Direct search for Higgs boson in LHCb and contribution to the development of the vertex detector

The LHCb experiment (Large Hadron Collider beauty) is one of the four experiments under construction at the LHC (Large Hadron Collider) at CERN near Geneva. It is planned to start in 2007 and its goal is the study of b-quark physics. The LHC is a circular accelerator in which collide protons-protons at a center-of-mass energy of √s = 14 TeV. This generates a large number of high energy bb pairs which are predominantly produced in the same forward cone. The LHCb detector is therefore a forward single arm spectrometer designed to exploit the large bb production cross section (σbb ~ 500 μb) and to perform precise measurements of CP violation in b-hadrons decays. One of the actual greatest challenges in High Energy Physics is the discovery of the Higgs boson which is responsible for the Model Standard particles mass generation through the Spontaneous Symmetry Breaking process. The Higgs mass is not known and cannot be predicted by the theory. However the recent results of LEP at CERN have shown that mH0 > 114 GeV/c2. Below ~ 150 GeV/c2 the Higgs decay into two b-quarks H0 → bb dominates. The two quarks emitted back-to-back in the H0 rest frame form a string which fragments, giving rise to hadronization in jets containing b-hadrons. The aim of this thesis is to assess the feasibility to discover a Higgs boson with intermediate mass at LHCb by using the detector sensibility to b-hadrons in order to reconstruct these jets using jets reconstruction algorithms. The study is focused on the mechanisms in which the Higgs boson is produced in association with a gauge boson decaying leptonically H0 + W± → bb + ℓνℓ and H0 + Z0 → bb + ℓ+ℓ- for Higgs masses in the range 100 - 130 GeV/c2. The gauge bosons decay produces hard leptons quite often isolated from the b-jets. Hence an isolated lepton with high transverse momentum is required in order to reject the large QCD background. Several important background channels which also provide two b-quarks and an isolated lepton – like tt → W+b W-b, Z0 + W± → bb + ℓνℓ, Z0 + Z0 → bb + ℓ+ℓ-, W± + b-jets, Z0 + b-jets and generic bb – are studied in parallel. The idea is to find observables which behave differently for backgrounds and Higgs signal and to exploit these differences in the framework of a neural network, precisely in order to discriminate background from signal. The LHCb experiment needs a high capability to identify b-hadrons despite their very short lifetime τB ~ 1.5 · 10-12 s. The Vertex Locator (VeLo) is a sub-detector placed around the p-p interaction point which has to provide accurate measurements of the b-hadrons production and decay points by reconstructing secondary vertices. The second part of this thesis is a technical contribution to the development of the VeLo analogue transmission line. It consists in testing several hardware and software methods to improve the VeLo analogue transmission between the on-detector part of the readout and the off-detector electronics. Because the ~ 60 m line introduces an important attenuation, several cables and line drivers configurations with frequency and gain compensation are studied in order to obtain the best results in terms of signal-to-noise ratio and channel crosstalk. The different contributions to the noise are also studied and an estimation of the contribution due to the Beetle pipeline non-uniformity is given in order to see if a specific correction is needed or if it can be suppressed by a standard common noise correction procedure

Examination of Gould's modified S1 (mS1) selective medium and Angle's non-selective medium for describing the diversity of Pseudomonas spp. in soil and root environments

Studies on the diversity of environmental culturable Pseudomonas populations are dependent on the isolation procedure. This procedure includes the use of selective media which may influence the recovery of strains and thus the diversity described. In this study, we assessed the use of two agar isolation media for describing the diversity of soil- and root-inhabiting Pseudomonas associated with the perennial grass Molinia coerulea. A total of 382 Pseudomonas strains were recovered on either non-selective Angle's medium, or on Gould's modified S1 (mS1) Pseudomonas-selective medium. Their diversity was assessed by restriction analysis of PCR (polymerase chain reaction)-amplified 16S-23S rDNA internal transcript spacer sequences. The comparison of mS1- and Angle-recovered populations showed that the use of mS1 selective medium led to an underestimation of both Pseudomonas counts and diversity, especially in the soil environmen

Observation of Bloch-point domain walls in cylindrical magnetic nanowires

Topological protection is an elegant way of warranting the integrity of quantum and nanosized systems. In magnetism one example is the Bloch-point, a peculiar object implying the local vanishing of magnetization within a ferromagnet. Its existence had been postulated and described theoretically since several decades, however it has never been observed. We con rm experimentally the existence of Bloch points, imaged within domain walls in cylindrical magnetic nanowires, combining surface and transmission XMCD-PEEM magnetic microscopy. This opens the way to the experimental search for peculiar phenomena predicted during the motion of Bloch-point-based domain walls

Improved Annealing Process for 6H-SiC p⁺-n Junction Creation by Al Implantation

International audienceFive-fold Al implantations at both room temperature and 300°C ranging from 25 keV to 300 keV and a total fluence of 1.75x10 15 cm-2 , have been performed in 6H-SiC epilayers to create p +-n junctions. The samples have been annealed at 1700°C during 30 mn in an inductively heated furnace especially configured. Surface effects, recrystallization, dopant distribution and electrical activation are investigated by XPS, RBS, SIMS and sheet resistance measurements. For both RT and 300°C-implanted samples, good recrystallization and surface stoichiometry are found as well as no dopant loosing and an interesting electrical activation (46% and 99%, respectively). Introduction p +-n junctions in SiC power devices must be realized by ion implantation due to very low diffusion coefficients of dopants in silicon carbide. SiC high density and its structural crystallinity involve a delicate post-implantation annealing. The implantation temperature, annealing environment, time and temperature of annealing and the heating rate are the essential parameters to reorder the crystal damage induced by ion implantation and to activate the dopants by migrating in SiC atomic sites. Initially, after ion implantation, almost all Al dopants are distributed in interstitial sites, where they are not electrically active. We utilized a JIPELEC TM rf induction furnace. This technique of annealing has significant advantages such as the very high rising slope in temperature and the very localized zone of heating (the susceptor). But this one implies high temperature variations, vertically in the enclosure and laterally on the surface of the SiC wafers. These temperature gradients may cause an etching of, or a layer deposition on the SiC surface. Moreover, Si is known to volatilize towards 1400°C at one atmosphere pressure, and in lack of a Si supersaturating vapor the carbonization of the surface is inevitable. This paper presents the results of an optimized thermal rf annealing, which avoids these problems

Broadband Setup for Magnetic-Field-Induced Domain Wall Motion in Cylindrical Nanowires

In order to improve the precision of domain wall dynamics measurements, we develop a coplanar waveguide-based setup where the domain wall motion should be triggered by pulses of magnetic field. The latter are produced by the Oersted field of the waveguide as a current pulse travels toward its termination, where it is dissipated. Our objective is to eliminate a source of bias in domain wall speed estimation while optimizing the field amplitude. Here, we present implementations of this concept for magnetic force microscopy (MFM) and synchrotron-based investigation

Improved Annealing Process for 6H-SiC p⁺-n Junction Creation by Al Implantation

International audienceFive-fold Al implantations at both room temperature and 300°C ranging from 25 keV to 300 keV and a total fluence of 1.75x10 15 cm-2 , have been performed in 6H-SiC epilayers to create p +-n junctions. The samples have been annealed at 1700°C during 30 mn in an inductively heated furnace especially configured. Surface effects, recrystallization, dopant distribution and electrical activation are investigated by XPS, RBS, SIMS and sheet resistance measurements. For both RT and 300°C-implanted samples, good recrystallization and surface stoichiometry are found as well as no dopant loosing and an interesting electrical activation (46% and 99%, respectively). Introduction p +-n junctions in SiC power devices must be realized by ion implantation due to very low diffusion coefficients of dopants in silicon carbide. SiC high density and its structural crystallinity involve a delicate post-implantation annealing. The implantation temperature, annealing environment, time and temperature of annealing and the heating rate are the essential parameters to reorder the crystal damage induced by ion implantation and to activate the dopants by migrating in SiC atomic sites. Initially, after ion implantation, almost all Al dopants are distributed in interstitial sites, where they are not electrically active. We utilized a JIPELEC TM rf induction furnace. This technique of annealing has significant advantages such as the very high rising slope in temperature and the very localized zone of heating (the susceptor). But this one implies high temperature variations, vertically in the enclosure and laterally on the surface of the SiC wafers. These temperature gradients may cause an etching of, or a layer deposition on the SiC surface. Moreover, Si is known to volatilize towards 1400°C at one atmosphere pressure, and in lack of a Si supersaturating vapor the carbonization of the surface is inevitable. This paper presents the results of an optimized thermal rf annealing, which avoids these problems

Study of 6H-SiC high voltage bipolar diodes under reverse biases

International audienceSilicon carbide presents electrical properties suitable for many applications especially for high voltage devices. 6H-SiC P+NN+ structures have been fabricated following ISE software simulations in order to block voltages as high as 1.5 kV. In particular, these diodes are realized by surrounding the emitter by a p-type region called junction termination extension (JTE). Electrical characterizations under reverse bias at, room temperature and in various environments (air, silicone oil) show a premature breakdown for the protected diodes. This breakdown is localized at the emitter periphery. Optical beam induced current (OBIC) measurements show a peak of photocurrent at the junction edge, indicating the presence of a high electric field. These results show a protection efficiency of 60% of the JTE. An electrical activation of the aluminum dopants implanted in the JTE around 30% is derived from the analysis of the presented results

Behavior of Space Charge in Polyimide and the Influence on Power Semiconductor Device Reliability

Polyimide is widely used in film form as a passivation material for power semiconductor devices such as Si, SiC, and GaN. The magnitude of the electric field at the edge termination area of these semiconductor devices is becoming higher due to the increase of operational voltage and/or demand for shrinking the edge termination area to increase device active area. Hence, it is concerned that the accumulation of space charge in the encapsulation and passivation material may affect the insulation performance of these devices, for example, the degradation of withstand voltage due to distortion of the internal electric field caused by space charge accumulation. To design space charge resistance of semiconductor devices, it is important to understand the space charge behavior in polyimide films with a thickness of several to several tens of micrometers. This chapter addresses practical implementation, specifications, and issues on space charge in polyimide insulation on power semiconductor devices focusing on the space charge measurements in thin polyimide films using the latest developed LIMM method and DC conductivity measurements

Population Pharmacokinetics of Palbociclib and Its Correlation with Clinical Efficacy and Safety in Patients with Advanced Breast Cancer.

Neutropenia is the most frequent dose-limiting toxicity reported in patients with metastatic breast cancer receiving palbociclib. The objective of this study was to investigate the pharmacokinetic-pharmacodynamic (PK/PD) relationships for toxicity (i.e., absolute neutrophil count, ANC) and efficacy (i.e., progression-free survival, PFS). A semi-mechanistic PK/PD model was used to predict neutrophils' time course using a population approach (NONMEM). Influence of demographic and clinical characteristics was evaluated. Cox proportional hazards models were developed to evaluate the influence of palbociclib PK on PFS. A two-compartment model with first-order absorption and a lag time adequately described the 255 palbociclib concentrations provided by 44 patients. The effect of the co-administration of proton-pump inhibitors in fasting conditions increased palbociclib clearance by 56%. None of the tested covariates affected the PD parameters. Model-based simulations confirmed the concentration-dependent and non-cumulative properties of palbociclib-induced neutropenia, reversible after treatment withdrawal. The ANC nadir occurred approximately at day 24 of each cycle. Cox analyses revealed a trend for better PFS with increasing palbociclib exposure in older patients. By characterizing palbociclib-induced neutropenia, this model offers support to clinicians to rationally optimize treatment management through patient-individualized strategies