The PADME experiment proposal Mauro Raggi Laboratori Nazionali

The PADME experiment proposal Mauro Raggi – Laboratori Nazionali di Frascati 49 th LNF scientific committee Frascati, 18 -19 May 2015 PADME website http: //www. lnf. infn. it/acceleratori/padme/ PADME Kick-off meeting http: //agenda. infn. it/event/padme-kickoff

The simplest dark sector model The simplest hidden sector model just introduces one extra U(1) gauge symmetry and a corresponding gauge boson: the “dark photon" or U boson. Two type of interactions with SM particles should be considered As in QED, this will generate new interactions of the type: e. A’ e+ Not all the SM particles need to be charged under this new symmetry In the most general case qf is different in between leptons and quarks and can even be 0 for quarks. [P. Fayet, Phys. Lett. B 675, 267 (2009). ] The coupling constant and the charges can be generated effectively through the kinetic mixing between the QED and the new U(1) gauge bosons g A’ In this case qf is just proportional to electric charge and it is equal for both quarks and leptons. M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 2

A’ production and decays A’ boson can be produced in e+ collision on target by: 1. Bremsstrahlung: e+N →e+NA’ 2. Annihilation: e+e-→ g. A’ 3. Meson decays If no dark matter candidate lighter than the A’ boson exists: A’→e+e-, m+m-, p+p-. These are the so called “visible” decays For MA’<210 Me. V A’ only decays to e+e- with BR(e+e-)=1 1. Bremsstrahlung 2. Annihilation 3. Meson decays Decays to “visibles” If any dark matter particle c with 2 Mc<MA’ exists A’ will dominantly decay into pure DM and BR(l+l-) becomes small ~ e 2 A'→cc ~ 1. These are the so called decays to “invisible” particles M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 3

Dark photon searches in the world A 1 @ MAMI WASA @ COSY HADES @ GSI Cornell Phenix @ RHIC ATLAS, CMS @ LHC P-348 @ SPS KLOE 2 @ DAFNE Ba. Bar @ PEP-II SHIP @ SPS PADME @ BTF JLAB: APEX NA 48/2 HPS, Mu 3 e @ PSI Dark. Light BDX VEPP-III Belle. II Super. KEKB Legenda: Publishing Approved Proposals M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 4

A’ visible searches status Favored parameters values explaining (g 2)m (green band) A’-boson light: 10 -100 Me. V Status of dark photon searches Beam dump experiments (grey): e+e- appearance after a dump Fixed target: Peak search over QED backgrounds Mesons decays: Peaks in M(e+e-) or M(m+m-) Indirect exclusion from ge-2 and gm-2 Recent tight limit in red filled area ar. Xiv: 1411. 1770 v 2 Many different techniques and assumptions on dark photon interaction models Kinetic mixing, decay to electrons, no dark sector particles (g-2)m band recently excluded by NA 48/2 measurement in meson decays M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 5

Status A’→cc invisible decays ar. Xiv: 1406. 2698 v 1 Babar ’ 08 Ar. Xiv 0808. 0017 Search for Invisible Decays of a Light Scalar in Radiative Transitions U 3 S� g. A’ ar. Xiv: 1309. 5084 v 1 e 2 and MA’ e 2, MA’, Mc and a. D Two different techniques are used: direct A’ search, c scattering searches Direct searches for A’ only depend on 2 parameters : e 2 and MA’ c scattering searches depend on 4 parameters: e 2, MA’, Mc and a. D Kaon indirect constraints are on the other hand model dependent M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 6

Invisible A’ model dependence Exclusion with Kaons Scattering exclusion In models assuming that the dark photon couples to SM through kinetic mixing eq≠ 0 K±→p±nn can be used to constrain K±→p±A’ Zd=A’ Depending on how the model is built the limit can change significantly for example allowing the mass mixing with SM Z. Phys. Rev. D. 89. 095006 M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 7

Combining visible and invisible N. B. This kind of exclusion plot fixes e with (g-2)m and shows a. D vs m. A’ PADME ar. Xiv: 1406. 2698 v 1 PADME can access the plot independently of a. D up to 20 -30 Me. V The exclusion by PADME is independent from the value of mc as well M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 8

The PADME approach At present all experimental results rely on at least one of the following model-dependent assumptions: A’ decays to e+e- (visible decays assumption) and thus BR(A’→e+e-) = 1 A’ couples with the same strength to all fermions (eq= el) (kinetic mixing) In the most general scenario (PADME) A’ can decay to dark sector particles with m<MA’/2, and BR(A’→e+e- <<1) Dump and meson decay experiment only limit e 2 BR(A’→e+e- <<1) A’ can couple to quark with a coupling constant smaller el or even 0 Suppressed or no production at hadronic machines and in mesons decays PADME aims at detecting A’ produced in e+e- annihilation and decaying into any final state by searching for missing mass in e+e -→g. A’, A’→cc No assumption on the A’ decays products and coupling to quarks Only minimal assumption: A’ bosons couples to leptons PADME will limit the coupling of any new light particle produced in e+ecollisions: scalars (Hd), vectors (A’ and Zd) M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 9

DAFNE Beam Test Facility (BTF) electrons Maximum energy [Me. V] 750 (1050) Me. V Linac energy spread [Dp/p] Typical Charge [n. C] positrons 550 (800) Me. V 0. 5% 1% 2 n. C Bunch length [ns] NIM A 515 (2003) 524– 542 0. 85 n. C 1. 5 - 40 Linac Repetition rate 1 -50 Hz Typical emittance [mm mrad] 1 ~10 Beam spot s [mm] 1 mm Beam divergence 1 -1. 5 mrad Longer Duty Cycle Standard BTF duty cycle = 50*10 ns = 5 x 10 -7 s Already obtained upgrade 50*40 ns= 20 x 10 -7 s work in progress to exceed 100 ns Energy upgrade possible in 2017. The accessible MA’ region is limited by beam energy Region from 0 -22 Me. V can be explored with 550 Me. V e+ beam M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 10

The PADME experiment 103 -104 e+ on target per bunch, at 50 bunch/s (1013 -1014 e+/year) Basic detector components: Active target, thin: 50 -100 mm diamond Magnetic spectrometer/veto ~1 m length Conventional magnet, B≈0. 6 T but large gap for gaining acceptance Available from CERN, former 1. 75 PS mto SPS transfer line H-dipole R=15 cm cylindrical crystal calorimeter with 1 x 1 x 20 cm 3 crystals M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 11

The PADME experiment By C. Capoccia LNF SPAS M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 12

The electromagnetic calorimeter 30 cm Cylindrical shape: radius 150 mm, depth of 200 mm Inner hole 4 cm radius Active volume 13120 cm 3, total of 656 crystals, 10 x 200 mm 3 Material LSO(Ce): high LY, high r, small X 0 and RM, short tdecay Material BGO: high LY, high r, small X 0 and RM, long tdecay, (free from L 3? ) Expected performance: s(E)/E =1. 1%/√E � 0. 4%/E � 1. 2% Super. B calorimeter test at BTF [NIM A 718 (2013) 107– 109] s(q) = 3 mm/1. 75 m < 2 mrad Angular acceptance 1. 5 -5 degrees M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 13

PADME Geant 4 simulation M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 14

Search in annihilation production M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 15

Experimental technique ECal Spectrometer g P 4 beam 550 Me. V e+ C target Spectrometer 2 s s i Mm A’ Search for the process: e+e- → g. A’ on target e- at rest (104 e+)/bunch beam on a 100 mm diamond target, 550 Me. V energy 40 ns long bunches, 49 bunches/s Collect 1013 e+ on target in 2× 107 s of data taking Measure in the calorimeter the Eg and qg angle wrt to beam direction Compute the Mmiss 2 = (P 4 e- + P 4 beam - P 4 g)2 P 4 e- =(0, 0, 0, me) and P 4 beam =(0, 0, 550, sqrt(5502 + me 2)) M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 16

Decay to invisible signal selection Selection cuts Only one cluster in calorimeter Rejects e+e-→gg, e+e-→gg(g) final states 5 cm < RCl < 13 cm Improve shower containment s(E)/E Positron veto: no tracks in the spectrometer in ± 2 ns Reject BG from Bremsstrahlung identifying primary positrons Photon veto: no g with Eg>50 Me. V in time in ± 1 ns in the additional small angle veto (SAV), covering the hole acceptance Cluster energy within: Emin(MA’) < ECl < Emax(MA’) Me. V Removes low energy bremsstrahlung photons and piled up clusters Missing mass in the region: Mmiss 2 ± s(Mmiss 2) M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 17

Main background sources Geant 4 simulation accounts for: Bremsstrahlung, 2 photon annihilation, Ionization processes, Bhabha and Moller scattering, and production ofδ-rays. Custom treatment of e+e-→gg(g) using Calc. Hep generator. e. A’ Signal: e+e-→g +missing mass (A’) g e+ Backgrounds e- g g e+ +1 electron g e- +1 g M. Raggi PADME LNF Scientific Committee g e+ +2 g Frascati 18/05/15 18

Bremsstrahlung background Present inefficiency is due to particles remaining very close to the beam spot due to the emission of low energy photons. Improving with an imaging veto? M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 19

Rejecting 3 g with SAV veto 3 g background 3 g no veto 3 g veto Low mass region is less suppressed due to the request of ESAV>50 Me. V Are the missing photon at large angle? Can we have veto detectors also at large angles? M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 20

PADME invisible sensitivity estimate Based on 2. 5 x 1010 fully GEANT 4 simulated 550 Me. V e+ on target events Number of BG events is extrapolated to 1 x 1013 electrons on target Using N(A’g)=s(NBG) d enhancement factor d(MA’) = s(A’g)/s(gg) with e=1 PADME invisible decays exclusion First inclusive analysis M. Raggi, V. Kozhuharov Advances in High Energy Physics Vol. 2014 ID 959802, M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 21

And much more… a. D=0. 1 mc=10 Me. V 1・ 1020, 1. 2 Ge. V electrons; 20 cm aperture at 50 cm from 10 cm W dump Ba. Bar NA 48/2 PADME ee PADME mm E 137 1. 2 Ge. V electrons Cs. I detector 60× 225 cm 3 built with crystals from dismounted Ba. Bar ECal? M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 22

PADME project plans Project has been presented as a “What Next” Project in INFN CSN 1 The project has received positive feedback form CSN 1 referees Proposal for R&D financing will be presented in the June 2015 CSN 1 meeting First test beams with calorimeter are ongoing Proto collaboration formed including LNF, Rome 1, Lecce and Sofia university Formal commitment of INFN groups by July 2015 CSN 1 meeting 6 weeks test beam time asked at DAFNE BTF in 2015 Study the prototype of BGO calorimeter solution (L 3 crystals) Photo-detector studies (Si. PM vs. APD) Readout electronics: pre-amp, readout boards, digitization, etc. Test diamond target prototypes (October 2015) Study the maximum beam current per bunch for PADME dump Study and optimize positron beam for PADME invisible: Spot size and stability Maximum positron energy Divergence and momentum spread Intensity Bunch length Charged and neutral background M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 23

Very preliminary results from BTF tests Primary beam (DAFNE running): 15 mm 2 mm FWHM Electrons, E 0=510 Me. V, 1 n. C BTF target at 1. 7 X 0 TB 3 UP, DOWN = 0. 1, 0. 1 mm TB 4 LEFT, RIGHT = OPEN TB 1 and TB 2 = OPEN Exit Be window 447 Me. V positrons = 88% E 0 ≈2000 particles/bunch 10 ns bunch width 4. 5 mm FWHM σy≈0. 8 mm Dominated by multiple scattering on 0. 5 mm Be window + 20 cm of air Further improved operating in vacuum σx≈2 mm FITPIX detector Dominated by momentum spread, due to TB 2 slits completely OPEN Can be improved by using an optimized (thinner) target and by closing the TB 2 slits A thinner target also allows to run closer to the primary energy Running in parallel to DAFNE injections implies some limitations: Bunch width fixed at 10 ns ( <<40 ns already achieved with present gun hardware) E 0<Emax(550 Me. V) Further limitation if BTF target is used for positron production (DAFNE needs both e + and e−) E<E 0 in order to have 103 -104 particles/pulse Overall limit: E ≤ 450 Me. V M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 24

A possible schedule for PADME-invisible Vacuum: design and build vessel and interface to BTF Magnet and positron veto: Cutting and polishing of available (≈70 crystals) Procurement of missing ≈150 L 3 BGO crystals and cutting and polishing Or: purchase of new LYSO crystals Choice of photo-sensor, design of front-end electronics DAQ and trigger already being developed Build SAV and – in case – large angle calorimeters Diamond Target Magnet transportation to Frascati, tests, field-mapping, cabling from main DAFNE power supply hall to BTF (Former splitter magnet power supplies available, 400 A/80 V) Scintillating bars with wavelength shifting fibers + Si. PM readout (<200 channels) EM Calorimeters Preliminary design done Construction and installation Thin diamond R&D Grafitization vs. metallization Readout Beam Positron beam at 550 Me. V/40 ns already available Assess longer pulse with acceptable energy spread New pulser (up to 1 ms) Try additional double phase inversions Proposed upgrade to 750 Me. V positrons or more under evaluation M. Raggi PADME LNF Scientific Committee Order of 1. 5 years starting from cash flow start Legenda: 2015 2016 2017+ Frascati 18/05/15 25

Conclusions An experiment running at the DAFNE BTF sensitive to both A’→invisible and A’→e+e- decays has been proposed to INFN. A model-independent exclusion limit in e 2 down to 1・ 10 -6 can be achieved in invisible decays with the present Linac/BTF beam parameters in the region MA’ 2 -22 Me. V with 1013 eot (2× 107 s at 49 Hz) Any increase of the bunch width will reflect in higher statistics and thus improved sensitivity: aiming at 150 -200 ns, but 500 ns seems to be possible Increasing the positron energy would extend the exclusion to higher A’ masses The proposed upgrade to 750 Me. V/1 Ge. V for primary positrons/electrons would extend the sensitivity to ≈30 Me. V M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 26

SPARE SLIDES M. Raggi PADME LNF Scientific Committee Frascati 18/05/15 27