Les Arcs, Moriond QCD, March 22-29, 2003
Tevatron Results on W and Z Boson Production
Tommaso Dorigo (Università di Padova)
• Introduction to Run II
• New W/Z cross section results
• Cross section ratios and ΓW
• Dielectron asymmetry
• WW production
• Concluding remarks
Les Arcs, Moriond QCD, March 22-29, 2003
Introduction to Run II at the Tevatron
√
The Tevatron runs at s = 1.96 T eV since
2001. So far Lmax = 4.0 × 1031 cm−2 s−1 .
Total delivered luminosity: 180 pb−1 .
Expect to collect ≥ 200 pb−1 in 2003.
The recycler will be integrated in data
taking this summer. It will bring luminosity up by a factor 2. Other improvements are in progress.
Tommaso Dorigo, Padova University
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Les Arcs, Moriond QCD, March 22-29, 2003
Tommaso Dorigo, Padova University
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Les Arcs, Moriond QCD, March 22-29, 2003
The new D0 and CDF II
Since Run I both detectors have undergone massive improvements:
⋆ CDF upgraded its silicon tracking (now 1+5+2 layers), extended
muon coverage to |η| < 1.5, and
built a brand new plug calorimeter
(→ e ID up to |η| < 2).
⋆ D0 inserted an inner silicon tracker
and a fiber tracker into a 2T axial
field magnet. New mini-drift tubes
for forward muons have been added;
a new preshower improves electron
triggering at low PT .
Tommaso Dorigo, Padova University
4
Les Arcs, Moriond QCD, March 22-29, 2003
W and Z production at the Tevatron
′
W and Z bosons are produced at the Tevatron through q q̄ ( ) annihilation.
The cleanest signatures involve high-PT electrons and muons: W → eν or → µν,
Z → e+ e− or → µ+ µ− ; the W → τ ν decay can also be observed with clarity
although backgrounds are larger.
Other decays are hard to use for precise EW measurements.
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1
0
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0
0
1
0
1
00
1
1
0
1
E
Electron
⇐ W → eν
PTW
Muon
PT
PTZ
PT
Neutrino
Muon
Underlying event
Hadronic recoil
11
00
00
11
00
11
00
11
T
11
00
Z→
µ+ µ− ⇒
Underlying event
PT
Hadronic recoil
E
U
Tommaso Dorigo, Padova University
10
0
01
1
0
1
1
0
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U
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Les Arcs, Moriond QCD, March 22-29, 2003
New σW measurements - 1: electrons
W
! e
8
Cross Setion Analysis Blessing, EWK Meeting, 13 Feb 2003
D0 and CDF presented 1.96 T eV cross sections last summer (ICHEP 02).
Bakground
FOR BLESSING:
CDF updated its result
adding data collected till Jan ’03
(L = 72.0 ± 4.3 pb−1 ).
Background sources:
Soures of the bakground
number
out of ±672
38628 andidate
• NQCD = 1344±82
(stat.)
(syst.);events
QCD proesses
1344 82stat 672sy st events
W ! ( ! e ) 768 22
• ZN!
22 (MC);
We→τ
+ e ν = 768 ±
344 17
• NZ→e+ e− = 344 ± 17 (MC);
(from MC study)
(from MC study)
Number of the QCD bakground events was estimated
from
⋆ Start with central electron
trigger (ET > 18 GeV );
2
1.8
> 10 GeV /c;
⋆ quality cuts on EHAD /EEM ,
Eiso , strip χ2 , E/P .
⇒ 38, 628 W candidates;
A = 24.62 ± 0.04(MC)±0.69(syst)%.
Tommaso Dorigo, Padova University
Isolation Fraction
⋆
vs.
MET
plot,
assuming
that
isolation
and
The QCD contamination is obtained
NC E
NB =N
/
by extrapolation Ninbg =
the
T vs A Ie plot:
/T > 25 GeV ;
⋆ ET > 25 GeV , E
PTe
Iso
MET are unorrelated.
Isolation vs. Missing Transverse Energy
A
C
1.6
CDF Run II Preliminary
∫ L ~ 70 pb
-1
1.4
QCD Background
C
1.2
1
=
B
A
0.8
0.6
W → e ν Candidates
0.4
0.2
B
0
0
10
20
30
40
50
60
70
80
90
100
E T (GeV)
6
Les Arcs, Moriond QCD, March 22-29, 2003
⋆ Material (0.29%)
Entries
93870
8000
7000
6000
5000
Total: 0.69%.
Other factors:
ǫID = 84.2 ± 0.7 ± 0.2%;
ǫZv = 95.1 ± 0.1 ± 0.5%;
ǫtrig = 96.6 ± 0.1%.
-1
E T Cut
DATA
Sum
W → eν MC
Z→ ee MC
W → τ ν MC
QCD
CDF Run II Preliminary, 72pb
Events per 2GeV/c 2
⋆ PDFs (0.58%)
CDF Run II Preliminary, 72pb
Events per 2GeV
Acceptance systematics
are dominated by:
3000
Entries
-1
38628
DATA
Sum
W → eν MC
Z→ ee MC
W → τν MC
QCD
2500
2000
1500
4000
3000
1000
2000
500
1000
0
0
10 20 30 40 50 60 70 80 90 100
E T, GeV
0
40
60
80
100
2
M T, GeV/c
120
140
Result:
σW B(W → eν) = 2.64 ± 0.01 (stat.) ±0.09 (syst.) ±0.16(lum.) nb.
ICHEP 02: 2.60 ± 0.07 ± 0.11 ± 0.26 nb (CDF), 2.67 ± 0.06 ± 0.33 ± 0.27 nb (D0);
Prediction by W.J.Stirling et al. (NNLO): 2.73 pb.
Tommaso Dorigo, Padova University
7
Les Arcs, Moriond QCD, March 22-29, 2003
New σW measurements - 2: muons
CDF updated its result for σW B(W → µν) with L = 72.0 ± 4.3 pb−1 .
⋆ Use central (|η| < 0.6) muon triggers
⋆ PT > 20 GeV /c;
⋆ EIso (∆R < 0.4) < 0.1 × PT ;
⋆ other fiduciality and matching cuts;
⋆ remove cosmics, Z → µµ;
/T > 20 GeV , 30 < MT < 120 GeV ;
⋆ E
Events per 3GeV/c 2
CDF Run II Preliminary, 72pb
2200
2000
1800
1600
1400
Entries
DATA
Sum
W →µν MC
Z → µµ MC
W →τ ν MC
QCD
Cosmic
-1
21599
1200
1000
800
600
400
⇒ 21,599 W → µν candidates
Tommaso Dorigo, Padova University
200
0
0
20
40
60
80
100
120
2
M T , GeV/c
8
Les Arcs, Moriond QCD, March 22-29, 2003
Tommaso Dorigo, Padova University
9
Les Arcs, Moriond QCD, March 22-29, 2003
Amount
Cosmics
Rev. ∆z cut
1.28 ± 0.08 ± 0.90%
QCD
1.03 ± 0.06 ± 0.26%
Z → µµ
/T vs EIso
E
MC
5.31 ± 0.04 ± 0.20%
W → τν
MC
3.20 ± 0.14 ± 0.02%
Total
CDF Run II Preliminary, 72pb
Events per 3GeV
Backgrounds:
Source Method
5000
W →µν MC
3000
Acceptance: A = 14.8 ± 5 (stat) ±0.51 (syst.)%;
2000
1000
0
-60
-40
-20
0
20
40
60
Recoil E , GeV
Events per 3GeV
CDF Run II Preliminary, 72pb
Entries
3500
(CDF ICHEP 02: 2.70 ± 0.04 ± 0.19 ± 0.27 nb;
D0 ICHEP 02: 2.67 ± 0.06 ± 0.33 ± 0.27 nb).
Tommaso Dorigo, Padova University
-1
26768
DATA
Sum
W → µν MC
Z → µµ MC
W → τ ν MC
QCD
Cosmic
3000
2500
Result:
σW B(µν) = 2.64 ± 0.02 (stat.) ±0.12 (syst.)
±0.16 (lum) nb
21599
Data
4000
10.08 ± 0.18 ± 0.96%
systematics mainly due to PDF (0.41%), recoil scale
(0.23%);
PDF contribution obtained by varying them to span
±1σ of dσZ /dy measured in Run I;
Recoil scale effect studied by shifting scale to get
better agreement with MC and recomputing A.
Entries
-1
2000
1500
1000
500
0
0
20
40
60
80
100
120
E T, GeV
10
Les Arcs, Moriond QCD, March 22-29, 2003
σW using τ leptons (CDF)
/T > 25 GeV L1 trigger, τ ID at L3.
Collect W → τ ν signal with E
1. Monojet events: ETj > 25 GeV , with
one PT > 4.5 GeV track in 10◦ cone, no
tracks in 10◦ − 30◦ ;
2. No other jet with ET > 5 GeV ;
1400
-1
W → τ ν : number of tracks, associated with the τ candidate
2345 events
1200
Data
W→ τν
W→ µν
W→eν
Z→ τ τ
QCD
1000
/T > 25 GeV ;
3. E
800
4. tight electrons removed;
600
⇒ 2341 evts (611 ± 56 from bgr sources).
Result:
σW B(τ ν) = 2.62 ± 0.07 ± 0.21 ± 0.16 nb.
∫ L = 72 pb
CDF Run II Preliminary,
400
200
0
0
1
2
3
4
5
6
7
8
9
10
number of tracks
Using W → eν signal removed at step (4), extract:
R = B(τ ν)/B(eν) = 0.99 ± 0.03 (stat.) ±0.04 (syst).
Tommaso Dorigo, Padova University
11
Les Arcs, Moriond QCD, March 22-29, 2003
for blessing
Z cross section:
- electrons
(CDF)
Data1With
Corretions
Data selection:
10
⋆ Two central electrons ET > 25 GeV ,
PT > 10 GeV ;
10
3
for blessin
Data With Corretions
CDF Run II Preliminary
∫ L dt = 70.7 pb
-1
Z → ee DATA
2
Z → ee MC
⋆ at least one must pass tight cuts;
10
⋆ 66 < Mee < 116 GeV , opposite charge.
1
⇒ 1830 evts / 10 ± 5 from backgrounds.
0
0.5
2
2.5
3
3.5
4
4.5
Other ingredients:
66< Mee <116
GeV/1 2 1.5
: Nand
5 43(stat.
Z OS (SS ) = 1830(22)
E
/ P
corr
250
⋆ Z efficiency: 87.2 ± 0.9%, ǫZv = 95.1 ± 0.5%;
150
<M <
Evts/ GeV/c
2
⋆ Acceptance: 11.49±0.62% (syst. mainly from
material
&eePDF116
uncertainties);
66
GeV/ 2 : Nand
(
Z
OS SS ) = 1830(22) 43(
Result:
σZ B(Z → ee) = 267.0 ± 6.3 ± 15.2 ± 16.0 pb.
(theory: 250.5 pb (Stirling, NNLO)).
Opposite Sign
Z → ee DATA
200
Z → ee MC
stat.
)
CDF Run II Preliminary
∫ L dt = 70.7 pb
100
-1
50
0
40
60
80
100
120
2
140
160
180
M ee (GeV/c )
Tommaso Dorigo, Padova University
corr
12
200
)
Les Arcs, Moriond QCD, March 22-29, 2003
Tommaso Dorigo, Padova University
13
Z cross section: 2 - muons
Both CDF and D0 have updated σZ B(Z → µµ).
Events / 3 GeV
Les Arcs, Moriond QCD, March 22-29, 2003
160
D0 Run II Preliminary
140
120
Data
100
MC
80
D0: L = 31.8 pb
−1
(Sept. 02 to Jan. 03).
60
40
• two good muons, ≥ 1 isolated;
20
• PT > 15 GeV /c, ∆Rµµ > 2.0,
EIso(0.5) < 2.5 GeV ;
Result:
σZ B(µµ) = 263.8 ± 6.8 ± 17.3 ± 26.4 pb
(ICHEP 02, electrons: 266 ± 20 ± 20 ± 21 pb)
50
100
150
200
250
CDF Run II Preliminary, 72pb
220
200
Entries
-1
1631
Data
Z→ µµ MC
180
160
140
120
100
CDF: 2 central µ, PT > 20 GeV /c;
⇒ 1632 candidates → NZ = 1618 ± 11.
Result: σZ B(µµ) = 246 ± 6 ± 12 ± 15 pb
80
60
40
20
0
Tommaso Dorigo, Padova University
300
M µ+ µ- (GeV)
Events per 1GeV/c 2
⇒ 1585 candidates, 1.5 ± 1.0% backgrounds;
Total acceptance: 0.163 ± 0.011.
0
0
70
75
80
85
90
95 100 105 110 115
M µµ, GeV/c 2
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Les Arcs, Moriond QCD, March 22-29, 2003
A global view of W/Z cross sections
What do we expect to learn from these
measurements ?
DØ and CDF Run2 Preliminary
_
⋆ Can use W yields to monitor acquired luminosity during the run
and normalize other measurements
involving electrons
⋆ Ratios of cross sections tell us more
Tommaso Dorigo, Padova University
σW, Z × B (pb)
⋆ W/Z cross section measurements
require critical understanding of
detector and DAQ. Good to do it
right from the start!
pp → W+X → lν+X
10 3
_
pp → Z+X → ll+X
10 2
DØ(e) Run2
DØ(µ) Run2
CDF(e) Run2
CDF(µ) Run2
DØ(e)
DØ(µ)
CDF(e)
CDF(µ)
UA1
UA2
1
Center of Mass Energy (TeV)
15
Les Arcs, Moriond QCD, March 22-29, 2003
σW /σZ ratio and W width (CDF)
ΓeW
Γµ
W
2006
CDF II (e+ µ )
2004
2002
2000
World
Average
CDF Run II Preliminary
∫
L dt = 72.0 pb
-1
D0 I (e+ µ )
1998
Year
Using the new W and Z cross section measurements CDF finds:
Re = σW B(W → eν)/σZ B(Z → ee) =
9.88 ± 0.24 (stat.)±0.47 (syst.),
Rµ = 10.69 ± 0.27 (stat.) ±0.33 (syst.).
(NNLO, Stirling: Rth = 10.92).
From WA values of W/Z widths and
σW /σZ = 3.361 ± 0.024 (Stirling, p.c.) we
σ Γ e ΓZ
can then extract ΓW = σWZ ΓW
:
R
Z
Standard Model
1996
CDF I (e)
1994
ee
= 2.29 ± 0.06 (stat.)±0.10 (syst.) GeV ,
= 2.11 ± 0.05 (stat.)±0.07 (syst.) GeV
(PDG: 2.118 ± 0.042 GeV ).
The combined result is:
ΓW = 2.146 ± 0.078 GeV
Tommaso Dorigo, Padova University
1992
UA2(e)
UA1(e+ µ )
1990
1988
1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8
Γ (W)
16
Les Arcs, Moriond QCD, March 22-29, 2003
AF B of electron pairs
Mee_CCs_MC
Mee_CCs_DT
Entries
AFB(QCD)
CDF used the new Run II data (5438 events) to
measure AF B of e+ e− pairs from pp̄ → Z(γ ∗ )X →
e+ e− X, with 40 < Mee < 600 GeV .
0.2
CDF Run II Preliminary
QCD bgr for CP combs
0.15
χ /ndf = 18.4/15
is obtained from high-Eiso
0.1
0.05
electrons.
-0
2
-0.05
-0.1
-0.15
-0.2
40 60
2
100
10
200 300
600
M ee (GeV)
Electron
scale/resolution calibrated in data and MC
in central and plug
regions
450
400
350
300
250
200
150
100
50
0
CDF Run II Preliminary
80
90
100
110
120
130
CC Invariant Mass (GeV)
87.77
74.69
13.25
18.89
Mee_CCs_DT
3
2.5
2
1.5
1
0.5
0
40
CDF Run II Preliminary
500
248
36
Mean
RMS
8
7 Points: data
6 Yellow: Simulation
5
4
3
2
1
0
40 50 60 70 80 90 100 110 120
CC Invariant Mass (M ee) Same Sign
50
60
70
80
Entries
-212
Mean
68.52
RMS
19.93
90 100 110 120
CC Invariant Mass (M ee ) Same Sign (MC subtracted)
400
300
200
100
0
80
90
100
110
120
CP Invariant Mass (GeV)
Tommaso Dorigo, Padova University
130
For CC pairs, same-sign electrons → NQCD = 21.5 ± 5.9
events; CP: NQCD = 128 ± 65.
17
⋆ The new AF B measurement is corrected for
acceptance, efficiency, resolution, and QED
radiation.
AFB
Les Arcs, Moriond QCD, March 22-29, 2003
1
0.8
0.6
CDF Run II Preliminary
∫ L=72pb
-1
0.4
⋆ Results agree with Pythia predictions.
0.2
Z/γ * → e+e- MC
10
10
3
Points: Data
Yellow:Simulation
2
-0.6
40
Total
60
2
100
10
200
300
600
M ee (GeV)
CDF Run II
Preliminary
∫
1
10
Statistical
-0.4
Green: Backgrounds
10
10
band includes
several theoretical
calculations
-0.2
L=72pb
AFB
Events/ 2 GeV
0
0.4
CDF Run II Preliminary
∫ L=72pb
-1
0.2
-1
0
-1
Z/γ * → e+e - MC
-0.2
band includes
several theoretical
calculations
-2
-0.4
40
60
100
10
2
200 300
M ee (GeV)
Tommaso Dorigo, Padova University
600
-0.6
70
Statistical
Total
75
80
85
90
M ee (GeV)
95
100
105
18
Les Arcs, Moriond QCD, March 22-29, 2003
Blessing Plots
Searches for WW production
∆φ(ET,closest l,jet)
In Run I CDF used 5 events (Nb = 1.2 ± 0.3) to 3.5
+6.2
3
measure σW W = 10.2−5.1
± 1.6 pb.
A similar search for dilepton candidates is going on 2.5
in the sample used to look for dilepton tt̄ production, 2
1.5
requiring Nj = 0.
Total backgrounds amount to 1.5 ± 0.6 events, the 1
expected W W signal yield is 2.7 ± 0.6 events.
0.5
Global
likelihood
So far 2 events have been observed in L = 56 pb−1 .
0
0
20
40
W + ud sample
MC WW
Data ee
Data e µ
Data µµ
distribution(ont'd)
60
80
100
120 140
ET (GeV)
{ CDF PRELIMINARY {
WW ! dilepton
0.6
0.5
0.4
0.3
0.2
0.1
0
-6
10
4
10
3
10
BG
RUNI WW
2
EVENTS
587
13.4
549.5
MEAN
-0.6
0.6
-0.7
RMS
1.6
1.3
1.4
10
1
RUN I data
WW
BG
-1
10
-2
10
-3
10
-6
-4
-2
0
2
4
6
8
10
Global Likelihood
Tommaso Dorigo, Padova University
39
S/BG
5

10
S/√BG
Number of events
In the Run I sample an optimized
search has been carried out for
pp̄ → W W + X → lνjj.
Limits have been set at σW W < 61 pb.
The search has established new methods to search for hadronic W → jj decays, useful for Run II searches.
Dave Waters
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
-6
-4
-2
0
2
4
Global likelihood cut
-4
-2
0
2
4
Global likelihood cut
We set the G.L threshold at 1.5 to minimize the expeted upper
19 limit
of W +W prodution.
Les Arcs, Moriond QCD, March 22-29, 2003
Concluding remarks
⋆ W and Z cross sections rise with s agrees well with NNLO;
√
Z asymmetry probed up to s = 600 GeV ; other searches have
started.
⋆ Run II is starting to deliver - xs results already reached accuracy levels
similar to Run I
⋆ → Next steps in EW physics are W mass, W asymmetry! We expect
first results soon.
⋆ Detectors largely understood with small caveats; not yet exploited to
fullest potential
⋆ Expect to collect at least 200 pb−1 in 2003; 320 pb−1 is “stretch” goal
Tommaso Dorigo, Padova University
20