# Presentation: 821025

## Top Mass in the all hadronic channel 

- Run I analysis strategy
- Mass Reconstruction in RunI
- Status with RunII MC and data
- Plans

- P. Azzi, T. Dorigo - Padova University & INFN
- Castro, A. Gresele – Bologna University & INFN
- I. Lazzizzera, S. Amerio – Trento University & INFN
- J. Konigsberg, G. Lungu, S. Sukhanov –  Florida University

- Mass Workshop June 23/24 2003

## Run I analysis strategy

- The all hadronic channel:
- BR is large (46%)  
- Events fully reconstructable  
- Large QCD background: S/B is very small  
- RunI Analysis had to cope with low statistics and a low double b-tagging efficiency
- Specific trigger was developed: S/B @trigger =1/500
- Two paths for improving S/B:
- A)Tight Kinematic + >=1 btag: S/B ~ 1/4
-  used for mass measurement
- B) Loose Kinematic + >=2 btag: S/B ~1/4

- Mass Workshop June 23/24 2003

## Run I Analysis Strategy (cont’d)

- Multijet Trigger Data Sample

- Large Jet Multiplicity
- Large Total Transverse Energy
- One B-tag jet present

- _Kinematic Cuts_
- Centrality
- Aplanarity

- _Two_ B-tagged jets

**Mass Reconstruction**
**M(t)=186±10±5.7 GeV/c****2**

**Cross Section**
******=7.6****+3.5****-2.7**** pb**

- Mass Workshop June 23/24 2003

## Run I Event Selection for Mass Reconstruction

- Jet counting definition:
- Et(raw)>15 GeV & |eta|<2
- Main background: QCD 22 processes with extra jets due to gluon radiation
- Kinematic very different from tt
- Use data before tag for the background shape
- Signal contamination negligible
- Cuts (corrected jet energies)
- 6N(jet) 8
- Et 200 GeV
- Et/ŝ0.75 (centrality)
- Aplanarity+0.0025 x 3Et 0.54

******E****T**

**<M(t)>**

- The Et cut has been lowered wrt to the value optimized for  the cross section selection b/c of its bias on the background shape

- 175

- Mass Workshop June 23/24 2003

## Mass Measurement in RunI

- Fully reconstructable final state
- Fit the six jets events to tt                                                 hypotesis (3 constraints):
- M(jjb)1 = M(jjj)2
- M(jj)1=M(W)
- M(jj)2=M(W)
- Combinations:
- No tag: 90
- 1 Tag: 30
- 2 Tag: 6
- Caveat: even in events with two tags we required only one of the b to be associated to the parton. In 30% of the cases the second tag is a charm from W decay.
- In Run I  we saw no significant improvement in top mass resolution from 1 to 2 tags

- One b

- Two b

- Mass Workshop June 23/24 2003

## Mass Measurement in Run I (cont’d)

**M(t)=186±10±5.7 GeV/c****2**

- Double tagged events
- (consistency check)

- Mass Workshop June 23/24 2003

## Run I Systematics

- Final weights in the combined mass result:
-  0.65 (l+jets), 0.19(dilepton), 0.15 (hadronic)

- Mass Workshop June 23/24 2003

## The RunII trigger and datasets 

- Dedicated trigger: TOP_MULTI_JET (after Run 143938)
- Requires: N(jet)>=4 with Et>=15 and Et>125 GeV
- Before Run 143938: L2 was only Et>130 GeV cut
- Total luminosity available now is: Lint~107 pb-1 (with good run list and SVX requirement)
- Available datasets (Andrea C.):
- Events before Jan shutdown processed with 4.9.1hpt1
- Full statistics up to May27th processed with 4.11.1
- Signal MC: use official tt MC of the Top Group (inclusive)

- Mass Workshop June 23/24 2003

## Work in progress and plans

- “Top Hadronic Group” meets informally every two weeks
- Basic philosophy for RunII analysis:
- Full characterization of the multi-jet datasets (Njet>=4) in terms of kinematical properties and heavy flavor content
- Currently we are validating data after the shutdown
- Use of new tools (ME MC such as Alpgen) to have an extra handle on the background determination
- In Run I no MC was available to properly describe high multiplicity events with heavy flavor
- Optimize analysis selection for a S/B~1/1 (or better) in the signal region
- Work in progress to evaluate a priori how well we can do in different luminosity scenarios

- Mass Workshop June 23/24 2003

## First look using Run II MC 

- Machinery for mass reconstruction is already in place.
- Work in progress to add top specific corrections
- Run II Herwig MC
- Jet corrected to Level7
- Compare the resolution for tt in the case of 0, 1 and 2 tags:
- In RunI width was 24 GeV(22 GeV) with 0tag (1 tag) with full AA corrections.

- Mass Workshop June 23/24 2003

## Comparison Run I vs Run II background shape 

- RUN II multi-jet data 0 tag after kinematical selection
- Top specific corrections missing!

- RUN I multi-jet data 0 tag after kinematical selection
- Full Run I jet corrections

- Entries=1153

- Mass Workshop June 23/24 2003

## Run II signal and background shape

- After a “Run I style” kinematical selection:
- 0 tag (veto) : S/B= 1/100 , negligible top contribution
- >= 1 tag: S/B=1/6
- >=2 tags: S/B=1/1

- Mass Workshop June 23/24 2003

## Future Plans

- Work in progress to reoptimize analysis to take full advantage of the CDF upgraded detector and increased statistics
- Need to fully characterize (again):
-  Correlations of kinematical and b-tagging requirement
- Issues on  mass reconstruction from the 2 tags requirement
- Background shape?
- improvements in resolution?
- Other ideas: bottom/charm difference? Interplay of different b-taggers?
- Plan is to have a preliminary results for this Winter

- Mass Workshop June 23/24 2003