jet physics at the tevatron lee sawyer louisiana tech university on behalf of the cdf & d0...

Jet Physics at the Tevatron

Lee Sawyer

Louisiana Tech University

On Behalf of the CDF & D0 Collaborations

July 28, 2004

"Jet Physics at the Tevatron" Lee Sawyer 2

Jet Physics at the Tevatron

• Why do QCD at the Tevatron?• The Experiments • From Detector Signals to Partons• Some Results

– From CDF:• Jet cross-sections: Cone jets and kT jets

• Jet Shapes

– From DØ:• Inclusive jet cross-section• Dijet Cross-Section• Dijet Azimuthal Decorrelations

July 28, 2004


The Fermilab Tevatron

• pp Collider at √s = 1.96 TeV (increased from 1.8 TeV in Run I)

• Main Injector replaces the old “Main Ring”

• Other improvements – p source

– Recycler

– electron cooling

aimed at improving p beam lifetime, increase luminosity.

• Increasing luminosity:– Run I (1992-95) ~0.1 fb-1

– Run IIa (2001~2005) ~1 fb-1

– Run IIb (2006-2009) ~4-8 fb-1

July 28, 2004


Tevatron Performance

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1

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9/29/03 9/29/04 9/30/05 10/1/06 10/2/07 10/2/08 10/3/09

Start of Fiscal Year

Inte

grat

ed L

umin

osit

y (

fb-1

)

Design Projection

Base Projection

Design Base Fiscal Year (fb-1) (fb-1) FY03 0.33 0.33 FY04 0.64 0.56 FY05 1.2 0.93 FY06 2.7 1.4 FY07 4.4 2.2 FY08 6.4 3.3 FY09 8.5 4.4

Instantaneous luminosities approaching 1032 cm-2 s-1

On 16 July, store# 3657 B0Lum 110.16 x 1030 cm-2 s-1 D0Lum 91.32 x 1030 cm-2 s-1

Integrated luminosity around 400 pb-1 per experiment.

Should reach 1fb-1 by 2005 shutdown.

July 28, 2004


The CDF Detector

• From Run I– Central Calorimeter – Solenoid– Muon System (with

Upgrades)• For Run II

– Plug and MiniPlug Calorimeters

– TOF and central Drift Chamber

– Silicon Microstrip Tracker– Forward Muon Detectors

=> Calorimeter coverage extended (||<3.6) while maintaining excellent tracking and vertex resolution.

July 28, 2004


CDF Data Taking Performance

Efficiency > 80%Around 450 pb-1 on tape

July 28, 2004


The DØ Detector

July 28, 2004


DØ Data Taking Performance

Around 400 pb-1 recorded

Efficiency regularly above 85%.

July 28, 2004


QCD at the Tevatron

– Higher √s means higher cross-sections

– Probe proton structure at large x– Test pQCD with increased

statistics– Search for high mass states (Z’,

W’, compsiteness, etc.)– QCD signals form the primary

background to most of the other measurements at the Tevatron

Inclusive jet spectrum

x2

July 28, 2004


What Is a Jet?

• (For details on jet algorithms, see talk by Bernard Andrieu.)

• DØ Run II cone algorthim w/ Rcone=0.7, pT

min=8 GeV/c, f=50%

– Any “particle” (MC, cal tower, etc) used as a seed.

– Make a cone in R=√()2+()2 < Rcone around seed

– Add particle 4-vectors in cone => “proto-jet”

– Draw new cone around proto-jet, iterate until stable solution found => cone axis = jet axis

– Remove proto-jets w/ pT,<pTmin.

– Merge jets if more than overlap fraction f of pT

jet is contained in the overlap region; otherwise split jets.

– Use midpoints between pairs of jets as seeds.

• CDF JETCLU algorthim w/ Rcone=0.7– Adds ET’s of cluster’s in cone

(“Snowmass”)– Does not use midpoints between pairs of

jets as seeds.

• kT algorthim– Not a “fixed cone” algorithm– Use relative momenta of

particles, merge by pairs.– Dmin =

min(pT2(i),pT

2(j)) Ri,j/D– D = Jet Size parameter.

Cone jetkT jet

July 28, 2004


From Detector Signals to Partons

• We do not see quarks and gluons– We do not really see ,K,p,,etc

• How do we go from calorimeter ADC counts to p of the outgoing partons? => Jet Energy Scale

• Factors impacting the JES include– Energy Offset (i.e. energy not from the hard

scattering process)– Detector Response

• For DØ, EM energy scale determined from Z→ee. Use pT balance in +jets, measured linearity corrections from calorimeter calibration. Extrapolate for very high pT

– Out-of-Cone showering – Resolution => Unsmearing

• Energy Scale uncertainties typically are the largest systematic errors in jet measurements.

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“par

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CH

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July 28, 2004


Inclusive Jet Cross-Section

Extends the Run I CDF measurement by approx. 150 GeV

Run I/Run II comparison plot includes 3% energy scale uncertainty band. Luminosity uncertainites not included.

July 28, 2004


Inclusive Jet Cross-Section as a Function of Rapidity

July 28, 2004


Inclusive Jet Cross-Section as a Function of Rapidity

Increased uncertainty in PDFs in forward region

Good agreement between theory and data at all rapidities

July 28, 2004


KT Jet Cross-Section

• CDF measures inclusive jet production using the KT algorithm

• Jets in the region 0.1 < |Y| < 0.7 and

• PT > 72 GeV/c.

• Results based on 145 pb-1

July 28, 2004


KT Cross-Section vs D

Data diverges from NLO prediction as D gets large, due to soft contributions

July 28, 2004


Dijet Cross-Section

• DØ measures the cross-section for dijet production in three rapidity bins – 0<Y<0.5

– 1.5<Y<2.0

– 2.0<Y<2.4

• d/dMjj measured for central rapidities

• Good agreement between data and NLO pQCD

July 28, 2004


Dijet Cross-Section

Data/Theory comparison for central rapidities

July 28, 2004


Dijet Mass Spectrum

July 28, 2004


Nifty Pictures I: Highest Mass Dijet Event From DØ

July 28, 2004


Nifty Pictures II: Highest Mass Dijet Event From CDF

ET = 666 GeV

= 0.43

ET = 633 GeV

= -0.19

Dijet Mass = 1364 GeV(probing distance ~10-19 m)

CDF (-r view)

July 28, 2004


Dijet Azimuthal Decorrelations

• Jet separation in is sensitive to final state radiation.

• At LO, • At higher order, a hard third

jet (k┴>0) leads to .– Measuring the dijet

spectrum tests O(s3)

predictions– No need to explicitly measure

third or greater jet

July 28, 2004


Dijet Azimuthal Decorrelations

• Use central inclusive dijet sample– Data binned in pT of the

leading jet

• Normalize cross-section for each pT-bin to inclusive cross-section

• Only look at to avoid overlap region between jets

• Hard leading jets have pT spectra more sharply peaked near .

July 28, 2004


Dijet Comparisons

• Comparison to fixed-order pQCD predictions

• Leading order (dashed blue curve) – Divergence at ΔΦ = (need soft processes)– No phase-space at ΔΦ<2/3 (only three partons)

• Next-to-leading order (red curve)– Good description over the

whole range, except in extreme ΔΦ regions

July 28, 2004


Dijet Comparisons

• Comparison to Monte Carlo predictions

• Herwig 6.505 (default)– Good overall description!

– Slightly too high in mid-range

• Pythia 6.223 (dash line=default)– Very different shape

– Too steep dependence

– Underestimates low ΔΦ

– Vary PARP(67) = 1 → 4• Varies ISR• Radiation starts for Q*PARP(67)

– With more ISR, closer agreement to data.

July 28, 2004


Jet Shapes

• CDF looks at the fraction of a jet ET within a subcone– Define = ET(r)/ET(R)

– Energy flow variable

• Sensitive to multiple gluon emission from the primary parton

• Also sensitive to underlying event.

July 28, 2004


Jet Shapes

Study uses Midpoint Algorithm w/ R=0.7. is corrected to the hadron level.

Central jets: Low pT High pT

July 28, 2004


Jet Shape vs pT

July 28, 2004


Lagniappe

• In addition to the study of high pT QCD, there is a rich program of diffractive studies and elastic scattering measurements at both experiments– About 40% of pp total cross-section is elastic or diffractive.– Portions of upgrades designed to enhance this capability

• See talk by Mary Convery on Saturday for “Diffractive Results from CDF”

• Want to mention a few low pT results from DØ

July 28, 2004


DØ Detector Details

• In addition to Calorimeter, can tag interaction with luminosity monitors near beampipe.

• Forward Proton Detector added to elastic scattering measurements

– Series of 18 Roman Pots arranged in 9 spectrometers

– Now fully commissioned and part of the DØ readout.

July 28, 2004


Diffractive Z Production

• Define a “rapidity gap” between calorimeter and luminosity monitors

• In Run I, identified a handful of events consistent with W→e and Z→ee with associated rapidity gap

• In Run II, have looked for Z→ plus forward rapidity gap.

July 28, 2004


Diffractive Z Production

“North” = Negative Rapidities

“South” = Positive Rapidities

Evidence for diffractive Z production, mass consistent.

More work to be done (backgrounds, efficiencies,..)

July 28, 2004


Elastic Scattering

• First results from Forward Proton Detector

• Measurement of ξ = Fraction of proton longitudinal momentum lost in the scattering

July 28, 2004


Conclusions

• Rich range of QCD topics to be pursued in Run II• First results from both experiments show generally

good agreement with theory for cross-sections• More detailed comparisons to theory needed for

details of event and jet shapes.• First DØ being produced for diffractive and elastic

physics• Both experiments will be able to explore high pT and

Mjj regions over a wide range of rapidities– Test high-x gluon contributions– Look for evidence of new physics

jet physics at the tevatron lee sawyer louisiana tech university on behalf of the cdf & d0...

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