# Presentation: 301574

## Mike Strauss

for the DØ Collaboration
The University of Oklahoma
The Oklahoma Center for High Energy Physics

- for the DØ Collaboration
- The University of Oklahoma
- The Oklahoma Center for High Energy Physics

**Rare Heavy Flavor Decays at D****Ø**

- XXXIII International Conference on High Energy Physics
- Moscow, Russia
- 26 July – 2 August, 2006

## Search for D+  + +– 
FCNC in Charm Sector
Search for Bs0  +– and Bs0  +–
FCNC in Bottom Sector

- FCNC in Charm Sector
- Search for* B**s*0  **+**–* *and *B**s*0  **+**–
- FCNC in Bottom Sector

**Outline**

## FCNC in the Charm Sector

- Experimental limits exist for *b**s* and *s**d*
- Some models predict violations from SM in up quark sector, but not down quark sector

- RPV in the up sector
*Burdman et.al. *
*hep-ph/0112234*
- Little Higgs Models
*Fajfer et.al. *
*hep-ph/0511048*

*c** * *u* **+**–

- SM

## c  u+– Analysis

- 1 fb–1 of data
- Find *D*s+  **+*** * **+**+**–
- (100% of *D*s+  **+**)
- BF(*D*s+**+**) = 0.036±0.009
- BF(****+**–) =
- 		  	(2.850±0.19)×10–4
- Search for *D*+  **+**+**–
- 			for *m*(**+**–) ≠ *m*(**)
- Add track to low mass dimuon candidate

**

**

## Selection and Optimization Criteria

- Isolation: *I**D = **p*(*D*)/*p*cone
*R* = (**2 + **2)1⁄2 < 1.0
- Transverse flight length significance: *S*D
- Collinearity angle: *D*
- Pion impact parameter significance: *S***
*M* = **2vtx + ****2 + *R***2
* ***** = 1/*p**T*(**)

## D+  +  ++–

- Loose
- cuts

- Resonance
- optimized
- cuts

- 0.96 < *m*(**+* ***–) < 1.06 GeV/*c*2

*n*(*D*+) = 26 ± 9     *n*(*D*s) = 65 ± 11

*D*+

*D*s

## Extracting the Resonant Branching Fraction

*f**c**D*: Fraction produced in fragmentation
*f**p*:     Prompt fraction
**:      Reconstruction efficiency

- SM: 1.77×10–6        CLEO-c (***ee*):

## Nonresonant D+  ++-

- 0.96 < *m*(**) < 1.06 GeV/*c*2

- 0.2 < *m*(**) < 0.96 GeV/*c*2
- 1.06 < *m*(**) < 1.76 GeV/*c*2

- BF(*D*+  **+**+**-) < 4.7×10–6 @ 90% C.L

## Bs0  +– 

- FCNC with zero cross section at tree level
- SM Branching Fraction:
- BF(*B**s*0  **+**–) = (3.42 ± 0.54) × 10–9
- BF(*B**d*0  **+**–) = (1.00 ± 0.14) × 10–10
- Non-SM processes can enhance BF(*B**s*0  **+**–)
- MSSM enhances BF up to 3 orders of magnitude
- 2HDM, minimal supergravity, minimal SO(10) GUT, all have BF enhancements

## Search for Bs0  +– 

- 300 pb-1 data analyzed (*PRL 94, 071802 (2005)*)
- Sensitivity for 0.7 fb-1 determined
- Blind analysis to avoid bias
- Side bands used for background determination
- Normalize to resonant decay *B**+* * J*/***K*+

*p**T*(**) >2.5 GeV/*c *
*|***(**)|< 2
-  **2vertex < 10
- CFT hits > 4
- SMT hits > 3
*p**T*(*B**s*) > 5 GeV/*c*
* ****L**xy** *< 0.15 mm

## Analysis and Optimization

- Optimization using MC signal and background from data sidebands using:
- Collinearity (Pointing) Angle
- Decay length significance
- Isolation

## Analysis and Normalization

* **R* = BF(*B**d*)/BF(*B**s*) is small due to |*V*td/*V*ts|2
** *****B*+/***B*s** **efficiency
** *****Bd* /***Bs*** **relative efficiency for *B**d* ****versus *B**s* ****
* **f**s***/***f**u*** **fragmentation ratio

- 0.3 fb–1

- additional
- 0.4 fb–1

## 300 pb-1 Limit (published 2005) 

- Observed 4, expect 4.3 ± 1.2

- BF(*B**s * ****×10–7 @ 95% C.L.

## DØ Sensitivity 0.7 fb-1

- For new dataset of 0.4 fb–1
- Expect 2.2 ± 0.7 background events
- Expect a sensitivity of about 3.0×10–7 @ 95% C.L.
- Combined 0.7 fb–1 sensitivity of 1.9×10–7 @ 95% C.L

- 0.4 fb–1

## Search for Bs0  +–

- 0.45 fb–1 of data
- Similar selection criteria to *B**s*0  **+**–
- 0.5 < *m*(**) < 4.4 GeV/*c*2 – excluding ±5** around *J*/**& **(2S)

* **** **K*+ *K*–
*p**T* (*K*)>0.7 GeV/c
- 1.008 < *m*(**) < 1.032 GeV/*c*2

## Analysis Method

- Blind analysis – Optimization using MC signal and background from data sidebands using:
- Pointing Angle < 0.1 rad
- Decay length significance > 10.3
- Isolation > 0.72

- Normalize to resonant decay *B**s* * J*/****

## Bs0  +– Results

- Expected background from sidebands: 1.6 ± 0.4 events
- Observe zero events in signal region

## Bs0  +– Results

- @ 95% C.L

- (10 times better than best limit)

- SM BF(*B**s*0  *** ***+**–) ~ 1.6 × 10–6  (30% uncertainty)
*	**	**	**	**	**(Geng and Liu, J. Phys G 29, 1103 (2003)*
- Accessible with about 4 fb–1 of data

- Accepted for PRD Rapid Communication

## Conclusions

- Searches for FCNC can give insight into physics beyond the Standard Model
- New DØ limits on *D*+  **+**+**–and *B**s*0  *** ***+**– are world’s best
- New limit on *B**s*0  **+**– should be coming soon