Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at [Formula: see text] using the ATLAS detector

Towards ultimate parton distributions at the high-luminosity LHC

Since its start of data taking, the LHC has provided an impressive wealth of information on the quark and gluon structure of the proton. Indeed, modern global analyses of parton distribution functions (PDFs) include a wide range of LHC measurements of processes such as the production of jets, electroweak gauge bosons, and top quark pairs. In this work, we assess the ultimate constraining power of LHC data on the PDFs that can be expected from the complete dataset, in particular after the High-Luminosity (HL) phase, starting in around 2025. The huge statistics of the HL-LHC, delivering L = 3 ab - 1 to ATLAS and CMS and L = 0.3 ab - 1 to LHCb, will lead to an extension of the kinematic coverage of PDF-sensitive measurements as well as to an improvement in their statistical and systematic uncertainties. Here we generate HL-LHC pseudo-data for different projections of the experimental uncertainties, and then quantify the resulting constraints on the PDF4LHC15 set by means of the Hessian profiling method. We find that HL-LHC measurements can reduce PDF uncertainties by up to a factor of 2 to 4 in comparison to state-of-the-art fits, leading to few-percent uncertainties for important observables such as the Higgs boson transverse momentum distribution via gluon-fusion. Our results illustrate the significant improvement in the precision of PDF fits achievable from hadron collider data alone, and motivate the continuation of the ongoing successful program of PDF-sensitive measurements by the LHC collaborations.

Parton distributions with small-x resummation: evidence for BFKL dynamics in HERA data

We present a determination of the parton distribution functions of the proton in which NLO and NNLO fixed-order calculations are supplemented by NLLx small-x resummation. Deep-inelastic structure functions are computed consistently at NLO+NLL x or NNLO+NLL x , while for hadronic processes small-x resummation is included only in the PDF evolution, with kinematic cuts introduced to ensure the fitted data lie in a region where the fixed-order calculation of the hard cross-sections is reliable. In all other respects, the fits use the same methodology and are based on the same global dataset as the recent NNPDF3.1 analysis. We demonstrate that the inclusion of small-x resummation leads to a quantitative improvement in the perturbative description of the HERA inclusive and charm-production reduced cross-sections in the small x region. The impact of the resummation in our fits is greater at NNLO than at NLO, because fixed-order calculations have a perturbative instability at small x due to large logarithms that can be cured by resummation. We explore the phenomenological implications of PDF sets with small-x resummation for the longitudinal structure function F L at HERA, for parton luminosities and LHC benchmark cross-sections, for ultra-high-energy neutrino-nucleus cross-sections, and for future high-energy lepton-proton colliders such as the LHeC.

Parton distributions in the LHC era

Analyses of LHC (and other!) experiments require robust and statistically accurate determinations of the structure of the proton, encoded in the parton distribution functions (PDFs). The standard description of hadronic processes relies on factorization theorems, which allow a separation of process-dependent short-distance physics from the universal long-distance structure of the proton. Traditionally the PDFs are obtained from fits to experimental data. However, understanding the long-distance properties of hadrons is a nonperturbative problem, and lattice QCD can play a role in providing useful results from first principles. In this talk we compare the different approaches used to determine PDFs, and try to assess the impact of existing, and future, lattice calculations.

Single-top and top-antitop cross sections

I present high-order calculations, including soft-gluon corrections, for single-top and top-antitop production cross sections and differential distributions. For single-top production, results are presented for the three different channels in the Standard Model, for associated production with a charged Higgs, and for processes involving anomalous couplings. For top-antitop pair production, total cross sections and top-quark transverse-momentum and rapidity distributions are presented for various LHC energies.

Denis RD, Stabile A, Stamen R, Stamm S, Stanecka E, Stanek RW, Stanescu C, Stanitzki MM, Stapf BS, Stapnes S, Starchenko EA, Stark GH, Stark J, Stark SH, Staroba P, Starovoitov P, Stärz S, Staszewski R, Stegler M, Steinberg P, Stelzer B, Stelzer HJ, Stelzer-Chilton O, Stenzel H, Stevenson TJ, Stewart GA, Stockton MC, Stoebe M, Stoicea G, Stolte P, Stonjek S, Stradling AR, Straessner A, Stramaglia ME, Strandberg J, Strandberg S, Strauss M, Strizenec P, Ströhmer R, Strom DM, Stroynowski R, Strubig A, Stucci SA, Stugu B, Styles NA, Su D, Su J, Suchek S, Sugaya Y, Suk M, Sulin VV, Sultan DMS, Sultansoy S, Sumida T, Sun S, Sun X, Suruliz K, Suster CJE, Sutton MR, Suzuki S, Svatos M, Swiatlowski M, Swift SP, Sykora I, Sykora T, Ta D, Tackmann K, Taenzer J, Taffard A, Tafirout R, Tahirovic E, Taiblum N, Takai H, Takashima R, Takasugi EH, Takeda K, Takeshita T, Takubo Y, Talby M, Talyshev AA, Tanaka J, Tanaka M, Tanaka R, Tanaka S, Tanioka R, Tannenwald BB, Tapia Araya S, Tapprogge S, Tarem S, Tartarelli GF, Tas P, Tasevsky M, Tashiro T, Tassi E, Tavares Delgado A, Tayalati Y, Taylor AC, Taylor AJ, Taylor GN, Taylor PTE, Taylor W, Teixeira-Dias P, Temple D, Ten Kate H, Teng PK, Teoh JJ, Tepel F, Terada S, Terashi K, Terron J, Terzo S, Testa M, Teuscher RJ, Thais SJ, Theveneaux-Pelzer T, Thiele F, Thomas JP, Thomas-Wilsker J, Thompson PD, Thompson AS, Thomsen LA, Thomson E, Tian Y, Tibbetts MJ, Ticse Torres RE, Tikhomirov VO, Tikhonov YA, Timoshenko S, Tipton P, Tisserant S, Todome K, Todorova-Nova S, Todt S, Tojo J, Tokár S, Tokushuku K, Tolley E, Tomlinson L, Tomoto M, Tompkins L, Toms K, Tong B, Tornambe P, Torrence E, Torres H, Torró Pastor E, Toth J, Touchard F, Tovey DR, Treado CJ, Trefzger T, Tresoldi F, Tricoli A, Trigger IM, Trincaz-Duvoid S, Tripiana MF, Trischuk W, Trocmé B, Trofymov A, Troncon C, Trottier-McDonald M, Trovatelli M, Truong L, Trzebinski M, Trzupek A, Tsang KW, Tseng JL, Tsiareshka PV, Tsipolitis G, Tsirintanis N, Tsiskaridze S, Tsiskaridze V, Tskhadadze EG, Tsukerman II, Tsulaia V, Tsuno S, Tsybychev D, Tu Y, Tudorache A, Tudorache V, Tulbure TT, Tuna AN, Turchikhin S, Turgeman D, Turk Cakir I, Turra R, Tuts PM, Ucchielli G, Ueda I, Ughetto M, Ukegawa F, Unal G, Undrus A, Unel G, Ungaro FC, Unno Y, Uno K, Unverdorben C, Urban J, Urquijo P, Urrejola P, Usai G, Usui J, Vacavant L, Vacek V, Vachon B, Vadla KOH, Vaidya A, Valderanis C, Valdes Santurio E, Valente M, Valentinetti S, Valero A, Valéry L, Valkar S, Vallier A, Valls Ferrer JA, Van Den Wollenberg W, van der Graaf H, van Gemmeren P, Van Nieuwkoop J, van Vulpen I, van Woerden MC, Vanadia M, Vandelli W, Vaniachine A, Vankov P, Vardanyan G, Vari R, Varnes EW, Varni C, Varol T, Varouchas D, Vartapetian A, Varvell KE, Vasquez JG, Vasquez GA, Vazeille F, Vazquez Furelos D, Vazquez Schroeder T, Veatch J, Veeraraghavan V, Veloce LM, Veloso F, Veneziano S, Ventura A, Venturi M, Venturi N, Venturini A, Vercesi V, Verducci M, Verkerke W, Vermeulen AT, Vermeulen JC, Vetterli MC, Viaux Maira N, Viazlo O, Vichou I, Vickey T, Vickey Boeriu OE, Viehhauser GHA, Viel S, Vigani L, Villa M, Villaplana Perez M, Vilucchi E, Vincter MG, Vinogradov VB, Vishwakarma A, Vittori C, Vivarelli I, Vlachos S, Vogel M, Vokac P, Volpi G, von der Schmitt H, von Toerne E, Vorobel V, Vorobev K, Vos M, Voss R, Vossebeld JH, Vranjes N, Vranjes Milosavljevic M, Vrba V, Vreeswijk M, Vuillermet R, Vukotic I, Wagner P, Wagner W, Wagner-Kuhr J, Wahlberg H, Wahrmund S, Walder J, Walker R, Walkowiak W, Wallangen V, Wang C, Wang C, Wang F, Wang H, Wang H, Wang J, Wang J, Wang Q, Wang RJ, Wang R, Wang SM, Wang T, Wang W, Wang W, Wang Z, Wanotayaroj C, Warburton A, Ward CP, Wardrope DR, Washbrook A, Watkins PM, Watson AT, Watson MF, Watts G, Watts S, Waugh BM, Webb AF, Webb S, Weber MS, Weber SM, Weber SW, Weber SA, Webster JS, Weidberg AR, Weinert B, Weingarten J, Weirich M, Weiser C, Weits H, Wells PS, Wenaus T, Wengler T, Wenig S, Wermes N, Werner MD, Werner P, Wessels M, Weston TD, Whalen K, Whallon NL, Wharton AM, White AS, White A, White MJ, White R, Whiteson D, Whitmore BW, Wickens FJ, Wiedenmann W, Wielers M, Wiglesworth C, Wiik-Fuchs LAM, Wildauer A, Wilk F, Wilkens HG, Williams HH, Williams S, Willis C, Willocq S, Wilson JA, Wingerter-Seez I, Winkels E, Winklmeier F, Winston OJ, Winter BT, Wittgen M, Wobisch M, Wolf TMH, Wolff R, Wolter MW, Wolters H, Wong VWS, Woods NL, Worm SD, Wosiek BK, Wotschack J, Wozniak KW, Wu M, Wu SL, Wu X, Wu Y, Wyatt TR, Wynne BM, Xella S, Xi Z, Xia L, Xu D, Xu L, Xu T, Xu W, Yabsley B, Yacoob S, Yamaguchi D, Yamaguchi Y, Yamamoto A, Yamamoto S, Yamanaka T, Yamane F, Yamatani M, Yamazaki T, Yamazaki Y, Yan Z, Yang H, Yang H, Yang Y, Yang Z, Yao WM, Yap YC, Yasu Y, Yatsenko E, Yau Wong KH, Ye J, Ye S, Yeletskikh I, Yigitbasi E, Yildirim E, Yorita K, Yoshihara K, Young C, Young CJS, Yu J, Yu J, Yuen SPY, Yusuff I, Zabinski B, Zacharis G, Zaidan R, Zaitsev AM, Zakharchuk N, Zalieckas J, Zaman A, Zambito S, Zanzi D, Zeitnitz C, Zemaityte G, Zemla A, Zeng JC, Zeng Q, Zenin O, Ženiš T, Zerwas D, Zhang D, Zhang D, Zhang F, Zhang G, Zhang H, Zhang J, Zhang L, Zhang L, Zhang M, Zhang P, Zhang R, Zhang R, Zhang X, Zhang Y, Zhang Z, Zhao X, Zhao Y, Zhao Z, Zhemchugov A, Zhou B, Zhou C, Zhou L, Zhou M, Zhou M, Zhou N, Zhou Y, Zhu CG, Zhu H, Zhu J, Zhu Y, Zhuang X, Zhukov K, Zibell A, Zieminska D, Zimine NI, Zimmermann C, Zimmermann S, Zinonos Z, Zinser M, Ziolkowski M, Živković L, Zobernig G, Zoccoli A, Zou R, zur Nedden M, Zwalinski L. Measurement of lepton differential distributions and the top quark mass in t t ¯ production in pp collisions at s = 8 TeV with the ATLAS detector

This paper presents single lepton and dilepton kinematic distributions measured in dileptonic t t ¯ events produced in 20.2 fb - 1 ofs = 8  TeV pp collisions recorded by the ATLAS experiment at the LHC. Both absolute and normalised differential cross-sections are measured, using events with an opposite-charge e μ pair and one or two b-tagged jets. The cross-sections are measured in a fiducial region corresponding to the detector acceptance for leptons, and are compared to the predictions from a variety of Monte Carlo event generators, as well as fixed-order QCD calculations, exploring the sensitivity of the cross-sections to the gluon parton distribution function. Some of the distributions are also sensitive to the top quark pole mass; a combined fit of NLO fixed-order predictions to all the measured distributions yields a top quark mass value ofm t pole = 173.2 ± 0.9 ± 0.8 ± 1.2  GeV, where the three uncertainties arise from data statistics, experimental systematics, and theoretical sources.

Parton distributions from high-precision collider data: NNPDF Collaboration

We present a new set of parton distributions, NNPDF3.1, which updates NNPDF3.0, the first global set of PDFs determined using a methodology validated by a closure test. The update is motivated by recent progress in methodology and available data, and involves both. On the methodological side, we now parametrize and determine the charm PDF alongside the light-quark and gluon ones, thereby increasing from seven to eight the number of independent PDFs. On the data side, we now include the D0 electron and muon W asymmetries from the final Tevatron dataset, the complete LHCb measurements of W and Z production in the forward region at 7 and 8 TeV, and new ATLAS and CMS measurements of inclusive jet and electroweak boson production. We also include for the first time top-quark pair differential distributions and the transverse momentum of the Z bosons from ATLAS and CMS. We investigate the impact of parametrizing charm and provide evidence that the accuracy and stability of the PDFs are thereby improved. We study the impact of the new data by producing a variety of determinations based on reduced datasets. We find that both improvements have a significant impact on the PDFs, with some substantial reductions in uncertainties, but with the new PDFs generally in agreement with the previous set at the one-sigma level. The most significant changes are seen in the light-quark flavor separation, and in increased precision in the determination of the gluon. We explore the implications of NNPDF3.1 for LHC phenomenology at Run II, compare with recent LHC measurements at 13 TeV, provide updated predictions for Higgs production cross-sections and discuss the strangeness and charm content of the proton in light of our improved dataset and methodology. The NNPDF3.1 PDFs are delivered for the first time both as Hessian sets, and as optimized Monte Carlo sets with a compressed number of replicas.

Measurement of double-differential cross sections for top quark pair production in pp collisions at [Formula: see text][Formula: see text] and impact on parton distribution functions

Normalized double-differential cross sections for top quark pair ([Formula: see text]) production are measured in pp collisions at a centre-of-mass energy of 8[Formula: see text] with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7[Formula: see text]. The measurement is performed in the dilepton [Formula: see text] final state. The [Formula: see text] cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and [Formula: see text] system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured [Formula: see text] cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.

Denis RD, Stabile A, Stamen R, Stamm S, Stanecka E, Stanek RW, Stanescu C, Stanescu-Bellu M, Stanitzki MM, Stapnes S, Starchenko EA, Stark GH, Stark J, Staroba P, Starovoitov P, Stärz S, Staszewski R, Steinberg P, Stelzer B, Stelzer HJ, Stelzer-Chilton O, Stenzel H, Stewart GA, Stillings JA, Stockton MC, Stoebe M, Stoicea G, Stolte P, Stonjek S, Stradling AR, Straessner A, Stramaglia ME, Strandberg J, Strandberg S, Strandlie A, Strauss M, Strizenec P, Ströhmer R, Strom DM, Stroynowski R, Strubig A, Stucci SA, Stugu B, Styles NA, Su D, Su J, Suchek S, Sugaya Y, Suk M, Sulin VV, Sultansoy S, Sumida T, Sun S, Sun X, Sundermann JE, Suruliz K, Susinno G, Sutton MR, Suzuki S, Svatos M, Swiatlowski M, Sykora I, Sykora T, Ta D, Taccini C, Tackmann K, Taenzer J, Taffard A, Tafirout R, Taiblum N, Takai H, Takashima R, Takeshita T, Takubo Y, Talby M, Talyshev AA, Tan KG, Tanaka J, Tanaka M, Tanaka R, Tanaka S, Tanioka R, Tannenwald BB, Tapia Araya S, Tapprogge S, Tarem S, Tartarelli GF, Tas P, Tasevsky M, Tashiro T, Tassi E, Tavares Delgado A, Tayalati Y, Taylor AC, Taylor GN, Taylor PTE, Taylor W, Teischinger FA, Teixeira-Dias P, Temming KK, Temple D, Ten Kate H, Teng PK, Teoh JJ, Tepel F, Terada S, Terashi K, Terron J, Terzo S, Testa M, Teuscher RJ, Theveneaux-Pelzer T, Thomas JP, Thomas-Wilsker J, Thompson PD, Thompson AS, Thomsen LA, Thomson E, Tibbetts MJ, Ticse Torres RE, Tikhomirov VO, Tikhonov YA, Timoshenko S, Tipton P, Tisserant S, Todome K, Todorov T, Todorova-Nova S, Tojo J, Tokár S, Tokushuku K, Tolley E, Tomlinson L, Tomoto M, Tompkins L, Toms K, Tong B, Tornambe P, Torrence E, Torres H, Torró Pastor E, Toth J, Touchard F, Tovey DR, Trefzger T, Tricoli A, Trigger IM, Trincaz-Duvoid S, Tripiana MF, Trischuk W, Trocmé B, Trofymov A, Troncon C, Trottier-McDonald M, Trovatelli M, Truong L, Trzebinski M, Trzupek A, Tseng JCL, Tsiareshka PV, Tsipolitis G, Tsirintanis N, Tsiskaridze S, Tsiskaridze V, Tskhadadze EG, Tsui KM, Tsukerman II, Tsulaia V, Tsuno S, Tsybychev D, Tu Y, Tudorache A, Tudorache V, Tuna AN, Tupputi SA, Turchikhin S, Turecek D, Turgeman D, Turra R, Tuts PM, Tyndel M, Ucchielli G, Ueda I, Ughetto M, Ukegawa F, Unal G, Undrus A, Unel G, Ungaro FC, Unno Y, Unverdorben C, Urban J, Urquijo P, Urrejola P, Usai G, Usui J, Vacavant L, Vacek V, Vachon B, Valderanis C, Valdes Santurio E, Valencic N, Valentinetti S, Valero A, Valery L, Valkar S, Valls Ferrer JA, Van Den Wollenberg W, Van Der Deijl PC, van der Graaf H, van Eldik N, van Gemmeren P, Van Nieuwkoop J, van Vulpen I, van Woerden MC, Vanadia M, Vandelli W, Vanguri R, Vaniachine A, Vankov P, Vardanyan G, Vari R, Varnes EW, Varol T, Varouchas D, Vartapetian A, Varvell KE, Vasquez JG, Vasquez GA, Vazeille F, Vazquez Schroeder T, Veatch J, Veeraraghavan V, Veloce LM, Veloso F, Veneziano S, Ventura A, Venturi M, Venturi N, Venturini A, Vercesi V, Verducci M, Verkerke W, Vermeulen JC, Vest A, Vetterli MC, Viazlo O, Vichou I, Vickey T, Boeriu OEV, Viehhauser GHA, Viel S, Vigani L, Villa M, Perez MV, Vilucchi E, Vincter MG, Vinogradov VB, Vittori C, Vivarelli I, Vlachos S, Vlasak M, Vogel M, Vokac P, Volpi G, Volpi M, von der Schmitt H, von Toerne E, Vorobel V, Vorobev K, Vos M, Voss R, Vossebeld JH, Vranjes N, Vranjes Milosavljevic M, Vrba V, Vreeswijk M, Vuillermet R, Vukotic I, Vykydal Z, Wagner P, Wagner W, Wahlberg H, Wahrmund S, Wakabayashi J, Walder J, Walker R, Walkowiak W, Wallangen V, Wang C, Wang C, Wang F, Wang H, Wang H, Wang J, Wang J, Wang K, Wang R, Wang SM, Wang T, Wang T, Wang W, Wanotayaroj C, Warburton A, Ward CP, Wardrope DR, Washbrook A, Watkins PM, Watson AT, Watson MF, Watts G, Watts S, Waugh BM, Webb S, Weber MS, Weber SW, Weber SA, Webster JS, Weidberg AR, Weinert B, Weingarten J, Weiser C, Weits H, Wells PS, Wenaus T, Wengler T, Wenig S, Wermes N, Werner M, Werner MD, Werner P, Wessels M, Wetter J, Whalen K, Whallon NL, Wharton AM, White A, White MJ, White R, Whiteson D, Wickens FJ, Wiedenmann W, Wielers M, Wiglesworth C, Wiik-Fuchs LAM, Wildauer A, Wilk F, Wilkens HG, Williams HH, Williams S, Willis C, Willocq S, Wilson JA, Wingerter-Seez I, Winklmeier F, Winston OJ, Winter BT, Wittgen M, Wittkowski J, Wolf TMH, Wolter MW, Wolters H, Worm SD, Wosiek BK, Wotschack J, Woudstra MJ, Wozniak KW, Wu M, Wu M, Wu SL, Wu X, Wu Y, Wyatt TR, Wynne BM, Xella S, Xu D, Xu L, Yabsley B, Yacoob S, Yamaguchi D, Yamaguchi Y, Yamamoto A, Yamamoto S, Yamanaka T, Yamauchi K, Yamazaki Y, Yan Z, Yang H, Yang H, Yang Y, Yang Z, Yao WM, Yap YC, Yasu Y, Yatsenko E, Yau Wong KH, Ye J, Ye S, Yeletskikh I, Yildirim E, Yorita K, Yoshida R, Yoshihara K, Young C, Young CJS, Youssef S, Yu DR, Yu J, Yu JM, Yu J, Yuan L, Yuen SPY, Yusuff I, Zabinski B, Zaidan R, Zaitsev AM, Zakharchuk N, Zalieckas J, Zaman A, Zambito S, Zanello L, Zanzi D, Zeitnitz C, Zeman M, Zemla A, Zeng JC, Zeng Q, Zenin O, Ženiš T, Zerwas D, Zhang D, Zhang F, Zhang G, Zhang H, Zhang J, Zhang L, Zhang M, Zhang R, Zhang R, Zhang X, Zhang Z, Zhao X, Zhao Y, Zhao Z, Zhemchugov A, Zhong J, Zhou B, Zhou C, Zhou L, Zhou L, Zhou M, Zhou N, Zhu CG, Zhu H, Zhu J, Zhu Y, Zhuang X, Zhukov K, Zibell A, Zieminska D, Zimine NI, Zimmermann C, Zimmermann S, Zinonos Z, Zinser M, Ziolkowski M, Živković L, Zobernig G, Zoccoli A, zur Nedden M, Zwalinski L. Measurements of top-quark pair differential cross-sections in the [Formula: see text] channel in pp collisions at [Formula: see text] TeV using the ATLAS detector

This article presents measurements of [Formula: see text] differential cross-sections in a fiducial phase-space region, using an integrated luminosity of 3.2 fb[Formula: see text] of proton-proton data at a centre-of-mass energy of [Formula: see text] TeV recorded by the ATLAS experiment at the LHC in 2015. Differential cross-sections are measured as a function of the transverse momentum and absolute rapidity of the top quark, and of the transverse momentum, absolute rapidity and invariant mass of the [Formula: see text] system. The [Formula: see text] events are selected by requiring one electron and one muon of opposite electric charge, and at least two jets, one of which must be tagged as containing a b-hadron. The measured differential cross-sections are compared to predictions of next-to-leading order generators matched to parton showers and the measurements are found to be consistent with all models within the experimental uncertainties with the exception of the Powheg-Box [Formula: see text] Herwig++ predictions, which differ significantly from the data in both the transverse momentum of the top quark and the mass of the [Formula: see text] system.