Dark Interactions: Perspectives from Theory and Experiment

11 Jun 2014, 08:45 → 13 Jun 2014, 12:30 US/Eastern

Physics Department, Bldg. 510, Large Seminar Room (Brookhaven National Laboratory)

Ketevi Adikle Assamagan (BNL)

Back to Workshop

To review and discuss the theoretical context as well as the status and future of the searches for dark sector particles, such as dark vector bosons, and the implications for dark matter.

Topics or Session Information:

• Theoretical Motivation for Dark Sectors
• Experimental Constraints from High Energy Colliders
• Constraints from non-Collider Experiments
• Cosmological Constraints
• Implications for Dark Matter
• Prospects for LHC Run 2 and future Intensity Frontier Experiments

pictures DarkInteractionsWorkShopBNLJune11-13-2014.jpeg

Wednesday 11 June

08:45 → 09:00 Workshop Opening

Opening address and information for participants

Convener: Dr Howard Gordon (BNL)

slides 2013_overview_BNL_slides__Dark_Interactions.pptx

09:00 → 10:30 Theoretical Motivation

Theoretical motivation for dark interactions

09:00 Theoretical Motivation for New Weakly Coupled States (includes axions, sub-MeV dark photons, ALPs, etc.)

Speaker: Neal Weiner (NYU)

09:40 Theory and Phenomenology of Dark Vector Bosons

New physics can be light relative to the electroweak scale provided it couples very weakly to the Standard Model. An attractive and well-motivated example of this is a new dark vector boson. In this talk I will cover the theory of dark vectors with an emphasis on kinetic mixing with the photon and mass mixing with the Z boson. I will also touch briefly on the experimental implications of various dark vector models.

Speaker: David Morrissey (TRIUMF)

Slides darksec-bnl.key darksec-bnl.pdf

10:20 Discussion

10:30 → 11:00 Break

11:00 → 12:30 Low-energy Direct Searches for Dark Photons

Convener: Rouven Essig (Stony Brook University)

11:00 Dark Light

The DarkLight experiment aims to search for a dark photon in the low mass region 10-100 MeV/c^2. By using the Jefferson Lab FEL’s high-intensity 100 MeV, 1 MW electron beam incident on a gaseous hydrogen target, the process ep -> ep,e+/e- will be studied. To search for a dark photon, full track reconstruction of the four-particle final state will be performed in order to observe a resonance on the e+/e- invariant mass spectrum. The design of a detector suited to this task and the status of its development will be presented.

Speaker: Charles Epstein (MIT)

Slides DarkLight_BNL.pdf

11:20 APEX - The APrime EXperiment at Jefferson Lab

APEX is a fixed target experiment in Experimental Hall A at Thomas Jefferson National Accelerator Facility (JLab) in Virginia, USA, that is designed to search for a new gauge boson (A') with sub-GeV mass and coupling to ordinary matter of g'/e ~ (1 - 10^-4). Electrons impinge upon a fixed target of high-Z material to produce an A' via a process analogous to photon bremsstrahlung. The A' then decays to an e+e- pair that is detected by the JLab Hall A High Resolution Spectrometers. A test run was held in July of 2010, covering an A' mass range from 175 to 250 MeV and couplings g'/e > 10^-3. A full run is approved, with coverage projections of m_A' ~ 65 to 525 MeV and g'/e > 2.3 x 10^-4. The JLab accelerator facility is currently being upgraded to deliver 12 GeV beam. While the Hall A schedule has not yet been finalized, APEX will be ready to run soon after the completion of the upgrade and beam commissioning. I will present the results of the test run and report on the preparations for the full run.

Speaker: James Beacham (New York University)

Slides Beacham_APEX_BNL_DarkInteractions_2014June11.pdf

11:40 HPS -- The Heavy Photon Search Experiment at JLab

HPS is an new experiment at Jefferson Laboratory designed to look for hidden sector photons in the mass range 20 - 1000 MeV with couplings a'/a in the range 10-5 to 10-10. Presently under construction, HPS will be installed this fall in Hall B at JLab, commission thereafter, and take data in 2015. Heavy photons are identified as invariant mass bumps and as separated decay verticies. The apparatus is a compact forward spectrometer, using silicon microstrip detectors inside a dipole analyzing magnet for momentum measurement and vertexing, and a highly segmented PbWO4 crystal calorimeter for fast triggering and electron ID. Fast triggering and 40 Mz readout electronics perfectly exploit CEBAF 12's 100% duty cycle to deliver the high luminosities needed to probe small couplings. This talk will review the experimental challenges before HPS, solutions adopted in our design, status of the project, and our plans and prospects for widening the search for heavy photons to whole new regions of parameter space.

Speaker: John A Jaros (SLAC National Accelerator Laboratory)

Slides HPS_The_Heavy_Photon_Search_at_Jefferson_Laboratory_v1.pptx

12:00 Mainz MAMI

The A1 collaboration at the Mainz Microtron has concluded a pilot study in 2011 and data taking periods in 2012/2013 to search for a dark photon. The focus of the experiment was on the mass range between 50-200 MeV where dark matter provides a possible explanation for the discrepancy in the anomalous magnetic moment of the muon (g-2). The analysis is finished and the final exclusion limits will be presented. The Mainz search for a dark photon will continue as a part of the new MESA (Mainz Energy-recovering Superconducting Accelerator) project. In this talk, the present status of the detector and target design will be shown.

Speaker: Michael Distler (University Mainz, Germany)

Slides DistlerDI2014.pdf

12:20 Discussion

12:30 → 12:40 Workshop Group Photo

12:40 → 14:00 Lunch

14:00 → 15:30 Light (sub-GeV) Dark Matter

Convener: Oliver Keith Baker (Yale University)

14:00 Theory motivation for sub-GeV DM + searches at proton beam dumps

Speaker: Brian Batell (University of Chicago)

Slides batell-BNL.pdf

14:30 Electron Beam Dump Experiments

Speaker: Philip Schuster (Perimeter Institute)

Slides BNL_2014_LightDMTalk.pdf

14:55 Direct Detection Prospects

Speaker: Jeremy Mardon (Stanford)

Slides BNL_Dark_Interactions_6:11:2014.pdf

15:20 Discussion

15:30 → 16:00 Break

16:00 → 17:40 Dark Bosons at e^+e^- Colliders, Meson Decays, and Parity Violation

Convener: Marciano William (BNL)

16:00 Search for Dark Photons and Higgs at BaBar

Extensions to the Standard Model allow for new particles, including low-mass Higgs bosons and dark photons, that may bridge the Standard Model to the Dark Sector. We present recent results of searches for such particles in electron-positron annihilation with the BaBar Detector at the SLAC National Accelerator Laboratory. We also report briefly on a measurement of antideuteron production at BaBar, and comment on its significance for dark matter searches.

Speaker: Prof. David Brown (University of Louisville)

Slides DI2014_BaBar_Brown.pdf

16:20 Belle/Belle II

We will present a new Belle (preliminary) limit in the search for a dark photon, A, and a dark Higgs, h', with A and h' prompt, mh' > 2mA, 100 MeV < mA < 3.5 GeV and 200 MeV < mh' < 10.5 GeV. We will also discuss possible future contributions of Belle II to dark sector particle searches.

Speaker: Igal Jaegle (University of Hawaii at Manoa)

Slides darksearch.pdf

16:40 Meson-Decay Experiments

The dark photon couples to Standard Model particles via kinetic mixing, so it may be produced in SM processes and decay to SM particles. Experiments that are designed for precise measurements of meson decay and detection of rare meson decay have high-resolution detectors and large data samples, making them well suited to search for dark photons. I will describe limits on dark photons from pion, kaon, and phi decay at SINDRUM, WASA-at-COSY, KLOE, NA48/2, NA62, and E787/949. I will also describe limits from electron-positron annihilation in KLOE.

Speaker: Elizabeth Worcester (BNL)

Slides etw_mesons.pdf

17:00 PHENIX Searches for Low Mass Dark Photons

Several theoretical models introduce an additional U(1) gauge boson, a "dark photon" which mixes with ordinary QED photons with very small mixing strength. The dark photon is considered as one of the strongest candidates to describe some astrophysical anomalies as well as the 3sigma deviation of the experimental muon g-2 value from the Standard Model calculation. The dark photon as the cause for the muon g-2 anomaly gets more important because of recent SUSY search result at the LHC. Recently the PHENIX experiment at RHIC searched for the dark photon in pi0 and eta Dalitz decays. With both a very good mass resolution of the PHENIX detector and a high statistics sample of pure e+e- pairs from Dalitz decays, we obtain the world's best upper limits on the dark photon mixing parameter space for m_U between 30 and 90 MeV/c^2. In this talk, the latest PHENIX result will be shown.

Speaker: Yorito Yamaguchi (University of Tokyo)

Slides di2014_phenix.pdf

17:20 Muon g-2 and dark parity violation

Speaker: Dr Hye-Sung Lee (College of William and Mary / Jefferson Lab)

Slides Muon_g-2_and_Dark_Parity_Violation_(Dark_Interactions_2014).pdf

18:00 → 19:00 Workshop Reception

Thursday 12 June

09:00 → 10:40 Higgs Window into Dark Sectors

Convener: Dr Ketevi Adikle Assamagan (BNL)

09:00 Exotic Higgs Decays (theory, various models)

Exotic Higgs decays may be our main window to new physics. They are common and often well-motivated in various new physics scenarios, partly due to the small natural width of the Higgs. Some exotic decay modes are cascades resulting in high multiplicity of the final state, and are therefore potentially spectacular. Still, they could easily be missed, partly due to triggering thresholds. This strongly suggests new dedicated experimental searches to be performed. I will review the motivation and show current and prospective estimated reach at LHC for a few exotic decay modes.

Speaker: Ze'ev Surujon (Stony Brook University)

Slides exotichiggs_DarkInt.pdf

09:30 Higgs decays to exotic particles at CMS

The results of searches for invisible decays of the Higgs boson in the vector boson fusion and associated ZH production modes, where Z decays to a pair of charged leptons or a bbbar quark pair, are presented. Searches performed using data collected in proton-proton collisions at center-of-mass energies of 7 TeV and 8 TeV by the CMS experiment at the LHC. With no excess of the observed data over the expected Standard Model backgrounds, limits on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, are set. Assuming the Standard Model Higgs boson cross sections, the limit on the invisible branching fraction of the Higgs boson is set and interpreted in terms of Higgs-portal model of dark matter. In addition, a search for non-SM Higgs boson decays to a pair of new light bosons, each of which subsequently decays into a collimated pair of muons, is presented. The search is performed using data collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 8 TeV. Results are interpreted in a model independent fashion applicable to a broad class of models predicting the same signature as well as in the context of the SUSY with hidden dark sector.

Speaker: Aysen Tatarinov (Texas A&M University)

Slides 2014_06_12_tatarinov_v2.pdf

09:55 Higgs decays to exotic particles at ATLAS

The discovery of a Higgs-like particle in ATLAS and CMS at the Large Hadron Collider opened a rich and interesting range of opportunities for discovery of exotic decays, i.e. decays that involve new light states beyond the SM. A large class of simplified and complete models gives rise to peculiar patterns of exotic decays of the Higgs boson, patterns that the ATLAS experiment is exploring with several dedicated analysis. The status of such searches in the data collected during the Run 1 of LHC, at center of mass energies of 7 and 8 TeV, will be reviewed, together with the perspectives for the new run at higher energy that will start in 2015. Particular emphasis will be given to the most recent results involving the direct search for invisible Higgs decays, and the indirect constraints on new phenomena obtained from coupling measurements of the Higgs boson, and the interpretation of these constraints in the context of the Higgs portal model to Dark Matter. Results of the searches performed in ATLAS for decays of the Higgs boson in exotic particles like lepton jets in Hidden Valley models, and multi-Higgs boson cascade predicted by many models beyond the SM will be also illustrated.

Speaker: Stefano Giagu (Sapienza University of Rome)

Slides ExoticHiggsDecays_ATLAS_BNL_DarkInt14.pdf

10:20 Charged Higgs probes of dark bosons

We suggest top quark decays as a venue to search for light dark force carriers. The top quark is the heaviest particle in the standard model whose decays are relatively poorly measured, allowing sufficient room for exotic decay modes from new physics. A very light (GeV scale) dark gauge boson (Z') is a recently highlighted hypothetical particle that can address some astrophysical anomalies as well as the 3.6 sigma deviation in the muon g-2 measurement. We present and study a possible scenario that top quark decays as t -> b W + Z's. This is the same as the dominant top quark decay (t -> b W) accompanied by one or multiple dark force carriers. The Z' can be easily boosted, and it can decay into highly collimated leptons (lepton-jet) with large branching ratio. We discuss the implications for the Large Hadron Collider experiments including the analysis based on the lepton-jets.

Speaker: Kyoungchul Kong (University of Kansas)

Slides DI2014.pdf

10:40 → 11:10 Break

11:10 → 12:30 LHC Probes of Dark Sectors I

Convener: stephane willocq (University of Massachusetts)

11:10 Dark Matter searches at ATLAS

Numerous independent astrophysical experiments have observed and measured the influence of the phenomenon named Dark Matter, but its nature is still unknown. If the assumption that Dark Matter is a particle which has a weak coupling to the Standard Model is valid, then collider searches have the ability to search for the production of this new Weakly Interacting Massive Particle (WIMP). Any Dark Matter particles produced in collisions would escape the detector without being observed. Signatures which include an initial-state radiated particle balancing a large amount of Missing Transverse Momentum, known as mono-X topologies, provide a generic means of conducting Dark Matter searches. ATLAS has conducted several mono-X searches, including recoiling jets, photons, W/Z bosons which decay hadronically, and Z bosons which decay leptonically. Searches were carried out with centre of mass energies of both 7 and 8 TeV, and with up to 20/fb of data. No evidence for physics beyond the Standard Model is observed, and thus limits are placed on both Effective Field Theory models and Simplified Models of Dark Matter. These constraints are converted into bounds on WIMP-nucleon cross sections and WIMP annihilation cross-sections.

Speaker: Steven Schramm (University of Toronto)

Slides DarkMatterSearchesAtATLAS-Final.pdf

11:30 Dark Matter Searches at CMS

Speaker: Jordan Damgov (Texas Tech University)

Slides Dark14_MonoX_CMS_JDamgov.pdf

11:50 Searches for Hidden Valleys at ATLAS

Hidden Valley models contain a hidden sector that communicates with the Standard Model via a scalar. The hidden sector phenomenology is unconstrained. It can be as complex or simple as desired, and prompt or long lived. In this case we explore the ATLAS program to search for long lived versions of the Hidden Valley model. The benchmark model is fairly simple, produces two hidden valley pions that decay somewhere in the detector. Many theories may generate these signatures. ATLAS has three custom triggers designed to capture these events, which are described, as well as an analysis designed to look for the very long decay length items. Sensitivity after the upgrade will also be addressed.

Speaker: Gordon Watts (University of Washington)

Slides 2014-06-12_-_Dark_Interactions_-_Hidden_Valley_at_ATLAS.pptx

12:10 Searches for Hidden Valleys at CMS

Speaker: John Paul Chou (Rutgers University)

Slides DarkInteractionsWorkshop.pdf

12:30 → 14:00 Lunch

14:00 → 15:30 LHC Probes of Dark Sectors II

Convener: John Paul Chou (Rutgers University)

14:00 SUSY Dark Matter searches at CMS

In this talk I will discuss Implications of CMS Run 1 SUSY searches for the SUSY neutralino as a WIMP Dark Matter candidate

Speaker: Fedor Ratnikov (Inst. für Exp. Kernphysik)

Slides 140612_SUSY_DM2014_v2.pdf

14:20 SUSY Dark Matter searches at ATLAS

Supersymmetry provides an excellent dark matter candidate. SUSY searches at ATLAS are sensitive to an extensive range of scenarios with either a neutralino or a gravitino as the lightest supersymmetric particle. In this talk I will present the latest results from analyses carried out using the Run 1 dataset collected by ATLAS at the LHC at 8 TeV center of mass energy.

Speaker: Estel Perez Codina (TRIUMF)

Slides DarkInteractions_EstelPerez_v11.pdf

14:40 Search for exotic particles at LHCb

LHCb, located on the LHC, is a fully instrumented forward detector with flexible triggers, low pileup, and excellent secondary vertex resolution which make it an ideal experiment to search for unique exotic signals. A review of current LHCb exotic particle searches is given. Searches for the anomalous decays of B-mesons and tau-leptons are presented, as well as direct searches through central exclusive production, di-tau production, bbbar asymmetry, and displaced secondary vertices.

Speaker: James Philip Ilten (Massachusetts Institute of Technology)

Slides ilten_20140612.pdf

15:00 Dark Photon Searches at ALICE

ALICE is one of the largest experiments at the Large Hadron Collider at CERN and is designed to study the physics of strongly interacting matter at extreme high temperature and energy densities created in high-energy heavy ion collisions. ALICE has a good potential to search for a dark photon signal in pi0 and eta Dalitz decays, thanks to the excellent resolution of the tracking system and the high statistics of di-electrons pairs from Dalitz decays. The upgrade of the major ALICE detectors is foreseen to take place during the 2018 Long Shutdown (LS2). In this way, the experiment will fully exploit the high-luminosity Pb-Pb collisions provided by the LHC, recording events at a 50kHz rate. These conditions will significantly increase the dark photon search capabilities of ALICE. In this presentation, the current status of dark photon searches in the Run1 data sample will be shown and the expected constraints for the dark photon mixing parameter in the Run-2 and Run-3 conditions will be discussed.

Speaker: Taku Gunji (Center for Nuclear Study, the University of Tokyo)

Slides gunji_v2.pdf

15:20 Discussion

15:30 → 16:00 Break

16:00 → 17:30 Dark Matter and Dark Interactions

Convener: Tobias Golling (Yale University)

16:00 Dark Matter Direct Detections

Speaker: Kathryn Zurek (University of Michigan)

Slides 14_BNL_DarkInteractions.pdf

16:30 Dark matter annihilations in the Galactic Center

Past studies have identified a spatially extended excess of ~1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the emission expected from annihilating dark matter. Recent improvements in the analysis techniques have found this excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. For example, the signal is very well fit by a 31-40 GeV dark matter particle annihilating to b quarks with an annihilation cross section of sigma v = (1.7-2.3) x 10^-26 cm^3/s. Furthermore, the angular distribution of the excess is approximately spherically symmetric and centered around the dynamical center of the Milky Way (within ~0.05 degrees of Sgr A*), showing no sign of elongation along or perpendicular to the Galactic Plane. The signal is observed to extend to at least 10 degrees from the Galactic Center, disfavoring the possibility that this emission originates from millisecond pulsars.

Speaker: Dan Hooper (Fermilab)

Slides Hooper-Brookhaven-2014.pdf

17:00 CMB Constraints on Dark Matter Annihilation

The Cosmic Microwave Background (CMB) is a remarkably powerful and clean probe of dark matter annihilation. I will review the constraints from existing CMB and low-redshift data, and discuss future prospects from current and upcoming CMB experiments such as Planck and Advanced ACTpol. Many simple models designed to explain various indirect detection anomalies can be decisively tested with the CMB in the next few years.

Speaker: Neelima Sehgal (Stony Brook University)

Slides BNL_DI_CMB_DM.key.zip BNL_DI_CMB_DM.pdf

17:20 Discussion

18:30 → 21:30 Workshop Dinner

The Fifth Season
34 E. Broadway
Port Jefferson, NY

Friday 13 June

09:00 → 10:30 Axions and Axion-like particles

Convener: Dr Hong Ma (BNL)

09:00 Black hole portal into hidden valleys

I will discuss electromagnetic signals of black hole superradiance in the presence of an axion coupled to a hidden QCD-like sector.

Speaker: Sergei Dubovsky (New York University)

Slides HiddenBNL.pdf

09:30 ADMX

The axion is a well-motivated cold dark matter candidate first postulated to explain the absence of CP violation in strong interactions. Dark matter axions may be detected via their resonant conversion into photons in a high-Q microwave cavity permeated by a strong magnetic field. The Axion Dark Matter eXperiment (ADMX) has used this technique to exclude axion models in the few μeV mass range. Much of axion dark matter parameter space has until recently been beyond the reach of experiment, but advances in amplifier technology have enabled quantum-limited axion detection around 20 μeV (5 GHz); ADMX-HF (high-frequency), currently under construction at Yale University, will have sufficient sensitivity to probe this region of parameter space. This talk will cover the principles of the microwave cavity axion search and the status of current experiments, with a focus on ADMX-HF. I will also discuss R&D efforts by the ADMX-HF collaboration aimed at extending the microwave cavity technique to weaker couplings and higher frequencies.

Speaker: Benjamin Brubaker (Yale University)

Slides Brubaker_Dark_Interactions_Slides.pdf

09:55 Cosmic Axion Spin Precession Experiment (CASPEr)

We propose an experiment to search for QCD axion and axion-like-particle (ALP) dark matter. Nuclei that are interacting with the background axion dark matter acquire time-varying CP-odd nuclear moments such as an electric dipole moment. In analogy with nuclear magnetic resonance, these moments cause precession of nuclear spins in a material sample in the presence of a background electric field. This precession can be detected through high-precision magnetometry. With current techniques, this experiment has sensitivity to axion masses m_a <~ 10^(-9) eV, corresponding to theoretically well-motivated axion decay constants f_a >~ 10^16 GeV. With improved magnetometry, this experiment could ultimately cover the entire range of masses m_a <~ 10^(-6) eV, just beyond the region accessible to current axion searches.

Speaker: Surjeet Rajendran (Stanford)

Slides BNL.pdf

10:20 Discussion

10:30 → 11:00 Break

11:00 → 12:30 Cosmology and astrophysics

Convener: Dr Mary Bishai (Brookhaven National Laboratory)

11:00 Neutrinos and hidden physics (sterile neutrinos)

The existence of sterile neutrinos has been presented as an explanation for many anomalous results in experimental astro-particle physics. This talk will discuss existing experimental indications for eV-scale sterile neutrinos, while surveying future prospects for resolving these hints at accelerator, reactor, and radioactive source neutrino experiments.

Speaker: Bryce Littlejohn (University Of Cincinnati)

Slides Littlejohn_DarkSector_Nu.pdf

11:30 Cosmology probes of dark sectors

Speaker: Kendrik Smith (Perimeter Institute)

Slides Kendrik-14-06-13-brookhaven.pdf

12:00 Concluding remarks and outlook

Speaker: Maxim Pospelov (University of Victoria)