Radiation-hard semiconductor detectors for SuperLHC Bruzzi, M.; Alfieri, G.; Assouak, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2005, Letnik:
541, Številka:
1
Journal Article
Recenzirano
An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 10
35
cm
−2
s
−1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a ...few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 10
16
cm
−2. The CERN-RD50 project “Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders” has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit.
The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
There are two key approaches in our CERN RD 39 Collaboration efforts to obtain ultra-radiation-hard Si detectors: (1) use of the charge/current injection to manipulate the detector internal electric ...field in such a way that it can be depleted at a modest bias voltage at cryogenic temperature range (⩽150
K), and (2) freezing out of the trapping centers that affects the CCE at cryogenic temperatures lower than that of the liquid nitrogen (LN
2) temperature.
In our first approach, we have developed the advanced radiation hard detectors using charge or current injection, the current injected diodes (CID). In a CID, the electric field is controlled by injected current, which is limited by the space charge, yielding a nearly uniform electric field in the detector, independent of the radiation fluence. In our second approach, we have developed models of radiation-induced trapping levels and the physics of their freezing out at cryogenic temperatures.
We processed pin-diodes on Czochralski silicon (Cz-Si), standard Float Zone silicon (Fz-Si) and oxygenated Fz-Si. The diodes were irradiated with 10, 20, and
30
MeV
protons. Depletion voltages and ...leakage currents were measured as a function of the irradiation dose. Additionally, the samples were characterized by TCT and DLTS methods. The high-resistivity Cz-Si was found to be more radiation hard than the other studied materials.
Abstract A search for a light pseudoscalar Higgs boson (A) produced in association with bottom quarks and decaying into a muon pair is reported. The search uses 19.7 fb−1 of proton-proton collisions ...at a center-of-mass energy of 8 TeV, collected by the CMS experiment. No signal is observed in the dimuon mass range from 25 to 60 GeV. Upper limits on the cross section times branching fraction, σpp→bb¯AℬA→μμ $$ \sigma \left(\mathrm{pp}\to \mathrm{b}\overline{\mathrm{b}}\mathrm{A}\right)\mathrm{\mathcal{B}}\left(\mathrm{A}\to \mu \mu \right) $$, are set.
Abstract Results are reported from a search for physics beyond the standard model in proton-proton collision events with a charged lepton (electron or muon), two jets identified as originating from a ...bottom quark decay, and significant imbalance in the transverse momentum. The search was performed using a data sample corresponding to 35.9 fb−1, collected by the CMS experiment in 2016 at s=13 $$ \sqrt{s}=13 $$ TeV. Events with this signature can arise, for example, from the electroweak production of gauginos, which are predicted in models based on supersymmetry. The event yields observed in data are consistent with the estimated standard model backgrounds. Limits are obtained on the cross sections for chargino-neutralino χ˜1±χ˜20 $$ \left({\tilde{\chi}}_1^{\pm }{\tilde{\chi}}_2^0\right) $$ production in a simplified model of supersymmetry with the decays χ1±→W±χ˜10andχ˜20→Hχ10 $$ {\chi}_1^{\pm}\to {\mathrm{W}}^{\pm }{\tilde{\chi}}_1^0\kern0.5em \mathrm{and}\kern0.5em {\tilde{\chi}}_2^0\to \mathrm{H}{\chi}_1^0 $$. Values of mχ˜1± $$ {m}_{{\tilde{\chi}}_1^{\pm }} $$ between 220 and 490 GeV are excluded at 95% confidence level by this search when the χ˜10 $$ {\tilde{\chi}}_1^0 $$ is massless, and values of mχ˜10 $$ {m}_{{\tilde{\chi}}_1^0} $$ are 1 excluded up to 110 GeV for mχ˜1±≈450 $$ {m}_{{\tilde{\chi}}_1^{\pm }}\approx 450 $$ GeV.
Abstract Properties of the Higgs boson are measured in the H → ZZ → 4ℓ (ℓ = e, μ) decay channel. A data sample of proton-proton collisions at s=13 $$ \sqrt{s}=13 $$ TeV, collected with the CMS ...detector at the LHC and corresponding to an integrated luminosity of 35.9 fb−1 is used. The signal strength modifier μ, defined as the ratio of the observed Higgs boson rate in the H → ZZ → 4ℓ decay channel to the standard model expectation, is measured to be μ = 1.05− 0.17+ 0.19 at m H = 125.09 GeV, the combined ATLAS and CMS measurement of the Higgs boson mass. The signal strength modifiers for the individual Higgs boson production modes are also measured. The cross section in the fiducial phase space defined by the requirements on lepton kinematics and event topology is measured to be 2. 92− 0.44+ 0.48(stat)− 0.24+ 0.28(syst)fb, which is compatible with the standard model prediction of 2.76 ± 0.14 fb. Differential cross sections are reported as a function of the transverse momentum of the Higgs boson, the number of associated jets, and the transverse momentum of the leading associated jet. The Higgs boson mass is measured to be m H = 125.26 ± 0.21 GeV and the width is constrained using the on-shell invariant mass distribution to be ΓH < 1.10 GeV, at 95% confidence level.
We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with
24
GeV
/
c
and 10
MeV protons. Samples were characterized with Capacitance-Voltage measurements (CV), ...Transient Current Technique (TCT) and secondary electron backscattering recorded by Scanning Electron Microscope (SEM). We present the evolution of the effective doping concentration as a function of irradiation fluence as well as the introduction rate of negative space charge,
β
-parameter. According to these measurements, we found that Cz-Si is more radiation hard than Fz-Si. Both TCT and SEM measurements indicated that Space Charge Sign Inversion (SCSI) occurred in the heavily irradiated Fz-Si and in the Cz-Si irradiated with 10
MeV protons. However, the SCSI did not take place in Cz-Si irradiated with
24
GeV
/
c
protons even after high irradiation fluence.
Abstract A search for dark matter is performed looking for events with large missing transverse momentum and a Higgs boson decaying either to a pair of bottom quarks or to a pair of photons. The data ...from proton-proton collisions at a center-of-mass energy of 13 TeV, collected in 2015 with the CMS detector at the LHC, correspond to an integrated luminosity of 2.3 fb−1. Results are interpreted in the context of a Z′-two-Higgs-doublet model, where the gauge symmetry of the standard model is extended by a U(1)Z ′ group, with a new massive Z′ gauge boson, and the Higgs sector is extended with four additional Higgs bosons. In this model, a high-mass resonance Z′ decays into a pseudoscalar boson A and a light SM-like scalar Higgs boson, and the A decays to a pair of dark matter particles. No significant excesses are observed over the background prediction. Combining results from the two decay channels yields exclusion limits in the signal cross section in the m Z ′ - m A phase space. For example, the observed data exclude the Z′ mass range from 600 to 1860 GeV, for Z′ coupling strength g Z ′ = 0.8, the coupling of A with dark matter particles g χ = 1, the ratio of the vacuum expectation values tan β = 1, and m A = 300 GeV. The results of this analysis are valid for any dark matter particle mass below 100 GeV.
Rhizobium meliloti, a symbiotic, nitrogen-fixing soil bacterium with complex flagella, as well as other members of the family Rhizobiaceae, rapidly lost motility when suspended in buffers lacking ...divalent cations but retained good motility in buffers containing calcium, magnesium, barium, or strontium. Loss of motility was associated with loss of flagella from the cells. Analysis of flagella by sedimentation, gel electrophoresis, and electron microscopy revealed that removal of divalent cations from the complex flagella of R. meliloti resulted in extensive dissociation of the flagellar filaments into low-molecular-weight subunits. Accordingly, divalent cations such as calcium and magnesium that are normally present at high concentrations in the soil solution may be crucial to the assembly and rigidity of complex flagella
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