# Presentation: 537674

## First measurement of the inclusive jet cross section in p+p collisions at ECM=200 GeV

- M.L. Miller (MIT)

- _Motivations:_
- Baseline for inclusive jet *A**LL*
- Constraining large-x pdf’s
- _Outline:_
- What do we mean by “jet”?
- Presentation of work in progress
- List of short- and long-term tasks towards final results

## What do we mean by “jet”?

- parton

- particle

- detector

## What do we mean by “jet”?

- parton

- particle

- detector

**Data**

- *(hep-ex/0005012)

- _midpoint-cone algorithm_*
- Search over “all” possible seeds for stable groupings
- Check midpoints between jet-jet pairs for stable groupings
- Split/merge jets based on Eoverlap
- Add track/tower 4-momenta

## What do we mean by “jet”?

- parton

- particle

- detector

- _midpoint-cone algorithm_*
- Search over “all” possible seeds for stable groupings
- Check midpoints between jet-jet pairs for stable groupings
- Split/merge jets based on Eoverlap
- Add track/tower 4-momenta

**Data**

**Simulation**

**GEANT**

- “geant” jets

- “pythia” jets

- _Correction philosophy_
- Use Pythia+GEANT to quantify detector response
- Estimate corrections to go from  “*detector*”  to the “*particle*” level

- pythia

- *(hep-ex/0005012)

## 2004 p+p data set

- |vertex-z|<60 cm
- rcone=0.4, fmerge=0.5
- 0.2< *η**jet* <0.8
- ratio<0.9
- (and *E**T-trig*>3.5 GeV/c for HT)

- _High Tower Trigger_
- BBC coincidence + one tower above threshold ***(not the best jet trigger!)***
*ε**Trig*(η=0.0)=1:     *E**T-tower*= 2.5 GeV
*ε**Trig*(η=0.8)=1:     *E**T-tower*= 3.3 GeV

- _TPC_
- 0<φ<2π
- 1< η<1
- _BEMC_
- 0<φ<2π
- 0< η<1
*in situ* MIP+e calibration

- 2004 *p+p* data set

- _2004 __*p+p*__ run_
- Sampled luminosity: ~0.16 pb-1
- 1.4 M High tower (HT) events
- 0.8 M highly pre-scaled minimum bias (MB) events
-  ~220k *p**T*>5 GeV jets in HT sample before cuts
- Commissioned 1x1 jet patch trigger– main jet trigger in 2005+

## 2004 p+p run
Sampled luminosity: ~0.16 pb-1
1.4 M High tower (HT) events
0.8 M highly pre-scaled minimum bias (MB) events
 ~220k pT>5 GeV jets in HT sample before cuts
Commissioned 1x1 jet patch trigger– main jet trigger in 2005+

- _2004 __*p+p*__ run_
- Sampled luminosity: ~0.16 pb-1
- 1.4 M High tower (HT) events
- 0.8 M highly pre-scaled minimum bias (MB) events
-  ~220k *p**T*>5 GeV jets in HT sample before cuts
- Commissioned 1x1 jet patch trigger– main jet trigger in 2005+

*p**T* (track/tower) > 0.2 GeV
- |vertex-z|<60 cm
- rcone=0.4, fmerge=0.5
- 0.2< *η**jet* <0.8
- ratio<0.9
- (and *E**T-trig*>3.5 GeV/c for HT)

- _High Tower Trigger_
- BBC coincidence + one tower above threshold ***(not the best jet trigger!)***
*ε**Trig*(η=0.0)=1:     *E**T-tower*= 2.5 GeV
*ε**Trig*(η=0.8)=1:     *E**T-tower*= 3.3 GeV

- 2004 *p+p* data set

- _TPC_
- 0<φ<2π
- 1< η<1
- _BEMC_
- 0<φ<2π
- 0< η<1
*in situ* MIP+e calibration

## Background Removal

- Data
- pythia+geant

- Cut to remove background

- Systematic uncertainty on yield from background less than ~5%

## Response & bin quality factors

- Consider detector response (*measured*) to known input (*true*)

- Simulation: ~25% ± 5% for 10<*p**T*<50 GeV/c
- Consistent number derived from (modest) sample of di-jet events

- “geant jets”

- “pythia jets”

- Simulation

## Response & bin quality factors

- Consider detector response (*measured*) to known input (*true*)

- “geant jets”

- “pythia jets”

- Simulation

- Simulation

## Response & bin quality factors

- Consider detector response (*measured*) to known input (*true*)

- “geant jets”

- “pythia jets”

- Bins of width 1-sigma   “purity” of ~35% over range on the diagonal.
- Motivates application of bin-by-bin correction factors.

- Simulation

- Simulation

## Uncorrected per-event yield

- Reasonable agreement between data/MC
- 10 weighted pythia samples
- Slope difference:
- Short term: incorporated into sys. uncertainty
- Long term: iterative re-weighting of MC sample

- Allows data/MC comparison before luminosity
- For HT, include trigger pre-scale:

## Bin-by-bin correction factors

- MB data statistics limited
- More advanced unfolding techniques currently under study

***ε******jet*** : decreases *c(p**T**)*
***resolution****: *increases *c(p**T**)*
***ε******Trig***: ~1 e-2 at *p**T-jet* =   5 GeV
-              ~1 at *p**T-jet* = 50 GeV

*“**measured”*

*“**true”*

- Simulation

## Towards a “corrected” cross section

- Only* data*-statistical errors shown
- Systematics and ratios on next slides

- Fortran code from hep-ph/0404057 (Jager et al.)
- rcone=0.4
- CTEQ 6.1
*μ**F*= *μ**R* =*p**T*
- Agrees with EKS NLO to better than 1%

- ±30% but invisible on this scale

- MB/HT overlap for 3 bins

- ~60%
- Under study

## Dominant systematic uncertainty estimates

- * Under Study

- * Under Study

- * Under Study

- Dominant uncertainty: 10% change in ECal  ~40% change in yield
- More under long term study (see last slide)

- Normalization

- Pythia slope

- Statistics of c(pt)

- Background

- BBC Trigger

- Energy Scale

- Fractional Change in x-section

## “Corrected” data vs. NLO calculation

- “Corrected” data vs. NLO calculation

- 50% systematic uncertainty from E-scale shown
*Agreement (within systematics) over 7 orders of magnitude*

## “Corrected” data vs. NLO calculation

- “Corrected” data vs. NLO calculation

- Things that could change this curve:
- Refined BEMC calibration (pi0 calibration)
- Improved correction for lost (no vertex) events (MC embedded in abort-gap data)
- Improved unfolding scheme
- Issues that won’t go away for 2004:
- HT trigger: fragmentation bias, slow turn on with *p**T**-jet*
- Jet energy scale (*need integrated luminosity for photon-jet!*)

- 50% systematic uncertainty from E-scale shown
*Agreement (within systematics) over 7 orders of magnitude*

## Much work to develop methods and techniques for jet triggering, reconstruction, and analyses
First look: 
Significant pT reach (~50 GeV/c)
Agreement within large systematics with NLO calculations
A few primary issues under study:
Refining in situ EMC calibrations (AuAu vs. CuCu vs. pp)
Overall scale corrections for no-vertex events
Improved unfolding methods
Fragmentation bias (e.g., Pythia vs. Herwig)
NLO clustering scheme
Goal:
Bring 2004 (and 2003) analyses to efficient closure
Large 2005 data set produced, thesis analyses underway
Long term cross section goals
Jet shapes, NLO comparisons
High stats  possible improvement of large-x pdf’s

- First look:
- Significant *p**T* reach (~50 GeV/c)
- Agreement within large systematics with NLO calculations
- A few primary issues under study:
- Refining *in situ* EMC calibrations (AuAu vs. CuCu vs. pp)
- Overall scale corrections for no-vertex events
- Improved unfolding methods
- Fragmentation bias (e.g., Pythia vs. Herwig)
- NLO clustering scheme
- Goal:
- Bring 2004 (and 2003) analyses to efficient closure
- Large 2005 data set produced, thesis analyses underway
- Long term cross section goals
- Jet shapes, NLO comparisons
- High stats  possible improvement of large-x pdf’s

- Summary and outlook

## Backup slides

## Jet Energy Scale Systematics

|  Charged Track Momentum | p/p TPC | 1% |
| --- | --- | --- |
|  Charged Track Inefficiency | 10% x 60% jet | 6%* |
|  Neutral Tower Energy | Gain/Gain = 10% | 40% in yield |
|  Neutral Energy Inefficiency | ∑ET from n+K0L/S+++ | 6-10%* |
|  MIP Subtraction | 10% Correction to  Jet ET | 1% |
|  Fiducial Detector Effects | Edges/Dead regions | 2% |
|  Jet  calculation | 1 tower = =0.05 | 3% |
| Background Trigger | Background trigger +MINBIAS event | 5% in yield |
| Background Energy | Jet + underlying Background |  0 |
| Underlying Event | Work in Progress |  NA |
| Fragmentation | Comparison to HERWIG ongoing |  NA |

**** Included in Correction Factor***

## 2004 BEMC Calibration

- Typical tower response to MIP candidate in 2004 AuAu

- All towers, *p**track* > 1.8 GeV

- Relative gain:
- tower-by-tower MIP response
- ~250 +- 50 MeV/mip
- Absolute gain:
- Eta ring TPC-electrons
- 2<*p**electron*<6 GeV/c

## Theory Systematics

- Changing the pdf

- Changing the scale

## Data vs. MC

- Clear background for ratio>0.9
- Data/MC agreement improves at higher pt

## Data vs. MC

## Data vs. MC

- Red  pythia + gstar
- Black  data
- All error bars statistical

- High tower trigger
- pt (jet) >10 GeV/c

## Data vs. MC

- Red  pythia + gstar
- Black  data
- All error bars statistical

- High tower trigger
- pt (jet) >10 GeV/c