Hidden Sector Photons Research Articles

The Heavy Photon Search (HPS) Software Environment

The Heavy Photon Search (HPS) is an experiment at the Thomas Jefferson National Accelerator Facility (JLab) designed to search for a hidden sector photon (A’) in fixed-target electro-production. It uses a silicon microstrip tracking and vertexing detector placed inside a dipole magnet to measure charged particle trajectories and a fast lead-tungstate crystal calorimeter located just downstream of the magnet to provide a trigger and to identify electromagnetic showers. The HPS experiment uses both invariant mass and secondary vertex signatures to search for the A’. The experimental collaboration is small and quite heterogeneous: it is composed of members of the nuclear physics as well as particle physics communities, from universities and national labs from around the US and Europe. Enabling such a disparate group to concentrate on the physics aspects of the experiment required that the software be easy to install and use, and having such limited manpower meant that existing solutions had to be exploited.HPS has successfully completed two engineering runs and completed its first physics run in the summer of 2019. We begin with an overview of the physics goals of the experiment followed by a short description of the detector design. We then describe the software tools used to design the detector layout and simulate the expected detector performance. Event reconstruction involving track, cluster and vertex finding and fitting for both simulated and real data was, to first order, adopted from existing software originally developed for Linear Collider studies. Bringing it all together into a cohesive whole involved the use of multiple software solutions with common interfaces.

Cross-Correlation Signal Processing for Axion and WISP Dark Matter Searches.

The search for dark matter is of fundamental importance to our understanding of the universe. Weakly interacting slim particles (WISPs) such as axions and hidden sector photons are well-motivated candidates for the dark matter. Some of the most sensitive and mature experiments to detect WISPs rely on microwave cavities, and the detection of weak photon signals. It is often suggested to power combine multiple cavities, which creates a host of technical concerns. We outline a scheme based on cross correlation for power combining cavities and increasing the signal-to-noise ratio of a candidate WISP signal.

Dark matter axion clump resonance of photons

Recently there has been interest in the physical properties of dark matter axion condensates. Due to gravitational attraction and self-interactions, they can organize into spatial localized clumps, whose properties were examined by us in refs. [1, 2]. Since the axion condensate is coherently oscillating, it can conceivably lead to parametric resonance of photons, leading to exponential growth in photon occupancy number and subsequent radio wave emission. We show that while resonance always exists for spatially homogeneous condensates, its existence for a spatially localized clump condensate depends sensitively on the size of clump, strength of axion-photon coupling, and field amplitude. By decomposing the electromagnetic field into vector spherical harmonics, we are able to numerically compute the resonance from clumps for arbitrary parameters. We find that for spherically symmetric clumps, which are the true BEC ground states, the resonance is absent for conventional values of the QCD axion-photon coupling, but it is present for axions with moderately large couplings, or into hidden sector photons, or from scalar dark matter with repulsive interactions. We extend these results to non-spherically symmetric clumps, organized by finite angular momentum, and find that even QCD axion clumps with conventional couplings can undergo resonant decay for sufficiently large angular momentum. We discuss possible astrophysical consequences of these results, including the idea of a pile-up of clump masses and rapid electromagnetic emission in the sky from mergers.

Scalar dark matter clumps with angular momentum

The behavior of light scalar dark matter has been a subject of much interest recently as it can lead to interesting small scale behavior. In particular, this can lead to the formation of gravitationally bound clumps for these light scalars, including axions. In ref. [1] we analyzed the behavior of these clumps, assuming spherical symmetry, allowing for both attractive and repulsive self-interactions. There is a maximum allowed mass for the clumps in the case of attractive interactions, and a minimum radius for the clumps in the case of repulsive interactions, which is saturated at large mass. Here we extend this work to include non-spherically symmetric clumps. Since the system tries to re-organize into a BEC ground state, we consider configurations with a conserved non-zero angular momentum, and construct minimum energy configurations at fixed particle number and fixed angular momentum. We find generalizations of the previous spherically symmetric results. In particular, while there is still a maximum mass for the attractive case, its value increases with angular momentum. Also, the minimum radius in the repulsive case is raised to higher radii. We clarify how a recent claim in the literature of an upper bound on angular momentum is due to inaccurate numerics. In a forthcoming paper we shall investigate the possibility of resonance of axion clumps into both visible and hidden sector photons, and analyze how the altered mass and radius from non-zero angular momentum affects the resonance.

The Heavy Photon Search beamline and its performance

The Heavy Photon Search (HPS) is an experiment to search for a hidden sector photon, aka a heavy photon or dark photon, in fixed target electroproduction at the Thomas Jefferson National Accelerator Facility (JLab). The HPS experiment searches for the e+e− decay of the heavy photon with bump hunt and detached vertex strategies using a compact, large acceptance forward spectrometer, consisting of a silicon microstrip detector (SVT) for tracking and vertexing, and a PbWO4 electromagnetic calorimeter for energy measurement and fast triggering. To achieve large acceptance and good vertexing resolution, the first layer of silicon detectors is placed just 10cm downstream of the target with the sensor edges only 500μm above and below the beam. Placing the SVT in such close proximity to the beam puts stringent requirements on the beam profile and beam position stability. As part of an approved engineering run, HPS took data in 2015 and 2016 at 1.05GeV and 2.3GeV beam energies, respectively. This paper describes the beam line and its performance during that data taking.

The Heavy Photon Search test detector

The Heavy Photon Search (HPS), an experiment to search for a hidden sector photon in fixed target electroproduction, is preparing for installation at the Thomas Jefferson National Accelerator Facility (JLab) in the Fall of 2014. As the first stage of this project, the HPS Test Run apparatus was constructed and operated in 2012 to demonstrate the experiment׳s technical feasibility and to confirm that the trigger rates and occupancies are as expected. This paper describes the HPS Test Run apparatus and readout electronics and its performance. In this setting, a heavy photon can be identified as a narrow peak in the e+e− invariant mass spectrum above the trident background or as a narrow invariant mass peak with a decay vertex displaced from the production target, so charged particle tracking and vertexing are needed for its detection. In the HPS Test Run, charged particles are measured with a compact forward silicon microstrip tracker inside a dipole magnet. Electromagnetic showers are detected in a PbW04 crystal calorimeter situated behind the magnet, and are used to trigger the experiment and identify electrons and positrons. Both detectors are placed close to the beam line and split top-bottom. This arrangement provides sensitivity to low-mass heavy photons, allows clear passage of the unscattered beam, and avoids the spray of degraded electrons coming from the target. The discrimination between prompt and displaced e+e− pairs requires the first layer of silicon sensors be placed only 10cm downstream of the target. The expected signal is small, and the trident background huge, so the experiment requires very large statistics. Accordingly, the HPS Test Run utilizes high-rate readout and data acquisition electronics and a fast trigger to exploit the essentially 100% duty cycle of the CEBAF accelerator at JLab.

Design and calibration of the 34 GHz Yale microwave cavity experiment

Several proposed models of the cold dark matter in the universe include light neutral bosons with sub-eV masses. In many cases their detection hinges on their infrequent interactions with Standard Model photons at sub-eV energies. We describe the design and performance of an experiment to search for aberrations from the broadband noise power associated with a 5K copper resonant cavity in the vicinity of 34GHz (0.1meV). The cavity, microwave receiver, and data reduction are described. Several configurations of the experiment are discussed in terms of their impact on the sensitivity of the search for axion-like particles and hidden sector photons.

Hidden-sector photon and axion searches using photonic band gap structures

Many proposed extensions of the standard model of particle physics predict the existence of weakly interacting sub-eV particles (WISPs) such as hidden-sector photons and axions, which are also of interest as dark matter candidates. In this paper we propose a novel experimental approach in which microwave photonic lattice structures form part of a ‘light shining through the wall’-type experiment to search for WISPs. We demonstrate the potential to match and exceed the sensitivities of conventional experiments operating in the microwave regime.

Cryogenic resonant microwave cavity searches for hidden sector photons

The hidden sector photon is a weakly interacting hypothetical particle with sub-eV mass that kinetically mixes with the photon. We describe a microwave frequency light shining through a wall experiment where a cryogenic resonant microwave cavity is used to try and detect photons that have passed through an impenetrable barrier, a process only possible via mixing with hidden sector photons. For a hidden sector photon mass of 53 $\mu$eV we limit the hidden photon kinetic mixing parameter $\chi < 1.7\times10^{-7}$, which is an order of magnitude lower than previous bounds derived from cavity experiments in the same mass range. In addition, we use the cryogenic detector cavity to place new limits on the kinetic mixing parameter for hidden sector photons as a form of cold dark matter.

First results of the CERN Resonant Weakly Interacting sub-eV Particle Search (CROWS)

The CERN Resonant WISP Search (CROWS) probes the existence of Weakly Interacting Sub-eV Particles (WISPs) like axions or hidden sector photons. It is based on the principle of an optical light shining through the wall experiment, adapted to microwaves. Critical aspects of the experiment are electromagnetic shielding, design and operation of low loss cavity resonators and the detection of weak sinusoidal microwave signals. Lower bounds were set on the coupling constant $g = 4.5 \cdot 10^{-8} $GeV$^{-1}$ for axion like particles with a mass of $m_a = 7.2 \mu$eV. For hidden sector photons, lower bounds were set for the coupling constant $\chi = 4.1 \cdot 10^{-9}$ at a mass of $m_{\gamma'} = 10.8 \mu$eV. For the latter we were probing a previously unexplored region in the parameter space.

Hidden sector photon coupling of resonant cavities

Many beyond the standard model theories introduce light paraphotons, a hypothetical spin-1 field that kinetically mixes with photons. Microwave cavity experiments have traditionally searched for paraphotons via transmission of power from an actively driven cavity to a passive receiver cavity, with the two cavities separated by a barrier that is impenetrable to photons. We extend this measurement technique to account for two-way coupling between the cavities and show that the presence of a paraphoton field can alter the resonant frequencies of the coupled cavity pair. We propose an experiment that exploits this effect and uses measurements of a cavities resonant frequency to constrain the paraphoton-photon mixing parameter, chi. We show that such an experiment can improve sensitivity to chi over existing experiments for paraphoton masses less than the resonant frequency of the cavity, and eliminate some of the most common systematics for resonant cavity experiments.

Microwave cavity hidden sector photon threshold crossing

Hidden sector photons are a weakly interacting slim particle arising from an additional U(1) gauge symmetry predicted by many standard model extensions. We present and demonstrate a new experimental method using a single microwave cavity to search for hidden sector photons. Only photons with a great enough energy are able to oscillate into hidden sector photons of a particular mass. If our cavity is driven on resonance and tuned over the corresponding threshold frequency, there is an observable drop in the circulating power signifying the creation of hidden sector photons. This approach avoids the problems of microwave leakage and frequency matching inherent in photon regeneration techniques.

Resonant regeneration in the sub-quantum regime – A demonstration of fractional quantum interference

Light shining through wall experiments (in the optical as well as in the microwave regime) are a powerful tool to search for light particles coupled very weakly to photons such as axions or extra hidden sector photons. Resonant regeneration, where a resonant cavity is employed to enhance the regeneration rate of photons, is one of the most promising techniques to improve the sensitivity of the next generation of experiments. However, doubts have been voiced if such methods work at very low regeneration rates where on average the cavity contains less than one photon. In this Letter we report on a demonstration experiment using a microwave cavity driven with extremely low power, to show that resonant amplification works also in this regime. In accordance with standard quantum mechanics this is a demonstration that interference also works at the level of less than one quantum. As an additional benefit this experiment shows that thermal photons inside the cavity cause no adverse effects.

Microwave cavity light shining through a wall optimization and experiment

It has been proposed that microwave cavities can be used in a photon regeneration experiment to search for hidden sector photons. Using two isolated cavities, the presence of hidden sector photons could be inferred from a ``light shining through a wall'' phenomenon. The sensitivity of the experiment has strong a dependence on the geometric construction and electromagnetic mode properties of the two cavities. In this paper we perform an in-depth investigation to determine the optimal setup for such an experiment. We also describe the results of our first microwave cavity experiment to search for hidden sector photons. The experiment consisted of two cylindrical copper cavities stacked axially inside a single vacuum chamber. At a hidden sector photon mass of $37.78\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$ we place an upper limit on the kinetic mixing parameter $\ensuremath{\chi}=2.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. Whilst this result lies within already established limits our experiment validates the microwave cavity ``light shining through a wall'' concept. We also show that the experiment has great scope for improvement, potentially able to reduce the current upper limit on the mixing parameter $\ensuremath{\chi}$ by several orders of magnitude.

Feasibility, engineering aspects and physics reach of microwave cavity experiments searching for hidden photons and axions

Using microwave cavities one can build a resonant ``microwave-shining-through-walls'' experiment to search for hidden sector photons and axion like particles, predicted in many extensions of the standard model. In this note we make a feasibility study of the sensitivities which can be reached using state of the art technology.

Probing hidden sector photons through the Higgs window

We investigate the possibility that a (light) hidden sector extra photon receives its mass via spontaneous symmetry breaking of a hidden sector Higgs boson, the so-called hidden-Higgs. The hidden-photon can mix with the ordinary photon via a gauge kinetic mixing term. The hidden-Higgs can couple to the standard model Higgs via a renormalizable quartic term---sometimes called the Higgs portal. We discuss the implications of this light hidden-Higgs in the context of laser polarization and light-shining-through-the-wall experiments as well as cosmological, astrophysical, and non-Newtonian force measurements. For hidden-photons receiving their mass from a hidden-Higgs, we find in the small mass regime significantly stronger bounds than the bounds on massive hidden sector photons alone.

On search for eV hidden-sector photons in Super-Kamiokande and CAST experiments

If light hidden sector photons (γ′s) exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical γ′-flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to the γ–γ′ mixing strength as small as 10−5≳χ≳10−9 for the γ′ mass region 10−4≲mγ′≲10−1 eV and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments for this mass region.

Laser experiments explore the hidden sector

Recently, the laser experiments BMV and GammeV, searching for light shining through walls, have published data and calculated new limits on the allowed masses and couplings for axionlike particles. In this paper we point out that these experiments can serve to constrain a much wider variety of hidden-sector particles such as, e.g., minicharged particles and hidden-sector photons. The new experiments improve the existing bounds from the older BFRT experiment by a factor of 2. Moreover, we use the new PVLAS constraints on a possible rotation and ellipticity of light after it has passed through a strong magnetic field to constrain pure minicharged particle models. For masses $\ensuremath{\lesssim}0.05\text{ }\text{ }\mathrm{eV}$, the charge is now restricted to be less than $(3\ensuremath{-}4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ times the electron electric charge. This is the best laboratory bound and comparable to bounds inferred from the energy spectrum of the cosmic microwave background.

A cavity experiment to search for hidden sector photons

We propose a cavity experiment to search for low mass extra U(1) gauge bosons with gauge-kinetic mixing with the ordinary photon, so-called paraphotons. The setup consists of two microwave cavities shielded from each other. In one cavity, paraphotons are produced via photon–paraphoton oscillations. The second, resonant, cavity is then driven by the paraphotons that permeate the shielding and reconvert into photons. This setup resembles the classic “light shining through a wall” setup. However, the high quality factors achievable for microwave cavities and the good sensitivity of microwave detectors allow for a projected sensitivity for photon–paraphoton mixing of the order of χ∼10−12–10−8, for paraphotons with masses in the μeV to meV range—exceeding the current laboratory and astrophysics-based limits by several orders of magnitude. Therefore, this experiment bears significant discovery potential for hidden sector physics.