# Presentation: 523584

## Slide 1

## Outline

-  Introduction
-  Jet cross sections
-  inclusive results
-  multi-jet results
- Photon cross sections
- Diffractive W and Z  production
- Run 2
-  status
-  first jet results
- Summary

- Marek Zielinski

## Jets at the Tevatron

- Here, jets of fixed cone size
- kT-jet results in the talk by U. Bassler
- Run 1:
- Add up towers
- 	around a “seed”
- Iterate until stable
- Jet quantities: ET, , 
- Modifications for Run 2:
- Use 4-vector scheme, pT instead of ET
- Add midpoints of
-     jets as additional
-     starting seeds
- Infrared safe
- Correct to particles
- Underlying event, previous/extra pp interactions, energy loss out of cone due to showering in the calorimeter, detector response, ET resolution

- _

- Marek Zielinski

## Inclusive Jet Cross Section at 1800 GeV

- Good Agreement with NLO QCD

- pQCD, PDFs, substructure?...

-  How well do we know proton
-    structure (PDFs) ?
-  Is NLO (s3) QCD “sufficient” ?
-  Are quarks composite ?

- NLO QCD
- (JETRAD, CTEQ4M)

-   **PRL 86, 1707 (2001)**

*******d******2************ dE******T ******d*************** (fb/GeV)**

- Marek Zielinski

## Rapidity-Dependent Inclusive at 1800 GeV

**Rapidity-Dependent Inclusive at 1800 GeV**

- DØ’s most complete cross section measurement
- covers || < 3.0
- complements  HERA x-Q2 range
- 90 data bins
- Full correlation of uncertainties
- Used in CTEQ6 and MRST2001 fits to determine gluon at large x “better than ever before”
**Enhanced gluon at large x**

- CTEQ6M comparison:

- CTEQ6M 2 = 65

- Marek Zielinski

**Notes:**

Sensitive to PDF, sensitive to mu.

## Ratio of Cross Sections: 630 GeV / 1800 GeV

- Data 10-15% below NLO QCD
- Agreement Probability (2 test)   with CTEQ4M, CTEQ4HJ, MRST: 25-80%
- Comparison with CDF
- Consistency at high xT, but not at low xT
- A ~3 GeV shift in jet energies could account for the discrepancies
- corrections for underlying event, showering in calorimeter, parton kT...?
- larger than experimental uncertainty...

**PRL 86, 2523 (2001)**

- vs.

-  Various theoretical and experimental
-     uncertainties tend to cancel in the ratio

- Marek Zielinski

## Inclusive R32: 3 Jets / 2 Jets at 1800 GeV

- A study of soft jet emission
- 70% of high-ET jet events have a 3rd jet above 20 GeV
- 50% have a jet above 40 GeV
- Ratios provide reduced systematic uncertainties
- We observe very little sensitivity to PDFs
- Using JETRAD, investigate sensitivity to scale R
**Single-scales (********0.3H****T********seem better than mixed-scales**
-    **PRL 86, 1955 (2001)**

- Marek Zielinski

## Low-ET Multi-jet Production at 1800 GeV

- Now looking at multi-jets at low        ET   20 GeV ...
- This region is sensitive to gluon radiation and multiple parton interactions
- ET distribution of  1, 2, 3, and 4 jet events compared with MC predictions (Pythia – solid, Herwig -- dotted)
- Without tuning, the MC predictions do not match the data:
- excess of events for  3 and 4 jets at low-ET end
- wrong  distributions
- Tune Pythia PARP(83) = 0.32   (fraction of core region of  hadronic matter distribution)
- Tune Herwig PTmin to 3.7 GeV        (minimum PT of hard processes)

- Each jet’s ET>20 GeV, ||<3

**D****Ø****  preliminary, hep-ex/0207046**

**E****T**

****

- Marek Zielinski

## Photons at 630 and 1800 GeV

- Slight excess at low xT?
- Smearing of the transverse momenta of initial partons by a few GeV can model such rise at low ET
- But: insignificant statistically
- Good agreement with NLO QCD

-   Probe pQCD without the complication
-      from jet identification and hadronization
-  DØ and CDF previously reported an
-      excess of  production for pT<30 GeV
-      at 1800 GeV  (DØ: PRL 84, 2786 (2000))

- First measurement at forward rapidities
**PRL 25, 251805 (2001)**

- s=630 GeV

- Marek Zielinski

## Diffractive W and Z Production at 1800 GeV

**Diffractive W and Z Production at 1800 GeV**

- New definitive observation of diffractive W signal:               **R****W****=(0.89 + 0.20 - 0.19)%**
- First observation of diffractive Z: **R****Z****=(1.44 + 0.62 - 0.16)%**
-      **D****Ø****  preliminary, paper in preparation**

**n****CAL**

**n****L0**

**Peak at (0,0) indicates diffractive process**
**W sample:****  ****91 of 12622 events in (0,0) bin**
**Z sample:**** ****9 of 811 events in (0,0) bin**

**n****L0****   ****=  #  hit tiles in L0 detector**

**n****CAL**** =  #  towers with energy **
**                ****above threshold in **
**                ****forward calorimeters**

-  Probe quark content of Pomeron
-  Measurement: look for rapidity gaps

-  In Run 2 we will be able to measure
-     the scattered proton using the
-     Forward Proton Detector:

- Marek Zielinski

## Start of Run 2 

**Start of Run 2 **

- Run 2 of the Tevatron started in March 2001
- Running at s=1.96 TeV
- Considerable fraction of collected luminosity devoted to the commissioning of the detector
- Significant progress in establishing and refining “physics objects”: e, , jets, EM and jet energy scale...
**6 pb****-1**** used for jet results             (March-May 2002)**

- KS  π+π-

- B±J/K±

- Marek Zielinski

## Run 2: Calorimeter

- Using Run 1 calorimeter
- Uranium-Liquid Argon
- stable, uniform response, radiation hard, fine segmentation
- Uniform, hermetic,      coverage || < 4.2
- Compensating (e/ ~1)
- Good energy resolution
- New readout electronics to operate in Run 2 environment

**Very stable running **
**~50 bad channels (0.1%)**

- Marek Zielinski

## Jet Energy Scale

- Measured jet energy is corrected to particle level
- Detector*** E****det *: jet energy in the detector, reconstructed with a cone algorithm
- Offset ***E****O *: energy due to previous events, multiple interactions, noise etc.
- Response ***R****jet* : calorimeter response to hadrons, measured from ET imbalance in +jet events
- Showering ***S ***: net fraction of particle-jet energy that remains inside jet cone after showering in the calorimeter

-  ET=27 GeV

- jet ET=24 GeV

- +jet Event

**Z********ee signal (Calorimeter only)**

- Marek Zielinski

## Jets Physics in Run 2

- At s=1.96 TeV, cross section 2x  larger compared to Run 1 for jets with pT > 400 GeV
- Higher statistics will allow:
- 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 (compositeness, W’, Z’, extra dimensions etc...)
- New algorithms:
- midpoints
- massive jets, using jet pT

- Inclusive jet spectrum

- Marek Zielinski

## Selecting Jets in Run 2 

- Jet sample:
- Data taken during March-May 2002 period
- Cone size R=0.7
- ||<0.7
- Run selections based on hardware status, missing ET
- Jet selection based on several calorimeter characteristics
- Missing ET < 0.7 pTjet1
- |zVTX| < 50 cm
- ECAL < 2 TeV

- Marek Zielinski

## Jet Triggers in Run 2 

- Hardware trigger (L1)
- Triggers on calorimeter towers
- Fast readout
- Multi-tower triggers
- Trigger coverage || < 0.8 for this data
**Expanded to |********| < 2.4 in June!**
- Software trigger (L3)
- Simple and fast jet algorithm on precision readout
**Improved turn-on**

**2-jet event**
-  ETjet1~230 GeV
-  ETjet2~190 GeV

- Marek Zielinski

## Run 2 Jet Results

- Only statistical errors
- Luminosity L = 5.8 pb-1 (±10%)
- Preliminary jet energy scale
- 30-50% syst. error in cross section
- Not fully corrected
- (for unsmearing, efficiencies)

- Coming shortly:
- Much expanded  range
- L2 triggers, L1 large tiles
- Improved energy scale
- Efficiency corrections
- Ever increasing lumi...

**Inclusive jet p****T**** spectrum**

-  **Dijet mass spectrum**

- Marek Zielinski

## Summary

**Run 1:**
- Jet results in good agreement with NLO QCD
- Good understanding of systematics, correlations
- Strong constraints on PDF’s, especially high-x gluon
- Photon results consistent with NLO QCD
- a hint of discrepancy at low pT?
- Clear observation of diffractive W production, first for the Z

**Run 2:**
- DØ detector is working well after upgrade
- Jet measurements are well underway
- First results available for
- Inclusive jet pT spectrum 60 < pT < 410 GeV
- Dijet mass spectrum         150 < Mjj <750 GeV
- Many precision measurements possible

**Looking forward to more data!**

- Marek Zielinski