Nuove rilevazioni del raggio del protone

[lowenz]

Ce l'ha più piccolo del 4% (sempre che si possa immaginarlo come una sfera perfetta si intende )

http://physicsworld.com/cws/article/news/43128

The radius of the proton is significantly smaller than previously thought, say physicists who have measured it to the best accuracy yet. The surprising result comes from studies of muonic hydrogen and could mean that physicists need to rethink how they apply the theory of quantum electrodynamics (QED) – or even that the theory itself needs a major overhaul.
A proton comprises three charged quarks bound by the strong force and its radius is defined as the distance at which the charge density drops below a certain value. The radius been measured in two ways – by scattering electrons from hydrogen and by looking very closely at the difference between certain energy levels of the hydrogen atom called the Lamb shift. Until recently the best estimate of the proton radius was 0.877 femtometres with an uncertainty of 0.007 fm
This Lamb shift is a result of the interactions between the electron and the constituent quarks of the proton as described by QED. These interactions are slightly different for electrons occupying the 2S and 2P energy levels and the resulting energy shift is partly dependent on the radius of the proton.

The Lamb shift also occurs in muonic hydrogen, where the electron is replaced by a muon. However, the shift is much more dependent upon the radius of the proton because the muon is heavier than the electron and therefore it spends more time very near to – and often within – the proton.
Now an international team led by Randolf Pohl at the Max Planck Institute for Quantum Optics in Garching, Germany has measured the Lamb shift in muonic hydrogen for the first time and found the proton radius to be 0.8418 fm with uncertainty 0.0007 fm. While this is by far the most precise measurement to date, it is in striking disagreement with previous measurements.
The team used a proton accelerator at the Paul Scherrer Institute in Switzerland to create a beam of muons, which was then fired at hydrogen gas. Every so often a muon will collide with a hydrogen molecule, knock it apart and replace the electron to create muonic hydrogen. About 1% of the time the muon finds itself in the 2S state, where it can be excited to the 2P state by absorbing a photon from a laser pulse. The 2P state then decays with the emission of an X-ray.

By counting the number of such X-rays while scanning the frequency of the laser pulse, the team could make a very precise measurement of the photon energy required to driver the 2S-2P transition. This is then fed into a complicated QED calculation to obtain the radius of the proton.
Pohl told physicsworld.com that the team has been working on the measurement for the past 12 years and got the first inklings of the anomalous result about six years ago. Since then, the researchers have reviewed, repeated and improved their measurements so that they are confident that the results are correct.
According to Jeff Flowers of the UK's National Physical Laboratory there are three possible explanations for the discrepancy. The most likely is that QED is correct, but has been misapplied in what he describes as a "very difficult calculation". A second possibility is that there is a problem with the experiment – but Flowers, who was not involved in the measurement, believes that Pohl's team has done an excellent job. The least likely – but most exiting – according to Flowers is that there is something wrong with QED.
While QED rests on a weak mathematical foundation, it has been extremely successful in predicting the outcome of experiments. "Changing QED would be big philosophical change for physicists", he said.
The result has already caused a flurry of experimental and theoretical activity, with some physicists carefully redoing Lamb shift calculations and others trying to improve electron-based measurements of the proton radius.
Meanwhile, Pohl's team will repeat its experiment and do a new series of measurements on muonic helium to measure the radius of the helium nucleus.

[DeBroglie]

imho i protoni hanno dimensione variabile, dipende dalla condizione in cui si trovano

[lowenz]

Se vuoi testare di persona possiamo esporre te al fascio di muoni

Ops, hai gà superato l'emivita vedo!

[frankytop]

Originariamente inviato da lowenz

Se vuoi testare di persona possiamo esporre te al fascio di muoni

Ops, hai gà superato l'emivita vedo!

[bellissima89]

ma non avete considerato l'effetto tunnel xò


W la Fisica !

[frankytop]

Originariamente inviato da bellissima89

ma non avete considerato l'effetto tunnel xò


W la Fisica !

Si bella la Fisica...e qualcosa mi dice che tu sei correlato (entanglement) con quello di prima: la sorte di una particella è lagata alla sorte dell'altra,staremo a vedere se l'entanglement è stato spezzato.

[frankytop]

cvd

Eh l'entanglement non è stato spezzato,un'ulteriore conferma della sua validità grazie al sacrificio di un'utenza che ha voluto donare se stessa alla Scienza.

[SaettaC]

Ma non è tantissimo, il 4%? Immagino gli acceleratori di particelle: non dovrebbero cambiare significativamente i risultati? Chiedo, eh, sono ignorante in materia

[lowenz]

Originariamente inviato da SaettaC

Ma non è tantissimo, il 4%? Immagino gli acceleratori di particelle: non dovrebbero cambiare significativamente i risultati? Chiedo, eh, sono ignorante in materia

Dipende da quanto impatta sulla sezione d'urto (che è una grandezza legata cmq a processi stocastici)!

[Raghnar-The coWolf-]

perchè la QED dovrebbe preoccuparsi del raggio di massa?