Search of the X17 @ 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 - 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 ". 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 of . v X17 boson could be a mediator of a , characterized by a strong coupling suppression of compared to . 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

e- 4 He+CO2 radiator (200 bar) Cerenkov light to buffers 3He target 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 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 , 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)