Transcript Jet Physics at 2 TeV

W/  Jets at T evatron
Alberto Cruz
On behalf of the
CDF collaboration
XXXIV International Symposium on Multiparticle Dynamics
Fermilab
Chicago

Booster
Florida
CDF
DØ
Tevatron
p source
Main Injector
Tevatron
• proton-antiproton collisions
s  1.96 TeV (Run I  1.8 TeV)
•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)
Long Term Luminosity Projection
Base Goal -> 4.4 fb-1 -1 -1
RUN
(2001~2005)
~1fb
RUNIIa
I (1992-95)
~0.1fb
(by end FY2009)
Design
-> 8.5
fb-1
Increasing Luminosity:
Tevatron Performance
Recent Luminosity Record of
10.3x1031 sec-1cm-2 (July 16, 2004)
CDF Run II Data
CDF Efficiency > 80%
CDF -> ~450 pb-1 on tape
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…)
In proton-antiproton
collisions
weus
cantooccasionally
The
Jet Algorithm
Allows
“see” the
have a “hard” parton-parton scattering resulting in
partons (or at least their fingerprints) in the
large transverse momentum outgoing partons.
final hadronic state.
“Hard” Scattering
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
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
T
2.
Draw a cone of radius R around each
seed and form “proto-jet”
E
jet

EK,

k
Pi
jet

(massive jets : PTjet ,Y
Pi K

k
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
Cross section calculable in pQCD
Arbitrary Rsep parameter still
present in pQCD calculation …
Comparison of the JetClu to MidPoint cone algorithms
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
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:
 W + 1 jet:
 W + 2, 3, 4 jets:
known at the level of NNLO
known at the level of NLO
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
Inclusive s (nb)
W + 1 parton +PS
Run I (1.8 TeV):
LO:
1.76
W+
2
partons
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
• Stringent test of pQCD predictions
• Test Ground for ME+PS techniques
(Special matching  MLM, CKKW to avoid
corrections
cover
doubleQCD
counting
on ME+PS interface)
this difference.
40% higher
than the RUNI
result
Alpgen + Herwig
LO  large uncertainty
W+ jet(s) Production (JetClu R=0.4)
ME+PS implementation tested using the
Nth jet spectrum in W+Njet events.
Dijet Mass in W+2jets
1st jet in W + 1p
2nd jet in W + 2p
Energy-scale
4th
3rd
Diphoton Production
•General agreement with NLO predictions
Testing
NLO
pQCD
and
Data: 2•isolated
γs in
central
region,
ET1,2 > 14, 13 GeV
resummation methods
• Signature of interesting physics
– One of main Higgs discovery
channels at LHC
γ+heavy flavour production
• Probes heavy-quark
PDFs
• b/c-quark tag based on displaced vertices
• Secondary vertex mass discriminates flavour
ET  25 GeV
MC templates for b/c & (uds) used to extract b/c fraction in data
γ+heavy flavour production
γ+b-quark
γ+c-quark
Good agreement with LO pQCD
within still very large stat. errors
Validates quark flavour separation
using secondary vertex mass
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.