# Presentation: 680076

- 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**

## 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**
- 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, 120dSVT1000um, 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 cuts at ntuple level
**0.144 < dM < 0.147**
**Lxy > 0**
**?? |d(SVT)-d(offline)|<200um**
**?? |d(D0)|<150um**
**?? 2.0 vs 2.5 sigma mass window**
**?? Add some kind of isolation cut?**

## D*: 0.144<dm<0.147

## Event yield

- See 117K D*-tagged D0->Kpi
- -> 44K after CMU fiducial cuts

## Event yield

- 2 kinds of BG:
**D0->pipi with double fake**
**combinatorial BG (real or fake muons)**

## K->mu, pi->mu BG

- Pi->mu fake rate is 1.25% (2.0% for K->mu)
- Thus, expect 1767*0.0125**2=0.3 events
- But don’t understand correlation -> 0.70.4

## Combinatorial BG

- With (loose) cuts, we see 7 sideband events in 1.9<m<2.05; scale by 2*25MeV/150MeV
- We think we already know how to get this down from 2.3 to 1.1 events
- This is added to 0.70.4 D0->pipi BG events

## 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**
- for optimization, we will use single-tagged (one and only one tag) D to avoid biasing BG estimate
**We have not yet done real cut optimization**
- From single-tagged DK, P()  1.25%, P(K)  2.0%.  But from double-tagged DKP(2tag)  3  P(tag)^2.  We still don’t understand this correlation.
**On the plus side, the combinatorial BG still exceeds the D******** BG (which is 0.7********0.4 events)**
- The tag rate for combinatorial BG tracks (measured from high-mass sideband) is ~6%, implying (I think) that there are real muons there; the double-tag rate is 1%, which is >> 6%**2
**We currently expect 2.3********0.9 comb. BG**
- Would be ~1.7 if we confirmed SVT impact parameter
- Would be ~1.4 if we reduced mass window to 2 sigma
- Would be ~1.1 if we requred |d(D)|<150um
**Each of these 3 cuts has ~ few % effect on signal**

## Treating BG properly

**Treating BG properly**

- Will use Cousins-Highland machinery for converting efficiency, syst(efficency), BG, syst(BG), Nobs into Nupper
- If we do no BG subtraction, then for Nobs=0,1,2,3,4 (and if no significant signal), limit is 2.3,3.9,5.3,6.7,8.0 x 1.43E-3/1850 = 1.8,3.1,4.2,5.3,6.3 E-6 @ 90% CL.

## What’s next?

- Still to do (!!):
**Check CMU good run list**
- do exactly as done in CDF 6288 (Bishai et al), but extend through full data-taking period
**Look for further handles to reduce comb BG**
- confirming SVT ip is a winner
**Understand correlations in ******** tags**
- tracks too close together in CMU??
**Understand (evidently real) muons in combinatorial BG**
- some kind of isolation cut?
**Optimize cuts for best possible discovery potential**
- Future directions:
**Let more data roll in, hopefully reach a few E-7**
**Rob wants to do**** ******
**Bill wants to do**** e******