# Presentation: 396653

## Update: inclusive b-jet cross sections(w/ Andreas Warburton & Greg Williams)

-  Analysis strategy
-  Data samples
-  Jet selection
-  Jet pT correction
-  Jet pT distributions
-  pT cuts and merging triggers
-  Di-(b)jet cross sections
-  MC reweighting
-  Monte Carlo
-  Data over MC
-  Unfolding
-  To do list
-  Summary

- Rob Snihur – McGill University
- QCD mtg., May 10, 2007

## Analysis strategy

**Use inclusive jet triggers**
**Complements SVT analyses**
**Extend existing analyses in a general way**
**Perform jet cross section analyses in parallel**
**b-taggers:**** SecVtx****, JetProb**** ****in association with**
**JetClu, MidPoint****, k****T**
**Cone = ****0.4, 0.7****, 1.0**
**>= ****1, 2****, 3 jets**
**Can also measure generic-jet cross sections**
**Use clones for Stntuple analysis modules**
**Motivation: debugging & easy cross-checks against blessed results**

## Data samples

**4 Inclusive jet triggers: jet20, 50, 70, 100**
**3 data running periods: ****d, h, i**
**12 Stntuple samples:**
**Gexo[0-3]****d****, gexo[0-3]****h****, gjt[1-4]b****i**
**Total integrated lumi = 1.00-1.02/fb **
**Breakdown for d,h,i: (****348, 525-542, 127**** pb****-1****)**
**Jet50 jobs for d & h failed: so only 127 pb****-1**
**Goodrun list v14: QCD with Si**
**MC: pythia dijet Gen6 with p****T****-hat >**
**18, 40, 60, 90 (120, 150 not yet included) GeV**
**Stntuple bt0s[q-t]b**

## Jet selection

**Generic jets with Midpoint 0.7**
**b-tagged jets with SecVtx**
**Using Midpoint 0.7**
**Using JetClu 0.4**
**QCD Good Run List v14 w/ Si**
**|z-vertex| < 60 cm**
**METSig < ****3.5, 5, 6, 7**
**|y| < 1.2**
**Uncorrected p****T**** > ****45, 70, 95, 130**** GeV**

## Jet pT correction

**An interim correction**** (same for all types of jets)**
**Apply a 4****th**** order polynomial (from Monica’s note)**

**Corrected jet p****T ****(Gev/c)**

**p****T ****of matched hadron jets**** ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**p****T:  ****uncorrected / corrected**** **

## Jet pT distributions

**No y or p****T**** cuts applied**
**MidPoint 0.7, SecVtx MP7, SecVtx JC4**
**Prescales accounted for by weighting each event by trigger table lookup**
**0i data only (for this slide)**

**MidPoint 0.7**

**SecVtx +MP7**

**SecVtx +JC4**

## pT cuts and merging triggers

**Select jets with**
**|y| < 1.2**
**Uncorrected p****T**** > ****45, 70, 95, 130**** GeV**
**Use these conservative p****T**** cuts for now, same for all algorithms**
**May be able to lower o****T**** cuts, on an algorithm-by-algorithm basis**
**Plot of N****events****/∫L = “cross section”**
**Rebinned: ****0,38,43,48,54,60,67,74,82,90,98,111,119,128,138,150,160,173,187,202,218,236,272,326,400,500,800**
**Each bin contains data from exactly one trigger**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**MidPoint 0.7**

**SecVtx +MP7**

**SecVtx +JC4**

## Di-(b)jet cross sections

**|y****2****| < 1.2**
**p****T****(2) > 20 GeV/c **
**N/∫L vs. leading jet p****T**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**MidPoint 0.7**

**SecVtx +MP7**

**SecVtx +JC4**

## MC reweighting 

**Follow R. Field (QCD mtg. feb21_2002)**
**Example: run 211315**** ****p****T**** -hat unweighted & weighted**
**The (q,r,s,t)=(18,40,70,90) GeV samples had 1815,1815,436,436 events.**
**Weighted cross sections appear x1000 too high**
**Suspect units problem**

** ****p****T****-hat (Gev/c)**

**p****T****-hat(Gev/c)**

** ****p****T****-hat (Gev/c)**

**Number of events**

**N/****∫****L**** ****(nb/ 5 Gev/c)**

**N/****∫****L**** ****(nb/5 Gev/c)**

**1 run**

**Full MC sample**

## Monte Carlo

**SecVtx:**
**Bump at ~190 GeV**
**Deficit at 350 GeV**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**N/****∫****L**** ****(nb/Gev/c)**

**MidPoint 0.7**

**SecVtx +MP7**

**SecVtx +JC4**

## Data over MC

**“****Cross section” ratio: ****data / MC**
**Both at CAL level**
**These ratios will be used to derive MC p****T**** spectrum reweighting**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**Data/MC**

**MidPoint 0.7**

**SecVtx +MP7**

**SecVtx +JC4**

**Data/MC**

**Data/MC**

## Unfolding

**Use MC to measure cross section at hadron-jet level and calorimeter-jet level**
**Ratio is the unfolding correction**
**Apply it bin-by-bin**
**Similarly, measure parton-jet cross section to derive hadronization correction (had/par), which will be applied to the theory**

**Corrected jet p****T ****(Gev/c)**

**Corrected jet p****T ****(Gev/c)**

**Hadron/calorimeter**

**MidPoint 0.7**

**MidPoint 0.7**

**Hadron/parton**

## To do list

**Reweighting**
**To match the data p****T**** spectrum**
**Derive jet corrections**
**GRL v16 **
**Check trigger efficiencies**
**Compare to blessed analyses**
**Theory (Andreas)**
**B fraction (Greg’s talk)**
**Tagging efficiency (Greg’s talk)**

## Summary

**Measuring N-jet and N-b-jet cross sections for 1+/fb**
**Will incorporate new data**
**Variety of jet & tagging algorithms in parallel**
**See Greg’s talk for b-fraction & tag-efficiency**

## Backups

## Trigger Efficiencies

- JetClu 0.7
- 99% @ 58 & 112 GeV
- We use 70 & 130 GeV

## Data vs. MC (backup)

- Ratio: MC / (0i data)
- LO MC sigma may be too low
- Need to reweight MC spectrum

## Unfolding (backup)

- Use MC to measure cross section at hadron-jet level and colorimeter-jet level
- Ratio is the unfolding correction
- Apply it bin-by-bin
- Still choppy!

## MC reweighting (backup)

## Sigma(b-jet) ratios

**0i**

**MC**

**MC/0d**

**MC/0i**

## B-jet cross section

- SecVtx tags w/ JetClu 0.4
- 0i data
- More choppy at low pT