Eur. Phys. J. C (2009) 62: 327-332
https://doi.org/10.1140/epjc/s10052-009-1068-1

Regular Article - Experimental Physics

New search for processes violating the Pauli exclusion principle in sodium and in iodine

¹ Dip. di Fisica, Università di Roma “Tor Vergata”, 00133, Rome, Italy
² INFN, sez. Roma “Tor Vergata”, 00133, Rome, Italy
³ Dip. di Fisica, Università di Roma “La Sapienza”, 00185, Rome, Italy
⁴ INFN, sez. Roma, 00185, Rome, Italy
⁵ Laboratori Nazionali del Gran Sasso, INFN, Assergi, Italy
⁶ IHEP, Chinese Academy, P.O. Box 918/3, Beijing, 100039, China
⁷ University of Jing Gangshan, Jiangxi, China

^* e-mail: rita.bernabei@roma2.infn.it

Received: 3 March 2009
Revised: 27 April 2009
Published online: 4 June 2009

Abstract

In this paper a new search for non-Paulian nuclear processes, i.e. processes normally forbidden by the Pauli Exclusion Principle (PEP), is presented. It has been carried out at the Gran Sasso National Laboratory of the INFN by means of the highly radiopure DAMA/LIBRA set-up (sensitive mass of about 250 kg highly radiopure NaI(Tl)). In particular, a new improved upper limit for the spontaneous non-Paulian emission rate of protons with energy E _p ≥ 10 MeV in ²³Na and ¹²⁷I has been obtained: 1.63 × 10⁻³³ s⁻¹ (90% C.L.). The corresponding limit on the relative strength (δ ²) for the searched non-Paulian transition is δ ²≲(3–4)×10⁻⁵⁵ (90% C.L.). Moreover, PEP-violating electron transitions in iodine atoms have also been investigated. Lifetimes shorter than 4.7×10³⁰ s are excluded at 90% C.L.; this allows us to derive the limit δ _e ² <1.28×10⁻⁴⁷ (90% C.L.). This latter limit can also be related to a possible finite size of the electron in composite models of quarks and leptons providing superficial violation of the PEP; the obtained upper limit on the electron size is r ₀<5.7×10⁻¹⁸ cm (energy scale of E≳3.5 TeV).