Angular distribution in s-channel formation of the pentaquark $Theta^+$ baryon

Using the DIANA data on the charge-exchange reaction $K^+n rightarrow pK^0$ on a bound neutron, in which the s-channel formation of the pentaquark baryon $Theta^+(1538)$ has been observed, we analyze the dependence of the background-subtracted $Theta^+ rightarrow pK^0$ signal on the $K^0$ emission angle in the $pK^0$ rest frame. In order to describe the observed $cosTheta_K^mathrm{cms}$ distribution, invoking the interference between the nonresonant s-wave and the $Theta^+$-mediated higher-wave contributions to the amplitude of the charge-exchange reaction is required at a 2.8$sigma$ level. The spin--parity assignment of 1/2$^-$ for the $Theta^+$ baryon is ruled out at a statistical level of 2.9 standard deviations. A physically-meaningful selection in $cosTheta_K^mathrm{cms}$ based on the observed angular dependence of the $Theta^+ rightarrow pK^0$ signal allows to boost the statistical significance of the signal up to 7.1 standard deviations. This is far in excess of previously reported signals and renders the $Theta^+$ existence more credible.

X-rays help to unfuzzy the concept of measurement

In the last decades huge theoretical effort was devoted to the development of consistent theoretical models, aiming to solve the so-called measurement problem, to which John Bell dedicated part of his thoughts. Among these, the Dynamical Reduction Models possess the unique characteristic to be experimentally testable, thus enabling to set experimental upper bounds on the reduction rate parameter $lambda$ characterizing these models. Analysing the X-ray spectrum emitted by an isolated slab of Germanium, we set the most stringent limit on the parameter $lambda$ up to date.

Unprecedented studies of the low-energy negatively charged kaons interactions in nuclear matter by AMADEUS

The AMADEUS experiment aims to provide unique quality data of $K^-$ hadronic interactions in light nuclear targets, in order to solve fundamental open questions in the non-perturbative strangeness QCD sector, like the controversial nature of the $Lambda(1405)$ state, the yield of hyperon formation below threshold, the yield and shape of multi-nucleon $K^-$ absorption, processes which are intimately connected to the possible existence of exotic antikaon multi-nucleon clusters. AMADEUS takes advantage of the DA$Phi$NE collider, which provides a unique source of monochromatic low-momentum kaons and exploits the KLOE detector as an active target, in order to obtain excellent acceptance and resolution data for $K^-$ nuclear capture on H, ${}^4$He, ${}^{9}$Be and ${}^{12}$C, both at-rest and in-flight. During the second half of 2012 a successful data taking was performed with a dedicated pure carbon target implemented in the central region of KLOE, providing a high statistic sample of pure at-rest $K^-$ nuclear interactions. For the future dedicated setups involving cryogenic gaseous targets are under preparation.

Beyond quantum mechanics? Hunting the impossible atoms (Pauli Exclusion Principle violation and spontaneous collapse of the wave function at test)

The development of mathematically complete and consistent models solving the so-called measurement problem, strongly renewed the interest of the scientific community for the foundations of quantum mechanics, among these the Dynamical Reduction Models posses the unique characteristic to be experimentally testable. In the first part of the paper an upper limit on the reduction rate parameter of such models will be obtained, based on the analysis of the X-ray spectrum emitted by an isolated slab of germanium and measured by the IGEX experiment. The second part of the paper is devoted to present the results of the VIP (Violation of the Pauli exclusion principle) experiment and to describe its recent upgrade. The VIP experiment established a limit on the probability that the Pauli Exclusion Principle (PEP) is violated by electrons, using the very clean method of searching for PEP forbidden atomic transitions in copper.

Low energy kaon-nuclei interaction studies through the Sigma^0pi^0 channel with the KLOE detector

The AMADEUS experiment aims to perform precision studies in the sector of low-energy kaon-nuclei interaction at the DAPhi NE collider at LNF-INFN, implementing a dedicated setup in the central region of the KLOE detector. As a first step towards the AMADEUS realization the existing KLOE data (runs from 2002 to 2005) were analysed using the detector itself as an active target. K^- nuclear interactions in the gas filling the KLOE drift chamber (Helium 90% and Isobutane 10%) and the drift chamber entrance wall (mainly Carbon) were explored. Starting point was the reconstruction of the Lambda(1116) trough its decay into a proton and a pion (BR = 63.9 pm 0.5%). Taking advantage of the good performances of the KLOE calorimeter in detecting photons we then focused on the investigation of the Lambda(1405), through its decay into Sigma^0pi^0. The details of the Sigma^0 pi^0 analysis and preliminary results are presented.

New experimental limit on Pauli Exclusion Principle violation by electrons (the VIP experiment)

The Pauli Exclusion Principle is one of the basic principles of modern physics and is at the very basis of our understanding of matter: thus it is fundamental importance to test the limits of its validity. Here we present the VIP (Violation of the Pauli Exclusion Principle) experiment, where we search for anomalous X-rays emitted by copper atoms in a conductor: any detection of these anomalous X-rays would mark a Pauli-forbidden transition. ] VIP is currently taking data at the Gran Sasso underground laboratories, and its scientific goal is to improve by at least four orders of magnitude the previous limit on the probability of Pauli violating transitions, bringing it into the 10**-29 - 10**-30 region. First experimental results, together with future plans, are presented.