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 k T jets Jet Shapes –From DØ: Inclusive jet cross-section Dijet Cross-Section Dijet Azimuthal Decorrelations

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 3 The Fermilab Tevatron p p 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 ( ) ~0.1 fb -1 –Run IIa (2001~2005) ~1 fb -1 –Run IIb ( ) ~4-8 fb -1

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 4 Tevatron Performance Instantaneous luminosities approaching cm -2 s -1 On 16 July, store# 3657 B0Lum x cm -2 s -1 D0Lum x cm -2 s -1 Integrated luminosity around 400 pb -1 per experiment. Should reach 1fb -1 by 2005 shutdown.

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 5 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 "Jet Physics at the Tevatron"Lee Sawyer 6 CDF Data Taking Performance Efficiency > 80% Around 450 pb -1 on tape

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 7 The DØ Detector

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 8 DØ Data Taking Performance Around 400 pb -1 recorded Efficiency regularly above 85%.

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 9 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 "Jet Physics at the Tevatron"Lee Sawyer 10 What Is a Jet? (For details on jet algorithms, see talk by Bernard Andrieu.) DØ Run II cone algorthim w/ R cone =0.7, p T min =8 GeV/c, f=50% –Any “particle” (MC, cal tower, etc) used as a seed. –Make a cone in  R=√(  ) 2 +(  ) 2 < R cone 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/ p T, <p T min. –Merge jets if more than overlap fraction f of p T jet is contained in the overlap region; otherwise split jets. –Use midpoints between pairs of jets as seeds. CDF JETCLU algorthim w/ R cone =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. –D min = min(p T 2 (i),p T 2 (j))  R i,j /D –D = Jet Size parameter. Cone jetk T jet

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 11 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. Time “parton jet” “particle jet” “calorimeter jet” hadrons  CH FH EM

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 12 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 "Jet Physics at the Tevatron"Lee Sawyer 13 Inclusive Jet Cross-Section as a Function of Rapidity

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 14 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 "Jet Physics at the Tevatron"Lee Sawyer 15 K T Jet Cross-Section CDF measures inclusive jet production using the K T algorithm Jets in the region 0.1 < |Y| < 0.7 and P T > 72 GeV/c. Results based on 145 pb -1

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 16 K T Cross-Section vs D Data diverges from NLO prediction as D gets large, due to soft contributions

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 17 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  /dM jj measured for central rapidities Good agreement between data and NLO pQCD

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 18 Dijet Cross-Section Data/Theory comparison for central rapidities

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 19 Dijet Mass Spectrum

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 20 Nifty Pictures I: Highest Mass Dijet Event From DØ

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 21 Nifty Pictures II: Highest Mass Dijet Event From CDF E T = 666 GeV  = 0.43 E T = 633 GeV  = Dijet Mass = 1364 GeV (probing distance ~ m) CDF (  -r view)

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 22 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(  s 3 ) predictions –No need to explicitly measure third or greater jet

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 23 Dijet Azimuthal Decorrelations Use central inclusive dijet sample –Data binned in p T 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 p T spectra more sharply peaked near .

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 24 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 "Jet Physics at the Tevatron"Lee Sawyer 25 Dijet  Comparisons Comparison to Monte Carlo predictions Herwig (default) –Good overall description! –Slightly too high in mid-range Pythia (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 Physics at the Tevatron"Lee Sawyer 26 Jet Shapes CDF looks at the fraction of a jet E T within a subcone –Define  = E T (r)/E T (R) –Energy flow variable Sensitive to multiple gluon emission from the primary parton Also sensitive to underlying event.

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 27 Jet Shapes Study uses Midpoint Algorithm w/ R=0.7.  is corrected to the hadron level. Central jets: Low p T High p T

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 28 Jet Shape vs p T

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 29 Lagniappe In addition to the study of high p T 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 p T results from DØ

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 30 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 "Jet Physics at the Tevatron"Lee Sawyer 31 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 "Jet Physics at the Tevatron"Lee Sawyer 32 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 "Jet Physics at the Tevatron"Lee Sawyer 33 Elastic Scattering First results from Forward Proton Detector Measurement of ξ = Fraction of proton longitudinal momentum lost in the scattering

July 28, 2004 "Jet Physics at the Tevatron"Lee Sawyer 34 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 p T and M jj regions over a wide range of rapidities –Test high-x gluon contributions –Look for evidence of new physics