Abstract
Neutrinos are so far the most elusive known particles, and in the last decades many sophisticated experiments have been set up in order to clarify several questions about their intrinsic nature, in particular their masses, mass hierarchy, intrinsic nature of Majorana or Dirac particles. Evidence of the Neutrinoless Double-Beta Decay (NDBD) would prove that neutrinos are Majorana particles, thus improving the understanding of the universe itself. Besides the search for several large underground experiments for the direct experimental detection of NDBD, the NUMEN experiment proposes the investigation of a nuclear mechanism strongly linked to this decay: the Double Charge Exchange reactions (DCE). As such reactions share with the NDBD the same initial and final nuclear states, they could shed light on the determination of the Nuclear Matrix Elements (NMEs), which play a relevant role in the decay. The physics of DCE is described elsewhere in this issue, while the focus of this paper will be on the challenging experimental apparatus currently under construction in order to fulfil the requirements of the NUMEN experiment. The overall structure of the technological improvement to the cyclotron, along with the newly developed detection systems required for tracking and identifying the reaction products and their final excitation level are described.
Highlights
Neutrinos are currently the most elusive known particles, even though during the last decades we have painfully started to know them better by means of bigger and bigger experiments with increased sensitivity [1,2,3,4]
The Double Charge Exchange reactions (DCE) reactions to be studied are quite simple: one sends a beam of a suitable nuclear species, typically 18 O or 20 Ne, on a target made of a Neutrinoless Double-Beta Decay (NDBD) candidate nuclear species, namely one among 48 Ca, 76 Ge, 76 Se, 82 Se, 96 Zr, 100 Mo, 106 Cd, 110 Pd, 116 Cd, 110 Sn, 124 Sn, 128 Te, 130 Te, 136 Xe, 130 Xe, 148 Nd, 150 Nd, 154 Sm, 160 Gd, 198 Pt
In order to disentangle the reactions of interest from the overwhelming amount of forward-going ions produced by all the other nuclear reactions, the solution is to use a high resolution and large acceptance magnetic spectrometer, capable of selecting outcoming particles in a very small range of kinetic energy, mass, and charge, while deflecting away all the rest, i.e., MAGNEX
Summary
Neutrinos are currently the most elusive known particles, even though during the last decades we have painfully started to know them better by means of bigger and bigger experiments with increased sensitivity [1,2,3,4]. An important ingredient of the NDBD is the so-called Nuclear Matrix Element (NME), which links the states of the decaying nucleus before and after the decay and enters the expression of the half-life T1/2 of the NDBD, possibly providing a handle on the Majorana effective neutrino mass determination. The NDBD decay rate can be expressed as a factorization of three terms: the phase-space factor G0ν, the NME M0ν, and the term f (mi , Uei , ξi ) containing a combination of the masses mi , the mixing coefficients Uei, and the Majorana phases ξi of the neutrino species [T1/2 ]−1 = G0ν ·|M0ν |2 · f (mi , Uei , ξi ) (1) E. From Equation (1), one can deduce that if the NMEs are established with sufficient precision, the neutrino masses and the mixing coefficients can be extracted from NDBD decay rate measurements. Discrepancy larger than a factor of two between the different models are presently reported in literature
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