Electroweak Physics at the LHC Precision Measurements and New Physics
1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak...
-
Upload
bethanie-clarke -
Category
Documents
-
view
214 -
download
0
Transcript of 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak...
![Page 1: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/1.jpg)
1
Electroweak PhysicsLecture 5
![Page 2: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/2.jpg)
2
Contents
• Top quark mass measurements at Tevatron
• Electroweak Measurements at low energy:
– Neutral Currents at low momentum transfer• normally called low Q2
• Q is the four momentum of the boson
– Precision measurements on muons• We didn’t get to this in the lecture• Slides are at the end
![Page 3: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/3.jpg)
3
Top Event in the Detector
• 2 jets from W decay• 2 b-jets• ℓ±νℓ
Nicest decay mode: Ws decay to lepton+jets
![Page 4: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/4.jpg)
4
Top Event Reconstruction
![Page 5: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/5.jpg)
5
Top Mass: Largest Systematic Effect
• Jet Energy Scale (JES)– How well do we know the response of the calorimeters to
jets?• In Lepton+Jets channels: 2 b-jets, 2 jets from W→qq, ℓ+ν• Use jets from W decay (known mass) to calibrate JES
• Example of CDF analysis:
simulation
Mtop = 173.5 +2.7/-2.6 (stat) ± 2.5 (JES) ± 1.5 (syst) GeV/c2
JES = −0.10 +0.78/−0.80 sigma
~16% improvement on systematic error
![Page 6: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/6.jpg)
6
Top Mass: Matrix Element Method
![Page 7: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/7.jpg)
7
Matrix Element Method in Run II
• Probability for event to be top with given mtop:
• Use negative log likelihood to find best value for mtop:
![Page 8: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/8.jpg)
8
Top Mass: Template Method• Dependence of
reconstructed mass on true mass parameterized from fits to MC
• Include background templates constrained to background fraction
![Page 9: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/9.jpg)
9
Top Quark Mass Results
![Page 10: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/10.jpg)
10
Top Quark Cross Section• Test of QCD prediction:
![Page 11: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/11.jpg)
11
Search for Single Top Production
• Can also produce single top quarks through decay of heavy W* boson
• Probe of Vtd
• Search in both s and t channel• Currently limit set <10.1 pb @
95%C.L. • Don’t expect a significant single
until 2fb-1 of data are collected
![Page 12: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/12.jpg)
12
W helicity in Top Decays• Top quarks decay before then
can hadronise• Decay products retain
information about the top spin• Measure helicity of the W to
test V-A structure of t→Wb decay
• F+ α mb²/mW²≈0
• Use W→ℓν decays• Effects in many variables:
– pT, cosθ* of lepton
– mass of (lepton+jet)
No discrepancies found, need more data for
precision
CDFII 200pb−1
![Page 13: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/13.jpg)
13
Tevatron Summary: mtop and MW• CDF and DØ have
extensive physics programme
• Most important EWK measurements are MW and mtop
• Stated aim for RunII:– mtop ±2.5 GeV/c2
– MW to ±40 MeV/c2 – Probably can do better
– Other EWK tests possible too!
![Page 14: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/14.jpg)
14
Two More Measurements for Our Plot
Extracted from σ(e+e−→ff)
Afb (e+e−→ℓℓ)
AL
R
τ polarisation asymmetry
b and c quark final states
From Tevatron
Tevatron + LEPII
![Page 15: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/15.jpg)
15
Electroweak Physics at Low Energy
• Low momentum transfer, Q, of the boson• Test whether EWK physics works at all energy
scales
• Møller Scattering • Neutrino-Nucleon Scattering• Atomic Parity ViolationPlus: muon lifetime and muon magnetic moment
![Page 16: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/16.jpg)
16
Running of sin²θW
• The effective value of sin²θeff is depend on loop effects
• These change as a function of Q², largest when Q²≈MZ, MW
• Want to measure sin²θeff
at different Q²
• For exchange diagram
~2.5%
![Page 17: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/17.jpg)
17
![Page 18: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/18.jpg)
18
E158: Møller Scattering• e−e−→e−e− scattering,
– first measurement at SLAC E158 in 2002 and 2003
• Beam of polarised electrons <Pe> ≈ 90%, Ee=48.3GeV– Both L and R handed electron beams
• Incident on liquid hydrogen target
• Average Q² of 0.027 (GeV/c)² (Qboson~0.16 GeV/c)
• Measure asymmetry between cross section for L and R beams:
meas R LLR e LR
R L
N NA P A
N N
![Page 19: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/19.jpg)
19
Tree Level Diagrams
• Photon exchange will be dominant• Asymmetry between L and R terms (parity violation) is from
Z-exchange → small asymmetry
24 4
(1 )1 sin
1 (1 )2R L F
LR WR L
G s y yA
y y
12 (1 cos )y
![Page 20: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/20.jpg)
20
Measured Asymmetry
• A = −131 ± 14 (stat) ± 10 (syst) ppb
• sin2θWeff(Q2=0.026) = 0.2397 ± 0.0010 (stat) ±
0.0008 (syst) • cf 0.2381 ± 0.0006 (theory) +1.1σ difference
![Page 21: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/21.jpg)
21
NuTeV
• NuTeV = neutrinos at the Tevatron• Inelastic neutrino-hadron scattering• Huge chunk of instrumented iron
– With a magnet!
![Page 22: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/22.jpg)
22
NuTeV Physics• Two interactions possible:• Neutral Current (NC) Charged Current
(CC)
• Pachos Wolfenstein Relationship• Requires both neutrino and anti-neutrino beams
No γ* interference
![Page 23: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/23.jpg)
23
NuTeV Beams
• Beam is nearly pure neutrino or anti-neutrino
• 98.2% νμ 1.8% νe
• Nu beam contamination < 10³
• Anti-nu beam contamination < 2 x 10³
![Page 24: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/24.jpg)
24
Events in the Detector
“Event Length” used to separate CC and NC interactions
![Page 25: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/25.jpg)
25
NuTeV Result
• Doesn’t agree with Z pole measurements
![Page 26: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/26.jpg)
26
Atomic Parity Violation• Test Z and γ interaction with nucleons at low Q²• Depends on weak charge of nucleon:
• Large uncertainty due to nuclear effects– eg nucleon spin
![Page 27: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/27.jpg)
27
sin²θW(Q) Results
Some disquiet in the Standard Model, perhaps?
![Page 28: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/28.jpg)
28
Low Energy Summary
• Important to test EWK Lagrangian at different energy scale
• Challenging to achieve the level of precision to compare with theory!
• Experimental Challenges overcome, very precise results achieved
• Some (small) discrepancies found between data and theory…
![Page 29: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/29.jpg)
29
• End of lecture
• Precision measurements on muons follow
![Page 30: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/30.jpg)
30
Muon Lifetime• The lifetime of the muon is one of the test predicted
parameters in the EWK
• μ+ → e+ νe νμ no hadronic effects
• One of the most precisely measured too, use it to set GF in the Lagrangian
• No recent measurement of just lifetime, current investigations of decay spectrum
2
1
2FG
v
τ(μ)=(2.19703 ± 0.00004)X10−6
![Page 31: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/31.jpg)
31
Prediction for the Lifetime
![Page 32: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/32.jpg)
32
TWIST Experiment
Highly polarized +
+ stop in Al target(several kHz)
Unbiased + (scintillator)
trigger
At TRIUMF in Vancouver
![Page 33: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/33.jpg)
33
Typical Decay Event
e+
![Page 34: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/34.jpg)
34
Muon Decay Spectrum
• SM predictions and measurements:
![Page 35: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/35.jpg)
35
Muon Dipole Moment• The Dirac equation predicts a muon magnetic
moment:
• Loop effects make gμ different from 2
• Define anomalous magnetic moment:
with gμ=2
![Page 36: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/36.jpg)
36
Very Precisely Predicted…
![Page 37: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/37.jpg)
37
The Experiment: E821 at Brookhaven
• polarised muons from pion decay
• procession proportional to aμ: ω=ω(spin)−ω(cyclontron)
• Precise momentum tuning, γ=29.3
![Page 38: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/38.jpg)
38
E821
![Page 39: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/39.jpg)
39
Decay Curve
Oscillations due to parityviolation in muon decay
Use ωa from fit
![Page 40: 1 Electroweak Physics Lecture 5. 2 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: –Neutral Currents at low momentum.](https://reader030.fdocuments.net/reader030/viewer/2022032703/56649f535503460f94c786fa/html5/thumbnails/40.jpg)
40
aμ: Results and Comparison
10( ) 11659214 8 11 10a
Very precise measurement!
Another hint of a problem?