5 ms·
Looking quickly through the two papers mentioned [0, 1], there is a (statistically) very solid result that something is going on with 8Be, which is only very ba
by yk 10y ago
Looking quickly through the two papers mentioned [0, 1], there is a (statistically) very solid result that something is going on with 8Be, which is only very barely a nucleus and is probably better thought of as a bound state of two alpha particles. In [0] there is a experimental observation of some kind of effect which can be explained by a 17 MeV boson. [1] looks at other experiments and finds a way around current experimental bounds by building a "protophobic" model, that is a boson that does not interact with protons. Interestingly they find that in this model they can explain the anomalous magnetic moment of the muon, if the parameters are somewhat close to already excluded limits. (Fig. 1 bottom panel in [1]) So the next generation of experiments should rule out or discover the X boson. (And actually there are many experiments which seem to have a shot at this.)
My take on this, it is probably a parametrization of something we do not understand in terms of a particle. This something may be a experimental effect or a theoretical lack of understanding or insufficient methods for calculation, or a new particle. The energy range is sort of interesting since it is close to the energy range of hadron spectroscopy, a field which is littered with 2-sigma 'tantalizing hints' of new physics. To end this, I believe it is a temptation to speculate (read I will claim I resisted the temptation until "told you so" is an appropriate response), that a heavy charged particle, cough di-photon excess, could be involved in creating the different couplings to u and d quarks.
[0] https://arxiv.org/abs/1504.01527 https://arxiv.org/abs/1504.01527
[1] https://arxiv.org/abs/1604.07411 https://arxiv.org/abs/1604.07411
- ssivark 10y agoAha! I'm currently at a conference where one of the authors of [1] gave a talk [2] about this and there was an interesting follow-up discussion. Never expected it to be on HN already! Some thoughts from the thick of things: 1. It's important to remember that nuclear physics backgrounds for such an experiment are hard to model (so that one can subtract them out). The field is littered with "anomalies" coming from systematics and backgrounds. This is why physicists are very cautious with this claim. The authors of the theoretical model claim that it should be easily testable (interesting signals in several different experiments) over the next 2-3 years, so that's one reason to be optimistic about knowing where this stands. 2. This model goes against the grain of most of our theories for how the baryonic matter (essentially nuclei of all kinds) could be created in the universe! If you believe in this newly proposed model as truly another force of nature, then one might need a new paradigm for generating all the matter we see. There are some theoretically intriguing aspects of the model, so I'm looking out for the follow-up paper by the authors (sometime in the next few weeks?) dealing with several of these aspects. -- Edited to add a link to the slides and elaborating on point #2 below For more advanced readers (along with the caveat that I don't fully understand the details of their model): We understand very well the production of nuclei soon after the big-bang [3] and there's no room to modify that theory. So, any more fundamental model will have to produce baryons before that era of the universe. The Sakharov conditions [4] for producing baryons require a breaking of Baryon number (you can't have a net excess of baryons over anti-baryons unless you break the symmetry between the two). Usual models produce baryon number by using the fact that U(1) baryon number is anomalous in the presence of electroweak sphalerons [5]. However, in the newly proposed theory U(1) B-L [6] is gauged and hence cannot be anomalous (thereby invalidating the conventional paradigm for generating baryons). Maybe a spontaneous breaking of that symmetry happens early enough in the universe to not mess with the theory of nucleosynthesis but I'm not aware of work along such a paradigm. -- [2]: https://indico.cern.ch/event/518614/contributions/1198831/attachments/1277655/1896398/1605texasam.pdf https://indico.cern.ch/event/518614/contributions/1198831/at... [3]: https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis [4]: https://en.wikipedia.org/wiki/Baryogenesis#Sakharov_conditions https://en.wikipedia.org/wiki/Baryogenesis#Sakharov_conditio... [5]: https://en.wikipedia.org/wiki/Sphaleron#Sphalerons_and_baryogenesis https://en.wikipedia.org/wiki/Sphaleron#Sphalerons_and_baryo... [6]: https://en.wikipedia.org/wiki/B_%E2%88%92_L https://en.wikipedia.org/wiki/B_%E2%88%92_L
- yk 10y agoCan you expand a bit on the 2. point? (Probably there are some implications for bariosynthesis, but I don't have a good feeling how they should look like.)
- Frompo 10y agoYeah, I found the lack of discussion about possible causes by modifying atomic physics rather than go directly to new particles disappointing. Maybe there is a good reason to trust that standard theory cannot be modified to introduce bumps in the angular distribution, but I think it really should be mentioned in that case. Honestly, this gives a very hep-th impression: "An anomaly! we solve it by adding an X-particle with properties that magically explain the anomaly. Hurray!" Its actually in hep-ph though, which I guess shows that I'm out of touch : / Anyway, exploit hunters have there uses too I guess.
- themartorana 10y agoSometimes I wish I had gone with physics in college. Nothing quite captures me like discussions about the bounds of our knowledge of the universe.