What upcoming experiments hold hope for physics BTSM?

[Kontilera]

Im sure this is a rather subjective matter, but as a layman Im curious. Im not really sure at which state the LHC experiments are at the moment, but I found an article[1] about the possibility of LHCb to detect "dynamics beyond the standard model that would elude searches that focus on energetic objects or precision measurements of known processes." So, to you who are professionals in the field, what experiments are you following with extra interest?

Thanks in advance.

[1]
https://iopscience.iop.org/article/10.1088/1361-6633/ac4649

 

[Vanadium 50]

All experiments have the potential to discover new physics.

 

[Kontilera]

All experiments have the potential to discover new physics.

In theory yes, physics beyond the standard model, no. However Im sure that there are different kinds of experiments that seems more promising that others. Im not looking for a discussion about which is more promising that the other, but it would be interesting to know if there are any experiments coming up that people who are well read on the field, personally, will follow with interest.
As for me, Im not really sure which areas that are relevant. The article above gave one example.

Although many experiments could have an interesting outcome, I guess, physics beyond the standard model is more likely to be discovered in experiments involving high energy using adquete measuring devices/detectors.

 

[Vanadium 50]

All experiments have the potential to discover new physics.

Asking which ones will before the data comes in is unscientific.

 

[ohwilleke]

The fairest way to consider this question is to consider where there have been anomalies in existing experiments that deviate from the SM and what we know about their potential causes.

The strongest evidence for some kind of physics beyond the Standard Model from existing experiments and observations are the astronomy observations of phenomena attribute to dark matter and dark energy. No terrestrial experiments have found any evidence for BSM physics that could explain this, but there are many BSM models to explain this that would escape detection by these means (e.g., truly "sterile" particles that don't interact via any SM forces), so the failure to detect dark matter particles so far isn't necessarily all that notable. Something certainly isn't consistent with the SM and with General Relativity as conventionally applied. But we're not really sure exactly what causes this phenomena.

New particles or forces that explain this would be beyond the Standard Model physics. Gravitational physics explanations would be an explanation involving General Relativity or modifications of General Relativity, rather than beyond the Standard Model physics in the strict sense.

Several observations that had previously pointed towards BSM physics, such as suggestions of violations of lepton universality in B meson decays, suggestions of neutrinos that travel faster than the speed of light, and suggestions of a proton size that is different in hydrogen with an electron than it is in hydrogen with a muon where the electron should be, have all been resolved in favor of the Standard Model in the end after issues with the experiments were identified. New physics claims that antimatter particles might be subject to a repulsive force from gravity rather the attractive force that applies to all other mass-energy has also recently been strongly disfavored by new experiments.

There are still some outstanding tensions between other aspects of B meson decays and the SM predictions, but these are only modestly above 2 sigma anomalies that are likely to eventually be resolved in favor of the SM (virtually all experimental anomalies under 3 sigma from the SM eventually end up getting resolved somehow in the end). And, we know statistically, that if you do enough experiments that some percentage of them will give statistically improbable results. It is hard in practice to quantify how many experiments are out there to exactly evaluate the question, but lots of mild anomalies in experiments that are "locally" significant are not statistically significant "globally" when you consider the fact that some percentage of experiments are expected to have statistically improbable result even if the SM is perfectly correct. And, thinking about anomalies in terms of probabilities is the correct way to think about it because the SM all involved quantum mechanics and quantum mechanists is inherently stochastic (i.e. probabilistic rather than deterministic).

Another area of research that has produced some results that show quite significant deviations from the SM are in neutrino physics. One experiment in Russia has claimed to find evidence of neutrinoless double beta decay (which is SM forbidden unless neutrinos have Majorana mass) despite the fact that every other experiment has ruled out the possibility that this Russian experiment claims to have seen. Several reactor neutrino experiments claim to have seen "sterile neutrinos" but the parameter spaces that their respective observations point to sterile neutrinos having are mutually exclusive. There have likely been experimental hints of "non-standard neutrino interactions", but those hints likewise have been in parameter spaces that other experiments have ruled out.

One of the biggest anomalies outstanding is the measurement of the anomalous magnetic moment of the muon (muon g-2) which is a measurable electromagnetic property of the muon whose exact numerical value can be calculated to parts per billion precision and can be measured with similar precision. Two consistent measurements of muon g-2 have been made to roughly this precision. These measurements are inconsistent with one of the leading calculations of what it's value should be in the SM, and are consistent with another very different leading calculation of what's value should be in the SM. Since the discrepancy between the two predicted values emerged, efforts have been made to see which of the two calculations is correct and while this hasn't been definitively resolved, almost all of the work done so far supports the calculation that is consistent with the SM over the calculation that is inconsistent with the SM - which may be inaccurate because of inaccuracies in old experiments that it relied upon.

There are searches underway to see if the Higgs boson observed has precisely the properties of the SM Higgs boson (so far there are no glaring anomalies on this front). There are also searches for additional Higgs bosons out there that are suggested by many theoretically proposed extensions of the SM, most of which have come up empty, but some of which have found some weak anomalies that are being investigated.

The ATLAS and CMS experiment continually search for new high mass supersymmetric particles and several other classes of theoretically conjectured high mass particles that are beyond the SM, but so far those searches have always come up empty too, excluding most of these into the high hundreds of GeV or low TeV range.

There are other areas where there are tensions with the SM. One of these is the mean lifetime of an unbound neutron , which is complicated by differences between inclusive and exclusive experimental measurements that have known, hard to quantify, systemic errors. Similarly, there are issues with getting the probabilities of one quark to transition into other kinds of quarks (quantified in the CKM matrix) to add up to 100% in every possibility. This anomaly also involves issues of systemic error between inclusive and exclusive measurements, among other things. But, if known systemic error issues could be overcome and these anomalies were still outstanding, this could point to BSM physics, although few scientists have proposed any plausible mechanisms to explain these anomalies if they really were due to BSM physics.

It isn't very uncommon for experimental observations of the properties of hadrons (i.e. composite particles bound by the strong force) to be inconsistent with their predicted values. New instances of this occurring are reported in preprints at arXiv maybe every month or two, on average. But in these cases, the means by which predictions are made are a mix of arts and science with various different recognized means of calculating predicted values often differing greatly from each other as well as from the experimentally measured value. For that reason, unexpected anomalies in hadron physics are rarely heralded as contradictions of the Standard Model even by the researchers discovering them. Instead, they are more often treated as "let's go back to the drawing board and figure out what's going on here" moments.

Similarly, there are lots of well established hadron physics phenomena, like scalar (i.e. spin-0 even parity) and axial vector mesons, about which there is no consensus about their structure or the source of their properties from fundamental physics, despite decades of efforts to figure out the answer to these questions.

In the same vein, even though glueballs (hadrons made up only of gluons with no quark component) have been predicted and described for 50 years in quantum chromodynamics (QCD), no one has ever observed a free glueball, possibly because they always blend with other less exotic hadrons with similar quantum numbers.

But almost no physicists in the hadron physics field see these unexplained phenomena as ground to doubt that correctness of the SM theory of the strong force known as QCD. This is largely because doing QCD calculations is so profoundly difficult that blaming problems with approximating the full rigorous QCD calculation for the problem is almost always a more plausible explanation than new physics.

One anomaly in the angles of decay products in certain nuclear decays (seen by only one experiment and not replicated by other experiments) has a proposed resolution of a new BSM particle called the X17 boson since the effect observed could be explained by a new boson with a mass of 17 MeV. But, there are potential explanations of this from ordinary SM physics. Efforts to confirm or rule out this anomalous result are underway (kodama at Physics Forums has followed this work closely in some threads that he has started such as this one).

 

[kodama]

One anomaly in the angles of decay products in certain nuclear decays (seen by only one experiment and not replicated by other experiments) has a proposed resolution of a new BSM particle called the X17 boson since the effect observed could be explained by a new boson with a mass of 17 MeV. But, there are potential explanations of this from ordinary SM physics. Efforts to confirm or rule out this anomalous result are underway (kodama at Physics Forums has followed this work closely in some threads that he has started such as this one).

https://indico.him.uni-mainz.de/eve...28/attachments/906/1399/2_menu23_domenici.pdf
sure taking a long time :(

 

[Kontilera]

.

Very interesting! Thanks! I will read more with this post as a reference source. :)

 

[Kontilera]

All experiments have the potential to discover new physics.

Asking which ones will before the data comes in is unscientific.

If you consider it unscientific to regard the LHCb data to have a higher likelihood of showing BSM physics than, say, a laboration measuring the spring constant in a high school classroom then we really got nothing to discuss.

Im sure its a difficult topic, but, again, Im not asking for a hierarchy among coming experiments. Im just, as a layperson, asking which experiments people within the field regards as promising (or at least having the potential) to show anything beyond the standrad model. Is it unreasonable? I think not. The post from Ohwilleke above was exactly an example of what I was looking for and I am very thankful for the time he spent writing that.

 

[Frabjous]

All experiments have the potential to discover new physics.

Asking which ones will before the data comes in is unscientific.

We do it all the time to make funding/access decisions.

 

[ohwilleke]

https://indico.him.uni-mainz.de/eve...28/attachments/906/1399/2_menu23_domenici.pdf
sure taking a long time :(

Physicists have nothing on lawyers.