Документ взят из кэша поисковой машины. Адрес оригинального документа : http://nuclphys.sinp.msu.ru/conf/lpp14/240809/Askew.pdf Дата изменения: Wed Sep 16 16:32:43 2009 Дата индексирования: Tue Oct 2 00:39:37 2012 Кодировка:

Recent Electroweak Measurements at the Tevatron
Andrew Askew Florida State University for the: and experiments.
14th Lomonosov Conference on Elementary Particle Physics


A Survey:




I will provide an overview some of the most recent/most impressive results from the DЬ and CDF experiments from Run II. Analyses use from 1.04.9 fb1. W: Z: Charge d/dy Asymmetry A FB Mass/Width


Diboson: WW/WZ VV>jj+E T


TGC
2

Andrew Askew, 14th Lomonosov conference


The Tevatron:
Chicago


CDF
CD F

DDь ь



Dь

Vector boson factory L~60pb1/ week produces:


Booster Tevatron

p p


p source

Main Injector & Recycler

~1,400,000 W ~300,000 Z ~800 WW, ~240 WZ, ~100 ZZ
p

p s =1.96 TeV t = 3 9 6 ns Run I 1992-96 Run II 2001-?

Andrew Askew, 14th Lomonosov conference

3


The Detectors:
Dь
Dь

CDF
Dь

CDF



No talk is complete without at least the pictures of our beloved detectors.
Andrew Askew, 14th Lomonosov conference

4


A Word about... Z
0

W

±



Due to large backgrounds from hadronic jets, W and Z events are typically reconstructed in leptonic decays (e, , and sometimes ). There are exceptions in this talk!
Andrew Askew, 14th Lomonosov conference

5


W Charge Asymmetry:




uquark typically carries more of the proton momentum than dquark. This causes an asymmetry in the production of W bosons Asymmetry sensitive to the relative momentum distribution within proton.

d/dy (nb)

s = 1.96 TeV
Rapidity y

Andrew Askew, 14th Lomonosov conference

6


Two Different Approaches:


Assume the W mass, select the most probable value for pZ, and calculate W rapidity.
d (W ) / dy d (W ) / dy A( y ) d (W ) / dy d (W ) / dy



A(l )

Or one can simply form the lepton asymmetry, requires convolution with W decay.
d (l ) / d d (l ) / d d (l ) / d d (l ) / d

Both methods require large lepton acceptance in , and low charge misidentification.
7

Andrew Askew, 14th Lomonosov conference


CDF Results: W asymmetry






CDF solves for the W rapidity, and plots the true charge asymmetry. First measurement of the true W asymmetry. Uncertainties are smaller than PDF uncert., largely still statistics driven.

PRL 102, 181801, 2009.
Andrew Askew, 14th Lomonosov conference

8


DЬ Results: Lepton Asymmetry




DЬ measures the lepton asymmetry, rather than perform the transformation to the W rapidity. Performed in both electron and muon channels:


PRL 101, 211801, 2008.



Electron: wide acceptance Muon: high statistics, over 2.3 million W candidates.
Andrew Askew, 14th Lomonosov conference

9


W Mass and Width:


Sketch of method:


MW = 81 GeV MW = 80 GeV



Build a parametrized simulation of the detector that incorporates all knowledge of both energy/momentum scale and resolution. Generate distributions with different MW, W. Form W transverse mass distribution from the data. Compare. M = 2 p p
l

MW: sensitive to the edge of M

T





T

T

T

(1 - cos l )

W: sensitive to the tail of MT

Andrew Askew, 14th Lomonosov conference

10


DЬ WWidth Result:



DЬ uses central electrons only, and 1 fb of data. Most precise single measurement to date. In good agreement with world average W = 2.028±0.072 GeV. 11
1
Andrew Askew, 14th Lomonosov conference


DЬ WMass Result:
arXiv.org:0908.0766



DЬ uses central electrons only, and 1 fb1 of data. Most precise single measurement to date. In good agreement with world average. 12 Andrew Askew, 14 Lomonosov conference
th


Tevatron Combination:


The current state of the art.




Tevatron combination now more precise than the LEP combination. World average is now 23 MeV, and Run II isn't over yet!
arXiv:0908.1374v1

Andrew Askew, 14th Lomonosov conference

13


High Statistics of Z events:



Through differential cross section measurements, one may probe different parts of the underlying production processes:




Z Rapidity: Parton distribution functions, and NLO calculations. AFB: Measurement of sin2W



Also: With high statistics of Z events, one can gain a better understanding of efficiencies and energy scale. 14 Andrew Askew, 14 Lomonosov conference
th


CDF Z rapidity:



At leading order, sensitive to PDFs:


Partons carry different momentum fractions, which then affect the rapidity of the produced */Z.



At nexttoleading order, one starts including gluons in the initial state, which also alter the rapidity of the produced */Z, and thus this measurement gives a test of these calculations.
Andrew Askew, 14th Lomonosov conference

15


CDF Z Rapidity (2)




~168 K */Z candidates (66 < Mee < 116), with small backgrounds. Coverage extending to 2.8 in yZ. Uncertainties are small, in most places small enough to improve the PDF modeling.
Andrew Askew, 14th Lomonosov conference



16


DЬ AFB measurement


Setting aside the rapidity, focusing instead on the di electron mass spectrum:


Test the neutral current coupling to fermions, measure sin2W. Look for evidence of additional structure at high mass.
Andrew Askew, 14th Lomonosov conference



17


DЬ AFB measurement:






AFB measured to be in good agreement with SM. sin2effW = 0.2326 ±0.0018(stat)±0.0006 (syst) With full Run II dataset, combined statistical power of CDF and DЬ measurements could rival world average.
Andrew Askew, 14th Lomonosov conference

PRL 101, 191801 (2008)

18


Diboson Production:
q W q




q Z

l

Required.

W

q

Forbidden.

Z

l

Search for pairs of bosons:




Trilinear boson vertices (like W, WZ) are a feature of the Standard Model (required!). There are also instances where these are forbidden (ZZ, Z). Any deviation is new physics.
Andrew Askew, 14th Lomonosov conference

19


WW>ll



WW probes both the WWZ and WW couplings.


Major backgrounds from mismeasured missing ET. Lots of interest here, major background to HWW.
Andrew Askew, 14th Lomonosov conference

20


DЬ WWll


Selects on dilepton events (ee, e, ), and missing ET. Measured WW = 11.5±2.2 pb Use lead and trail pT to set anomalous coupling limits (or e/ pT).
Andrew Askew, 14th Lomonosov conference





arXiv.org:0904.0673

21


CDF WWll:




Using a matrix element method, select dilepton candidates (ee, e, , e+track, +track), veto on jets, and perform a fit to the likelihood ratio. 12.1+1.81.7 (stat+syst) pb
22

Andrew Askew, 14th Lomonosov conference


CDF WW AC Limits:




Using the leading lepton pT, the WW candidate spectrum from data is compared to different AC limits. An excess is observed in the highest bins, which leads to much looser observed limits.
23

Andrew Askew, 14th Lomonosov conference


DЬ WW/WZ>ljj


Uses multivariate discriminant to fit the candidate events, from ejj, jj. (WW+WZ) = 20.2 ± 4.5 pb, 4.4 significance. Set anomalous coupling limits:





PRL 102, 161801 (2009) arXiv.org:0907.4398
Andrew Askew, 14th Lomonosov conference

24


CDF WZ/WWljj




(WW+WZ) = 14.4 ± 3.8 pb, 4.6 significance. Simple 2 fit of dijet mass distribution to signal mass shape plus backgrounds shapes from data and Monte Carlo (relative normalizations fixed, absolute normalization free).

Andrew Askew, 14th Lomonosov conference

25


CDF VVjj + MET


Inclusively select two jet plus missing ET. Exploit information on MET from both tracker and calorimeter (find QCD background shape from data). Fit to measure (VV+X)= 18.0±2.8(stat)±2.4(syst) ±1.1(lumi) pb, at 5.3 significance.
Andrew Askew, 14th Lomonosov conference





arXiv:0905.4714

26


DЬ Anomalous Couplings:



Combination of anomalous coupling limits from Wl, WZlll, WWll, WW+WZljj.

arXiv.org:0907.4952

Andrew Askew, 14th Lomonosov conference

27


Conclusions:


Exciting times:


High statistics analyses making serious statements about theory and proton structure. New level of precision on MW. Full suite of diboson measurements (and some novel ones), and coupling measurements.





Still more to come!

Andrew Askew, 14th Lomonosov conference

28


Integrated Luminosity:
For some perspective on the integrated luminosity used in the analyses shown.

Andrew Askew, 14th Lomonosov conference

29


BACKUPS

Andrew Askew, 14th Lomonosov conference

30


D0 W Mass Uncertainties:

Andrew Askew, 14th Lomonosov conference

31


D0 W mass parametrized sim. Z>ee

Andrew Askew, 14th Lomonosov conference

32


D0 e/ comparison

Andrew Askew, 14th Lomonosov conference

33


D0 WW pT leptons:

Andrew Askew, 14th Lomonosov conference

34