The PADME experiment, hosted at the Laboratori Nazionali di Frascati, will
search for a Dark Photon that decays in invisible channels with a mass up to
$23.7\,\mbox{MeV}$ and coupling constant down to $10^{-3}$.Comment: 3 pages, 2 figures, to be published in the IFAE2016 proceedings on
  Nuovo Cimento C - Colloquia on Physic

Piperno, G.

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arXiv

The PADME experiment, hosted at the Laboratori Nazionali di Frascati, will search for a Dark Photon that decays in invisible channels with a mass up to 23.7MeV and coupling constant down to 10−3

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DOI 10.1393/ncc/i2017-17029-2Colloquia: IFAE 2016IL NUOVO CIMENTO 40 C (2017) 29The PADME experimentG. Piperno for the PADME CollaborationINFN Laboratori Nazionali di Frascati - Via E. Fermi, 40, I-00044 Frascati (Rome), Italyreceived 17 October 2016Summary. — The PADME experiment, hosted at the Laboratori Nazionali diFrascati, will search for a Dark Photon that decays in invisible channels with a massup to 23.7 MeV and coupling constant down to 10−3.1. – IntroductionSince first cosmological evidences, the Dark Matter (DM) direct detection remainsan open issue. This puzzle can be solved hypothesizing that the DM does not directlyinteract with the Standard Model (SM) gauge fields, but only by means of “portals” thatconnect our world with this dark sector. The simplest model adds a U(1) symmetry andits corresponding vector boson A′ [1]: SM particles are neutral under this symmetry,while the new field, thanks to the possible mixing with the photon, could couple to SMwith an effective charge εe and for this reason is often called Dark Photon (DP).Recently it has been noted that an A′ with mass in the range 1 MeV to 1 GeV andconstant ε ≈ 10−3 can explain the discrepancy between theory and experiment on themuon anomalous magnetic moment (g − 2)μ [2].2. – The experimentApproved by the INFN at the end of 2015, PADME will search for DP that decays intoinvisible channels (DM or long lived A′ independently of the decay products nature) [3,4].The experiment is designed to detect as missing energy the A′ produced in the reactione+e− → A′γ, where e+, provided by the LNF linac, is incident on a fixed target. Sincethe initial state kinematic is known (Pe− and Pbeam for the e− and the e+, respectively),the A′ invariant mass can be determined measuring the photon in the final state (Pγ):M2miss =(Pe− + Pbeam − Pγ)2,where Pe− = 0 and Pbeam has the nominal value of 550 MeV along the z-axis.Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 G. PIPERNO for the PADME COLLABORATIONcalorimetersmall angle calorimeterhigh energypositron vetopositron veto spectrometeractivetargetelectron veto spectrometerimaging vetovacuum vesseleγRoutnot interacting beam+BTFvacuumFig. 1. – PADME detector layout. The distance between the target and the calorimeter (whichhas a radius of 29 cm) is 3 m, while the small angle calorimeter is a square of 14 cm side.Fig. 2. – PADME sensitivity for different bunch lengths and in absence of background (SES) atthe nominal beam energy of 550 MeV.Figure 1 shows the experiment layout. The detector consists in an active target(diamond with graphitic strips to determine the beam position), a MBP-S dipole,that deflects the exaust beam and direct the e+ that lost energy (the majority forbremsstrahlung) towards the vetoes, an electromagnetic calorimeter (616 2× 2× 22 cm3bismuth germanate crystals, energy resolution ∼ (1−2)%√E), that measures energy and an-gle of the produced γ, with a central opening to let bremsstrahlung radiation to pass,which is then identified by the small-angle calorimeter (49 2 × 2 × 20 cm3 SF57 leadglasses for Cherenkov light).Main backgrounds to be reduced with the detector geometry are the e+ e− annihilationinto 2 or 3γ and the bremsstrahlung, while the pile-up, being connected to the bunchdensity, will be the most important limiting factor to the PADME sensitivity.The collaboration aims to build the detector by the end of 2017 and to collect1013 550MeV positrons on target by the end of 2018, reaching a sensitivity on theDP coupling constant to the SM charge ε of ∼ 10−3 and a DP mass up to 23.7MeV(see fig. 2).REFERENCES[1] Holdom B., Phys. Lett. B, 166 (1986) 196.[2] Pospelov M., Phys. Rev. D, 80 (2009) 095002.[3] Raggi M. and Kozhuharov V., Adv. High Energy Phys., 2014 (2014) 959802.[4] Raggi M., Kozhuharov V. and Valente P., EPJ Web of Conferences, 96 (2015) 01025.

The PADME experiment

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The PADME experiment

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