The detectors of the SHiP experiment at CERN

SHiP is a proposed general purpose fixed target facility at the CERN SPS accelerator. The main focus will be the physics of the Hidden Sector, \textit{i.e.} search for heavy neutrinos, dark photons and other long lived very weakly interacting particles. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with exotic particles in the GeV mass range. Another dedicated detector will allow the study of Standard Model neutrino cross-sections and angular distribution, and allow detection of light dark matter with world leading sensitivity.Comment: 2 pages, 3 figures. Proceedings of the 14th Pisa meeting on Advanced Detector

Search for New Physics in SHiP and at future colliders

SHiP is a newly proposed fixed-target experiment at the CERN SPS with the aim of searching for hidden particles that interact very weakly with SM particles. The work presented in this document investigates SHiP's physics reach in the parameter space of the Neutrino Minimal Standard Model ($\nu$MSM), which is a theory that could solve most problems left open by the Standard Model with sterile neutrinos. A model introducing an extra $U(1)$ symmetry in the hidden sector, providing a natural candidate for dark matter, is also explored. This work shows that the SHiP experiment can improve by several orders of magnitude the sensitivity to Heavy Neutral Leptons below 2 GeV, scanning a large part of the parameter space below the $B$ meson mass. The remainder of the $\nu$MSM parameter space, dominated by right-handed neutrinos with masses above 2 GeV, can be explored at a future $e^+e^-$ collider. Similarly, SHiP can greatly improve present constraints on $U(1)$ dark photons.Comment: Proceedings for the INFIERI 2014 schoo

Luminosity at LHCb in Run 3

The LHCb detector optimised its performance in Runs~1 and~2 by stabilising the instantaneous luminosity during a fill. This was achieved by tuning the distance between the two colliding beams according to the measurement of instantaneous luminosity from hardware-based trigger counters. The upgraded LHCb detector operates at fivefold instantaneous luminosity compared to the previous runs, and it has a fully software-based trigger. Consequently, a new approach to the luminosity measurement is adopted. New counters, with particular attention to maximum stability in time, and a new dedicated detector have been introduced for Run~3. Additionally, in order to verify linearity from calibration to data taking conditions, per-fill emittance scans are performed. We present an overview of the newly implemented methods for luminosity measurement, as well as early achievements obtained during the first few weeks of data taking.Comment: Proceedings of the International Conference on High Energy Physics (ICHEP) 202

Testing lepton flavour universality in semileptonic Λb→Λc∗\Lambda_b \to \Lambda_c^* decays

Lepton Flavour Universality tests with semileptonic $\Lambda_b\to\Lambda_c^*$ decays are important to corroborate the present anomalies in the similar ratios $R_{D^{(*)}}$, and can provide complementary constraints on possible origins of these anomalies beyond the Standard Model. In this paper we provide - for the first time - all the necessary theoretical ingredients to perform and interpret measurements of $R_{\Lambda_c^*}$ at the LHCb experiment. For this, we revisit the heavy-quark expansion of the relevant hadronic matrix elements, and provide their expressions to order $\alpha_s$ and $1/m$ accuracy. Moreover, we study the sensitivity to the form factor parameters given the projected size and purity of upcoming and future LHCb datasets of $\Lambda_b\to \Lambda_c^*\mu\bar{\nu}$ decays. We demonstrate explicitly the need to perform a simultaneous fit to both $\Lambda_c^*$ final states. Finally, we provide projections for the uncertainty of $R_{\Lambda_c^*}$ based on the form factor analysis from semimuonic decays and theoretical relations based on the heavy-quark expansion.Comment: 27 pages, 6 figures. v2: Fixed error in subleading IW function, added supplementary information; conclusions unchange

A GPU-based real time trigger for rare kaon decays at NA62

Abstract This thesis reports a study for a new real-time trigger for the NA62 experiment based on Graphical Processing Units (GPUs). The NA62 experiment was devised to study with unprecedented precision the ultra-rare decay K+ → π+ ν anti-ν, a process mediated by Flavour-Changing Neutral Currents (FCNC) whose exceptional theoretical cleanliness provides a unique probe to test the Standard Model. The use of a high-rate kaon beam will result in an event rate of about 15 MHz, so high that it will be impossible to store data on disk without an efficient selection. The experiment therefore devised three trigger levels, allowing to reduce the data rate fed to the readout PC farm down to ∼10 kHz. For this thesis I developed an online trigger algorithm that uses data fed by the RICH (Ring Imaging CHerenkov counter) detector in real-time to allow a rejection of the dominant background K+ → π+ π 0 based on kinematical constraints. As a starting point for the development of this algorithm, I verified the feasibility of such a trigger through Montecarlo simulations. I measured the reconstruction resolution, achieved by the RICH detector alone, of the kinematical variables used for the event selection. After that, I analysed the background rejection power and the signal efficiency of several kinematical constraints, and I designed an actual trigger algorithm. The necessity of running the algorithm in real-time, with a maximum latency of 1 ms per event, drove the choice of exploiting the parallel computing power of GPUs. A parallelized algorithm was therefore developed, that can fit up to 4 Cherenkov rings per event. Moreover, a large number of events are processed concurrently. No parallelized and seedless multi-ring fitting algorithm existed before. The developed algorithm consists of a pattern recognition stage, to assign the hits to up to 4 ring candidates, and of a robust single-ring fit routine. The program was tested on GPUs, and its performance and execution latency proved to be compatible with the requirements. This work proves that alternative trigger designs are possible for the NA62 experiment, and represents a starting point for the introduction of flexible GPU-based real-time triggers in High Energy Physics. Sommario La mia tesi costituisce uno studio per un algoritmo di trigger in tempo reale basato su GPU (Graphical Processing Units) per l’esperimento NA62. NA62 è un esperimento progettato per misurare con precisione il decadimento ultra raro K+ → π+ ν anti-ν, un canale mediato da correnti neutre flavour-changing estremamente sensibile all’eventuale presenza di nuova fisica. L’elevato rate di eventi rivelati, dell’ordine di 15 MHz, non permetterà una archiviazione su disco dei dati non moderata da severi criteri di selezione. Sono perciò necessari dei livelli di trigger che consentano di ridurre il rate di eventi salvati fino a circa una decina di kHz. L’algoritmo sviluppato si basa sull’uso del rivelatore RICH (Ring Imaging CHerenkov counter). Le informazioni primitive inviate dal RICH vengono valutate in tempo reale, per produrre una decisione di trigger basata prevalentemente su considerazioni di cinematica. In una prima fase ho verificato, tramite simulazione Montecarlo, la fattibilità e significatività di tale progetto. Ho dapprima misurato la risoluzione sulla ricostruzione di alcune quantità cinematiche ricavate utilizzando unicamente il rivelatore RICH, poiché per un trigger di primo livello in tempo reale non sarà possibile mettere in relazione dati forniti da rivelatori diversi. Ho studiato poi fino a che livello fosse possibile separare il segnale dal fondo, misurando l’efficienza di reiezione e l’accettanza per il segnale al variare di alcuni parametri di selezione. Data la necessità di eseguire il programma in tempo reale, con una latenza massima di 1 ms per evento, si è deciso di sfruttare il potere computazionale parallelo proprio delle GPU (processori grafici ad elevato parallelismo). E’ stato quindi sviluppato un algoritmo in grado di eseguire simultaneamente non solo le istruzioni relative ad eventi diversi, ma anche i fit di fino a 4 anelli Cherenkov diversi appartenenti allo stesso evento. Nessun algoritmo parallelo e seedless di questo tipo esisteva in letteratura. L’algoritmo implementato è composto di due parti: una iniziale di riconoscimento di pattern, che estrae il numero di anelli presenti nella matrice ed identifica gli hit appartenenti a ciascuno di essi, ed una di fit dei singoli cerchi. Il programma è stato testato su GPU, ed efficienza e tempi di esecuzione risultano compatibili con le richieste. Questo lavoro apre la possibilità di implementare trigger alternativi e flessibili per NA62 e rappresenta un primo esempio prototipale dell’uso di GPU in tempo reale

Les droits disciplinaires des fonctions publiques : « unification », « harmonisation » ou « distanciation ». A propos de la loi du 26 avril 2016 relative à la déontologie et aux droits et obligations des fonctionnaires

The production of tt‾ , W+bb‾ and W+cc‾ is studied in the forward region of proton–proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98±0.02 fb−1 . The W bosons are reconstructed in the decays W→ℓν , where ℓ denotes muon or electron, while the b and c quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.The production of $t\overline{t}$, $W+b\overline{b}$ and $W+c\overline{c}$ is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 \mbox{fb}^{-1}. The $W$ bosons are reconstructed in the decays $W\rightarrow\ell\nu$, where $\ell$ denotes muon or electron, while the $b$ and $c$ quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions

Measurement of the B0s→μ+μ− Branching Fraction and Effective Lifetime and Search for B0→μ+μ− Decays

A search for the rare decays Bs0→μ+μ- and B0→μ+μ- is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4  fb-1. An excess of Bs0→μ+μ- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(Bs0→μ+μ-)=(3.0±0.6-0.2+0.3)×10-9, where the first uncertainty is statistical and the second systematic. The first measurement of the Bs0→μ+μ- effective lifetime, τ(Bs0→μ+μ-)=2.04±0.44±0.05  ps, is reported. No significant excess of B0→μ+μ- decays is found, and a 95% confidence level upper limit, B(B0→μ+μ-)<3.4×10-10, is determined. All results are in agreement with the standard model expectations.A search for the rare decays $B^0_s\to\mu^+\mu^-$ and $B^0\to\mu^+\mu^-$ is performed at the LHCb experiment using data collected in $pp$ collisions corresponding to a total integrated luminosity of 4.4 fb$^{-1}$. An excess of $B^0_s\to\mu^+\mu^-$ decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be ${\cal B}(B^0_s\to\mu^+\mu^-)=\left(3.0\pm 0.6^{+0.3}_{-0.2}\right)\times 10^{-9}$, where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s\to\mu^+\mu^-$ effective lifetime, $\tau(B^0_s\to\mu^+\mu^-)=2.04\pm 0.44\pm 0.05$ ps, is reported. No significant excess of $B^0\to\mu^+\mu^-$ decays is found and a 95 % confidence level upper limit, ${\cal B}(B^0\to\mu^+\mu^-)<3.4\times 10^{-10}$, is determined. All results are in agreement with the Standard Model expectations

Measurement of CP violation parameters and polarisation fractions in Bs0→J/ψK‾∗0 {\mathrm{B}}_{\mathrm{s}}^0\to \mathrm{J}/\psi {\overline{\mathrm{K}}}^{\ast 0} decays

The first measurement of ${C\!P}$ asymmetries in the decay ${B_s^0\to J/\psi \overline{K}^{*}(892)^{0}}$ and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of $3.0\,fb^{-1}$ of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of $7$ and $8\,\mathrm{TeV}$. Together with constraints from ${B^0\to J/\psi \rho^0}$, the results are used to constrain additional contributions due to penguin diagrams in the ${C\!P}$-violating phase ${{\phi}_{s}}$, measured through ${B_s^0}$ decays to charmonium.The first measurement of CP asymmetries in the decay ${B}_s^0\to J/\psi {\overline{\mathrm{K}}}^{\ast }{(892)}^0$ and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of 3.0 fb^{−}^{1} of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. Together with constraints from B$^{0}$ → J/ψ ρ$^{0}$, the results are used to constrain additional contributions due to penguin diagrams in the CP -violating phase ϕ$_{s}$ , measured through B$_{s}^{0}$ decays to charmonium.The first measurement of ${C\!P}$ asymmetries in the decay ${B_s^0\to J/\psi \overline{K}^{*}(892)^{0}}$ and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of $3.0\,fb^{-1}$ of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of $7$ and $8\,\mathrm{TeV}$. Together with constraints from ${B^0\to J/\psi \rho^0}$, the results are used to constrain additional contributions due to penguin diagrams in the ${C\!P}$-violating phase ${{\phi}_{s}}$, measured through ${B_s^0}$ decays to charmonium

Measurement of the J/ψ pair production cross-section in pp collisions at s=13 \sqrt{s}=13 TeV

The production cross-section of J/ψ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 279 ±11 pb$^{−1}$. The measurement is performed for J/ψ mesons with a transverse momentum of less than 10 GeV/c in the rapidity range 2.0 < y < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the J/ψ pair are measured and compared to theoretical predictions.The production cross-section of $J/\psi$ pairs is measured using a data sample of $pp$ collisions collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s} = 13 \,{\mathrm{TeV}}$, corresponding to an integrated luminosity of $279 \pm 11 \,{\mathrm{pb^{-1}}}$. The measurement is performed for $J/\psi$ mesons with a transverse momentum of less than $10 \,{\mathrm{GeV}}/c$ in the rapidity range $2.0<y<4.5$. The production cross-section is measured to be $15.2 \pm 1.0 \pm 0.9 \,{\mathrm{nb}}$. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the $J/\psi$ pair are measured and compared to theoretical predictions