BaBar Preliminary


B±h±τl Analysis Details

Extract event yields using an unbinned Max. Likelihood fitUse poisson PDFs for the three tau channels (en)Assume uniform 3-body phase space for the signal decaysSet 90% UL CL using Feldman-Cousins procedure

Reject continuum (e+e-qq) background using a likelihood ratio

Variables include: costhrust neutral energy in calorimeter muon quality (primary, tau daughter)

BaBar Preliminary


B±h±τl ResultsLook at 8 channels, NO signals, Only ULs

Combine modes assuming B(B+h+τl )= B(B-h-τl )

5X better model independent bounds onNP scale in μτ flavorchanging operators.Λbd>11 TeV, Λbs>15 TeVD. Black, et al, PRD 66, 053002 (2002)

BaBar Preliminary BaBar Preliminary

more details in “extra slides”


BD(*)τν

Large mass of tau adds sensitivity to additional helicity amplitude. For BD(*)τν we have:

-

D(*)

H-,W-

We can compare our rate measurements with the SM predictions for:

003.0252.0)(

)()(017.0293.0

)(

)()(

*

**

DBB

DBBDR

DBB

DBBDR

These ratios are sensitive to physics beyond the SM

arXiv:1205.5442submitted to PRL

S. Fajfer, J. F. Kamenik, I. Nisandzic, arXiv:1203.2654, , J. F. Kamenik, F. Mescia, PRD 78 014003 (2008)


Analysis DetailsUse BaBar data sample: 471x106 BB pairs taken at Y(4S)Divide the event into a signal B and a tag BFully reconstructed tag B using hadronic decaysSignal B reconstructed from a lepton (e) & D(*)

No additional charged particles allowed in event Require q2 =(pB-pD(*))2 > 4 GeV2

Backgrounds are suppressed using Boosted Decision TreesExtract event yields using an unbinned 2-D Max. Likelihood fitPerform fit using lepton momentum in B rest frame (pl

*) & (missing mass)2

mm2=(pe+e--ptag-pD(*) -pl)2

Signal Samples: D0l, D*0l, D+l, D*+l with l= e or Fixed backgrounds: B0-B+ cross feed, combinatorial, continuumUse data control samples for corrections & validation: BD**lν, D(*)lν

control samples

BaBar Preliminary

BaBar Preliminary


BD*τν Yields

D*0

Eve

nts/

25 M

eV

Eve

nts/

100

MeV

m2miss (GeV2) pl* (GeV)

D*+

D*0

D*+Eve

nts/

100

MeV

Free yields

Fixed yield

BaBar Preliminary

D*0 D*+ D*

Nsig 693±62 245±27 888±63

Stat. sig. () 11.3 11.6 16.4

R(D*) 0.322±0.032 0.355±0.039 0.332±0.024

B(BD*τν ) % 1.71±0.17 1.74±0.19 1.76±0.13

statistical errors only

fit assumesR(D*0)=R(D*+)


BDτν Yields

Free yields

Fixed yield

D0

Eve

nts/

25 M

eV

Eve

nts/

100

MeV

M2miss (GeV2) pl* (GeV)

D+

D0

D+

BaBar Preliminary

D0 D+ D

Nsig 314±60 177±31 489±63

Stat. sig. () 5.5 6.1 8.4

R(D) 0.429±0.082 0.469±0.084 0.440±0.058

B(BDτν ) % 0.99±0.19 1.01±0.18 1.02±0.13

statistical errors only

fit assumesR(D0)=R(D+)


Systematic Errors & Results

R(D)=0.440±0.058±0.042R(D*)=0.332±0.024±0.018

SM Averagedoes not include this measurement

=correlation coeff.

Source R(D) % R(D*) %

D**lv bkg 5.8 3.7 0.62

MC statistics 5.0 2.5 -0.48

Cont. & BB bkg 4.9 2.7 -0.30

sig/norm 2.6 1.6 0.22

System. Uncert. 9.5 5.3 0.05

Statist. Uncert. 13.1 7.1 -0.45

Total Uncertainty 16.2 9.0 -0.27


Comparison with SM R(D) R(D*)BABAR 0.440 +/- 0.071 0.332 +/- 0.029SM 0.293 +/- 0.017 0.252 +/- 0.003 2.0 2.7

The combination of the two measurements (-0.27 correlation) yields 2=14.6 for 2 DOF and p-value = 6.9x10-4 Data differ from SM rate by 3.4


Charged Higgs?Compare our R(D) & R(D*) measurements with Type II 2HDM

red=theory ±1blue=exp ± 1

PDF shapes and efficiencies are recalculated vs tan/mH

Data match the 2HDM model for: R(D): tan/mH=0.44 ±0.02 & R(D*): tan/mH=0.75 ±0.04

Exclude Type II 2HDM at 99.8% CL

SM:tan/mH=0


Summary & Conclusions

*Search for B0invisible (γ): improved upper limits: BR(B0invisible) <2.4x10-5

BR(B0invisible + γ) <1.7x10-5

*Search for Charged Lepton Flavor Violation in B decay

*Measurement of BD(*)τν: Larger than SM predictions

BR(B+K+ τμ) <4.8x10-5

BR(B+K+ τe) <3.0x10-5

BR(B+π+ τμ) <7.2x10-5

BR(B+π+ τe) <7.5x10-5

new

improved

R(D) R(D*)BABAR 0.440 +/- 0.071 0.332 +/- 0.029SM 0.293 +/- 0.017 0.252 +/- 0.003 2.0 2.7

Exclude Type II 2HDM at 99.8% CL

submitted to PRLarXiv:1205.5442

submitted to PRDarXiv:1204.2852v1


Extra slides


B±h±τl Analysis DetailsUse BaBar data sample: 472x106 BB pairs taken at Y(4S)Divide the event into a signal B and a tag BThe tag B is fully reconstructed using hadronic decays B±D(*)0X-

with X-=n1π, n2K, n3Ks, n4π0, n1+n2 ≤ 5, n3 ≤2, n4 ≤2The signal B is reconstructed from B±h± l charged tracks h= π or K l=e or indirectly reconstruct the tau (use 1-prong taus: en): p=-ptag- ph- pl E=Ebeam– Eh- El m2

=E2- |p|2 |m-mPDG|<60 MeV/c2

Use BD(*)0lv, D0Kπ as a control sample for BF normalization NDlv /ND*lv /ND**lv determined from ML fit to data

0SBB

NBN lhlhDl

tag

lhtag

DlDl

Dllhlhlh

BD(*)0 μv D0

D*0

D**0≈1

BaBar Preliminary


B±h±τl Resultssubmitted to PRD arXiv:1204.2852v1


BD(*)τν YieldsarXiv:1205.5442


PEP-II at SLAC asymmetric e+e− collider: 9 GeV (e-)/3.1 GeV (e+)

PEP-II Peak Luminosity 1.2 x 1034 cm-2s-1

BaBar recorded 429 fb-1 at Y(4S)

asymmetric e+e− collider: 9 GeV (e-)/3.1 GeV (e+)

PEP-II Peak Luminosity 1.2 x 1034 cm-2s-1

BaBar recorded 429 fb-1 at Y(4S)4.7 x 108 (4S)→BB events


1.5 T Solenoid Electromagnetic Calorimeter

(EMC)Detector of Internally

Recflected Cherenkov

Light (DIRC)

Instrumented Flux Return

(IFR)

Silicon Vertex Tracker (SVT)

Drift Chamber (DCH)e- (9 GeV)

e+ (3.1 GeV)

BaBar BaBar DetectorDetector

SVT, DCH: charged particle tracking: vertex & mom. resolution, K0

s/Λ

EMC: electromagnetic calorimeter: /e/π0/η

DIRC, IFR, DCH: charged particle ID: π/μ/K/p

Highly efficient trigger for B mesons


Threshold kinematics: we know the initial energy (E*beam) of the Y(4S) system Therefore we know the energy & magnitude of momentum of each B meson

Background Background

(spherical)

(jet-structure)

Signal Signal

Analysis Technique

Also, use neural networks + unbinned maximum likelihood fits

2*2*BbeamES pEm **

beamB EEE Event topology


BaBar DIRC

BaBar K/BaBar K/IDID

D*+ → D0+

D0→ K+ -

CIPANP Richard Kass 1 Searches for new physics in B decays at BaBar Outline of Talk Searches for: B...

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