Showing papers in "Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields in 2014"
TL;DR: In this article, the role played by the top quark mass in the choice between the full stability and the metastability conditions is analyzed in detail, and the present experimental value of the top mass do not support the possibility that the SM potential is stable up to the Planck scale but favor an electroweak vacuum sufficiently long-lived to be metastable.
Abstract: I discuss the stability of the SM scalar potential in view of the discovery of a Higgs boson with mass around 125 GeV. The role played by the top quark mass in the choice between the full stability and the metastability conditions is analyzed in detail. The present experimental value of the top mass do not support the possibility that the SM potential is stable up to the Planck scale but favor an electroweak vacuum sufficiently long-lived to be metastable.
4 citations
TL;DR: In this article, a review of recent results in QCD and LHC phenomenology is presented, covering progress in parton distribution functions, automation of NLO calculations, merging and matching at NLO, new calculations at NNLO accuracy and their matching to parton showers, and new developments and techniques in jet physics and jet substructure tools.
Abstract: Perturbative Quantum Chromodynamics has experienced an impressive progress in the last few years, boosted by the requirements of the LHC experimental program. In this contribution, I briefly review a selection of recent results in QCD and LHC phenomenology, covering progress in parton distribution functions, automation of NLO calculations, merging and matching at NLO, new calculations at NNLO accuracy and their matching to parton showers, and new developments and techniques in jet physics and jet substructure tools.
4 citations
TL;DR: In this paper, several manifestations of charged lepton flavour violation at high energies are discussed, focusing on a supersymmetric type I seesaw, considering constrained and semi-constrained supersymmetry breaking scenarios, both at the LHC and at a future Linear Collider.
Abstract: We discuss several manifestations of charged lepton flavour violation at high energies. Focusing on a supersymmetric type I seesaw, considering constrained and semi-constrained supersymmetry breaking scenarios, we analyse different observables, both at the LHC and at a future Linear Collider. We further discuss how the synergy between low- and high-energy observables can shed some light on the underlying mechanism of lepton flavour violation.
3 citations
TL;DR: The theory of neutrino mass and mixing is still on the cross-road as mentioned in this paper, despite the enormous experimental progress in determination of the neutrinos parameters, the crossroad is still open.
Abstract: In spite of enormous experimental progress in determination of the neutrino parameters, theory of neutrino mass and mixing is still on the cross-roads. Guidelines could be (i) the connection between zero neutrino charges (and therefore a possibility to be Majorana particle), smallness of the neutrino mass and large lepton mixing, (ii) joint description of leptons and quarks, (iii) existence of the right handed (RH) neutrinos without special quantum numbers. Properties of the RH neutrinos and the UV completion of the seesaw may turn out to be the key to understand the neutrino mass and mixing. In view of the
3 citations
2 citations
TL;DR: In this paper, the mass of the new Higgs boson with mass around 125 GeV was measured at the LHC using collision data from the H → ZZ → 4 channel ( = e, μ).
Abstract: The latest results on the measurement of the properties of the new
boson with mass around 125 GeV are reported. The analysis uses pp collision data
recorded by the CMS detector at the LHC, corresponding to integrated luminosities
of 5.1 fb−1 at √s = 7 TeV and 19.6 fb−1 at √s = 8 TeV. The boson is observed in
the H → ZZ → 4 channel ( = e, μ) and its mass is measured, giving the most
precise result ever achieved. Moreover, the first experimental constraint on Higgs
total width using H → ZZ → 4 events is presented, setting an upper limit of
33 MeV at 95% confidence level (42 MeV expected). The spin-parity of the boson is
studied and the pure scalar hypothesis is found to be consistent with the observation,
when compared to the other spin-parity hypotheses. No other significant Standard
Model Higgs-like excess is found in the search and upper limits at 95% confidence
level exclude the range 129.5–832.0 GeV.
1 citations
TL;DR: Comb beams are sub-picosecond, high-brightness electron bunch trains generated via the velocity bunching technique as discussed by the authors, which can be used to drive tunable and narrow band THz sources, FELs and plasma wake field accelerators.
Abstract: Comb beams are sub-picosecond, high-brightness electron bunch trains generated via the velocity bunching technique. Such bunch trains can be used to drive tunable and narrow band THz sources, FELs and plasma wake field accelerators. In this paper we present recent results at SPARC-LAB on the generation of comb beams for particle-driven plasma-based accelerators.
1 citations
TL;DR: In this article, the Drell-Yan Z-boson invariant mass distribution at low and high mass regions was measured by the ATLAS experiment and the impact of each component of the final prediction was estimated.
Abstract: Parton distributions with QED corrections open new scenarios for high precision physics. We recall the need for accurate and improved predictions which keeps into account higher order QCD corrections together with electroweak effects. We study predictions obtained with the improved Born approximation and the $G_{\mu}$ scheme by using two public codes: DYNNLO and HORACE. We focus our attention on the Drell-Yan Z-boson invariant mass distribution at low- and high-mass regions, recently measured by the ATLAS experiment and we estimate the impact of each component of the final prediction. We show that electroweak corrections are larger than PDF uncertainties for modern PDF sets and therefore such corrections are necessary to improve the extraction of future PDF sets.
1 citations
TL;DR: In this paper, the authors briefly summarise the constraints on vector-like quarks and their possible signatures at the LHC, focusing in particular on a model-independent description of single production processes for vectorlike quark that mix with all generations.
Abstract: Vector-like quarks are predicted in various scenarios of new physics, and their peculiar signatures from both pair and single production have been already investigated in detail. However no signals of vector-like quarks have been detected so far, pushing limits on their masses above 600–700 GeV, depending on assumptions on their couplings. Experimental searches consider specific final states to pose bounds on the mass of a vector-like quark, usually assuming it is the only particle that contributes to the signal of new physics in that specific final state. However, realistic scenarios predict the existence of multiple vector-like quarks, possibly with similar masses. The reinterpretation of mass bounds from experimental searches is therefore not always straightforward. In this analysis I briefly summarise the constraints on vector-like quarks and their possible signatures at the LHC, focusing in particular on a model-independent description of single production processes for vector-like quark that mix with all generations and on the development of a framework to study scenarios with multiple vector-like quarks.
1 citations
TL;DR: In this paper, Giacomelli introduced the round table on neutrinos held in February 2014, and the topics selected for the discussion are: 1) the neutrinoless double beta decay rate (interpretation in terms of light neutrininos, nuclear uncertainties); 2) the physics in the gigantic water Cherenkov detectors (proton decay, atmospheric neutrions); 3) the study of neutrino oscillations.
Abstract: This talk, dedicated to the memory of G. Giacomelli, introduced the round table on neutrinos held in February 2014. The topics selected for the discussion are: 1) the neutrinoless double beta decay rate (interpretation in terms of light neutrinos, nuclear uncertainties); 2) the physics in the gigantic water Cherenkov detectors (proton decay, atmospheric neutrinos); 3) the study of neutrino oscillations (mass hierarchy and CP violation; other neutrino states); 4) the neutrino astronomy at low and high energies (solar, supernova, cosmic neutrinos). The importance of an active interplay between theory and experiment is highlighted.
1 citations
TL;DR: In this article, Weinberg et al. showed that the bare mass term in the Higgs potential must have had a large positive value, enhanced by the quadratic divergence of the bare Higgs mass in the early universe, which is a result of a conspiracy between the SM couplings and their screening/antiscreening behavior.
Abstract: We review a recent analysis presented in arXiv:1304.7813 [hep-phys] and 1305.6652 [hep-phys]. After the discovery of the Higgs the most relevant struc- tures of the SM have been verified and for the first time we know all parameters of the SM within remarkable accuracy. Together with recent calculations of the SM renormalization group coefficients up to three loops we can safely extrapolate run- ning couplings high up in energy. Assuming that the SM is a low energy effective theory of a cutoff theory residing at the Planck scale, we are able to calculate the effective bare parameters of the underlying cutoff system. For my specific set of MS input parameters, it turns out that the bare mass term changes sign not far below the Planck scale, which means that in the early universe the SM was in the symmetric phase. The sign-flip, which is a result of a conspiracy between the SM couplings and their screening/antiscreening behavior, triggers the Higgs mechanism. Above the Higgs phase transition the bare mass term in the Higgs potential must have had a large positive value, enhanced by the quadratic divergence of the bare Higgs mass. The Higgs mass term thus provides the large dark energy density in the early universe, which triggers Gaussian slow-roll inflation, i.e. the SM Higgs is the inflaton scalar field. Reheating is dominated by the decay of the heavy Higgses into (in the symmetric phase) massless top/anti-top quark pairs. The Higgs mechanism stops inflation and the subsequent electroweak phase transition provides the masses to the SM particles in proportion to their coupling strength. The previously most abundantly produced particles are now the heaviest and decay into the lighter ones, by cascading down the Cabibbo-Kobayashi-Maskawa (CKM)-matrix from top and bottom to normal matter. Baryon-number B violating interactions are naturally provided by Weinberg’s set of close-by dimension 6 four-fermion effective interac- tions. Since matter is produced originating in the primordial heavy Higgs fields via C -and CP -violating decays we have actually a new scenario which could explain the baryon-asymmetry essentially in terms of SM physics.
TL;DR: In this paper, the Drell-Yan process is used to access Transverse Momentum Dependent Parton Distribution Functions (TMD PDFs), such as the Sivers and the Boer-Mulders functions, providing complementary information to what is known from Semi Inclusive Deep Inelastic Scattering (SIDIS) data.
Abstract: The Drell-Yan process can be used to access Transverse Momentum Dependent Parton Distribution Functions (TMD PDFs), such as the Sivers and the Boer-Mulders functions, as well as the transversity function providing complementary information to what is known from Semi Inclusive Deep Inelastic Scattering (SIDIS) data. The COMPASS experiment offers the possibility to study single polarized Drell-Yan processes (π− + p↑ → μμ + X), making use of its large acceptance spectrometer and its unique transversely polarised proton target. Moreover a fundamental test of the factorization theorem in the non-perturbative QCD can be performed, by verifying the sign change of the T-odd Boer-Mulders and Sivers functions depending if they are accessed via SIDIS or Drell-Yan process. As the start of the Drell-Yan program at COMPASS is approaching, foreseen in late 2014, the spectrometer has been updated to fulfill the needs of this measurement
TL;DR: In this article, a simulation of Higgs boson production accurate at next-to-next-to leading order and matched to a parton shower can be built by combining the POWHEG and MiNLO methods and using HNNLO results as input.
Abstract: We describe how a simulation of Higgs boson production accurate at next-to-next-to-leading order and matched to a parton shower can be built by combining the POWHEG and MiNLO methods and using HNNLO results as input.
TL;DR: A review of the most recent measurements of top quark strong and electroweak production performed by using data collected with the ATLAS detector in proton-proton collisions at 7 and 8 TeV at the Large Hadron Collider corresponding to integrated luminosities of up to about 4.7/fb and 20/fb, respectively is presented in this article.
Abstract: A review is presented of the most recent measurements of top quark strong and electroweak production performed by using data collected with the ATLAS detector in proton-proton collisions at sqrt(s) = 7 and 8 TeV at the Large Hadron Collider corresponding to integrated luminosities of up to about 4.7/fb and 20/fb, respectively.
TL;DR: The Legacy of Bruno Pontecorvo: the Scientist and the Man, held in Roma, Universita La Sapienza, 11-12 September, 2013, are summarised and illustrated as discussed by the authors.
Abstract: The highlights of the conference: The Legacy of Bruno Pontecorvo: the Scientist and the Man, held in Roma, Universita La Sapienza, 11-12 September, 2013, are summarised and illustrated.