The R&D undertaken by the VELO group in order to produce a sensor that satisfies the tight radiation hardness, efficiency, resolution and low material requirements of LHCb has resulted in the choice ...of an n-on-n double metal layer solution. First, measurements of the performance of the latest prototype and its related front end electronics, designed to function at the LHC speed of 40
MHz, are presented here. In addition, research has been carried out into new materials which could retain good performance in high-radiation environments at and beyond the LHC, and could provide an alternative for a possible VELO upgrade. For the first time, a full size Czochralski silicon detector sample with
50
μ
m
pitch strips has been irradiated with high energy protons and its performance has been measured in a test beam with 40
MHz electronics. The results of this test will be presented.
Cryogenic detector modules and edgeless silicon sensors Rouby, X.; Eremin, V.; Grohmann, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2007, Letnik:
570, Številka:
2
Journal Article
Recenzirano
We are studying the operation of silicon microstrip detector with readout electronics in the temperature range from 90 to 130
K. The sensor can be operated in the current-injection mode which ...significantly improves its radiation hardness. A first module prototype has been built, with APV25 readout chips and an embedded microtube, providing efficient low-mass cooling of the whole module with a two-phase flow of
N
2
or Ar. First pedestal and pulse shape temperature dependencies are presented for this module. We have also built an edgeless test module with two pairs of laser cut sensors, with both angular and parallel cuts with respect to the strips (at
120
μ
m
pitch). We are studying the efficiency of the microstrip sensors very close (
<
200
μ
m
) to the physical border of the cut silicon crystal and present here some electrical characteristics.
Abstract A search is presented for decays beyond the standard model of the 125 GeV Higgs bosons to a pair of light bosons, based on models with extended scalar sectors. Light boson masses between 5 ...and 62.5 GeV are probed in final states containing four τ leptons, two muons and two b quarks, or two muons and two τ leptons. The results are from data in proton-proton collisions corresponding to an integrated luminosity of 19.7 fb−1, accumulated by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV. No evidence for such exotic decays is found in the data. Upper limits are set on the product of the cross section and branching fraction for several signal processes. The results are also compared to predictions of two-Higgs-doublet models, including those with an additional scalar singlet.
Abstract A measurement of the t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ production cross section at s = 13 $$ \sqrt{s}=13 $$ TeV is presented using proton-proton collisions, corresponding to an ...integrated luminosity of 2.2 fb−1, collected with the CMS detector at the LHC. Final states with one isolated charged lepton (electron or muon) and at least one jet are selected and categorized according to the accompanying jet multiplicity. From a likelihood fit to the invariant mass distribution of the isolated lepton and a jet identified as coming from the hadronization of a bottom quark, the cross section is measured to be σ t t ¯ = 888 ± 2 , stat − 28 + 26 syst ± 20 lumi $$ {\sigma}_{\mathrm{t}\overline{\mathrm{t}}}=888\pm 2,{\left(\mathrm{stat}\right)}_{-28}^{+26}\left(\mathrm{syst}\right)\pm 20\left(\mathrm{lumi}\right) $$ pb, in agreement with the standard model prediction. Using the expected dependence of the cross section on the pole mass of the top quark (m t), the value of m t is found to be 170.6 ± 2.7 GeV.
Abstract A search for the production of heavy resonances decaying into top quark-antiquark pairs is presented. The analysis is performed in the lepton+jets and fully hadronic channels using data ...collected in proton-proton collisions at s = 13 $$ \sqrt{s}=13 $$ TeV using the CMS detector at the LHC, corresponding to an integrated luminosity of 2.6 fb−1. The selection is optimized for massive resonances, where the top quarks have large Lorentz boosts. No evidence for resonant t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ production is found in the data, and upper limits on the production cross section of heavy resonances are set. The exclusion limits for resonances with masses above 2 TeV are significantly improved compared to those of previous analyses at s = 8 $$ \sqrt{s}=8 $$ TeV.
Abstract A measurement of the cross section for top quark-antiquark ( t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ ) pairs produced in association with a photon in proton-proton collisions at s = 8 $$ ...\sqrt{s}=8 $$ TeV is presented. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb1. The signal is defined as the production of a t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ pair, and the cross section is measured relative to the inclusive t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ pair production cross section. The fiducial cross section for associated t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ pair and photon production is found to be 127 ±27 (stat+syst) fb per semileptonic final state. The measured value is in agreement with the theoretical prediction.
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