Top quark physics: from Tevatron to LHC Page: 4 of 9
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decaying W boson in top quark pair production. This technique has proven to significantly
redure the total error due to JES. The most recent measurement from CDF using 5.6 fb-1
of data 11 yields mt = 173.0 0.7(stat) 0.6(JES) 0.9(syst) GeV, corresponding to a total
uncertainty of 1.2 GeV and a relative uncertainty of 0.7%. Figure 2 (left) shows the result of
the simultaneous fit of the JES and mt to data.
A summary of the top quark mass measurements at Tevatron and their combination as of July
2010 are presented in Fig.2 (right). They agree between different channels and different methods.
Taking correlated uncertainties properly into account the resulting preliminary Tevatron average
mass of the top quark is mt = 173.3 1.1 GeV 12. The largest uncertainty on the combined
mass of 0.46 GeV comes from the statistical component of in-situ JES determined from the fit to
data followed by the uncertainties associated with the different aspects of the signal modeling.
As the former is expected to go down with the increase of integrated luminosity, the latter will
soon become a limiting factor for the precise measurement of mt.
Mass of the Top Quark
July 2010 (* preliminary)
CDF- dilepton 167.4 i11.4(10 3141)
DO-1 dilepton 168.4i12.8(23 1 s)
CDF-II dilepton 170.6 i 3.8 (2 31)
DO-II dilepton 174.7 i 3.8 9 124)
CDF Run II Preliminary 5.6 fb1 CDF-Il epton+jets 176.1i7.4 ( 11 53)
0.8 - DO-lepton+jets 180.1 + 5.3 39 3 )
0.61_ CDF-II lepton+jets 173.0 i 1.2 711 1)
0.4 - 0-11 lepton+jets 173.7+ 1.8 ( o -1
- CDF- alljets 186.0 +11.5(10 0 5 7)
CDF-II alljets 174.8 i 2.5 1 19)
CDF-II track 175.3+ 6.9 623 0)
- A(In L) = -2.5 Tevatron combination 173.3+ 1.1 ('o6"o9)
- A(In L) = -4.5 1 1
170 171 172 173 174 175 150 160 170 180 190 200
m, (GeV/c2) m, (0eV/c2)
Figure 2: Left: result of the simultaneous fit of the JES and mt. Right: summary of the top quark mass
measurements at Tevatron and their combination.
Top quark mass measurements assume that the top quark mass is equal to the antitop
quark mass as demanded by CPT theorem. The measurement of the quark and antiquark mass
difference would probe CPT invariance. For all known quarks but the top quark this quantity has
been never measured directly because the quarks are never observed in isolation. Top quarks,
however, make this measurement possible because they decay before hadronization. DO has
published the first such measurement in 1 fb-1 of data using a matrix element technique and
found AM = 3.8 3.7 GeV 13. The CDF collaboration studied the top quark mass difference
in 5.6 fb-1 of data 14 using a template method. In this method, distributions of variables
strongly correlated with mt and derived from simulations for different mt hypotheses are used
as templates to extract mt from the fit to the measured distribution in data. CDF finds AM =
-3.3 1.4(stat) 1.0(syst) GeV. Both measurements are in good agreement with the SM within
large uncertainties dominated by statistical one which can be significantly reduced by the end
of the Tevatron run.
The first top quark mass measurements at LHC are expected to be carried out with -100
pb-1 of integrated luminosity. Both CMS and Atlas experiments plan to use template method
in the early data in combination with the jet energy calibration information provided by the
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Shabalina, E.K. & /Gottingen U., II. Phys. Inst. Top quark physics: from Tevatron to LHC, article, October 1, 2010; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc1012260/m1/4/: accessed April 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.