Dark Sectors 2016 ! Theory and Visible Dark Photons Primer Natalia Toro ! Prepared with Rouven Essig & Philip Schuster Welcome! 2 Looking Back In 2009, SLAC held a “Dark Forces” workshop. At that time… • Astrophysics data spurred renewed theoretical interest Dark Forces Workshop 2009 • Re-analysis of data from multi- purpose detectors opened window to the dark sector • First-generation experiments were starting to take shape. 3 Searching in Dumps Now is a greatdiscoverable with new, low- time! power beam dump 0.01 0.1 1 106 seconds @ 100 nA, 6 GeV 0.01 0.01 10-4 Scalar Thermal Relic DM Broad, one signal event per hour KLOE -3 10 LHC HADES KLOE -5 BaBar -4 3 3 10 a,5 APEX 10 10 10 PHENIX Test -5 LEP favored A1 10 * a,±2 NA48/2 E774 -6 10-6 10 ae international 4 4 4 E774 CRESST II 10 10 ) 10-7 BaBar E141(10cm, A' -7 m -8 10 / 10 XENON 10 5 .3 mC) 5 2 -9 ⇥ ⇥ 10 10 10 m activity ( -8 E141 -10 E137 10 D 10 E137 -11 Density 6 6 2 10 Relic (200m, 30 C) 10 10 -9 -12 LSND 10 = 10 +CERN, milli- y searching for -13 MegaWatt x Year 10 7 7 -10 x SIDM 10 charge 10 10 10-14 LSND lower limit Orsay U70 10-15 -11 dark sectors! 8 8 10 10-16 10 10 -3 -2 -1 (dump10 experiments10 also constrain10 1 1 10 102 103 0.01 0.1 1 longer-lived decaym modes,A' [GeV ] m (MeV) mA' GeV see Schuster, NT, Yavin to appear) *E774: 20cm, .3 mC 8 Many of the first-generation dedicated experiments are still ongoing. Their reach can be anticipated reliably, and it’s clear what limits they run into. It’s a perfect time to ask: Where do we go next?! That’s the focus of this workshop. Next 3 talks: assessing the state of the field today, to set stage for these discussions. 4 Where to now? • What new ideas will propel us past the obstacles found in designing the first-generation experiments? • What important possibilities are we overlooking, that we should be searching for? • What opportunities do we have with upcoming facilities and/or new technologies that didn’t exist 7 years ago? • What do we want this field to look like in 5-10 years? What is within reach? What should we focus on? 5 Outline • Why Dark Sectors? • Organizing Questions • Visibly Decaying Dark Photon Searches – Properties – Search Strategies – Outstanding Challenges 6 Why Dark Sectors? • Nature seems well described by SU(3)xSU(2)xU(1) gauge theory – We need to check this assumption!! • Precedent in Standard Model for rare/subtle effects to be important (Radioactivity, Rutherford scattering, neutrinos, parity violation…) • We already know we are missing something… 7 There is a dark sector! Baryons Dark energy Dark matter • What is it? • Where did it come from? 8 Theory Prejudice Least addition of new particles? ! Motivates SM weak multiplet or axion [SM itself is far from minimal in this sense] Theory Prejudice Least addition of new Parallel structure to particles? Standard Model ⇒ ! Motivates SM weak Motivates weak multiplet or axion coupling searches at modest energy [SM itself is far from minimal in this sense] Looking for Dark Sectors Whatever is in the dark sector, only three sizeable interactions allowed by Standard Model symmetries: 1 Y µν Vector Portal 2 Y Fµν F 0 2 2 Higgs Portal h ⇥ exotic rare Higgs decays h | | | | Neutrino Portal ⌫ (hL)⇥ not-so-sterile neutrinos 10 New gauge interactions ¯ µ Gauge Portal g qi iσ¯ iVµ i X A new vector can also couple to anomaly-free global symmetries of the Standard Model (or, with appropriate new matter, to anomalous symmetries) e.g. B-L, Lμ-Lτ, … Looking for Dark Sectors Whatever is in the dark sector, only three sizeable interactions allowed by Standard Model symmetries: focus for this talk – 1 Y µν Vector Portal 2 Y Fµν F 0 big opportunity for low- energy experiments 2 2 Higgs Portal h ⇥ exotic rare Higgs decays h | | | | Neutrino Portal ⌫ (hL)⇥ not-so-sterile neutrinos ¯ µ Gauge Portal g qi iσ¯ iVµ sometimes “bycatch” in vector portal searches, but i X some interesting cases 12 require dedicated searches! Sources and Sizes of Kinetic 1 Y µν Mixing 2 Y Fµν F 0 • If absent from fundamental theory, can still be generated by perturbative (or non-perturbative) quantum effects – Simplest case: one heavy particle ψ with both EM charge & dark charge ψ γ e gD A0 egD m 2 4 generates ✏ 2 log M 10− 10− ⇠ 16⇡ ⇤ ⇠ − 13 Sources and Sizes of Kinetic 1 F Y F µν Mixing 2 Y µν 0 • If absent from fundamental theory, can still be generated by perturbative (or non-perturbative) quantum effects – In Grand Unified Theory, symmetry forbids tree-level & 1-loop mechanisms. GUT-breaking enters at 2 loops ψ γ X e gD A0 3 5 generating ✏ 10− 10− 7 ⇠ − (→ 10 − if both U(1)’s are in unified groups) 14 Effects of Kinetic Mixing Regardless of where it comes from, kinetic mixing can always be re-interpreted as (mainly) giving matter of electric charge qe an A′ coupling ∝ qεe A′ e × + e− e µ,⇡,... Dark-sector matter can have an independent coupling gD to A′ Hints of Dark Forces? • High-energy cosmic ray anomalies • Direct detection anomalies • Muon g-2 • Muonic hydrogen Lamb shift • 8Be decay resonance • Astrophysical hints of dark matter self-interaction? • 511 keV line • keV γ-ray excess • Galactic center excess 16 Taxonomy of Dark Sectors A few simple questions about the new physics… 1. What is the mediator? Kinetically mixed dark photon? Scalar? Flavor gauge boson? SM dipole interaction? 2. Is it lighter or heavier than… – any dark matter in dark sector? (invisible decays) – relevant SM particles? 2 me (visible decays) – new unstable particles? (“rich” multi-body decays) 17 Taxonomy of Dark Sectors If dark matter is relevant… 3. How is it produced? – Thermally (through annihilation to SM)? – Asymmetric? – Other? May imply constraints/relations among dark-sector couplings 4. Fermion or scalar? 5. Elastic (mass-diagonal) or inelastic (mass-off-diagonal) interactions? Affect signals in various experiments and the comparisons among them 18 Taxonomy of Dark Sectors Kinetically mixed dark photon decays to SM Not produced on-shell * can still mediate dark sector production heavy Visible decays – 2 width Γ~αmAʹϵ 2 me Dark photon mass Long-lived Aʹ➝3γ 0 Dark sector millicharges Taxonomy of Dark Sectors Kinetically mixed dark photon decays to SM Not produced on-shell * can still mediate dark sector production heavy Visible decays – Visible & missing 2 width Γ~αmAʹϵ mass searches 2 me Cosmological & stellar Dark photon mass Long-lived Aʹ➝3γ bounds, solar production, light thru walls 0 Dark sector millicharges Taxonomy of Dark Sectors Kinetically mixed dark photon coupled to DM Not produced on-shell * can still mediate DM production heavy ⇒ invisible signal Aʹ DM Visible decays – m Decays mainlyD to 2 ʹ = 2 m width Γ~αmAʹϵ DM anti-DM pair, mA 2 me width Γ~ α + subleasing visible decay Long- Dark photon mass lived Aʹ➝3γ 0 Dark matter mass Taxonomy of Dark Sectors DM Signals at colliders Contact operator heavy DM production Resonant DM DM production ʹ = 2 m mA 2 me Near-threshold DM production Dark photon mass (off-shell light mediator) 0 Dark matter mass Sub-MeV Dark Photons [Figure from 2013 Intensity Frontier report – Javier Redondo] Sub-MeV Dark Photons Light thru walls Cavity searches Solar+scatter 4 4 frequency Hz kHz MHz GHz !4 1 inside the detector. Given the significant enhancement 10 Jupiter Earth 0.1 in the low-energy part of the solar dark photon spec- Coulomb ALPS CROWS CROWS 10[Figure-2 from 2013Coulomb Intensity Frontiertrum, report Fig. 1, a detector– Javier with a Redondo] low threshold energy of !6 limit 10 CAST 10-3 O(100) eV will have a clear advantage. To date, the only using published 10-4 longitudinal work that considers limits on dark photons from direct !8 -5 10 10 limit DM detection is by HPGe collaboration, Ref. [9]. How- Sun mode 10-6 CMB ever, it used incomplete calculations of the solar flux, and HB this Κ ∂ Future HB ! XENON10 10-7 work as we will show in the following, the low-energy ioniza- 10 10 high CoGeNT - Sun 10 8 -Q H tion signals by the XENON10 [10] and CoGeNT [11, 12] microwave -9 collaborations yield far more stringent limits. 10 L ALPS II !12 cavity 10 10-10 The XENON10 collaboration has published a study experiment 10-11 on low-energy ionization events in [10]. With 12.1 eV !14 10-12 ionization energy, the absorption of a dark photon with 10 10-13 300 eV energy can produce about 25 electrons. To get a -16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 ! ! ! 10 10 10 10 10 10 10 10 10 10 10 10 10 10 conservative constraint we count all the ionization events 10 6 10 4 10 2 100 102 104 mg' eV within 20 keV nuclear recoil equivalent in Ref. [10], which mV !eV" FIG. 2: The reach of cavity searches for hidden photons, taking advantage of the improved transmissioncorresponds of the to a signal of about 80 electrons. The total @ D longitudinal modes. The solid blue region is the published limit from the CROWS experiment [29],number calculated of using events is 246, which indicates a 90% C.L up- FIG. 2: Constraints on κ as functions of mV .Thesolid, the results of [25].