# Presentation: 636453

## Search for Bs+- and Bd+- 

**Decays at CDF**
- Cheng-Ju S. Lin
- (Fermilab)
-                                                 The 13th International Conference on
-                                                  Supersymmetry  and Unification of
-                                                    Fundamental Interactions
-                                            IPPP Durham
-                                            18 July 2005

## Introduction

-   In the Standard Model, the FCNC decay of B +- is heavily
-    suppressed

-   SM prediction is below the sensitivity of current experiments
-    (CDF+D0):  SM   Expect to see 0 events at the Tevatron

- (Buchalla & Buras, Misiak & Urban)

-   Bd is further suppressed by CKM coupling (vtd/vts)2

- SM prediction 

**Any signal would indicate new physics!!**

- Cheng-Ju Lin  (Fermilab)     SUSY05

## BEYOND STANDARD MODEL

**BEYOND STANDARD MODEL**

-   In many SUSY models, the BR could be enhanced by many
-    orders of magnitude:

-   For examples:
-        - MSSM:  Br(B) is proportional
-          to tan6BR could be as large as
-          ~100 times the SM prediction
-       - Tree level diagram is allowed in
-          R-parity violating (RPV) SUSY
-          models.  Possible to observe decay
-          even for low value of tan

**  **In context of mSUGRA, Br(B) search complements
-    direct SUSY searches:  (A. Dedes et al, hep-ph/0207026)
-       Low tan()  observation of trilepton events
-       Large tan()  observation of Br(B)

## PROBE OF NEW PHYSICS

-    New physics may enhance Bs and
-      Bd differently
-    Minimal-flavor-violation (MFV)
-      assumption in SUSY yields SM
-      relations between Bs and Bd
-  decays
-    Can observe both Bs and Bd: unique to
-      Tevatron
-   CDF has the mass resolution to
-     distinguish two decays, M~23MeV :
-     unique to CDF
-   Either observation or null search, results will provide important
-    clues about possible scenarios of new physics beyond SM

- M(Bs)-M(Bd)~90MeV

## TEVATRON

**Main Injector**

**Tevatron**

**DØ**

**CDF**

-   Tevatron is the highest energy collider in the world
- 	              Ecm(pp) = 1.96 TeV

-   RunII physics run began in Mar 2001 (>1 fb-1 delivered so far)
-    Expect 8fb-1 (design spec)  by 2009.

-   B production cross-sec
-    is ~30b at Tevatron
-    (1nb at PEPII)
-  All B species are produced
-    (B+ : Bd : Bs : b,)

## CDF II Detector

- Central Drift Chamber
- (COT)

- Silicon Vertex Detector
-   (L00, SVXII, ISL)

**Central Muon Chambers: ****CMU****, CMP**
**(|********| < 0.6)**

**Central Muon Extension: CMX**
**(0.6< |********| < 1.0)**

- Important components relevant
- to the analysis highlighted:

- Superconducting
- Solenoid (1.4T)

## Data Sample

-   Using 364pb-1 of data (Feb 02 – Aug 04) from di-muon triggers:
- 	-  CMU(P) + CMU   (central-central)
- 	-  CMU(P) + CMX   (central-extended)
-   Central-central and central-extended channels treated independently
-     in this analysis (background and efficiencies are different)

- Search region

**Rare B di-muon triggers**
- requires additional cuts to
- reduce background relative
- to inclusive **J/******** di-muon**
- trigger

- Cheng-Ju Lin  (Fermilab)  SUSY05

## Ingredients of the Analysis

- Key elements in the analysis:
-     -  Construct discriminant to select Bs signal and suppress bkg
-     -  understanding the background
-     -  accurately measure the acceptance and efficiency ratios
- Analysis optimization:
-      Figure of merit  expected 90% C.L. upper limit
-      Performed unbiased optimization

- Overall picture:
-     -  Reconstructing di-muon events in the B mass window
-     -  Measure the branching ratio or set a limit
-         Normalized to BJ/ K decays

- Cheng-Ju Lin  (Fermilab)  SUSY05

## Reconstruct “normalization mode”

- Selection Requires:
-  pT(B)>4 GeV && |y(B)|<1
-  pT(K+)>1GeV
-  good vertex fit quality
-   > 2
-    = proper decay length
-  (B+) = ~502m]

- B+K+ in rare B trigger Sample:
**  ****N(CMU/P-CMU) = 1785****±****60**
**N(CMU/P-CMX) = 696****±****39**

- Count the # of B++-K+ candidates

- CMU-CMU

## For Bs+-:

**Pre-selection requires:**
-  pT(B)>4 GeV && |y(B)|<1
-   > 2
-  good vertex fit quality

- Bs Search Sample:
- N(CMU-CMU) = 22459
- N(CMU-CMX) = 14305
- (completely Bgd dominated)

**“****Baseline” cuts are loose cuts to**
**reject events that are clearly background **

**B****s**** Sample Selection**** “****baseline cuts”**

- CMU-CMU

**Background shapes are linear**
**for both channels**

- [ (Bs) = ~502mm]

- Cheng-Ju Lin  (Fermilab)  SUSY05

- Invariant +- mass, Mvtxwithin +/- 60MeV (2.5)
- Proper decay-length ():
- Isolation (Iso):
-         (fraction of pT from B within R=(2+2)1/2 cone of 1)
- “pointing ()”:
-                (3D opening angle between Bs momentum and decay axis)

- We have explored various discriminating variables for selecting
- B events and suppress bkg.  The chosen ones are:

**Enhance Bs,d************and Suppress Background**

- Cheng-Ju Lin  (Fermilab)  SUSY05

## Discriminating Variables (Sig vs BKG)

- To further reduce Bgd,
-       we apply the additional cuts:
- <0.70 rad
- &&
- Iso > 0.50
- eff(signal) ~ 92%

- This leaves in  data:
- N(CMU-CMU) = 6242
- N(CMU-CMX) = 4908

**Discriminating Variables (Sig vs BKG)**

- ~x3 down in bkg
-   but still...

- Cheng-Ju Lin  (Fermilab)  SUSY05

##   We use a likelihood ratio method:

- Ps/b is the probability for a given sig/bkg to have a value
- of *x*, where *i* runs over all discriminating variables.

-   The chosen variables are:
-  - isolation (iso)
-  - 3D pointing (),
-        - proper decay length probability [P()=exp(-/Bs)]
-   PDF for the individual likelihood is reconstructed from the
-    data sideband for background and Pythia MC for signal

**Likelihood Ratio Discriminant**

- Cheng-Ju Lin  (Fermilab)  SUSY05

## Likelihood PDFs and LH Ratio

**Likelihood PDFs and LH Ratio**

- Input PDFs for Likelihood Ratio

- Likelihood Ratio Discriminant

**(CMU/P-CMU channel)**

**(Isolation)**

**Prob(********)**

**(Pointing Angle)**

- Cheng-Ju Lin  (Fermilab)  SUSY05

## Background Estimate

**  ****Extrapolate the number of events in the sidebands to the signal region **
**    ****and scale by the expected rejection of the likelihood ratio cut**
**  ****Use toy-MC to estimate bkg rejection of likelihood ratio cut**
**   ****based on input distributions from data sidebands**

- 1.)  OS- :  opposite-charge dimuon
-                  < 0
- 2.)  SS+ :  same-charge dimuon
-                   > 0
- 3.)  SS-  :  same-charge dimuon
-                   < 0
- 4.)  FM  : fake muon sample
-                 (at least one leg failed
-                   muon stub chi2 cut)

**Control sample for bkg**
**estimate cross-check:**

- Note: Using a wide ±100MeV window
-           around B mass for bkg cross-check

## Compute Acceptance and Efficiencies

-   Most efficiencies are determined directly from data using inclusive
-    J/events.  The rest are taken from Pythia MC.
-    (B+/Bs) = 0.297 +/- 0.008  (CMU-CMU)
-                      = 0.191 +/- 0.006  (CMU-CMX)
-    LH(Bs): ranges from 70% for LH>0.9 to
-                                          40% for LH>0.99
-   trig(B+/Bs) = 0.9997 +/- 0.0016 (CMU-CMU)
-                        = 0.9986 +/- 0.0014 (CMU-CMX)

-   reco-(B+/Bs) = 1.00 +/- 0.03 (CMU-CMU/X)
-   vtx(B+/Bs) = 0.986 +/- 0.013 (CMU-CMU/X)
-   reco-K(B+) = 0.938 +/- 0.016 (CMU-CMU/X)

- Red = From MC
- Green = From Data
- Blue = combination of MC
-             and Data

*f*u/*f*s=3.83±0.57
-           (HFAG 2004)

## Analysis Optimization

- We used the set of requirements which yielded the minimum
*a priori* expected BR Limit:

**Analysis Optimization**

-  For optimization, we scan over a range of LH values
-  Assume 1 fb-1 of data
**   ********  ****Optimal cuts:  LH>0.99**

##  Looking at Results

- For optimized cuts of  LH >0.99 and pT(B) > 4GeV
- and a  60 MeV  window around world avg B mass

- CMU-CMU Channel

- CMU-CMX Channel

- We observed 0 event in the signal region!

- Cheng-Ju Lin  (Fermilab)  SUSY05

## Bs Summary:

- CMU-CMU:
- 	Single event sensitivity = (1.0±0.2) ×10-7
- 	Expected # bkg (364pb-1) = 0.81 ± 0.12
- CMU-CMX:
- 	Single event sensitivity = (1.6±0.3) ×10-7
- 	Expected # bkg (336pb-1) = 0.66 ± 0.13
- We observed 0 event which yields a combined limit of:
-      **Br(Bs************) <**** ****1.5×10****-7**** @ 90% CL ; 2.0×10****-7**** @ 95% CL**
**Bd******** Summary:**
- We also observed 0 event which yields a combined limit of:
-      **Br(Bd************) < 3.8×10****-8**** @ 90% CL ; 4.9×10****-8**** @ 95% CL**

**Both B****s**** and B****d**** results are a x2 better than best published results!**
-    D0 PRL 94 (2005) 042001   (240pb-1) BaBar PRL 94 (2005) 221803 (111fb-1)

**B************ Limits**

- Cheng-Ju Lin  (Fermilab)  SUSY05

## mSUGRA  M0 vs M1/2

-   We are beginning to carve
-     into mSUGRA space
-   For mh~115GeV implies
-    10-8<Br(Bs)<3×10-7

- Solid red = excluded by theory or experiment
- Dashed red line = light Higgs mass (mh)
- Dashed green line = (a)susy  (in units of 10-10)
- Black line = Br(Bs)

- M0 [GeV]

- Excluded

- Excluded

## Excluded by this

-   We are beginning to carve
-     into mSUGRA space
-   For mh~115GeV implies
-    10-8<Br(Bs)<3×10-7

- Solid red = excluded by theory or experiment
- Dashed red line = light Higgs mass (mh)
- Dashed green line = (a)susy  (in units of 10-10)
- Black line = Br(Bs)

- M0 [GeV]

- Excluded

- Excluded

- new result

## SO(10) Unification Model

**JHEP 0304 (2003) 037**

**SO(10) Unification Model**

-  tan()~50 constrained by
-   unification of Yukawa coupling
-   White region is not excluded
-  Unification valid for small M1/2
-   (~500GeV)

- Red regions are excluded by either theory or experiments
- Green region is the WMAP preferred region
- Blue dashed line is the Br(Bs) contour
- Light blue region excluded by old Bs analysis

- h2>0.13

- m+<104GeV

- mh<111GeV

## SO(10) Unification Model

-   New Br(Bs limit strongly
-    disfavors this solution for
-    mA= 500 GeV

- Red regions are excluded by either theory or experiments
- Green region is the WMAP preferred region
- Blue dashed line is the Br(Bs) contour
- Light blue region excluded by old Bs analysis

- h2>0.13

- m+<104GeV

- mh<111GeV

- Excluded by this
- new result

**R. Dermisek *****et al*****.,  **
**JHEP 0304 (2003) 037**

## Summary

-   Bs is a powerful probe of new physics.  Could potentially
-    provide the first hint of SUSY at the Tevatron
-   Using 364pb-1 of data, CDF has obtained world best limits on
-    Bs and Bd  channels:
-       CDF:   Br(Bs) < 1.5×10-7  (2.0×10-7)   @ 90%  (95%) CL
-                   Br(Bd) < 3.8×10-8  (4.9×10-8)  @ 90% (95%) CL
-   TEVNPWG is combining CDF and D0 limits.  Expect ~20%
-     improvements over CDF limits alone
**      **
-   The limits are now starting to constrain interesting regions
-     of SUSY parameter space
-   We have covered an order of magnitude since Run I.  Will
-     cover at least another order of magnitude before the end of RunII

- Cheng-Ju Lin  (Fermilab)  SUSY05

## BACKUP SLIDES

## Correlations Between Variables

**Correlations Between Variables**

- Correlations between
- discriminating variables
- are negligible:
-    straighforward to construct
-        likelihood discriminant
-        (see next slide)

##  Checking MC Modeling of Signal LH 

- For CMU-CMU:
-  MC reproduces Data
-    efficiency vs LHood cut
-    to 10% or better
-  Assign 10% (relative)
-   systematic
-   CMU-CMX MC vs Data
-    agreement is better

- Compare B+ Data and MC

##  Checking MC Modeling of Signal LH 

-  MC reproduces Data
-   efficiency vs LHood cut
-   to 5% or better
-  Assign 5% (relative)
-   systematic for
-   CMU-CMX

-  **Checking MC Modeling of Signal LH **

##  MC modeling checked by comparing LH(B+)

** **determined from Bs MC
-  MC modeling checked by comparing LH(B+)
-   between MC and sideband subtracted Data

- (stat uncertainties only)

## Estimate LH Bkg Rejection (RLH)

- to estimate RLH based on input distributions from data SB

**Estimate LH Bkg Rejection (R****LH****)**

- KS-Prob(CMU)=11%
- KS-Prob(CMX)=5%

- Likelihood Ratio Data vs Toy MC

-                             RLH
-    Cut             CMU-CMU          CMU-CMX
- LH>0.85  0.0245+/-0.0005  0.0226+/-0.0005
- LH>0.92  0.0130+/-0.0004  0.0120+/-0.0003
- LH>0.99  0.0014+/-0.0001  0.0015+/-0.0001

- Likelihood Ratio Rejection  from
-                   Toy MC

- (Errors are stat only)

- LH strongly suppresses bkg

## RPV SUSY EXCLUSION

- B. Dutta et al, PLB 538 (2002) 121

-   Possible to exclude phase space
-    even for small tan()
-   Exclusion strongly depends on the
-    coupling.

- Excluded

## B Sensitivity To Heavy Higgs

**B************ Sensitivity To Heavy Higgs**

- MFV MSSM  (tan=50)
- (A. Dedes et al, hep-ph/0407285)

- (Excluded by Bs)

-   Br(Bs) is sensitive
-    to the mass of heavy Higgs
-   If the branching ratio is
-    measured  sets an upper
-    limit on the mass of the
-    heavy Higgs
-   mA mass limit is where
-    BR crosses the green curve
-    (same argument hold of
-     any tan≤ 50)
-   The mass limit is fairly
-     model independent

## Bs Limit Projection

-   Extrapolate based on the
-    current analysis which was
-    optimized for 1/fb
-   Assume background and
-    single-event-sensitivity
-    scale linearly with luminosity
-   Will need to re-optimize the
-    analysis for > 3/fb