cipanp richard kass 1 searches for new physics in b decays at babar outline of talk searches for: b...
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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
CIPANPRichard Kass 2
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
CIPANPRichard Kass 3
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
CIPANPRichard Kass 4
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
CIPANPRichard Kass 5
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
CIPANPRichard Kass 6
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
CIPANPRichard Kass 7
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
CIPANPRichard Kass 8
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
CIPANPRichard Kass 9
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”
CIPANPRichard Kass 10
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)
CIPANPRichard Kass 11
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
CIPANPRichard Kass 12
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*+)
CIPANPRichard Kass 13
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+)
CIPANPRichard Kass 14
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
CIPANPRichard Kass 15
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
CIPANPRichard Kass 16
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
CIPANPRichard Kass 17
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
CIPANPRichard Kass 18
Extra slides
CIPANPRichard Kass 19
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
CIPANPRichard Kass 20
B±h±τl Resultssubmitted to PRD arXiv:1204.2852v1
CIPANPRichard Kass 21
BD(*)τν YieldsarXiv:1205.5442
CIPANPRichard Kass 22
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
CIPANPRichard Kass 23
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
CIPANPRichard Kass 24
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
CIPANPRichard Kass 25
BaBar DIRC
BaBar K/BaBar K/IDID
D*+ → D0+
D0→ K+ -