Calorimetric readout of Superfluid 4He for sensitivity to dark matter of keV-MeV mass Scott Hertel (U. of Massachusetts Amherst) Dan McKinsey, Junsong Lin, Vetri Velan, Andreas Biekert (UC Berkeley) Workshop: Table-Top Experiments with Skyscraper Reach MIT, Aug 10th, 2017 understanding the WIMP as one model among many 1020 10-25 The basic WIMP hypothesis electroweak 1018 mass scale 10-27 (neutrino-like interactions) ] 1016 10-29 2 ) 1014 10-31 2 Z-mediated 1012 10-33 1010 10-35 108 10-37 106 10-39 104 10-41 2 -43 WIMP-nucleon cross section ( zb ) 10 10 WIMP-nucleon cross section ( cm 100 10-45 WIMP-nucleon cross section [ zb ] WIMP-nucleon cross 10-2 10-47 section [ cm WIMP-nucleon cross 10-4 keV MeV GeV TeV understanding the WIMP as one model among many 1020 10-25 The basic WIMP hypothesis electroweak 1018 mass scale 10-27 (neutrino-like interactions) ] -ruled out by ~1991 1016 10-29 2 ) 1014 10-31 2 Z-mediated 1012 Gotthard 1990 10-33 1010 10-35 108 10-37 106 10-39 104 10-41 2 -43 WIMP-nucleon cross section ( zb ) 10 10 WIMP-nucleon cross section ( cm 100 10-45 WIMP-nucleon cross section [ zb ] WIMP-nucleon cross 10-2 10-47 section [ cm WIMP-nucleon cross 10-4 keV MeV GeV TeV understanding the WIMP as one model among many 1020 10-25 The basic WIMP hypothesis electroweak 1018 mass scale 10-27 (neutrino-like interactions) ] -ruled out by ~1991 1016 10-29 2 ) 1014 10-31 2 We keep digging down at this Z-mediated 12 Gotthard 1990 -33 same mass range... 10 10 1010 10-35 108 10-37 106 10-39 104 10-41 2 -43 WIMP-nucleon cross section ( zb ) 10 10 WIMP-nucleon cross section ( cm 100 LUX 2016 10-45 WIMP-nucleon cross section [ zb ] WIMP-nucleon cross 10-2 10-47 section [ cm WIMP-nucleon cross 10-4 keV MeV GeV TeV understanding the WIMP as one model among many 1020 10-25 The basic WIMP hypothesis electroweak 1018 mass scale 10-27 (neutrino-like interactions) ] -ruled out by ~1991 1016 10-29 2 ) 1014 10-31 2 We keep digging down at this Z-mediated 12 Gotthard 1990 -33 same mass range... 10 10 1010 10-35 ...meaning, we keep 108 10-37 broadening the interaction type prior to increasing un-natural 106 10-39 versions of weak interaction. 104 10-41 2 -43 WIMP-nucleon cross section ( zb ) 10 H-mediated 10 WIMP-nucleon cross section ( cm 100 LUX 2016 10-45 WIMP-nucleon cross section [ zb ] WIMP-nucleon cross 10-2 10-47 section [ cm WIMP-nucleon cross loop-mediated 10-4 keV MeV GeV TeV understanding the WIMP as one model among many 1020 10-25 The basic WIMP hypothesis electroweak 1018 mass scale 10-27 (neutrino-like interactions) ] -ruled out by ~1991 1016 10-29 2 ) 1014 10-31 2 We keep digging down at this Z-mediated 12 Gotthard 1990 -33 same mass range... 10 10 1010 10-35 ...meaning, we keep 108 10-37 broadening the interaction type prior to increasing un-natural 106 10-39 versions of weak interaction. 104 10-41 2 -43 WIMP-nucleon cross section ( zb ) 10 H-mediated 10 WIMP-nucleon cross section ( cm 0 LUX 2016 -45 Not sustainable for ever: 10 solar-ν 10 WIMP-nucleon cross section [ zb ] WIMP-nucleon cross 1. increasingly un-natural section [ cm WIMP-nucleon cross 10-2 10-47 2. unavoidable backgrounds loop-mediated atm-ν 10-4 keV MeV GeV TeV Time to broaden other priors? understanding the WIMP as one model among many One way to loosen the priors: 1) retain assumption of thermal production 2) stop assuming we already know all the force mediators First order effects: - more unknowns (more theories) - thermal production works down to ~keV mass scale (note: new ‘freeze-in’ modes) - light mediators avoid standard collider searches understanding the WIMP as one model among many 1020 10-25 thermal production electroweak 18 -27 10 new mediator mass scale 10 ] 1016 10-29 2 ) 1014 10-31 2 1012 10-33 1010 10-35 108 10-37 106 10-39 104 10-41 2 -43 WIMP-nucleon cross section ( zb ) 10 10 WIMP-nucleon cross section ( cm 100 10-45 WIMP-nucleon cross section [ zb ] WIMP-nucleon cross 10-2 10-47 section [ cm WIMP-nucleon cross 10-4 keV MeV GeV TeV DM kinetic energies DM particle velocities cut off by (local) escape velocity: vmax ≃ 540 km/s 2 KEmax ≃ 1/2 mDM vmax 107 106 105 proportionality of 104 mDM to KEmax 103 [eV] 2 2 10 MeV/c ➔ eV max 2 101 GeV/c ➔ keV KE TeV/c2 ➔ MeV 100 -1 10 at cutoff DM KE 10-2 10-3 103 104 105 106 107 108 109 1010 1011 1012 1013 M [eV/c2] DM nuclear recoil energies when mDM ≃ mtarget , efficient coupling of KEDM into target order-GeV mass ➞ order-keV recoil endpoint energies order-MeV mass ➞ order-meV recoil endpoint energies 107 106 Xe 105 Si He 104 103 102 101 100 -1 10 at cutoff DM Elastic Recoil Endpoint [eV] KE 10-2 10-3 103 104 105 106 107 108 109 1010 1011 1012 1013 M [eV/c2] DM nuclear recoil energies when mDM ≃ mtarget , efficient coupling of KEDM into target order-GeV mass ➞ order-keV recoil endpoint energies order-MeV mass ➞ order-meV recoil endpoint energies 107 106 Xe 105 Si He 104 103 102 101 100 -1 10 at cutoff 100meV He endpoint DM Elastic Recoil Endpoint [eV] -2 KE 10 5meV Ge endpoint 10-3 103 104 105 106 107 108 109 1010 1011 1012 1013 M [eV/c2] DM nuclear recoil energies when mDM ≃ mtarget , efficient coupling of KEDM into target order-GeV mass ➞ order-keV recoil endpoint energies order-MeV mass ➞ order-meV recoil endpoint energies 107 106 Xe 105 Si He two punchlines: 104 103 1) light target particle desirable 102 2) meV-scale excitations desirable 101 100 -1 10 at cutoff 100meV He endpoint DM Elastic Recoil Endpoint [eV] -2 KE 10 5meV Ge endpoint 10-3 103 104 105 106 107 108 109 1010 1011 1012 1013 M [eV/c2] DM the recent cresst/ν-cleus example arXiv:1707.06749v2 Al2O3 bronze balls clamp wire bonds copper Al2O3 + TES holder 5x5x5mm (0.49g) 20 eV threshold (on oxygen ➞ 140 MeV mass threshold) 2.27h exposure above ground, no shielding, with ~0.2Bq Fe55 source my two cents: we are entering new regime - sensitivity: energy threshold matters more than target mass - backgrounds: dark counts & noise matter more than radiogenics counts [5eVbinning] eV ie, we are entering the tabletop regime of this workshop Excitations in superfluid 4He eV-scale excitations: Excimers (He2*) He He* singlet: ~ns halflife (observable as scintillation) triplet: 13s halflife (observable as ballistic molecules) (+ a little IR from excitations to higher atomic states) meV-scale excitations: phonons, R- rotons, R+ rotons (observable as athermal evaporation) Excitations in superfluid 4He : partitioning Nuclear Recoil 1 0.8 0.6 4He: atomic cross sections well measured, well understood. 0.4 Recoil energy partitioning can be estimated from the ground up. Energy Fraction 0.2 0 101 102 103 104 105 Recoil Energy [eV] NR and ER have quite different partitioning in a three-way Electron Recoil George Seidel, unpub. partition (kinetic + triplet + singlet). 1 Singlet Excimers 0.8 Triplet Excimers IR photons Phonons/R-/R+ 0.6 Beauty of calorimetric sensors: All recoil energy appears as observable excitations. 0.4 Energy Fraction 0.2 0 101 102 103 104 105 Recoil Energy [eV] Reading out Singlet Excitations (16eV photons) Detecting photons is a standard calorimetry application. simple detector: box with calorimetry inside Operating calorimetry in LHe: less standard. Possible, thanks to 1) huge LHe-solid Kapitza resistance 2) fast conversion of photon energy in calorimeter to trapped excitations (eg, Al quasiparticles) 16eV photon 4He Reading Out Triplet Excitations (ballistic molecules) Superfluid ➔ friction-free ballistic propagation simple detector: box with calorimetry inside Touching a solid supplies mechanism for decay Some fraction of energy appears in surface -energy transferred through electron exchange (not phonons) -fraction dependent on material’s electron density of states ballistic molecule Reading Out Triplet Excitations (ballistic molecules) Superfluid ➔ friction-free ballistic propagation simple detector: box with calorimetry inside Touching a solid supplies mechanism for decay Some fraction of energy appears in surface -energy transferred through electron exchange (not phonons) -fraction dependent on material’s electron density of states ballistic molecule 1 triplet 0.8 molecules 0.6 singlet photons 0.4 counts (scaled) counts (arbitrary) 0.2 Journal of Low Temperature Physics 0 0 2 4 6 8 10 12 14 16 18 20 February 2017, Volume 186, Issue 3, pp 183–196 [eV] Energy in TES [eV] https://arxiv.org/abs/1605.00694 Excitations in superfluid 4He eV-scale excitations: Excimers (He2*) ✔ detection: easy He He* singlet: ~ns halflife (observable as scintillation) triplet: 13s halflife (observable as ballistic molecules) ✔ detection: easy (+ a little IR from excitations to higher atomic states) meV-scale excitations: phonons, R- rotons, R+ rotons (observable as athermal evaporation) 4He Quasiparticles 1.5 phonons R- R+ Things to know: Emaxon meV-scale (hear ‘MeV-scale DM’...) 1 Not on a crystal lattice (isotropic dispersion) Ballistic propagation Eroton Most downconversions forbidden energy [meV] 0.5 Multiple ‘flavors’ with distinguishing characteristics: - slope is velocity - R- propagation opposite to momentum Below atomic excitation energy, all recoil energy appears in these kinetic modes 0 0 1 2 3 4 momentum [keV/c] 4He Quasiparticles Don’t let the word ‘roton’ distract you.