News about ghost particles

News about ghost particles
This model of the GERDA experiment shows the onion-like structure which suppresses interfering signals from the environment. The germanium diodes in the center of the cryostat filled with liquid argon (–186°C) are to a larger scale. Credit: MPI for Nuclear Physics
(Phys.org) —Neutrinos are the most elusive particles having extremely weak interactions with all other particles. They have rather unusual properties and are even expected to be identical with their own antiparticles. So far this property is, however, not experimentally verified even though many studies of neutrinos over the last 60 years have already boosted our understanding of elementary particle physics.

Now scientists of the GERDA collaboration obtained new strong limits for the so-called neutrino-less double beta decay, which tests if neutrinos are their own . The result rules out an earlier claim and has various important implications for cosmology, astrophysics and particle physics and it adds information about neutrino masses.

Besides photons, neutrinos are the most abundant particles in the Universe. They are often called `ghost particles', because they interact extremely weakly with matter. They are therefore an invisible, but very important component of the Universe, which could carry altogether as much mass as all other known forms of matter, albeit traveling almost at the over fantastic distances. Their tiny masses have also important consequences for the structures in the Universe and they are the driving element in the explosion of Supernovae. But their most remarkable and important property has been proposed by Ettore Majorana in the 1930ies: Unlike all other particles that form the known matter around us, neutrinos may be their own antiparticles.

The GERDA (GERmanium Detector Array) experiment, which is operated at the Laboratori Nazionali del Gran Sasso underground laboratory of the Istituto Nazionale di Fisica Nucleare in Italy, is aiming to resolve the question whether neutrinos are in fact their own antiparticles, and to determine their mass. GERDA looks for so-called double beta decay processes in the germanium isotope Ge-76 with and without the emission of neutrinos, the latter being a consequence of the Majorana properties. In normal beta decay, a neutron inside a nucleus decays to a proton, an electron and an antineutrino. For nuclei like Ge-76, normal beta decay is energetically forbidden, but the simultaneous conversion of two neutrons with the emission of two antineutrinos is possible and has been measured by GERDA recently with unprecedented precision. This is one of the rarest decays ever observed with a half-life of about 2*1021 years, which is about 100 billion times longer than the age of the Universe. If neutrinos are Majorana particles, neutrino-less double beta decay should also occur at an even lower rate. In this case, the antineutrino from one beta decay is absorbed as neutrino by the second beta-decaying neutron, which becomes possible if are their own antiparticle.

In GERDA germanium crystals are both source and detector. Ge-76 has an abundance of about 8% in natural germanium and its fraction was therefore enriched more than 10-fold before the special detector crystals were grown. Searching for a needle in a haystack is trivial compared to the detection of double beta decay, since environmental radioactivity is a background occurring at a rate at least a billion times higher than double beta decay. The GERDA detector crystals and the surrounding detector parts were therefore very carefully chosen and processed. The observation of the extremely rare process requires in addition very delicate techniques to further suppress backgrounds from cosmic particles, natural radioactivity of the surroundings and even the experiment itself. The scientists met this challenge by mounting the detectors in the center of a huge vessel that is filled with extremely clean liquid argon, lined by ultrapure copper, which in turn is surrounded by a 10-meter-diameter tank filled with highly pure water; the whole located underground below 1400 meter of rock. Combining all these innovative and pioneering techniques it was possible to reduce the background to unprecedented levels.

Data taking started in fall 2011 using 8 detectors the size of a tin can and weighting two kilograms each. Subsequently, 5 additional newly designed detectors were commissioned. Until recently, the signal region was blinded and the scientists focused on the optimization of the data analysis procedures. The experiment has now completed its first phase with 21 kg?years of data accumulated. The analysis in which all calibrations and cuts had been defined before the data in the signal region were processed, revealed no signal of neutrino-less in Ge-76 which leads to the world's best lower limit for the half-life of 2,1*1025 years. Combined with information from other experiments, this result rules out an earlier claim for a signal by others. The new results from GERDA have interesting consequences for the knowledge on neutrino masses, extensions of the standard model of elementary particle physics, astrophysical processes and cosmology.

The next steps for GERDA will be to add additional newly produced detectors effectively doubling the amount of Ge-76. Data taking will then continue in a second phase after some further improvements are implemented to achieve even stronger background suppression.


Explore further

MAJORANA, the search for the most elusive neutrino of all

Provided by Max Planck Society
Citation: News about ghost particles (2013, July 17) retrieved 25 June 2019 from https://phys.org/news/2013-07-news-ghost-particles.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
0 shares

Feedback to editors

User comments

Jul 17, 2013
Say what? Did they show that the neutrino was likely to be its own antiparticle or what? A press release shouldn't be so complicated that you have to reason out the answer from the raw numbers.

Jul 17, 2013
While neutrino-less double beta decay is theoretically possible find one is not very likely. So not finding one is not conclusive evidence that a neutrino is not its own antiparticle.

Jul 17, 2013
Neutrinos are the most elusive particles having extremely weak interactions with all other particles. They have rather unusual properties and are even expected to be identical with their own antiparticles. So far this property is, however, not experimentally verified….

Besides photons, neutrinos are the most abundant particles in the Universe. They are often called `ghost particles', because they interact extremely weakly with matter. They are therefore an invisible, but very important component of the Universe, which could carry altogether as much mass as all other known forms of matter, albeit traveling almost at the speed of light over fantastic distances….

….In normal beta decay, a neutron inside a nucleus decays to a proton, an electron and an antineutrino….


It is interesting to note that we do know a lot about the neutrino, but we do not know what it is, how it was arisen from the neutron. Maybe this simple idea could explain its mechanism…
http://www.vacuum...=9〈=en

Jul 17, 2013
"News about ghost particles"

Can we not do a better headline than that?

"Besides photons, neutrinos are the most abundant particles in the Universe. They are often called `ghost particles'"

They are also often called "neutrinos". But who am I to say what name should be used to refer to them in a Physorg headline?

Here's my attempt at a descriptive headline:

Experiment to detect antineutrino-free double-beta decay of Germanium 76 detects nothing.

Jul 18, 2013
Maybe this simple idea could explain its mechanism…


Or maybe it couldn't. Equally plausible as my personal dense cheesehole theory of the universe.

Agree with pdorell, this article hasn't enlightened me on the subject of neutrino's for the least bit.

Jul 18, 2013
Perhaps it's ruled by the same Uncertainty Principle as any other particle, i.e., until you open the box to see whether the cat is dead or not, you don't know if it is it or it's anti.

Jul 18, 2013
This article starts out by saying:
Neutrinos are the most elusive particles....
And then in the third paragraph they say:
Besides photons, neutrinos are the most abundant particles....
So which is it? Abundant or elusive?


How about both? They are the most abundant, but they don't interact with baryonic matter that much, so they're hard to detect.

Jul 19, 2013
This is one of the rarest decays ever observed with a half-life of about 2*1021 years, which is about 100 billion times longer than the age of the Universe.

Umm, the universe is a lot older than 2*1021 = 2042 years...
which leads to the world's best lower limit for the half-life of 2,1*1025 years.

And what is that number supposed to mean? Considering the rarity of actual data in this article, would it be too much to ask to print that little data correctly? Please: if you write a scientific article, do learn to properly write scientific numbers!

Also, FYI, "half-life" is a _statistical_ property that can only be sensibly evaluated if you have _many_ data points to look at. This experiment delivered none so far, so what is it, exactly, that this value is based on?

"I couldn't pull a rabbit out of this top-hat over the course of the past 12.5 years, so that means it's got a half-life of 2 to the power of 173 years"

Yes. Right.

Jul 21, 2013
I take issue with the statement "... are even expected to be identical with their own antiparticles." Anti-neutrinos should spin in the opposite direction.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more