Craig Buttar

The LCFIVertex package: vertexing, flavour tagging and vertex charge reconstruction with an ILC vertex detector

The precision measurements envisaged at the International Linear Collider (ILC) depend on excellent instrumentation and reconstruction software. The correct identification of heavy flavour jets, placing unprecedented requirements on the quality of the vertex detector, will be central for the ILC programme. This paper describes the LCFIVertex software, which provides tools for vertex finding and for identification of the flavour and charge of the leading hadron in heavy flavour jets. These tools are essential for the ongoing optimisation of the vertex detector design for linear colliders such as the ILC. The paper describes the algorithms implemented in the LCFIVertex package as well as the scope of the code and its performance for a typical vertex detector design.

Test beam results of 3D silicon pixel sensors for the ATLAS upgrade

Results on beam tests of 3D silicon pixel sensors aimed at the ATLAS Insertable B-Layer and High Luminosity LHC (HL-LHC) upgrades are presented. Measurements include charge collection, tracking efficiency and charge sharing between pixel cells, as a function of track incident angle, and were performed with and without a 1.6 T magnetic field oriented as the ATLAS inner detector solenoid field. Sensors were bump-bonded to the front-end chip currently used in the ATLAS pixel detector. Full 3D sensors, with electrodes penetrating through the entire wafer thickness and active edge, and double-sided 3D sensors with partially overlapping bias and read-out electrodes were tested and showed comparable performance.

τ Production and decay with the cello detector at petra

Abstract The reaction e + e − → τ + τ − has been studied at centre of mass energies between 14.0 and 46.8 GeV with the CELLO detector at the PETRA e + e − collider. We present results for the cross section σ τ and the charge asymmetry A τ . The results are in good agreement with the standard model. We have also measured the topological decay rates BR 1 , BR 3 and BR 5 for the inclusive decay of the τ lepton into one, three and five charge particles. The results confirm and improve earlier CELLO measurements at other energies. We find for the combined values at all energies BR 1 = (84.9 ± 0.4 ± 0.3)%, BR 3 = (15.0 ± 0.4 ± 0.3)% and BR 5 = (0.16 ± 0.13 ± 0.04)%.

Charge collection studies in irradiated HV-CMOS particle detectors

Charge collection properties of particle detectors made in HV-CMOS technology were investigated before and after irradiation with reactor neutrons. Two different sensor types were designed and processed in 180 and 350 nm technology by AMS. Edge-TCT and charge collection measurements with electrons from 90Sr source were employed. Diffusion of generated carriers from undepleted substrate contributes significantly to the charge collection before irradiation, while after irradiation the drift contribution prevails as shown by charge measurements at different shaping times. The depleted region at a given bias voltage was found to grow with irradiation in the fluence range of interest for strip detectors at the HL-LHC. This leads to large gains in the measured charge with respect to the one before irradiation. The increase of the depleted region was attributed to removal of effective acceptors. The evolution of depleted region with fluence was investigated and modeled. Initial studies show a small effect of short term annealing on charge collection.

A search for single photons at petra

Abstract A search for single photons, produced in e + e − collisions together with particles interacting only weakly with matter, has been performed using the CELLO detector operating at the PETRA storage ring. From the absence of any signal, an upper limit is set at 15 (90% CL) on the number of light neutrino species, and lower limits on various supersymmetric particle masses are derived. For massless photinos, mass degenerate scalar partners of the left- and right-handed electrons are excluded below 37.7 GeV/ c 2 (90% CL).

Neutrino counting with the CELLO detector and search for supersymmetric particles

A search for single photons, produced in e+e− collisions together with particles interacting only weakly with matter, has been performed using the CELLO detector at the PETRA storage ring. We report on results from data taken at 35 GeV < √s<46.57 GeV. An upper limit of 8.7 (90% CL) on the number of light neutrino species is set. Combining our result with published results from other e+e− experiments the number of light neutrinos is limited to Nv < 4.6 at 90% CL. We also set lower limits on the masses of supersymmetric particles.

Search for production of charged Higgs particles

Abstract A search has been performed for the production of charged Higgs bosons in e+ e− annihilation at center of mass energies up to 46.8 GeV. From the absence of both hadronic and leptonic decay signatures, we exclude them up to a mass of 19 GeV/c2 independent of the hadronic and leptonic branching ratios.

A measurement of the Muon pair production in e+e− annihilation at 38.3⩽s⩽46.8GeV

Abstract The e+e−→μ+μ− reaction has been studied at centre of mass energies ranging between 38.3 abd 46.8 GeV with the CELLO detector at PETRA. We present results on the cross section and the charge asymmetry for this channel. Combining all the data at the average energy 〈 s 〉=43 GeV we obtain Rμμ=〈σμμ/σ0〉=0.98±0.04±0.04, 〈Aμμ〉=(−14.1±3.7±1.0)%, where σ0 is the QED cross section and Aμμ is the charge asymmetry corrected for pure radiative effects. These results are in good agreement with the expected values of Rμμ=1.01 and Aμμ=−14.5% at that energy.

Searches for supersymmetric particles with the CELLO detector at PETRA

Mass limits are presented for various supersymmetric particles: scalar partners of electrons, muons, taus and quarks; photinos, winos and zinos. They were obtained from the analysis of an exposure of 48.6 pb−1 of the CELLO detector at the PETRAe+e− storage ring up to a center of mass energy of 46.8 GeV. Special attention has been given to the case where the photino is assumed to be the lightest supersymmetric particle, but other possibilities have also been considered.

K s 0 Kπ production in tagged and untagged γγ interactions

AbstractWe have searched for resonance production in the reaction γγ→Ks0Kπ. No signal was found for theηc and an upper limit for the radiative with