# Presentation: 098713

## Sherlock

- Bruce Knuteson
- Berkeley

- _Dave Toback_
- Maryland

## Quasi-Model-Independent Search at DØ: Sherlock

- Assume nothing about the new physics except that is high mass
- High mass assumption  Quasi-Model Independent
- Systematically look at events by the final state signature
- Search for new physics by looking for excesses in multi-dimensional data distributions

## Overview of Sherlock

- Define final state signatures
- (Signature based search)
*A priori* prescription for defining variables and regions of space in those variables
- A systematic look for regions with an excess (more events than expected) with large ET
- Find most interesting region
- Compare with the expectations from hypothetical similar experiments using background expectations
- Take into account systematic errors and the  the large number of regions searched

## Labeling Final State Signatures

- Final State particles:
- e, , j, b, c, MET, W or Z
- Each event is uniquely identified:
- All events which contain the same number of each of these objects belong to the same final state
- Need standard object ID

## General rule for picking variables

- Looking for new high mass physics
- Mass-Energy Relationship
- Decay to known Standard Model particles
- light in comparison
- High energy long lived particles in final state
- High Mass  High ET
- Look at ET of the final state particles

## Sherlock Algorithm

- Look at various regions
- Find most interesting region (largest excess)
- Run _hypothetical similar experiments_ using background expectations
- Fraction of hypothetical similar experiments (from backgrounds alone) which have an excess more significant than the one observed

- Background expectation
- Example signal events

- ET of X

- ET of Y

## Using Sherlock on Run I Data

- Look in events with an electron and a muon for a excess which might indicate new physics
- Why e? (why not?)
- Lots of theory models
- Supersymmetry? Anomalous Top quarks?
- Backgrounds include good example of heavy particles to look for
- Top quarks, W bosons

## tt and WW production

- _P

- P

- _P

- P

- _e____ + 0 Jets_

- _e____ + 2 Jets_

-  High ET relative to other backgrounds

## Testing Sherlock

- Both WW and top quark pair production are good examples of high ET events which might show up with Sherlock
- Run Mock Experiments pretending we don’t know about WW andtt production
- 4 Samples:
- e + 0 Jets WW
- e + 1 Jet
- e + 2 Jetstt
- e + 3 Jets

## Mock data with no signal

- Fraction of hypothetical similar experiments (from backgrounds alone) which have an excess more significant than the one observed

- _Probability is _
- _flat as expected_

- e + 1 Jets

- e + 0 Jets

- e + 3 Jets

- e + 2 Jets

- Small P is interesting Smallest bin is <5%
- No indication of anything interesting

## Sherlock with WW andtt

- e + 1 Jets

- e + 0 Jets

- e + 3 Jets

- e + 2 Jets

- Pretend we don’t know about WW andtt
- Mock experiments with WW andtt as part of the sample
- Observe an excess in        0 Jets (WW production)                  2 Jets (tt production)               in the mock trials Remember: 		      Small P is interesting Smallest bin is <5%

## Combining Results

- All overflows in last bin

- Significance of excess in standard deviations

- Excesses corresponding
- to WW andtt found

- DØ Preliminary

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- Mock Experiments

- Bkg only

- Bkg +WW +tt

- Pick most significant excess
- Take into account that we looked in 4 datasets

## Sherlocktt

- Include WW as a background
- Expect an excess in 2 Jets only
- tt production

- e + 1 Jets

- e + 0 Jets

- e + 3 Jets

- e + 2 Jets

## Findingtt alone

- Findingtt alone

- All overflows in last bin

- Significance of excess in standard deviations

- Excess corresponding tott

- DØ Preliminary

- Use all backgrounds excepttt and look for excesses

**/**
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- Mock Experiments

- Bkg only

- Bkg +tt

## Final Sherlock Results

- We see no evidence for new physics at high PT in the eX data

- DØ Preliminary

- Use all backgrounds and look for excesses

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## Thoughts & Conclusions

- Sherlock is sensitive to finding new physics when it is there to be found
- Would have pointed out either WW ortt if we didn’t know about them
- Would find events like the ee+MET naturally
- Should  be sensitive to many SUSY signatures
- While it can’t be as sensitive as a dedicated search, it may be our only shot if we guess wrong about where to look in our data.
- A natural complement to the standard searches
- PRD with collaboration now. Released in June(?)