1 New Electroweak Results from DZero Observation and Cross Section times Branching Fraction Diboson Studies: W, Z, WW, WZ D D Tevatron Chicago DØ Main Injector Tom Diehl Fermi National Accelerator Laboratory “Wine + Cheese” January 28, 2005 For the DØ Collaboration
Chicago . DØ. Tevatron. Main Injector. New Electroweak Results from DZero. Z -> tt Observation and Cross Section times Branching Fraction Diboson Studies: W g , Z g , WW, WZ. “Wine + Cheese” January 28, 2005. For the D Ø Collaboration. Tom Diehl - PowerPoint PPT Presentation
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1
New Electroweak Results from DZero
Observation and Cross Section times Branching Fraction
Diboson Studies: W, Z, WW, WZ
DD
Tevatron
Chicago
DØ
MainInjector
Tom DiehlFermi National Accelerator Laboratory
“Wine + Cheese” January 28, 2005
For the DØ Collaboration
2
Outline
DØ Run II Data The DØ Detector
Inner tracker, calorimeter, & muon systems
Br(Z) at 1.96 TeV Motivation Event Selection Tau reco, classification, & ID Cross Section measurement
Dibosons: WW, WZ, W, Z Motivation WW and WWZ Couplings &
Anomalous Couplings WW (Dileptons)
Cross Section @ 1.96 TeV
WZ (Trileptons) Limit on (WZ)(WZ), and AC
limits. W in e and channels
W Cross Section, Photon ET Spectrum, and limits on AC.
Progress on Rad. Zero Z in ee and channels
Z Cross Section, Photon ET Spectrum, Event Characteristics, and limits on ZZ and Z AC.
Summary
3
The DZero Collaboration
19 Countries 86 institutions ~620 physicists
4
DZero Run II Data
~700 pb-1 pp collisions at sqrt(s) = 1960 GeV since the start of Run II.
Since the end of the 2004 shutdown the Tevatron has returned to high-performance operation. Stores routinely in the 80-
100e30 cm-1 s-1 range. Peak luminosity increases
due to effort in A.D. Challenges DZero to adapt to
increasingly higher luminosities Trigger List Reconstruction
So far, so good.
650 pb-1
520 pb-1
Monthly
Eff’y
Analyzed to here:
pp collisions at sqrt(s) = 1960 GeV
5
The DZero Detector in Run II: Inner Tracker
Tracker
SMTSMT
SMT
6
The DZero Detector in Run II: Calorimeter
Fitted Z(ee) peak has 3.7 GeV/c2 mass resolution in Run II.
Fine Longitudinal and Transverse Segmentation
7
The DZero Detector in Run II: MUONS
Run IIRun Ia Fitted Z() peak has
8.1 GeV/c2 mass resolution in Run II.
No Shielding
D0 Shielding
’s in
Central Scint.
Counters
t(ns)
Simulation
Run II Data
Unbiased
Triggers
8
Physics Motivation Test consistency of SM couplings
to all leptons Benchmark our level of
understanding of the experiment. Tau is most difficult lepton to ID Develop Tau ID, Efficiencies,
backgrounds We use this signal to tune up our
triggers and algorithms for non-SM searches such as
certain parts of SUSY space New Phenomena such as heavy
resonances that decay with enhanced coupling to 3rd generation.
)(Br)( ZZ What do we know about this?
NNLO calculation* predicts (Z) = 242+-9 pb.
Br(Z) is well measured.
measured.been beforenever
has )(Br)( ZZpp*from Hamberg, van Neervan, and Matsura,
Nucl. Phys. B359, 343 (1991), using CTEQ6L
9
The analysis is complicated.
)(Br)( ZZ
Classify tau
candidates Extract
Cross Section
Preselection: single muon
events
Reconstruct
taus
Divide Events into
OS and SS
(For BKGD Estimate)
Lepton Pairs
Final Event
Selection
Start
10
One must decay to . Event Selection starts with an isolated muon
One w/ pT()>12 GeV/c This muon carries the sign of it’s tau lepton
The other can go to any of 3 decay modes
Event Selection
L=226 pb-1 L/L = 6.5%
hadronsor
e
XZ
)%07.0(20.15)prong" 3"Br(
)%13.0(71.84)prong" 1"Br(
)%06.0(84.17)Br(
)%06.0(37.17)Br(
e
Tau Decay Signature For reference:
Z
11
Start with the Calorimeter CAL. ET (R=0.5) > 5 GeV & ET (R=0.3) > 3 GeV Taus have narrow jets
Then use the Tracker N(tracks w/ pT>1.5 GeV/c in the narrow cone) > 0
Start with the highest pT track If there’s a second track such that Mass(2-
tracks)<1.1 GeV/c2, add that track to the tau list If a third track such that Mass(3-tracks)< 1.7 GeV/c2,
add it unless total charge = 3 or -3. If total charge = 0, discard the tau candidate.
Require > 2.5 (These are low pT Z’s) Reconstruct EM subclusters with ET > 800 MeV
Reconstruct Tau Candidates
I.P.
Charged Particle
Cones of size R=0.3 and 0.5
25.0)(RMS2
ET
ETR iCalTowers
ii
12
Classify the tau candidates into three types
1. “One-prong”, a single track w/ no EM subclusters
2. “One-prong” + EM, a single track w/ EM subclusters (cleanest)
3. “Multi-prong”, more than one track
Tau Identification: Classification
TRK + CALType 1
o
no TRK, but EM sub-cluster
TRK + CAL
Type 2
1 TRK
+wide CAL cluster
Type 3
“One-prong” “One-Prong + EM” “Multi-Prong”
And there are selection criteria
discriminating them from each other
And rejecting background.
13
Classify the tau candidates into three types “One-prong”, a single track w/ no
EM subclusters “One-prong” + EM, a single track
w/ EM subclusters (cleanest) “Multi-prong”, more than one
track
Tau Identification: Classification
TRK + CALType 1
o
no TRK, but EM sub-cluster
TRK + CAL
Type 2
1 TRK
+wide CAL cluster
Type 3
“One-prong” “One-Prong + EM” “Multi-Prong”
7.0
/)(
GeV/c 5
GeV/c 7
GeV 5
GeV 10
5.05.0track
trkT
trkxCH
trksT
trksT
T
T
PEE
P
P
E
E
Gets rid of eventsw/ extra ’s
14
Classify the tau candidates into three types
1. “One-prong”, a single track w/ no EM subclusters
2. “One-prong” + EM, a single track w/ EM subclusters (cleanest)
3. “Multi-prong”, more than one track
No attempt to separate hadron channels from electron channels.
At this point we have the charge sign of and
Tau Identification: Classification
TRK + CALType 1
o
no TRK, but EM sub-cluster
TRK + CAL
Type 2
1 TRK
+wide CAL cluster
Type 3
“One-prong” “One-Prong + EM” “Multi-Prong”
7.0
/)(
GeV/c 5
GeV/c 7
GeV 5
GeV 10
5.05.0track
trkT
trkxCH
trksT
trksT
T
T
PEE
P
P
E
E
Gets rid of eventsw/ extra ’s
15
Divide 29,021 events into SS and OS lepton-lepton candidates.
We still have a large background from multijets. Jets tend to be wider than ’s have higher track multiplicity have higher mass than M() be less isolated from other hadronic energy than
are tau’s from Z’s. A Feed-forward neural network
8 input nodes (each a new criteria), a single hidden layer with 8 more nodes, and a single output (the answer). Not all inputs for all tau types.
Train the 3 types separately on expected signal and backgrounds.
Tau Identification: Neural Network
Jet-Background
q
o
o
1 TRK +wide CAL cluster + EM sub-cluster
“One-Prong”
“One-Prong”+ EM
“Multi-Prong” “All Types”
16
Events predicted and events observed before and after P(NN)>0.8 criteria for all 3 types. QCD background is scaled
from same-sign data The other bkgds and expected
Z() from MC. Eff’y(NN)=0.78 Signal/Bkgd ~
0.82 #Z() Observed = 86555
after M()>60 GeV/c2
Eff’y = 1.52% for M() > 60 GeV/c2.
Tau Identification: # Candidates
type contribution to signal:
13% Type1, 58% Type 2, 29% Type 3
TOTAL Number of Events
After NN
Before NN QCD 13881264 10024W 434153Z/* 117443SUM 15589309OS Events 15911
Energy scale 2.5% NN MC inputs 2.6% Backgrounds 4.6% PDF’s 1.7% Eff’y & Accept. 2.6% Trigger Eff’y 3.5%
Total 7.5%
Figures show ET() and pT() for: MC vs. background subtracted data
UNCERTAINTY IN
18
Cross Section Calculation
Submitted to PRL.
hep-ex/0412020
FERMILAB-PUB-04/381-E
Theory: Matsura + van Neervan
)(Br)( ZZ
AL
bN)Br(Z
For m()>60 GeV/c2
After removing the * contribution
pb .)(19.)(16252
)Br(Z
sysstat
pb .)(15.)(18.)(15
237)Br(Z
lumsysstat
19
What else can we say about Taus?
Z mass peak We can find states
that decay to tau’s. Not some other large
source of tau pairs. Searches for Higgs,
SUSY etc with tau final states are available and more are coming
Lepton Universality Use DØ’s Run II
preliminary muon and electron results
Upper Left: Mass() for Bkgd vs. Signal MC for type 1 and type 2 tau tracks
Upper Right: Mass() for (OS events Bkgd) vs Signal MC
09.084.0)Br(Z and )eeBr(Z
)Br(Z--
-
1.96 TeV
20
Dibosons (Outline)
Dibosons: WW, WZ, W, Z Motivation WW and WWZ Couplings & Anomalous Couplings WW Dileptons
Cross Section @ 1.96 TeV WZ Trileptons in Run II
Limit on (WZ), (WZ), and AC limits. W in e and channels
W Cross Section, Photon ET Spectrum, and limits on AC. Progress on Rad. Zero
Z in ee and channels Z Cross Section, Photon ET Spectrum, Event Characteristics, and
limits on ZZ and Z Anomalous Couplings.
21
Dibosons: Introduction Motivations
Multiple vector bosons provide a high-pT Standard Model process with a cross section and interesting physics
Cross sections are useful for New Phenomena search analyses.
a SM parameter to measure: the gauge boson “self-couplings”
hep-ph/9704448
SM Higgs Branching Fractions
More Motivation We are on the lookout for very
massive particles that decay to the heaviest gauge bosons.
Like the Higgs. Or the Higgs that doesn’t decay to
fermions. Or whatever.
22
WW and WWZ Couplings
Cancellation of t- and u-channel by s-channel amplitude removes tree-level unitarity violation (in W, WW, and WZ, too). Textbook example t-channel: At high energy limit and
with massless quarks (simpler calculation). violates unitarity.
t-channel u-channel
s-channel
)cot( we e
WW Coupling WWZ Coupling
s-channel: Term of opposite sign cancels unitarity violating part.
3)(
2 sGWW F
Self-interactions are direct consequence of the non-Abelian SU(2)L x U(1)Y gauge symmetry. SM specific predictions.
23
WW and WWZ Anomalous Couplings
VWW VWW
)WVWVWW(/L
†2
V†V
††1VWWVWWV
WM
gg
QeW = e () / M2
W
W = e/ 2MW
Characterized by effective Lagrangian 5 CP Conserving SM Parameters:
(
g
gg
In W production, only the WW couplings.
In WZ, only WWZ couplings.
In WW, both and one has to make an assumption as to how they are related.
W+ Boson Static Properties
24
Effect of Non-SM WW and WWZ Couplings
Cross section increases especially for High ET bosons (W/Z/). Unitarity Violation avoided by introducing a form-factor scale
, modifying the A.C. at high energy. e.g.:
WW Production
( )( / )
ss n
1 2n 2 for WW ,WWZ
PT(W)(s^(0.5)=1800 GeV)
# E
vent
s/20
GeV
/c
25
Anomalous Couplings – LEP and Tevatron
DØ and CDF put limits on anomalous WWg and WWZ Couplings in Run 1. WW and WWZ couplings from WW WW couplings from W analyses * WWZ couplings from WZ *
DØ Combined W, WW, WZ (1999) TeV 2
C.L. 95%
0.1918.0
53.029.0
Tightest from
the Tevatron
LEP Combined (1D 95% CL)
1cos2
1)-(g (D0) constraintw/
1)-(tang and
2Z1
2Z1ZZ
w
w
0.0340.051
0.026059.0
069.0105.0
1
Zg
“HISZ” SU(2)xU(1) coupling relations
Didn’t use a form-factor dependence in their couplings.
*(complementary in several ways)
LEP EWK Working Group hep-ex/0412015
26
WW Production and Decay
Dileptons
e and Br = 2.5 and 1.2%
Pure and efficientLow branching
Frac.
Lepton+jets
en+jets, +jets
Br = 15%
EfficientNot very pure
All-jets
All-jets
Br = 47%
Very EfficientNever Mind
Decay Modes are named like top pairs. In fact, WW is one of the top backgrounds.
(WW) ~ 13.5 pb-1 at Run II Tevatron energy*.
Campbell & Ellis
* Ohnemus (1991), (1994) and Campbell & Ellis (1999).
27
WW to Dileptons in Run I
WW to dileptons @ DØ and CDF Cross section limit and anomalous
coupling limits @ DØ (PRL and several PRDs)
Evidence for WW Production and anomalous coupling limits @ CDF in 1997 PRL.
Leptons + jets channels provided more restrictive A.C. limits than dileptons at DØ and CDF but we couldn’t isolate a signal from the much bigger W+jets background.
( ) . ...WW
10 2 165 16 5 pb
TeV 1
9.0 8.0
3.11.1
TeV 1
C.L. 95%
1.0||
2.1||
C.L.) (95% pb 37
)(
XWW
1D AC limits
28
Run 2: WW -> Dileptons Event Selection
Preselection Criteria Two oppositely-charged e or
w/ pT>15 GeV/c. At least one has pT>20 GeV/c.
MET > 30, 40, & 20 GeV/c2 in eee channels to remove Z/*.
Missing Transverse Energy After Preselection Criteria
Shows agreement between data and signal plus backgrounds.
D0 D0 D0
ee Channel Channel e Channel
channel
29
e channel criteria No third lepton so that 61<
M(l+l-) < 121 GeV/c2. Minimal Transverse Mass > 20
8.4 times as much Z signal as all of Run I in 3.1 times the Lum’y.
55
ZEvent Characteristics
DØ Data Z data shows FSR, Zg ISR, and DY ISR for the 1st time.
Require M(ll)>65 GeV/c2 & M(ll)>100 GeV/c2
117 Z events left MC indicates 80% are ISR
and predicts ~ 0.94 pb.
D0
Prelim.
D0
Prelim.
x
Z Bosons
Drell-Yan leptons
Final State
Radiation pb .)(07.0
.).(15.007.1
)Z(
lum
sysstat
pp
D0 Preliminary
ET() >8 GeV R>0.7
56
ZAnomalous Couplings
Using the full sample: Form a binned-likelihood
based on pT() in an h30 and h40 grid including bkgd.
The ZZ and Z
AC contours are similar.
DØ Prelim.
95% CL2D
Unitary
ZZ Coupling Limits
019.0||
22.0||
40
30
h
h
GeV 1000
DØ
Prelim.
019.0||
21.0||
40
30
Z
Z
h
h
These are the new standard.
What about LEP?
Limits on h20 & h10 will be nearly identical to h40 & h30, respectively (CP-odd).
57
What about ZZ and Z@ LEP?
LEP Studies e+e-Z/* Z LEP results (no form factor)
included (again some correction)
12.005.0
07.020.0
071.0078.0
13.013.0
40
30
20
10
Z
Z
Z
Z
h
h
h
h
034.0002.0
008.0049.0
025.0045.0
055.0056.0
40
30
20
10
h
h
h
h
There’s a difference between LEP and Tevatron AC definitions
LEP is measuring the real part of the couplings and Tevatron is measuring the imaginary part
It’s documented that there is no or very little interference between SM and Anomalous couplings. Limits on real and imaginary parts should be the same.
LEP Results
LEP EWK Working Group hep-ex/0412015
D0 has most restrictive limits in “h4” and “h2”
LEP has most restrictive limits in “h1” and “h3”
58
Summary: D0 EWK results with power of Run II Luminosity
First measurement of:
pb .)(15.)(18.)(15
237)ZppBr(
lumsysstat
Measurement of (WW) @ 1.96 TeV using dileptons pb .)(9.0
.)(.)(8.13)( 2.19.0
3.48.3
lum
sysstatWW
Evidence for WZ production, (WZ) @ 1.96 TeV, tightest model-independant WWZ AC Limits
C.L.) (95% pb 3.13
)(
XWZ
pb 5.4ZW( 5.36.2
)pp Studies of W production,
tightest model-independant WW AC Limits, Hints of Rad 0. 0.2222.0
97.093.0
Studies of Z production (10x Run 1 sample), Characteristics, AC Limits 019.0||
22.0||
40
30
h
h
019.0||
21.0||
40
30
Z
Z
h
h
DØ Prelim.
59
Barrier Slide 1
This slide and all that follow are not part of my talk. Acknowledgements Previous Drafts of slide that I made in case there was
additional detail Some detailed slides that I didn’t use at all. Some “backup” slides with more information.
60
Acknowledgements
Thanks, as always, to DZero collaboration. Serban Protopopescu, Cristina Galea, Abid Patwa, Silke Nelson Thomas Nunneman, Johannes Elmsheuser, Marc Hohfeld Qichun Xu, Bing Zhou, James Degenhardt Sean Mattingly, Andrew Askew Yurii Maravin, Drew Alton Marco Verzocchi, Stefan Soldner, Tim Bolton, Dmitri Denisov,
Ia Iashvili, Avto Karchilava CDF
61
We still have a large background from multijets. Jets tend to be wider than ’s have higher track multiplicity have higher mass than M() be less isolated from other hadronic energy than
tau’s from Z’s. A Feed-forward neural network
8 input nodes, a single hidden layer with 8 more nodes, and a single output (the answer). Not all inputs for all tau types.
Divide 29,021 events into SS and OS lepton-lepton candidates.
Tau Identification: Neural Network
Jet-Background
q
o
o
1 TRK +wide CAL cluster + EM sub-cluster
“One-Prong”
“One-Prong”+ EM
“Multi-Prong” “All Types”Train 3 types separately
62
Events predicted and events observed before and after P(NN)>0.8 criteria for all 3 types. There’s correction factors fi on
the SS backgrounds of 3 to 9% determined from a non-isol sample.
The other bkgds are from MC. Eff’y(NN)=0.75 &
R(NN)=1.6 (14 if swap cut order)
Signal/Bkgd ~ 0.82 Eff’y = 1.52% for M()
> 60 GeV/c2.
Before NN
Tau Identification: # Candidates
type contribution to signal: 13% 58% 29%
After NN
TOTAL
63
Z Neural Network Input Params.
64
WW Dileptons @ Tevatron in Run I
D0 Results (97 pb-1) 5 candidates w/ background
of events (mostly Z’s and W+jets).
Expected WW events
Consistent with S.M. Limits on Anomalous WW
and WWZ couplings in 1995 PRL and 1998 PRD.
CDF Results (108 pb-1) 5 candidates w/ similar but
smaller backgrounds of 1.2+-0.3 events.
Expected 5.21.8 WW events. Limits on AC “Evidence for WW
Production” in a 1997 PRL.
( ) . ...WW
10 2 165 16 5 pb
TeV 1
9.0 8.0
3.11.1
TeV 1
C.L. 95%
1.0||
2.1||
C.L.) (95% pb 37
)(
XWW
Leptons + jets channels provided more restrictive A.C. limits than dileptons.
1D AC limits
65
Anomalous Couplings - Previous Results
D0 and CDF put limits on anomalous WWg and WWZ Couplings in Run 1. WW and WWZ couplings from WW WW couplings from W analyses WWZ couplings from WZ
D0 Combined W, WW, WZ TeV 2
C.L. 95%
0.1918.0
39.025.0
Z
Z
Tightest from
the Tevatron
LEP Combined (1D 95% CL)
1)-(tang and 2Z1ZZ w
0.0340.051
0.026059.0
069.0105.0
1
Zg
“HISZ” SU(2)xU(1) coupling relations
Didn’t use a form-factor dependence in their couplings.