33 research outputs found
Complementary constraints on couplings at the LHC
We propose a new strategy to probe the boson couplings to bottom and
charm quarks at the LHC. In this work we mainly focus on the case of bottom
quarks. Here, the boson is produced in association with two -jets and
decays to electrons or muons. In this final state, tagging the charge of the
-jets allows us to measure the charge asymmetry and thus to directly probe
the couplings. The leptonic final state not only allows us to
cleanly reconstruct the boson but also to mitigate the otherwise
overwhelming backgrounds. Furthermore, while LEP could only scan a limited
range of dilepton invariant masses, there is no such limitation at the LHC.
Consequently, this allows us to make full use of the interference between the
amplitudes mediated by a boson and a photon. Using the full high-luminosity
LHC dataset of and with the current flavor and
charge-tagging capabilities would allow us to reject the wrong-sign
right-handed coupling solution by 4. Further improving the
charge-tagging efficiency would disfavor it by 6.Comment: 18 + 8 pages, 9 figure
Higgs Boson Properties at Colliders
Since its discovery at the large hadron collider (LHC) in 2012, the Higgs boson and its properties are under intense investigation from both theorists and experimentalists. As the only scalar particle in the Standard Model (SM), the Higgs is believed to be closely related to the nature of electroweak symmetry breaking and the mass generation of fundamental massive particles. Respectively, they manifest as the couplings between the Higgs to the massive bosons (gauge couplings) and the Higgs to the massive fermions (Yukawa couplings). Thus, measurements of the Higgs sector properties are highly motivated either to confirm our current theory, the standard model, or to reveal possible new theories.
With the ongoing effort at the LHC, the Higgs is studied through various production and decay channels. However at a hadron collider, the large background and the ignorance of the partonic center of mass energy make testing many parameters of the Higgs sector challenging. For this dissertation I studied Higgs processes at a lepton collider, explored mass determination abilities for certain processes at a lepton collider and also studied the challenging Higgs decay to light jets at the LHC. These studies suggest new observables to improve our sensitivity to the Higgs sector and to constrain possible new physics deviations.
In order, I present in Chapter 1 an introduction of the Standard Model Higgs and its detection at colliders. Chapter 2 details the study on Higgs production through the ZZ fusion process at the lepton collider and the measurement of the inclusive rate. Our study improves the prospecting sensitivities on the standard model couplings, and puts further constraints on dimension-6 effective operators which are generic in quantifying beyond standard model (BSM) deviations. Chapter 3 describes the Higgs to light jets decays through the boosted Vh associated production at the LHC. Extrapolation of sensitivities on small Yukawa couplings at the hadron collider are discussed and achieved. Chapter 4 presents another study on linear collider, further exploring its many advantages on kinematic reconstruction and precision measurement
Confronting the fourth generation two Higgs doublet model with the phenomenology of heavy Higgs bosons
A sequential fourth generation is known to be excluded because the
non-decoupling contribution to , the Higgs coupling modifier with a
gluon pair, is unacceptably large. Recently a new way to save the model was
suggested in the Type-II two Higgs doublet model: if the Yukawa couplings of
down-type fermions have wrong-sign, the contributions from and to
are cancelled. We study the theoretical and experimental constraints
on this model, focusing on the heavy Higgs bosons. Two constraining features
are pointed out. First the exact wrong-sign limit does not allow the alignment,
which makes the perturbative unitarity for the scalar-scalar scattering put the
upper bounds on the heavy Higgs boson masses like GeV
and GeV. Secondly, the Yukawa couplings of the fourth
generation fermions to the heavy Higgs bosons are generically large as being
proportional to the heavy fermion mass and, for the down-type fermions, to
as well. The gluon fusion productions of and through the
fourth generation quark loops become significant. We found that the current LHC
data on for along with the theoretical and indirect
constraints exclude the model at leading order.Comment: 30 pages with 17 figure
Exploring dynamical CP violation induced baryogenesis by gravitational waves and colliders
By assuming a dynamical source of CP violation, the tension between
sufficient CP violation for successful electroweak baryogenesis and strong
constraints from current electric dipole moment measurements could be
alleviated. We study how to explore such scenarios through gravitational wave
detection, collider experiments, and their possible synergies with a
well-studied example.Comment: Published version in Physical Review D, 30 pages, 7 figures, and 3
table
Probing New Physics by the Tail of the Off-shell Higgs in Mode
Off-shell Higgs at the high mass tail may shed light on the underlying
mechanism of the electroweak symmetry breaking. Due to the large cancellation
in the standard model (SM) between the box and Higgs-mediated triangle
diagrams, the process in the SM is dominated by the
transverse-mode at the high mass tail. The cancellation does not necessarily
hold, when there is a sufficiently large new physics contribution resulting in
longitudinal mode, which is commonly the case when the Higgs sector is
modified. Thus the final states in the high mass tail can be utilized
as a sensitive probe for such models. In the paper we focus on a study of the
process in the fully leptonic decay modes, proposing to utilize the
polarization modes of the off-shell Higgs to probe new physics, whose
contribution mainly shows in the longitudinal mode. As examples, we analyze
three different Higgs sector new physics cases (Higgs portal with a light
scalar, a broad-width scalar that mixes with the Higgs, and quantum critical
Higgs models), and demonstrate that the angular information relating to the
polarization serves as very sensitive probe for such new physics.Comment: 6 pages, 2 figures, 1 tabl
Electroweak corrections to Higgs boson production via Z Z fusion at the future LHeC
An important mechanism for production of the Higgs boson at the prospective
Large Hadron-electron Collider (LHeC) is via neutral current (NC) weak boson
fusion (WBF) processes. Aside from its role in measurements of Higgs couplings
within the standard model, this production mode is particularly useful in
searchings of Higgs decays into invisble particles in various models for the
Higg portal dark matter. In this work we compute the electroweak corrections
for the NC WBF at the LHeC up to the 1-loop level. For a center-of-mass energy
of 1.98 TeV, the magnitudes of the relative corrections for the total cross
section at next-to-leading (NLO) order are respectively 8% and 17%, in the two
renormalization schemes we use. The NLO terms also distort various
distributions (notably, those for Higgs and electron observables) computed at
the leading order. Along with our previous treatment of the charge current
processes, this paper completes the calulation of the NLO EW effects for the
dominant Higgs production modes at the LHeC.Comment: 14 pages, 10 figures. arXiv admin note: text overlap with
arXiv:2207.1451
Precision Higgs physics at the CEPC
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
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.Comment: 46 pages, 37 figure
Complementary constraints on couplings at the LHC
We propose a new strategy to probe the boson couplings to bottom and charm quarks at the LHC. In this work we mainly focus on the case of bottom quarks. Here, the boson is produced in association with two -jets and decays to electrons or muons. In this final state, tagging the charge of the -jets allows us to measure the charge asymmetry and thus to directly probe the couplings. The leptonic final state not only allows us to cleanly reconstruct the boson but also to mitigate the otherwise overwhelming backgrounds. Furthermore, while LEP could only scan a limited range of dilepton invariant masses, there is no such limitation at the LHC. Consequently, this allows us to make full use of the interference between the amplitudes mediated by a boson and a photon. Using the full high-luminosity LHC dataset of and with the current flavor and charge-tagging capabilities would allow us to reject the wrong-sign right-handed coupling solution by 4. Further improving the charge-tagging efficiency would disfavor it by 6