arXiv subjects

S. Ask

Publications and source records attributed to S. Ask.

7 recordsLinked to original sources

arXiv2011

Identifying the colour of TeV-scale resonances

We explore how the colour of any new TeV-scale resonances that decay into top quark pairs can be identified by studying the dependence of the observed cross-section on a central jet veto. To facilitate this study, colour octet resonance production was implemented in Pythia8 and colour singlet resonance production is simulated after minor modifications. We find that the colour of a 2 TeV resonance can be identified with 10/fb of data at a centre-of-mass energy of 14 TeV for a wide range of couplings, but only if the uncertainty in the theoretical prediction is dramatically reduced from its current level.

hep-ph↗

arXiv2011

Using gamma+jets Production to Calibrate the Standard Model Z(nunu)+jets Background to New Physics Processes at the LHC

The irreducible background from Z(nunu)+jets, to beyond the Standard Model searches at the LHC, can be calibrated using gamma+jets data. The method utilises the fact that at high vector boson pT, the event kinematics are the same for the two processes and the cross sections differ mainly due to the boson-quark couplings. The method relies on a precise prediction from theory of the Z/gamma cross section ratio at high pT, which should be insensitive to effects from full event simulation. We study the Z/gamma ratio for final states involving 1, 2 and 3 hadronic jets, using both the leading-order parton shower Monte Carlo program Pythia8 and a leading-order matrix element program Gambos. This enables us both to understand the underlying parton dynamics in both processes, and to quantify the theoretical systematic uncertainties in the ratio predictions. Using a typical set of experimental cuts, we estimate the net theoretical uncertainty in the ratio to be of order 7%, when obtained from a Monte Carlo program using multiparton matrix-elements for the hard process. Uncertainties associated with full event simulation are found to be small. The results indicate that an overall accuracy of the method, excluding statistical errors, of order 10% should be possible.

hep-ph↗

arXiv2010

Real Emission and Virtual Exchange of Gravitons and Unparticles in Pythia8

Models with large extra dimensions as well as unparticle models could give rise to new phenomena at collider experiments due to real emission or virtual exchange of gravitons or unparticles. In this paper we present the common implementation of these processes in the Monte Carlo generator Pythia8, using relations between the parameters of the two models. The program offers several options related to the treatment of the UV region of the effective theories, including the possibility of using a form factor for the running gravitational coupling. Characteristic results obtained with Pythia8 have been used to validate the implementations as well as to illustrate the key features and effects of the model parameters. The results presented in this paper are focused on mono-jet, di-photon and di-lepton final states at the LHC.

hep-ph↗

arXiv2009

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.

hep-ex↗

arXiv2007

Search for one large extra dimension with the DELPHI detector at LEP2

Single photons detected by the DELPHI experiment at LEP2 in the years 1997-2000 are used to investigate the existence of a single extra dimension in a modifed ADD scenario with slightly warped large extra dimensions. The data collected at centre-of-mass energies between 180 and 209 GeV for an integrated luminosity of ~650 pb^-1 agree with the predictions of the Standard Model and allow a limit to be set on graviton emission in one large extra dimension. The limit obtained on the fundamental mass scale MD is 1.69 TeV at 95% CL, with an expected limit of 1.71 TeV.

hep-ex↗

arXiv2006

Luminosity measurement at ATLAS - development, construction and test of scintillating fibre prototype detectors

We are reporting about a scintillating fibre tracker which is proposed for the precise determination of the absolute luminosity of the CERN LHC at interaction point 1 where the ATLAS experiment is located. The detector needs to track protons elastically scattered under micro-rad angles in direct vicinity to the LHC beam. It is based on square shaped scintillating plastic fibres read out by multi-anode photomultiplier tubes and is housed in Roman Pots. We describe the design and construction of prototype detectors and the results of a beam test experiment at DESY. The excellent detector performance established in this test validates the detector design and supports the feasibility of the proposed challenging method of luminosity measurement.

physics.ins-det↗

arXiv2003

A Review of the Supersymmetry Searches at LEP

The searches for supersymmetric particles by the four LEP experiments, ALEPH, DELPHI, L3, OPAL, have been made for many different theoretical models and phenomenological scenarios. Since no significant signs of a SUSY signal have been observed the results have been used to set exclusion limits and to constrain the supersymmetric parameter space. This talk will focus on combined SUSY searches, within the mSUGRA framework, from the four LEP experiments. The results are based mainly on the data recorded between the years 1996-2000, which corresponds to an integrated luminosity of 2.7 fb$^{-1}$ and center-of-mass energies from 161 up to 208 GeV.

hep-ex↗