Exploiting the Higgs breakthrough

After the Higgs: status and prospects of the electroweak fit of the SM and beyond - with Gfitter

Dr Max Baak, CERN, Switzerland

Abstract

Today, all fundamental Standard Model parameters are known and the global electroweak fit is used as a powerful tool to assess the validity of the Standard Model and to constrain scenarios for new physics. We present and discuss the Standard Model predictions of several key observables of the electroweak fit, which are dramatically improved by the knowledge of the Higgs mass. These results are compatible with, and exceed in precision, the direct measurements.

Constraints from the electroweak fit on loop contributions from beyond-SM models are also obtained, through an analysis of the so-called oblique parameters.  We discuss the impact of the electroweak fit on Higgs coupling studies and vice versa. Future measurements at the Large Hadron Collider and the International Linear Collider promise to improve the experimental precision of key observables used in the fit. We present the prospects of the global electroweak fit in view of these improvements.

An Overview of ATLAS measurements

Dr Kostas Nikolopoulos, University of Birmingham, UK

Abstract

Following the observation of a new boson during the summer of 2012, the ATLAS Collaboration has analysed the complete LHC Run I proton-proton collision dataset of 4.7/fb at the centre-of-mass-energy of 7 TeV and 20.7/fb at 8 TeV. An overview of the most recent results, including both the boson and fermion decay channels will be presented, and the current status of the coupling and spin/CP properties measurements of the Higgs boson will be presented.

Higgs Boson Studies at the Tevatron

Dr Jonathan Hays, Queen Mary University of London, UK

Abstract

Run II at the Tevatron ran until September 2011, colliding protons with anti-protons at a centre of mass energy of 1.96 TeV. The combination of results from the CDF and D0 experiments for searches for a Standard Model Higgs boson using an integrated luminosity of

10fb-1 are presented. These are also interpreted in the context of fermiophobic and 4th generation models. An excess of events in the mass range 115 GeV to 140 GeV is observed consistent with the Higgs signal discovered at the LHC.

Higgs measurements from CMS

Dr Nick Wardle, CERN, Switzerland

Abstract

Since the discovery of a new boson in the summer of 2012, the CMS collaboration have focused attention on understanding the nature of this particle and its interactions. The complete Run 1 dataset corresponding to 4.1/fb and 19.7/fb of proton-proton collisions and centre of mass energies 7 and 8 TeV has been analysed.

The talk will provide an overview of the most recent measurements in both bosonic and fermionic decay Higgs decay channels using the full Run 1 dataset.

SUSY Higgs bosons

Dr Sasha Nikitenko, Imperial College, UK

Abstract

Several Higgs bosons with masses smaller or larger that 125 GeV are predicted in the best-motivated extension of the Standard Model - supersimmetry (SUSY). I will talk about searches for SUSY Higgs bosons at LHC experiments, ATLAS and CMS with data accumulated during 2010-2013 runs at 7 and 8 TeV and about prospects for the future runs with increased center of mass energy, 13-14 TeV.

I will also talk about searches for the non-standard model decays of the discovered Higgs boson with mass 125 GeV, in particular about decays into Dark Matter particles.

Alternative Higgs Scenarios

Dr Matthew Dolan, SLAC National Accelerator Laboratory, USA

Abstract

In this talk I will present and discuss some alternatives to the Standard Model Higgs which are consistent with current LHC measurements. I will distinguish between the two possibliities that the observed Higgs is either a fundamental scalar or a composite state, and emphasise the importance of top partner searches in both of these scenarios. I will also show how a variety of exotic Higgs decays can arise in these models, and briefly discuss search strategies for these.

Higgs coupling results from ATLAS and CMS

Dr Giovanni Petrucciani, CERN, Switzerland

Abstract

The combined results from searches for the Higgs boson separately for ATLAS and CMS will be presented, focusing on how the couplings of the boson can be tested from the measurements in many complementary final states. The compatibility of the data with the predictions for the standard model Higgs boson will be assessed in the context of benchmark models probing different patterns of deviations in the couplings expected from new physics scenarios.

The combination of the measurements of the Higgs boson mass and of the exclusions for different boson spin and parity hypotheses will also be briefly discussed.

Higher-dimensional operators

Dr Veronica Sanz, University of Sussex, UK

Abstract

The approach to discover new physics could be the detailed study of effects in the Higgs couplings. Indeed, new physics could show up as higher-dimensional operators which exhibit interesting kinematic properties, besides modifying the total rates. More data and a better theoretical understanding of the Standard Model is required to perform these studies, and in this talk we will discuss the road-map to perform to a consistent treatment of these effects.

The LHC Higgs cross section working group: predictions for the Higgs discovery and precision measurements

Dr Sven Heinemeyer, IFCA (CSIC, Santander), Spain

Abstract

The search for the Higgs boson at the LHC, its discovery and subsequent precision measurements require theory predictions at the highest possible level of accuracy. The LHC Higgs Cross Section Working Group (LHCHXSWG) was created to provide and facilitate theory predictions for Higgs boson production cross sections and branching ratios at the LHC to the ATLAS and CMS collaborations. The group also provides recommendations for extraction and measurement of Higgs boson quantities such as spin, CP quantum numbers and Higgs boson couplings. The predictions and recommendations of the LHCHXSWG are reviewed.

The stability of the Electroweak Vacuum

Professor José R Espinosa, ICREA/IFAE Barcelona Spain

Abstract

The discovery of the Higgs boson by the LHC in 2012, and especially the determination of its mass around 126 GeV, together with the absence of any trace of new physics, make it conceivable that we live in a metastable electroweak vacuum. This vacuum turns out to be extremely long-lived as that particular mass value means we  live quite close to the stability boundary. I will describe the state-of-the-art calculation that leads to this intriguing conclusion and elaborate on possible implications as well as a simple cure of this instability of the Higgs potential.

Future experimental measurements from LHC Run 2 to HL-LHC

Dr Sinead Farrington, CERN, Switzerland

Abstract

The LHC will reach a record-breaking centre of mass energy of 13 or 14 TeV during 2015. This will extend the capability of the LHC experiments to move from a discovery to a precision era in Higgs Physics. This will allow the Higgs couplings and spin and CP quantities to be measured with a precision that will further test the Standard Model.  Looking ahead several more years from now, the LHC and its experiments aim to undergo further upgrades which would provide very high rates of collisions (so-called High Luminosity LHC) which opens the possibility of measurements of the Higgs self-coupling and di-Higgs production.  This talk will anticipate these upgraded phases and the physics precision that they will yield, discussing projected expectations of experimental reach.

Ideas for other Higgs measurements

Dr Christoph Englert, University of Glasgow, UK

Abstract

In this talk I will review proposals to measure non-standard Higgs properties related exotic decays and non-doublet gauge representations that would also manifest in non-SM contributions to longitudinal gauge boson scattering unitarisation. I will discuss examples of how to improve and complement current measurement strategies through exploiting new analysis techniques and BSM interference effects in Standard Model Higgs production processes. The described programme not only provides an opportunity to phenomenologically gain insights into the mechanism of electroweak symmetry breaking itself, but also allows to establish a "no-hide" theorem for natural extensions of the Standard Model through precision analyses at a future lepton collider.

Precision calculations for the LHC

Professor Nigel Glover FRS, Durham University, UK

Abstract

I review recent progress and developments in precision calculations for benchmark and multiparticle processes at the Large Hadron Collider.  Particular attention will be given to perturbative QCD calculations at next-to-leading order, next-to-next-to-leading order and beyond.

Prospects for measurements of Higgs boson pair production and the HHH self-coupling

Dr James Ferrando, University of Glasgow, UK

Abstract

In this talk, prospects for measurements of Higgs boson pair production at the LHC and future colliders will be reviewed. Particular attention will be paid to the sensitivity of such measurements to the Higgs self-coupling. Measuring the Higgs self-coupling is important to establish the Higgs mechanism as being responsible for electroweak symmetry breaking.

Vector Boson scattering

Dr Chiara Mariotti , INFN Torino, Italy

Abstract

Boson-boson scattering holds the key to electroweak symmetry breaking.  The identity of the Higgs boson comes from its role in the unitarization of the longitudinal boson scattering. Thus this measurement is necessary as a closure test of the Standard Model theory, and to determine the nature of the Higgs boson discovered at LHC.

The measurement of the vector boson scattering at LHC is very challenging, due to the presence of many other subprocesses that contribute to the 6-fermion final state, and because of the difficult experimental environment created by the expected very high pileup.

Recent studies will be reviewed and prospect for the measurements in the future runs will be presented.

Future circular colliders

Dr Michael Benedikt, CERN, Switzerland

Higgs physics at a future linear collider

Dr Mark Thomson, University of Cambridge, UK

Abstract

The International Linear Collider (ILC) is one of the main options for the next generation particle collider, possibly to be hosted in Japan. It will operate in the energy range 250-500 GeV, with the possibility of an upgrade to 1 TeV. The clean environment of a lepton collider will allow precise measurements of the properties of the Higgs boson. In this presentation, I will discuss the prospects for precise Higgs boson measurements at the ILC and how these measurements provide model-independent determinations of its couplings to fermions and gauge bosons with the precision of order 1 %. I will also discuss Higgs physics at CLIC, which is an option for a post-LHC electron-positron collider operating in the centre-of-mass range 350 GeV - 3 TeV.

HL-LHC status and detector upgrades

Professor Philip P Allport, University of Liverpool, UK

Abstract

Building on the spectacular successes of the LHC, the High-Luminosity LHC reflects planning to considerably extend the physics reach over that of the initially proposed LHC programme. The planned factor of 10 increase in accumulated data will bring: significantly improved precision measurements of the properties of the newly discovered Higgs boson, enhanced studies of rare processes including reaching sensitivity to key low rate decays of the Higgs, extended searches for physics beyond the Standard Model at the world’s highest energy facility and a broad programme of high precision measurements on the decays and properties of Standard Model particles. If further new particles are found when the LHC reaches its design energy, their masses will be such that the HL-LHC will also be needed to properly determine their properties. There is also scope for a rich programme of heavy ion collision physics with much increased statistics. The potential of this programme is recognised in the European Strategy for Particle Physics, published earlier this year https://cds.cern.ch/record/1551933/files/Strategy_Report_LR.pdf?version=1 and adopted at the special European Strategy Session of CERN Council in Brussels on 30th May 2013. In that document, the priorities are set for European particle physics taking account of the Higgs boson discovery at the LHC in 2012 and of the global frontier energy research landscape. This contains a key message for the HL-LHC programme: “Europe’s top priority should be the exploitation of the full potential of the LHC, including the high-luminosity upgrade of the machine and detectors with a view to collecting ten times more data than in the initial design, by around 2030. This upgrade programme will also provide further exciting opportunities for the study of flavour physics and the quark-gluon plasma.”

In this presentation, some of the key physics benefits of this programme are discussed, along with the status of the work towards realising the HL-LHC and meeting the severe challenges posed by the very high collision rates required to achieve the desired integrated luminosity.