# Presentation: 511240

## XXXIV International Symposium on Multiparticle Dynamics

## Fermilab

## 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)

- Increasing Luminosity:

- RUN I (1992-95) ~0.1fb-1

- RUN IIa (2001~2005) ~1fb-1

## Tevatron Performance

**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 time
- Rest coming from very careful operation
- of detector’s HV due to machine losses
-   (...to preserve silicon & trackers...)

- CDF ->   ~450 pb-1 on tape

## 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

- Define a list of seeds  using CAL towers with E   > 1 GeV
- Draw a cone of radius R around each seed and form  “proto-jet”
- Draw new cones around “proto-jets” and iterate until stable cones
- Put seed in  Midpoint (-) for each pair of proto-jets    **separated by less than 2R** and iterate for stable jets
- Merging/Splitting

- Cross section calculable in  pQCD

- T

- Arbitrary Rsep parameter still
- present in pQCD calculation ...

## Comparison of the JetClu to MidPoint cone algorithms 

- 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 + Herwig
- LO  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:  ****	****1.76**
**NLO:****	****2.41**
**NNLO:****	****2.50**
**CDF I:****	****2.38********0.24**
**Run II (1.96 TeV):**
**LO:  ****	****1.94**
**NLO:****	****2.64**
**NNLO:****	****2.73**
**CDF II:  ****	****2.64********0.18**

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

**1****st **** jet in W + 1p**

**2****nd**** jet in W + 2p**

**3****rd**

**4****th**** **

- 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

## γ+heavy flavour production

- 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 way
- Heavy 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 aspects
- LO + Pythia give reasonable description of W+n jets
- We don’t see any discrepancies.