Standard Model Electroweak

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Standard Model Electroweak ATLAS-IFAE
meeting dec 20-21, 2005 IFAE
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Outline
Group Group convener background Group
resources List of major institutions in the
group Overview of the main analyses TDR vs
current status Triggering Backgrounds Group
goals for 2007
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Standard Model WG
This group studies all SM topics excluding all
for which there are separated WG (Higgs, top and
beauty physics) Their studies can be divided
into Electroweak physics and QCD physics (see
talk by Sigrid)
Convenors Marteen Boonekamp (SPP, Service de
Physique des Particules) Craig Buttar (Glasgow
University) Group Resources http//atlas.web.ce
rn.ch/Atlas/GROUPS/PHYSICS/SM/sm.htmlMailing Lis
t of major institutions in the group BNL Glasgo
w University SPP, France University of Michigan
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SM Electroweak
Precision EW measurements Drell-Yan Z ll
production, W mass, (based on TDR ch16 and on
the E.B.Klinby talk in Rome) Gauge boson pair
production, (based on TDR ch16 and on the H.Ma
talk in Rome) Weinberg's angle (
) Current SM activities for W/Z physics W
mass, Lepton E-scale from Z mass, pT(Z)
spectrum, Di-boson studies, Tri-boson
studies Topics open for study Measurement of
the from Afb, Lepton pair production
(high mass region), Different aspects to be
studied on current analyses Goals after Rome
Continue current analyses and start new ones,
Evaluate SM model benchmarks and uncertainties
(How to tune MC), Detector studies (triggers
and calibration)
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Measurement of the W mass
MOTIVATION Precise measurement of the W mass and
the top mass will allow constraining the Higgs SM
boson mass
Radiative corrections and log
allows better constraintment of the mH than in
LEP2 and TeVatron
2 GeV
Momentum of the system recoiling against the W in
the transverse plane
METHODS (calibration/comparison between W and
Z) 1. TEMPLATE Varying mW and tunning Z
(absolute effects isolated but requires a lot on
MC) 2. RATIO Treat Z events as W's and shift
spectra by RWZ (Most effects in both samples but
less dependent on MC) Applying both methods will
help to disentangle systematics There are 3
transverse variables to fit (mT(W), pT(l), pT(
)), which are correlated but have different
systematics
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Measuring the W mass
Previous measurements
CDF (2001) 80.433 - 0.079GeV D0(2002) 80.483
- 0.084 GeV
50 x Data sample (i.e. 60M W events!) (i.e. 6M Z
events!)
LHC W/Z cross sections 10 x TeVatron LHC
luminosity first year 5 x TeVatron
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Measuring the W mass
Selection criteria
1. Isolated charged lepton with pT gt 25 GeV (only
in the region of precision physics) 2. Etmiss gt
25 GeV 3. No jets in the event with pT gt 30 GeV
4. For the recoil, u lt 20 GeV
Applied to reject the W's produced with high pT,
since for large pT(W) the mT resolution
deteriorates and the QCD bkg increases

• Efficiency
• 20 at the time of the TDR
• 25 for the Rome workshop
• Comments
• The optimization of these cuts should NOT be done
  for statistical reasons
• Some cuts should be made to make W and Z look
  alike once the systematic errors have been fully
  mapped

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Measuring the W mass
Fitting distributions
Red MC Truth Black Full simulation MC
Sensitivity through edges
Template method m(W) 80.5029 - 0.0018
GeV Ratio method m(W)/m(Z) 0.912 -
0.003(stat)
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Measuring the W mass
Expected uncertainties current vs TDR
Statistical uncertainty lt 2MeV (L10 )
(large statistics expected) Systematic
uncertainty GOAL is a total error of 20 MeV,
so individual contributions should be much
smaller than 10 MeV Major component due to MC
simulation (detector physics effects)
Knowledge
Uncert. (MeV) W pT and angular
distrib.(recoil model) (th) use Z recoil
pT(W)/pT(Z) 6 (5, TDR) pdf's
(exp/th) current error (CTEQ6) 20
(10, TDR) W width (exp) straight
forward variation 7 (TDR) Radiative decays
(exp/th) PHOTOS lt10 (TDR) Lepton
E-p scale (exp) 0.01 (0.02 , TDR)
10 (15, TDR) E-p resolution (exp)
1 (better than
1.5, TDR) 5 (5, TDR) Background (exp) if
ignored 5 (TDR) Lepton ID/Jet rejection
(exp)
small? Material
(exp)
Mapped with Pile-up UE event
Measure in
events
Total uncertainty expected from TDR 25 (20, 15)
MeV considering only one lepton species
(combining both channels, combining ATLAS and
CMS). Current status (Rome, 2005) first
realistic estimations of the uncertainties.
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Di-boson studies with multilepton final states
MOTIVATIONS Measurements of the Triple Gauge
Couplings (TGCs) test the SM and the EW symmetry
breaking, prove for new physics in the bosonic
sector Properties of the W New physics control
samples Discoveries Higgs, understand SM
backgrounds for SUSY
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Previous measurements
Di-boson studies
LEP accuracy 1 Anomalous TGCs (WWZ, WW )
limits NO ZW production TeVatron D0 WZ only 3
events with L 300 WW CDF WZWW studied
together 3 events with L 194 WW Signal
significance 5 There are large statistical
uncertainties which are not expected for the
LHC Production cross sections at NLO
Di-boson TeVatron LHC ZZ 1.4 16.8
WZ 3.7 57.7 WW 13.5 127.5
TDR limits on precision
Coupling Ideal case 0.035 0.046 0.028 0
.0025 0.0027 0.0023 0.0078 0.0089 0.0053
TeVatron a few events with lepton final states
for 300 . LHC a few K events for 10
(1st year) with pure leptonic decays.
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Di-boson studies
Current WG goals for di-boson physics
study Establish the SM di-boson multi-lepton
signals in full simulation Understand the sources
of background to the SM signal Search for new
physics from di-boson final states Control
samples single boson production Z
samples calibrate the energy scale determine
lepton ID selection cuts efficiencies W
samples check the missing Et resolution control
the missing Et systematic errors Particle
identification (CBNT) Analysis performed with
both CBNT (Michigan group) and AOD (BNL)
Electron ID
Muon ID (Muonboy)
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Di-boson studies
Event selection
Z 4l selection WZ trilepton
selection For the W For the Z WW ee/
/e Etmiss selection
134 selected ZZ events for
Eff 15-20 Expected signal 1344 - 58(
) Expected bkg 1169 - 570 accuracy
10 for 1 data
Most significant background is Zjets and
tt (same conclusion from DO analysis)
Rejects jet activities from tt events Rejects low
pT fake events from ZZ, Zjet, Zph
Channels Signal 5185 - 204
4034 - 184 Background 8904 - 1166 3203
- 450
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Di-boson studies
ZW inv mass
Mt (ZW)
WW bkg rejection cuts
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Di-boson studies
Expected uncertainties in measurements
Work plans towards 1st year data taking
Improve signal event generation Incorporate
boson width into event generation in MC at
NLO Uncertainty due to PDFs Better understanding
of the background with larger MC
statistics Wjets, Zjets Improve
resonstruction and optimize cuts Develop
techinque to determine the background rate
assess the uncertainties Lepton fake rate and
Etmiss resolution Extract the anomalous
TGCs Study various methods (Rate measurements
and multiple variables, e.g. pT(W) vs
pT(Z) Effective way to evaluate acceptance vs
couplings Study WLZL and ZLZL scattering in the
high mass region
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Triggering
and selections are provided
by inclusive lepton and di-lepton triggers LVL1
TRIGGER MENUS LOW LUMINOSITY HIGH
LUMINOSITY Trigger Rate (kHz) Trigger Rate
(kHz) MU6 23 MU 20 3.9 MU6 x 2
1 EM20I 11 EM30I 22 EM15I x
2 2 EM20I x 2 5 LVL2 TRIGGER MENUS LOW
LUMINOSITY HIGH LUMINOSITY Trigger Rate
(Hz) Trigger Rate (Hz) 200 200
80 100 e30i 600 e15i x 2 few
Hz e20 i x 2 20
Red trigger for both channels Blue trigger for
W channel Black trigger for Z channel
A trigger on an isolated electron with a lower
threshold and an additional Etmiss requirement is
under study at high lumi in LVL1 and LVL2 in
order to recover efficiency for the inclusive
selection.
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Summary

• Many analyses in progress and other open
  activities related to Electroweak physics (see
  the introduction talk in the SM session at the
  Rome workshop).
• Here only reported the status of the W mass
  measurement and some di-boson studies.

• A factor 10 of more production than in TeVatron
  is available at the LHC. This guarantees an
  important reduction of the statistical error for
  the LHC experiments even in the 1st year of data
  taking.

• Main motivation to measure the W mass is
  constraint the SM Higgs mass.
• Available two alternative methods which have
  different systematics Template method and Ratio
  method. Both use the Z mass as a reference.
• Expected total uncertainty in the W mass from
  the TDR predictions (maybe slightly optimistic)
  is about 20 MeV for L 10 .
• Current status first realistic estimations of
  the uncertainties are provided.

• Di-boson studies with multilepton final states
  will provide measurements of the TGCs and may
  help to discover the Higgs and the SUSY, among
  others.
• Current goals tune MC, understand the
  SMbackground, search for new physics.
• Main background contribution is from Zjets, ZZ,
  tt events, depending on the channel.

• Event selection is provided by inclusive lepton
  and di-lepton triggers.

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Most useful references
GENERAL GROUP INFORMATION SM WG web
page http//atlas.web.cern.ch/Atlas/GROUPS/PHYSICS
/SM/sm.html TDR GOALS AND STATUS ATLAS TDR
chapter 16 (Vol II) http//atlas.web.cern.ch/Atlas
/GROUPS/PHYSICS/TDR/TDR.html CURRENT STATUS AND
FUTURE PLANS Rome Workshop talks http//agenda.cer
n.ch/fullAgenda.php?idaa044738s1 Conveners
introduction http//agenda.cern.ch/askArchive.p
hp?baseagendacatega044738ida044738s1t1/transp
arencies w mass measurement http//agenda.cern.ch/
askArchive.php?baseagendacatega044738ida04473
8s1t7/moreinfo Di-boson studies http//agenda.cern
.ch/askArchive.php?baseagendacatega044738ida0
44738s1t8/transparencies