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Electroweak Measurements at the Tevatron
Cairo International Conference on HEPJanuary 9, 2001
Results from D0 and CDF’s Run IProspects for the 1st 2 fb-1 of Run II
Tom DiehlFermi National Accelerator Laboratory
Batavia, Illinois
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Acknowledgements
Thanks as always to D0 and CDF collaborations. Some material in this talk comes from previous presentations
by Uli Heintz, Meena Narain, Georg Steinbruck, John Butler, Natalia
Sotnikova, and Darien Wood.
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Electroweak Measurements at the Tevatron
IntroductionW and Z Boson Properties
General Features of Production Inclusive Cross SectionW Boson Width & MassTrilinear Gauge Boson Couplings
Top Quark PropertiesGeneral Features Top Pair Production Cross Section & Production DynamicsTop Quark MassBranching Ratios & Rare DecaysElectroweak Top Quark Production
Standard Model Higgs Boson M(top), M(W), and M(Higgs)Standard Model Higgs Boson Search
Run 1 Results and
Prospects for Run II
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DD The Run 1 D0 Detector
Electroweak analyses use all of the detector
capability
Non-magnetic central tracking and no silicon detector
Calorimeter Hermetic
x x
EM)=15%/E1/2
had)=50%/E1/2
Large muon toroids
pp
p in GeV/c
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Run 1 CDF Detector
Calorimeter:
EM)=15%/E1/2
had)=50%/E1/2
Magnetic central tracking w/ large radius & a silicon detector for vertices
Muon detector provides ID. Momentum measurement from central tracker
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D0 Upgrade
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CDF Upgrade
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W/Z Physics
TopicsGeneral Features of Production Inclusive Cross SectionW Boson Width W Boson Mass PreliminariesW Boson MassTrilinear Gauge Boson Couplings
W Bosons Detected:
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General Features of W and Z Production
pq q
pW(Z)
l
(l)
qq-
%9.69
%0.20
%4.30
, 8.5%6
e%6.10
or ,,eeZ
or ,,eW
nb 2.0
nb 2
XXZpp
XXWpp
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Luminosity: L(D0) = 1.062 x L(CDF)D0 uses world avg. (pp)inel, CDF uses CDF measurement
• B(Wl ) ~ 2.2 nb
• B(Zl+ l-) ~ 0.22 nb
•Cross section measurement uncertainty:
Stat Sys ~ 2%,
Luminosity error ~ 4%
•Theory prediction uncertainty:
~ 3%, NNLO, O(s2)
Dominated by PDF’s at NLO…
(need NNLO)
Inclusive Cross Section
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W Boson Width
Indirect Method Direct Method (CDF) Model independent Study high-end tail of MT(l).
(SM:2.093 0.002)Form ratio:
LEP
)(
)(
)(
)(
)(
)(
)(
)(
W
lW
llZ
Z
Z
W
llZBRXZpp
lWBRXWppR
PerturbativeQCD
SM E
W)(047.0)(021.0171.2
)(
sysstat
GeVW
CDF+D0 combined
)(075.0)(100.0055.2
)(
sysstat
GeVW
(LEP combined:2.12 0.11)
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W Boson Mass Preliminaries
Input from theorist’s calculations tuned by our measurements.
PT(W) Ladinsky-Yuan
W Spin Orientation
E. Mirkes. (1992)
PDF’s
W Boson Production
& Decay Model
PT(Z) spectrum
*cos
)(
ddp
Wd
T
W DecayAsymmetry
A sample of our published results:
D0 very recent
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W Boson Mass
W Mass measurements from MT(W) @ CDF+D0 PT(lepton) @ D0 ET() @ D0
Using electron channels @ CDF+D0 muon channels @ CDF
CDF (e+) combined (2000)
D0 Run 1 (e) Result (2000)
2GeV/c 079.0433.80)( WM
2GeV/c 091.0482.80)( WM
0)LEP(12/200D0CDF UA2
@ GeV/c 037.0436.80)( 2
WM
Uncertainty example (CDF electrons) Statistical: 65 MeV/c2
Systematic: 92 MeV/c2
ET Scale: 75 MeV/c2
Detector resolution: 25 MeV/c2 PDF’s: 15 MeV/c2
PT(W): 15 MeV/c2
Recoil Model: 37 MeV/c2
Backgrounds: 5 MeV/c2
exp.)(per MeV/c 30)(: 2 2-1 WMfb
D0 CC electron channel
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Gauge Boson Self-Interactions
We study gauge boson couplings byinvestigating properties of vector boson pair productionW, WW, WZ, Zin various final states
t-channel u-channel
s-channel
Self-interactions are a direct consequence of the non-Abelian SU(2)L x U(1)Y gauge symmetry.
Trilinear Coupling Diagrams are involved in Vector Boson Pair Production.
SM makes specific predictions for the strength of the couplings.
WW and WWZ Couplings related to the static W properties
QeW = e () / M2
WW = e/ 2MW
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WW and WWZ Couplings In Run 1:
Established the EW coupling of W to and W to Z. The W and WW processes were observed. Candidate WZ events observed.
Anomalous Coupling Limits W, WW, and combined WZ results from D0 (equal +Z couplings):
Another set of relations among couplings
)( 6.12.10)( 5.61.5 CDFpbXWWpp
CLat %95 )0( 18.018.0
0)( 31.025.0
In 2 fb-1:
2000 e+ events per exp. Observe “radiation zero” Sensitivity to anomalous couplings ~2-3X better.
e+
34.034.0
10.009.0
08.0
00.0
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ZZ, Z, and ZZZ Couplings
Z+photon final state Tests ZZand Z
couplings ZZand Z = 0 in SM
(no s-channel diagrams)
14 pb-1 & ee + pb-1
05.0||
36.0||
40
30
Z
Z
h
h
PRD 4/1/98
At 95% CL
Run 1 Limits on coupling parameters
In 2 fb-1 we expect ~600 Z events per experiment sensitivity to limits about 5X
smaller Our first ZZZ limits (CDF
observed ZZ candidate with 4 muons in 1995)
(Z coupling limits similar)
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Top Physics
Pair production mechanisms provide cross section which depends on top mass.
Top heavier than m(b)+m(W) decays primarily to Wb.
ttgg ttqq Topics
General Features Top Pair Production Cross Section & Production DynamicsTop Quark MassBranching Ratios & Rare DecaysElectroweak Top Quark Production
The Tevatron is the only
place where we can produce top.
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Top Physics: General Features
bbbbb
qqqql-l-W-
t
bbbbb
qql+qql+W+
t
p
pt
b
W
W b
t
l
“Lepton+Jets Event”
5% eee
15% jetse
15% jets
21% X tau
44% hadronic All
All hadronic and tau+X have big backgrounds
Lepton + jets, Dilepton are our best measured channels
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Run 1 result at 1.8 TeV
Run 2 Tevatron beam energy is
increased from 1.8 TeV to 2.0 TeV => increase in (ttbar) of 40%.
Uncertainties on signal and backgrounds scale by N-1/2 . Uncertainty on luminosity doesn’t (~5% in Run 1).
Top-AntiTop Production
Event Yields In Run 2a (per experiment)
Expect @D0 (similar @ CDF).
Run 1 Results Run II Prospects
*1.7
1.4-
1.77.1
(CDF) pb 6.7
)0D( pb 9.5
Xtt
1:12 600 btags 2
4jets/Lepton
1:3 1,400 btag
jets/3Lepton
1:2 1,800 4jetsLepton
1:5 200 Dilepton
Bkgd:Signal fb 2 Channel -1
* unpublished update of 1998 CDF Pub.
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Properties of the top events (D0+CDF)
Top Quark Production Dynamics
Distributions as expected from SM ttbar production
massinvariant tt
spectrum )(pT t
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Top Quark Mass in Run I
4/1)1995(
)2000(
T
T
m
m
%4T
T
m
m
AverageTevatron
2.55.173 topmCDF: Lepton + Jets
D0: Lepton + Jets
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Top Quark Mass Uncertainties
Uncertainties in Run I Lepton+jets mass measurement @ D0 (CDF)
Total Systematic: 5.5 (4.9) GeV/c2
Jet energy scale: 4.0 (4.4) GeV/c2
Monte Carlo Top Modeling: 3.5 (2.3) GeV/c2
Principally from uncertainty in Initial and final state radiation
Background model (Vecbos flavors) 2.0 (1.3) GeV/c2
Methods 1.2 (0) GeV/c2
Statistical [~13 GeV/c2 per event]: 5.6 (4.8) GeV/c2
How that’s improved in Run II (2fb-1)
Conservative Estimates Systematic: 2.5 GeV/c2
Jet Energy Scale: 2.2 GeV/c2
Recalibrate jet energy scale with +jet, Z+jet, Z->b-bbar, W->jj in top events. There is room for improvement here.
M. C. Signal Model: 1.0 GeV/c2
Constrain top production w/ data Background Model: 0.5 GeV/c2
Statistical: 1.0-1.3 GeV/c2
Reduce combinatorics because of double tags
Total ~ 2.8 GeV/c2
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Top Branching Ratios and Rare Decays
Within the Standard Model:
Using indirect estimates of |Vtd| and |Vts|, unitarity, assuming 3 gens: 0.99989 < |Vtb|<0.9993 @ 90% CL
%cZ)B(tuZ)B(t
%.cB(tuB(t
33
23))
0///
HZgWbt
d,s,b)(qWqt
222
2
||||||
||
)(
)(
tbtstd
tb
VVV
V
qWtB
bWtBR
c.l.) 90% (@ 78.0||
97.0||
94.016.012.0
31.024.0
tb
tb
V
V
R
CDF Result (new) uses ratios of tags in lepton+jets and dilepton events. 0:1:double:2 tags and
assuming 3 gens.
Run 2a (2fb-1): Vtb|~2%
(95% CL)
CDF FCNC Search S.M. Pred. O(10-10)
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Top Quark Decay Vertex
Top Quark is unique in that it usually decays before it hadronizes, V-A implies W+ is l.h. (h=-1) or long. (h=0) i.e. charged lepton tends to be emitted in direction
opposite to W line-of-flight.
S.M. f long ~ 0.7
longWtWleft fMMMf 1)/(2 222
13.037.091.0 :CDF longf
Kane, Ladinsky, Yuan PRD 1992
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Measure angle between the off-diagonal basis and the lepton flight direction in rest frame of the top -, +
Spin correlation correlation in + vs - space. (SM: 0.9)
D0 Measured
Top Quark Decay Correlation
Spin Configurations
Optimal spin quantization axis Determined once the velocity and
scattering angle is known Only like-spin combinations are
produced in this optimized basis G. Mahlon and S. Parke, PLB
411, 173 (1997)
q
t
tq
Spin quant. axis:
4
coscos1
)(cos)(cos
1 2
dd
d
t l+
b
Rest frame of top
> -0.25 @ 68% CL> -0.25 @ 68% CL
Fermilab-Pub-00/046-E
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Single Top Production
Direct access to W tb vertex
Measure top quark width and |Vtb| Measure of CKM element
without any assumptions on number of generations
(qq tb) (t W+b) |Vtb|2
Theoretical predictions: Smith+Willenbrock, Stelzer et al. For M(top) = 175 GeV
pb 24.070.1)(
pb 10.070.0)(
channelt
channels
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Single Top Results: Run 1 vs. Run 2
D0 Run 1 result at 1.8 TeV Signature is e(jj events
where one jet is b-tagged with a muon. 90 pb-1. Acceptances:
Bkgds (W+jets, QCD, top) is 15 events. Expected signal < 1
Observe 17 events. @95%CL:
)( pb 58
)( pb 39
channeltXtqb
channelsXtb
0.010.08 0.020.17
0.010.11 0.020.26
muon electron :Channel
tqb
tb
Accepted for pub. in PRD
CDF Preliminary < 13.5 pb at 95% CL
Run 2a (2 fb-1) will provide a 20% measurement of tb giving Vtb| of 14% at both D0 and CDF.
CDF’s has better Run I b-tagging (SVX):
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Top Quark Mass and W Boson Mass
W boson mass + top mass Constrains Higgs mass
Tevatron Averages
M(top)=174.3+-5.1 GeV
M(W)=80.454+-0.063
HW
2TW
ln mm
mm
Run 1
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Search for SM Higgs in Run II
(H+X) at Tevatron (2 TeV) Branching Fractions vs. M(Higgs)
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Search for SM Higgs in Run II
For M(Higgs)<135 GeV/c2
depends most on b-tagging efficiency and background rejection
a few signal events per fb-1. Background is W+jets S/B ~ 1/10
) (including Z
bbH
bbWHpp
leptons 4
ZZHpp
WWHpp
Best Options for finding Higgs depend on M(Higgs)
For M(Higgs)>135 GeV/c2
Backgrounds are more prosaic forms of diboson production and t-tbar.
longitudinally polarized W and Z provides some handles on angular distributions
S/B depends on M(Higgs) Varies from 3/30 to 1/4
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Search for SM Higgs in Run II
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Top Quark Mass and W Boson Mass
W boson mass + top mass Constrains Higgs mass
M(top)=3.0 GeV
M(W)=40 MeVRun 2
Uncertainties shown are slightly bigger than what we think we can do in 2 fb-1.
At Run I central values of M(W) & M(top)
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Conclusions
The D0 and CDF p-pbar collider experiments have a rich set of preliminary and published results including
Vector Boson Properties W mass, W width, Trilinear gauge boson couplings, and W and Z
production properties. 3.2 million W to and e expected (per experiment) in 2 fb-1. M(W) ~ 30 MeV/c2 per experiment in first 2 fb-1.
Top Quark Properties Top Pair Production Cross Section & Production Dynamics, Top Quark
Mass, Branching ratios and Rare Decays. M(top) ~ 2.8 GeV/c2 per experiment in first 2 fb-1.
SM Higgs Boson Measurements of M(W) and M(top) hint it is light. We restrict the allowed range and find it depending on it’s mass.
