Starship Asterisk*

Céline Richard wrote:Hello

I have visited the LHC while it was still under construction, in August 2007.

I remember researchers seek an elementary particle, the Boson de Higgs.
It is curious, because it is supposed not to have a mass.

http://en.wikipedia.org/wiki/Higgs_boson wrote:

Excluded Higgs Mass Possibilities

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<<As of December 2010, the Higgs boson has yet to be confirmed experimentally,despite large efforts invested in accelerator experiments at CERN and Fermilab.

Prior to the year 2000, the data gathered at the LEP collider at CERN allowed an experimental lower bound to be set for the mass of the Standard Model Higgs boson of 114.4 GeV/c2 at 95% confidence level. The same experiment has produced a small number of events that could be interpreted as resulting from Higgs bosons with mass just above said cutoff—around 115 GeV—but the number of events was insufficient to draw definite conclusions. The LEP was shut down in 2000 due to construction of its successor, the Large Hadron Collider which is expected to be able to confirm or reject the existence of the Higgs boson.

At the Fermilab Tevatron, there are ongoing experiments searching for the Higgs boson. As of July 2010, combined data from CDF and DØ experiments at the Tevatron were sufficient to exclude the Higgs boson in the range between 158 GeV/c2 and 175 GeV/c2 at the 95% confidence level. Data collection and analysis in search of Higgs are intensifying since March 30, 2010 when the LHC began operating at 3.5 Tev and is rapidly approaching in its design range of 7 Tev, well above that at which detection should occur.

It may be possible to estimate the mass of the Higgs boson indirectly. In the Standard Model, the Higgs boson has a number of indirect effects; most notably, Higgs loops result in tiny corrections to masses of W and Z bosons. Precision measurements of electroweak parameters, such as the Fermi constant and masses of W/Z bosons, can be used to constrain the mass of the Higgs. As of 2006, measurements of electroweak observables allowed the exclusion of a Standard Model Higgs boson having a mass greater than 285 GeV/c2 at 95% CL, and estimated its mass to be 129⁺⁷⁴₋₄₉ GeV/c2 (the central value corresponds to approximately 137 proton masses { one over the fine structure constant }). As of August 2009, the Standard Model Higgs boson is excluded by electroweak measurements above 186 GeV at 95% CL. However, it should be noted that these indirect constraints make the assumption that the Standard Model is correct. One may still discover a Higgs boson above 186 GeV if it is accompanied by other particles between Standard Model and GUT scales.

In a 2009 preprint, it was suggested (and reported under headlines such as Higgs could reveal itself in Dark-Matter collisions) that the Higgs Boson might not only interact with the above-mentioned particles of the Standard model of particle physics, but also with the mysterious WIMPs ("weakly interacting massive particles") of the Dark matter, playing a most-important role in recent astrophysics. In this case, it is natural to augment the above Feynman diagrams by terms representing such an interaction.

In principle, a relation between the Higgs particle and the Dark matter would be "not unexpected", since the Higgs field does not directly couple to the quanta of light (i.e. the photons), while at the same time it generates mass. However, "dark matter" is a metonym for the discrepancy between the apparent observed mass of the universe and that given by the standard model and is not a component of any known theory of physics. Consequently, the usefulness of this conjecture is limited.

Barring discovery during current intensive efforts, it will be sometime after the end of the current physics fill at the LHC in 2011 and some further months or years of analysis of the collected data before scientists can confidently believe that the Higgs Boson does not exist.>>

neufer wrote:DisCERN, v. t. [F. disCERNer, L. disCERNere, discretum; dis- + CERNere to separate, distinguish.]

neufer wrote:It is curious, because Higgs is supposed to be the primary source of mass.

Céline Richard wrote:

neufer wrote:
It is curious, because Higgs is supposed to be the primary source of mass.

Actually, i thought it was the contrary although a particle without mass seems unreal.

http://en.wikipedia.org/wiki/Neutrino#Mass wrote:
<<The Standard Model of particle physics assumed that neutrinos are massless, although adding massive neutrinos to the basic framework is not difficult. Indeed, the experimentally established phenomenon of neutrino oscillation requires neutrinos to have nonzero masses. This was originally conceived by Bruno Pontecorvo in the 1950s.

The strongest upper limit on the masses of neutrinos comes from cosmology: the Big Bang model predicts that there is a fixed ratio between the number of neutrinos and the number of photons in the cosmic microwave background. If the total energy of all three types of neutrinos exceeded an average of 50 eV per neutrino, there would be so much mass in the universe that it would collapse. This limit can be circumvented by assuming that the neutrino is unstable; however, there are limits within the Standard Model that make this difficult. A much more stringent constraint comes from a careful analysis of cosmological data, such as the cosmic microwave background radiation, galaxy surveys, and the Lyman-alpha forest. These indicate that the sum of the neutrino masses must be less than 3.0 eV.

In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos do indeed flavor oscillate, and therefore have mass.

In 2009 lensing data of a galaxy cluster were analyzed to predict a neutrino mass of about 1.5 eV. All neutrino masses are then nearly equal, with neutrino oscillations of order meV. They lie below the Mainz-Troitsk upper bound of 2 eV for the electron anti-neutrino. The latter will be tested in 2015 in the KATRIN experiment, that searches for a mass between 0.2 eV and 2 eV. If it is found around 1.5 eV, then the Cold Dark Matter particle likely does not exist.

Currently a number of efforts are under way to directly determine the absolute neutrino mass scale in laboratory experiments. The methods applied involve nuclear beta decay (KATRIN and MARE) or neutrinoless double beta decay (e.g. GERDA, CUORE/Cuoricino, NEMO-3 and others).

In May 2010, it was reported that physicists from CERN and the Italian National Institute for Nuclear Physics' Gran Sasso National Laboratory had observed for the first time a transformation in neutrinos; evidence that they have mass.

In July 2010 3-D MegaZ experiment suggested that the upper limit of the combined mass the three neutrino to be less than 280 meV, a disagreement with the astronomical evidence that requires resolution.>>