New CTEQ Global Analysis with High Precision Data from the LHC
Tie-Jiun Hou, Keping Xie, Jun Gao, Sayipjamal Dulat, Marco Guzzi, T. J. Hobbs, Joey Huston, Pavel Nadolsky, Jon Pumplin, Carl Schmidt, Ibrahim Sitiwaldi, Dan Stump, C. -P. Yuan
We present the new CTEQ-TEA global analysis of quantum chromodynamics (QCD). In this analysis, parton distribution functions (PDFs) of the nucleon are determined within the Hessian method at the next-to-next-to leading order (NNLO) in perturbative QCD, based on the most recent measurements from the Large Hadron Collider (LHC) and a variety of world collider data. Because of difficulties in fitting both the ATLAS 7 and 8 TeV $W$ and $Z$ vector boson production cross section data, we present two families of PDFs, named CT18 and CT18$Z$ PDFs, respectively, without and with the ATLAS 7 TeV $W$ and $Z$ measurements. We study the impact of the CT18 family of PDFs on the theoretical predictions of standard candle cross sections at the LHC.
Detailed studies have been carried out on the impact of the LHC top quark pair production data on gluon PDF, in the context of the CTEQ-TEA global PDF fit, with the ePump-updating method. The considered $t\bar{t}$ data include single differential distributions from ATLAS and double differential distributions from CMS, both at 8 TeV. All analyses have been carried out at the NNLO, using fastNNLO tables. We show that the sensitivity per data point of the LHC $t\bar{t}$ data is similar to that of jet data, as included in the CT14HERA2 fit, while the total sensitivity of the present $t\bar{t}$ dat…
We discuss heavy-flavor production at hadron colliders in recent global QCD analyses to determine parton distribution functions (PDFs) in the proton. We discuss heavy-flavor treatments in precision theory predictions at the LHC. In particular, we discuss factorization schemes in presence of heavy flavors in proton-proton collisions, as well as the impact of heavy-flavor production at the LHC on PDFs. We show results of recent updates beyond CT18, the latest global QCD analysis from the CTEQ-TEA group.
We present the new CTEQ-TEA global analysis of quantum chromodynamics (QCD). In this analysis, parton distribution functions (PDFs) of the nucleon are determined within the Hessian method at the next-to-next-to-leading order (NNLO) in perturbative QCD, based on the most recent measurements from the Large Hadron Collider (LHC) and a variety of world collider data. Because of difficulties in fitting both the ATLAS 7 and 8 TeV $W$ and $Z$ vector boson production cross section data, we present four families of (N)NLO CTEQ-TEA PDFs, named CT18, A, X and Z PDFs, respectively. We study the impact of …
We present the new parton distribution functions (PDFs) from the CTEQ-TEA collaboration, obtained using a wide variety of high-precision Large Hadron Collider (LHC) data, in addition to the combined HERA I+II deep-inelastic scattering data set, along with the data sets present in the CT14 global QCD analysis. New LHC measurements in single-inclusive jet production with the full rapidity coverage, as well as production of Drell-Yan pairs, top-quark pairs, and high-$p_T$ $Z$ bosons, are included to achieve the greatest sensitivity to the PDFs. The parton distributions are determined at NLO and N…
We study the uncertainties of the Higgs boson production cross section through the gluon fusion subprocess at the LHC (with $\sqrt s=7, 8$ and $14$ TeV) arising from the uncertainties of the parton distribution functions (PDFs) and of the value of the strong coupling constant $α_s(M_Z)$. These uncertainties are computed by two complementary approaches, based on the Hessian and the Lagrange Multiplier methods within the CTEQ-TEA global analysis framework. We find that their predictions for the Higgs boson cross section are in good agreement. Furthermore, the result of the Lagrange Multiplier me…
The possibility of a (sizable) nonperturbative contribution to the charm parton distribution function (PDF) in a nucleon is investigated together with theoretical issues arising in its interpretation. Results from the global PDF analysis are presented. The separation of the universal component of the nonperturbative charm from the rest of the radiative contributions is discussed and the potential impact of a nonperturbative charm PDF on LHC scattering processes is illustrated. An estimate of nonperturbative charm magnitude in the CT14 and CT14HERA2 global QCD analyses at the next-to-next-to le…
We investigate the possibility of a (sizable) nonperturbative contribution to the charm parton distribution function (PDF) in a nucleon, theoretical issues arising in its interpretation, and its potential impact on LHC scattering processes. The "fitted charm" PDF obtained in various QCD analyses contains a process-dependent component that is partly traced to power-suppressed radiative contributions in DIS and is generally different at the LHC. We discuss separation of the universal component of the nonperturbative charm from the rest of the radiative contributions and estimate its magnitude in…
We review progress in the global QCD analysis by the CTEQ-TEA group since the publication of CT18 parton distribution functions (PDFs) in the proton. Specifically, we discuss comparisons of CT18 NNLO predictions with the LHC 13 TeV measurements as well as with the FNAL SeaQuest and BNL STAR data on lepton pair production. The specialized CT18X PDFs approximating saturation effects are compared with the CT18sx PDFs obtained using NLL/NLO small-$x$ resummation. Short summaries are presented for the special CT18 parton distributions with fitted charm and with lattice QCD inputs. A recent comparat…
I discuss advances in the determination of strange, charm, and bottom quark parton distribution functions obtained in the CTEQ6.5 and CTEQ6.6 global analyses. These results affect electroweak precision observables and certain new physics searches at the Large Hadron Collider. I focus, in particular, on high-energy implications of the consistent treatment of heavy-quark threshold effects in DIS in the general-mass factorization scheme; an independent parametrization for the strangeness PDF; and the possible presence of nonperturbative ("intrinsic") charm.
In the context of a recent CTEQ6.6 global analysis, we review a new technique for studying correlated theoretical uncertainties in hadronic observables associated with imperfect knowledge of parton distribution functions (PDFs). The technique is based on the computation of correlations between the predicted values of physical observables in the Hessian matrix method. It can be used, for example, to link the dominant PDF uncertainty in a hadronic cross section to PDFs for individual parton flavors at well-defined $(x,μ)$ values. As an illustration, we apply the PDF correlation analysis to study…
The latest CTEQ6.6 parton distributions, obtained by global analysis of hard scattering data in the framework of general-mass perturbative QCD, are employed to study theoretical predictions and their uncertainties for significant processes at the Fermilab Tevatron and CERN Large Hadron Collider. The previously observed increase in predicted cross sections for the standard-candle W and Z boson production processes in the general-mass scheme (compared to those in the zero-mass scheme) is further investigated and quantified. A novel method to constrain PDF uncertainties in LHC observables, by eff…
Kashi University（喀什大学）；Michigan State University（密歇根州立大学）；Xinjiang University（新疆大学）；Kennesaw State University（肯尼索州立大学）；Argonne National Laboratory（阿贡国家实验室）；Shanghai Jiao Tong University（上海交通大学）
We study the global analysis for parton distributions as a function of the QCD strong coupling strength alpha_s, and present a new series of distributions that span the range 0.110 < alpha_s(m_Z) < 0.128. We use these distributions to explore the correlation between alpha_s and the gluon distribution; the viability of global analysis as a method to measure alpha_s; and the dependence on alpha_s of predictions for W, Z, inclusive jet, and Higgs boson production ($b \bar{b} \to H$ and $gg \to H$) cross sections at the Tevatron and the LHC. We find that the uncertainty in alpha_s is the dominant …
We present an updated study of the systematic errors in the measurements of the electroweak boson cross-sections at the LHC for various experimental cuts for a center of mass energy of 7, 10 and 14 TeV. The size of both electroweak and NNLO QCD contributions are estimated, together with the systematic error from the parton distributions. The effects of new versions of the MSTW, CTEQ, and NNPDF PDFs are considered.
We analyze the impact of the recent HERA run I+II combination of inclusive deep inelastic scattering cross-section data on the CT14 global analysis of PDFs. New PDFs at NLO and NNLO, called CT14$_{\textrm{HERA2}}$, are obtained by a refit of the CT14 data ensembles, in which the HERA run I combined measurements are replaced by the new HERA run I+II combination. The CT14 functional parametrization of PDFs is flexible enough to allow good descriptions of different flavor combinations, so we use the same parametrization for CT14$_{\textrm{HERA2}}$ but with an additional shape parameter for descri…
Experimental measurements in deep-inelastic scattering and lepton-pair production on deuterium targets play an important role in the flavor separation of $u$ and $d$ (anti)quarks in global QCD analyses of the parton distribution functions (PDFs) of the nucleon. We investigate the impact of theoretical corrections accounting for the light-nuclear structure of the deuteron upon the fitted $u, d$-quark, gluon, and other PDFs in the CJ15 and CT18 families of next-to-leading order CTEQ global analyses. The investigation is done using the $L_2$ sensitivity statistical method, which provides a common…
We present predictions for relevant LHC observables obtained with the NNPDF2.0 set. We compute the combined PDFs uncertainties on these observables, and show that combining errors in quadrature yields an excellent approximation to exact error propagation. We then compare the NNPDF2.0 results to the other global PDF fits using a common value of $α_s$. At LHC 7 TeV, reasonable agreement, both in central values and in uncertainties, is found for NNPDF2.0, CTEQ6.6 and MSTW08.
We discuss implementation of the LHC experimental data sets in the new CT18 global analysis of quantum chromodynamics (QCD) at the next-to-next-leading order of the QCD coupling strength. New methodological developments in the fitting methodology are discussed. Behavior of the CT18 NNLO PDFs for the conventional and "saturation-inspired" factorization scales in deep-inelastic scattering is reviewed. Four new families of (N)NLO CTEQ-TEA PDFs are presented: CT18, A, X, and Z.
We study at a quantitative level the impact of the uncertainties on the value of the W boson mass measured at hadron colliders due to: the proton parton distribution functions (PDFs), the value of the strong coupling constant alpha_S and the value of the charm mass used in the PDF determination. The value of the W boson mass is extracted, by means of a template fit technique, from the lepton-pair transverse mass distribution measured in the charged current Drell-Yan process. We study the determination of M_W at the Tevatron and at the LHC with 7 and 14 TeV of center-of-mass energy in a realist…
Challenges for precision measurements at the LHC are discussed and a proposal how to move forward to overcome the LHC-specific precision brick-walls is presented.
We compare the sensitivity of precision measurements of lepton flavour observables to the reach of the LHC in a case study of lepton-flavour violating operators of dimension six with two leptons and two quarks. For light quarks precision measurements always yield the more stringent constraints. The LHC complements precision measurements for operators with heavier quarks. Competitive limits can already be set on the cutoff scale $Λ$ > 600 - 800 GeV for operators with right-handed $τ$ leptons using the LHC run 1 data.
A new implementation of the general PQCD formalism of Collins, including heavy quark mass effects, is described. Important features that contribute to the accuracy and efficiency of the calculation of both neutral current (NC) and charged current (CC) processess are explicitly discussed. This new implementation is applied to the global analysis of the full HERA I data sets on NC and CC cross sections, with correlated systematic errors, in conjunction with the usual fixed-target and hadron collider data sets. By using a variety of parametrizations to explore the parton parameter space, robust n…
Precision measurements of the Drell-Yan (DY) cross section at the LHC constrain new physics scenarios that involve new states with electroweak (EW) charges. We analyze these constraints and apply them to models that can address the LHC diphoton excess at 750 GeV. We confront these findings with LEP EW precision tests and show that DY provides stronger constraints than the LEP data. While 8 TeV data can already probe some parts of the interesting region of parameter space, LHC14 results are expected to cover a substantial part of the relevant terrain. We derive the bounds from the existing data…
The prospects for electroweak precision physics at the LHC and the ILC are reviewed. This includes projections for measurements of the effective Z pole weak mixing angle, sin^2 theta_W (eff.), as well as top quark, W boson, and Higgs scalar properties. The upcoming years may also see very precise determinations of sin^2 theta_W (eff.) from lower energies.
This review describes the current status of precision QCD studies at the LHC. We introduce the main experimental and theoretical methods, discussing also their cross-stimulated developments and recent advances. The different types of QCD observables that are measured at the LHC, including cross-sections, event- and jet-level properties, for various final states, are summarised. Their relation to fundamental QCD dynamics and their impact on Standard Model parameter determinations are discussed on specific examples. The impact of QCD-related observables on direct and indirect searches for rare p…
A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work significantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errors for both new and old data sets; (ii) a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the Hessian method. The new gluon distribution is considerably harder than that of previous stan…
Several new physics scenarios, motivated e.g. by dark matter, feature new electroweakly charged states where the lightest particle in the multiplet is stable and neutral. In such cases direct searches at LHC are notoriously difficult, while electroweak precision tests both at hadron and lepton colliders offer the possibility to indirectly probe those states. In this work, we assess the sensitivity of the high-luminosity phase of the LHC on new electroweak multiplets via the modification of neutral and charged Drell-Yan processes, and compare the reach of future hadron and lepton colliders pres…
The staged increase of the LHC beam energy provides a new class of interesting observables, namely ratios and double ratios of cross sections of various hard processes. The large degree of correlation of theoretical systematics in the cross section calculations at different energies leads to highly precise predictions for such ratios. We present in this letter few examples of such ratios, and discuss their possible implications, both in terms of opportunities for precision measurements and in terms of sensitivity to Beyond the Standard Model dynamics.
The question of naturalness of the Standard Model (SM) has been a hot topic since the discovery that the Higgs boson has a relatively light mass. It has been pointed out in the past that the mass of a scalar boson can be destabilized by loop corrections. Many theories have been proposed beyond the SM to address this problem. It is possible that such mechanisms contribute to the running of the Higgs mass with the energy scale. We present predictions for the precision of the Higgs mass measurement up to a Higgs boson transverse momentum of 1 TeV for the LHC in Run 3 with a luminosity of 300 fb-1…
We present next-to-next-to-leading order (NNLO) parton distribution functions (PDFs) from the CTEQ-TEA group. The CT10NNLO PDF fit is based on essentially the same global data sets used in the CT10 and CT10W NLO PDF analyses. After exploring the goodness of the fits to the HERA combined data and the Tevatron jet data, we present various predictions at NNLO accuracy for both existing and forthcoming precision measurements from the CERN Large Hadron Collider. The range of variations in the gluon distribution introduced by correlated systematic effects in inclusive jet production is also examined…
As part of a recent analysis of exclusive two-photon production of W+ W- pairs at the LHC, the CMS experiment used di-lepton data to obtain an "effective" photon-photon luminosity. We show how the CMS analysis on their 8 TeV data, along with some assumptions about the likelihood for events in which the proton breaks up to pass the selection criteria, can be used to significantly constrain the photon parton distribution functions, such as those from the CTEQ, MRST, and NNPDF collaborations. We compare the data with predictions using these photon distributions, as well as the new LUXqed photon d…
Using the new schemes provided by the CTEQ and MRST collaborations and by Alekhin, we analyse the uncertainties due to the parton distribution functions (PDFs) on the next-to-leading-order cross sections of the four main production processes of the Standard Model Higgs boson at the LHC and the Tevatron. In the Higgs mass range where the production rates are large enough, the spread in the uncertainties when the three sets of PDFs are compared is of about 15% in all processes and at both colliders. However, within one given set of PDFs, the deviations from the values obtained with the reference…
This thesis discusses recent advances in precision calculations of quantum chromodynamics and their application to the Large Hadron Collider (LHC) physics program and beyond.
Exploiting the large number of collected events and the symmetries in the W production and decay at LHC, it is possible to measure the W double differential cross section of transverse momentum and rapidity and the angular coefficients. With the proposed method a determination of the integrated spectrum of transverse momentum of W bosons is possible with an unprecedented granularity and increased precision with respect to the state-of-the-art generators. This enables the possibility to perform a theory-agnostic measurement of the W mass with competitive uncertainty by constraining the W produc…
LHCb is a dedicated heavy flavour physics precision experiment at the LHC searching for New Physics (NP) beyond the Standard Model (SM) through the study of very rare decays of beauty and charm-flavoured hadrons and precision measurements of CP-violating observables. In this review I will present a selection of recent precision measurements of CP-violating observables in the decays of beauty and charm-flavoured hadrons. These measurements are based on an integrated luminosity of up to $1.0 \rm{fb}^{-1}$ collected by LHCb in 2011.
We present state-of-the-art high-precision theory predictions for the dominant angular coefficients parametrizing the spin-correlations in the production and decay of a W-boson produced at transverse momentum larger than 30 GeV. The computation at NNLO QCD and NLO EW accuracy are combined to obtain differential distributions in the W-boson transverse momentum and rapidity. The found results show up to 10 % corrections in certain regions of phase space, while the scale bands are significantly reduced as compared to NLO QCD.
We present precise predictions for the Higgs boson rapidity distribution at the LHC in the gluon fusion production mode. Our approach relies on the fully analytic computation of six terms in a systematic expansion of the partonic differential cross section around the production threshold of the Higgs boson at next-to-next-to-next-to leading order (N$^3$LO) in QCD perturbation theory. We observe a mild correction compared to the previous perturbative order and a significant reduction of the dependence of the cross section on the perturbative scale throughout the entire rapidity range.
Several proposals exist for energy-frontier facilities after the HL-LHC. In this contribution I review the potential of these facilities to perform key measurements of top quark properties and interacions. Top quark precision physics at a lepton collider provides excellent opportunities for the determination of the top quark mass and its couplings to neutral electro-weak gauge bosons. Measurements at very high center-of-mass energy at a new hadron collider likely offer the ultimate precision on the QCD interaction of the top quark and its coupling to the Higgs boson. The combination of a lepto…
The impact of recent precision measurements of DIS structure functions and inclusive jet production at the Tevatron on the global QCD analysis of parton distribution functions is studied in detail. Particular emphasis is placed on exploring the range of variation of the gluon distribution $G(x,Q)$ allowed by these new data. The strong coupling of $G(x,Q)$ with $α_s$ is fully taken into account. A new generation of CTEQ parton distributions, CTEQ4, is presented. It consists of the three standard sets (\mbox{\small {$\overline {\rm MS}$}}, {\protect \small DIS} and leading order), a series that …
The inclusive same-sign dilepton channel is already recognized as a promising discovery signature for supersymmetry in the early days of the LHC. We point out that it can also be used for precision measurements of sparticle masses after the initial discovery. As an illustration, we consider the LM6 CMS study point in minimal supergravity, where the same-sign leptons most often result from chargino decays to sneutrinos. We discuss three different techniques for determining the chargino and sneutrino masses in an inclusive manner, i.e. using only the two well measured lepton momenta, while treat…
A QCD fit analysis to the combined HERA inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for $e^\pm p$ scattering to extract HERAPDF sets is presented. The results are used for predictions of $ p\bar{p}$ processes at Tevatron and $pp$ processes at the LHC. The QCD analysis has been extended to include the combined HERA II measurements at high $Q^2$ resulting in the HERAPDF1.5 sets, with full estimation of uncertainties. The precision of the new PDFs at high $x$ is considerably improved, particularly in the valence sector. In addition, inclusion of the HERA jet…
Absolute normalisation of the LHC measurements with O(1%) precision and their relative normalisation, for the data collected at variable centre-of-mass energies, or for variable beam particle species, with O(0.1%) precision is crucial for the LHC experimental programme but presently beyond the reach for the general purpose LHC detectors. This paper is the third in the series of papers presenting the measurement method capable to achieve such a goal.
We present a resummation-improved prediction for $VH$ + 0 jets production at the Large Hadron Collider. We focus on highly-boosted final states in the presence of jet veto to suppress the $t{\bar t}$ background. In this case, conventional fixed-order calculations are plagued by the existence of large Sudakov logarithms $α_s^n \log^m (p_T^{veto}/Q)$ for $Q\sim m_V + m_H$ which lead to unreliable predictions as well as large theoretical uncertainties, and thus limit the accuracy when comparing experimental measurements to the Standard Model. In this work, we show that the resummation of Sudakov …
We investigate the uncertainties for current and future measurements of electroweak (EW) parameters at hadron colliders. These include the measurement of the mass of the top quark ($M_T$), the direct measurement of the mass of the W boson ($M_W^{direct}$), the measurement of the effective EW mixing angle $\sin^2θ^{\rm lept}_{\rm eff}$(M$_Z$), and the measurement of the on-shell EW mixing angle $\sin^2θ_{W}= 1- M_W^2/M_Z^2$ which is equivalent to an indirect measurement of the W mass ($M_W^{indirect}$). Reduction of a factor of 2 to 3 in the measurement errors is expected in the future.
We study the effect of the charm quark mass in the CTEQ global analysis of parton distribution functions (PDFs) of the proton. Constraints on the $\bar{\rm MS}$ mass of the charm quark are examined at the next-to-next-to-leading order (NNLO) accuracy in the S-ACOT-$χ$ heavy-quark factorization scheme. The value of the charm quark mass from the hadronic scattering data in the CT10 NNLO fit, including semiinclusive charm production in DIS at HERA collider, is found to agree with the world average value. Various approaches for constraining $m_{c}$ in the global analysis and impact on LHC cross se…
We calculate cross-sections and cross-section ratios of a charm quark production in association with a $W$ gauge boson at next-to-leading order QCD using MadGraph and CT10NNLO, CT14NNLO, and MSTW2008NNLO PDFs. We compare the results with measurements from the CMS detector at the LHC at a center-of-mass energy of 7TeV. Moreover, we calculate absolute and normalized differential cross-sections as well as differential cross-section ratios as a function of the lepton pseudorapidity from the $W$ boson decay. The correlation between the CT14NNLO PDFs and predictions for $W+$ charm data are studied a…
This documents the proceedings from a workshop titled `Illuminating Standard candles at the LHC: V+jets' held at Imperial College London on 25th-26th April 2017. It summarises the numerous contributions to the workshop, from the experimental overview of V+jets measurements at CMS and ATLAS and their role in searching for physics beyond the Standard Model to the status of higher order perturbative calculations to these processes and their inclusion in state of the art Monte Carlo simulations. An executive summary of the ensuing discussions including a list of outcomes and wishlist for future co…
Motivated by the restoration of $SU(2)\times U(1)$ at high energy, we suggest that certain ratios of diboson differential cross sections can be used as high-precision observables at the LHC. We rewrite leading-order diboson partonic cross sections in a form that makes their $SU(2)\times U(1)$ and custodial $SU(2)$ structure more explicit than in previous literature, and identify important aspects of this structure that survive even in hadronic cross sections. We then focus on higher-order corrections to ratios of $γγ$, $Zγ$ and $ZZ$ processes, including full next-to-leading-order corrections a…
Following previous works regarding electroweak precision tests in supersymmetry, we continue to explore their implications to the MSSM and NMSSM both of which are tightly constrained by the Higgs mass and its decay experiments at the LHC. We adopt universal squark, slepton mass of three generations, and A-term of all SM fermions. We determine the flows of both MSSM and NMSSM in the $S$-$T$ plane with increasing $\tanβ$ and/or $γγ$ rate. Either increasing the value of $R_γ$ or $\tanβ$, we find that the benchmark points tend to be pushed outside the contour at 99% CL in the MSSM, however, conver…
