# Presentation: 253742

## Search for Rare b-Hadron Decays at CDF II

- Michael Milnik (University of Karlsruhe)
-  for the CDF Collaboration

- HEP 2007, Manchester

## Covered in This Talk

- Bs/d → 
- B →  h
- Bu →  K
- Bd →  K*
- Bs →  

- Results from CDF on B0,Bs→h+h-’ covered by M. Morello later in this session

- HEP 2007, Manchester

- 2007/07/21

## Search for Bs/d → 

- Motivation:
- In the SM, B→ heavily suppressed (need FCNC)
- 	expectation:
- Bd→ further Cabbibo-suppressed
- Expect to see nothing, if something seen  new physics

- Search for Bs/d → 

- A.J. Buras, Phys. Lett. B566, 115 (2003)

- HEP 2007, Manchester

- 2007/07/21

## Search Methodology

- Unbiased (blinded) selection optimisation using
- signal event sample: MC simulation
- background sample: data sidebands
- Normalize to well-known B → J/ K decay			 cancellation of many systematic effects
- Apply cuts on search mode and normalization mode
- Estimate Backgrounds
- Unblind

- HEP 2007, Manchester

- 2007/07/21

## Selection Procedure

- Form likelihood ratio from following discriminating variables:
- displacement of reconstructed B vertex (long B lifetime)
- isolation (expect B to be isolated)
- “pointing angle” between reconstructed B momentum and direction to primary vertex (should be small)
- Optimize on best limit with 90% C.L.

- HEP 2007, Manchester

- 2007/07/21

## Apply Selection

- Observation in agreement with background expectation
- Set limits

- HEP 2007, Manchester

- 2007/07/21

## Results

- World’s best limit

- HEP 2007, Manchester

- 2007/07/21

## Search for B→h

- Search for B→h

- Non-resonant decays B → h via box or penguin	 diagrams
- 	  new physics may be observable through interference with		SM amplitudes
- Already observed (BaBar, Belle):
- Bu →  K
- Bd →  K*
- Missing:
- Bs →  
- prediction: BR(Bs  )=1.6x10-6

- PRD 73, 092001 (2006)
- PRL 96, 251801 (2006)

- C.Q. Geng and C.C. Liu, J. Phys. G 29, 1103 (2003)

- HEP 2007, Manchester

- 2007/07/21

## Search Methodology

- Similar method than for Bs→
- Unbiased (blinded) selection optimisation using
- signal event sample: MC simulation
- background sample: data sidebands
- Normalize to analogous resonant B → J/ h decay
- Apply cuts on search mode and normalization mode
- Remove resonant  by cutting out J// (2S) mass ranges
- Unblind

- HEP 2007, Manchester

- 2007/07/21

## Optimize selection based on cuts on similar quantities as used for Bs→(decay length, isolation, pointing angle)

Optimize on best value for

- Optimize on best value for

- Selection Strategy

- HEP 2007, Manchester

- 2007/07/21

## Observations

|  | Bu→ K | Bd→ K* | Bs→ |
| --- | --- | --- | --- |
| # events signal range | 90 | 35 | 11 |
| # estim. BG events | 45.3 ± 5.8 | 16.5 ± 3.6 | 3.5 ± 1.5 |
| Significance | 4.5  | 2.9  | 2.4  |

- HEP 2007, Manchester

- 2007/07/21

## Results

- BR(B+→ K+) = [0.72 ± 0.15(stat.) ± 0.05(syst.)]x10-6
- BR(B0→ K*) = [0.82 ± 0.31(stat.) ± 0.10(syst.)]x10-6

- HEP 2007, Manchester

- 2007/07/21

## Summary & Outlook

- CDF set limits for Bs/d→
- currently probe the 10-8 level
- limits severely constrain new physics models
- growing dataset will allow deeper probing			in the future
- CDF investigating B → h modes
- results in agreement with those of b-factories
- most stringent limit on Bs→
- More data – better results: watch out!

- HEP 2007, Manchester

- 2007/07/21

## Backup

- HEP 2007, Manchester

- 2007/07/21

## Bs/d → Backgrounds

- Bs/d → Backgrounds

- Estimate backgrounds from:
-  sidebands (combinatoric)
-  branching fractions B→h+ h- and fake rates

- HEP 2007, Manchester

- 2007/07/21