Narrow Results

Jet substructure in heavy-ion collisions is a rapidly evolving area with lots of intriguing new measurements. This contribution presents a selection of recent jet-substructure measurements from experiments at the LHC, in particular, soft-drop groomed radii of jets and reclustered large-radius jets from ATLAS, jet axis difference and generalized jet angularities from ALICE, as well as dijet shapes and b-jet shapes from the CMS experiment.

In recent years, intense usage of computing has been the main strategy of investigations in several scientific research projects. The progress in computing technology has opened unprecedented opportunities for systematic collection of experimental data and the associated analysis that were considered impossible only few years ago.

This paper focuses on the strategies in use: it reviews the various components that are necessary for an effective solution that ensures the storage, the long term preservation, and the worldwide distribution of large quantities of data that are necessary in a large scientific research project.

The paper also mentions several examples of data management solutions used in High Energy Physics for the CERN Large Hadron Collider (LHC) experiments in Geneva, Switzerland which generate more than 30,000 terabytes of data every year that need to be preserved, analyzed, and made available to a community of several tenth of thousands scientists worldwide.

We study the Minimal Supersymmetric Standard Model (MSSM) with large gluino mass . In particular, we discuss the LHC supersymmetry discovery signatures with , n ≥ 0 for the MSSM with large gluino mass. We show that for some relations among squark and neutralino masses leptonic signatures with , n ≥ 1 do not allow to discover supersymmetry at the LHC and the only supersymmetry discovery signature is the signature with no . Moreover, for LSP mass close to squark masses the LHC discovery potential for this signature is strongly reduced.

No-scale supergravity is a framework where it is possible to naturally explain radiative electroweak symmetry breaking and correlate it with the effective SUSY breaking scale. Many string compactifications have a classical no-scale structure, resulting in a one-parameter model (OPM) for the supersymmetry breaking soft terms, which results in a highly constrained subset of mSUGRA. We investigate the allowed supersymmetry parameter space for a generic one-parameter model taking into account the most recent experimental constraints. We also survey the possible signatures which may be observable at the Large Hadron Collider (LHC). Finally, we compare collider signatures of OPM to those from a model with non-universal soft terms, in particular those of an intersecting D6-brane model.

The Large Hadron Collider (LHC) began 7 TeV C.M. energy operation in April, 2010. The CMS experiment immediately analyzed the earliest data taken in order to "rediscover" the Standard Model (SM) of high energy physics. By the late summer, all SM particles were observed and CMS began to search for physics beyond the SM and beyond the present limits set at the Fermilab Tevatron. The first LHC run ended in Dec., 2010 with a total integrated luminosity of about 45 pb^-1 delivered to the experiments.

The first year of LHC data taking provided an integrated luminosity of about 35 pb^-1 in proton–proton collisions at . The accelerator and the experiments have demonstrated an excellent performance. The experiments have obtained important physics results in many areas, ranging from tests of the Standard Model to searches for new particles. Among other results, the physics highlights have been the measurements of the W-, Z-boson and production cross-sections, improved limits on supersymmetric and other hypothetical particles and the observation of jet-quenching, elliptical flow and J/ψ suppression in lead–lead collisions at .

In 1964, a new particle was proposed by several groups to answer the question of where the masses of elementary particles come from; this particle is usually referred to as the Higgs particle or the Higgs boson. In July 2012, this Higgs particle was finally found experimentally, a feat accomplished by the ATLAS Collaboration and the CMS Collaboration using the Large Hadron Collider at CERN. It is the purpose of this review to give my personal perspective on a brief history of the experimental search for this particle since the '80s and finally its discovery in 2012. Besides the early searches, those at the LEP collider at CERN, the Tevatron Collider at Fermilab, and the Large Hadron Collider at CERN are described in some detail. This experimental discovery of the Higgs boson is often considered to be the most important advance in particle physics in the last half a century, and some of the possible implications are briefly discussed. This review is partially based on a talk presented by the author at the conference "Higgs Quo Vadis," Aspen Center for Physics, Aspen, CO, USA, March 10–15, 2013.

We investigate the possible large extra dimensions (LED) effects induced by the Kaluza–Klein (KK) gravitons up to the QCD next-to-leading order (NLO) on ZZW production at the large hadron collider (LHC). The integrated cross-sections and some kinematic distributions are presented in both the Standard Model (SM) and the LED model. The numerical results demonstrate that the NLO QCD corrections are sizeable and remarkably reduce the leading order (LO) LED effect depending strongly on the phase space. The NLO LED relative discrepancies of the total cross-section could become sizable for the ZZW production, if we apply proper event selection criteria. We find that the LO result overestimates the LED effect and is insufficient to provide a believable theoretical prediction.

We report on the current status of non-minimal universal extra dimension (NMUED) models. Our emphasis is on the possible extension of the minimal UED (MUED) model by allowing bulk masses and boundary localized terms. We take into account the data from the Large Hadron Collider (LHC) as well as direct and indirect searches of dark matter (DM) and electroweak (EW) precision measurements.

Although they do not address the hierarchy problem, models with Universal Extra Dimensions have attracted a lot of attention as simple benchmark models characterized by small mass splittings and a dark matter (DM) WIMP played by the Lightest Kaluza–Klein particle (LKP). We review their status, with emphasis on minimal implementation in five dimensions (MUED) in which the LKP is a massive hypercharge gauge boson. In this case, the mass range accounting for the correct DM abundance (around 1.4 TeV) remains untouched by LHC8 and is out of reach of present DM direct detection experiments. However, LHC14 can probe the relevant region in the 3-lepton channel.

Energy distributions of decay products carry information on the kinematics of the decay in ways that are at the same time straightforward and quite hidden. I will review these properties and discuss their early historical applications, as well as more recent ones in the context of (i) methods for the measurement of masses of new physics particle with semi-invisible decays, (ii) the characterization of Dark Matter particles produced at colliders, (iii) precision mass measurements of Standard Model particles, in particular of the top quark. Finally, I will give an outlook of further developments and applications of energy peak method for high energy physics at colliders and beyond.

The Standard Model (SM) extensions with vector-like states which have either zero hypercharge or zero weak isospin are rather poorly constrained by the electroweak precision measurements. Such new states would however modify the running of the gauge couplings at high energies. As a result, the Drell–Yan process $pp\to {\ell }^{+}{\ell }^{-}$ at the LHC places useful constraints on these models. The relevant observables include both the dilepton invariant mass distribution $M_{\ell \ell }$ and the forward–backward asymmetry $A_{\mathrm{\text{FB}}}$. We find that the LHC Run 1 data and the initial data from Run 2 surpass the sensitivity of LEP and already put meaningful constraints on the existence of such particles, which will become progressively stronger with more data.

The aim of this paper is to compare the recent LHC data at $\sqrt{s}$ =13 TeV with our previous theoretical proposal that the true Higgs boson H_T should be a broad heavy resonance with mass around 750 GeV. We focus on the so-called golden channel H_T$\to$ZZ where the pair of Z bosons decay leptonically to ${\ell }^{+}{\ell }^{-}{\ell }^{+}{\ell }^{-}$, $\ell$ being either an electron or a muon. We use the data collected by the ATLAS and CMS collaborations at $\sqrt{s}$ = 13 TeV with an integrated luminosity of 36.1 and 77.4 fb${}^{-1}$ respectively. We find that the experimental data from both the LHC collaborations do display in the golden channel a rather broad resonance structure around 700 GeV with a sizeable statistical significance. Our theoretical expectations seem to be in fair good agreement with the experimental observations. Combining the data from both the ATLAS and CMS collaborations we obtain an evidence of the heavy Higgs boson in this channel with an estimated statistical significance of more than five standard deviations.

The stransverse mass variable $M_{T2}$ was originally proposed for the study of hadron collider events in which $N=2$ parent particles are produced and then decay semi-invisibly. Here we consider the generalization to the case of $N\ge 3$ semi-invisibly decaying parent particles. We introduce the corresponding class of kinematic variables $M_{\mathrm{\text{TN}}}$ and illustrate their mathematical properties. Many of the celebrated features of the $M_{T2}$ kinematic endpoint are retained in this more general case, including the ability to measure the mass of the invisible daughter particle from the stransverse mass kink. We describe and validate a numerical procedure for computing $M_{\mathrm{\text{TN}}}$ in practice. We also identify the configurations of visible momenta which result in nontrivial ($M_{\mathrm{\text{TN}}}\ne 0$) values, and derive a pure phase-space estimate for the fraction of such events for any N.

The framework of large extra dimensions provides a way to explain why gravity is weaker than the other forces in nature. A consequence of this model is the possible production of D-dimensional black holes in high energy p–p collisions at the Large Hadron Collider. The present work uses the CATFISH black hole generator to study quantitatively how these events could be observed in the hadronic channel at midrapidity using a particle-tracking detector.

An experimental review of the current status of the top quark physics program at hadron colliders is presented. Since the discovery of the top quark at the Fermilab Tevatron collider in 1995, its production and the decay have been studied with an extraordinary level of sophistication both at the Tevatron and at the Large Hadron Collider. The top quark is the heaviest known elementary particle, with possible unique connections to the mechanism of electroweak symmetry breaking.

Dark matter remains one of the most puzzling mysteries in Fundamental Physics of our times. Experiments at high-energy physics colliders are expected to shed light to its nature and determine its properties. This review focuses on recent searches for dark matter signatures at the Large Hadron Collider, also discussing related prospects in future e⁺e^- colliders.

The journey in search for the Higgs boson with the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN started more than two decades ago. But the first discussions motivating the LHC project dream date back even further into the 1980s. This article will recall some of these early historical considerations, mention some of the LHC machine milestones and achievements, focus as an example of a technological challenge on the unique ATLAS superconducting magnet system, and then give an account of the physics results so far, leading to, and featuring particularly, the Higgs boson results, and sketching finally prospects for the future. With its emphasis on the ATLAS experiment it is complementary to the preceding article by Tejinder S. Virdee which focused on the CMS experiment.

Since 2010 there has been a rich harvest of results on standard model physics by the ATLAS and CMS experiments operating on the Large Hadron Collider. In the summer of 2012, a spectacular discovery was made by these experiments of a new, heavy particle. All the subsequently analysed data point strongly to the properties of this particle as those expected for the Higgs boson associated with the Brout–Englert–Higgs mechanism postulated to explain the spontaneous symmetry breaking in the electroweak sector, thereby explaining how elementary particles acquire mass. This article focuses on the CMS experiment, the technological challenges encountered in its construction, describing some of the physics results obtained so far, including the discovery of the Higgs boson, and searches for the widely anticipated new physics beyond the standard model, and peer into the future involving the high-luminosity phase of the LHC. This article is complementary to the one by Peter Jenni⁴ that focuses on the ATLAS experiment.