1,970 research outputs found
Decays of the Littlest Higgs Z_H and the Onset of Strong Dynamics
The Little Higgs mechanism, as realized in various models, requires a set of
new massive gauge bosons, some of which mix with gauge bosons of the Standard
Model. For a range of mixing angles the coupling of gauge bosons to scalars can
become strong, ultimately resulting in a breakdown of perturbative calculation.
This phenomenon is studied in the Littlest Higgs model, where the approach to
strong dynamics is characterized by increasing tree-level decay widths of the
neutral Z_H boson to lighter gauge bosons plus multiple scalars. These
increasing widths suggest a distinctive qualitative collider signature for the
approach to the strong coupling regime of large Higgs and other scalar
multiplicities. In this work we catalog the kinematically allowed three-body
decays of the Z_H, and calculate the partial width of the process Z_H to Z_L H
H. This partial width is found to be larger than the comparable two-body decay
Z_H to Z_L H for values of the SU(2) mixing angle cosine(theta) less than 0.13,
indicating divergence of the littlest Higgs sigma field expansion at values of
cosine(theta) larger than a simple parametric calculation would suggest.
Additionally, we present analytical expressions for all two-body decays of the
Littlest Higgs Z_H gauge boson, including the effects of all final-state
masses
M: A New Muon Missing Momentum Experiment to Probe and Dark Matter at Fermilab
New light, weakly-coupled particles are commonly invoked to address the
persistent anomaly in and serve as mediators between
dark and visible matter. If such particles couple predominantly to heavier
generations and decay invisibly, much of their best-motivated parameter space
is inaccessible with existing experimental techniques. In this paper, we
present a new fixed-target, missing-momentum search strategy to probe invisibly
decaying particles that couple preferentially to muons. In our setup, a
relativistic muon beam impinges on a thick active target. The signal consists
of events in which a muon loses a large fraction of its incident momentum
inside the target without initiating any detectable electromagnetic or hadronic
activity in downstream veto systems. We propose a two-phase experiment, M
(Muon Missing Momentum), based at Fermilab. Phase 1 with muons
on target can test the remaining parameter space for which light
invisibly-decaying particles can resolve the anomaly, while Phase 2
with muons on target can test much of the predictive parameter
space over which sub-GeV dark matter achieves freeze-out via muon-philic
forces, including gauged .Comment: 28 pages, 11 figures, 2 appendice
DISCOVERY AND CHARACTERIZATION OF A HIGGS-LIKE RESONANCE USING THE MATRIX ELEMENT LIKELIHOOD APPROACH
Understanding the exact mechanism of electroweak symmetry breaking through
the discovery and characterization of the Higgs boson is one of the primary goals of
the Large Hadron Collider (LHC). Two searches for a Higgs boson decaying to a pair
of Z bosons with subsequent decays to either 2l2q or 4l are presented using data
recorded with the Compact Muon Solenoid (CMS). The discovery and characteriza-
tion of a Higgs-like resonance using a new set of tools is reported. The foundations of
such tools are developed and prospects for their use in other Higgs channels and at
future colliders are addressed. Although the Standard Model (SM) of electroweak in-
teractions has been extremely successful in describing a number of phenomena, there
are still questions to be addressed pertaining to its naturalness and its possible con-
nection to beyond the SM physics. Results are interpreted in the context of possible
extensions to the SM and their effect on our understanding of the universe
New Searches for Muonphilic Particles at Proton Beam Dump Spectrometers
We introduce a new search strategy for visibly decaying muonphilic particles
using a proton beam spectrometer modeled after the SpinQuest experiment at
Fermilab. In this setup, a 100 GeV primary proton beam impinges on a
thick fixed target and yields a secondary muon beam. As these muons traverse
the target material, they scatter off nuclei and can radiatively produce
hypothetical muonphilic particles as initial- and final-state radiation. If
such new states decay to dimuons, their combined invariant mass can be measured
with a downstream spectrometer immersed in a Tesla-scale magnetic field. For a
representative setup with muons on target with typical
energies of 20 GeV, a invariant mass resolution, and an effective
100 cm target length, this strategy can probe the entire parameter space for
which 200 MeV -- GeV scalar particles resolve the muon anomaly. We
present sensitivity to these scalar particles at the SpinQuest experiment where
no additional hardware is needed and the search could be parasitically executed
within the primary nuclear physics program. Future proton beam dump experiments
with optimized beam and detector configurations could have even greater
sensitivity.Comment: v2: references added. v1: 16 pages, 11 figure
Recommended from our members
New searches for muonphilic particles at proton beam dump spectrometers
We introduce a new search strategy for visibly decaying muonphilic particles using a proton beam spectrometer modeled after the SpinQuest experiment at Fermilab. In this setup, a primary proton beam impinges on a thick fixed target and yields a secondary muon beam. As these muons traverse the target material, they scatter off nuclei and can radiatively produce hypothetical muonphilic particles as initial- and final-state radiation. If such new states decay to dimuons, their combined invariant mass can be measured with a downstream spectrometer immersed in a Tesla-scale magnetic field. For a representative setup with muons on target with typical energies of , a 15% invariant mass resolution, and an effective 100 cm target length, this strategy can probe the entire parameter space for which scalar particles resolve the muon anomaly. We present sensitivity to these scalar particles at the SpinQuest experiment where no additional hardware is needed and the search could be parasitically executed within the primary nuclear physics program. Future proton beam dump experiments with optimized beam and detector configurations could have even greater sensitivity
US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report
This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in
Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
A high efficiency photon veto for the Light Dark Matter eXperiment
Fixed-target experiments using primary electron beams can be powerful discovery tools for light dark matter in the sub-GeV mass range. The Light Dark Matter eXperiment (LDMX) is designed to measure missing momentum in high-rate electron fixed-target reactions with beam energies of 4 GeV to 16 GeV. A prerequisite for achieving several important sensitivity milestones is the capability to efficiently reject backgrounds associated with few-GeV bremsstrahlung, by twelve orders of magnitude, while maintaining high efficiency for signal. The primary challenge arises from events with photo-nuclear reactions faking the missing-momentum property of a dark matter signal. We present a methodology developed for the LDMX detector concept that is capable of the required rejection. By employing a detailed Geant4-based model of the detector response, we demonstrate that the sampling calorimetry proposed for LDMX can achieve better than 10⁻¹³ rejection of few-GeV photons. This suggests that the luminosity-limited sensitivity of LDMX can be realized at 4 GeV and higher beam energies
A high efficiency photon veto for the Light Dark Matter eXperiment
Fixed-target experiments using primary electron beams can be powerful discovery tools for light dark matter in the sub-GeV mass range. The Light Dark Matter eXperiment (LDMX) is designed to measure missing momentum in high-rate electron fixed-target reactions with beam energies of 4 GeV to 16 GeV. A prerequisite for achieving several important sensitivity milestones is the capability to efficiently reject backgrounds associated with few-GeV bremsstrahlung, by twelve orders of magnitude, while maintaining high efficiency for signal. The primary challenge arises from events with photo-nuclear reactions faking the missing-momentum property of a dark matter signal. We present a methodology developed for the LDMX detector concept that is capable of the required rejection. By employing a detailed Geant4-based model of the detector response, we demonstrate that the sampling calorimetry proposed for LDMX can achieve better than 10⁻¹³ rejection of few-GeV photons. This suggests that the luminosity-limited sensitivity of LDMX can be realized at 4 GeV and higher beam energies
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