37 research outputs found
Impact of Resonance on Thermal Targets for Invisible Dark Photon Searches
Dark photons in the MeV to GeV mass range are important targets for
experimental searches. We consider the case where dark photons decay
invisibly to hidden dark matter through . For generic masses,
proposed accelerator searches are projected to probe the thermal target region
of parameter space, where the particles annihilate through in the early universe and freeze out with the correct relic density.
However, if , dark matter annihilation is resonantly
enhanced, shifting the thermal target region to weaker couplings. For degeneracies, we find that the annihilation cross section is generically
enhanced by four (two) orders of magnitude for scalar (pseudo-Dirac) dark
matter. For such moderate degeneracies, the thermal target region drops to weak
couplings beyond the reach of all proposed accelerator experiments in the
scalar case and becomes extremely challenging in the pseudo-Dirac case.
Proposed direct detection experiments can probe moderate degeneracies in the
scalar case. For greater degeneracies, the effect of the resonance can be even
more significant, and both scalar and pseudo-Dirac cases are beyond the reach
of all proposed accelerator and direct detection experiments. For scalar dark
matter, we find an absolute minimum that sets the ultimate experimental
sensitivity required to probe the entire thermal target parameter space, but
for pseudo-Dirac fermions, we find no such thermal target floor.Comment: 17 pages, 2 figures; v2: improved agreement with existing
non-resonant results, added extensive discussion of implications for direct
detection experiment
Dark Photons from the Center of the Earth: Smoking-Gun Signals of Dark Matter
Dark matter may be charged under dark electromagnetism with a dark photon
that kinetically mixes with the Standard Model photon. In this framework, dark
matter will collect at the center of the Earth and annihilate into dark
photons, which may reach the surface of the Earth and decay into observable
particles. We determine the resulting signal rates, including Sommerfeld
enhancements, which play an important role in bringing the Earth's dark matter
population to their maximal, equilibrium value. For dark matter masses 100 GeV - 10 TeV, dark photon masses MeV - GeV, and kinetic
mixing parameters , the resulting
electrons, muons, photons, and hadrons that point back to the center of the
Earth are a smoking-gun signal of dark matter that may be detected by a variety
of experiments, including neutrino telescopes, such as IceCube, and space-based
cosmic ray detectors, such as Fermi-LAT and AMS. We determine the signal rates
and characteristics, and show that large and striking signals---such as
parallel muon tracks---are possible in regions of the
plane that are not probed by direct detection, accelerator experiments, or
astrophysical observations.Comment: 26 pages, 10 figures. v2: minor revisions to match published version;
v3: updated direct detection and CMB constraints and corrected decay length
in code, moving the region of experimental sensitivity to values of epsilon
that are lower by an order of magnitud
Protophobic Fifth-Force Interpretation of the Observed Anomaly in \u3csup\u3e8\u3c/sup\u3eBe Nuclear Transitions
Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e+e− pairs produced in 8Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, 8Be∗ → 8Be X, and then decays through X → e+e−. The X boson mediates a fifth force with a characteristic range of 12 fm and has millicharged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon’s anomalous magnetic moment
Protophobic Fifth-Force Interpretation of the Observed Anomaly in \u3csup\u3e8\u3c/sup\u3eBe Nuclear Transitions
Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e+e− pairs produced in 8Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, 8Be∗ → 8Be X, and then decays through X → e+e−. The X boson mediates a fifth force with a characteristic range of 12 fm and has millicharged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon’s anomalous magnetic moment
FASER: ForwArd Search ExpeRiment at the LHC
FASER, the ForwArd Search ExpeRiment, is a proposed experiment dedicated to
searching for light, extremely weakly-interacting particles at the LHC. Such
particles may be produced in the LHC's high-energy collisions in large numbers
in the far-forward region and then travel long distances through concrete and
rock without interacting. They may then decay to visible particles in FASER,
which is placed 480 m downstream of the ATLAS interaction point. In this work,
we describe the FASER program. In its first stage, FASER is an extremely
compact and inexpensive detector, sensitive to decays in a cylindrical region
of radius R = 10 cm and length L = 1.5 m. FASER is planned to be constructed
and installed in Long Shutdown 2 and will collect data during Run 3 of the 14
TeV LHC from 2021-23. If FASER is successful, FASER 2, a much larger successor
with roughly R ~ 1 m and L ~ 5 m, could be constructed in Long Shutdown 3 and
collect data during the HL-LHC era from 2026-35. FASER and FASER 2 have the
potential to discover dark photons, dark Higgs bosons, heavy neutral leptons,
axion-like particles, and many other long-lived particles, as well as provide
new information about neutrinos, with potentially far-ranging implications for
particle physics and cosmology. We describe the current status, anticipated
challenges, and discovery prospects of the FASER program.Comment: 13 pages, 4 figures, submitted as Input to the European Particle
Physics Strategy Update 2018-2020 and draws on FASER's Letter of Intent,
Technical Proposal, and physics case documents (arXiv:1811.10243,
arXiv:1812.09139, and arXiv:1811.12522
Technical Proposal for FASER: ForwArd Search ExpeRiment at the LHC
FASER is a proposed small and inexpensive experiment designed to search for
light, weakly-interacting particles during Run 3 of the LHC from 2021-23. Such
particles may be produced in large numbers along the beam collision axis,
travel for hundreds of meters without interacting, and then decay to standard
model particles. To search for such events, FASER will be located 480 m
downstream of the ATLAS IP in the unused service tunnel TI12 and be sensitive
to particles that decay in a cylindrical volume with radius R=10 cm and length
L=1.5 m. FASER will complement the LHC's existing physics program, extending
its discovery potential to a host of new, light particles, with potentially
far-reaching implications for particle physics and cosmology.
This document describes the technical details of the FASER detector
components: the magnets, the tracker, the scintillator system, and the
calorimeter, as well as the trigger and readout system. The preparatory work
that is needed to install and operate the detector, including civil
engineering, transport, and integration with various services is also
presented. The information presented includes preliminary cost estimates for
the detector components and the infrastructure work, as well as a timeline for
the design, construction, and installation of the experiment.Comment: 82 pages, 62 figures; submitted to the CERN LHCC on 7 November 201
FASER's Physics Reach for Long-Lived Particles
FASER,the ForwArd Search ExpeRiment,is a proposed experiment dedicated to
searching for light, extremely weakly-interacting particles at the LHC. Such
particles may be produced in the LHC's high-energy collisions and travel long
distances through concrete and rock without interacting. They may then decay to
visible particles in FASER, which is placed 480 m downstream of the ATLAS
interaction point. In this work we briefly describe the FASER detector layout
and the status of potential backgrounds. We then present the sensitivity reach
for FASER for a large number of long-lived particle models, updating previous
results to a uniform set of detector assumptions, and analyzing new models. In
particular, we consider all of the renormalizable portal interactions, leading
to dark photons, dark Higgs bosons, and heavy neutral leptons (HNLs); light B-L
and gauge bosons; axion-like particles (ALPs) that are coupled
dominantly to photons, fermions, and gluons through non-renormalizable
operators; and pseudoscalars with Yukawa-like couplings. We find that FASER and
its follow-up, FASER 2, have a full physics program, with discovery sensitivity
in all of these models and potentially far-reaching implications for particle
physics and cosmology