741 research outputs found
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 (MSM), which is a
theory that could solve most problems left open by the Standard Model with
sterile neutrinos. A model introducing an extra 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 meson mass. The remainder of the MSM
parameter space, dominated by right-handed neutrinos with masses above 2 GeV,
can be explored at a future collider. Similarly, SHiP can greatly
improve present constraints on 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
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
Testing lepton flavour universality in semileptonic decays
Lepton Flavour Universality tests with semileptonic
decays are important to corroborate the present anomalies in the similar ratios
, 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 at the LHCb experiment. For this, we revisit
the heavy-quark expansion of the relevant hadronic matrix elements, and provide
their expressions to order and accuracy. Moreover, we study
the sensitivity to the form factor parameters given the projected size and
purity of upcoming and future LHCb datasets of decays. We demonstrate explicitly the need to perform
a simultaneous fit to both final states. Finally, we provide
projections for the uncertainty of 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
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 , and 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 \mbox{fb}^{-1}. The bosons are reconstructed in the decays , where denotes muon or electron, while the and quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions
Multidifferential study of identified charged hadron distributions in -tagged jets in proton-proton collisions at 13 TeV
Jet fragmentation functions are measured for the first time in proton-proton
collisions for charged pions, kaons, and protons within jets recoiling against
a boson. The charged-hadron distributions are studied longitudinally and
transversely to the jet direction for jets with transverse momentum 20 GeV and in the pseudorapidity range . The
data sample was collected with the LHCb experiment at a center-of-mass energy
of 13 TeV, corresponding to an integrated luminosity of 1.64 fb. Triple
differential distributions as a function of the hadron longitudinal momentum
fraction, hadron transverse momentum, and jet transverse momentum are also
measured for the first time. This helps constrain transverse-momentum-dependent
fragmentation functions. Differences in the shapes and magnitudes of the
measured distributions for the different hadron species provide insights into
the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb
public pages
Study of the decay
The decay is studied
in proton-proton collisions at a center-of-mass energy of TeV
using data corresponding to an integrated luminosity of 5
collected by the LHCb experiment. In the system, the
state observed at the BaBar and Belle experiments is
resolved into two narrower states, and ,
whose masses and widths are measured to be where the first uncertainties are statistical and the second
systematic. The results are consistent with a previous LHCb measurement using a
prompt sample. Evidence of a new
state is found with a local significance of , whose mass and width
are measured to be and , respectively. In addition, evidence of a new decay mode
is found with a significance of
. The relative branching fraction of with respect to the
decay is measured to be , where the first
uncertainty is statistical, the second systematic and the third originates from
the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb
public pages
Measurement of the ratios of branching fractions and
The ratios of branching fractions
and are measured, assuming isospin symmetry, using a
sample of proton-proton collision data corresponding to 3.0 fb of
integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The
tau lepton is identified in the decay mode
. The measured values are
and
, where the first uncertainty is
statistical and the second is systematic. The correlation between these
measurements is . Results are consistent with the current average
of these quantities and are at a combined 1.9 standard deviations from the
predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb
public pages
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