A
bstract
SHiP is a proposed high-intensity beam dump experiment set to operate at the CERN SPS. It is expected to have an unprecedented sensitivity to a variety of models containing feebly ...interacting particles, such as Heavy Neutral Leptons (HNLs). Two HNLs or more could successfully explain the observed neutrino masses through the seesaw mechanism. If, in addition, they are quasi-degenerate, they could be responsible for the baryon asymmetry of the Universe. Depending on their mass splitting, HNLs can have very different phenomenologies: they can behave as Majorana fermions — with lepton number violating (LNV) signatures, such as same-sign dilepton decays — or as Dirac fermions with only lepton number conserving (LNC) signatures. In this work, we quantitatively demonstrate that LNV processes can be distinguished from LNC ones at SHiP, using only the angular distribution of the HNL decay products. Accounting for spin correlations in the simulation and using boosted decision trees for discrimination, we show that SHiP will be able to distinguish Majorana-like and Dirac-like HNLs in a significant fraction of the currently unconstrained parameter space. If the mass splitting is of order 10
−
6
eV, SHiP could even be capable of resolving HNL oscillations, thus providing a direct measurement of the mass splitting. This analysis highlights the potential of SHiP to not only search for feebly interacting particles, but also perform model selection.
A
bstract
Heavy neutral leptons (HNLs) are hypothetical particles, motivated in the first place by their ability to explain neutrino oscillations. Experimental searches for HNLs are typically ...conducted under the assumption of a single HNL mixing with a single neutrino flavor. However, the resulting exclusion limits may not directly constrain the corresponding mixing angles in
realistic HNL models
— those which can explain neutrino oscillations. The reinterpretation of the results of these experimental searches turns out to be a non-trivial task, that requires significant knowledge of the details of the experiment. In this work, we perform a reinterpretation of the latest ATLAS search for HNLs decaying promptly to a tri-lepton final state. We show that in a realistic model with two HNLs, the actual limits can vary by several orders of magnitude depending on the free parameters of the model. Marginalizing over the unknown model parameters leads to an exclusion limit on the total mixing angle which can be up to 3 orders of magnitude weaker than the limits reported in ref. 1. This demonstrates that the reinterpretation of results from experimental searches is a
necessary
step to obtain meaningful limits on realistic models. We detail a few steps that can be taken by experimental collaborations in order to simplify the reuse of their results.
Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning ...of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV-scale, or even radically below, down to sub-eV scales, and with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data provide numerous hints for such possibility. A vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
4.
Feebly-interacting particles Carenza, Pierluca; Milstead, David A.; Wallisch, Benjamin
The European physical journal. C, Particles and fields,
12/2023, Letnik:
83, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Particle physics today faces the challenge of explaining the mystery of dark matter, the origin of matter over anti-matter in the Universe, the origin of the neutrino masses, the apparent fine-tuning ...of the electro-weak scale, and many other aspects of fundamental physics. Perhaps the most striking frontier to emerge in the search for answers involves new physics at mass scales comparable to familiar matter, below the GeV-scale, or even radically below, down to sub-eV scales, and with very feeble interaction strength. New theoretical ideas to address dark matter and other fundamental questions predict such feebly interacting particles (FIPs) at these scales, and indeed, existing data provide numerous hints for such possibility. A vibrant experimental program to discover such physics is under way, guided by a systematic theoretical approach firmly grounded on the underlying principles of the Standard Model. This document represents the report of the FIPs 2022 workshop, held at CERN between the 17 and 21 October 2022 and aims to give an overview of these efforts, their motivations, and the decadal goals that animate the community involved in the search for FIPs.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Search for Hidden Particles (SHiP) Collaboration has shown that the CERN SPS accelerator with its 400 GeV/c proton beam offers a unique opportunity to explore the Hidden Sector 1–3. The proposed ...experiment is an intensity frontier experiment which is capable of searching for hidden particles through both visible decays and through scattering signatures from recoil of electrons or nuclei. The high-intensity experimental facility developed by the SHiP Collaboration is based on a number of key features and developments which provide the possibility of probing a large part of the parameter space for a wide range of models with light long-lived super-weakly interacting particles with masses up to (10) GeV/c2 in an environment of extremely clean background conditions. This paper describes the proposal for the experimental facility together with the most important feasibility studies. The paper focuses on the challenging new ideas behind the beam extraction and beam delivery, the proton beam dump, and the suppression of beam-induced background.
This paper presents a fast approach to simulating muons produced in interactions of the SPS proton beams with the target of the SHiP experiment. The SHiP experiment will be able to search for new ...long-lived particles produced in a 400 GeV/c SPS proton beam dump and which travel distances between fifty metres and tens of kilometers. The SHiP detector needs to operate under ultra-low background conditions and requires large simulated samples of muon induced background processes. Through the use of Generative Adversarial Networks it is possible to emulate the simulation of the interaction of 400 GeV/c proton beams with the SHiP target, an otherwise computationally intensive process. For the simulation requirements of the SHiP experiment, generative networks are capable of approximating the full simulation of the dense fixed target, offering a speed increase by a factor of (106). To evaluate the performance of such an approach, comparisons of the distributions of reconstructed muon momenta in SHiP's spectrometer between samples using the full simulation and samples produced through generative models are presented. The methods discussed in this paper can be generalised and applied to modelling any non-discrete multi-dimensional distribution.
While the standard regimen of the BNT162b2 mRNA vaccine for SARS-CoV-2 includes two doses administered 3 weeks apart, some public health authorities are spacing these doses, raising concerns about ...efficacy. However, data indicate that a single dose can be up to 90% effective starting 14 days post-administration. To assess the mechanisms contributing to protection, we analyzed humoral and T cell responses three weeks after a single BNT162b2 dose. We observed weak neutralizing activity elicited in SARS-CoV-2 naive individuals but strong anti-receptor binding domain and spike antibodies with Fc-mediated effector functions and cellular CD4+ T cell responses. In previously infected individuals, a single dose boosted all humoral and T cell responses, with strong correlations between T helper and antibody immunity. Our results highlight the potential role of Fc-mediated effector functions and T cell responses in vaccine efficacy. They also provide support for spacing doses to vaccinate more individuals in conditions of vaccine scarcity.
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•Three weeks after the first BNT162b2 dose, weak neutralizing antibodies are elicited•These antibodies have robust Fc-mediated effector functions•Vaccination of individuals previously infected boosts humoral and cellular responses•Strong correlations between T helper cell and humoral responses are observed
Tauzin and Nayrac et al. characterize humoral and cellular responses 3 weeks after a single dose of mRNA BNT162b2 vaccine. They show, in SARS-CoV-2-naive individuals, that the antibodies elicited have weak neutralizing activity but potent Fc-mediated effector functions, and in SARS-CoV-2 previously infected individuals, that all responses are significantly boosted.
Abstract SND@LHC is a compact and stand-alone experiment designed to perform measurements with neutrinos produced at the LHC in the pseudo-rapidity region of 7.2 < η < 8.4. The experiment is located ...480 m downstream of the ATLAS interaction point, in the TI18 tunnel. The detector is composed of a hybrid system based on an 830 kg target made of tungsten plates, interleaved with emulsion and electronic trackers, also acting as an electromagnetic calorimeter, and followed by a hadronic calorimeter and a muon identification system. The detector is able to distinguish interactions of all three neutrino flavours, which allows probing the physics of heavy flavour production at the LHC in the very forward region. This region is of particular interest for future circular colliders and for very high energy astrophysical neutrino experiments. The detector is also able to search for the scattering of Feebly Interacting Particles. In its first phase, the detector is ready to operate throughout LHC Run 3 and collect a total of 250 fb -1 .
Abstract
In July 2018 an optimization run for the proposed charm
cross section measurement for SHiP was performed at the CERN SPS. A
heavy, moving target instrumented with nuclear emulsion films
...followed by a silicon pixel tracker was installed in front of the
Goliath magnet at the H4 proton beam-line. Behind the magnet,
scintillating-fibre, drift-tube and RPC detectors were placed. The
purpose of this run was to validate the measurement's feasibility,
to develop the required analysis tools and fine-tune the detector
layout. In this paper, we present the track reconstruction in the
pixel tracker and the track matching with the moving emulsion
detector. The pixel detector performed as expected and it is shown
that, after proper alignment, a vertex matching rate of 87% is
achieved.
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