Differential cross sections in the top quark sector measured at the Fermilab
Tevatron collider are presented. CDF used 2.7 fb$^{-1}$ of data and measured
the differential cross section as a function of the invariant mass of the
$t\bar{t}$ system. The measurement shows good agreement with the standard model
and furthermore is used to derive limits on the ratio $\kappa /M_{Pl}$ for
gravitons which decay to top quarks in the Randall-Sundrum model. D0 used 1.0
fb$^{-1} of data to measure the differential cross section as a function of the
transverse momentum of the top quark. The measurement shows a good agreement to
the higher order perturbative QCD prediction and various predictions based on
various Monte-Carlo generators.Comment: To appear in the Proceedings of TOP2011, 4th International Workshop
  on Top Quark Physics, Spai

Jung, Andreas W.

English

arXiv

Differential cross sections in the top quark sector measured at the Fermilab Tevatron collider are presented. CDF used 2.7 fb−1 of data and measured the differential cross section as a function of the invariant mass of the t¯t system. The measurement shows good agreement with the standard model and furthermore is used to derive limits on the ratio κ/MPl for gravitons which decay to top quarks in the Randall-Sundrum model. DØ used 1.0 fb−1 of data to measure the differential cross section as a function of the transverse momentum of the top quark. The measurement shows a good agreement to the higher order perturbative QCD prediction and various predictions based on various Monte Carlo generators

Jung, A. W.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2012-11219-4Colloquia: TOP2011IL NUOVO CIMENTO Vol. 35 C, N. 3 Maggio-Giugno 2012Top differential cross section measurements (Tevatron)A. W. Jung for the DØ CollaborationFermi National Accelerator Laboratory (Fermilab) - USAricevuto l’ 1 Marzo 2012pubblicato online il 28 Maggio 2012Summary. — Differential cross sections in the top quark sector measured at theFermilab Tevatron collider are presented. CDF used 2.7 fb−1 of data and measuredthe differential cross section as a function of the invariant mass of the tt¯ system.The measurement shows good agreement with the standard model and furthermoreis used to derive limits on the ratio κ/MPl for gravitons which decay to top quarksin the Randall-Sundrum model. DØ used 1.0 fb−1 of data to measure the differentialcross section as a function of the transverse momentum of the top quark. The mea-surement shows a good agreement to the higher order perturbative QCD predictionand various predictions based on various Monte Carlo generators.PACS 14.65.Ha – Top quarks.1. – IntroductionThe top quark is the heaviest known elementary particle and was discovered at theTevatron pp¯ collider in 1995 by the CDF and DØ collaboration [1,2] at a mass of around175GeV. The production is dominated by the qq¯ annihilation process with 85% asopposed to gluon-gluon fusion which contributes only 15%. Both measurements presentedhere are performed using the l+jets channel, where one of the W bosons (stemming fromthe decay of the top quarks) decays leptonically. The other W boson decays hadronically.The l+jets channel is a good compromise between signal and background contributionwhilst having high event statistics. The branching fraction for top quarks decaying intoWb is almost 100%. Jets containing a beauty quark are identified by means of a neuralnetwork (NN) built by the combination of variables describing the properties of secondaryvertices and of tracks with large impact parameters relative to the primary vertex.2. – Measurement of the transverse momentum distribution of the top quarksThe measurement of the transverse momentum distribution of the top quarks [3]selects events with an isolated lepton with a transverse momentum pT of at least 20GeVand a pseudo-rapidity of |η| < 1.1 (e+jets) or |η| < 2.0 (μ+jets). A cut on the missingc© Societa` Italiana di Fisica 5556 A. W. JUNG for the DØ COLLABORATION]2 [GeV/cttUnfolded M0 200 400 600 800 1000 1200 140010210Unfoldedtt-1 2.7 fb≈ L ∫CDF II Data, CDF II Preliminary [GeV/c]Ttop quark p0 50 100 150 200 250 300 350 400-1 [GeV/c]T   dN / dp-210-110110 -1DØ data, 1 fbreconstructedcorrected-1 [GeV/c]T   dN / dpa) b)Fig. 1. – Panel a) compares the background-subtracted reconstructed top-quark pT distribu-tion [3] with the one corrected for the effects of finite experimental resolution (two entries perevent). Inner error bars represent the statistical uncertainty, whereas the outer one is statisticaland systematic added in quadrature. Panel b) shows the unfolded invariant mass distributionof the tt¯ system [4] compared to signal tt¯ MC.transverse energy (ET ) of 20GeV is applied. Furthermore at least four jets are requiredwith pT > 20GeV and |η| < 2.5, an additional cut of pT > 40GeV is applied for theleading jet. Finally at least one jet needs to be identified as a b-jet. For the reconstructionof the event kinematics additional constraints are used: the masses of the two W bosonsare constrained to 80.4GeV. Furthermore the masses of the two reconstructed top quarksare assumed to be equal. All possible permutations of objects are considered where thefinal solution is the one with the smallest χ2.Figure 1a) shows the background-subtracted reconstructed top-quark pT distributioncompared to the one corrected for finite experimental resolution. The latter is derivedby using regularized matrix unfolding. Figure 1b) compares the unfolded invariant massdistribution of the tt¯ system to the expectation using tt¯ signal MC. The correction forfinite detector resolution is again done using regularized unfolding.Figure 2a) shows the differential cross section as a function of top-quark pT , where theleptonic and hadronic decay of the W boson to the top-quark cross section are combined.All predictions use the proton parton density function (PDF) CTEQ61 with the scaleset to μr = μf = mt (mt = 170GeV) except for the approximate NNLO perturbativeQCD (pQCD) prediction which uses the MSTW08 PDF. The normalization is nicelydescribed by pQCD in (N)NLO, however there is an offset for PYTHIA and ALPGEN innormalization. Figure 2b) shows that the shape is reasonable described by all predictions.The inclusive total cross section for tt¯ production is measured to σ = 8.31±1.28(stat.) pband in good agreement with the latest theoretical predictions of σ = 6.41±0.510.42 pb [5] andσ = 7.46±0.480.67 pb [6].3. – Measurement of the invariant mass distribution of the tt¯ systemThis measurement of the invariant mass distribution of the tt¯ system Mtt¯ [4] selectsevents with an isolated lepton with a pT of at least 20GeV and a pseudo-rapidity ofTOP DIFFERENTIAL CROSS SECTION MEASUREMENTS (TEVATRON) 57 [GeV/c]Ttop quark p0 50 100 150 200 250 300 350 400Shape ratio to NLO pQCD0.60.81.01.21.41.61.82.0 -1 DØdata, 1 fbNLO pQCD scale uncertaintyApprox. NNLO pQCDMC@NLOPYTHIAALPGENShape ratio to NLO pQCD [GeV/c]Ttop quark p0 50 100 150 200 250 300 350 400]-1 [pb/GeVcT / dpσ   d0.020.040.060.080.10.120.140.16 -1DØ data, 1 fbNLO pQCDApprox. NNLO pQCDMC@NLOPYTHIAALPGEN]-1 [pb/GeVcT / dpσ   da) b)Fig. 2. – a) Differential cross section data (points) as a function of top-quark pT (two entriesper event) [3] compared with expectations from NLO pQCD (solid lines), from an approximateNNLO pQCD calculation, and for several event generators (dashed and dot-dashed lines). Thegray band reflects uncertainties on the pQCD scale and parton distribution functions. Innererror bars represent the statistical uncertainty, whereas the outer one is statistical and system-atic added in quadrature. b) shows the ratio of (1/σ)dσ/dpT relative to NLO pQCD for anapproximate NNLO pQCD calculation and of predictions for several event generators.|η| < 1.1. A cut on the missing transverse energy of 20GeV is applied. Furthermore atleast four jets are required with pT > 20GeV and |η| < 2.0. Finally at least one jet needsto be identified as a b-jet. The hadronic W decay is used to constrain the Jet EnergyScale (JES). Mtt¯ is reconstructed by using the four-vectors of the b-tagged jet and thethree remaining leading jets in the event, the lepton and the transverse components ofthe neutrino momentum, given by ET .]2 [GeV/cttUnfolded M0 200 400 600 800 1000 1200 1400]2[fb/GeV/ctt/dMσd-110110SM ExpectationSM Uncertainties-1 2.7 fb≈ L ∫CDF II Data, CDF II PreliminaryPl/Mκ0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2CL00.20.40.60.81CL-1 2.7 fb≈ L ∫CDF II Data, Expected CL Uncertaintyσ1 Uncertaintyσ2Observed CL2 = 600 GeV/c1mCDF II Preliminarya) b)Fig. 3. – (Color online) Panel a) shows the differential tt¯ cross section (circles) as a function ofMtt¯ [4] compared to the standard model expectation (line). The SM uncertainty (green band)reflects all systematic uncertainties, except for the luminosity uncertainty in each bin. Panel b)shows limits on the ratio κ/MPl for gravitons which decay to top quarks in the Randall-Sundrummodel, where the mass of the first resonance is fixed at 600GeV. Values of κ/MPl > 0.16 areexcluded at the 95% confidence level.58 A. W. JUNG for the DØ COLLABORATIONFigure 3a) shows the differential tt¯ cross section as a function of Mtt¯ compared tothe standard model expectation using the proton PDF CTEQ5L PDF with a top massof 175GeV. The SM uncertainty reflects all systematic uncertainties, except for theluminosity uncertainty in each bin. Especially the tail of Mtt¯ is sensitive to broad en-hancements as well as to narrow resonances, which is why the agreement between dataand SM expectation has been evaluated. There is no indication of beyond standardmodel contributions to the differential cross section. The analysis also measured theinclusive total cross section for tt¯ production to: σ = 6.9± 1.0(stat. + JES) pb, which isin good agreement with latest theoretical predictions [5,6] as well as with the DØ result.Furthermore the distribution has been used to derive a limit on gravitons which decayto top quarks in the Randall-Sundrum model. The mass of the first resonance is fixed to600GeV and gravitons are modeled using MadEvent plus Pythia. Figure 3b) shows thederived limits, values of κ/MPl > 0.16 are excluded at the 95% confidence level.4. – ConclusionTwo differential cross section measurements have been presented. The cross sectionas a function of the transverse momentum of the top quark by DØ [3] and as a functionof the invariant mass of the tt¯ system by CDF [4]. Both presented results are consistentwith the standard model cross section predictions. The final Tevatron data sample has5–10 times the presented statistics allowing for more precise measurements in the nearfuture being one of the legacy measurements of the Tevatron.REFERENCES[1] Abe F. et al. (CDF Collaboration), Phys. Rev. Lett., 74 (1995) 2626 [arXiv:hep-ex/9503002].[2] Abachi S. et al. (DØ Collaboration), Phys. Rev. Lett., 74 (1995) 2632 [arXiv:hep-ex/9503003].[3] Abazov V. et al. (DØ Collaboration), Phys. Lett. B, 693 (2010) 515 [arXiv.org:1001.1900].[4] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 102 (2003) 22 [arXiv.org:0903.2850].[5] Ahrens V., Ferroglia A., Neubert M., Pecjak B. D. and Yang L. L., JHEP, 09(2010) 097; Ahrens V., Ferroglia A., Neubert M., Pecjak B. D. and Yang L. L.,Nucl. Phys. Proc. Suppl., 205-206 (2010) 48.[6] Moch S. and Uwer P., Phys. Rev. D, 78 (2008) 034003; Langenfeld U., Moch S. andUwer P., Phys. Rev. D, 80 (2009) 054009; Aliev M. et al., Comput. Phys. Commun., 182(2011) 1034.

Top differential cross section measurements (Tevatron)

Differential cross sections in the top quark sector measured at the Fermilab Tevatron collider are presented. CDF used 2.7 fb{sup -1} of data and measured the differential cross section as a function of the invariant mass of the t{bar t} system. The measurement shows good agreement with the standard model and furthermore is used to derive limits on the ratio {kappa}/M{sub Pl} for gravitons which decay to top quarks in the Randall-Sundrum model. D0 used 1.0 fb{sup -1} of data to measure the differential cross section as a function of the transverse momentum of the top-quark. The measurement shows a good agreement to the next-to-leading order perturbative QCD prediction and various other standard model predictions

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IL NUOVO CIMENTO Vol. ?, N. ? ?Top differential cross section measurements (Tevatron)Andreas W. Jung(1) (for the DØ collaboration)(1) Fermi National Accelerator Laboratory (Fermilab), USAE-mail: ajung@fnal.govFERMILAB-CONF-11-677-PPDSummary. — Differential cross sections in the top quark sector measured at theFermilab Tevatron collider are presented. CDF used 2.7 fb−1 of data and measuredthe differential cross section as a function of the invariant mass of the tt̄ system. Themeasurement shows good agreement with the standard model and furthermore isused to derive limits on the ratio κ/MPl for gravitons which decay to top quarks inthe Randall-Sundrum model. DØ used 1.0 fb−1 of data to measure the differentialcross section as a function of the transverse momentum of the top-quark. Themeasurement shows a good agreement to the next-to-leading order perturbativeQCD prediction and various other standard model predictions.PACS 13,14 –PACS . – 13,14.1. – IntroductionThe top quark is the heaviest known elementary particle and was discovered at theTevatron pp̄ collider in 1995 by the CDF and DØ collaboration [1, 2] at a mass of around175 GeV. The production is dominated by the qq̄ annihilation process with 85% asopposed to gluon-gluon fusion which contributes only 15%. Both measurements presentedhere are performed using the l+jets channel, where one of the W bosons (stemming fromthe decay of the top quarks) decays leptonically. The other W boson decays hadronically.The l+jets channel is a good compromise between signal and background contributionwhilst having high event statistics. The branching fraction for top quarks decaying intoWb is almost 100%. Jets containing a beauty quark are identified by means of a neuralnetwork (NN) build by the combination of variables describing the properties of secondaryvertices and of tracks with large impact parameters relative to the primary vertex.2. – Measurement of the transverse momentum distribution of the top-quarksThe measurement of the transverse momentum distribution of the top-quarks [3] se-lects events with an isolated lepton with a transverse momentum pT of at least 20 GeVc© Società Italiana di Fisica 1FERMILAB-CONF-11-677-PPDOperated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.  2 ANDREAS W. JUNG (FOR THE DØ COLLABORATION)and a pseudo-rapidity of |η| < 1.1. A cut on the missing energy of 20 GeV is done. Fur-thermore at least four jets are required with pT > 20 GeV and |η| < 2.5, an additionalcut of pT > 40 GeV is applied for the leading jet. Finally at least one jet needs to beidentified as a b-jet. For the reconstruction of the event kinematics additional constraintsare used: the mass of the W boson for the hadronic W decay and the mass of the topquark for combining the b-jet to the W candidate.Figure 1a) shows the background-subtracted reconstructed top-quark pT distribution]2 [GeV/cttUnfolded M0 200 400 600 800 1000 1200 140010210Unfoldedtt-1 2.7 fb≈ L ∫CDF II Data, CDF II Preliminary [GeV/c]Ttop quark p0 50 100 150 200 250 300 350 400-1 [GeV/c]T   dN / dp-210-110110 -1DØ data, 1 fbreconstructedcorrected-1 [GeV/c]T   dN / dpa) b)Fig. 1. – a) compares the background-subtracted reconstructed top-quark pT distribution [3]with the one corrected for the effects of finite experimental resolution (two entries per event).Inner error bars represent the statistical uncertainty, whereas the outer one is statistical andsystematic added in quadrature. b) shows the unfolded invariant mass distribution of the tt̄system [4] compared to signal tt̄ MC.(line, two entries per event) compared to the one corrected for finite experimental reso-lution (circles, two entries per event). The latter is derived by using regularized matrixunfolding. b) compares the unfolded invariant mass distribution of the tt̄ system (cir-cles) to the expectation using tt̄ signal MC. The correction for finite detector resolutionis again done using regularized unfolding.Figure 2a) shows the differential cross section as a function of pT , where the leptonicand hadronic decay of the W boson to the top-quark cross section are combined. Allpredictions use the proton parton density function (PDF) CTEQ61 with the scale setto µr/f = mt (mt = 170 GeV) except for the approximate NNLO perturbative QCD(pQCD) prediction which uses the MSTW08 PDF. The normalization is nicely describedby pQCD in (N)NLO, however there is an offset for PYTHIA and ALPGEN in normal-ization. Figure 2b) shows that the shape is reasonable described by all predictions. Theinclusive total cross section for tt̄ production is measured to σ = 8.31 ± 1.28(stat.) pband in good agreement with the latest theoretical predictions of σ = 6.41 ±0.510.42 pb [5]and σ = 7.46 ±0.480.67 pb [6].3. – Measurement of the invariant mass distribution of the tt̄ systemThis measurement of the invariant mass distribution of the tt̄ system Mtt̄ [4] selectsevents with an isolated lepton with a pT of at least 20 GeV and a pseudo-rapidity ofTOP DIFFERENTIAL CROSS SECTION MEASUREMENTS (TEVATRON) 3 [GeV/c]Ttop quark p0 50 100 150 200 250 300 350 400Shape ratio to NLO pQCD0.60.81.01.21.41.61.82.0 -1 DØdata, 1 fbNLO pQCD scale uncertaintyApprox. NNLO pQCDMC@NLOPYTHIAALPGENShape ratio to NLO pQCD [GeV/c]Ttop quark p0 50 100 150 200 250 300 350 400]-1 [pb/GeVcT / dpσ   d0.020.040.060.080.10.120.140.16 -1DØ data, 1 fbNLO pQCDApprox. NNLO pQCDMC@NLOPYTHIAALPGEN]-1 [pb/GeVcT / dpσ   da) b)Fig. 2. – a) Differential cross section data (points) as a function of top-quark pT (two entriesper event) [3] compared with expectations from NLO pQCD (solid lines), from an approximateNNLO pQCD calculation, and for several event generators (dashed and dotdashed lines). Thegray band reflects uncertainties on the pQCD scale and parton distribution functions. Innererror bars represent the statistical uncertainty, whereas the outer one is statistical and system-atic added in quadrature. b) shows the ratio of (1/σ)dσ/dpT relative to NLO pQCD for anapproximate NNLO pQCD calculation and of predictions for several event generators.|η| < 1.1. A cut on the missing energy of 20 GeV is done. Furthermore at least fourjets are required with pT > 20 GeV and |η| < 2.0. Finally at least one jet needs to beidentified as a b-jet. The hadronic W decay is used to constrain the Jet Energy Scale(JES). Mtt̄ is reconstructed by using the four-vectors of the b-tagged jet and the threeremaining leading jets in the event, the lepton and the transverse components of theneutrino momentum, given by 6ET .Figure 3a) shows the differential tt̄ cross section (circles) as a function of Mtt̄ comparedto the standard model expectation (line) using the proton PDF CTEQ5L PDF with a topmass of 175 GeV. The SM uncertainty (green band) reflects all systematic uncertainties,except for the luminosity uncertainty in each bin. Especially the tail of Mtt̄ is sensitive tobroad enhancements as well as to narrow resonances, which is why the agreement betweendata and SM expectation has been evaluated. There is no indication of beyond standardmodel contributions to the differential cross section. The analysis also measured theinclusive total cross section for tt̄ production to: σ = 6.9± 1.0(stat. + JES) pb, which isin good agreement with latest theoretical predictions [5, 6] as well as with the DØ result.Furthermore the distribution has been used to derive a limit on gravitons which decayto top quarks in the Randall-Sundrum model. The mass of the first resonance is fixed to600 GeV and gravitons are modeled using MadEvent plus Pythia. Figure 3b) shows thederived limits, values of κ/MPl > 0.16 are excluded at the 95% confidence level.4. – ConclusionTwo differential cross section measurements have been presented. The cross sectionas a function of the transverse momentum of the top quark by DØ [3] and as a function4 ANDREAS W. JUNG (FOR THE DØ COLLABORATION)]2 [GeV/cttUnfolded M0 200 400 600 800 1000 1200 1400]2[fb/GeV/ctt/dMσd -110110SM ExpectationSM Uncertainties-1 2.7 fb≈ L ∫CDF II Data, CDF II PreliminaryPl/Mκ0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2CL00.20.40.60.81CL-1 2.7 fb≈ L ∫CDF II Data, Expected CL Uncertaintyσ1 Uncertaintyσ2Observed CL2 = 600 GeV/c1mCDF II Preliminarya) b)Fig. 3. – a) shows the differential tt̄ cross section (circles) as a function of Mtt̄ [4] compared tothe standard model expectation (line). The SM uncertainty (green band) reflects all systematicuncertainties, except for the luminosity uncertainty in each bin. b) shows limits on the ratioκ/MPl for gravitons which decay to top quarks in the Randall-Sundrum model, where the massof the first resonance is fixed at 600 GeV. Values of κ/MPl > 0.16 are excluded at the 95%confidence level.of the invariant mass of the tt̄ system by CDF [4]. Both presented results are consistentwith the standard model cross section predictions.REFERENCES[1] F. Abe et al. (CDF Collaboration), Phys. Rev. Lett. 74, 2626 (1995)[arXiv:hep-ex/9503002].[2] S. Abachi et al. (DØ Collaboration), Phys. Rev. Lett. 74, 2632 (1995)[arXiv:hep-ex/9503003].[3] V. Abazov et al (DØ Collaboration), Phys. Lett. B 693, 515 (2010), [arXiv.org:1001.1900].[4] T. Aaltonen et al. (CDF Collaboration), PRL 102 222003, [arxiv.org:0903.2850].[5] V. Ahrens, A. Ferroglia, M. Neubert, B. D. Pecjak, and L. L. Yang, J. High Energy Phys.09, 097 (2010); V. Ahrens, A. Ferroglia, M. Neubert, B. D. Pecjak, and L. L. Yang, Nucl.Phys. Proc. Suppl. 205-206, 48 (2010).[6] S. Moch and P. Uwer, Phys. Rev. D 78, 034003 (2008); U. Langenfeld, S. Moch, and P.Uwer, Phys. Rev. D 80, 054009 (2009);M. Aliev et al., Comput. Phys. Commun. 182, 1034(2011).

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Top differential cross section measurements (Tevatron)

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