Discovery Of The Higgs Boson Research Articles

Bayesian and frequentist approaches to resonance searches

We investigate Bayesian and frequentist approaches to resonance searches using a toy model based on an ATLAS search for the Higgs boson in the diphoton channel. We draw pseudo-data from the background only model and background plus signal model at multiple luminosities, from 10−3/ fb to 107/ fb. We chart the change in the Bayesian posterior of the background only model and the global p-value. We find that, as anticipated, the posterior converges to certainty about the model as luminosity increases. The p-value, on the other hand, randomly walks between 0 and 1 if the background only model is true, and otherwise converges to 0. After briefly commenting on the frequentist properties of the posterior, we make a direct comparison of the significances obtained in Bayesian and frequentist frameworks. We find that the well-known look-elsewhere effect reduces local significances by about 1σ. We furthermore find that significances from our Bayesian framework are typically about 1−2σ smaller than the global significances, though the reduction depends on the prior, global significance and integrated luminosity. This suggests that even global significances could significantly overstate the evidence against the background only model. We checked that this effect—the Bayes effect—was robust with respect to fourteen choices of prior and investigated the Jeffreys-Lindley paradox for three of them.

Model landscapes and event signatures in elementary particle physics

The current state of particle physics is conflicting. One has a marvellously working theory, the Standard Model, that leaves many questions open. This tension has led to a variegated landscape of models of physics beyond the Standard Model that is guided by epistemic and pragmatic values of model preference. Whereas these preferences are shared by experimentalists and theorists, their use of models within research practice differs. Experimentalists focus on event signatures that have many-to-many relations to models. We argue that physicists’ three-pronged approach distinguishing raw data, signatures, and models resembles the analysis of Bogen and Woodward, establishing the autonomy of phenomena. Using signatures opens the door for explorative experimentation, which becomes crucial for managing the uncertainty about the direction of particle physics that has emerged after the discovery of the Higgs boson.

Higgs and BSM Studies at the LHC

The discovery and study of the Higgs boson at the Large Hadron Collider of CERN has proven the validity of the Brout–Englert–Higgs mechanism of mass creation in the standard model via spontaneous symmetry breaking. The new results obtained by the ATLAS and CMS Collaborations at the LHC show that all measured cross-sections agree within uncertainties with the predictions of the theory. However, the standard model has obvious difficulties (nonzero neutrino masses, hierarchy problem, existence of dark matter, non-existence of antimatter galaxies, etc.), which point towards more possible violated symmetries. We first summarize the present status of the studies of the Higgs boson, including the latest results at 13 TeV p-p collision energy, then enlist some of the problems with possible solutions and the experimental situation regarding them.

The SHiP experiment and the RPC technology

The discovery of the Higgs boson has fully confirmed the Standard Model of particles and fields. Nevertheless, there are still fundamental phenomena, like the existence of dark matter and the baryon asymmetry of the Universe, which deserve an explanation that could come from the discovery of new particles. The SHiP experiment at CERN meant to search for very weakly coupled particles in the few GeV mass domain has been recently proposed. The existence of such particles, foreseen in Beyond Standard Models, is largely unexplored. A beam dump facility using high intensity 400 GeV protons is a copious source of such unknown particles in the GeV mass range. The beam dump is also a copious source of neutrinos and in particular it is an ideal source of tau neutrinos, the less known particle in the Standard Model. We report the physics potential of such an experiment and describe the use of the RPC technology therein. An anchillary measurement of the charm cross-section will be carried out in July 2018 and RPC are used as a muon detector. We also describe the design and construction of these new chambers.

From a boson to the standard model Higgs: a case study in confirmation and model dynamics

Our paper studies the anatomy of the discovery of the Higgs boson at the Large Hadron Collider and its influence on the broader model landscape of particle physics. We investigate the phases of this discovery, which led to a crucial reconfiguration of the model landscape of elementary particle physics and eventually to a confirmation of the standard model (SM). A keyword search of preprints covering the electroweak symmetry breaking (EWSB) sector of particle physics, along with an examination of physicists own understanding of the discovery as documented in semiannual conferences, has allowed us an empirical investigation of its model dynamics. From our analyses we draw two main philosophical lessons concerning the nature of scientific reasoning in a complex experimental and theoretical environment. For one, from a confirmation standpoint, some SM alternatives could be considered even more confirmed by the Higgs discovery than the SM. Nevertheless, the SM largely remains the commonly accepted account of EWSB. We present criteria for comparing degrees of confirmation and expose some limits of a purely logical approach to understanding the Higgs discovery as a victory for the SM. Second, we understand the persistence of SM alternatives in the face of disfavourable evidence by borrowing the Lakatosian concept of a research programme, where the core idea behind a group of models survives, while other aspects adapt to incoming data. In order to apply this framework to the model landscape of EWSB, we must introduce a new category of research programme, the model-group, and we test its viability using the example of composite Higgs models.

Precision Higgs physics at the CEPC * *Supported by the National Key Program for S&T Researh and Development (2016YFA0400400); CAS Center for Excellence in Particle Physics; Yifang Wang’s Science Studio of the Ten Thousand Talents Project; the CAS/SAFEA International Partnership Program for Creative Research Teams (H751S018S5); IHEP Innovation Grant (Y4545170Y2); Key Research Program of Frontier Sciences, CAS (XQYZDY-SSW-SLH002); Chinese Academy

The discovery of the Higgs boson with its mass around 125 GeV by the ATLAS and CMS Collaborations marked the beginning of a new era in high energy physics. The Higgs boson will be the subject of extensive studies of the ongoing LHC program. At the same time, lepton collider based Higgs factories have been proposed as a possible next step beyond the LHC, with its main goal to precisely measure the properties of the Higgs boson and probe potential new physics associated with the Higgs boson. The Circular Electron Positron Collider (CEPC) is one of such proposed Higgs factories. The CEPC is an e + e − circular collider proposed by and to be hosted in China. Located in a tunnel of approximately 100 km in circumference, it will operate at a center-of-mass energy of 240 GeV as the Higgs factory. In this paper, we present the first estimates on the precision of the Higgs boson property measurements achievable at the CEPC and discuss implications of these measurements.

Physics, lasers and the nobel prize

Like every year, we have been waiting for the announcement of the most important award for natural sciences, the Nobel Prize in Physics. Perhaps it is since 2013, the year in which the award was given for the discovery of the Higgs boson, that the Nobel Prize has great media visibility. The public, scientific or otherwise, is waiting to know who will be awarded.

Search for the Higgs Boson Decaying to Two Muons in Proton-Proton Collisions at sqrt[s]=13 TeV.

A search for the Higgs boson decaying to two oppositely charged muons is presented using data recorded by the CMS experiment at the CERN LHC in 2016 at a center-of-mass energy sqrt[s]=13 TeV, corresponding to an integrated luminosity of 35.9 fb^{-1}. Data are found to be compatible with the predicted background. For a Higgs boson with a mass of 125.09GeV, the 95%confidence level observed (background-only expected) upper limit on the production cross section times the branching fraction to a pair of muons is found to be 3.0 (2.5) times the standard model expectation. In combination with data recorded at center-of-mass energies sqrt[s]=7 and 8TeV, the background-only expected upper limit improves to 2.2 times the standard model value with a standard model expected significance of 1.0 standard deviation. The corresponding observed upper limit is 2.9 with an observed significance of 0.9 standard deviation. This corresponds to an observed upper limit on the standard model Higgs boson branching fraction to muons of 6.4×10^{-4} and to an observed signal strength of 1.0±1.0(stat)±0.1(syst).

Overview of the CMS Detector Performance at LHC Run 2

The Compact Muon Solenoid (CMS) detector is one of the two multipurpose experiments at the Large Hadron Collider (LHC). It has successfully collected data during Run 1 (2010–2013) and achieved important physics results, like the discovery of the Higgs boson announced in 2012. Willing to unravel further open questions not yet explained by the standard model, intense activities have been performed to further improve the detector and the trigger before the LHC restart in 2016 (Run 2), in parallel with the upgrade of the LHC. The achieved global performance of the CMS experiment and of several subdetectors will be presented.

Isobar Collisions at RHIC to Test Local Parity Violation in Strong Interactions

The discovery of the Higgs boson has completed the Standard Model of fundamental interactions. The Standard Model describes the strong and electroweak interactions by generalizing the concept of local gauge invariance that underlies the Maxwell theory of electromagnetism to non-Abelian gauge groups. A non-Abelian group has the elements that do not commute, such as the group of rotations in three dimensions, where a rotation around axis x followed by a rotation around axis γ yields a different result from doing these rotations the other way around. The resulting theory is both elegant and powerful—it is believed to describe all known properties of the physical world, except gravity. In spite of their deceptively simple structure, non-Abelian gauge theories possess many surprising features that are still not understood.

The SHiP experiment at CERN

The discovery of the Higgs boson has fully confirmed the Standard Model of particles and fields. Nevertheless, fundamental phenomena like the existence of dark matter and the baryon asymmetry of the Universe still deserve an explanation that could come from the discovery of new particles. The SHiP experiment proposal at CERN is meant to search for particles in the few GeV mass domain, very weakly coupled with ordinary particles. The existence of such particles, foreseen in Beyond Standard Models, is largely unexplored. A beam dump facility using high intensity 400 GeV protons is a copious source of such unknown particles in the GeV mass range. The beam dump is also a copious source of neutrinos and in particular it is an ideal source of tau neutrinos, the less known particle in the Standard Model. We report the physics potential of such an experiment. We also describe an ancillary measurement of the charm cross-section carried out in July 2018.

Recent highlights in top quark and Higgs boson physics from the LHC

The LHC represents the current energy frontier in collider experiments. Its most notable result so far was the experimental discovery of the Higgs boson, by the ATLAS and CMS collaborations. It is also very well suited to explore the physics of the top quark, the heaviest known elementary particle, with a Yukawa coupling of order 1. The data collected by these experiments during the LHC Run II allowed the measurement of top and Higgs experimental results, which provide very stringent tests of the Standard Model expectations near the electroweak scale, and therefore likely windows into new physics. The present article discusses the most recent experimental highlights in this area.

LHC CELEBRATES 10 YEARS

The CERN Large Hadron Collider is a complex machine consisting of a 27 km underground ring where protons circulate in opposite directions and collide at a new energy frontier. The goal is to progress in the understanding of the fundamental structure of matter. Large detectors surround the collision points. They are capable of detecting all the particles produced in the proton collisions. The first 10 years of operation of the machine lead to the discovery of the Higgs boson, en important milestone for particle physics. Spanish research groups and industry participated in the construction. This participation generates returns. The future High Luminosity LHC upgrade will provide new opportunities.

Model choice and crucial tests. On the empirical epistemology of the Higgs discovery

Our paper discusses the epistemic attitudes of particle physicists on the discovery of the Higgs boson at the Large Hadron Collider (LHC). It is based on questionnaires and interviews made shortly before and shortly after the discovery in 2012. We show, to begin with, that the discovery of a Standard Model (SM) Higgs boson was less expected than is sometimes assumed. Once the new particle was shown to have properties consistent with SM expectations – albeit with significant experimental uncertainties –, there was a broad agreement that ‘a’ Higgs boson had been found. Physicists adopted a two-pronged strategy. On the one hand, they treated the particle as a SM Higgs boson and tried to establish its properties with higher precision; on the other hand, they searched for any hints of physics beyond the SM. This motivates our first philosophical thesis: the Higgs discovery, being of fundamental importance and establishing a new kind of particle, represented a crucial experiment if one interprets this notion in an appropriate sense. Duhemian underdetermination is kept at bay by embedding the LHC into the tradition of previous precision experiments and the experimental strategies thus established. Second, our case study suggests that criteria of theory (or model) preference should be understood as epistemic and pragmatic values that have to be weighed in factual research practice. The Higgs discovery led to a shift from pragmatic to epistemic values in physicists’ assessment of the mechanisms of electroweak symmetry breaking. Complex criteria, such as naturalness, combine epistemic and pragmatic values, but are coherently applied by the community.

Charged lepton flavor violating Higgs decays at future e^+e^- colliders

After the discovery of the Higgs boson, several future experiments have been proposed to study the Higgs boson properties, including two circular lepton colliders, the CEPC and the FCC-ee, and one linear lepton collider, the ILC. We evaluate the precision reach of these colliders in measuring the branching ratios of the charged lepton flavor violating Higgs decays Hrightarrow e^pm mu ^mp , e^pm tau ^mp and mu ^pm tau ^mp . The expected upper bounds on the branching ratios given by the circular (linear) colliders are found to be {mathcal {B}}(Hrightarrow e^pm mu ^mp ) < 1.2~(2.1) times 10^{-5}, {mathcal {B}}(Hrightarrow e^pm tau ^mp ) < 1.6~(2.4) times 10^{-4} and {mathcal {B}}(Hrightarrow mu ^pm tau ^mp ) < 1.4~(2.3) times 10^{-4} at 95% CL, which are improved by one to two orders compared to the current experimental bounds. We also discuss the constraints that these upper bounds set on certain theory parameters, including the charged lepton flavor violating Higgs couplings, the corresponding parameters in the type-III 2HDM, and the new physics cut-off scales in the SMEFT, in RS models and in models with heavy neutrinos.

Search for the Higgs boson produced in association with a vector boson and decaying into two spin-zero particles in the H \u2192 aa \u2192 4b channel in pp collisions at sqrt{s}=13 TeV with the ATLAS detector

A search for exotic decays of the Higgs boson into a pair of spin-zero particles, H → aa, where the a-boson decay sin to b-quarks promptly or with a mean proper lifetime cτa up to 6 mm and has a mass in the range of 20–60 GeV, is presented. The search is performed in events where the Higgs boson is produced in association with a W or Z boson, giving rise to a signature of one or two charged leptons (electrons or muons) and multiple jets from b-quark decays. The analysis is based on the dataset of proton-proton collisions at sqrt{s}=13 TeV recorded in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb−1. No significant excess of events above the Standard Model background prediction is observed, and 95% confidence-level upper limits are derived for the production cross-sections for pp → WH, ZH and their combination, times the branching ratio of the decay chain H → aa → 4b. For a-bosons which decay promptly, the upper limit on the combination of cross-sections for WH and ZH times the branching ratio of H → aa → 4b ranges from 3.0 pb for ma = 20 GeV to 1.3 pb for ma = 60 GeV, assuming that the ratio of WH to ZH cross-sections follows the Standard Model prediction. For a-bosons with longer proper lifetimes, the most stringent limits are 1.8 pb and 0.68 pb, respectively, at cτa ∼ 0.4 mm.

Search for a lighter Higgs boson in the Next-to-Minimal Supersymmetric Standard Model**Supported by National Natural Science Foundation of China (11505208, 11661141007, 11705016, 11875275), China Ministry of Science and Technology (2018YFA0403901) and partially by the France China Particle Physics Laboratory (FCPPL) and CAS Center for Excellence in Particle Physics (CCEPP)

Following the discovery of the Higgs boson with a mass of approximately 125 GeV at the LHC, many studies have been performed from both the theoretical and experimental viewpoints to search for a new Higgs Boson that is lighter than 125 GeV. We explore the possibility of constraining a lighter neutral scalar Higgs boson h1 and a lighter pseudo-scalar Higgs boson a1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h2 to be the one observed at the LHC after applying the phenomenological constraints and those from experimental measurements. Such lighter particles are not yet completely excluded by the latest results of the search for a lighter Higgs boson in the diphoton decay channel from LHC data. Our results show that some new constraints on the Next-to-Minimal Supersymmetric Standard Model could be obtained for a lighter scalar Higgs boson at the LHC if such a search is performed by experimental collaborations and more data. The potentials of discovery for other interesting decay channels of such a lighter neutral scalar or pseudo-scalar particle are also discussed.

Novel methods of constraining the parton distribution function uncertainty in the measurement of the W -boson mass

The measurement of the mass of the $W$ boson is one of the most precise and impactful measurements to test the standard model (SM). Following the discovery of the Higgs boson and the measurement of its mass, all SM parameters are sufficiently well known in order to make precise predictions for electroweak observables such as the $W$ boson mass. These observables receive corrections in extensions of the SM. Experimentally, the dominant uncertainty in the $W$-boson mass measurement at hadron colliders arises due to parton distribution functions (PDFs). We present novel in situ methods of constraining the PDF variation and of reducing the PDF impact on the $W$-mass measurement uncertainty at hadron colliders. These methods can exploit the very high-statistics samples of $W$-boson candidate events at the LHC.

Popularising the Higgs boson: a corpus-assisted approach to reporting scientific discovery in online media

This study explores the scientific popularisation process and how science knowledge is recontextualised and rewritten in the transfer from one context or genre to another genre. It does this through a case study of the discovery of the Higgs boson, a new physics particle that is commonly known as the God Particle, and by focussing on the meta-discursive strategies that emerged from the texts after corpus-assisted analysis. Extensive use was made of exemplification and generalisation through analogies and metaphors, and through ideational content representing epistemic uncertainty in the newspaper discourse. Prominence is given to science popularisation in the British press, because online newspapers capture a wide non-expert public, the aim being to offer an analysis of how the discursive perspective of complex science news (particle physics) is conveyed to the general public, and can allow a systematic investigation into ‘how’ a scientific event is constructed and made newsworthy. Two corpora, consisting of texts from the scientific journal, Physics Letters B, and from online media blogs, were also compiled for contrastive purposes. In this way, prominent lexico-semantic textual properties are identified in the main corpus (containing newspapers) through standard corpus linguistic techniques, in particular through key semantic domain annotation, leading to more insight into how complex science is linguistically constructed and conveyed to a lay audience.

Supersymmetry at a 28 TeV hadron collider: HE-LHC

The discovery of the Higgs boson at $\sim 125$ GeV indicates that the scale of weak scale supersymmetry is higher than what was perceived in the pre-Higgs boson discovery era and lies in the several TeV region. This makes the discovery of supersymmetry more challenging and argues for hadron colliders beyond LHC at $\sqrt s=14$ TeV. The Future Circular Collider (FCC) study at CERN is considering a 100 TeV collider to be installed in a 100 km tunnel in the Lake Geneva basin. Another 100 km collider being considered in China is the Super proton-proton Collider (SppC). A third possibility recently proposed is the High-Energy LHC (HE-LHC) which would use the existing CERN tunnel but achieve a center-of-mass energy of 28 TeV by using FCC magnet technology at significantly higher luminosity than at the High Luminosity LHC (HL-LHC). In this work we investigate the potential of HE-LHC for the discovery of supersymmetry. We study a class of supergravity unified models under the Higgs boson mass and the dark matter relic density constraints and compare the analysis with the potential reach of the HL-LHC. A set of benchmarks are presented which are beyond the discovery potential of HL-LHC but are discoverable at HE-LHC. For comparison, we study model points at HE-LHC which are also discoverable at HL-LHC. For these model points, it is found that their discovery would require a HL-LHC run between 5-8 years while the same parameter points can be discovered in a period of few weeks to $\sim 1.5$ yr at HE-LHC running at its optimal luminosity of $2.5\times 10^{35}$ cm$^{-2}$ s$^{-1}$. The analysis indicates that the HE-LHC possibility should be seriously pursued as it would significantly increase the discovery reach for supersymmetry beyond that of HL-LHC and decrease the run period for discovery.