# Berkeley Workshop on Dark Matter Detection

chaired by , ,
from to (US/Pacific)
at Lawrence Berkeley National Laboratory ( Building 50 Auditorium )
1 Cyclotron Road, Berkeley CA 94720
 Description LBNL's Institute for Nuclear and Particle Astrophysics (INPA) and UC Berkeley's BEPP Center (Berkeley Experimental Particle Physics) are pleased to announce the Berkeley Workshop on Dark Matter Detection to take place June 8-9, 2015 in the LBNL, Building 50 Auditorium. The theme for the 2015 workshop will be Dark Matter detection beyond G2 - new ideas and directions.  The workshop will: Review and update the theoretical models for matter and highlight additional potential targets; Review the current status of dark matter searches and the anticipated reach of the G2 experiments; Provide an opportunity to present new ideas, technology advances, and novel techniques for future experiments. Registration: For workshop registration, email Melissa Barclay at mbarclay@berkeley.edu
Go to day
• Monday, 8 June 2015
• 08:00 - 08:15 Welcome 15'  Speaker: Kevin Lesko (LBNL) Material:
• 08:15 - 09:00 Beyond the WIMP: theory overview 45'  Speaker: Kathryn Zurek (LBNL) Material:
• 09:00 - 09:30 Effective Field Theory and WIMP Observables 30'
This talk will cover two applications of effective field theory techniques for WIMP dark matter observables.  The first example is the use of Soft-Collinear Effective Theory to improve the convergence of perturbation theory when calculating the annihilation rate of heavy WIMPs to line photons.  This has implications for the interpretation of data from experiments such as H.E.S.S. as applied to constraining minimal WIMP models such as the thermal Wino.  The second case will be a discussion of the benefits and pitfalls of the contact operator approach to collider searches for WIMP dark matter.  Particular attention will be paid to the comparison between these limits and direct detection experiments in the context of Simplified Model UV completions.
 Speaker: Timothy Cohen (University of Oregon) Material:
• 09:30 - 10:00 keV sterile neutrinos and Q balls: status update 30'  Speaker: Alexander Kusenko (UCLA) Material:
• 10:00 - 10:15 Break
• 10:15 - 10:45 Direct Detection Signatures of Self-Interacting Dark Matter with a Light Mediator 30'
Self-interacting dark matter (SIDM) is motivated by new ideas in hidden sector model building and astrophysical puzzles on galactic and sub-galactic scales. This talk will discuss current constraints from LUX and SuperCDMS on a simple SIDM model and prospects to distinguish the interactions of SIDM with nuclei from contact interactions.
 Speaker: Manoj Kaplinghat (UC Irvine) Material:
• 10:45 - 11:15 New Avenues to Search for sub-GeV Dark Matter 30'
Dark matter with MeV to GeV masses is a theoretically and phenomenologically appealing possibility.  In this talk, I will provide a broad overview of the motivation, models, constraints, and novel searches for such dark matter.  I will focus on how direct detection experiments can probe this largely unexplored mass range and present several search strategies.  A particularly promising possibility is that dark matter scatters off electrons, causing ionization of atoms in a detector target material, which can lead to single- or few-electron events.  I will review existing constraints from XENON10 data, and discuss how other experiments like SuperCDMS and DAMIC, as well as new dedicated experiments, could significantly improve the sensitivity.  I will also discuss several other search strategies for sub-GeV dark matter, including colliders, high-intensity fixed-target experiments, and indirect detection.
 Speaker: Rouven Essig (Stony Brook University) Material:
• 11:15 - 11:45 Status of the LUX and LZ Programs 30'
The LUX (Large Underground Xenon) and upcoming LZ (LUX-ZEPLIN) experiments are two-phase xenon time projection chambers, optimized for observing coherent scattering of WIMPs off xenon nuclei.  Existing results from the initial LUX exposure (April to August 2013, 85.3 live-days with a fiducial mass of 118 kg) will be reviewed.  The design of the next-generation LZ detector (~7000 kg active mass) will be presented, along with the expected backgrounds and projected sensitivity.
 Speaker: Scott Hertel (Yale University) Material:
• 11:45 - 12:15 Status of SuperCDMS Soudan and Plans for SuperCDMS SNOLAB 30'
The SuperCDMS experiment at Soudan is coming to a close, with a successful run of over a decade of very good control of backgrounds at low thresholds. The lessons learned and the technologies developed will be utilized in the recently approved SuperCDMS SNOLAB experiment.This talk will review recent SuperCDMS Soudan results and present plans for the SNOLAB experiment.
 Speaker: Rupak Mahapatra (Texas A&M) Material:
• 12:15 - 13:00 Lunch at the Cafeteria ( LBNL Cafeteria )
• 13:00 - 13:30 DM@LHC 30'
I will review results of searches for DM from Run1 and the plans for Run2 and discuss interpretations.
 Speaker: Maria Spiropulu (Caltech)
• 13:30 - 14:00 Hunting the Dark Matter Axion with the ADMX Experiment 30'
The nature of dark matter is one of the great mysteries of modern physics. Its existence has been inferred by gravitational effects over many distance scales but currently no known particle can account for the observed data. As a result, new particles beyond the standard model have been suggested. The Axion, originally conceived as a solution to the strong-CP problem in nuclear physics, is one well-motivated candidate. The Axion Dark Matter eXperiment (ADMX), and its sister experiment ADMX-High Frequency (ADMX-HF), are designed to detect axions by using large microwave cavities immersed in a strong magnetic field to resonantly convert the axions into detectable photons. In this talk I will describe the history of axion searches and the ADMX experiment in particular, which ran at Lawrence Livermore National Laboratory (LLNL) for over a decade before being moved to the University of Washington (UW). I will then discuss the upgrades to the ADMX experiment as it prepares for it’s upcoming search with orders of magnitude greater sensitivity. I will also outline R&D efforts that are currently being undertaken to expand the search range of ADMX further and ultimately determine if axions are or are not, the major dark matter component of the Universe.
 Speaker: Gianpaolo Carosi (LLNL) Material:
• 14:00 - 14:30 Improving the Energy Sensitivity of Massive Calorimeters to Search for Light Mass Dark Matter 30'
The kinetic energy transferred to nuclei during elastic scattering with a light mass dark matter candidate (100MeV-5GeV) is below the experimental energy threshold of current generation direct detection experiments and consequently, vast unexplored areas of parameter space could become accessible over the next decade with significant improvements in the sensitivity of large mass calorimeters.
In this talk, we discuss the progress made in achieving these sensitivity improvements in calorimeters over the past year and why we believe an additional 2 orders of magnitude improvement in energy sensitivity will be achievable over the next decade.
 Speaker: Matt Pyle (UC Berkeley) Material:
• 14:30 - 15:00 Break
• 15:00 - 15:30 Status of the KIMS Experiment 30'
Since DAMA's claim on the detection of an annual modulation signature, several experiments were performed to find such a signal. Yet, unambiguous confirmation using the NaI(Tl) crystal has not been established. The Korea Invisible Mass Search (KIMS) program plans to confirm or dispute the claim using the same type of NaI(Tl) crystals with a similar technique. The KIMS-NaI experiment aims to achieve a background level better than what DAMA reported, by reaching less than 1 count/kg/keV/day at energies around 2 keV. In this workshop, we present preliminary R&D results for six NaI(Tl) crystals tested within the existing CsI(Tl) array at the YangYang underground laboratory. Then, the next step towards the construction of a 200 kg NaI(Tl) array will be discussed.

 Speaker: Chang Hyon Ha (Institute for Basic Science, Korea) Material:
• 15:30 - 16:00 SABRE—Test of DAMA/LIBRA Using NaI(Tl) 30'
For over a decade, the DAMA Collaboration has been observing a rate modulation in a large array of high purity NaI(Tl) crystal detectors at LNGS, which may be explained by dark matter interactions. This observation is both significant and controversial. Several experiments have claimed to rule out DAMA/LIBRA as evidence for dark matter, but these tests were made based on dark matter halo models and dark matter-matter interaction models that are currently unknown. Therefore, the SABRE Collaboration plans to carry out an unambiguous test of DAMA/LIBRA by using NaI(Tl) crystals with the lower residual background than that of DAMA/LIBRA. I will report the development of ultra-high purity SABRE NaI(Tl) crystals, the study of NaI(Tl) scintillation efficiency under Na nuclear recoils, and the progress of SABRE toward testing DAMA/LIBRA.
 Speaker: Jingke Xu (Princeton) Material:
• 16:00 - 16:30 New Directions in Searching for the Dark Universe 30'
Ultra-light bosonic fields such as axions and massive vector bosons are natural dark matter candidates. These candidates are difficult to detect in conventional dark matter scattering experiments since they deposit small amounts of energy and have highly suppressed interaction cross-sections. However, they have a large number density and can be better described as classical fields. This classical field oscillates at a frequency equal to the mass of the dark matter, which in many cases is at frequencies ~ Hz - GHz that are accessible in the laboratory. These oscillations induce a variety of time dependent phenomena such as nucleon dipole moments that lead to spin precession. This spin precession can be observed through precision magnetometry. In other cases, the dark matter leads to time varying accelerations on nucleons and electrons, which can be observed through precision resonators and accelerometers.
 Speaker: Surjeet Rajendran (UC Berkeley) Material:
• 16:30 - 17:00 Hidden Photon Dark Matter 30'
A hidden photon -- a new, light vector boson coupling to the electromagnetic current -- is a natural extension to the Standard Model which may provide the dark matter of the universe. I will review several promising avenues for detecting hidden photons, including a "dark matter radio" experiment currently being planned at SLAC. I will also review how the hidden photon's abundance may be generated by inflationary fluctuations, imprinting a distinctive spectrum potentially observable in direct detection experiments.
 Speaker: Jeremy Mardon (Stanford) Material:
• 17:00 - 17:30 Searching for keV Sterile Neutrino Dark Matter with X-ray Microcalorimeter Sounding Rockets 30'
High-resolution X-ray spectrometers onboard suborbital sounding rockets can search for dark matter candidates that produce X-ray lines, such as decaying keV-scale sterile neutrinos. Even with exposure times and effective areas far smaller than XMM and Chandra observations, high-resolution, wide field-of-view observations with sounding rockets have competitive sensitivity to decaying sterile neutrinos. We analyze a subset of the 2011 observation by the XQC instrument, and show that better sensitivity is achievable with future observations of the galactic center by the Micro-X instrument, providing a definitive test of the sterile neutrino interpretation of the reported 3.56 keV excess from galaxy clusters.
 Speaker: Enectali Figueroa-Feliciano (MIT) Material:
• 17:30 - 18:00 Atom-interferometry constraints on dark energy theories 30'
If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field, it might be detectable with normal-matter objects. The simplest such models would lead to a fifth force in conflict with results from experiments using macroscopic test masses such as torsion balances [1]. These constraints on fifth forces can be easily evaded through a variety of screening mechanisms in the presence of typical laboratory matter densities. However, dilute atoms in an ultra-high vacuum environment can serve as ideal test masses which avoid this screening [2]. In our recently developed optical cavity atom interferometer [3] we place new limits [4] on anomalous accelerations at millimeter scale distances from a spherical source mass. These limits rule out a large parameter range of scalar field theories, such as chameleons, which would be consistent with the cosmological dark energy density. With further improvements in sensitivity, atom interferometry will be able to rule out many scalar field dark energy theories with coupling strengths up to the Planck mass.
 Speaker: Philipp Haslinger (UC Berkeley) Material:
• 18:00 - 18:30 Contingency time
• Tuesday, 9 June 2015
• 08:00 - 08:30 Coffee
• 08:30 - 09:00 Towards the ultimate ionization threshold in semiconductor detectors 30'
A number of particle and astroparticle physics searches provide the motivation to develop semiconductor detectors with thresholds sensitive to single- or few-electron ionization events.  Borrowing from experience gained with noble-liquid detectors used in the search for dark matter, I discuss an idea for a novel semiconductor detector design that could allow the long sought-after single electron ionization threshold to be reached with relatively simple and mature technologies.  Several potential challenges and features will be discussed, along with possible benchmark tests that could be used to easily validate this technique.
 Speaker: Aaron Manalaysay (UC Davis) Material:
• 09:00 - 09:30 Beyond DarkSide-50: Very Large Argon TPCs for Heavy WIMP Searches 30'
The DarkSide program aims at detecting weakly interacting particle dark matter using dual-phase Liquid Argon Time Projection Chambers (LAr TPC) of increasing sensitivity, down to the so-called “atmospheric neutrino floor”.  One of the distinctive features of the program is the use of underground argon with significantly lower 39Ar than atmospheric argon.

The first detector of the program, DarkSide-50 (DS-50) is running at LNGS since 2013. It is the first detector of its kind with a large (30 tonnes), liquid scintillator neutron veto and water Cherenkov (1,000 tonnes) muon veto concentrically enveloping the dark matter target.  An initial 1,422 kg*day exposure run with atmospheric argon yielded a null result of the dark matter search and zero background from radioactive sources.   Operations with underground argon started in March 2015, and indicate a >300-fold reduction of 39Ar relative to atmospheric argon. The background levels combined with its demonstrated background rejection capability point to a possible background-free exposure of 1 tonne-yr for DS-50.

We will review the DS-50 results and illustrate its physics reach.  We will present the future of the DarkSide program: the 20-tonne DS-20k experiment, and the 200-tonne Argo concept.  DS-20k is designed for a background-free exposure of 100 tonne-years, with a projected sensitivity to WIMP-nucleon cross section of better than 10-47 cm2 for WIMPs of mass 1 TeV/c2, a mass scale of special interest because above the reach of the LHC.  Argo is conceived to reach an exposure of 1,000 tonne-years free of background, with the exception of nuclear recoil events induced by atmospheric neutrinos, and a WIMP-nucleon cross section sensitivity of better than 10-48 cm2 for WIMPs of mass 1 TeV/c2.

Other auxiliary ideas will be discussed as time allows.

 Speaker: Andrea Pocar (Univ. Mass.) Material:
• 09:30 - 10:00 Searching for New Short Range Forces Using Optically Levitated Microspheres 30'
We are developing novel techniques to search for new forces at micron length scales using optically levitated dielectric microspheres in vacuum.  At high vacuum, dissipation of the microsphere's motion due to residual gas collisions becomes small, allowing sub-attonewton force sensitivity.  As a first demonstration of these techniques, we have performed a search for stable, millicharged particles bound in the microspheres.  It is possible that such millicharged particles are a component of the universe's dark matter.  These techniques can also enable extremely sensitive searches for new forces that couple to mass or charge at short distance.  Such forces can arise in hidden sector dark matter models containing dark photons or light millicharged particles, or as exchange forces from new light scalars.  We will describe the experimental apparatus, the results from the search for millicharged particles, and the expected sensitivity of searches for non-Newtonian and non-Coulombic forces at micron length scales.

 Speaker: David Moore (Stanford) Material:
• 10:00 - 10:30 Dark Matter Detection with Kinetic Inductance Detectors 30'
Kinetic inductance detectors (KIDs) are a highly multiplexable and potentially highly sensitive technology for detecting phonons produced by dark-matter induced low-energy nuclear recoils.  I discuss some possible KID-based dark matter detector architectures and progress to date on using KIDs in phonon-mediated detectors.
 Speaker: Sunil Golwala (Caltech) Material:
• 10:30 - 10:45 Break
• 10:45 - 11:15 Light Noble Gases for Light Dark Matter Detection 30'
Liquid helium-4 is an attractive target material for a future generation dark matter search, taking advantage of the favorable kinematic matching of the helium-4 nucleus to light dark matter particles. Calculations will be presented on nuclear recoil signal strengths and electron recoil background rejection efficiency, using cross-sections for ionization and electronic excitation that are available in the published literature. Liquid helium detector schemes using prompt scintillation (S1) and proportional scintillation (S2) will be presented. Also considered is the possibility of doping liquid xenon with neon or helium, thereby combining self-shielding with efficient excitation production, and potentially allowing enhanced sensitivity to light dark matter particles.

 Speaker: Dan McKinsey (UC Berkeley) Material:
• 11:15 - 11:45 Superfluid Helium: a Unique Detector Material for Low Energies 30'
Like other liquid nobles, helium is easily purified and scaled, and incident radiation is expressed as paired scintillation and ionization.  In a superfluid state, helium adds to these standard signals with several unique 'messenger' excitations.  All of these messengers should be observable with high efficiency and low thresholds using another of helium's unique traits: its compatibility with mK-scale calorimetric readout.  In addition to describing the general possibilities of superfluid helium as a detector material, some recent R&D work at Yale will be shown, demonstrating the calorimetric detection of one of those new helium 'messengers': long-lived He2* triplet excimers.
 Speaker: Scott Hertel (Yale University) Material:
• 11:45 - 12:15 Large-size germanium detectors with low-energy threshold and n/g discrimination at 77K for dark matter 30'
We intend to establish a global Collaboration for developing germanium (Ge) detectors and technologies to be used for direct detection of dark matter and neutrino properties. Led by the University of South Dakota, the Collaboration involves five universities, one private sector company, and three government supported labs. Our goals are to: (1) develop novel Ge detectors for next generation experiments at the ton-scale with low-energy threshold and neutron/gamma (n/γ) discrimination and (2) increase knowledge and ultimately advance frontier physics education and training for undergraduate STEM majors, graduate students, post-docs, and early career faculty. The Collaboration will leverage best-in-class facilities, resources and expertise in the United States, China, Germany, France, Italy, and Taiwan to accomplish the following objectives: (1) develop research techniques in zone refinement and crystal growth to guarantee the purity and uniformity of large-size (up to 15 cm in diameter) detector-grade crystals; (2) create innovative planar Ge detectors with low-energy thresholds (<100 eV) and n/γ discrimination for dark matter, neutrino-nucleus coherent scattering, neutrino magnetic moment and milli-charged neutrinos; (3) improve electron/gamma discrimination and segmentation for neutrinoless double-beta decay (0νββ); and (4) accelerate education and training for young scientists.
 Speaker: Dongming Mei (USD) Material:
• 12:15 - 12:45 Scintillating Bubble Chambers for Direct Dark Matter Detection 30'
The scintillating bubble chamber has the potential to be an incredibly powerful new tool for dark matter detection.  Combining the world-leading electron recoil rejection of a bubble chamber with the energy information available in a liquid scintillator, these devices should achieve unprecedented discrimination against all backgrounds while working with a variety of target materials.  New possibilities include Xenon-based detectors with 10^10 discrimination against electron recoils, argon-based detectors with discrimination down to few-keVr (or even sub-keVr) thresholds, and organic and fluorinated-organic scintillator detectors immune to the alpha-induced backgrounds that likely limit existing bubble chamber experiments.  We'll present progress by groups at SUNY Albany and Northwestern University towards the world's first working scintillating bubble chambers, starting with liquid Xenon targets.  With the potential to cover spin-dependent, spin-independent, and low-mass WIMPs, and the scalability already demonstrated by both bubble chambers and liquid scintillators, this technology could rapidly become a contender for G3 dark matter searches.
 Speakers: Jeremy Mock (SUNY Albany and LBL), Jianjie Zhang (Northwestern University) Material:
• 12:45 - 13:45 Lunch