Dark Photon search with PADME at LNF Gabriele Piperno for the PADME collaboration Particles and Nuclei International Conference - Beijing, China - September 3, 2017
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 The Dark Matter problem Evidences : • spiral galaxies • Cosmic Microwave Background • gravitational lensing • galaxy clusters • Big Bang Nucleosynthesis • large scale structures Properties : Open questions : • stable (half life ∼ universe age) • DM nature • interaction(s) w/ SM • cold (non relativistic) • A whole new dark sector? • gravitational force • dark sector forces? • non baryonic 2/18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Dark Photon Dark Sector Possible solution to the DM elusiveness: DM does not interact directly w/ SM, but by Portals (A’) means of “portals”. • SM particles are neutral The simplest model under this symmetry adds a U(1) gauge • new field couples to the symmetry and its boson: SM w/ effective charge ε q the Dark Photon A’ Additionally the A’ could (partially) explain the (g-2) μ discrepancy A’ characteristics in the simplest model above: • 1 MeV < m A’ < 1 GeV A’ • ε ≳ 10 -3 Purely indicative numbers: it has been recently discarded as a solution 3/18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Dark Photon production In e + /e - collisions Dark Photon can be produced in 3 main ways: A’ e - A’ e + e + γ N e + γ Annihilation Bremsstrahlung A’ π 0 , η γ Mesons dec. (after production) 4 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Dark Photon decay Visible decays If DM particles w/ m DM < m A’ /2 do not exist: • A’ → SM (visible) decays A’ visible decays assuming • up to 2m μ , BR(e + e - ) = 1 (if m A’ > 2m e ) universal coupling ε q (q = charge) 1.00 e + − e 0.50 A’ lifetime proportional to: hadrons 1/( αε 2 m A’ ) 0.20 0.10 BR A' + − μ μ 0.05 + − W W 0.02 Invisible decays 0.01 If DM particles w/ m DM < m A’ /2 exist: 0.1 0.2 0.5 1.0 2.0 5.0 10.0 m (GeV /c ) 2 • A’ → DM (invisible) decays w/ (likely) BR ≃ 1 A' • SM decays suppressed by a factor ε 2 A’ lifetime proportional to: 1/( α D m A’ ) α D : A’ coupling constant to the Dark Sector 5/18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Visible search status Techniques : target e − • beam dump (bremsstrahlung) shield γ ′ detector e − • A’ decay products detection after high z E γ ′ e + E 0 target (A’ production) + shield (SM absorption) L tot L sh L dec • fixed target (bremsstrahlung, -2 10 annihilation) KLOE 2014 KLOE 2013 B A B AR ε 2009 • bump hunt in invariant mass (g-2) e WASA spectrum, displaced vertices APEX HADES (g-2) 2 ± σ B A B AR µ PHENIX A1 BESIII 2014 favored • meson decay NA48/2 -3 10 • only if A’ couples w/ quarks • old experiments reanalysis E774 E141 (g-2) μ excluded in the simplest -4 10 model, but still a lot of interest -2 -1 10 10 1 10 2 m [GeV/c ] ' γ 6 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Invisible search status Techniques : • DM scattering (bremsstrahlung) • missing mass search (annihilation) • detect by scattering the produced DM • kinematically constrained process • needed 4 parameters ( ε ,m A’ ,m DM , α D ) • no assumption on A’ decay chain .... − 2 10 K → π ν ν ε (g-2) ± 5 σ µ B A B AR 2017 favored 3 − 10 Not directly (g-2) NA64 comparable e 4 − 10 3 − − 2 − 1 10 10 10 1 10 m (GeV) A' 7 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 The PADME approach A’ search in e + e - annihilations looking for missing mass (invisible decay) in a kinematically constrained condition 2 MMiss for different M A' A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 22 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV A' mass= 20 MeV 600 A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 18 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV A' mass= 16 MeV ECAL A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV A' mass= 14 MeV e - 500 A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 12 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV A' mass= 10 MeV (target) A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV A' mass= 8 MeV γ 400 A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV A' mass= 6 MeV e + A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 4 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV A' mass= 2 MeV 300 (beam) A’ (missing energy) 200 100 0 0 100 200 300 400 500 600 2 MMiss (MeV) • known beam energy and position m 2Miss = ( P beam + P e - P γ ) 2 • measured photon energy and position • minimal model dependent assumptions: A’ couples to leptons • coupling of any new light particle produced in e + e - annihilation can be limited : Dark Photon, Axion Like Particles, Dark Higgs 8/18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 The detector (high energy) e + /e - veto active target small angle • plastic scintillator bars • diamond (low z) calorimeter • 100 μ m thickness • 25 PbF 2 • info on beam time, 3 × 3 × 15 cm 3 spot size, e + number • 0-20 mrad ang. cov. electromagnetic calorimeter • 616 2.1 × 2.1 × 23 cm 3 BGO • cylindrical shape w/ central hole • 20-95 mrad ang. cov. • (1-2)%/ √ E e + beam • 550 MeV MBP-S dipole (upper part not shown) • 5000 e + per bunch • 0.5 T • 40 ns bunch, • 1 m lenght. × 23 cm gap every 20 ms 9 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Detector top view (w/ signal) Signal: • single γ in the calorimeter • nothing in the other detector components A’ e - e + γ 3 m 10 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Active target Test detector Features: • Diamond (low z, reduced brems.) • Dim.: 20 × 20 × 0.1 mm 3 • 16 horiz. × 16 vert. active graphitic strips (average informations on beam) • σ x-y (beam position) < 2 mm • in vacuum w/ movement system Test detector results Beam position scan 11 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Electromagnetic calorimeter (1) Features: 616 BGO 2.1 × 2.1 × 23 cm 3 • σ E ≈ (1-2)%/ √ E @ 3 m from the target • high γ statistic • containment • cluster time resolution < 1 ns • angular resolution ≲ 1 mrad • angular coverage: [20,93] mrad • angular acceptance: [26,83] mrad • central hole for brems. to SAC (faster) 2° best choice, for free from L3 best choice, but very expensive Figura 1 : Schema del calorimetro dell’esperimento PADME, composto da 616 cristalli scintillanti di BGO, 21×21×230 mm 3 . 12 /18
Dark Photon search with PADME at LNF - Gabriele Piperno - PANIC 2017 Electromagnetic calorimeter (2) Dipole gap limits the angular acceptance ECAL target SAC dipole side view a/ √ E ⊕ b/E ⊕ c M. Raggi et al., NIM 862, 31 (2017) Results w/ a 5 × 5 BGO (2 × 2 × 22 cm 3 ) matrix test 250 MeV and multiples 450 MeV and multiples 13 /18
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