Angular distributions of the decay B 0 → K * 0 µ + µ − are studied using a sample of proton-proton collisions at √ s = 8 TeV collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb −1 . An angular analysis is performed to determine the P 1 and P 5 parameters, where the P 5 parameter is of particular interest because of recent measurements that indicate a potential discrepancy with the standard model predictions. Based on a sample of 1397 signal events, the P 1 and P 5 parameters are determined as a function of the dimuon invariant mass squared. The measurements are in agreement with predictions based on the standard model.
The angular distributions and the differential branching fraction of the decay B 0 → K * (892) 0 µ + µ − are studied using a data sample corresponding to an integrated luminosity of 5.2 fb −1 collected with the CMS detector at the LHC in pp collisions at √ s = 7 TeV. From more than 400 signal decays, the forward-backward asymmetry of the muons, the K * (892) 0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the square of the dimuon invariant mass. The measurements are in good agreement with standard model predictions.
We present a novel neutron detector based on an ultra-thin 3D silicon sensor with a sensitive volume only 10 µm thick. This ultra-thin active volume allows a high gamma-ray rejection, a key requirement in order to discriminate the signal coming from the neutrons in a mixed neutron-gamma ray environment. The device upper-side is covered with a novel boronbased compound that detects neutrons by means of the 10 B(n,α) 7 Li nuclear reaction. The performance of test devices has been investigated first with a gamma-ray source to evaluate the gamma-ray rejection factor, and then with an 241 AmBe neutron source to assess the neutrongamma ray discrimination properties.
The accurate detection and dosimetry of neutrons in mixed and pulsed radiation fields is a demanding instrumental issue with great interest both for the industrial and medical communities. In recent studies of neutron contamination around medical linacs, there is a growing concern about the secondary cancer risk for radiotherapy patients undergoing treatment in photon modalities at energies greater than 6 MV. In this work we present a promising alternative to standard detectors with an active method to measure neutrons around a medical linac using a novel ultra-thin silicon detector with 3D electrodes adapted for neutron detection. The active volume of this planar device is only 10 µm thick, allowing a high gamma rejection, which is necessary to discriminate the neutron signal in the radiotherapy peripheral radiation field with a high gamma background. Different tests have been performed in a clinical facility using a Siemens PRIMUS linac at 6 and 15 MV. The results show a good thermal neutron detection efficiency around 2% and a high gamma rejection factor.
In this paper we present the first direct microdosimetric measurements of 62 MeV proton beams using ultra-thin 3D silicon detectors at different depths in a solid-water phantom. The detectors have 3D columnar electrodes that penetrate a 10 µm thick silicon membrane, resulting in a micrometric scale sensitive volume. The 62 MeV proton beam was generated in a cyclotron CYCLONE-110 at Centre de Recherches du Cyclotron (CRC) at Louvain-la-Neuve. The proton beam average energy was modulated with stacked tissue-equivalent solid water layers. The energy loss profile was studied through the Bragg curve and pulse height spectra. The experimental silicon microdosimetric spectra showed the lineal energy dependence along the Bragg curve. This work demonstrates the potential capability of the ultra-thin 3D silicon detectors as 3D detector technology-based microdosimeters.
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