Neutrinos from Type Ia and failed core-collapse supernovae at dark matter detectors Nirmal Raj TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada Neutrinos produced in the hot and dense interior of the next galactic supernova would be visible at dark matter experiments in coherent elastic nuclear recoils. While studies on this channel have focused on successful core-collapse supernovae, a thermonuclear (Type Ia) explosion, or a core- collapse that fails to explode and forms a black hole, are as likely to occur as the next galactic supernova event. I show that generation-3 noble liquid-based dark matter experiments such as darwin and argo, operating at sub-keV thresholds with ionization-only signals, would distinguish between (a) leading hypotheses of Type Ia explosion mechanisms by detecting an O(1) s burst of O(1) MeV neutrinos, and (b) progenitor models of failed supernovae by detecting an O(1) s burst of O(10) MeV neutrinos, especially by marking the instant of black hole formation from abrupt stoppage of neutrino detection. This detection is sensitive to all neutrino flavors and insensitive to neutrino oscillations, thereby making measurements complementary to neutrino experiments. The next galactic supernova is imminent. This could atmospheric, and relic supernova neutrinos, the \neu- be induced by thermonuclear runaway fusion (Type Ia su- trino floor". These experiments could also dedicate pernova) or a rapid core-collapse, estimated to occur at searches to neutrinos from various sources (including +1:4 +7:3 a rate of respectively 1.4−0:8 and 3.2−2:6 per century [1]. dark matter) [19{29]. While neutrino experiments { The core-collapse often successfully blows away accret- whose detection is usually restricted to only the flavors ing outer layers and leaves behind a neutron star, such νe and νe { have larger exposures, dark matter experi- as believed to have happened in the last observed galac- ments could compensate with enhanced detection rates tic supernova sn 1987a; yet 10%-50% of them fail to ex- due to nuclear coherence, and by detecting all flavors plode, unable to prevent intense accretion, leaving behind (νe; νe; νµ; νµ; ντ ; ντ ). This latter feature enables them a black hole1. In all types of supernovae, their hot and to reconstruct a supernova neutrino burst without un- dense environments produce neutrinos that escape them certainties from neutrino oscillations in the supernova, and serve as the first particle messengers of this once- and to measure the energy emitted in each flavor. in-a-lifetime event. The neutrino signal would inform The supernova neutrino phase space is best sampled by whether, when, and where to look for the electromagnetic detectors that are large and operating at low thresholds. signal, and would reveal vital information about the ex- I will thus compute event rates at future generation-3 de- plosive conditions of the progenitor, of which there is cur- tectors2: the xenon-based darwin [30] and argon-based rently little measurement or consensus. Neutrino experi- argo [31]. Projected with O(100)-tonne target mass, ments such as IceCube, Hyper-K, dune, juno, and halo these are said to be \ultimate" detectors that could will be prepared to detect supernova neutrinos in a range probe down to the lowest reachable dark matter-nucleon of channels [3, 4], but lately it has been recognized that cross sections and the highest reachable dark matter dark matter experiments, designed for detecting coherent masses [32]. These detectors are also capable of very elastic nuclear recoils, are an equally important player low, sub-keV thresholds, as I will discuss later. capable of uncovering complementary physics. Whilst studies have been performed on elastic nuclear recoils Explosion characteristics and neutrino fluxes. produced by neutrinos from successful core-collapse su- Type Ia supernovae. Despite their well-known utility as pernovae [5{13] and pre-supernova nuclear burning [14], standard candles that suggest that the universe is ac- they are lacking for neutrinos from Type Ia and failed celerating [33{35], little is known about how Type Ia arXiv:1907.05533v2 [hep-ph] 9 Apr 2020 core-collapse. The purpose of this note is to close these supernova progenitors explode [36], or even what they gaps, and to comment on this detection channel vis-`a-vis are, although it is argued that they are carbon-oxygen those at neutrino experiments. white dwarfs accreting mass from a binary companion Neutrinos and dark matter experiments are intimately that triggers explosive carbon burning. Determining the connected. The \direct detection" program began when explosion mechanism from extragalactic supernovae will a proposal to detect neutrinos via coherent elastic scat- be challenging due to telescope limitations, but a super- tering [15] { a process observed only recently [16, 17] nova in the Milky Way would help settle the question via { was adapted for dark matter searches [18]. With not only electromagnetic signals, but also neutrinos and ever-increasing exposure, these experiments would even- gravitational waves. In particular, neutrinos { produced tually run into an irreducible background from solar, 2 Should a galactic supernova occur during the running of current 1 Violent explosions collapsing into themselves also leave behind or next-generation dark matter experiments, my event rates may other singularities [2]. be trivially rescaled by the target mass. 2.0×1058 ) -1 ) -1 1055 deflagration-to-detonation 1.5×1058 transition (DDT) LS220 - s40s7b2 (quick disappearance) ) ) 1 1 - - 53 58 s 10 s ( 1.0×10 ( dt dt / / ν ν dN gravitationally confined dN 1051 detonation (GCD) LS220 - s40 .0 (slow disappearance) 5.0×1057 Neutrino number luminosity (s Neutrino number Neutrino number luminosity (s Neutrino number 1049 4.50.0 0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 t (s) 24 LS220 - s40s7b2t (s) 4.0 22 (quick disappearance) DDT 3.5 20 ) LS220 - s40 .0 ) 3.0 (slow disappearance) MeV MeV 18 >( >( ν ν 2.5 E Ε 16 < < 2.0 14 GCD GCD 1.5 Mean neutrino energy (MeV) 12 Mean neutrino energy (MeV) 1.0 10 0.5000.0 0.5 1.0 1.5 2.0 2.5 3.0 100 0.5 1.0 1.5 2.0 2.5 distance to supernova d* = 10 kpc distancet (s) to supernova d* = 1 kpc t (s) LS220 - s40s7b2 80 (quick disappearance) 0.100 xenon, 50 tonnes, 0.1 keV threshold (DARWIN) DDT argon, 300 tonnes, 0.6 keV threshold (ARGO) 0.050 60 100 ms 150 ms / / 1 for d* = 100 pc 0.010 LS220 - s40 .0 Events/150 ms Events Events 40 (slow disappearance) 0.005 Events/100 ms xenon, 50 tonnes, 0.1 keV threshold (DARWIN) GCD GCD 20 argon, 300 tonnes, 0.6 keV threshold (ARGO) 0.001 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 2.5 t (s) t (s) FIG. 1. Left: Type Ia supernovae, right: failed core-collapse supernovae. Shown as a function of time are number luminosities of supernova neutrinos (summed over all flavors) emitted at the source (top), mean neutrino energies for all flavors combined (middle), and events per binned time at generation-3 dark matter detectors (bottom). Explosion mechanisms of Type Ia supernovae and progenitor models of failed supernovae are visibly distinguished by these detectors. The wiggles in the top- right and middle-right plots reflect those in Ref. [4]. through e+e− annihilations and e± capture on nucleons upon turbulence shreds it, and cold fuel and hot ashes and nuclei, and carrying away ∼1% of the star's gravi- mix. This triggers supersonic combustion { detonation tational binding energy [37] { could distinguish between { of the remaining fuel. In the second mechanism, grav- explosion mechanisms even if the electromagnetic signals itationally confined detonation (gcd), deflagration ash are alike. Since the Type Ia supernova core is not dense floats to the star surface, but is kept from escaping by enough to trap neutrinos, their flux is reliably computed the star's gravity, whereupon it envelopes the surface, as there is no neutrino transport or self-interactions to converges, compresses, and detonates the rest of the fuel. account for, unlike for core-collapse supernovae. As neutrinos propagate through the supernova medium References [38, 39] computed these fluxes using 3D sim- they oscillate, and their flavor composition at emission ulations of near-Chandrasekhar mass white dwarfs for would depend on both the density profile along the line two leading hypotheses of the explosion mechanism. In of sight (as the explosion is asymmetric), and on neu- the first mechanism, deflagration-to-detonation transi- trino mass ordering. However, for detection via elastic tion (ddt), the flame front of subsonic combustion of the nuclear scattering flavors are not relevant, only the to- fuel { deflagration { reaches low density regions, where- tal flux is. I use tables of neutrino fluences provided by 2 0.010 argon 10 xenon 2 ) 2 * ) * d 5 / d / xenon 0.001 deflagration kpc ( -to 10 kpc - ( argon detonation transition 1 argon -4 tonne x 10 / 0.50 tonne x xenon gravitationally / confined LS220- s40s7b2 Events 10-5 detonation (quick disappearance) Events 0.10 LS220- s40 .0 (slow disappearance) 0.05 0.5 1.0 1.5 2.0 0.5 1.0 1.5 2.0 Energy threshold(keV) Energy threshold(keV) FIG. 2. Events detected per tonne of target as a function of detector energy threshold for neutrinos from Type Ia (left) and failed core-collapse (right) supernovae, normalized to a supernova distance of 1 kpc and 10 kpc respectively. J. Kneller [40] (parts of which are plotted in [38, 39]) Whereas neutrinos from successful core-collapses diffuse to compute energy-differential number luminosities (in out of the proto-neutron star over O(10) s (the duration units of s−1MeV−1) summed over all flavors, as a func- of the neutrino signal detected), those from failed super- 2 tion of post-explosion time.