New Muon Beam Missing Momentum Experiments @ FNAL ( g − 2) µ & Dark Matter Yoni Kahn, Gordan Krnjaic Nhan Tran, Andrew Whitbeck arXiv:1803.XXXXX Precision Science Discussion Mar 20, 2018
Overview & Motivation 1) Model independent test of g-2 anomaly 2) Probe models of muon-philic dark matter
Overview & Motivation 1) Model independent test of g-2 anomaly 2) Probe models of muon-philic dark matter
Muon Anomalous Magnetic Moment Longstanding ∼ 3 . 7 − 4 . 1 σ anomaly in ( g − 2) µ Theory updates have only widened disagreement a µ ≡ a µ (obs) − a µ (SM) = (28 . 8 ± 8 . 0) × 10 − 10 Mangano, Keshavarzi, Nomura, Teubner 1802.02995 a µ ≡ a µ (obs) − a µ (SM) = (31 . 3 ± 7 . 7) × 10 − 10 Jegerlehner 1705.00263 Remains a great hint of possible new physics Soon FNAL g-2 experiment will shrink error bars
Many popular new physics models are now ruled out… − 2 10 K → π ν ν ε (g-2) ± 2 σ µ B A B AR 2017 favored 3 − 10 (g-2) NA64 e 4 − 10 − 3 2 1 − − 10 10 10 1 10 m (GeV) A' BABAR:1702.03327 Cosmic Visions 1707.04591 Weak scale models also under tension (e.g. MSSM) Conclusions based on first-generation measurements Motivates better understanding muon-philic interactions
Best viable BSM explanation: new muon-philic particles µ γ ? µ New particle couples to muons & decays invisibly How do we directly test this scenario?
Basic Setup: muon beam incident on fixed target µ ( E ⌧ 15 GeV) 20 CM M AGNET EC AL µ ( E ∼ 15 GeV) TAGGING TRACKER μ - HC AL RECOIL / E TRACKER µ − µ − V 6 E Trigger missing energy Z veto on all other SM particles Kahn, GK, Tran, Whitbeck 1803.XXXX Chen, Pospelov, Zhong 1701.07437 Gninenko, Krasnikov, Matveev 1412.1400
Generic test of light new particles in ( g − 2) µ Phase 1 ∼ 10 10 MOT Phase 2 ∼ 10 13 MOT
Overview & Motivation 1) Model independent test of g-2 anomaly 2) Probe models of muon-philic dark matter
Zeroth Order Outstanding Problems Matter Asymmetry Inflation Neutrino Masses Accelerated Cosmic Expansion What is this stuff ? Also Quantum Gravity 2
DM Prognosis? DM Prognosis? Bad news: DM-SM interactions are not obligatory If nature is unkind, we may never know the right scale must be composite must be bosonic m P l ∼ 10 − 20 eV ∼ 100 M � ∼ 10 19 GeV ∼ 100 eV m DM Good news: most discoverable DM candidates are in thermal equilibrium with us in the early universe Why is this good news?
DM Prognosis? DM Prognosis? Bad news: DM-SM interactions are not obligatory If nature is unkind, we may never know the right scale must be composite must be bosonic m P l ∼ 10 − 20 eV ∼ 100 M � ∼ 10 19 GeV ∼ 100 eV m DM Good news: most discoverable DM candidates are in thermal equilibrium with us in the early universe Why is this good news?
Thermal Equilibrium Advantage #0: Hard to avoid L e ff = g 2 χγ µ χ )( ¯ If interaction rate exceeds Λ 2 (¯ f γ µ f ) Hubble expansion T 2 ∼ g 2 T 5 � � H ∼ n σ v ⇒ = � Λ 4 m P l � T = m χ Equilibrium is easily achieved in the early universe if ◆ 3 / 2 ◆ 2 ✓ GeV ✓ Λ g & 10 − 8 10 GeV m χ Applies to nearly all discoverable models (except axions)
Thermal Equilibrium Advantage #1: Minimum Annihilation Rate DM is overproduced, need to annihilate away the excess! d 3 p Ω χ ⇠ h σ v i − 1 Z g i n (eq . ) e E/T ± 1 ∼ T 3 DM = (2 π ) 3 Observed density requires σ v sym ∼ 3 × 10 − 26 cm 3 s − 1 Freeze out *Predictive rate *Known initial condition *Insensitive to high scales Griest et. al. 1992
Thermal Equilibrium Thermal Equilibrium Advantage #2: Narrows Viable Mass Range Advantage #2: Narrows Mass Range m DM nonthermal nonthermal ∼ 10 − 20 eV ∼ 100 M � m P l ∼ 10 19 GeV < MeV < 10 keV > 100 TeV GeV m Z MeV { too much { Neff / BBN too hot Light DM “WIMPs” Most of current Direct Detection (Alan Robinson) ```` Search program Indirect Detection (Alex Drlica-Wagner) Colliders (Yang Bai) 18
Decades of direct detection: null results SuperCDMS Soudan Low Threshold XENON 10 S2 (2013) 10 � 39 CDMS-II Ge Low Threshold (2011) 10 � 3 CoGeNT P (2012) 10 � 40 10 � 4 I C CDMS Si O (2013) 2 SIMPLE (2012) 5 10 � 41 10 � 5 WIMP � nucleon cross section � cm 2 � 0 ) 2 1 0 WIMP � nucleon cross section � pb � - 2 DAMA ( P C P U ZEPLIN-III (2012) O 3 C F 8 10 � 42 CRESST 10 � 6 ) 9 0 0 2 ( e S G I u I S p SuperCDMS Soudan M e D C r 1 ) 1 C 0 2 ( S 10 � 43 D S 10 � 7 I E W M L E D E ) 2 S 1 0 S 2 N ( O 0 L DarkSide 50 0 N A 1 B n o EU n e X T 10 � 44 10 � 8 R I N LUX O PICO250-CF3I C 7 Be C A T T E O H T S E R R N E I N G Neutrinos 8 B 10 � 45 10 � 9 Xenon1T Neutrinos DEAP3600 DarkSide G2 10 � 46 10 � 10 Z L 10 � 47 10 � 11 (Green&ovals)&Asymmetric&DM&& (Violet&oval)&Magne7c&DM& G T TERI N A C (Blue&oval)&Extra&dimensions&& T S s o 10 � 48 N 10 � 12 n R E i r t E u H e N O (Red&circle)&SUSY&MSSM& C B N O S IN D R U T d E n &&&&&MSSM:&Pure&Higgsino&& N a c i r e h p s 10 � 49 o 10 � 13 m &&&&&MSSM:&A&funnel& t A &&&&&MSSM:&BinoEstop&coannihila7on& &&&&&MSSM:&BinoEsquark&coannihila7on& 10 � 14 10 � 50 & 1 10 100 1000 10 4 WIMP Mass � GeV � c 2 � Cushman et al. arXiv:1310.8327
Null LHC results cast doubt on weak scale SUSY Where else should we look?
Thermal Equilibrium How to test most elusive light DM models? Advantage #2: Narrows Mass Range m DM nonthermal nonthermal ∼ 10 − 20 eV ∼ 100 M � m P l ∼ 10 19 GeV < MeV < 10 keV > 100 TeV GeV m Z MeV { too much { Neff / BBN too hot Light DM “WIMPs” Most of current ? Direct Detection (Alan Robinson) ```` Search program Indirect Detection (Alex Drlica-Wagner) Colliders (Yang Bai) 18
Light DM is different! LDM must be a SM singlet Otherwise would have been discovered (LEP etc.) LDM needs new forces Would be overproduced without light “mediators” χ f σ v ∼ α 2 m 2 ∼ 10 − 29 cm 3 s − 1 ⇣ m χ ⌘ 2 W, Z χ m 4 GeV Z χ f Lee/Weinberg ‘79 How do we look for new forces?
Emerging New Program of Light DM Experiments Scalar Elastic DM ( Kinetic Mixing ) 0 0 10 - 6 COHERENT 1 SHiP / 0 1 N O X E N N 10 - 7 o D o E B i X B n i M 10 - 8 BaBar y = ϵ 2 α D ( m χ / m A' ) 4 10 - 9 MMAPS 10 - 10 CRESST II SBN π E137 NA64 10 - 11 Belle II LSND t 10 - 12 e g r a T c i l e LDMX R SENSEI r a l a 10 - 13 c S Super CDMS e N NEWS B S SNOLAB 10 - 14 10 - 15 Cosmic Visions Report 1707.04591 10 - 16 10 2 10 3 1 10 m χ [ MeV ] … but all probe electron & proton couplings!
Major Blind Spot: Muon-Philic Dark “Mediators” µ, τ µ χ Z 0 χ µ µ, τ New force couple DM to muons, sets relic abundance � � L ⊃ Z 0 µ γ ν µ + g χ ¯ χγ ν χ g µ ¯ ν e.g. — gauged U(1) muon-tau number, no electron coupling (mediator can be same Z’ responsible for g-2 anomaly)
Same setup as before: radiate missing energy µ ( E ⌧ 15 GeV) 20 CM M AGNET EC AL µ ( E ∼ 15 GeV) TAGGING TRACKER μ - HC AL RECOIL / E TRACKER µ − µ, τ ¯ µ − χ µ χ A Z 0 Z 0 χ χ µ µ, τ Tests same interaction that sets relic abundance
Cover nearly all predictive thermal DM models
Cover nearly all predictive thermal DM models Including common g-2 regions
Summary Muonic forces poorly constrained New fixed-target missing momentum experiment Trigger on large missing energy, veto SM particles Utilize existing muon sources beams at Fermilab Phase 1: 1e10 MOT robustly test g-2 BSM Phase 2: 1e13 MOT cover thermal dark matter
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