First observed in 1995, the top quark is the third-generation uptype quark of the standard model of particle physics (SM). The CDF and DØ

collaborations have analyzed many tt

¯ events produced by the Tevatron collider,

studying many properties of the top quark. Among these, the mass of the top quark

is a fundamental parameter of the SM, since its value constrains the mass of the yet

to be observed Higgs boson. The analyzed events were used to measure the mass of

the top quark mt  173.2 GeV/c2 with an uncertainty of less than 1 GeV/c2. We

report on the latest top mass measurements at the Tevatron, using up to 6 fb−1 of

data for each experiment

Potamianos, K.

English

First observed in 1995, the top quark is the third-generation up-type quark of the standard model of particle physics (SM). The CDF and D0 collaborations have analyzed many t{bar t} events produced by the Tevatron collider, studying many properties of the top quark. Among these, the mass of the top quark is a fundamental parameter of the SM, since its value constrains the mass of the yet to be observed Higgs boson. The analyzed events were used to measure the mass of the top quark m{sub t} {approx_equal} 173.2 GeV/c{sup 2} with an uncertainty of less than 1 GeV/c{sup 2}. We report on the latest top mass measurements at the Tevatron, using up to 6 fb{sup -1} of data for each experiment

Potamianos, Karolos

UNT (University of North Texas) Digital Library

IL NUOVO CIMENTO Vol. ?, N. ? ?Top Mass Measurements at the TevatronK. Potamianos(1)(1) Purdue University, West Lafayette, IN, USASummary. — First observed in 1995, the top quark is the third-generation up-type quark of the standard model of particle physics (SM). The CDF and DØcollaborations have analyzed many tt̄ events produced by the Tevatron collider,studying many properties of the top quark. Among these, the mass of the top quarkis a fundamental parameter of the SM, since its value constrains the mass of the yetto be observed Higgs boson. The analyzed events were used to measure the mass ofthe top quark mt ≃ 173.2 GeV/c2 with an uncertainty of less than 1 GeV/c2. Wereport on the latest top mass measurements at the Tevatron, using up to 6 fb−1 ofdata for each experiment.PACS 14.65.Ha – Top quarks.1. – IntroductionThe top quark is the third generation up-type quark. It was discovered in 1995 by theCDF and DØ experiments at the Tevatron [1], in events where it is produced togetherwith an antitop quark. It has a charge of + 23e and a mass ofmt = 173.2± 0.9 GeV/c2 [2];it is the most massive elementary particle known to date. According to the standardmodel (SM), it has a Yukawa coupling to the Higgs boson close to unity, which hints toa possible special role in electroweak symmetry breaking. It interacts primarily throughthe strong interaction but also through the weak force. In 2009, the CDF and DØ exper-iments observed the production of a single top quark through the weak interaction [3].Since its observation, the top quark has been extensively studied, and is currently oneof the main physics programs at the Tevatron. It has a very short lifetime (∼ 10−25 s)and hence decays before hadronizing, providing a unique opportunity to study a barequark. Therefore, top quark physics is a window into new physics.The mass of the top quark mt is a parameter of the standard model, and must bedetermined experimentally. Its precise determination constrains the mass of the SM Higgsboson as well as models beyond the SM. We summarize the latest top mass measurementsfrom the CDF and DØ collaborations. A much more detailed account is given in Ref. [4].c© Società Italiana di Fisica 1FERMILAB-CONF-11-697-PPDOperated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.  2 K. POTAMIANOS2. – Top Quark PhysicsAt the Tevatron pp̄ collider, the top quark is mainly produced in top-antitop (tt̄) pairsthrough quark-antiquark (85% contribution) and gluon-gluon (15% contribution) fusion.It decays through the weak force almost exclusively into a W boson and a b quark.The production of top pairs is studied according to the tt̄ decay mode: dilepton, lep-ton+jets and all-hadronic, depending on whether two, one, or none of the W decayedleptonically. The lepton+jets is considered the golden channel because it combined agood branching fraction (∼ 30%) with a good signal to background ratio. The dilepton(ee, eµ, µµ) channel is the cleanest but suffers from a small branching fraction (∼ 5%).The all-hadronic channel has the largest branching fraction (∼ 45%) but suffers froma huge level of background from QCD multijet production. An additional channel,6ET+jets, is used to recover events where the e or µ is not identified in the detector,or when the τ decays hadronically; it also suffers from a large QCD background.3. – Mass Measurement TechniquesTop mass measurements usually proceed with the reconstruction of mt from the decayproducts of the top quark. For this purpose, the lepton+jets and all-hadronic channelsare amenable to kinematic fitting using χ2 minimization, since the number of kinematicconstraints available exceeds that of unknown quantities. This method is known as thetemplate method. For the dilepton and 6ET+jets signatures, the kinematic constraintsare insufficient to determine mt and requires determining the kinematic properties of theneutrinos compatible with the observed 6ET (e.g., neutrino weighting algorithms).In another technique, the matrix element method (MEM), one calculates event obser-vation probabilities by integrating over all parton-level quantities in the reaction phasespace; this method is an application of the Bayesian principle of integrating overall un-observed degrees of freedom with a prior provided by the theory (SM). The ideogrammethod is similar to the MEM, except in the evaluation of the signal and backgroundevent probabilities forming the event observation probability.For details on the different analysis techniques used at the Tevatron, we redirect thereader to Ref. [4].4. – Top Mass MeasurementsThe most precise determination of mt from a single channel comes from lepton+jets(Fig. 1(a)). Both experiments use a MEM with in situ jet energy scale (JES) calibra-tion (1). We measure mt = 173.0± 1.2 GeV/c2 (CDF) [5] and mt = 174.9± 1.5 GeV/c2(DØ) [6]. The CDF all-hadronic analysis (Fig. 1(c)) extracts the top mass from eventswith 6 to 8 jets, of which one at least is determined to originate from a b quark,obtaining mt = 172.5± 2.0 GeV/c2 [7]. In the dilepton channel, we measure mt =170.3±3.7 GeV/c2 (CDF) [8] and mt = 174.0± 3.1 GeV/c2 (DØ) [9]. The CDF analysisalso performs a simultaneous fit of the top mass in the lepton+jets and dilepton chan-(1) The JES is constrained by measuring the mass of the hadronically decaying W simulta-neously to that of the top mass (Fig. 1(b)). Using this technique the uncertainty on the JESbecomes statistical rather than systematic, significantly increasing the sensitivity of the mea-surements.TOP MASS MEASUREMENTS AT THE TEVATRON 3 GeVtm170 172 174 176 178 180 182JESk0.980.9911.011.021.031.041.051.06-1DØ, 2.6 fb 1sd2sd3sd(a) DØ lepton+jets]2 [GeV/crecWm20 40 60 80 100 120 140 160 180 200]2Events/[5.0 GeV/c020406080100120140]2Events/[5.0 GeV/c  2-tag events≥     Datat Fitted t Fitted Bkg/Ndof = 38.2 / 312χProb = 0.174)-1CDF Run II Preliminary (5.8 fb(b) CDF all-hadronic mW]2 [GeV/crectm100 150 200 250 300]2Events/[5.0 GeV/c010203040506070]2Events/[5.0 GeV/c  2-tag events≥     Datat Fitted t Fitted Bkg/Ndof = 30.7 / 242χProb = 0.162)-1CDF Run II Preliminary (5.8 fb(c) CDF all-hadronic mt)2 (GeV/chad,recotm50 100 150 200 250 300 350 400 450)2Events/(16 GeV/c0102030405060)-1Data (5.7 fbSignal+BkgdBkgd only 2-taghad,recotm(d) CDF 6ET+jetsTop quark pole mass (GeV)150 160 170 180 190 (pb)ttσ2468101214+X)t t→p(pσMeasured σMeasured dependence of Approximate NNLONLO+NNLL (pb)ttσ-1DØ, L=5.3 fb (e) DØ pole mass (GeV)tm170 175 180 (GeV)tm170175180(a) -1DØ 3.6 fbe+jets(f) DØ ∆mFig. 1. – Several top mass measurements. (a) DØ lepton+jets [6], (b) in-situ JES calibrationfrom hadronic reconstruction of mW , (c) CDF all-hadronic [7], (d) CDF 6ET+jets [10], (e) DØpole mass from tt̄ cross-section measurement [12], and (f) DØ determination of mt vs. m′t [14].nels, yielding mt = 172.1± 1.4 GeV/c2; this fit brings the JES determination from thelepton+jets channel to the dilepton channel.The 6ET+jets CDF analysis uses two different templates reconstructing the hadroni-cally decaying top quark (Fig. 1(d)). We measure mt = 172.3 ± 2.6 GeV/c2 [10]. TheCDF analysis in the hadronic τ+jets channel measures the mass of the top quark for thefirst time in this signature. Using 2.2 fb−1, we measure mt = 172.7± 10.0 GeV/c2 [11].DØ also determines mt from the tt̄ cross-section (Fig. 1(e)). We measure mpolet =167.5 ± 5.0 GeV/c2 and mMSt = 160.0 ± 4.6 GeV/c2 [12]. The experimental mt cor-responds to the pole mass.The difference between the top mass and that of its antiparticle, ∆m = mt − m′t(Fig. 1(f)). If CPT is conserved, ∆m = 0. This assumption is used for all top massdeterminations. We determine ∆m = −3.3 ± 1.7 GeV/c2 (CDF) [13] and ∆m = 0.8 ±1.9 GeV/c2 (DØ) [14], in agreement with SM predictions. The CDF analysis measuresdirectly ∆m, while the DØ analysis measures mt and m′t separately.5. – Tevatron CombinationThe published Run I (1992–1996)measurements from CDF and DØ are combined withthe most precise published and preliminary Run II (2001-2011) measurements using up to5.8 fb−1 of data. Taking uncertainty correlations into account, and adding in quadrature4 K. POTAMIANOS)2 (GeV/ctopm150 160 170 180 190 200015CDF March’07  2.7±     12.4  2.2)± 1.5 ±(Tevatron combination *  0.9±     173.2  0.8)± 0.6 ±(  syst)± stat  ±(CDF-II MET+Jets *  2.6±     172.3  1.8)± 1.8 ±(CDF-II track  9.5±     166.9  2.9)± 9.0 ±(CDF-II alljets *  2.1±     172.5  1.5)± 1.4 ±(CDF-I alljets 11.5±     186.0  5.7)±10.0 ±(DØ-II lepton+jets  1.5±     174.9  1.2)± 0.8 ±(CDF-II lepton+jets  1.2±     173.0  1.1)± 0.6 ±(DØ-I lepton+jets  5.3±     180.1  3.6)± 3.9 ±(CDF-I lepton+jets  7.4±     176.1  5.3)± 5.1 ±(DØ-II dilepton  3.1±     174.0  2.5)± 1.8 ±(CDF-II dilepton  3.8±     170.6  3.1)± 2.2 ±(DØ-I dilepton 12.8±     168.4  3.6)±12.3 ±(CDF-I dilepton 11.4±     167.4  4.9)±10.3 ±(Mass of the Top Quark(* preliminary)July 2011/dof = 8.3/11 (68.5%)2χ(a)Analysis |Wi| in the Tevatron combination∑|Wi|/ 00.10.20.30.40.5 CDF-II lepton+jetsDØ-II lepton+jetsCDF-II alljetsCDF-II MET+JetsCDF-I lepton+jetsDØ-II dileptonCDF-II dileptonCDF-I dileptonCDF-I alljetsCDF-II trackDØ-I dileptonDØ-I lepton+jets(b)Fig. 2. – (a) Tevatron top mass combination together with the results from the individualanalyses. (b) Relative weight of each analysis in the combination.the statistical and systematic uncertainties, the resulting preliminary Tevatron averagemass of the top quark is mt = 173.2±0.9 GeV/c2 [2]. The uncertainty is for the first timebelow 1 GeV/c2. These results are summarized in Fig. 2. The precise determination ofmt and other properties of the top quark will remain an important legacy of the Tevatron.REFERENCES[1] S. Abachi et al., Phys. Rev. Lett., 74:2632–2637, 1995F. Abe et al., Phys. Rev. Lett., 74:2626–2631, 1995.[2] Tevatron EW Working Group, CDF and DØ Collaborations, arXiv:1107.5255 [hep-ex].[3] T. Aaltonen et al., Phys.Rev.Lett., 103:092002, 2009V. M. Abazov et al. [D0 Collaboration], Phys. Rev. Lett. 103 (2009) 092001[4] A. B. Galtieri et al. [CDF and D0 Collaboration], arXiv:1109.2163 [hep-ex].[5] T. Aaltonen et al. [CDF Collaboration], Phys. Rev. Lett. 105 (2010) 252001[6] V. M. Abazov et al. [The D0 Collaboration], Phys. Rev. D 84 (2011) 032004[7] T. Aaltonen et al. [CDF Collaboration], CDF/PHYS/TOP/PUBLIC/10456T. Aaltonen et al. [The CDF Collaboration], Phys. Rev. D 81 (2010) 052011[8] T. Aaltonen et al. [CDF Collaboration], Phys. Rev. D 83 (2011) 111101[9] V. M. Abazov et al. [D0 Collaboration], Phys. Rev. Lett. 107 (2011) 082004[10] T. Aaltonen et al. [CDF Collaboration], Phys. Rev. Lett. 107 (2011) 232002[11] T. Aaltonen et al. [CDF Collaboration], CDF/PUB/TOP/PUBLIC/10562[12] V. M. Abazov et al. [D0 Collaboration], Phys. Lett. B 703 (2011) 422[13] T. Aaltonen et al. [CDF Collaboration], Phys. Rev. Lett. 106 (2011) 152001[14] V. M. Abazov et al. [D0 Collaboration], Phys. Rev. D 84 (2011) 052005

Top Mass Measurements at the Tevatron

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2012-11227-4Colloquia: TOP2011IL NUOVO CIMENTO Vol. 35 C, N. 3 Maggio-Giugno 2012Top mass measurements at the TevatronK. PotamianosPurdue University - West Lafayette, IN, USAricevuto l’ 1 Marzo 2012pubblicato online il 31 Maggio 2012Summary. — First observed in 1995, the top quark is the third-generation up-type quark of the standard model of particle physics (SM). The CDF and DØcollaborations have analyzed many tt¯ events produced by the Tevatron collider,studying many properties of the top quark. Among these, the mass of the top quarkis a fundamental parameter of the SM, since its value constrains the mass of the yetto be observed Higgs boson. The analyzed events were used to measure the mass ofthe top quark mt  173.2GeV/c2 with an uncertainty of less than 1GeV/c2. Wereport on the latest top mass measurements at the Tevatron, using up to 6 fb−1 ofdata for each experiment.PACS 14.65.Ha – Top quarks.1. – IntroductionThe top quark is the third generation up-type quark. It was discovered in 1995 by theCDF and DØ experiments at the Tevatron [1], in events where it is produced togetherwith an antitop quark. It has a charge of +23e and a mass of mt = 173.2± 0.9GeV/c2 [2];it is the most massive elementary particle known to date. According to the standardmodel (SM), it has a Yukawa coupling to the Higgs boson close to unity, which hints toa possible special role in electroweak symmetry breaking. It interacts primarily throughthe strong interaction but also through the weak force. In 2009, the CDF and DØ exper-iments observed the production of a single top quark through the weak interaction [3].Since its observation, the top quark has been extensively studied, and is currently oneof the main physics programs at the Tevatron. It has a very short lifetime (∼ 10−25 s)and hence decays before hadronizing, providing a unique opportunity to study a barequark. Therefore, top quark physics is a window into new physics.The mass of the top quark mt is a parameter of the standard model, and must bedetermined experimentally. Its precise determination constrains the mass of the SM Higgsboson as well as models beyond the SM. We summarize the latest top mass measurementsfrom the CDF and DØ collaborations. A much more detailed account is given in ref. [4].c© Societa` Italiana di Fisica 103104 K. POTAMIANOS2. – Top quark physicsAt the Tevatron pp¯ collider, the top quark is mainly produced in top-antitop (tt¯) pairsthrough quark-antiquark (85% contribution) and gluon-gluon (15% contribution) fusion.It decays through the weak force almost exclusively into a W boson and a b quark.The production of top pairs is studied according to the tt¯ decay mode: dilepton, lep-ton+jets and all-hadronic, depending on whether two, one, or none of the W decayedleptonically. The lepton+jets is considered the golden channel because it combined agood branching fraction (∼ 30%) with a good signal to background ratio. The dilepton(ee, eμ, μμ) channel is the cleanest but suffers from a small branching fraction (∼ 5%).The all-hadronic channel has the largest branching fraction (∼ 45%) but suffers froma huge level of background from QCD multijet production. An additional channel,ET+jets, is used to recover events where the e or μ is not identified in the detector,or when the τ decays hadronically; it also suffers from a large QCD background.3. – Mass measurement techniquesTop mass measurements usually proceed with the reconstruction of mt from the decayproducts of the top quark. For this purpose, the lepton+jets and all-hadronic channelsare amenable to kinematic fitting using χ2 minimization, since the number of kinematicconstraints available exceeds that of unknown quantities. This method is known as thetemplate method. For the dilepton and ET+jets signatures, the kinematic constraintsare insufficient to determine mt and requires determining the kinematic properties of theneutrinos compatible with the observed ET (e.g., neutrino weighting algorithms).In another technique, the matrix element method (MEM), one calculates event obser-vation probabilities by integrating over all parton-level quantities in the reaction phasespace; this method is an application of the Bayesian principle of integrating overall un-observed degrees of freedom with a prior provided by the theory (SM). The ideogrammethod is similar to the MEM, except in the evaluation of the signal and backgroundevent probabilities forming the event observation probability.For details on the different analysis techniques used at the Tevatron, we redirect thereader to ref. [4].4. – Top mass measurementsThe most precise determination of mt from a single channel comes from lepton+jets(fig. 1(a)). Both experiments use a MEM with in situ jet energy scale (JES) calibra-tion (1). We measure mt = 173.0± 1.2GeV/c2 (CDF) [5] and mt = 174.9± 1.5GeV/c2(DØ) [6]. The CDF all-hadronic analysis (fig. 1(c)) extracts the top mass fromevents with 6 to 8 jets, of which one at least is determined to originate from a bquark, obtaining mt = 172.5± 2.0GeV/c2 [7]. In the dilepton channel, we measuremt = 170.3 ± 3.7GeV/c2 (CDF) [8] and mt = 174.0± 3.1GeV/c2 (DØ) [9]. The CDFanalysis also performs a simultaneous fit of the top mass in the lepton+jets and dileptonchannels, yielding mt = 172.1± 1.4GeV/c2; this fit brings the JES determination fromthe lepton+jets channel to the dilepton channel.(1) The JES is constrained by measuring the mass of the hadronically decaying W simultane-ously to that of the top mass (fig. 1(b)). Using this technique the uncertainty on the JES becomesstatistical rather than systematic, significantly increasing the sensitivity of the measurements.TOP MASS MEASUREMENTS AT THE TEVATRON 105Fig. 1. – Several top mass measurements. (a) DØ lepton+jets [6], (b) in situ JES calibrationfrom hadronic reconstruction of mW , (c) CDF all-hadronic [7], (d) CDF ET+jets [10], (e) DØpole mass from tt¯ cross-section measurement [12], and (f) DØ determination of mt vs. m′t [14].Fig. 2. – (a) Tevatron top mass combination together with the results from the individualanalyses. (b) Relative weight of each analysis in the combination.106 K. POTAMIANOSThe ET+jets CDF analysis uses two different templates reconstructing the hadron-ically decaying top quark (fig. 1(d)). We measure mt = 172.3 ± 2.6GeV/c2 [10]. TheCDF analysis in the hadronic τ+jets channel measures the mass of the top quark for thefirst time in this signature. Using 2.2 fb−1, we measure mt = 172.7 ± 10.0GeV/c2 [11].DØ also determines mt from the tt¯ cross-section (fig. 1(e)). We measure mpolet =167.5 ± 5.0GeV/c2 and mMSt = 160.0 ± 4.6GeV/c2 [12]. The experimental mt cor-responds to the pole mass.The difference between the top mass and that of its antiparticle, Δm = mt − m′t(fig. 1(f)). If CPT is conserved, Δm = 0. This assumption is used for all top massdeterminations. We determine Δm = −3.3 ± 1.7GeV/c2 (CDF) [13] and Δm = 0.8 ±1.9GeV/c2 (DØ) [14], in agreement with SM predictions. The CDF analysis measuresdirectly Δm, while the DØ analysis measures mt and m′t separately.5. – Tevatron combinationThe published Run I (1992–1996) measurements from CDF and DØ are combined withthe most precise published and preliminary Run II (2001-2011) measurements using up to5.8 fb−1 of data. Taking uncertainty correlations into account, and adding in quadraturethe statistical and systematic uncertainties, the resulting preliminary Tevatron averagemass of the top quark is mt = 173.2±0.9GeV/c2 [2]. The uncertainty is for the first timebelow 1GeV/c2. These results are summarized in fig. 2. The precise determination of mtand other properties of the top quark will remain an important legacy of the Tevatron.REFERENCES[1] Abachi S. et al., Phys. Rev. Lett., 74 (1995) 2632; Abe F. et al., Phys. Rev. Lett., 74(1995) 2626.[2] Tevatron EW Working Group, CDF and DØ Collaborations, arXiv:1107.5255[hep-ex].[3] Aaltonen T. et al., Phys. Rev. Lett., 103 (2009) 092002; Abazov V. M. et al. (D0Collaboration), Phys. Rev. Lett., 103 (2009) 092001.[4] Galtieri A. B. et al. (CDF and D0 Collaboration), arXiv:1109.2163 [hep-ex].[5] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 105 (2010) 252001.[6] Abazov V. M. et al. (The D0 Collaboration), Phys. Rev. D, 84 (2011) 032004.[7] Aaltonen T. et al. (CDF Collaboration), CDF/PHYS/TOP/PUBLIC/10456.Aaltonen T. et al. (The CDF Collaboration), Phys. Rev. D, 81 (2010) 052011.[8] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. D, 83 (2011) 111101.[9] Abazov V. M. et al. (D0 Collaboration), Phys. Rev. Lett., 107 (2011) 082004.[10] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 107 (2011) 232002.[11] Aaltonen T. et al. (CDF Collaboration), CDF/PUB/TOP/PUBLIC/10562.[12] Abazov V. M. et al. (D0 Collaboration), Phys. Lett. B, 703 (2011) 422.[13] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 106 (2011) 152001.[14] Abazov V. M. et al. (D0 Collaboration), Phys. Rev. D, 84 (2011) 052005.

Top mass measurements at the Tevatron

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Top mass measurements at the Tevatron

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