arXiv subjects

M. R. J. Williams

Publications and source records attributed to M. R. J. Williams.

4 recordsLinked to original sources

arXiv2022

Spatial resolution and efficiency of prototype sensors for the LHCb VELO Upgrade

A comprehensive study of the spatial resolution and detection efficiency of sensor prototypes developed for the LHCb VELO upgrade is presented. Data samples were collected at the CERN SPS H8 beam line using a hadron mixture of protons and pions with momenta of approximately 180 GeV/c. The sensor performance was characterised using both irradiated and non-irradiated sensors. Irradiated samples were subjected to a maximum fluence of $\mathrm{8\times10^{15}~1~MeV~n_{eq}~cm^{-2}}$, of both protons and neutrons. The spatial resolution is measured comparing the detected hits to the position as predicted by tracks reconstructed by the Timepix3 telescope. The resolution is presented for different applied bias voltages and track angles, sensor thickness and implant size.

physics.ins-det↗

arXiv2020

Charge collection properties of prototype sensors for the LHCb VELO upgrade

An extensive sensor testing campaign is presented, dedicated to measuring the charge collection properties of prototype candidates for the Vertex Locator (VELO) detector for the upgraded LHCb experiment. The charge collection is measured with sensors exposed to fluences of up to $8 \times 10^{15}~1~\mathrm{\,Me\kern -0.1em V}~ \mathrm{ \,n_{eq}}~{\mathrm{ \,cm}}^{-2}$, as well as with nonirradiated prototypes. The results are discussed, including the influence of different levels of irradiation and bias voltage on the charge collection properties. Charge multiplication is observed on some sensors that were nonuniformly irradiated with 24 GeV protons, to the highest fluence levels. An analysis of the charge collection near the guard ring region is also presented, revealing significant differences between the sensor prototypes. All tested sensor variants succeed in collecting the minimum required charge of 6000 electrons after the exposure to the maximum fluence.

physics.ins-det↗

arXiv2018

Mapping the material in the LHCb vertex locator using secondary hadronic interactions

Precise knowledge of the location of the material in the LHCb vertex locator (VELO) is essential to reducing background in searches for long-lived exotic particles, and in identifying jets that originate from beauty and charm quarks. Secondary interactions of hadrons produced in beam-gas collisions are used to map the location of material in the VELO. Using this material map, along with properties of a reconstructed secondary vertex and its constituent tracks, a $p$-value can be assigned to the hypothesis that the secondary vertex originates from a material interaction. A validation of this procedure is presented using photon conversions to dimuons.

physics.ins-det↗

arXiv2011

Evidence for an anomalous like-sign dimuon charge asymmetry

We present a measurement of the like-sign dimuon asymmetry in semileptonic $b$-hadron decays, performed using 6.1 fb$^{-1}$ of $p\bar{p}$ collisions recorded with the D0 detector at a center-of-mass energy $\sqrt{s}=1.96$ TeV at the Fermilab Tevatron collider. This measured value is $A^b_{\rm sl} = [-0.957\pm0.251\thinspace({\rm stat})\pm0.146\thinspace({\rm syst})]$ %, which disagrees with the Standard Model prediction at a statistical level of 3.2 $σ$, and provides the first evidence of anomalous CP violation in the mixing of neutral $B$ mesons.

hep-ex↗