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Status of the HOLMES Experiment


The absolute neutrino mass is still an unknown parameter in the modern landscape of particle physics. The HOLMES experiment aims at exploiting the calorimetric approach to directly measure the neutrino mass through the kinematic measurement of the decay products of the weak process decay of \(^{163}\)Ho. This low energy decaying isotope, in fact, undergoes electron capture emitting a neutrino and leaving the daughter atom, \(^{163}\)Dy\(^*\), in an atomic excited state. This, in turn, relaxes by emitting electrons and, to a considerably lesser extent, photons. The high-energy portion of the calorimetric spectrum of this decay is affected by the non-vanishing neutrino mass value. Given the small fraction of events falling within the region of interest, to achieve a high experimental sensitivity on the neutrino mass, it is important to have a high activity combined with a very small undetected pileup contribution. To achieve these targets, the final configuration of HOLMES foresees the deployment of a large number of \(^{163}\)Ho ion-implanted TESs characterized by an ambitiously high activity of 300 Hz each. In this paper, we outline the status of the major tasks that will bring HOLMES to achieve a statistical sensitivity on the neutrino mass as low as 2 eV/c\(^2\).

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Fig. 2


  1. 1.

    Two events happening in a time interval greater than the time resolution are recognized as pileups if the second pulse occurs on the decay of the first. In these cases, the safest analysis approach is to discard both events, causing a dead time due to the loss of a fraction of events which is equal to few times the product between the activity and the decay time.

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    The limitation to only 16 channels is due to the usage of just half bandwidth by the firmware currently used.


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The HOLMES experiment is funded by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC Grant Agreement No. 340321. We also acknowledge support from the NIST Innovations in Measurement Science program.

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Correspondence to M. Faverzani.

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Faverzani, M., Alpert, B., Balata, M. et al. Status of the HOLMES Experiment. J Low Temp Phys (2020).

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  • Neutrino mass
  • Transition edge sensors
  • Electron capture