Showing papers by "Robert S. Thorne published in 2016"

PDF4LHC recommendations for LHC Run II

Abstract: We provide an updated recommendation for the usage of sets of parton distribution functions (PDFs) and the assessment of PDF and PDF+$\alpha_s$ uncertainties suitable for applications at the LHC Run II. We review developments since the previous PDF4LHC recommendation, and discuss and compare the new generation of PDFs, which include substantial information from experimental data from the Run I of the LHC. We then propose a new prescription for the combination of a suitable subset of the available PDF sets, which is presented in terms of a single combined PDF set. We finally discuss tools which allow for the delivery of this combined set in terms of optimized sets of Hessian eigenvectors or Monte Carlo replicas, and their usage, and provide some examples of their application to LHC phenomenology.

Handbook of LHC Higgs Cross Sections: 4. Deciphering the Nature of the Higgs Sector

Abstract: This Report summarizes the results of the activities of the LHC Higgs Cross Section Working Group in the period 2014-2016. The main goal of the working group was to present the state-of-the-art of Higgs physics at the LHC, integrating all new results that have appeared in the last few years. The first part compiles the most up-to-date predictions of Higgs boson production cross sections and decay branching ratios, parton distribution functions, and off-shell Higgs boson production and interference effects. The second part discusses the recent progress in Higgs effective field theory predictions, followed by the third part on pseudo-observables, simplified template cross section and fiducial cross section measurements, which give the baseline framework for Higgs boson property measurements. The fourth part deals with the beyond the Standard Model predictions of various benchmark scenarios of Minimal Supersymmetric Standard Model, extended scalar sector, Next-to-Minimal Supersymmetric Standard Model and exotic Higgs boson decays. This report follows three previous working-group reports: Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002), Handbook of LHC Higgs Cross Sections: 2. Differential Distributions (CERN-2012-002), and Handbook of LHC Higgs Cross Sections: 3. Higgs properties (CERN-2013-004). The current report serves as the baseline reference for Higgs physics in LHC Run 2 and beyond.

Handbook of LHC Higgs cross sections: 4. Deciphering the nature of the Higgs sector

Abstract: This Report summarizes the results of the activities of the LHC Higgs Cross Section Working Group in the period 2014-2016 The main goal of the working group was to present the state-of-the-art of Higgs physics at the LHC, integrating all new results that have appeared in the last few years The first part compiles the most up-to-date predictions of Higgs boson production cross sections and decay branching ratios, parton distribution functions, and off-shell Higgs boson production and interference effects The second part discusses the recent progress in Higgs effective field theory predictions, followed by the third part on pseudo-observables, simplified template cross section and fiducial cross section measurements, which give the baseline framework for Higgs boson property measurements The fourth part deals with the beyond the Standard Model predictions of various benchmark scenarios of Minimal Supersymmetric Standard Model, extended scalar sector, Next-to-Minimal Supersymmetric Standard Model and exotic Higgs boson decays This report follows three previous working-group reports: Handbook of LHC Higgs Cross Sections: 1 Inclusive Observables (CERN-2011-002), Handbook of LHC Higgs Cross Sections: 2 Differential Distributions (CERN-2012-002), and Handbook of LHC Higgs Cross Sections: 3 Higgs properties (CERN-2013-004) The current report serves as the baseline reference for Higgs physics in LHC Run 2 and beyond

Charm and beauty quark masses in the MMHT2014 global PDF analysis

Abstract: We investigate the variation in the MMHT2014 PDFs when we allow the heavy-quark masses [Formula: see text] and [Formula: see text] to vary away from their default values. We make PDF sets available in steps of [Formula: see text] and [Formula: see text], and present the variation in the PDFs and in the predictions. We examine the comparison to the HERA data on charm and beauty structure functions and note that in each case the heavy-quark data, and the inclusive data, have a slight preference for lower masses than our default values. We provide PDF sets with three and four active quark flavours, as well as the standard value of five flavours. We use the pole mass definition of the quark masses, as in the default MMHT2014 analysis, but briefly comment on the [Formula: see text] definition.

The impact of the final HERA combined data on PDFs obtained from a global fit.

Abstract: We investigate the effect of including the HERA run I + II combined cross section data on the MMHT2014 PDFs. We present the fit quality within the context of the global fit and when only the HERA data are included. We examine the changes in both the central values and the uncertainties in the PDFs. We find that the prediction for the data is good, and only relatively small improvements in \(\chi ^2\) and changes in the PDFs are obtained with a refit at both NLO and NNLO. PDF uncertainties are slightly reduced. There is a small dependence of the fit quality on the value of \(Q^2_{\min }\). This can be improved by phenomenologically motived corrections to \(F_L(x,Q^2)\) which parametrically are largely in the form of higher-twist type contributions.

The impact of the final HERA combined data on PDFs obtained from a global fit

Abstract: We investigate the effect of including the HERA run I + II combined cross section data on the MMHT2014 PDFs. We present the fit quality within the context of the global fit and when only the HERA data are included. We examine the changes in both the central values and uncertainties in the PDFs. We find that the prediction for the data is good, and only relatively small improvements in $\chi^2$ and changes in the PDFs are obtained with a refit at both NLO and NNLO. PDF uncertainties are slightly reduced. There is a small dependence of the fit quality on the value of $Q^2_{\min}$. This can be improved by phenomenologically motived corrections to $F_L(x,Q^2)$ which parametrically are largely in the form of higher-twist type contributions.

Summary of structure functions and PDFs working group

Abstract: This summary presents personal highlights from the Structure Functions and PDFs Working Group (WG1).

Updates of the MMHT2014 PDFs

Abstract: We briefly discuss some of the developments since the publication of the MMHT14 parton distributions. In particular we explore the impact of recent LHC data for $W^\pm,Z$ and $t\bar{t}$ production, and perform a preliminary new analysis including these data. In this re-fit (which we tentatively call `MMHT16') there are few changes of significance in the central values of the PDFs, but some data reduce the uncertainties, mainly in the strange and valence quark distributions. We find that an extended $\bar{d}-\bar{u}$ parametrization only leads to minor changes, with the difference going to zero as $x \to 0$. We comment on the determination of the photon PDF.

Summary of Structure Functions and PDFs Working Group

Abstract: This summary presents personal highlights from the Structure Functions and PDFs Working Group (WG1) at DIS 2016.

PDFs and Top Physics

Abstract: I present the results from the recent PDF4LHC study, and the resulting new recommendation for combining PDFs sets for LHC calculations. In order to put this into context I summarise continuing developments in PDFs. This includes improvements and recent updates of particular PDF sets due to theory improvements and a variety of new data sets, including most of the up-todate LHC data. I will emphasise particular issues relevant for top physics.