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Eder Izaguirre

Publications and source records attributed to Eder Izaguirre.

At least 19 recordsLinked to original sources
arXiv2019

The Platinum Channel: Higgs Decays to as many as 8 Leptons

We propose a search for Higgs decays with as many as eight leptons in the final state. This signal can arise in a simple model with a hidden vector ($A_d$) that gets mass via a hidden scalar ($h_d$) vacuum expectation value. The 125 GeV Higgs can then decay $H\rightarrow h_d h_d \rightarrow 4A_d\rightarrow 8f$, where $f$ are Standard Model fermions. We recast current searches and show that a branching ratio of $H\rightarrow h_dh_d$ as large as 10% is allowed. We also describe a dedicated search that could place bounds on BR($H\rightarrow h_dh_d$) as low as $10^{-5}$ using only 36 fb$^{-1}$ of data, with significant improvements coming from greater integrated luminosity.

hep-ph↗
arXiv2018

Testing Light Dark Matter Coannihilation With Fixed-Target Experiments

In this paper, we introduce a novel program of fixed-target searches for thermal-origin Dark Matter (DM), which couples inelastically to the Standard Model. Since the DM only interacts by transitioning to a heavier state, freeze-out proceeds via coannihilation and the unstable heavier state is depleted at later times. For sufficiently large mass splittings, direct detection is kinematically forbidden and indirect detection is impossible, so this scenario can only be tested with accelerators. Here we propose new searches at proton and electron beam fixed-target experiments to probe sub-GeV coannihilation, exploiting the distinctive signals of up- and down-scattering as well as decay of the excited state inside the detector volume. We focus on a representative model in which DM is a pseudo-Dirac fermion coupled to a hidden gauge field (dark photon), which kinetically mixes with the visible photon. We define theoretical targets in this framework and determine the existing bounds by reanalyzing results from previous experiments. We find that LSND, E137, and BaBar data already place strong constraints on the parameter space consistent with a thermal freeze-out origin, and that future searches at Belle II and MiniBooNE, as well as recently-proposed fixed-target experiments such as LDMX and BDX, can cover nearly all remaining gaps. We also briefly comment on the discovery potential for proposed beam dump and neutrino experiments which operate at much higher beam energies.

hep-ph↗
arXiv2017

Rare $Z$ Boson Decays to a Hidden Sector

We demonstrate that rare decays of the Standard Model $Z$ boson can be used to discover and characterize the nature of new hidden-sector particles. We propose new searches for these particles in soft, high-multiplicity leptonic final states at the Large Hadron Collider. The proposed searches are sensitive to low-mass particles produced in $Z$ decays, and we argue that these striking signatures can shed light on the hidden-sector couplings and mechanism for mass generation.

hep-ph↗
arXiv2017

A New Flavor of Searches for Axion-Like Particles

We propose new searches for axion-like particles (ALPs) produced in flavor-changing neutral current (FCNC) processes. This proposal exploits the often-overlooked coupling of ALPs to W bosons, leading to FCNC production of ALPs even in the absence of a direct coupling to fermions. Our proposed searches for resonant ALP production in decays such as $B\rightarrow K^{(*)}a,\,a\rightarrow γγ$ and $K\rightarrow πa, \,a\rightarrow γγ$ could greatly improve upon the current sensitivity to ALP couplings to Standard Model particles. We also determine analogous constraints and discovery prospects for invisibly decaying ALPs.

hep-ph↗
arXiv2016

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.

hep-ph↗
arXiv2016

A Letter of Intent to Install a milli-charged Particle Detector at LHC P5

In this LOI we propose a dedicated experiment that would detect "milli-charged" particles produced by pp collisions at LHC Point 5. The experiment would be installed during LS2 in the vestigial drainage gallery above UXC and would not interfere with CMS operations. With 300 fb$^{-1}$ of integrated luminosity, sensitivity to a particle with charge $\mathcal{O}(10^{-3})~e$ can be achieved for masses of $\mathcal{O}(1)$ GeV, and charge $\mathcal{O}(10^{-2})~e$ for masses of $\mathcal{O}(10)$ GeV, greatly extending the parameter space explored for particles with small charge and masses above 100 MeV.

physics.ins-det↗
arXiv2016

Illuminating New Electroweak States at Hadron Colliders

In this paper, we propose a novel powerful strategy to perform searches for new electroweak states. Uncolored electroweak states appear in generic extensions of the Standard Model (SM) and yet are challenging to discover at hadron colliders. This problem is particularly acute when the lightest state in the electroweak multiplet is neutral and all multiplet components are approximately degenerate. In this scenario, production of the charged fields of the multiplet is followed by decay into nearly invisible states; if this decay occurs promptly, the only way to infer the presence of the reaction is through its missing energy signature. Our proposal relies on emission of photon radiation from the new charged states as a means of discriminating the signal from SM backgrounds. We demonstrate its broad applicability by studying two examples: a pure Higgsino doublet and an electroweak quintuplet field.

hep-ph↗
arXiv2015

Discovering Inelastic Thermal-Relic Dark Matter at Colliders

Dark Matter particles with inelastic interactions are ubiquitous in extensions of the Standard Model, yet remain challenging to fully probe with existing strategies. We propose a series of powerful searches at hadron and lepton colliders that are sensitive to inelastic dark matter dynamics. In representative models featuring either a massive dark photon or a magnetic dipole interaction, we find that the LHC and BaBar could offer strong sensitivity to the thermal-relic dark matter parameter space for dark matter masses between ~100 MeV-100 GeV and fractional mass-splittings above the percent level; future searches at Belle II with a dedicated monophoton trigger could also offer sensitivity to thermal-relic scenarios with masses below a few GeV. Thermal scenarios with either larger masses or splittings are largely ruled out; lower masses remain viable yet may be accessible with other search strategies.

hep-ph↗
arXiv2015

MeV-Scale Dark Matter Deep Underground

We demonstrate that current and planned underground neutrino experiments could offer a powerful probe of few-MeV dark matter when combined with a nearby high-intensity low-to-medium energy electron accelerator. This experimental setup, an underground beam-dump experiment, is capable of decisively testing the thermal freeze-out mechanism for several natural dark matter scenarios in this mass range. We present the sensitivity reach in terms of the mass-coupling parameter space of existing and planned detectors, such as Super-K, SNO+, and JUNO, in conjunction with a hypothetical 100 MeV energy accelerator. This setup can also greatly extend the sensitivity of direct searches for new light weakly-coupled force-carriers independently of their connection to dark matter.

hep-ph↗
arXiv2015

Looking for milli-charged particles with a new experiment at the LHC

We propose a new experiment at the Large Hadron Collider (LHC) that offers a powerful and model-independent probe for milli-charged particles. This experiment could be sensitive to charges in the range $10^{-3}e - 10^{-1}e$ for masses in the range $0.1 - 100$ GeV, which is the least constrained part of the parameter space for milli-charged particles. This is a new window of opportunity for exploring physics beyond the Standard Model at the LHC.

hep-ph↗
arXiv2015

A Milli-Window to Another World

The kinetic mixing of the vector boson of hypercharge with the vector boson(s) associated with particle sectors beyond the Standard Model is one of the best motivated windows to new physics. The resulting phenomenology depends on whether the new vector boson is massive or massless. The phenomenology associated with the massive phase has received considerable attention in recent years with many theoretical explorations and new experimental efforts, while the massless phase is linked to the phenomenology of milli-charged particles. In this paper we introduce the more general case where the kinetic mixing is with a vector boson that is a linear combination of both a massive and a massless state (as hypercharge is in the Standard Model). We demonstrate that the general phase is only weakly constrained when the mass scale associated with it is above about 100 MeV. Finally, we show that a new dedicated experiment at the LHC, proposed recently in Ref. [1], can explore large parts of the parameter space in the mass range between 100 MeV and 100 GeV. In particular, it is uniquely sensitive to a new signature that only arises in the general phase.

hep-ph↗
arXiv2015

Testing GeV-Scale Dark Matter with Fixed-Target Missing Momentum Experiments

We describe an approach to detect dark matter and other invisible particles with mass below a GeV, exploiting missing energy-momentum measurements and other kinematic features of fixed-target production. In the case of an invisibly decaying MeV-GeV-scale dark photon, this approach can improve on present constraints by 2-6 orders of magnitude over the entire mass range, reaching sensitivity as low as $ε^2\sim 10^{-14}$. Moreover, the approach can explore essentially all of the viable parameter space for thermal or asymmetric dark matter annihilating through the vector portal.

hep-ph↗
arXiv2015

Accelerating the Discovery of Light Dark Matter

We analyze the present status of sub-GeV thermal dark matter annihilating through Standard Model mixing and identify a small set of future experiments that can decisively test these scenarios.

hep-ph↗
arXiv2015

A facility to Search for Hidden Particles at the CERN SPS: the SHiP physics case

This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (Search for Hidden Particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, $τ\to 3μ$ and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the Standard Model and describe interactions between new particles and four different portals - scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the Standard Model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation

hep-ph↗
arXiv2015

Multilepton and Lepton Jet Probes of Sub-Weak-Scale Right-Handed Neutrinos

We propose new searches that exploit the unique signatures of decaying sterile neutrinos with masses below $M_W$ at the LHC, where they can be produced in rare decays of Standard Model gauge bosons. We show that for few-GeV-scale sterile neutrinos, the LHC experiments can probe mixing angles at the level of $10^{-4}-10^{-3}$ through powerful searches that look for prompt leptons in association with displaced lepton jets. For higher-mass sterile neutrinos, ${\it i.e.}$, $M_N \gtrsim 15$ GeV, Run II can explore similarly small mixing angles in prompt multilepton final states. This represents an improvement of up to two orders of magnitude in sensitivity to the sterile neutrino production rate.

hep-ph↗
arXiv2015

Strong Optimized Conservative Fermi-LAT Constraints on Dark Matter Models from the Inclusive Photon Spectrum

We set conservative, robust constraints on the annihilation and decay of dark matter into various Standard Model final states under various assumptions about the distribution of the dark matter in the Milky Way halo. We use the inclusive photon spectrum observed by the Fermi Gamma-ray Space Telescope through its main instrument, the Large-Area Telescope (LAT). We use simulated data to first find the "optimal" regions of interest in the gamma-ray sky, where the expected dark matter signal is largest compared with the expected astrophysical foregrounds. We then require the predicted dark matter signal to be less than the observed photon counts in the a priori optimal regions. This yields a very conservative constraint as we do not attempt to model or subtract astrophysical foregrounds. The resulting limits are competitive with other existing limits, and, for some final states with cuspy dark-matter distributions in the Galactic Center region, disfavor the typical cross section required during freeze-out for a weakly interacting massive particle (WIMP) to obtain the observed relic abundance.

hep-ph↗
arXiv2015

A New Observable for Identifying Dijet Resonances

The development of techniques for identifying hadronic signals from the overwhelming multi-jet backgrounds is an important part of the Large Hadron Collider (LHC) program. Of prime importance are resonances decaying into a pair of partons, such as the Higgs and $\rm W$/$\rm Z$ bosons, as well as hypothetical new particles. We present a simple observable to help discriminate a dijet resonance from background that is effective even when the decaying resonance is not strongly boosted. We find consistent performance of the observable over a variety of processes and degree of boosts, and show that it leads to a reduction of the background by a factor of $3-5$ relative to signal at the price of $10-20\%$ signal efficiency. This approach represents a significant increase in sensitivity for Standard Model (SM) measurements and searches for new physics that are dominated by systematic uncertainties, which is true of many analyses involving jets - particularly in the high-luminosity running of the LHC.

hep-ph↗