This paper is an experimental review of the study of processes with a single top quark at the LHC. The pioneering times are over, and this is now a sector of “precision physics” at colliders. Angular ...distributions of the decay products of singly-produced top quarks are unique tests of the electroweak interaction. Searches for rare final states of the form t+X (where X=γ,Z,H) are very sensitive to new physics, and will enter with Run II in a very interesting zone of the parameter space of some theories. The relative sign of the Yukawa coupling of the top quark with respect to the Higgs coupling to gauge bosons will be conclusively measured very soon in the tHq final state.
Atmospheric muons as an imaging tool Bonechi, Lorenzo; D’Alessandro, Raffaello; Giammanco, Andrea
Reviews in physics,
November 2020, 2020-11-00, 2020-11-01, Volume:
5
Journal Article
Peer reviewed
Open access
Imaging methods based on the absorption or scattering of atmospheric muons, collectively named under the neologism “muography”, exploit the abundant natural flux of muons produced from cosmic-ray ...interactions in the atmosphere. Recent years have seen a steep rise in the development of muography methods in a variety of innovative multidisciplinary approaches to study the interior of natural or human-made structures, establishing synergies between usually disconnected academic disciplines such as particle physics, geology, and archaeology. Muography also bears promise of immediate societal impact through geotechnical investigations, nuclear waste surveys, homeland security, and natural hazard monitoring. Our aim is to provide an introduction to this vibrant research area, starting from the physical principles at the basis of the methods and describing the main detector technologies and imaging tools, including their combination with conventional techniques from other disciplines, where appropriate. Then, we discuss critically some outstanding issues that affect a broad variety of applications, and the current state of the art in addressing them. Finally, we review several recent developments in the application of muography methods to specific use cases, without any pretence of exhaustiveness.
We show that heavy-ion collisions at the LHC provide a promising environment to search for signatures with displaced vertices in well-motivated new physics scenarios. Compared to proton collisions, ...they offer several advantages: (i) the number of parton level interactions per collision is larger, (ii) there is no pileup, (iii) the lower instantaneous luminosity compared to proton collisions allows one to operate the LHC experiments with very loose triggers, and (iv) there are new production mechanisms that are absent in proton collisions We focus on the third point and show that the modification of the triggers alone can increase the number of observable events by orders of magnitude if the long-lived particles are predominantly produced with low transverse momentum. Our results show that collisions of ions lighter than lead are well motivated from the viewpoint of searches for new physics. We illustrate this for the example of heavy neutrinos in the Neutrino Minimal Standard Model.
A
bstract
Motivated by the expectation that new physics may manifest itself in the form of very heavy new particles, most of the operation time of the Large Hadron Collider (LHC) is devoted to ...proton-proton (
pp
) collisions at the highest achievable energies and collision rates. The large collision rates imply tight trigger requirements that include high thresholds on the final-state particles’ transverse momenta
p
T
and an intrinsic background in the form of particle pileup produced by different collisions occurring during the same bunch crossing. This strategy is potentially sub-optimal for several well-motivated new physics models where new particles are not particularly heavy and can escape the online selection criteria of the multi-purpose LHC experiments due to their light mass and small coupling.
A solution may be offered by complementary datasets that are routinely collected by the LHC experiments. These include heavy ion collisions, low-pileup runs for precision physics, and the so-called “parking” and “scouting” datasets. While some of them are motivated by other physics goals, they all have the usage of mild
p
T
thresholds at the trigger-level in common. In this study, we assess the relative merits of these datasets for a representative model whose particular clean signature features long-lived resonances yielding displaced dimuon vertices. We compare the reach across those datasets for a simple analysis, simulating LHC data in Run 2 and Run 3 conditions with the Delphes simulation. We show that the scouting and parking datasets, which afford low-
p
T
trigger thresholds by only using partial detector information and delaying the event reconstruction, respectively, have a reach comparable to the standard
pp
dataset with conventional thresholds. We also show that heavy ion and low-pileup datasets are far less competitive for this signature.
We show that heavy-ion collisions at the LHC provide a promising environment to search for new long-lived particles in well-motivated new physics scenarios. One advantage lies in the possibility to ...operate the main detectors with looser triggers, which can increase the number of observable events by orders of magnitude if the long-lived particles are produced with low transverse momentum. In addition, the absence of pileup in heavy-ion collisions can avoid systematic nuisances that will be present in future proton runs, such as the problem of vertex misidentification. Finally, there are new production mechanisms that are absent or inefficient in proton collisions. We show that the looser triggers alone can make searches in heavy-ion data competitive with proton data for the specific example of heavy neutrinos in the neutrino minimal standard model, produced in the decay of B mesons. Our results suggest that collisions of ions lighter than lead, which are currently under discussion in the heavy-ion community, are well motivated from the viewpoint of searches for new physics.
Single top quark production cross sections at hadron colliders are traditionally used to extract the modulus of the Vtb element of the Cabibbo-Kobayashi-Maskawa matrix under the following assumption: ...|Vtb| ≫ |Vtd|, |Vts|. For the first time, direct limits on |Vtd| and |Vts| are obtained using experimental data without the assumption of the unitarity of the CKM matrix. Limits on the |Vtd|, |Vts| and |Vtb| are extracted from differential measurements of single top quark cross sections in t-channel as a function of the rapidity and transverse momentum of the top quark and the light jet recoiling against the top quark. We have shown that the pseudorapidity of the forward jet in the single top production is one of the most powerful observables for discriminating between the |Vtd| and |Vtb| events. We perform a global fit of top quark related CKM elements to experimental data from the LHC Runs I and II and Tevatron. Experimental data include inclusive and differential single top cross sections in t-channel, inclusive tW production cross section, and top quark branching ratio to b quark and W boson. We present bounds on |Vtb|, |Vts| and |Vtd| using current data and project the results for future LHC data sets corresponding to luminosities of 300 and 3000 fb−1.
A portable muon telescope based on small and gas-tight resistive plate chambers Wuyckens, Sophie; Giammanco, Andrea; Cortina Gil, Eduardo ...
Philosophical transactions - Royal Society. Mathematical, Physical and engineering sciences/Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences,
12/2018, Volume:
377, Issue:
2137
Journal Article
Peer reviewed
Open access
We report on the first steps in the development of a small-size muon telescope based on glass resistive plate chambers with small active area (16 × 16 cm
). The long-term goal of this project is to ...focus on applications of muography where the telescope may have to be operated underground and/or inside small rooms, and in challenging logistic situations. Driving principles in our design are therefore compact size, light weight, gas tightness and robustness. The first data-taking experiences have been encouraging, and we elaborate on the lessons learnt and future directions for development.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.
The simulation of muon tomography requires a multi-directional particle source that traverses a number of horizontal detectors of limited angular acceptance that are used to track cosmic-ray muons. ...In this study, we describe a simple strategy that can use GEANT4 simulations to produce a hemispherical particle source. We initially generate random points on a spherical surface of practical radius by using a Gaussian distribution for the three components of the Cartesian coordinates, thereby obtaining a generating surface for the initial position of the particles to be tracked. Since we do not require the bottom half of the sphere, we take the absolute value of the vertical coordinate, resulting in a hemisphere. Next, we direct the generated particles into the target body by selectively favoring the momentum direction along the vector constructed between a random point on the hemispherical surface and the origin of the target, thereby minimizing particle loss through source biasing. We also discuss a second scheme where the coordinate transformation is performed between the spherical and Cartesian coordinates, and the above-source biasing procedure is applied to orient the generated muons towards the target. Finally, a recipe based on restrictive planes from our previous study is discussed. We implement our strategies by using G4ParticleGun in the GEANT4 code. While we apply these techniques to simulations for muon tomography via scattering, these source schemes can be applied to similar studies for atmospheric sciences, space engineering, and astrophysics where a 3D particle source is a necessity.
The performance of cosmic-ray tomography systems is largely determined by their tracking accuracy. With conventional scintillation detector technology, good precision can be achieved with a small ...pitch between the elements of the detector array. Improving the resolution implies increasing the number of read-out channels, which in turn increases the complexity and cost of the tracking detectors. As an alternative to that, a scintillation plate detector coupled with multiple silicon photomultipliers could be used as a technically simple solution. In this paper, we present a comparison between two deep-learning-based methods and a conventional Center of Gravity (CoG) algorithm, used to calculate cosmic-ray muon hit positions on the plate detector using the signals from the photomultipliers. In this study, we generated a dataset of muon hits on a detector plate using the Monte Carlo simulation toolkit GEANT4. We demonstrate that two deep-learning-based methods outperform the conventional CoG algorithm by a significant margin. Our proposed algorithm, Fully Connected Network, produces a 0.72 mm average error measured in Euclidean distance between the actual and predicted hit coordinates, showing great improvement in comparison with CoG, which yields 1.41 mm on the same dataset. Additionally, we investigated the effects of different sensor configurations on performance.
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