# Presentation: 279552

## New (QCD) Results from the Tevatron

- Sarah Eno
- U. Maryland
- For the D0 and CDF collaborations
- 14 Apr 2004

- DIS 2004

- 14 Apr 2004

**Notes:**
I’m going to tell you about the new results for the winter conference season from the Tevatron. And, especially, since this is a conference on Deep Inelastic scattering and QCD, I’m going to concentrate on our new results in these areas.  (We *finally* have a very large number of new results, and so, given the nature of this conference, I’ll concentrate on our QCD results)

## Tevatron

- Run 0 ’88/’89
- 20 pb-1
- Run I ’92/’96
- 120 pb-1
- Upgraded 2000
- 1.8 TeV1.96 TeV
- Goal:
-   20 pb-1/week
-   10E31 cm-2 s-1
-    2 fb-1

- (from summary taped onto my office wall in ’92)

- DIS 2004

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## Tevatron

- DØ

- Data: 1.0 years

- Commission: 1.5 years

- Nov 2002 D0
- March 2002 CDF

**Run I record**

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## Tevatron

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## CDF and D0

- Cal: Ur-liquid Ar

- Cal: Pb-scintillator

- DØ

- CDF

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**Notes:**
Then most important detector element for *most* (but not all) of the analyses I’m going to show is the calorimeter, so I’ll just remind you that...  part of the CDF calorimeter is new for Run II

## QCD: Run0/Run I

-  Rapidity Gaps/Diffractive Physics/Elastic Physics (10 papers)
-  PDF’s: double parton interactions (1 paper), W charge asymmetry (3 papers)
-  Non-Perturbative QCD: jet shapes (4 papers), W/Z boson PT spectra (8 papers), other (9 papers)
-  Perturbative QCD, particle cross sctions: W/Z bosons (9 papers), prompt photons ( 8 papers), jets (14 papers), top (6 papers), b/c quarks (lots of papers)
- Perturbative QCD with W/Z bosons ( 6 papers)
-  Perturbative QCD with jets: s (1 paper), jet topologies (12 papers)

- 84 papers! (+ lots of b/c papers)

- New results in all these areas for this winter’s conferences.
- It’s not all top and electroweak physics!

- DIS 2004

- 14 Apr 2004

**Notes:**
So, when you think of the Tevatron, you usually think of the top, then maybe new particle searches, then maybe W physics.  But, both CDF and D0 have very active QCD grounds.   The Run II QCD groups are as active as the Run I ones

## Run II, 2003 Winter Conferences

- CDF
-  **inclusive jet cross section, central region**
** ****dijet mass spectra**
** ****jet shapes and energy flow in dijet events**
** ****diffractive jets**
** ****photon plus heavy quark**

- DØ
-  **inclusive jet cross section, central region**
** ****dijet mass**
** ****uncorrected dijet ******
** ****elastic scattering data**

- DIS 2004

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## New Results for 2004

- CDF
-  **jet multiplicities in W+jet events    (127 pb-1)**
** ****Underlying event in jet events/minbias data**
**Di-photon Cross section (207 pb****-1****)**
** ****W/Z cross sections (72 pb****-1****)**
** ****top cross sections (126-200 pb****-1****)**

- DØ
-  **inclusive jet cross section, forward region (143 pb****-1****)**
** ****dijet cross section (143 pb****-1****)**
** ****azimuthal decorrelation in dijet events (150 pb****-1****)**
** ****elastic scattering **
**Z’s with rapidity gaps (117 pb****-1****)**
** ****top cross sections (140-156 pb****-1****)**

- Channel-by-channel luminosity variations due to detector-specific good run selection
- Harder analyses tend to freeze their data sample earlier, and thus have less luminosity

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## Jet Cross Section, Run I

- High ET jets probe large x PDF’s, especially gluon PDF.  Run II has extended reach in jet ET

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## New Algorithm

- Use Run II cone algorithm
- Combine particles in a R=0.7 cone
- Use the four vector of every tower as a seed
- Rerun using the midpoints between pairs of jets as seeds
- Overlapping jets merged if the overlap area contains more than 50% of lower Pt jet, otherwise particles assigned to nearest jet.

**Both groups now using same algorithm**

**Reduced sensitivity to soft radiation**

**E-scheme recombination**

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## CDF Update

- 177 pb-1

- More luminosity since winter 2003

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## DØ Results

- First corrected run II jet cross section for forward jets
- Important PDF information is in the cross section versus rapidity

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## Uncertainties, Central Jets

- Uncertainties dominated by jet energy scale.  Jet energy scale is systematics dominated in central.

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## Uncertainties, Forward Jets

- Energy scale error large.  Systematics dominated. Expect improvement soon.

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## DØ DiJet Cross Section

- Often used to search for new resonances

- Uncertainty dominated by jet energy scale

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## CDF, Dijet Mass

- CDF’s highest mass dijet event M=1364 GeV, ET’s=633,666

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## DØ,  Decorrelation

- Leading Order pQCD

- Jets are back-to-back

- 3 jets in pQCD

- 12 = 

- 12 < 

- 12 is sensitive to jet formation without having to measure 3rd jet directly!

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## Azimuthal Decorrelation

- For small , data agrees well with herwig and reasonably well with LO perturbative calculation (JETRAD)

**jetrad**

**herwig**

**bkfl**

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## Azimuthal Decorrelation

- Run II. Differential measurement at small .
- LO (in 3rd jet) perturbative calculation  (JETRAD) does not agree.
- Not too surprising...
- Calculation diverges at 
-  no phase space beyond 2/3
- lots of 4 jet events at smaller .
- NLO not so bad!

- DIS 2004

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## Azimuthal Decorrelation

- okay agreement with herwig, pythia. Tuned pythia gives best agreement.  NLO is better in intermediate region.
- Pythia distribution sensitive to “maximum virtuality for the initial-state parton shower in terms of the hard matrix scale”  (PARP(67)).

- Tune “A” is the CDF UE tune discussed later.

- DIS 2004

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**Notes:**
The limitations of fixed order pQCD are cured by calculations that resume leading logarathmic terms to all orders in alpha_x.  Monte carlo event generators with parton shower models are good approximatios to such resummed calculations

## CDF, Di-Photon

- Two isolated and energetic high Et photons in the central region

- CDF Run I: cross section 3x prediction from NLO QCD (Bailey, Owens, Ohnemus, Phys. Rev. D 46, 2018 (1992)

- Correlations between the 2 photons can be used to test NLO QCD and study the transverse momentum of the initial partons (KT)

- DIS 2004

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## Di-Photon

- Plotted versus mass of 2 photons instead of photon PT

**DIPHOX hep-ph/9911340**
**                 ****Eur.Phys.J C16, 311**
**Additional “fragmentation” diagrams**
**ResBos hep-ph/9712471**

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## CDF W+Jets

**Systematic uncertainty (10% in ********1**** to**
** ****40% in ********4****) limits the measurement **
**sensitivity**

**Results agree with LO QCD predictions within the errors!**

- Crucial to be able to calculate/understand this for top/higgs physics
- ALPGEN LO matrix element interfaced with HERWIG for parton shower
- Not more than one parton associated with a reconstructed jet

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## CDF W+jets

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## CDF, Underlying Event

- The “underlying event” consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions.

**Studies of min bias events, Jet events in Run I produced  “PYTHIA Tune A” **
**Run II:**
**Look at distributions/correlations of charged particles with ********<1, p****T****>500 MeV**
**Studies of mini-jets in min bias events**
**Lots has work has been done, far too much to summarize here**

- DIS 2004

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## CDF, Underlying Event

**“****Back-to-Back”**
**(********12****>150****o****,ETj****2****/ETj****1****>0.8)**

**Transverse regions are sensitive to underlying event**

**The ****“underlying event”**** consists of hard initial & final-state radiation plus the “beam-beam remnants” and possible multiple parton interactions.**

- DIS 2004

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## Underlying Event

- Min Bias

- With and without requiring the 2nd jet back-to-back with leading jet

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## Underlying Event

- Pythia tuned using Run I data can describe data better than (untuned) Herwig

**Compared to pythia Tune A**

**Compared to untuned herwig**

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## Min Bias Data

- Look for min bias events with a track over a threshold.  Look at distribution of charged PT in  relative to that track.  Compare to Tune A

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## 3rd Jet

- Better job at predicting the emergence of the little jets in back-to-back dijet events than in Min Bias.  Herwig also good

**Tune A**

**Herwig**

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**Notes:**
Select track with maximum PT in the “tranverse” region

## DØ, Elastic Scattering

- Pomeron, Odderon Exchange: intact proton,antiproton

- t ~ θ2, where θ is scattering angle

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## Elastic Scattering

- ISR and E710 data

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## Elastic Results

- normalization is arbitrary!

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## Diffractive Z’s

- Collision between a “pomeron” and a proton or antiproton: intact p or pbar
- Quark-like pomeron has larger event rate and larger fraction of events without jets than Gluon-like pomeron

- Tevatron “gap” data from jet, b, J/Psi events favor hard-gluon pomeron, but rate is too high compared to extrapolation of DESY data.  Tev data at 630 GeV further complicates the extrapolation picture.  SCI model (Edin, Ingelman, Rathsman, J. Phys. G22, 943 (1996) , which does not involve pomerons, may better describe the data.

**Intact proton**

**Can we do at higher luminosity?**

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## Run I

- CDF: 8246 We’s with a gap fraction of 1.15+-0.6.   Jet distribution consistent with quark-like pomeron from the jet fraction, gluon-like for the absolute rate.
- DØ: 12622 W e’s with gap fraction of 0.89 +-0.2%, 811 Z ee’s with gap fraction of 1.44+-0.6%.  Event characteristics of diffracive and non-diffractive W’s agree well.  Unlike diffractive jet events, central W’s have larger gap fraction than forward W’s
- Some discussion regarding how to correct for the fraction of diffractive events that do not contain a gap.  If this is done, the measurements are not in as good of agreement as above implies (500% for DØ, 20% for CDF for pomeron model)

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## Run II

**Already same order as we had W’s in Run I**

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## W/Z Cross Section

- New results from CDF for winter 2004 in all channels.

**http://tevewwg.fnal.gov/**

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## PDF Uncertainty

- Michael Schmitt, Northwestern U, CDF

- Uncertainty on ratio of acceptances  using CTEQ6 SF, LO calculation of the cross section, and a parameterization of the acceptance versus boson rapidity.  CTEQ6 has a nominal PDF and 40 error PDF’s, corresponding displacing each of the X parameters by +/- 1 sigma.

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## Top Cross Section

**Theory cross sections**
**Kidonakis NNLO-NNNLL hep-ph/0303185**
**Cacciari et al hep-ph/0303085**
**Uncertainty dominated by large-x gluon pdf and ********s**

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## Prospects

- Both Collaborations expect many publications before summer.

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## Prospects

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## Prospects

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## Talks in Working Groups

- Jets – Alexei Safonov
- Dijet Mass - Pavel Demine
- Inclusive Jet Cross Section – Miroslav Kopal
- Underlying Event: Niccolo Moggi
- Diffraction – Koji Terashi
- Diffractive Z production/elastic results - Tamsin Edwards
- Pentaquarks: Igor Gorelov

-  bottom and charm: Peter Bussey
- Upsilon and X – Franck Lehner
-  B physics –Tulika Bose
- EWK: Susana Cabrera
- Top Physics – Sebastien Greder
- Top: Roman Lysak
- SUSY Searches – Tibor Kurca
- B decays: Simone Donati
- Leptoquarks: Dan Ryan
- Other searchs: Arnold Pompos
- Higgs Physics – Stephanie Beauceron

- DIS 2004

- 14 Apr 2004