What a dilemma! What Herculean efforts to uncover the secrets of the universe! I am in awe! So we need even bigger machines or a novel approach!
"Using a 200-ton, blimplike metal chamber that looks like something out of Fritz Lang’s classic sci-fi movie Metropolis, 149 physicists have tried to measure the mass of the neutrino, the lightest and most elusive of matter particles—and have found that it’s too small to be weighed.
The Karlsruhe Tritium Neutrino Experiment (KATRIN) in Germany aims to weigh the nearly massless neutrino by observing the beta decay of tritium, a nucleus containing one proton and two neutrons. In the decay, one neutron turns into a proton, spitting out an electron and a neutrino and turning the nucleus into helium-3. By observing billions of decays and measuring the maximum energy of the electrons, researchers can infer the mass of the neutrino.
KATRIN finds that the neutrino must be lighter than 0.45 electronvolts (eV), lowering its previous limit by a factor of 2 “We now know very directly that the neutrino is at least a million times lighter than the next lightest fundamental particle, which is an electron,” ..."
From the editor's summary and abstract:
"Editor’s summary
The neutrino, a weakly interacting, uncharged elementary particle, has been shown to have a nonzero mass, the exact value of which remains unknown. This is not what the usually very reliable Standard Model of particle physics predicts, which means that measuring the neutrino mass may offer hints of physics that this model cannot account for.
The KATRIN Collaboration used the beta-decay of molecular tritium to directly measure the mass of the antiparticle of a particular flavor of the neutrino ...
Abstract
That neutrinos carry a nonvanishing rest mass is evidence of physics beyond the Standard Model of elementary particles. Their absolute mass holds relevance in fields from particle physics to cosmology.
We report on the search for the effective electron antineutrino mass with the KATRIN experiment. KATRIN performs precision spectroscopy of the tritium β-decay close to the kinematic endpoint. On the basis of the first five measurement campaigns, we derived a best-fit value of
eV2, resulting in an upper limit of mν < 0.45 eV at 90% confidence level. Stemming from 36 million electrons collected in 259 measurement days, a substantial reduction of the background level, and improved systematic uncertainties, this result tightens KATRIN’s previous bound by a factor of almost two."
New KATRIN results (original news release) "Neutrinos weigh less than 0.45 electronvolts/c2 – precision scale KATRIN sets new record "
Direct neutrino-mass measurement based on 259 days of KATRIN data (no public access)
Direct neutrino-mass measurement based on 259 days of KATRIN data (preprint, open access)
No comments:
Post a Comment