Electroweak Physics
description
Transcript of Electroweak Physics
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ELECTROWEAK PHYSICS
Heidi Schellman – Northwestern University
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What is not in this talk Results from previous years – except for context Top quark mass and single top production
Mousumi Datta The CKM matrix
Dave Hitlin and Tom Browder The MNS matrix
Bonnie Flemming The Higgs
Mark Kruse Weak boson production (QCD)
Don Lincoln These are arguably all electroweak measurements.
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What’s left Precision measurements
of electroweak couplings and mass The W mass Measurements of the
weak mixing angle. Very rare electroweak
processes. Diboson production
And the future…
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Predictions of GSW theory
A neutral Z0 boson
W, Z0 and g couplings and masses have tightly constrained relations: MW/MZ = cos qw e = g sin qw
Symmetry breaking would like a Higgs Field
There should be at least one physical scalar Higgs boson left over to observe
Couplings and Masses Higgs Field
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Why constants aren’t constant
This is an electron
This is a closeup of an electron
This is a real closeup of an electron.
Properties depend on distance/energy scale and properties of all other particles which can couple
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Renormalization
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Relations of masses and angles6
Δr1sinθ1
FG2πα
WMW
Dr ∞ Mt 2 Dr ∞ logMH
Measure qW, predict MWConsistency of indirect and direct measures?
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LEP/SLD measurements of MZ, MW ,sin2qw
LEP/SLD e+e-
Measure Z mass 91.1876+/- 0.0021 GeV Measure Z weak couplings to all fermions by
measuring g*/Z interference and the Z width. Precise measurement of sin2qw Measure the W mass with 0.033 GeV resolution
Tevatron - hadron-hadron scattering Forward backward asymmetry AFB MW
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Z’s at hadron colliders
LEP recorded 17M Z events eeff of Which 1.7M were to Leptons (including tau’s)
Tevatron now has reconstructed ~ 0.2-0.6M events x 2 channels (ee+mm) x 2 expts (D0/CDF)~ up to 1.6 M Zll already depending on cuts.Close to LEP statistics! LHC experiments expected to have much higher cross
sections with ~2 M Z ll in the first fb-1 !
35,626 events qq ee
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Signatures uu + dd Z ll
Tevatron is mainly valence-valence scattering.
LHC is mainly valence-sea scattering and must choose boosted Z’s to tell valence from sea. PDF’s will be a
dominant uncertainty.
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Current measurement from D0
Junjie Zhu
AFB
qqZ/g* eesin2qw=0.2326±0.0018(stat)
±0.006(syst)Phys. Rev. Lett. 101, 191801 (2008), arXiv.org:0804.3220
Trang HoangFriday EWK IIII
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AFB measurements
Future measurements from the Tevatron and the LHC are expected to reach 0.0005 or better accuracy. The limiting factor is probably PDF’s.
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W mass from CDF - 2007
Both muon and electron channelsScale set by the CDF trackerAbsolute measurement of MW
Chris HaysTuesday EWK I
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New W mass measurement 1 fb-1 of data taken 2002-2006 ~ 18,725 Z and 499,830 W candidates in the
electron channel only. Use data to determine corrections wherever
possible Blind analysis – central mass value hidden until
everything has been reviewed. Because Zee is the main calibration, this is
effectively a MW/MZ measurement – many physics effects cancel.
NOT very correlated with the CDF measurement!
Jyotsna OstaTuesdayEWK I
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W boson mass - W -> en mode
Cannot measure n or W momentum along beam Use variables defined in transverse plane
pTe
ET = inferred neutrino pTn
mT = √2 pTe ET (1-cosDf)
Only electrons with |h| < 1.1 used
ET
pTe
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Crosschecks
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Check everything… Results: Z e e data
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pT(e)
GeVGeV
GeVGeV
uT
m(ee)
pT(ee)
Good agreement between parameterized MC and collider data.
DØ Preliminary, 1 fb-1
DØ Preliminary, 1 fb-1
DØ Preliminary, 1 fb-1
DØ Preliminary, 1 fb-1
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W boson mass
Fit data to simulated distributions by varying mW Hid the fitted W mass
value until all control plots were OK
mT
Also fit pTe, pT
n
mW = 80.401 ± 0.023± 0.037 GeV
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W boson mass
Limited by Z->ee statistics, will improve with more data
mW(mT) = 80.401 ± 0.023 (stat) ± 0.037 (syst) GeV mW(pTe) = 80.400 ± 0.027 (stat) ± 0.040 (syst) GeV mW(pTn) = 80.402 ± 0.023 (stat) ± 0.044 (syst) GeV
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Summary of direct measurements20
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Higgs Mass ConstraintsMH from Standard fit:• Central value ±1: • 2 interval: [42, 158] GeV
Green band due to Rfit treatment of theory errors, fixed errors lead to larger 2
min
MH from Complete fit:• Central value ±1: • 2 interval: [114, 153] GeV
MH 116 1.3 16 GeV
Complete fitStandard fit
MH 80 23 30 GeV
Andreas Hoecker (CERN)EPS 2009
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The future…
D0 e only
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Elastically scattered electrons
Quartz barcosmic tests
QWeak Parity violation in e-p scattering at Q2 = 0.026 (GeV/c)2.
Scheduled for ~223 days at 1.165 GeV. Start construction 2009End data taking 2012
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Qweakincreasing
Qweakdecreasing
far close
scale dependence of weak mixing angle in MS schemeRunning of sin2qw
screening
anti-
scre
enin
g
PDG 2008 Review: “Electroweak and constraints on New Physics Model” J. Erler & P. Langacker
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DIS08 - UCL
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April 8, 200825
NuSonG neenee
Proposed 5 kT fine grained neutrino detector using a revived Tevatron neutrino beam
~1G DIS events measure r and sin2qw
Structure Functions 70K nee nee 7K anti-nee anti-nee
measure r and sin2qw
700K nme nem for clean flux measurements
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Dibosons and Anomalous Couplings
Last year, CDF and D0 finished off the dibosons (except for HW)
6 ZZ llll events between the two experiments with minimal background
CDF 3m+t event
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Summary of Bosons at the Tevatron
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What to do for an encore? Highlights this year are
Use of much larger data samples the difficult channels with Z vv and W/Z
jj. Improved limits on anomalous couplings
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General Effective Lagrangian for charged (WWγ/WWZ):
νλμν
*λμ2
W
Vμνν
*μV
μνν
*μ
νμ*μν
V1
WWV
WWV VWWMλi VWWiκ)WVWVW(Wigg
L
ρν*
μλνλ*
μμνλρV
5μννμ
ν*
μV4 V WWWWεgVVWWg- νλμ
ν*
λμ2W
Vμνν
*μV VWWM
λiVWWki ~~~~
General Effective Lagrangian for neutral (ZZγ/Zγγ):
EM gauge inv. (g1γ = 1), C and P conserving 5 couplings: κV, λV, g1
Z
νμα4
Z
2VαμνV
4μνV
2ν2Z
2V
μμνV
3μνV
1γZV VMm ZFhFhVM
m ZFhFhieL ~~ □□
CP conserving → h3,4V couplings (V = γ, Z)
: SM 0hλ 1,κg V3,4VV
Z1 :Deviations SM 0hΔh 0,λΔλ
1κΔκ 1,gΔgV3,4
V3,4VV
VVZ1
Z1
COUPLINGS ANOMALOUS
0 Δ
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Charged Triple Gauge CouplingsProbed by WW, WZ, and Wγ productionGeneral Lagrangian has 14 parametersAssume EM gauge invariance and C and P conservation⇒ 5 TGC parameters: g1
Z, kγ, kZ, λγ, λZ
g1 and k are 1 in the SM, the rest are zero
Neutral Triple Gauge CouplingsProbed by ZZ and Zg productionGeneral Lagrangian has 8 TGC parametersAssume CP conservation⇒ 4 non-SM TGC parameters: h3
γ, h3Z, h4
γ, h4Z all
0 in SM
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Strategies These are very rare processes First do pure leptonic final states
Very small statistics Very low background
New! 3-5 times more data analyzed New! Can use more difficult signatures to get more
statistics Z+g vvg is harder W+W/Z lvjj is really hard Z + W/Z vvjj is really really hard
Wg lngZg ll gWW lnlnWZ lvllZZ llll observation by D0 and CDF in 2008
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nng candidate event
g
MET
Mike StrangThursdayEWK II
g
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Zg vvgSelect interactions with large,
significant Missing transverse momentum
Zg vvg avoids radiation off of the Z!
Limits on the anomalous couplings of Z’s to photons. The standard model wants 0
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CDF WW lvlv with 3.6 fb-1
Use matrix method likelihood method to assign probability to signal/background based on event kinematics
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CDF Observation of VV MET+jj
18±2.8(stat)±2.4(syst)±1.1(lumi) pb 16.8±0.5 pb (SM)
Events with 2 jets and MET > 60 GeV and high MET significance
Eric JamesThursdayEWK III
arXiv:0905.4714
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Charged Anomalous Couplings
Set limits on charged Anomalous couplings
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D0 – set charged TGC limits using pt in 4 channels
WZ→lvll
Wγ→lvγ
WW lvjjWW→lvlv
JadrankaSekaricThursdayEWK III
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D0 limits on anomalous couplingsfrom Wg, WW, WZ
Can be interpreted as measurements of the magnetic dipole and quadrupole moments.
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Prospects for the future D0 and CDF can anticipate 3-10
times more data per channel Combining channels and
experiments will increase the TGC sensitivity by a factor of 3-5.
LHC experiments have 10 times the cross section 10 fb-1 of data factor of 100 in statistics and 10 in sensitivity relative to current Tevatron.
200 fully reconstructed ZZ events in first 10 fb-1 !!
ATLAS PROJECTIONS from MTWW
ZZ polarization 100 fb-1
( Eyal Brodet ATLAS)
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Electroweak summary Major progress Precision EWK
W mass precision on track for 25 MeV/expt at Tevatron – maybe 10 MeV at LHC!
We are at the beginning of a new generation of measurements of sin2qW at colliders and fixed target
DiBosons All diboson channels seen even in hadronic final states LHC will have enough statistics to do precision
measurements of couplings and event kinematics very soon!
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BACKUP slide
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s
(nb
)
103
107
106
109
100
103
√s (TeV)1 10
0.01
108
105
102
101
104
106
p-p (or p-p)
Rate
s per
seco
nd a
t 103
2
WZ
b
jet>100
top
higgs?
total
WWWZZZ