Using MKIDs for the Direct Detection of sub-GeV Dark Matter? Rouven Essig C.N. Yang Institute for Theoretical Physics, Stony Brook University MKIDs workshop @ Fermilab, Aug 27, 2013 with: J. Mardon, T. Volansky ( 1108.5383, PRD ) A. Manalaysay, J. Mardon, P . Sorensen, T. Volansky ( 1206.2644, PRL ) + several works in progress 1
The Search for Dark Matter • Major efforts are underway to detect dark matter in the laboratory with “direct detection” experiments • existing efforts usually focus on detecting elastic nuclear recoils from a 5-1000 GeV WIMP (e.g. neutralino) • improvements expected from: • bigger detectors (to probe lower cross sections) • lower thresholds (to better probe 1-10 GeV WIMPs) This program is clearly important and should be pursued But are we looking everywhere we can and should? 2
The Search for Dark Matter • The answer is no: DM does not have to be associated with Weak scale (with mass~ 5-1000 GeV) • Many other excellent DM candidates exist • In particular, many theoretical scenarios give rise to DM candidates with masses in the MeV-GeV range Contrary to popular belief, sub-GeV DM is viable & can be probed with direct detection experiments! 3
So instead of considering only this… � 36 � 10 10 Cross � section [cm 2 ] (normalised to nucleon) � 38 � 38 10 10 � � 40 10 � � 42 10 � � 44 10 � � � 46 10 0 1 2 3 10 10 10 10 WIMP Mass [GeV/c 2 ] 4
What if DM is here ? � � 36 � 36 � 36 � 10 10 10 10 Cross � section [cm 2 ] (normalised to nucleon) Cross � section [cm 2 ] (normalised to nucleon) � � 38 � � 38 � 38 10 10 10 ? � � 40 � � � 40 10 10 � 42 � � � � 42 10 10 � 44 � � � � 44 10 10 � � � � � 46 � � 46 � 46 10 10 10 0 0 1 2 3 10 0 1 2 10 -3 10 -2 10 -1 10 10 10 10 10 10 10 10 WIMP Mass [GeV/c 2 ] mass ~ MeV - GeV 4
Cannot use elastic nuclear recoils for detection Recall: Heavy DM DM Atom 5
Cannot use elastic nuclear recoils for detection Recall: Heavy DM DM 5
Cannot use elastic nuclear recoils for detection Recall: Heavy DM DM large recoil… “no problem” 5
Cannot use elastic nuclear recoils for detection nuclear recoil energy � 36 10 Cross � section [cm 2 ] (normalised to nucleon) � 38 10 keV � 40 10 E NR � 42 10 eV � 44 10 MeV GeV TeV � 46 10 DM mass 0 1 2 3 10 10 10 10 WIMP Mass [GeV/c 2 ] for sub-GeV DM, nuclear recoil energy is too small to limits absent produce visible scintillation, below ~few GeV ionization, or phonon signal ! 6
But, total energy available is much larger: keV E tot eV MeV GeV TeV DM mass enough energy to excite or ionize an atom, or dissociate molecules (just not from nuclear recoils!) 7
How to detect sub-GeV DM • ionization • excitation • molecular dissociation 8
DM scattering off an electron: 1 DM Atom 9
DM scattering off an electron: 1 DM We have a proof of principle that this works Atom Ionization threshold ~ 1-100 eV Signal: single (or few) electron events existing technologies can measure ionization, even of a single electron ! 9
How to detect sub-GeV DM • ionization • excitation • molecular dissociation 10
DM scattering off an electron: 2 DM Atom 11
DM scattering off an electron: 2 γ DM threshold ~ 1-100 eV Atom Excitation Excite atom… & look for de-excitation photon Signal: photons Use MKIDs to detect these photons? 11
How to detect sub-GeV DM • ionization • excitation • molecular dissociation 12
DM (or ν ) scattering off nuclei Break apart molecules threshold ~ few eV Signal: various possibilities We are calculating rates & talking w/ several experimentalists/chemists to investigate feasibility… 13
A Proof of Principle exists for Ionization Signal arXiv:1206.2644 XENON 10 was set-up to trigger on single e - events (with S 1 = 0 ) for only 12.5 days in 2006 Can use this data to set a limit (next page) 14
Limits on sub-GeV DM from XENON10 10 - 34 Excluded by 10 - 35 XENON10 data 1 electron s e @ cm 2 D 2 electrons 10 - 36 3 electrons 10 - 37 Hidden - 10 - 38 Photon models 10 - 39 1 10 100 10 3 Dark Matter Mass @ MeV D Note: MeV scale! 15
One possibility to use MKIDs? • use MKIDs to detect γ from DM-induced atomic excitations • e.g. instrument outer parts of target material with MKIDs (could use mirrors/focusing Target MKIDs to decrease number of Material MKIDs needed) • material can be transparent if use photons γ from a double transition (easy to have forbidden transitions from symmetry) 16
Future? • With ~20-30 yrs of research, direct detection w/ elastic nuclear recoils are almost “background free” experiments • use two handles to distinguish signal from background, e.g. ionization & scintillation in 2-phase TPC’s for XENON100/LUX (background has larger ionization) • w/o 2 handles, can always use annual modulation (e.g. DAMA) • need to start a similar program focused on sub-GeV DM • e.g. one idea: use MKIDs in combination with two-phase TPC to veto events with ionization? Can we use MKIDs for direct detection of sub-GeV DM? 17
Backup 18
Elastic nuclear recoils don’t work nuclear ∼ ( µv ) 2 ∼ ( m DM v ) 2 recoil E nr 2 m N 2 m N energy ◆ 2 ⌘ 2 ✓ 10 GeV ◆ ✓ m DM v ⇣ ∼ 1 eV m N 300 km / s 100 MeV keV too small to excite E NR or ionize an atom or eV produce enough phonons ! MeV GeV TeV DM mass 28
nuclear ◆ 2 ⌘ 2 ✓ 10 GeV ◆ ✓ m DM v recoil ⇣ E nr ∼ 1 eV energy m N 300 km / s 100 MeV But, total energy available is much larger! ◆ 2 E tot ∼ 1 ⌘ ✓ m DM v ⇣ 2 m DM v 2 ∼ 50 eV 300 km / s 100 MeV much larger ! keV E tot eV MeV GeV TeV DM mass 28
The XENON 10 data on average, a single electron produces about 27 detected photo-electrons in principle, easy to detect in XENON 10 But XENON 10 was set-up to trigger on single e - events (with S 1 = 0 ) for only 12.5 days in 2006 … only 15 kg-days exposure P . Sorensen (XENON 10 ) used this data to set limits on ~ 10 GeV DM from nuclear recoils , constraining DAMA/CoGeNT region 19
The XENON 10 data P . Sorensen (XENON 10 ) used this data to set limits on ~ 10 GeV DM from nuclear recoils , constraining DAMA/CoGeNT region (2011) 20
The XENON 10 data ? P . Sorensen (XENON 10 ) used this data to set limits on ~ 10 GeV DM from nuclear recoils , constraining DAMA/CoGeNT region (2011) 20
The XENON 10 data ~ 500 events w/ 1- , 2- , or 3- electrons are observed 100 Best fit Counts / 0.1 electrons Allowed at 90% upper limit 1- electron events single 10 electron 2- electron events double 3- electron events 1 electron triple electron 0.1 1 1.5 2 2.5 3 3.5 4 Ionization Signal [electrons] 21
The XENON 10 data ~ 500 events w/ 1- , 2- , or 3- electrons are observed 100 Best fit Counts / 0.1 electrons Allowed at 90% upper limit single 10 electron double 1 electron triple electron 0.1 1 1.5 2 2.5 3 3.5 4 Ionization Signal [electrons] What are these events ?? Origin unclear! Some possibilities: • Photo-dissociation of negatively charged impurities • spontaneous emission of e - trapped in potential barrier at liquid-gas interface • field emission in region of cathode 21
The XENON 10 data ~ 500 events w/ 1- , 2- , or 3- electrons are observed 100 90% c.l. upper bounds Best fit Counts / 0.1 electrons Allowed at 90% upper limit on rates: single 10 electron 1 e - : 34.5 counts/kg/day double 1 2 e - : 4.5 counts/kg/day electron 3 e - : 0.83 counts/kg/day triple electron 0.1 1 1.5 2 2.5 3 3.5 4 Ionization Signal [electrons] Note: DM can give rise to 2- and 3-electron events: • outgoing e - can ionize further e - ’s • ionizing an inner-shell e - gives a de-excitation photon that can ionize other e - ’s 21
Results 10 - 34 Excluded by 10 - 35 XENON10 data 1 electron s e @ cm 2 D 2 electrons 10 - 36 3 electrons 10 - 37 Hidden - 10 - 38 Photon models 10 - 39 1 10 100 10 3 Dark Matter Mass @ MeV D 22
Summary for XENON 10 “accidentally” already sets meaningful limits on DM-electron recoils But: • only a measly 15 kg-days • designed to study nuclear recoils How well can an experiment do that purposefully looks for sub-GeV DM ? 23
Projected reach for various elements Cross section Sensitivity and Event Rate H per kg ◊ year L XENON 10 10 - 33 10 - 3 10 - 34 F DM H q L = 1 limit 10 - 2 g D = 0.1 Event Rate H s e = 10 - 37 cm 2 L 10 - 35 0.1 Excluded by XENON 10 10 - 36 He 1 Ar g D = 10 - 2 Helium 10 - 37 s e @ cm 2 D Xe 10 Ge Hidden photon 10 - 38 Xenon 10 2 g D = 10 - 3 10 - 39 Argon 10 3 ˙ MeV ¯ DM 10 - 40 10 4 Germanium 10 - 41 g D = 10 - 4 10 5 10 - 42 10 6 10 - 43 1 10 10 2 10 3 Dark Matter Mass @ MeV D 1 kg-year NB: semi-conductors (e.g. Ge) ⇒ reach to very low masses ! = 25
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