# Presentation: 679894

## Inclusive & Di-Jet Mass Cross Sections 

**Bob Hirosky**
**University of Virginia**
**On Behalf of the D****Ø**** Collaboration**

- QCD at highest Q2 at the Tevatron
- Precision tests of pQCD
- Phenomenological models for “soft” aspects of QCD
- Tuning of Monte Carlo generators
- Probing for new physics
- Understanding backgrounds to many processes of interest

- at sqrt(s) = 1.96 TeV

## The Fermilab Tevatron Collider

- ∫ Luminosity
- Run I    (1992-95)	~0.1 fb-1
- √s = 1.8 TeV
- Run IIa (2001~2005)	~1 fb-1
- Run IIb (2006-2009)	~4-8 fb-1
- √s = 1.96 TeV

- Highest-energy collider until LHC

## DØ Data Taking Performance

- Results presented today are from first  143 pb-1

- Run II Integrated Luminosity  04/02 - 08/04

**Delivered 0.59 fb****-1**
**Recorded .47 fb****-1**

## The DØ Detector

- The DØ Detector

## DØ Calorimetry

- DØ Calorimetry

**Run II upgrades:**
- shorter bunch crossing times → 396 ns → faster trigger and readout electronics
- more material before calorimeter → magnet, tracker, new pre-shower detector
- effectively a new detector

## Jet Physics at DØ at s=1.96 TeV

- Jet Physics at DØ at s=1.96 TeV

- RunII d/dPT ~5x higher for jets w/ pT > 600 GeV (vs. s=1.8 TeV)

-  Higher statistics important for:
- better determination of proton structure at large x
- testing pQCD at a new level (resummation, NNLO theory, NLO event generators)
- continued searches for new physics while testing distances ~10-19 m
- compositeness, W’, Z’, extra dimensions etc...
- understanding primary backgrounds to new physics, production dynamics affecting precision measurements, etc.

- pT/GeV

**d********incl jet**** ****/ dp****T**** / (pb/GeV)**

## IR Safe Cone Jet Definitions in Run II

- Modifications for Run II:
- Use 4-vector scheme, PT instead of ET
- Add midpoints of jets as additional
-     starting seeds
- Infrared safe
- Correct to particle energies
- Offset: Underlying event, previous/extra _ _interactions
- Energy response (from +jet events)
- Energy loss out of cone due to showering in the calorimeter
- Resolution (unsmearing)

- (For details on RunII jet algorithms, see hep-ex/0005012 + recent talk by B. Andrieu at ISMD 2004)

## Systematic errors dominated by uncertainties in jet energy scale

Scale is determined in-situ, improvements with integrated luminosity +jet statistics), refined cell-level calibrations, studies of showering effects (particularly in forward regions)

- Scale is determined in-situ, improvements with integrated luminosity +jet statistics), refined cell-level calibrations, studies of showering effects (particularly in forward regions)

- Inclusive Jet Cross Section: Run II Cone

## Inclusive Jet Cross-Section vs. Rapidity

- 1st corrected Run II cross section for forward jets
- Good agreement between data and theory at all rapidities
- Important PDF information in  vs. rapidity

- 2<|y|<2.4

- 1.5<|y|<2.0

- |y|<0.5

##      Substantial uncertainties in

-      Substantial uncertainties in
- large-x gluon

-      Ratio to CTEQ6 fit

- Gluon at Q = 3.16 GeV

-    10-3.01   .05 .1   .2         .5         1
- x

- 2.0

- 1.0

- 0.5

-  2 < || < 3

-  0 < || < 0.5

- qg

- qq

- gg

- qg

- qq

- gg

## Central region |yjet| < 0.5, data sample ~143 pb-1
Run II midpoint algorithm
Agreement within uncertainties with NLO/CTEQ6M
Jet Energy Scale (<7%) -- dominant error on the measurement

- Run II midpoint algorithm
- Agreement within uncertainties with NLO/CTEQ6M
- Jet Energy Scale (<7%) -- dominant error on the measurement

- Dijet Mass Spectrum d/dMjj for |y| < 0.5

## Highest Mass Dijet Event From DØ

## Concluding Remarks

- First results show generally good agreement with theory for cross-sections
- Increasingly precise QCD measurements to be pursued in Run II
- Explore high PT and Mjj regions over a wide range of rapidities
- Direct search for evidence of new physics
- Constrain high-*x* gluon contributions
- QCD knowledge from Tevatron is essential for:
- Precision measurements and searches for New Physics
- Expectations for LHC
- Substantial increases in precision are anticipated with increasing luminosity and detector characterization.