XXXIV International Symposium on Multiparticle Dynamics

Tevatronat JetsW/

XXXIV International Symposium on Multiparticle Dynamics

Alberto Cruz

On behalf of the CDF collaboration

Main Injector

Tevatron

DØCDF

Chicago

p source

Booster

Fermilab

Florida

Tevatron

• proton-antiproton collisions

•Main injector (150 GeV proton storage ring)

• antiproton recycler (commissioning)

• Electron cooling this year• Operational on June’05• 40% increase in Luminosity

• 36 bunches (396 ns crossing time)

TeV) 1.8 I(Run TeV 1.96s

Long Term Luminosity Projection(by end FY2009)

Base Goal -> 4.4 fb-1Design -> 8.5 fb-1Increasing Luminosity: RUN I (1992-95) ~0.1fb-1RUN IIa (2001~2005) ~1fb-1

Tevatron Performance

Recent Luminosity Record of 10.3x1031 sec-1cm-2 (July 16, 2004)

CDF Run II Data

CDF Efficiency > 80%

DAQ runs with 5% to 10% dead timeRest coming from very careful operation of detector’s HV due to machine losses (…to preserve silicon & trackers…)

CDF -> ~450 pb-1 on tape

In proton-antiproton collisions we can occasionally have a “hard” parton-parton scattering resulting in

large transverse momentum outgoing partons.

Proton AntiProton

“Hard” Scattering

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event Underlying Event

Initial-State Radiation

Final-State Radiation

The Jet Algorithm Allows us to “see” the partons (or at least their fingerprints) in the

final hadronic state.

Jet algorithms & physics

• Final state partons are revealed through collimated flows of hadrons called jets

• Measurements are performed at hadron level & theory is parton level (hadron parton transition will depend on parton shower modeling)

• Precise jet search algorithms necessary to compare with theory and to define hard physics

• Natural choice is to use a cone-based algorithm in - space (invariant under longitudinal boost)

Run II -> MidPoint algorithm

1. Define a list of seeds using CAL towers with E > 1 GeV

2. Draw a cone of radius R around each seed and form “proto-jet”

3. Draw new cones around “proto-jets” and iterate until stable cones

4. Put seed in Midpoint (-) for each pair of proto-jets separated by less than 2R and iterate for stable jets

5. Merging/Splitting

),P : jets(massive

,

jetT

jet

k

Ki

jeti

k

Kjet

Y

PPEE

Cross section calculable in pQCD

T

Arbitrary Rsep parameter still

present in pQCD calculation …

Comparison of JetClu and MidPoint for HERWIG MC

Differences between MidPoint and JetClu found to be due to “ratcheting”.

JetClu 0.5-2% higher ET jets

Comparison of the JetClu to MidPoint cone algorithms

W/Z/+jets) production: introduction

QCD-wise, are W/Z/ cross sections of interest?

Smaller subset of diagrams, different mix of initial partons Below is a set of LO diagrams for W/Z and W/Z/ + 1 jet

Inclusive distributions are not affected by jet finding uncertainties

More theoretical work is needed, e.g.: W inclusive: known at the level of NNLO W + 1 jet: known at the level of NLO W + 2, 3, 4 jets: known at the level of LO

(MCFM does proved W + 2 jets at NLO, it just isn’t an event generator)

W+jet(s) Production (JetClu R=0.4)• Background to top and Higgs Physics

• Stringent test of pQCD predictions

• Test Ground for ME+PS techniques (Special matching MLM, CKKW to avoid double counting on ME+PS interface)

Alpgen + HerwigLO large uncertainty

W + 1 parton +PS

W+ 2 partons

40% higher than the RUNI

result

QCD corrections cover this difference.

Inclusive (nb)

Run I (1.8 TeV):LO: 1.76NLO: 2.41NNLO: 2.50CDF I:2.380.24

Run II (1.96 TeV):LO: 1.94NLO: 2.64NNLO: 2.73CDF II: 2.640.18

W+ jet(s) Production (JetClu R=0.4)

1st jet in W + 1p

2nd jet in W + 2p

3rd 4th

ME+PS implementation tested using the Nth jet spectrum in W+Njet events.

Dijet Mass in W+2jets

Energy-scale

Diphoton Production• Testing NLO pQCD and resummation methods• Signature of interesting physics

– One of main Higgs discovery channels at LHC

Data: 2 isolated γs in central region, ET1,2 > 14, 13 GeV

•General agreement with NLO predictions

γ+heavy flavour production

• Probes heavy-quark PDFs• b/c-quark tag based on displaced vertices• Secondary vertex mass discriminates flavour

MC templates for b/c & (uds) used to extract b/c fraction in data

GeVET 25

γ+heavy flavour production

Good agreement with LO pQCD within still very large stat. errors

Validates quark flavour separation using secondary vertex mass

γ+b-quark

γ+c-quark

Summary Tevatron and CDF are performing well

Data samples already significantly exceed those of Run I On track for accumulating 4-8 fb-1 by 2009

Robust QCD program is underway Jets, photons, W+jets, heavy flavors

Jet energy scale is the dominant systematics – improvements on the wayHeavy flavor identification is working well

Verifying and tuning tools: NLO calculations, Monte Carlo generators, resummation techniques, combining ME with PS

NLO does well for hard aspectsLO + Pythia give reasonable description of W+n jets

We don’t see any discrepancies.