A search is presented for an extended Higgs sector with two new particles, X and $\phi$, in the process X $\to$ $\phi\phi$ $\to$ $(\gamma\gamma)(\gamma\gamma)$. Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb$^{-1}$. No evidence of such resonances is seen. Upper limits are set on the production cross section versus the resonance masses, representing the most sensitive search in this channel.

Liquid argon is an excellent medium for detecting particles, given its yields and transport properties of light and charge. The technology of liquid argon time projection chambers has reached its full maturity after four decades of continuous developments and is, or will be, used in world class experiments for neutrino and dark matter searches. The collection of ionization charge in these detectors allows to perform a complete tridimensional reconstruction of the tracks of charged particles, calorimetric measurements, particle identification. This work proposes a novel approach to the problem of charge recombination in liquid argon which moves from a microscopic model and is applied to the cases of low energy electrons, alpha particles and nuclear recoils. The model is able to describe precisely several sets of experimental data available in the literature, over wide ranges of electric field strengths and kinetic energies and can be easily extended to other particles.

We report a methodology to determine the quality factor ($Q$) in implementations of the so-called dielectric haloscope, a new concept of wavy dark matter detector equipped with a multilayered resonator. An anechoic chamber enables the observation of the resonance frequency and its amplitude for an unlimited series of layers for the first time, which is conveniently filtered. The frequency-normalized power enhancement measured in a Dark-photons \& Axion-Like particles Interferometer (DALI) prototype is a few hundred per layer over a sweep bandwidth of half a hundred MHz. In light of this result, this scaled-down prototype is sensitive to axions saturating the local dark matter density with a coupling to photons between $g_{a\gamma\gamma}\gtrsim10^{-12}$ GeV$^{-1}$ and $g_{a\gamma\gamma}\gtrsim$ few $\times 10^{-14}$ GeV$^{-1}$ at frequencies of several dozens of GHz once cooled down to the different working temperatures of the experiment and immersed in magnetic fields ranging from 1 T to 10 T; while the sensitivity of the full-scale DALI is projected at $g_{a\gamma\gamma}\gtrsim\mathrm{few}\times10^{-15}$ GeV$^{-1}$ over the entire 25--250 {\mu}eV range since $Q\gtrsim10^4$ is expected.

In the recent decades of high-energy physics research, it was demonstrated that strongly interacting quark-gluon plasma (sQGP) is created in ultra-relativistic nucleus-nucleus collisions. Investigation and understanding of the properties of the hadronic matter are among the most important goals of the NA61/SHINE collaboration at CERN SPS. Mapping of the phase diagram is achieved by varying the collision energy (5 GeV $\sqrt{s_{NN}}<17$ GeV) and by changing the collision system ($p$+$p$, $p$+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb). Femtoscopic correlations reveal the space-time structure of the hadron emitting source. In this article, we report on the measurement of femtoscopic correlations in small to intermediate systems. Comparing the measurements to calculations based on symmetric L\'evy sources, we discuss the results on L\'evy source parameters as a function of average pair transverse mass. One of the physical parameters is of particular importance, the L\'evy exponent $\alpha$, which describes the shape of the source and may be related to the critical exponent $\eta$ in the proximity of the critical point. Therefore, measuring it may shed light on the location of the critical endpoint of the QCD phase diagram.

We study the production of $X(3872)$ mesons in photon-induced nuclear reactions near the threshold within the collision model based on the nuclear spectral function. The model accounts for direct photon-nucleon $X(3872)$ production processes as well as five different scenarios for their internal structure. We calculate the absolute and relative excitation functions for $X(3872)$ production off $^{12}$C and $^{184}$W target nuclei at near-threshold incident photon energies of 8--16 GeV, the absolute differential cross sections for their production off these target nuclei at laboratory angles of 0$^{\circ}$--10$^{\circ}$ and for incident photon energy of 13 GeV as well as the A dependences of the relative (transparency ratios) cross sections for $X(3872)$ production from ${\gamma}A$ collisions at photon energies around 13 GeV within the adopted scenarios for the $X(3872)$ meson internal structure. We show that the absolute and relative observables considered reveal distinct sensitivity to these scenarios. Therefore, the measurement of such observables in a dedicated experiment at the CEBAF facility in the near-threshold energy range will allow us to get valuable information on the $X(3872)$ inner structure.

Liquid argon detectors are ubiquitous in particle, astroparticle, and applied physics. They reached an unprecedented level of maturity thanks to more than 20 years of R&D and the operation of large-scale facilities at CERN, Fermilab, and the Gran Sasso laboratories. This article reviews such an impressive advance - from the grounding of the experimental technique up to cutting-edge applications. We commence the review by describing the physical and chemical properties of liquid argon as an active and target medium for particle detection, together with advantages and limitations compared with other liquefied noble gases. We examine the opportunities and challenges of liquid argon detectors operated as calorimeters, scintillators, and time projection chambers. We then delve into the core applications of liquid argon detectors at colliders (ATLAS), accelerator neutrino beams (SBN, DUNE), and underground laboratories (DarkSide, DEAP, ICARUS) for the observation of rare events. We complete the review by looking at unconventional developments (pixelization, combined light-charge readout, Xe-doped devices, all-optical readout) and applications in medical and applied physics to extend this technology's scope toward novel research fields.

Based on the expectations that the lowest-lying double-bottom tetraquark $T_{bb\bar u \bar d}$ ($J^P=1^+$) and the bottom-charm tetraquark $T_{bc\bar u \bar d}$ ($J^P=0^+$) are stable against strong and electromagnetic decays, we work out a number of semileptonic and non-leptonic weak decays of these hadrons, making use of the heavy quark symmetry. In doing this, we concentrate on the exclusive decays involving also tetraquarks in the final states, i.e., transitions such as $T_{bb\bar u \bar d} \to T_{bc\bar u \bar d} (\ell^- \nu_\ell, h^-)$ and $T_{bc\bar u \bar d} \to T_{cc\bar u \bar d} (\ell^- \nu_\ell, h^-)$, where $h^-=\pi^-,\rho^-,a_1^-$. So far, only the $J^P=1^+$ tetraquark $T_{cc\bar u \bar d}$ has been discovered, which we identify with the $I=0$ $T_{cc}^{+}$ object, compatible with $J^P=1^+$ and having the mass and decay widths $\delta m =M(T_{cc}^+) -(M(D^{*+}) - M(D^0))= -360 \pm 40 ^{+4}_{-0}$ keV and $\Gamma(T_{cc}^+)=48^{+2}_{-14}$ keV. Experimental discoveries of the transitions worked out here will go a long way in establishing the nature of these tetraquarks as (mainly) compact four-quark objects.

This paper presents a novel method for low maintenance, low ambiguity in-situ drift velocity monitoring in large volume Time Projection Chambers (TPCs). The method was developed and deployed for the 40m^3 TPC tracker system of the NA61/SHINE experiment at CERN, which has a one meter of drift length. The method relies on a low-cost multi-wire proportional chamber (MWPC) placed downstream of the TPCs to be monitored. The drift velocity is then determined by matching the reconstructed tracks in the TPC to the hits of the pertinent monitoring chamber, called Geometry Reference Chamber (GRC), which is then used as a differential length scale. An important design requirement on the GRC was minimal added complexity to the existing system, in particular, compatibility with Front-End Electronics (FEE) cards already used to read out the TPCs. Moreover, the GRC system was designed to operate both in large and small particle flux. The system is capable of monitoring the evolution of the in-situ drift velocity down to a one permil precision, with a few minutes of time sampling.

We propose to measure the weak decay constant $\alpha_-$ for the decay $\Lambda\rightarrow p\pi^-$ using a both circularly and linearly polarized photon beam with the GlueX spectrometer in Hall D. The measurement will take advantage of the fact that a measurement with both linear and circular photon beam polarization results in an over-constrained set of amplitudes which can be fitted to data and used to extract $\alpha_-$ which will be left as a free parameter in the fit. We expect to determine $\alpha_-$ with statistical uncertainties comparable to existing measurements and independent systematic uncertainties. This measurement can be performed alongside GlueX-II running and requires no new hardware or new beam time. The measurement requires that a sufficient fraction of the electron beam polarization be longitudinal in the Hall D tagger.

The reconstruction of photon conversions is importantin order to improve the reconstruction efficiency of the physics measurements involving photons. However, there are significant number of conversions in which only one of the two tracks emitted electrons is reconstructed in the detector due to very asymmetric energy sharing between the electron-positron pair. The momentum determination of the parent photon can be improved by estimating the missing energy in such conversions. In this study, we propose a simple statistical method that can be used to determine the mean value of the missing energy. By using simulated minimum bias events at LHC conditions and a toy detector simulation, the performance of the method is tested for several decay channels commonly used in particle physics analyses. A considerable improvement in the mass reconstruction precision is obtained when reconstructing particles decaying to photons whose energies are less than 20 GeV.