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Search for FCNC Decays Bs(d) → μμ-

Motivation

Analysis Method

Results

Conclusion

Matthew Herndon, University of Wisconsin

For Doug Glenzinski, Hauke Held, Teruki Kamon,

Vyacheslav Krutelyov, Cheng-Ju Lin, Michael Weinberger CDF Paper Seminar

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Why Beyond Standard Model?Standard Model predictions validated to high precision, however

Billions of B and Charm events on tapeCan look for some very unusual processes

M. Herndon

Gravity not a part of the SM

What is the very high energy behaviour?

At the beginning of the universe?

Dark Matter?

Astronomical observations of indicate

that there is more matter than we see

Where is the Antimatter?

Why is the observed universe mostly matter?

How to look for new physics

Direct Searches - limited by energy reach of accelerator

Indirect searches:

Standard Model fails to answer many fundamental questions

CDF Paper Seminar 2007

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Bs(d) → μ+μ- Beyond the SMLook at processes that are suppressed in the SM

Excellent place to spot small contributions from non SM contributions

Bs(d) →μμ-

SM:

No tree level decay

CKM ,GIM and helicity

suppressed

BF(Bs →μμ-) = 3.5x10-9

New Physics:

Loop: MSSM: mSugra, Higgs Doublet

3 orders of magnitude enhancement

Rate tan6β/(MA)4

M. Herndon

Same particles/vertices occur in both B decay diagrams

and in dark matter scattering or annihilation diagrams

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CDF Paper Seminar 2007

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Bs → μμExperimental Challenge

M. Herndon

Primary problem is large background at hadron colliders

Analysis and trigger cuts must effectively reduce the large background around mBs

= 5.37GeV/c2 to find a possible handful of events

Key elements of the analysis are determining the efficiency and rejection

of the discriminating variables and estimating the background level

200M Events

CDF Paper Seminar 2007

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Data Sample

M. Herndon

Start the with di-muon trigger: 1.9fb-1

2 CMU muons or 1 CMU and 1CMX muon with pTμ > 5.0GeV/c

CMU: pT(μ) > ~1.5 GeV/c, |η| < ~0.6, CMX: pT(μ) > ~2.0 GeV/c, 0.6 < |η| < 1.0

Apply basic quality cuts

Track, vertex and muon quality cuts

Muon Likelihood and dE/dx selection (New Element)

High efficiency: 97%, Removes 35% combinatoric background (46K previously)

Reduces B hh to negligible levels (tenth of an event or less)

Loose preselection on analysis cuts

PT(μμ-) > 4.0 GeV/c, 3D Decay length significance > 2 …

In the mass region around the Bs: 4.669 < Mμμ < 5.969 GeV/c2

Blind region: 4σ(Mμμ), 5.169 < Mμμ < 5.469 GeV/c2

Sideband region 0.5 GeV/c2 on either side of the blinded region

200M Events

30K Events

CDF Paper Seminar 2007

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Bs(d) → μ+μ- Method

M. Herndon

Relative normalization search

Measure the rate of Bs(d) → μ+μ- decays

relative to B J/K+

Apply same sample selection criteria

Systematic uncertainties will cancel out in

the ratios of the normalization

Example: muon trigger efficiency same for

J/ or Bs s for a given pT

€

BF(Bs → μ +μ−) =(Ncand − Nbg )

α BsεBs

•α

B +εB +

NB +

•fu

f s

•

BR(B+ → J /ψK +) • BR(J /ψ → μ +μ−)

1.9 X 108 B+ events

CDF Paper Seminar 2007

Need to discriminate signal from background

Reduce background by a factor of > 1000

Signal characteristics

Final state fully reconstructed

Bs is long lived (cτ = 438 μm)

B fragmentation is hard: few additional tracks

Background contributions and characteristics

Sequential semi-leptonic decay: b → cμ-X → μ+μ-X

Double semileptonic decay: bb → μ+μ-X

Continuum μ+μ-

μ + fake, fake+fake

Partially reconstructed, lower pT, short lived,

has additional tracks

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Signal vs. Background

M. Herndon

+

-

L3D

primary vertex

di-muon vertex

P()L3D

L3D

primary vertex

di-muon vertex

+

-P()

L3D

-

Cut on mass, lifetime, pT , how well p points to the vertex and isolation

30K Events

CDF Paper Seminar 2007

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Discriminating Variables

M. Herndon

Mass m

2.5σwindow: σ = 24MeV/c2

λ=cτ/cτBs, λ

α : |φB – φvtx| in 3D

Isolation: pTB/( trk + pTB

)

pT and pT second muon

Combine all but m in NN(New Element)

Removes 25% of the background

Set limits in using 3 NN bins and 5 mass

bins (New Element)

Improves expected limit by 25%

Unbiased optimization

Based on simulated signal and data sidebands

7 primary discriminating variables

DSU 2007CDF Paper Seminar 2007

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ExpectationsNN Efficiencies and Background: Bs

M. Herndon

Expected Bs limit: 4.9x10-8 95% CL Previous CDF publication 2.4x10-7

NN NN

Bhh Background

Total Background

Expected SM Signal

0.995-1.0 44% 0.039 3.5 ± 0.2 0.3 ± 0.1

0.95-0.995 23% 0.020 18.0 ± 0.7 0.15 ± 0.05

0.8-0.95 12% 0.011 49.5 ± 0.9 0.08 ± 0.03

An extrapolation based on the previous publication using 364pb-1

indicated that we would have expected 8x10-8

We achieved a factor of 5 improvement: Progression in the limit with L

CDF Paper Seminar 2007

Previous Bs result: 2.010-7

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Bs(d) → μ+μ- Search Results

M. Herndon

BF(Bs +- ) < 5.8x10-8 at 95% CL

BF(Bd +- ) < 1.8x10-8 at 95% CL

NNTotal

BackgroundObserved Events

0.995-1.0 3.5 ± 0.2 3

0.95-0.995 18.0 ± 0.7 21

0.8-0.95 49.5 ± 0.9 44

1 event in most signal like bin and

one in the adjoining bin! The hint

of the first Bs(d) → μ+μ- signal?

What does it all mean?

CDF Paper Seminar 2007

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Bs → μ+μ-Physics Reach

Strongly limits specific SUSY models: SUSY SO(10) models

Allows for massive neutrino

Incorporates dark matter results

BF(Bs +- ) < 5.8x10-8 at 95% CL

Excluded at 95% CL

(CDF result only)

BF(Bs +- ) = 1.0x10-7

BF(Bs +- ) = 5x10-8

Dark matter constraints

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

L. Roszkowski et al. JHEP 0509 2005 029

A close shave for the

theorists

Typical example of SUSY Constraints

However, large amount of recent work

specifically on dark matter CDF Paper Seminar 2007

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Bs → μ+μ- and Dark MatterBs →μμ- correlated to dark matter searches

CMSSM supergravity model

Bs →μμ- and neutralino scattering cross sections are both a strong

functions of tanβ

In high tanβ(tanβ ~ 50), positive μ, CDM allowed

Current bounds on Bs →μμ- exclude parts of

the parameter space for direct dark matter detection

M. Herndon

More general scan in m0, m1/2 and A0, allowed region

S. Baek, D.G. Cerdeno Y.G. Kim, P. Ko, C. Munoz, JHEP 0506 017, 2005

CDF Paper Seminar 2007

R. Austri, R. Trotta, L. Roszkowski, hep-ph/0705.2012

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B Physics and Dark MatterPutting everything together

including most recent theory work

on b s and g-2

M. Herndon

Current experiments starting to probe interesting regions

Analysis shows a preference for the Focus Point

region

Higgsino component of Neutralino is

enhanced.

Enhances dominant Higgs exchange

scattering diagrams and Bs → μ+μ-

Interesting relative to SUSY Higgs searches at

Tevatron and LHC

However

Xenon 10 Preliminary

Excluded by new Bs →μμ-

tan=50

CDF Paper Seminar 2007

R. Austri, R. Trotta, L. Roszkowski, JHEP 0605 002, 2006

S. Baek, et.al.JHEP 0506 017, 2005

M. Herndon 14

Conclusions

Best Bs and Bd results: well ahead of D0 and the B factories

Limit excludes part of parameter space allowed by SO(10) models

Expanding sensitivity to interesting areas of MSSM parameter space

Results correlated with some of the other most interesting topics in

physics such as Higgs searches and dark matter!

B(s,d) →μ+μ- results

BF(Bs +- ) < 5.8x10-8 at 95% CL

BF(Bd +- ) < 1.8x10-8 at 95% CL

Worlds Best Limits!

CDF Paper Seminar 2007