XXXIV International Symposium on Multiparticle Dynamics
description
Transcript of 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.