# Presentation: 905486

- Bill Ashmanskas, U. Chicago,
- Rob Harr, Wayne State
- Recall that
**B(D0********) ******** 3********10****-13**** in SM,**
**but can be as large as 3.5********10****-6**** in some RPV SUSY models (squarks behave as leptoquarks).**
**Best limit (BEATRICE) is 4.1********10****-6**** @ 90% CL.**
**We think we can meet or surpass that with data in hand.  (How well depends on BG level.)**
****** ****proto-CDFnote (6273): ****http://hep.uchicago.edu/~ashmansk/scratch/d0mumu.ps**

**D****0**** ******** ******** update**

**Note is coming ...**

## Competition from the B factories?

- We can probably do better:
**BABAR reconstructed 158K D*-tagged D****0********K******** events in 58 fb****-1****, or 2.7 pb.**
**CDF reconstructs about 2 nb in this mode**
**So far, we log pb****-1**** faster than they log fb****-1****, and our rate had better be going up!**
****** ****ID is similar, too: BELLE quotes 80-85% efficiency and 1-2% fake rate**

## Analysis summary

- Use SVT D0 sample, recorded with SVT trigger, for normalization, then simply tag muons to look for signal
**kinematically ******** identical to D****0******
- acceptance effects cancel
**need relative ********/******** efficiency**
- CDF 6029 quotes 971%  stub efficiency after isFiducial() requirement
**We can check later using ********+SVT sample**
**Also important to check CMU good run status, J/******** yield by run, etc., to avoid throwing away the signal**
**Could there be a correlated inefficiency, e.g. two tracks too close together in CMU??**
- CDF 6114 finds chsqXPosition<9 (a.k.a. MOXFTM) to be >98% efficient over entire 2-10 GeV range
- CDF 6018 finds a 4.50.2%  reco inefficiency due to decays-in-flight and hadronic interactions
**We inflate the errors and take ********(********/******** to be 1.012********0.045**
**Using CMU only, ****isFiducial()**** acceptance is 59% per track, 38% per pair; CMX ******** ********1.5**

## Event selection

- Start with hbot0h on CAF1
**40M events, runs 138425-156116, ~70 pb****-1**
- defTracks; COTXFTSVT match
- pT2, numCTHitsAx25, numCTHitsSt25, numSIHitsPhi3, dSVT120um, d*d<0, q*q<0
**No use of offline impact parameters, except in computation of track momenta at intersection!**
- Use CTVMFT to calculate intersection, momenta (no 2 cut)
- 1.5 < m(< 2.05 GeV (use  hypothesis)
-  selects 8% of hbot0h
- Add bachelor pion
**no SVX cut, pT ******** 0.375 GeV, ********m < 0.17 GeV**
- Tighten mass window cuts at ntuple level

## Event yield

- Due to an embarrassing ntuple booboo, I don’t have the plot for the full sample, final cuts.
- With full lumi, after acceptance, expect 1700-2000  events.  For Nobs=0,1,2,3,4, no BG subt, limit is 2.3,3.9,5.3,6.7,8.0 x 1.14E-3/1850 = 1.4,2.4,3.3,4.1,4.9 E-6 @ 90% CL.

## Backgrounds & cut optimization

- Giovanni Punzi derives figure of merit S/(1.5+B)
**Makes sense: ~S for small B, ~S/********B for large B**
**Can use S ******** N******
**Need to estimate B = expected BG**
- Using this FOM, naively, using D* tag is not a winner.  But I think it still is a winner if there is a substantial uncertainty on BG estimate.
- From single-tagged DK, P()  1.25%, P(K)  2.0%.  But from double-tagged DKP(2tag)  1.6  P(tag)^2.  Need to understand this correlation.  (E.g. chamber noise?)
- Even more disconcerting, the tag rate for combinatorial BG tracks (measured from high-mass sideband) is ~6%, implying (I think) that there are real muons there, e.g. from heavy quark decay; here, too, the double-tag rate seems to be about 1.5 or so what the single-tag rate would predict.
- Unless we fix this, we expect about 2 BG events (3:1 :: combinatorial:resonant); would be 0.3 if tags factored & combinatorial BG were negligible

## What’s next?

- Immediate plans:
**Refine background estimates**
**Understand correlations in ******** tags**
**Understand (evidently real) muons in combinatorial BG**
**Look for further handles to reduce comb BG**
**Optimize cuts for best possible discovery potential**
**Check CMU good run list**
**Can we present a more complete analysis next week?  Currently scheduled to prebless on 2/20.**
- Future directions:
**Pull all the pieces together this week for blessing of initial search this winter**
**Let more data roll in, hopefully reach a few E-7**
**Rob wants to do**** ******
**Bill wants to do**** e******