arXiv subjects

Emily Nurse

Publications and source records attributed to Emily Nurse.

7 recordsLinked to original sources

arXiv2019

Monte Carlo event generators for high energy particle physics event simulation

Monte Carlo event generators (MCEGs) are the indispensable workhorses of particle physics, bridging the gap between theoretical ideas and first-principles calculations on the one hand, and the complex detector signatures and data of the experimental community on the other hand. All collider physics experiments are dependent on simulated events by MCEG codes such as Herwig, Pythia, Sherpa, POWHEG, and MG5_aMC@NLO to design and tune their detectors and analysis strategies. The development of MCEGs is overwhelmingly driven by a vibrant community of academics at European Universities, who also train the next generations of particle phenomenologists. The new challenges posed by possible future collider-based experiments and the fact that the first analyses at Run II of the LHC are now frequently limited by theory uncertainties urge the community to invest into further theoretical and technical improvements of these essential tools. In this short contribution to the European Strategy Update, we briefly review the state of the art, and the further developments that will be needed to meet the challenges of the next generation.

hep-ph↗

arXiv2015

Methods to Select Soft Diffraction Dissociation at the LHC

Diffractive events at hadron colliders are typically characterised by a region of the detector without particles, known as a rapidity gap. In order to observe diffractive events in this way, we consider the pseudorapidity acceptance in the forward region of the ATLAS and CMS detectors at the Large Hadron Collider (LHC) and discuss the methods to select soft diffractive dissociation for pp collisions at sqrt(s) = 7 TeV. We showed that in the limited detector rapidity acceptance, it is possible to select diffractive dissociated events by requiring a rapidity gap in the event, however, it is not possible to distinguish single diffractive dissociated events from double diffractive dissociated events with a low diffractive mass.

hep-ph↗

arXiv2011

LO vs NLO comparisons for Z + jets: MC as a tool for background determination for NP searches at LHC

The leptonic decays of the heavy gauge bosons W and/or Z provide a clear experimental signature at hadron colliders. The production of accompanying jets is an excellent signal to probe QCD, while also being the main background to many searches for new physics. Describing the complex final state of W or Z + jets is a theoretical challenge with most existing calculations combining matrix elements for high energy jet production with a parton shower for lower energy jet production. We focus on two models: SHERPA, which uses Leading Order matrix elements for boson and jet production; and POWHEG with HERWIG++, which uses a Next-To-Leading Order Matrix element for Z production. In order to isolate the impact of the matrix elements for jet production, it is first essential to constrain the differences in the rest of the calculation in each case: specifically, the Multiple Parton Interaction models, and the tuning of the parton shower interfaced to the matrix elements. We test all three aspects of these models against data from the Tevatron, and perform a study of some basic kinematic variables at the LHC energy.

hep-ph↗

arXiv2011

General-purpose event generators for LHC physics

We review the physics basis, main features and use of general-purpose Monte Carlo event generators for the simulation of proton-proton collisions at the Large Hadron Collider. Topics included are: the generation of hard-scattering matrix elements for processes of interest, at both leading and next-to-leading QCD perturbative order; their matching to approximate treatments of higher orders based on the showering approximation; the parton and dipole shower formulations; parton distribution functions for event generators; non-perturbative aspects such as soft QCD collisions, the underlying event and diffractive processes; the string and cluster models for hadron formation; the treatment of hadron and tau decays; the inclusion of QED radiation and beyond-Standard-Model processes. We describe the principal features of the ARIADNE, Herwig++, PYTHIA 8 and SHERPA generators, together with the Rivet and Professor validation and tuning tools, and discuss the physics philosophy behind the proper use of these generators and tools. This review is aimed at phenomenologists wishing to understand better how parton-level predictions are translated into hadron-level events as well as experimentalists wanting a deeper insight into the tools available for signal and background simulation at the LHC.

hep-ph↗

arXiv2008

W and Z properties at the Tevatron

I present measurements of W and Z boson properties by the CDF and D0 collaborations. This includes measurements that test the production mechanism of the bosons and precision measurements of electroweak parameters. In the former category I present CDF measurements of the Z rapidity and W charge asymmetry that will help further constrain Parton Distribution Functions in future global fits, and a D0 measurement of the Z transverse momentum distribution that can be used to test the predictions of quantum-chromodynamics. In the later category I present a D0 measurement of the Z/gamma* forward-backward asymmetry and the subsequent extraction sin2theta_W = 0.2327 +/- 0.0018 (stat.) +/- 0.0006 (syst.) and a CDF measurement of the W width Gamma_W using a fit to the tail of the W transverse mass distribution in W->enu and W->munu events that yields Gamma_W = 2032 +/- 73 MeV.

hep-ex↗

arXiv2007

W production and properties at CDF

I present measurements of the W boson charge asymmetry and the W boson width G_W using 350 pb-1 of CDF Run II data. The charge asymmetry is the first direct measurement, which uses a new technique to reconstruct the W rapidity by constraining its mass; the result will further constrain Parton Distribution Functions in future fits. The width measurement relies on a fit to the W transverse mass distribution. We measure G_W = 2032 +/- 71 MeV which is in good agreement with the Standard Model prediction.

hep-ex↗

arXiv2007

W mass and width measurements at the Tevatron

I present a measurement of the W boson mass (M_W) and width (G_W) using 200 and 350 pb-1 of CDF Run II data respectively. The measurements, performed in both the electron and muon decay channels, rely on a fit to the W transverse mass distribution. We measure M_W = 80413 +/- 48 MeV and G_W = 2032 +/- 71 MeV which represent the world's single most precise measurements to date.

hep-ex↗