Electroweak Physics at the Tevatron Adam Lyon / Fermilab for the DØ and CDF collaborations 15 th...
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Transcript of Electroweak Physics at the Tevatron Adam Lyon / Fermilab for the DØ and CDF collaborations 15 th...
Electroweak Physics at the Tevatron
Adam Lyon / Fermilabfor the DØ and CDF collaborations
15th Topical Conference on Hadron Collider PhysicsJune 2004
Outline Importance Methodology Single Boson Measurements Summary & Outlook W/Z+and Diboson Results
up next
2A. Lyon (HCP2004)
Learning from Electroweak Physics mW , mt , and mH are
related Constrain Higgs mass
Test of standard model couplings (and see M. Kirby's talk)
Study higher order QCD Many uses in detector
studies and luminosity determination
3A. Lyon (HCP2004)
Uncertainties in mW
Run 1 uncertainties (from hep-ex/0311039)
Source CDF m CDF e DØ eW statistics 100 65 60Lepton scale 85 75 56Lepton resolution 20 25 19p T (W) 20 15 15Recoil model 35 37 35Selection bias 18 — 12Backgrounds 25 5 9
Uncorrelated Uncertainties (MeV/c 2)
Source DØPDF & luminosity 7 4Radiative corrections 12G
W 101110
Correlated Systematics (MeV/c 2)
CDF15
Uncorrelated uncertainties scale with luminosity Correlated systematics improve as theory improves Perhaps can reach 40 MeV/c2 per channel & exp with 2 fb-1
4A. Lyon (HCP2004)
Collider: Tevatron for Run II
Base goal is 4.4 fbBase goal is 4.4 fb-1-1
(Design is 8.5 fb(Design is 8.5 fb-1-1) by end of FY09) by end of FY09
5A. Lyon (HCP2004)
Detectors: CDFSaved from Run I
SolenoidCentral CalorimeterCentral Muon System
New/Improved in Run II8 layer Si tracking (|| < 2)Central Outer Tracker (|| < 1)Plug Calorimeter (1.0 < || < 3.6)Extended muon coverage to || < 1.5New and improved trigger and DAQ
Luminosity~400 pb-1 on tapeAnalyses shown here use 65 - 200 pb-1
6A. Lyon (HCP2004)
Detectors: DØ
Saved from Run IHermetic LAr CalorimeterMuon Toroid and proportional drift
tubes
New in Run II2T Superconducting SolenoidInner Tracker (Si Microstrips and
Scintillating Fiber tracker)Preshower detectorsUpgraded muon system (including
better shielding)New and improved trigger and DAQ
8A. Lyon (HCP2004)
W/Z Production and Event Topology
Use clean leptonic decays
W (energetic lepton + ET) Z0 (energetic opposite sign
leptons)
9A. Lyon (HCP2004)
W and Z events are extremely useful Measure cross sections
Calibration of detectors, luminosity measurements Lepton universality, W width
Measure W and Z properties (pT(W), pT(Z), y(Z), lepton angular distributions) Constrain PDFs, fit for couplings, look for new resonances
Measure W mT , lepton pT spectra Yields mW , W width
W/Z + Jets Backgrounds to Higgs and Top analyses
W/Z + , Dibosons Probe electroweak gauge structure Backgrounds to New Phenomena searches
10A. Lyon (HCP2004)
Analysis Methodologies Both DØ and CDF follow
similar strategies
Triggers: Calorimeter triggers for
electrons Track triggers for muons
Selection: W - a lepton and large
missing transverse energy Z - two opposite charge
leptons
Electron requirements: Isolated EM cluster Shower shape (CDF uses
shower max, DØ has finely segmented calorimeter)
Track pointing to calorimeter EM cluster
Muon requirements: Track matched to calorimeter
MIP trace and/or muon system track
Reject cosmics by timing and impact parameter
Track and calorimeter isolation
Measure identification efficiencies with Z events
Measure backgrounds with QCD Dijet events
Systematics Luminosity (~6%) PDF (use CTEQ6 and MRST) (1-
2%) Lepton ID (~1%) Backgrounds, E scale, Recoil
model, Detector Description
11A. Lyon (HCP2004)
Z ee Cross Section 2 EM objects with
pT > 25 GeV/c CDF: central + plug cal
(||< 2.8) DØ: central only
Small backgrounds QCD Z
pb2.159.32.254 5.54.5 lumsysstat
pb28992.275 lumsysstat
CDF:
DØ:
12A. Lyon (HCP2004)
Z mm Cross Section pT cut lowered to 15-20
GeV/c for muons DØ efficient for
mmm > 30 GeV/c2
DØ applies a Drell-Yan correction
Very small backgrounds:QCD (b-jets), Z
pb9.149.59.248 0.72.6 lumsysstat
pb2.269.80.58.261 lumsysstat CDF:
DØ:
13A. Lyon (HCP2004)
W e Cross Section Requirements:
1 electron with ET > 25 GeV
ET > 25 GeV(CDF plug analysis used 20 GeV)
CDF: central & plug DØ requires || < 1.1 Track match required Backgrounds
QCD, Z ee, W
14A. Lyon (HCP2004)
W e Cross Section
pb167142782 6156 lumsysstat
pb284128212844 lumsysstat
CDF (central):
DØ:
pb172167342874 lumsysstat CDF (plug):
15A. Lyon (HCP2004)
W m Cross Section Require m pT, ET > 20 GeV Backgrounds: QCD (b-jets),
Z mm, W
pb166162772 6460 lumsysstat
pb3221001283226 lumsysstat CDF:
DØ:
16A. Lyon (HCP2004)
Cross section comparisons
Experiment Channel # events Purity Lum. (pb-1) e * A || coverage
CDF W e 48045 94.0% 72 23.1% 2.8DØ W e 27370 95.7% 42 18.4% central
CDF W m 31722 90.0% 72 14.4% centralDØ W m 8302 88.0% 17 13.2% 1.6
CDF ee 4242 98.5% 72 22.7% 2.8
DØ ee 831* 98.3% 42 10.0% centralCDF mm 1785 98.5% 72 10.2% centralDØ mm 1139 98.9% 117 16.4% 1.8
dtLA
NNBr bkg
e
* Track match required
CDF and DØ are rather similar, except in angular coverageCDF uses plug calorimeter for far e coverageDØ uses forward muon system for far mcoverage
17A. Lyon (HCP2004)
)(
)(
)(
)(
)(
)(
)(
)(
W
W
Z
Z
Zpp
Wpp
Zpp
WppR
GG
GG
Use measured W and Z cross sections and R
Measured (CDF Preliminary)
Theory (NNLO, PDG)
LEP
Infer the W width (Preliminary)
sysstateR 16.018.086.10
sysstatR 17.027.010.11 m
024.0368.3)(/)( ZppWpp 0021.01093.0)( WBR
)%002.0366.3()(/)( GG ZZ
MeV 402071)( G W
18A. Lyon (HCP2004)
Analyses with Taus Reconstructing leptons
is challenging Must use hadronic decays
for ID (1 or 3 charged tracks plus 0's)
But these are hadronic jets; high QCD background
Look for tracks in a narrow 10° cone pointing toward a narrow calorimeter cluster
Require 30° cone isolation for tracks
Reconstruct 0's (in shower max for CDF)
Require effective mass of tracks and 0's to be < 1.8 GeV/c2 (m + resolution)
0n3)or 1(
19A. Lyon (HCP2004)
W (CDF Run II Preliminary) Start with track + ET trigger Require
ET > 25 GeV, ET > 25 GeV No other jets above 5 GeV
2345 candidates in 72 pb-1
Bkg = 612 61 events eID· A = 1.06 0.064 %
nb )16.021.007.062.2()( lumsysstatWBR
sysstateWBRWBR
egg 04.002.099.0/ )()(
20A. Lyon (HCP2004)
Z Look for 1-prong decays Look for other via e or m Understand tau ID Important for searches Proof of principle that
resonances are seen at the Tevatron
0Zm)or (e
0n
pb 152648242)/( * sysstatZpp CDF:
21A. Lyon (HCP2004)
Charge asymmetry in W e Goal is to improve understanding of PDFs using W charge asymmetry
Since u quarks on average carry more of the p momentum than d quarks, W + produced in ud W + are boosted along p W - produced in du W - are boosted along p
The e from the W decay carries information on the W direction, but
true W direction cannot be reconstructed due to unmeasured pz of Use the e
direction to measure AyW convoluted with V-A decay distribution
Results are sensitive to ratio of PDFs for u and d Do for low and high ET [NEW APPROACH]
(at higher e ET, e dir is closer to W dir; less cancellation with V-A) Sensitivity is best at high || where it is least constrained
dyWddyWd
dyWddyWdAyW /)(/)(
/)(/)(
22A. Lyon (HCP2004)
Charge asymmetry in W e Require
e ET and ET > 25 GeV 50 < mT < 100 GeV No other EM object
with ET > 25 GeV
In forward region, use "calorimeter seeded Si tracking" to utilize new forward Silicon This along with drift chamber
can determine charge within || < 2
Measure charge mis-id rate with data using Zs < ~1% within || < 1.5 < ~4% far forward
Backgrounds Z [MC], W [MC],
QCD [data]
23A. Lyon (HCP2004)
Drell-Yan Forward Backward Asymmetry
Interference of * and Z f = u, d, e
Leads to AFB in
Depends on uuZ, ddZ and
eeZ couplings Can probe couplings Near the Z resonance, AFB
is related to sin2 W
New interactions may modify the SM AFB prediction
Z*
f
f f ’
f ’+
f
f f ’
f ’ eeZpp */
)0(cos)0(cos
)0(cos)0(cos
dd
ddAFB
cos)cos1(cos 2 BAdd
q q
e-
e+
24A. Lyon (HCP2004)
Drell-Yan Forward Backward AsymmetryCDF Run II Preliminary Require 2 isolated
electrons with pT > 20 GeV/c
5211 candidates in 72 pb-1
No asymmetry seen in dijet background
Use Collins-Soper reference frame for measuring electron scattering angle Reduces uncertainty in
scattering angle due to pT of incoming partons
25A. Lyon (HCP2004)
Drell-Yan Forward Backward AsymmetryCDF Run II Preliminary Fit for weak mixing angle
Fits for couplings are in good agreement with world averages
No evidence of new interactions above the Z pole
0.14/71.12ndf/
0020.00046.02238.0sin2
2
sysstatW
26A. Lyon (HCP2004)
High Mass Drell-Yan Spectrum Sensitive to new physics
New gauge bosons (e.g. Z'), extra dimensionsRun 1 limits surpassed and new models explored
27A. Lyon (HCP2004)
Summary Current preliminary results consistent with
SM
(Theory lines NNLO from Hamberg, van Neerven, Matsuura)
28A. Lyon (HCP2004)
Outlook 1.96 TeV cross sections nearing publication Tevatron electroweak working group will make
combinations Stay tuned for further analyses; > 300 pb-1 on
tape Preliminary W mass measurements soon