Olivier Schneider | Searcharxiv

arXiv2025

Microlens-enhanced SiPMs

A novel concept to enhance the photo-detection efficiency (PDE) of silicon photomultipliers (SiPMs) has been applied and remarkable positive results can be reported. This concept uses arrays of microlenses to cover every second SiPM pixel in a checkerboard arrangement and aims to deflect the light from the dead region of the pixelised structure towards the active region in the center of the pixel. The PDE is improved up to 24%, external cross-talk is reduced by 40% compared to a flat epoxy layer, and single photon time resolution is improved. This detector development is conducted in the context of the next generation LHCb scintillating fibre tracker located in a high radiation environment with a total of 700'000 detector channels. The simulation and measurement results are in good agreement and will be discussed in this work.

physics.ins-det↗

arXiv2025

Cryogenic operation of silicon photomultiplier arrays

The LHCb experiment at CERN has been upgraded for the Run 3 operation of the Large Hadron Collider (LHC). A new concept of tracking detector based on Scintillating Fibres (SciFi) read out with multichannel silicon photomultipliers (SiPMs) was installed during its upgrade. One of the main challenges the SciFi tracker will face during the Run 4 operation of the LHC is the higher radiation environment due to fast neutrons, where the SiPMs are located. To cope with the increase in radiation, cryogenic cooling with liquid nitrogen is being investigated as a possible solution to mitigate the performance degradation of the SiPMs induced by radiation damage. Thus, a detailed performance study of different layouts of SiPM arrays produced by Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics K.K. is being carried out. These SiPMs have been designed to operate at cryogenic temperatures. Several SiPMs have been tested in a dedicated cryogenic setup down to 100 K. Key performance parameters such as breakdown voltage, dark count rate, photon detection efficiency, gain and direct cross-talk are characterized as a function of the temperature. The main results of this study are going to be presented here.

hep-ex↗

arXiv2019

Using an amplitude analysis to measure the photon polarisation in $B \to Kππγ$ decays

A method is proposed to measure the photon polarisation parameter $λ_γ$ in $b\to sγ$ transitions using an amplitude analysis of $B\to Kππγ$ decays. Simplified models of the $Kππ$ i system are used to simulate $B^+ \to K^+π^-π^+γ$ and $B^0\to K^+π^-π^0$ decays, validate the amplitude analysis method, and demonstrate the feasibility of a measurement of the $λ_γ$ parameter irrespective of the model parameters. Similar sensitivities to $λ_γ$ are obtained with both the charged and neutral hadronic systems. In the absence of any background and distortion due to experimental effects, the statistical uncertainty expected from an analysis of $B^+ \to K^+π^-π^+γ$ decays in an LHCb data set corresponding to an integrated luminosity of $9\,$fb$^{-1}$ is estimated to be $0.009$. A similar measurement using $B^0\to K^+π^-π^0$ decays in a Belle II data sample corresponding to an integrated luminosity of $5\,$ab$^{-1}$ would lead to a statistical uncertainty of $0.018$

hep-ph↗

arXiv2018

Characterisation of silicon photomultipliers based on statistical analysis of pulse-shape and time distributions

A detailed and accurate characterisation of silicon photomultiplier detectors is required for a better understanding of the signal and noise in many applications. The collected information is a valuable feedback to the manufacturers in their attempt to improve the performances. In this paper, we provide a detailed description of how to characterise these photo-detectors. The correlated noise probabilities, the important time constants and the photon detection efficiency are obtained with a statistical analysis of pulse-shape and time distributions. The method is tested with different detectors. The quench resistor, the breakdown voltage and the dark count rate are measured from IV characteristics.

physics.ins-det↗

arXiv2010

Physics with first LHCb data

The LHCb experiment is designed for hadronic flavour physics and will look for New Physics manifestations in the decay of charm and bottom hadrons abundantly produced at the LHC. All parts of the LHCb physics programme can be embarked on with the expected statistics to be collected during the first 2010-2011 physics run at $\sqrt{s}$ = 7 TeV. We present first preliminary results on strangeness production, and demonstrate, using the few nb-1 of already collected data, the potential for initial measurements in heavy-flavour physics.

hep-ex↗

arXiv2008

B0-B0bar mixing

The subject of particle-antiparticle mixing in the neutral B meson systems is reviewed. The formalism of B0-B0bar mixing is recalled and basic Standard Model predictions are given, before experimental issues are discussed and the latest combinations of experimental results on mixing parameters are presented, including those on mixing-induced CP violation, mass differences, and decay-width differences. Finally, time-integrated mixing results are used to improve our knowledge on the fractions of the various b-hadron species produced in Z decays and at high-energy colliders.

hep-ex↗

arXiv2006

B0-B0bar mixing

The subject of particle-antiparticle mixing in the neutral B meson systems is reviewed. The formalism of B0-B0bar mixing is recalled and basic Standard Model predictions are given, before experimental issues are discussed and the latest combinations of experimental results on mixing parameters are presented, including those on mixing-induced CP violation, mass differences, and decay-width differences. Finally, time-integrated mixing results are used to improve our knowledge on the fractions of the various b-hadron species produced in Z decays and at high-energy colliders.

hep-ex↗

arXiv2005

Sur la dimension de l'ensemble des points base du fibre determinant sur l'espace des modules des fibres vectoriels semi stables sur une courbe

Resume Soit SU_C(r) l'espace des modules des fibrés vectoriels semi-stables de déterminant trivial sur une courbe lisse $C$ de genre $g \geq 2$ sur $\mathbb{C}$. On étudie dans cet article, un exemple de fibré introduit par Raynaud dans ~\cite{R}, ne possédant pas de diviseur thêta. On construit ensuite des extensions stables de ce fibré ce qui conduit à une majoration de la codimension du lieu de base du fibré déterminant sur $\mathcal{SU}_{C}(r)$. Abstract Let $\mathcal{SU}_{C}(r)$ be the moduli space of semi stable bundles with trivial determinant on a smooth curve $C$ of genus $g\geq 2$ on $\mathbb{C}$. In this article, we are studiying a vector bundle introduced by Raynaud in ~\cite{R}, with no theta divisor. Then we build some stable extension of this bundle wich gives us an upper bound of the codimension of the base locus of the determinant bundle on $\mathcal{SU}_{C}(r)$.

math.AG↗

arXiv2004

B0-B0bar mixing

The subject of particle-antiparticle mixing in the neutral B meson systems is reviewed. The formalism of B0-B0bar mixing is recalled and basic Standard Model predictions are given, before experimental issues are discussed and the latest combinations of experimental results on mixing parameters are presented, including those on mixing-induced CP violation, mass differences, and decay-width differences. Finally, time-integrated mixing results are used to improve our knowledge on the fractions of the various b-hadron species produced at high-energy colliders.

hep-ex↗

arXiv2003

Stabilité des fibrés $Λ^{p}E_{L}$ et condition de Raynaud

Let $C$ be a smooth curve of genus $g \geq 2$ on $\C$. Let $L$ be a line bundle on $C$ generated by its global sections and let $E_{L}$ be the dual of the kernel of the evaluation map $e_{L}$. We are studying here the relation between the stability the fact that the bundle is verifying a condition $(R)$ introduced by Raynaud : we prove that $E_{L}$ is semi stable when $C$ is general. We also prove that $E_{L}$ is verifying $(R)$ when $°(L) \geq 2g$ or when $L$ is generic. Finally we prove that for each $p$ in $\{2,..., \mathrm{rg}(E_{L})-2\}$, if $°(L) \geq 2g+2$ then $Λ^{p}E_{L}$ is not verifying $(R)$.

math.AG↗

arXiv2003

Vanishing thetanulls and hyperelliptic curves

Let $\mathcal{M}_{g,2}$ be the moduli space of curves of genus $g$ with a level-2 structure. We prove here that there is always a non hyperelliptic element in the intersection of four thetanull divisors in $\mathcal{M}_{6,2}$. We prove also that for all $g\geqslant3$, each component of the hyperelliptic locus in $\mathcal{M}_{g,2}$ is a connected component of the intersection of $g-2$ thetanull divisors.

math.AG↗

arXiv2002

B0-B0bar mixing

The subject of particle-antiparticle mixing in the neutral B meson systems is reviewed. The formalism of B0-B0bar mixing and basic Standard Model predictions are given, before experimental issues are discussed and the latest combinations of experimental results on mixing parameters are presented, including those on mixing-induced CP violation, mass differences, and decay-width differences. Finally, time-integrated mixing results are used to improve our knowledge on the fractions of the various b-hadron species produced at high energy colliders.

hep-ph↗