The COHERENT Experiment Andrew Eberhardt Marija Glisic

Introduction COHERENT is a neutrino physics experiment currently being planned Intend to test various properties of the neutrino over a multi-phase experiment The experiment will involve a large detector at the Oak Ridge National Lab Road Map: 1.Theory and Relevant Physics 2.Source and Experimental Design 3.Detectors: physics and candidates 4.Applications and Implications

Theory: Neutrino Interaction Review Charge current (CC) interactions involve the exchange of a W boson Neutral current (NC) interactions involve the exchange of a Z boson Neutral current interactions are flavor blind But Charge current interactions are not

Theory: Neutrino Interactions Review Elastic scattering requires that kinetic energy is conserved Elastic neutrino scattering then requires that the number of neutrinos in the scattering event is conserved (i.e. no charged leptons are created)

Theory: CENNS Neutrino scatters off of entire nucleus Existence is non-controversial but has yet to be observed Cross section goes weak nuclear charge squared

Theory: CENNS Particles have characteristic wavelengths inversely related to momentum If deBroglie wavelength is on the order of the nuclear radius, incident neutrino would “see” all of the nuclides in a nucleus Neutrino scatters off all of the nuclides coherently Incident neutrinos of tens of MeVs scattering off of a hundreds GeV nucleus could generate a nuclear recoil on the order of keV humb/f/f0/Nucleus_drawing.svg/2000px- Nucleus_drawing.svg.png ν

Theory: CENNS Looking for nuclear recoils Eluded detection despite large relatively cross section because of detector energy thresholds Recoil scales with neutrino energy BUT neutrino with energy too high will scatter off individual nuclides

Theory: NSI Neutrinos may interact with matter in ways not predicted by the standard model E.g. flavor changing interactions with quarks The interactions would have several measurable effects COHERENT is in a position to measure two of them

Theory: NSI Neutrinos may be able to scatter off quarks through some interaction that is neither exchange of a Z or W This interaction may not be flavor conservative This would act as a perturbation to the neutrino Hamiltonian as it propagates through matter The adjusted Hamiltonian is shown below for electron neutrinos propagating through matter

Theory: NSI through CENNS Additional quark neutrino interactions would alter our cross section for CENNS Equation represents CENNS cross section including NSI parameters

Theory: NSI through CENNS Would effect total cross section for CENNS A good measurement of the CENNS cross section could bound NSI parameters

Theory: NSI through CENNS COHERENT would offer an unprecedented sensitivity to NSI parameter space Best sensitivity would require multiple target types

Theory: Neutrino Oscillation Neutrino flavor and energy eigenstates are distinct Neutrinos interact with other particles in flavor eigenstates Propagate and oscillate as a super position of energy eigenstates Some probability that neutrinos created in one flavor eigenstate are detected in another

Theory: NSI through Solar ν Neutrino oscillation affects the probability an electron neutrino created in the sun will remain an electron neutrino by the time it gets to a detector This survival probability depends on the NSI params

Theory: NSI through Solar ν Electron neutrino oscillation into an additional flavor is called level crossing Recall our Hamiltonian included terms allowing neutrinos to scatter off of quarks in flavor changing interactions

Theory: NSI through Solar ν The high matter density in the sun means that survival probability is highly sensitive to neutrino quark interactions Pee dependence on NSI parameters overlaps with peak energy for B8 neutrinos Deviation from SM prediction could be proof of NSI

Solar Neutrino Detection A large detector could directly detect neutrinos through CC interactions COHERENT would be sensitive to these parameters

Theory: Sterile Neutrinos Additional neutrino flavors may exist which does not interact with Z or W bosons Motivated by many theories including dark matter, dark energy, pulsars, neutrino mass, leptogenesis, etc. Liquid Scintillator Neutrino Detector anomaly results consistent with 1 or 2 additional neutrino eigenstates

Theory: Sterile Neutrinos Oscillation to sterile flavor will cause a deficit in NC or CC signal Small total effect

Theory: ν Magnetic Moment Neutrinos can couple to EM via loop diagrams This means that the neutrino has a magnetic moment The limits on this moment depend on the Dirac or Majorana nature of the neutrino Current experiment limitations (GEMMA) put an upper limit on the moment at around

Theory: ν Magnetic Moment Magnetic moment would have its own contribution to the CENNS cross section This would manifest itself as larger cross section at low energies Difficult to detect because of low energy position

Challenges of Neutrino Experiments CENNS requires neutrinos to have energies of tens of MeV Incident neutrinos of tens of MeV cause nuclear recoils of only a few keV – very hard to detect 1. Need neutral charge current detectors sensitive to few keV 2. Need large number of high-energy neutrinos FacilityLocation Proton Energy (GeV) Power (MW) Bunch Structure RateTarget LANSCEUSA (LANL) µs120 HzVarious ISISUK (RAL) × 200 ns50 Hz Water-cooled tantalum BNBUSA (FNAL) µs5-11 HzBeryllium SNSUSA (ORNL) ns60 HzMercury MLFJapan (J-PARC)312 × ns25 HzMercury ESSSweden (planned)1.352 ms17 HzMercury DAEδALUSTBD (planned)0.7~7 x 1100 ms2 HzMercury

Spallation Neutron Source

Most spallation products stop in mercury target. Neutrino detectors set up up 20 m away Only neutrinos get through, 2 x 10 7 neutrinos / s* cm 2 of each flavor at 20m

Experimental Plan Multi-phase experiment for different objectives PhaseDetector ScalePhysics Goals Phase 1Few to few tens kgCENNS detection Phase 2Tens to hundreds kgSM test (NSI and sterile ν effects) Phase 3Tonnes to few tonnes Neutrino magnetic moment

Scintillator Detectors Scintillators work by absorbing radiation and exciting electrons to their conduction band. Electrons then lose energy and emit a photon with an equal energy difference. The scintillator is coupled with a photomultiplier tube (PMT) which converts the emitted photon to an electron through a series of dynodes to an anode which sends an output signal proportional to the photon’s energy. Detectors must be efficient (energy to photon), transparent, have photons in a detectable spectrum, and fast decay time. Nuclear recoils are not as efficient as electron recoils (to a few percent) which is why detector thresholds must be as low as possible

CsI[Na] Detectors High mass of Cs and I makes for high CENNS event rate (10s events /kg*year) 10 keV threshold Low internal radioactivity improves signal to background ratio Fast decay time helps detection of faint signals Temperature variation is small (15-30 C) and materials are inexpensive

Two-Phase LXe Detectors Liquid Xenon detector scintillate with weakly-interacting particles, two signals per absorbtion Considered for neutrino magnetic moment detection for energies below 100 keV 1 keV threshold Expected 1470 events/year Built huge (100kg) for neutrino magnetic moment

HPGe Detectors High-Purity Germanium detectors have an outer n-type contact and an inner p-type contact. Don’t scintillate but create e- hole pairs when superconducting Relatively long drift time, but timing the pulses can allow statistical separation of prompt and delayed neutrino reactions. Should have ~ 40 events/ kg *year 20m from target Detection threshold around 3 keV

Lowering the Background 60 Hz Pulses allow for background readings between bursts All proposed detectors have low noise 18 cm of Ultra-Low Background lead shielding around CsI[Na] detector Out-of-beam: mostly muons. In-beam: mostly neutrons Currently measuring backgrounds at SNS

Supernova Implication HALO in Canada aims to detect supernova neutrinos to alert astronomers of supernova events – 1974 event only caught by two observers HALO plans to detect with neutrons from 208 Pb + ν e → e Bi* and the excited bismuth nucleus emits up to three neutrons 18 cm of lead shielding surrounds the CsI[Na] detector which will scintillate from neutrons A cross section of the lead to bismuth reaction can be obtained for HALO’s use

What We Could Learn? First observation of CENNS Test of standard model and the effects of sterile neutrinos and non- standard interactions CENNS background for dark matter searches Understanding of supernovae, both for HALO and modeling them Sterile neutrinos, if detected, could contribute to dark matter Neutrino magnetic moment

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