# Presentation: 325715

## Update on Combinatorial Background for Partially Reconstructed Modes

- Amanda Deisher
- B Mixing and Lifetimes
- May 30, 2006

## Outline

- Mass Distributions
- Mass shape of WS in partially reconstructed mass regions
- Possible physics backgrounds in WS
- Lifetime Distributions
- RS and WS in upper sideband
- Mass dependence of RS
- Mass dependence of WS
- Conclusions

## Ingredients

- Data Sample:      *B**0* *D**- *[*K*+ *** **-**** **-*] *** *+** **
- 			       xbhd0h(0i)
*                              *Wrong Sign (WS)*:   D**- *[*K*+ *** **-**** **-*]*** **-*
- Metric for Agreement:
- Binned 2 test
- Unbinned Kolmogorov test
-  ***c* veto:  Remove if 2.26 <  *m*(c ) < 2.31 GeV/*c*2
*D** veto:  Remove if *m(K****) - m(K****)* < 0.18 GeV/*c*2
- Lifetime:

- The definition I’ve been using for this analysis

- Definition Jeff Miles has been using

## Mass Distributions

- R < 1.5
- PT > 1.2
- Lxy(B)/Lxy(B) > 11.
- Lxy(BD) > -0.0300

- |d0B| < 0.0110
- 2xy(B) < 15.0
- 2xy(D) < 15.0
- candPT > 5.5

- Analysis cuts only

- +c veto
- +D* veto

## Mass Shape of WS in PR region

- Does the WS distribution in the partially reconstructed region agree with the RS combinatorial background extrapolation?
-  Procedure:
- Fit exponential + flat background to RS upper sideband
- Extend curve to PR region & compare

- Results depend on sideband definition:
- Varied fit range            (multiple curves)
-         (5.6,6.38)  (5.8,6.38)
- Note: shape of combinatorial will be constrained with full mass fit (see CCKMP...)

**RS****WS**

## WS Single B Physics Background

- Look at *B**+* *D*+X  and* B**0* *D*+X   Monte Carlo

**RS:** reco’d as  ***D******+ ************ *****-**

**WS:** reco’d as  ***D******+ ************ *****+**

**25000**

**35**

- Physics background in WS **small** and **below** region of interest

## WS and RS Agreement in Upper Sideband

- 5.4 < *m *< 5.7 GeV/*c*2
- RS , WS

- ct (cm)

- ct (cm)

- ct (cm)

- 6.0 < *m *< 6.3 GeV/*c*2
- RS , WS

- 5.7 < *m *< 6.0 GeV/*c*2
- RS , WS

## WS and RS Agreement in Upper Sideband 

|  | 2            (%) | 2mPDG (%) | KS  (%) | KSmPDG (%) |
| --- | --- | --- | --- | --- |
| 5.4 < m < 5.7 GeV/c2 | 62.6 | 24.9 | 5.79 | 0.983 |
| 5.7< m < 6.0 GeV/c2 | 20.5 | 23.8 | 43.2 | 48.8 |
| 6.0 < m < 6.3 GeV/c2 | 22.1 | 52.0 | 19.3 | 12.9 |

| (5.4 , 5.5)  (5.6, 5.7) |  |  | 12.2 | 2.92 |
| --- | --- | --- | --- | --- |

- Mass structure in (5.5,5.6) region not understood.  Try looking at agreement without this contribution.

- WS and RS agree very well in the upper sideband, independent of *ct* definition

## Mass Dependence of RS ct 

- ct (cm)

- Normalized to unit area

## Mass Dependence of RS ct

|  | 2            (%) | 2mPDG (%) | KS  (%) | KSmPDG (%) |
| --- | --- | --- | --- | --- |
| ( 5.4 , 5.7 )( 5.7 , 6.0 ) | 0.132 | 7E-11 | 4E-4 | 3E-16 |
| ( 5.4 , 5.7 )( 6.0 , 6.3 ) | 5.9 | 6E-18 | 2E-3 | 1E-30 |
| ( 5.7 , 6.0 )( 6.0 , 6.3 ) | 89.7 | 30.8 | 14.1 | 8E-3 |

| (5.4 , 5.5)  (5.6, 5.7)( 5.7 , 6.0) |  |  | 6E-5 | 3E-14 |
| --- | --- | --- | --- | --- |
| (5.4 , 5.5)  (5.6, 5.7)( 6.0 , 6.3) |  |  | 1E-4 | 7E-27 |

- Removing region (5.5,5.6) with unexplained mass structure

- Using the visible mass  some mass dependence,   	          	significantly less than when using PDG mass

| (5.6,5.85)(5.85,6.1) |  |  | 9.1 | 6E-4 |
| --- | --- | --- | --- | --- |
| (5.6,5.85)(6.1,6.35) |  |  | 8.1 | 4E-10 |
| (5.85,6.1 )(6.1,6.35) |  |  | 77.4 | 4.1 |

- What if we just start above 5.6?

## Mass Dependence of WS ct

- ct (cm)

- Normalized to unit area

## Mass Dependence of WS ct

|  | 2            (%) | 2mPDG (%) | KS  (%) | KSmPDG (%) |
| --- | --- | --- | --- | --- |
| ( 5.4 , 5.7 )( 5.7 , 6.0 ) | 65.7 | 8E-2 | 32.5 | 5E-5 |
| ( 5.4 , 5.7 )( 6.0 , 6.3 ) | 14.7 | 2E-13 | 6E-2 | 3E-23 |
| ( 5.7 , 6.0 )( 6.0 , 6.3 ) | 18.2 | 0.3 | 2.89 | 2E-6 |

- Removing region (5.5,5.6) with unexplained mass structure

| (5.4 , 5.5)  (5.6, 5.7)( 5.7 , 6.0) |  |  | 1.6% | 1E-5 |
| --- | --- | --- | --- | --- |
| (5.4 , 5.5)  (5.6, 5.7)( 6.0 , 6.3) |  |  | 2E-4 | 3E-23 |

| (5.6 , 5.85)(5.85 , 6.1) |  |  | 4.1 | 6E-4 |
| --- | --- | --- | --- | --- |
| (5.6 , 5.85)(6.1 , 6.35) |  |  | 3E-3 | 2E-16 |
| (5.85, 6.1 )(6.1 , 6.35) |  |  | 7.2 | 8E-3 |

- What if we just start above 5.6?

- Hmm, the first and last mass bins don’t agree at all

## Mass Dependence of WS ct

| ( 4.8 , 5.1 )( 5.1 , 5.4 ) | 2E-6 | 0 | 5E-12 | 0 |
| --- | --- | --- | --- | --- |
| ( 4.8 , 5.1 )( 5.4 , 5.7 ) | 0 | 0 | 4E-20 | 0 |
| ( 4.8 , 5.1 )( 5.7 , 6.0 ) | 0 | 0 | 8E-20 | 0 |
| ( 4.8 , 5.1 )( 6.0 , 6.3 ) | 0 | 0 | 3E-26 | 0 |

|  | 2            (%) | 2mPDG (%) | KS  (%) | KSmPDG (%) |
| --- | --- | --- | --- | --- |
| ( 5.1 , 5.4 )( 5.4 , 5.7 ) | 0.3 | 9E-17 | 2E-4 | 3E-25 |
| ( 5.1 , 5.4 )( 5.7 , 6.0 ) | 2E-6 | 0 | 2E-8 | 0 |
| ( 5.1 , 5.4 )( 6.0 , 6.3 ) | 3E-10 | 0 | 5E-11 | 0 |

- Looking WS ct in the partially reconstructed region (4.8,5.1)

- Looking WS ct in the signal region (5.1,5.4)

- Definite mass dependence.  Still need to work on optimizing cuts in this region.

## Conclusions

- Full mass fit necessary to evaluate level of agreement between WS and current combinatorial background model
- Initial studies show little WS single B physics background in PR or signal region
- RS and WS ct distributions agree in the upper sideband and show same mass dependence
- Using visible mass in ct calculation greatly reduces mass dependence
- WS seems to track mass dependence of RS in the region where we can test it.  While we will use the wrong sign as a proxy, we need to look at reducing the systematics by optimizing S/B in the PR region.

## To-Do List

- Perform full mass fit with templates for PR and then compare the shape of the extrapolated RS combinatorial bkgd and the WS combinatorial bkgd in the PR region
- Evaluate systematic uncertainty on the B lifetime introduced by the uncertainties in the mass and lifetime dependence of the combinatorial bkgd
- Re-optimize cuts to minimize this uncertainty