Search of the X17 Boson @ n_ToF Carlo Gustavino, INFN Roma Outline: Introduction X17 search @ ATOMKI X17 search @ n_ToF Possible Setup Conclusion Introduction A significant anomaly has been recently observed in the emission of electron-positron pairs in the 7Li(p,e+e-)8Be and 3H(p,e+e-)4He reactions. Krasznahorkay, A.J.; et al.: "Observation of Anomalous Internal Pair Creation in 8Be: A Possible Indication of a Light, Neutral Boson". Physical Review Letters. 116 (42501): 042501 (2016). Krasznahorkay, A.J.; et al.: "New evidence supporting the existence of the hypothetic X17 particle". arXiv:1910.10459v1 [nucl-ex] (23 October 2019). Reaction MX17(MeV) DMX17_STAT DMX17_SYST Statistical evidence 7Li(p,e+e-)8Be 16,70 0,35 0,50 >5 sigma 3H(p,e+e-)4He 16,84 0,16 0,20 >7,2 sigma v This anomaly has been interpreted as the signature of a Jp=1+ particle (hereafter X17) not foreseen in the standard model of particle physics. v X17 boson could be a mediator of a fifth force, characterized by a strong coupling suppression of protons compared to neutrons. v This evidence/scenario is presently not confirmed or excluded by other experiments or groups. 7Li(p,e+e-)8Be reaction @ ATOMKI + 18.2 1 Ep=1030 keV 17.6 1+ Ep=441 keV 7Be + p 3.0 2+ 0 0+ NIM, A808, 21 (2016) 3H(p,e+e-)4He reaction @ ATOMKI 0- G + 21.1 Ep=1.7 MeV (0 )=0.5 MeV + G - E =0.9 MeV 0 (0 )=0.84 MeV p 20.2 3H + p Q=19.8 MeV Ep=0.9 MeV E0+=0.53 MeV E0-=1.8 MeV 0 0+ 3H(p,e+e-)4He reaction @ ATOMKI Plastic scintillator Carbon fiber tube G(0+)=0.5 MeV G(0-)=0.84 MeV Q=19.8 MeV Ep=0.9 MeV E0+=0.53 MeV Target - Silicon strips e E0-=1.8 MeV e+ v 3H adsorbed on Ti layer v 6 plastic scintillator 82x86x80 mm3 v 6 double-sided silicon strip detector (3 mm wide strips, 0.5 mm thick) v 1 mm thick carbon fiber tube v Ep=0.9 MeV X17 @ nToF Basic idea: Exploiting the conjugate reaction: 3H(p,e+e-)4He 3He(n,e+e-)4He 0- E =0.9 MeV 21.1 En=0.7 MeV p 3He + n 0+ E =0-2 MeV 20.2 n 3H + p 0 0+ Signal/background 100<En(keV)<1000 Target lenght (cm) 20 v The e+e pairs due to X17 have a unique diameter (cm) 2,54 signature., i.e. they produce e+e-pairs with Pressure (bar) 30 Etot~9+9 MeV at large angle (~120°). v As the hungarian group did, the signal is the rate p (s-1) 1,3E+06 net area of the peak at large angle on the rate gamma (s-1) 13 3He(n,e+e-)4He monotone background. v The 18 MeV shower of the 3He(n,g)4He rate IPC (day-1) 66,3 reaction can be easily identified and rejected (single shower of ~18 MeV) v Protons due to the 3He(n,p)3H reaction have at very low energy (Q=764 keV) and low velocity. v Cosmic ray background (muon) can be measured with off spill measurements. v Gamma flash are in advance (T>1300 ns if En<1 MeV) and well identified by the calorimeter and the TPC. v R&D to increases the target density (high pressure and/or cooling). PossiBile setup e- 4 He+CO2 radiator (200 Bar) Cerenkov light to Buffers 3He target neutron beam (200 bar) SiPM Plexiglass Bottle e+ No signals due to protons ~20 MeV Gammas signals suppressed and well discriminated Segmented calorimeter and/or Coaxial Magnetic field can be implemented Conclusion (1) v A spectacular anomaly has been recently observed in the emission of electron- positron pairs in the 7Li(p,e+e-)8Be and 3H(p,e+e-)4He reaction. v This anomaly has been interpreted as the signature of a particle (X17 boson) not foreseen in the standard model of particle physics. v The X17 boson could be a mediator of a fifth force, characterized by a strong coupling suppression of protons compared to neutrons. v This scenario may be related to Dark Matter and to the 3.6 ss anomaly of muon magnetic moment. v A new measurement to confirm (or reject) the claimed is mandatory. New informations on X17 coupling are necessary to define a theoretical framework. v The proposed experiment at n_ToF is a study of X17 by an indipendent collaboration, using an improved setup and exploiting a new nuclear process. v The goal is to measure the parameter of X17 boson (mass, parity, life time..) and to shed light on the protophobic nature of fifth force (neutron induced reaction). v Standard 3He(n,e+e-)4He and 3He(n,g)4He reactions are also of great interest in nuclear physics, providing an important experimental footing for "ab initio" calculations. Conclusion (2) v Broad energy range at n_toFà X17 quantic numbers v Both the proposed setup allow the identification of e+e- pairs at large relative angle and a background rejection better than the ATOMKI group. v Specific R&D and theoretical calculations still needed (and in progress). v Setup suitable for other measurements. Concerning X17: 7Be(n,e+e-)8Be @ n_ToF 3H(p,e+e-)4He, 7Li(p,e+e-)8Be, 11B(p,e+e-)12C @ LUNA Thanks for the attention! SPARES PossiBile setup scintillator tiles e- 4 He+CO2 radiator (100 Bar) Cerenkov light to Buffers 3He target neutron beam (200 bar) SiPM Plexiglass Bottle e+ No signals due to protons ~20 MeV Gammas signals suppressed and well discriminated Segmented calorimeter and/or Coaxial Magnetic field can be implemented Possibile setup (1) E.M. calorimeter (e.g. Scintillator tiles with SiPM) TPC with MPGD e- (GEM/µMegas/RWELL) n-beam He3 target e+ TPC: tracks and vertex recognition e.m. calorimeter: T0 for the TPC, energy measurement TPC+calorimeter: background rejection Target DEFAULT target: commercial 3He tubes Diameter: 1 inch (25.4 mm) Pressure: 30 bar Thickness: 500 µm Material: 344 stainless steel Lenght: 10-100 cm X0= 0.029 Cost for a 20 cm long tube: 10 kEuro Tracker TPC with MPGD readout (GEM/µM/RWELL) 15-20 cm 15-20 cm ED= 0.2÷0.5 kV/cm ED 10 cm 15 cm ED 5 cm He3 target Gas drift volumes Ar/CO2/CF4 Ar/CO2 Central annular MPGD anular end plate cathode Thikcness (um) X0 (cm) % X0 Cu 3 1,43 0,021 kapton 50 28,6 0,017 glue 30 33,5 0,009 MILLIFOAM/honeycomb 3000 1312,5 0,023 glue 50 33,5 0,015 Cylindrical Supports kapton 30 28,6 0,010 0,096 Layering of inner/outer cylinder including field cage (in Cu) Field cage (inner/outer) cylinders ~0.1 radiation lenghts Tracker TPC MPGD readout (GEM/µM/RWELL) 15-20 cm 15-20 cm ED 10 cm 15 cm ED He3 target MPGD anular end plate Each quadrant could be divided in n.128 r-strips (0,78 mm pitch – max length ~ 15 cm) and n.640 (128-192-320) φ-strips with a pitch of 12 – 8 – 5 mrad (roughly 0,58 – 0,62 – 0,53 mm). Globally each quadrant will be readout with 768 (analog) electronic channels 768x4=3072 channel. MPGD END PLATES The most common MPGD as readout options: • triple-GEM • MicroMegas • µ-RWELL never used as TPC readout. ALICE TPC KEK TPC foreseen as Cylindrical- RWELL for CREMLIN-plus Micromegas looks the best solution (known technology and limited ion feedback) E.M. Calorimeter In progress: Scionix EJ200 tiles with SiPM readout e.m calorimeter+ SiPM readout TPC+µMegas end plate Fresnel Lens Target Scintillator bar SiPM FEE & DAQ (tentative estimate) • 768 chs/quadrant (n.128 r-strips + n.640 φ-strips) à n.6 APV25 • 3072 chs/end-plate à n.24 APV25 • 6144 chs/TPC à n.48 APV25 (n.3 x (8 master + 8 slave)) ……….. 7152 CHF • n.3 ADC …………………………………………………………………………………….. 3708 CHF • n.3 FEC …………………………………………………………………………………….. 4785 CHF • n.1 SRS-crate ……………………………………………………………………………. 809 CHF • Connectors, cables etc ……………………………………………………………... 3000 CHF TOT 19.454 CHF L'elettronica ha una profondità di 5x192= 5 µs à drift max=20 cm Costo Totale elettronica 40.000 CHF TPC (tentative estimate) Dear Carlo I've made an estimate (+/- 30%) for the production of: -Item 1 -->1 x Anode Micromegas detector : -30 cm active area with -Resistive protection -Radial and angle strips STIMA COSTI (+/- 30%, chiavi in mano) -3072 Channels -24 panasonic connectors or equivalent Costo totale (mezza camera) 21.000 CHF -Item 2-->1 x TPC field cage : -20cm high Costo Totale (camera intera) 36.000 CHF -one Inner tube 10cm diameter -one Outer tube 30cm diameter -Glued frames at both ends for gas tight assembly with o-rings -2 resistors chain per tube -No shielding -Single layer strips on 0.2mm Flex glass/epoxy tube -item3-->1 x Cathode circuit : -30cm active area Item1: Design cost between 3000 to 6000 CHF (depending on symmetries we can find to simplify the layout) Tooling costs: 2500 CHF Detector production : 6000 CHF Item2: Design cost: 1000 CHF Tooling costs: 1500 CHF Field cage production : 4500 CHF Item 3: Design cost : 300CHF Tooling costs: 300 CHF Cathode production : 800 CHF These 3 parts can be assembled with s simple screw driver. Possibile setup (2) 9 MeV positron Cerenkov Ring neutron beam SiPM 3He Plexiglass 9 MeV electron No signals due to protons ~No signal due to gammas Possible Coaxial Magnetic field + Plexiglass tube close to PMT's for e+e- identification Possible external e.m calorimeter (rough granularity) .