32,874 research outputs found

    Testing pALPIDE sensors for particle detection and Characterization of a Laser beam using a webcam CMOS sensor

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    The upgrade program of the Large Hadron Collider (LHC) was implemented during the second Long Shutdown program (2019/2020). For this program, the ALICE Collaboration (A Large Ion Collider Experiment) proposed, among others, a new detector called Muon Forward Tracker (MFT). The primary goal of the MFT detector, installed on December 2021 and located between the Inner Tracker System (ITS) and the Muon Spectrometer, is to improve the capability of vertex reconstruction. The MFT is equipped with the same pixel sensors used for the ITS upgrade. These sensors are the ALICE Pixel Detectors (ALPIDE), a kind of monolithic active pixel sensor. The MFT is composed of five arrays of pixel sensors which are configured as parallel discs covering −3.6 < η < −2.45. Some prototypes were designed in order to achieve the final version of the ALPIDE, such as the pALPIDE family, which was divided into three versions (i.e., pALPIDE-1,2,3). The ALICE upgrade also included a new system for the data taking and simulation called Online-offline (O2) to replace AliRoot. We designed the geometry of two non-active parts of the MFT and included them in the O2 system. The first goal of this thesis is focused on the characterization of the pALPIDE-2. This sensor is segmented into four groups corresponding to four types of pixels. This characterization includes the test of analogue and digital. According to these tests, we identified a group of pixels that do not work correctly. The threshold scan tests showed the threshold level in each pixel is influenced by the input capacitance according to its n-well size and the surrounding area. Also, we studied the response of the pALPIDE-2 when it was exposed to a soft x-ray source, varying the distance between them. This test showed that the hit count changed according to the inverse square of the distance. iv The second goal of this thesis was to implement a low-cost tool based on a CMOS sensor to characterize laser beams. This tool comprises a Raspberry, a Pi Camera with a pitch size of 1.4 µm, and an optical system. To test the accuracy of the results of this tool, we made similar measurements with other sensors. A photodiode and a light-dependent resistor performed these measurements, which showed the spot radius size compatibility. However, the CMOS sensor expressed the highest precision and is a more affordable tool than commercial devices

    One-Loop Analytic Results for the Higgs Boson Plus Four Partons and Searches for Supersymmetry

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    In this thesis we present compact analytic expressions for the production of the Higgs boson plus two jets at one-loop mediated by both a scalar and a fermion. The results are derived using generalised unitarity methods and retain the full mass dependence of the mediating particle. We use the relationship between the fermion and scalar theories to simplify the algebra in the fermion theory; many of the required integral coefficients are identical and for those that differ, the difference is of a lower rank than the scalar result. We use these calculations to study the production of the Higgs boson plus two jets in the Minimal Supersymmetric Standard Model, assuming stop squarks are the dominant mediator. This is a potential channel for an indirect search for stop squarks, in particular we focus on the region where the lightest stop squark mass is similar to that of the top quark. However, although the 1-jet process shows improved discrimination over the inclusive process, we find there is no benefit gained from the 2-jet process

    Lepton Flavor Specific Extended Higgs Model

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    In extended Higgs models, a discrete symmetry is needed in the quark sector to avoid tree-level flavor-changing neutral currents. However, this is not necessary the case in the lepton sector. We consider a model in which one Higgs couples to quarks and three others couple to the electron, muon and tau, respectively. This four-doublet model is presented with the full scalar potential and the gauge and Yukawa couplings. The constraints from boundedness, perturbativity and oblique parameters are incorporated as well as constraints from meson-antimeson mixing, radiative B-decays and the diphoton Higgs decay rate. We also consider bounds from searches for heavy neutral and charged scalars at the LHC. Since the Standard Model Higgs couplings match predictions very well, we focus on the alignment limit of the model. It is shown that for a wide range of parameters, the lightest additional scalar, pseudoscalar and charged scalar can have substantial decays into electrons and muons (in contrast to the usual leptonic decays into taus). An interesting signature in the neutral sector would be the production, through vector boson fusion, of a pair of scalars, each of which decays into an electron or muon pair.Comment: 35 pages, 3 figures, 6 table

    Effects of the Axion Through the Higgs Portal on Primordial Gravitational Waves During the Electroweak Breaking

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    We investigate the effects of short axion kination eras on the energy spectrum of the primordial gravitational waves corresponding to modes that re-enter the Hubble horizon at the post-electroweak symmetry breaking epoch, well within the radiation domination era. Our main assumption is the existence of an extremely weakly coupled hidden sector between the Higgs and the axion, materialized by higher order non-renormalizable dimension six and dimension eight operators, active at a scale M of the order 20-100TeV. This new physics scale M which is way higher than the electroweak scale, is motivated by the lack of new particle observations in the large hadron collider to date, beyond the electroweak scale. Once the electroweak symmetry breaking occurs at T\sim 100 GeV, the axion potential acquires a new minimum due to the new terms generated by the electroweak breaking, and the axion oscillations at the origin are destabilized. In effect after some considerable amount of time, the axion rolls swiftly to its new minimum, experiencing a short kination epoch, where its energy density redshifts as ρaa6\rho_a\sim a^{-6}. After it reaches the new minimum, since the latter is energetically less favorable that the Higgs minimum, it decays to the Higgs minimum and the Universe is described again by the Higgs minimum. The axion returns to the origin and commences again oscillations initiated by quantum fluctuations, redshifts as dark matter, and the same procedure is repeated perpetually. These short axion kination eras may disturb the background total equation of state parameter during the radiation domination era. As we show, the energy spectrum of the gravitational waves mainly depends on how many times the short axion kination epochs occur.Comment: PRD Accepted, Abstract reduced due to arXiv limitation

    NaNu: Proposal for a Neutrino Experiment at the SPS Collider located at the North Area of CERN

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    Several experiments have been proposed in the recent years to study the nature of tau neutrinos, in particular aiming for a first observation of tau anti-neutrinos, more stringent upper limit on its anomalous magnetic moment as well as new constrains on the strange-quark content of the nucleon. We propose here a new low-cost neutrino experiment at the CERN North area, named NaNu (North Area NeUtrino), compatible with the realization of the future SHADOWS and HIKE experiments at the same experimental area.Comment: 7 pages, 6 figure

    Constraining SMEFT BSM scenarios with EWPO and ΔCKM\Delta_{CKM}

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    Precision observables are well known for constraining most of the Beyond Standard Model (BSM) scenarios tightly. We present here a simple and comprehensive fitting framework for various BSM scenarios to these observables. We start with the fit of SS, TT and VV parameter and their correlations using the Electroweak Precision Observables (EWPO) including the recent mWm_W measurement from CDF-II. Utilizing these observables, we also fit various New Physics (NP) scenarios consisting of different subsets of dimension-6 Standard Model Effective Field Theory (SMEFT) operators out of a total of 10 appearing at tree level in EWPO. To further constrain these scenarios, we augment these observables with ΔCKM\Delta_{CKM} measurement using 1-loop matching of the Low Energy Effective Field Theory (LEFT) to SMEFT operators at the Z-pole. We show that the inclusion of ΔCKM\Delta_{CKM} constraint indeed results in stronger bounds on the SMEFT Wilson Coefficients. We also constrain the UV parameters of BSM extensions like Vectorlike leptons (VLL) and find out that such a minimal extension is in tension with the forward-backward asymmetry in bb-sector (AbFBA_b^{FB}) and the recent measurement of MWM_W. In order to lift the two blind directions, which one encounters while fitting all the 10 SMEFT WCs at tree-level, we also include the LEP-II observables pertaining to the WWWW production and present the results for the fits with and without ΔCKM\Delta_{CKM} constraint.Comment: 32 pages, 6 figures, 19 table

    Central exclusive diffractive production of single photon in high-energy proton-proton collisions within the tensor-pomeron approach

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    We discuss central-exclusive production (CEP) of photons via different fusion processes in the reaction ppppγpp \to pp \gamma at high energies, available at RHIC and LHC, within the tensor-pomeron model. We consider two types of processes, the photoproduction contribution via the photon-pomeron and photon-reggeon fusion reactions, and the purely diffractive contribution via the reggeon-pomeron and odderon-pomeron fusion reactions. We present predictions for the measurements of photons at midrapidity, y<2.5|{\rm y}| < 2.5, and at relatively low transverse momentum, 0.1 GeV<k<1 GeV0.1~{\rm GeV} < k_{\perp} < 1~{\rm GeV}. To check the main results of our study the measurement of the outgoing protons is not necessary. This is of relevance, e.g., for the present version of the ALICE detector at the LHC. Several differential distributions, for instance, in y{\rm y}, kk_{\perp} and ω\omega, the rapidity, the absolute value of the transverse momentum, and the energy of the photon, respectively, are presented. We show that the photoproduction is an important process in the kinematic region specified above. There it gives a much larger cross section than diffractive bremsstrahlung. This is remarkable as the CEP cross section is of order αem3\alpha_{\rm em}^{3} whereas the bremsstrahlung one is only of order αem\alpha_{\rm em}. On the other hand, the soft-photon bremsstrahlung where the basic pppppp \to pp reaction is due to strong interaction diffraction is more important than CEP in the forward rapidity range, y>4|{\rm y}| > 4, and/or at very low kk_{\perp}. We leave it as a challenge for the planned ALICE 3 experiment at the LHC to study these two contributions to soft photon production in pppp collisions. This could shed new light on the so called ``soft photon puzzle'' in hadron-hadron collisions.Comment: 27 pages, 13 figure

    The present and future status of heavy neutral leptons

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    Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiereThe existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as heavy neutral leptons (HNLs). In this white paper, we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenario

    Heterogeneous Graph Neural Network for Identifying Hadronically Decayed Tau Leptons at the High Luminosity LHC

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    We present a new algorithm that identifies reconstructed jets originating from hadronic decays of tau leptons against those from quarks or gluons. No tau lepton reconstruction algorithm is used. Instead, the algorithm represents jets as heterogeneous graphs with tracks and energy clusters as nodes and trains a Graph Neural Network to identify tau jets from other jets. Different attributed graph representations and different GNN architectures are explored. We propose to use differential track and energy cluster information as node features and a heterogeneous sequentially-biased encoding for the inputs to final graph-level classification.Comment: 14 pages, 10 figures, 4 table

    Jet charge identification in ee-Z-qq process at Z pole operation

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    Accurate jet charge identification is essential for precise electroweak and flavor measurements at the high-energy frontier. We propose a novel method called the Leading Particle Jet Charge method (LPJC) to determine the jet charge based on information about the leading charged particle. Tested on Z - bb and Z - cc samples at a center-of-mass energy of 91.2GeV, the LPJC achieves an effective tagging power of 20%/9% for the c/b jet, respectively. Combined with the Weighted Jet Charge method (WJC), we develop a Heavy Flavor Jet Charge method (HFJC), which achieves an effective tagging power of 39%/20% for c/b jet, respectively. This paper also discusses the dependencies between jet charge identification performance and the fragmentation process of heavy flavor jets, and critical detector performances
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