5,644 research outputs found
Was the Higgs boson discovered?
The standard model has postulated the existence of a scalar boson, named the
Higgs boson. This boson plays a central role in a symmetry breaking scheme
called the Brout-Englert-Higgs mechanism (or the
Brout-Englert-Higgs-Guralnik-Hagen-Kibble mechanism, for completeness) making
the standard model realistic. However, until recently at least, the
50-year-long-sought Higgs boson had remained the only particle in the standard
model not yet discovered experimentally. It is the last but very important
missing ingredient of the standard model. Therefore, searching for the Higgs
boson is a crucial task and an important mission of particle physics. For this
purpose, many theoretical works have been done and different experiments have
been organized. It may be said in particular that to search for the Higgs boson
has been one of the ultimate goals of building and running the LHC, the world's
largest and most powerful particle accelerator, at CERN, which is a great
combination of science and technology. Recently, in the summer of 2012, ATLAS
and CMS, the two biggest and general-purpose LHC collaborations, announced the
discovery of a new boson with a mass around 125 GeV. Since then, for over two
years, ATLAS, CMS and other collaborations have carried out intensive
investigations on the newly discovered boson to confirm that this new boson is
really the Higgs boson (of the standard model). It is a triumph of science and
technology and international cooperation. Here, we will review the main results
of these investigations following a brief introduction to the Higgs boson
within the theoretical framework of the standard model and Brout-Englert-Higgs
mechanism as well as a theoretical and experimental background of its search.
This paper may attract interest of not only particle physicists but also a
broader audience.Comment: LateX, 23 pages, 01 table, 9 figures. To appear in Commun. Phys.
Version 2: Minor changes, two references adde
The International Linear Collider
In this article, we describe the key features of the recently completed
technical design for the International Linear Collider (ILC), a 200-500 GeV
linear electron-positron collider (expandable to 1 TeV) that is based on 1.3
GHz superconducting radio-frequency (SCRF) technology. The machine parameters
and detector characteristics have been chosen to complement the Large Hadron
Collider physics, including the discovery of the Higgs boson, and to further
exploit this new particle physics energy frontier with a precision instrument.
The linear collider design is the result of nearly twenty years of R&D,
resulting in a mature conceptual design for the ILC project that reflects an
international consensus. We summarize the physics goals and capability of the
ILC, the enabling R&D and resulting accelerator design, as well as the concepts
for two complementary detectors. The ILC is technically ready to be proposed
and built as a next generation lepton collider, perhaps to be built in stages
beginning as a Higgs factory.Comment: 41 page
Benefits to the U.S. from Physicists Working at Accelerators Overseas
We illustrate benefits to the U.S. economy and technological infrastructure
of U.S. participation in accelerators overseas. We discuss contributions to
experimental hardware and analysis and to accelerator technology and
components, and benefits stemming from the involvement of U.S. students and
postdoctoral fellows in global scientific collaborations. Contributed to the
proceedings of the Snowmass 2013 Community Summer Study.Comment: 23 pages, 1 figur
Complementarity of a Low Energy Photon Collider and LHC Physics
We discuss the complementarity between the LHC and a low energy photon
collider. We mostly consider the scenario, where the first linear collider is a
photon collider based on dual beam technology like CLIC.Comment: 29 pages, 37 figure, LP-200
The Compact Linear ee Collider (CLIC): Physics Potential
The Compact Linear Collider, CLIC, is a proposed ee collider at the
TeV scale whose physics potential ranges from high-precision measurements to
extensive direct sensitivity to physics beyond the Standard Model. This
document summarises the physics potential of CLIC, obtained in detailed
studies, many based on full simulation of the CLIC detector. CLIC covers one
order of magnitude of centre-of-mass energies from 350 GeV to 3 TeV, giving
access to large event samples for a variety of SM processes, many of them for
the first time in ee collisions or for the first time at all. The high
collision energy combined with the large luminosity and clean environment of
the ee collisions enables the measurement of the properties of Standard
Model particles, such as the Higgs boson and the top quark, with unparalleled
precision. CLIC might also discover indirect effects of very heavy new physics
by probing the parameters of the Standard Model Effective Field Theory with an
unprecedented level of precision. The direct and indirect reach of CLIC to
physics beyond the Standard Model significantly exceeds that of the HL-LHC.
This includes new particles detected in challenging non-standard signatures.
With this physics programme, CLIC will decisively advance our knowledge
relating to the open questions of particle physics.Comment: Input to the European Particle Physics Strategy Update on behalf of
the CLIC and CLICdp Collaboration
Testing Naturalness
Solutions to the electroweak hierarchy problem typically introduce a new
symmetry to stabilize the quadratic ultraviolet sensitivity in the self-energy
of the Higgs boson. The new symmetry is either broken softly or collectively,
as for example in supersymmetric and little Higgs theories. At low energies
such theories contain naturalness partners of the Standard Model fields which
are responsible for canceling the quadratic divergence in the squared Higgs
mass. Post the discovery of any partner-like particles, we propose to test the
aforementioned cancellation by measuring relevant Higgs couplings. Using the
fermionic top partners in little Higgs theories as an illustration, we
construct a simplified model for naturalness and initiate a study on testing
naturalness. After electroweak symmetry breaking, naturalness in the top sector
requires at leading order, where and
are the Higgs couplings to a pair of top quarks and top partners, respectively.
Using a multivariate method of Boosted Decision Tree to tag boosted particles
in the Standard Model, we show that, with a luminosity of 30 at a 100
TeV -collider, naturalness could be tested with a precision of 10 % for a
top partner mass up to 2.5 TeV.Comment: 20 pages, 7 figures, 2 table
Higgs Physics at future Linear Colliders - A Case for precise Vertexing
The discovery of a Higgs boson by the experiments at the LHC marks a major
breakthrough in particle physics, with far-reaching consequences for our
understanding of the fundamental principles of our Universe. To fully explore
this unique particle, experiments at high-energy electron-positron colliders
are being planned, providing substantial added benefit over the capabilities of
the LHC alone, such as model-independent measurements of couplings, constraints
on invisible decays and precise measurements of the self-coupling. This
contribution summarizes the Higgs physics program at such future facilities,
highlighting in particular also the role of precise vertexing in achieving the
ambitious goals of these experiments.Comment: 9 pages, 4 figures, to be published in the proceedings of the 22nd
International Workshop on Vertex Detectors VERTEX 2013, Lake Starnberg,
Germany, September 2013, v2 updated references. arXiv admin note: substantial
text overlap with arXiv:1211.724
A Staged Muon-Based Neutrino and Collider Physics Program
We sketch a staged plan for a series of muon-based facilities that can do
compelling physics at each stage. Such a plan is unique in its ability to span
both the Intensity and Energy Frontiers as defined by the P5 sub-panel of the
US High Energy Physics Advisory Committee. This unique physics reach places a
muon-based facility in an unequaled position to address critical questions
about the nature of the Universe.Comment: Contribution to the CERN Council Open Symposium on European Strategy
for Particle Physics, 10-12 Sept. 2012, Krakow, Polan
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