First of all, I'm old! I started being in a student in physics since the early 1980's (do your own math). During all of that time when I have paid attention to physics, I've seen a lot of major milestones, including the discovery of High-Tc superconductors, discovery of exoplanets, the cold-fusion debacle, etc...etc.
The one thing that pops up every now and then is the claim of the possible discovery of this "fifth force". Honestly, even back in the 1980's, there were already such claims being made. None of the have amounted to anything as far as I can tell. Therefore, you can understand my "Oh no, this again?" reaction when I read the latest claim of the possible detection of the Yukawa particle as an indication of the existence of this fifth force (that article contains a link to the actual PRL paper that you can download).
This is not a knock on this work, heavens no. But the publicity surrounding this makes it sound as if this has not happened before. I guess it is not surprising that people have short memory, which is why mistakes are often repeated.
I'm going to wait a year and revisit this post and see if we have gone beyond first based on this discovery.
The big news of the week that got all the media coverage is the result that came out of Fermilab's Muon g-2 experiment that confirmed an earlier result from Brookhaven more than a dozen years ago. Fermilab even announced it like.
However, as with any scientific discovery or announcement, one has to take a deep breath and let the process works itself out before we put our stamp of validity to it. This is because there is a theoretical calculation that has also been published along with this result that basically recalculates what the Standard Model predicts as the magnetic moment of a muon, and they found that the new calculation produces a result consistent with the experiment. In other words, there is no new physics if this calculation is verified, because the old Standard Model does, in fact, predicted this new result.
One of the major difficulties in physics is that in many situations, we do not have a simple equation that we can plug-and-chug to get numbers out. In fact, this is why predicting the weather is difficult, because the non-linear differential equations that need to be solved to get the number out can only be done numerically, i.e. it has to be done via some numerical algorithm.
This is made worse when there are a gazillion interactions involved in a system. So one ends up making simplifying models or adopt calculational techniques to allow us to get to some numerical answers. We benchmark the technique to known values and known systems to make sure that it gives accurate and sensible answers, but as we push the boundary even more, there is no guarantee that that calculational technique will work all the time.
The author of the theoretical paper used a calculational technique called lattice QCD. This is a known calculational model that has been described in simple terms in the link I provided above. It appears that using this method, the Standard Model does provide a value for the muon magnetic moment that is consistent with the experiment. If this is true, then it means that the old calculation of the magnetic moment was incorrect in the first place, and that there is discrepancy between what the Standard model predicts, and what the experiment measures.
While this is good news for the Standard Model and is another evidences of why it is an amazing theory, those who are looking for new physics beyond the Standard Model will obviously not be jumping for joy. But that isn't the issue here and not what I want to highlight. Rather, it is the constant reminder that in science, and especially in such exotic areas of physics, every discovery or new ideas must not be overblown or overhyped, because those require multiple verification over a period of time. It is not a situation for instant gratification. A lot of hard work is still to come because we have seen way too many times where something that was touted turned out to not be valid.
This announcement received a lot of media coverage. I just hope that this is a valid "new physics" and not just something that turned out to be what the old theory did predict.
The latest report on T2K results has been published[1], and it looks good for the upcoming long neutrino baseline experiment at DUNE and T2HK. The result may suggest that these two upcoming experiments may finally nail down CP violation in neutrinos, which will be a substantial advancement in our understanding on why there are more mater than antimatter in our universe.
The discovery of substantial leptonic CP violation would be
groundbreaking. Its observation, together with evidence that a quantity
known as lepton number has been violated (that is, not conserved), would
provide strong circumstantial evidence for leptogenesis as the origin
of the matter–antimatter imbalance.
I suppose if I want to be accurate, I should say it is the electron antineutrino, since they measured this from beta decays, but nowadays, we don't have a clear cut idea of the difference between the neutrino and its antiparticle. For all we know, they can possibly also be a Majorana particle.
I'll be giving this report to my students in the general physics class, and see if they can convert the 1.1 eV into "kg". :)
The latest and most accurate experiment to detect any hint of an electric dipole moment of an electron has revealed that there isn't any.
Now, the Advanced Cold Molecule Electron
Electric Dipole Moment, or ACME, search, based at Harvard University,
has probed the electron’s EDM with the most precision ever — and still found no sign of smooshing, the team reports online October 17 in Nature.
The finding improves the team’s last best measurement (SN Online: 12/19/13) by a factor of 10 to find an EDM of 10-29 electron
charge centimeters. That’s as round as if the electron were a sphere
the size of the Earth, and you shaved less than two nanometers off the
North Pole and pasted it onto the South Pole, says Yale University
physicist David DeMille, a member of the ACME team.
This improves upon the previous measurement that I mentioned a year ago. Looks like if any theory predicts the possible structure of an electron, they have some severe constraints to overcome.
In this video, Fermilab's Don Lincoln tackles less about physics, but more about history and classification of our current Standard Model of elementary particles.
I decided to modify a bit the title of the Symmetry article that I'm linking to, because in that article, the possible link between the Higgs boson and dark matter is made. This allows for the study of the decay of the Higgs to be used to detect the presence of dark matter.
The Standard Model not only predicts all the different possible
decays of Higgs bosons, but how favorable each decay is. For instance,
it predicts that about 60 percent of Higgs bosons will transform into a
pair of bottom quarks, whereas only 0.2 percent will transform into a
pair of photons. If the experimental results show Higgs bosons decaying
into certain particles more or less often than predicted, it could mean
that a few Higgs bosons are sneaking off and transforming into dark
matter.
Of course, these kinds of precision measurements cannot tell
scientists if the Higgs is evolving into dark matter as part of its
decay path—only that it is behaving strangely. To catch the Higgs in the
act, scientists need irrefutable evidence of the Higgs schmoozing with
dark matter.
So there you have it.
If you are not up to speed on the discovery of the Higgs (i.e. you've been living under a rock for the past few years), I've mentioned a link to a nice update here.
If it is covered in CNN, then it has to be a big-enough news. :)
I mentioned earlier that the g-2 experiment at Fermilab was about to start (it has started now), which is basically a continuation and refinement of what was done several years ago at Brookhaven. In case the importance of this experiment escapes you, Don Lincoln of Fermilab has written a piece on the CNN website on this experiment and why it is being done.
If you are not in science, you need to keep in mind this important theme: scientists, and definitely physicists, like it A LOT when we see hints at something that somehow does not fit with our current understanding. We like it when we see discrepancies of our results with the things that we already know.
This may sound odd to many people, but it is true! This is because this is why many of us get into this field in the first place: to explore new and uncharted territories! Results that do not fit with our current understanding give hints at new physics, something beyond what we already know. This is exploration in the truest sense.
This is why there were people who actually were disappointed that we saw the Higgs, and within the energy range that the Standard Model predicted. It is why many, especially theorists working on Supersymmetry, are disappointed that the results out of the LHC so far are within what the Standard Model has predicted.
The old muon g-2 experiment that was at Brookhaven was taken apart, and rebuilt at Fermilab. Now, after the logistic challenge of moving the huge magnet from there, and after the long hard work of rebuilding the facility, the muon g-2 is now about ready to start its run.
The facility is now better than ever, and physicists are hoping that there will be an anomaly in the measurement, indicating new physics beyond the Standard Model.
In 2013, the g-2 team lugged the experiment on a 5000-kilometer odyssey from Brookhaven to Fermilab, taking the ring by barge around the U.S. eastern seaboard and up the Mississippi River.
Since then, they have made the magnetic field three times more uniform,
and at Fermilab, they can generate far purer muon beams. "It's really a
whole new experiment," says Lee Roberts, a g-2 physicist at Boston
University. "Everything is better."
Over 3 years, the team aims to collect 21 times more data than during
its time at Brookhaven, Roberts says. By next year, Hertzog says, the
team hopes to have enough data for a first result, which could push the
discrepancy above 5 σ.
Ethan Siegel has yet another nice article. This time, he tackles on why we have an abundant of matter in our universe, but hardly any antimatter, when all our physics seems to indicate that there should be equal amount of both, or simply a universe filled with no matter.
I have highlighted a number of CP-violation experiments on here, which is something mentioned in the article. But it is nice to have a layman-type summary of the baryo-lepton-genesis ideas that are floating out there.
There have been experiments to measure the electric dipole moment of an electron, if any, which would indicate that (i) an electron has an internal structure and (ii) consequently it isn't a point particle that we have been assuming within QED. So far, all the experiments have not found any, and each measurement continues to increase the precision of the previous measurement.
Chalk this one up to follow the same trend[1]. This time, they are using a different technique to measure the electron dipole moment by using trapped molecular ions. The result of the experiment is an even more precise measurement, and lowered the upper bound of the dipole moment by several orders of magnitude when compared to the previous result.
Electron is still a spherical cow!
Zz.
[1] W.B. Cairncross et al., Phys. Rev. Lett. v.119, p.153001 (2017).
This is a nice and simple article on why we are searching for the neutrinoless double-beta decay.
In this new study, physicists are seeking so-called neutrinoless double-beta decay.
Normally, some radioactive atoms' unstable nuclei will lose a neutron
via beta decay — the neutron transforms into a proton by releasing an
electron and a tiny particle called an electron antineutrino. A mirror
image can also occur, in which a proton turns into a neutron, releasing a
positron and an electron neutrino — the normal-matter counterpart to
the antineutrino. Double-beta decay happens when two electrons and two
antineutrinos (the antimatter counterparts of neutrinos) are released:
basically, the beta decay happens twice. Scientists have long theorized a
neutrinoless version of this process — something that would suggest
that the two neutrinos annihilated each other before being released from
the atom. Essentially, the neutrino behaves as its own antimatter
sibling.
A large portion of high-energy physics experiments around the world are done using neutrinos (Daya Bay, MINOS, NOvA, SuperK, etc...). It won't surprise me one bit that the another major discovery will be made with these particles.
I'm going to highlight this latest video by Fermilab's Don Lincoln for a number of reasons. First, the video:
Second, this is one video packed with a number of very important and illuminating stuff. First he explains about the concept of "spin" in both the classical and quantum picture. This is important because to many people who do not study physics, the word "spin" conjures up a certain idea that is not correct when applied to quantum mechanics. So this video hopefully will enlighten the idea a bit.
But what is more fascinating here is his brief historical overview of the first proposal of the connection between the weak interaction and spin, and how Chien Shiung Wu should have received the Nobel Prize for this with Yang and Lee. This might be another case of gender bias that prevented a brilliant Chinese female physicist from a deserving prize. Considering the time that she lived in and the societal and cultural obstacles that she had to overcome, she simply had to be just too outstanding to be able to get to where she was.
So this is one terrific video all around, and you get to learn a bit about the weak interaction to boot!
A new theoretical paper in PRL has extended the Standard Model of elementary particles to include new particles, and tries to mash different ideas and theories into this new standard model called SMASH - Standard Model Axion See-saw Higgs portal inflation (yeah, it's a mouthful).
SMASH adds six new particles to the seventeen fundamental particles of
the standard model. The particles are three heavy right-handed
neutrinos, a color triplet fermion, a particle called rho that both
gives mass to the right-handed neutrinos and drives cosmic inflation
together with the Higgs boson, and an axion, which is a promising dark
matter candidate. With these six particles, SMASH does five things:
produces the matter–antimatter imbalance in the Universe; creates the
mysterious tiny masses of the known left-handed neutrinos; explains an
unusual symmetry of the strong interaction that binds quarks in nuclei;
accounts for the origin of dark matter; and explains inflation.
Of course, with ANY theoretical ideas, which often has long gestation period, a lot of patient waiting and testing will have to be done to verify many of its predictions. But this seems to create quite an excitement in revamping the Standard Model.
Carrying out the whole procedure 11 times, the group found that on
average just under 60% of antiatoms left the trap with the laser tuned
to the 1s-2s transition, while no antiatoms (within the bounds of
statistical error) dropped out when the laser was tuned to a different
frequency or when it was switched off. The researchers say that the
antiatoms underwent the transition at the expected frequency and
therefore behaved no differently from normal hydrogen.
I'm sure there will be many more to come. The ability to store antihydrogen long enough to study it is a major accomplishment in itself.
John Timmer on Ars Technica has written a wonderful article on the "proton radius problem". The article gives a brief background on an earlier discovery, and then moves on to a new result on a deuterium atom.
This area is definitely a work-in-progress, and almost as exciting as the neutrino mass deficiency mystery from a many years ago.
It is always nice when non-science media carries physics news. Unfortunately, often times, the accuracy is lacking and, in many cases, gives misleading ideas. This is one such case.
At the T2K experiment, researchers looked for a difference between neutrinos and antineutrinos oscillations. Their findings,
announced at the International Conference on High Energy Physics in
Chicago, suggest that there are — more muon neutrinos were found
changing into electron neutrinos than muon antineutrinos changing into
electron antineutrinos.
The researchers, who had expected to
detect 23 electron neutrinos and seven electron antineutrinos, observed
32 electron neutrinos and 4 electron antineutrinos.
.
.
.
If confirmed with a greater level of certainty, this would point to a
violation of charge-parity (CP) symmetry in neutrinos. CP symmetry tells
us that a system remains unchanged even if two fundamental properties —
charge and parity, which refers to a 180-degree flip in spatial
configuration — are reversed. If a violation of CP symmetry is
confirmed, it would not only hint at the existence of physics beyond the
Standard Model — a theory of almost everything — it would also help us
understand why the universe is completely devoid of antimatter.
There's nothing wrong with the report. However, it is inaccurate with regards to what it left out. If you don't know any better, you'd think that this is something new, and that this is the first instance of CP violation. This is not true. CP violation has been seen in other particle systems. So there is no longer a question on whether such violation exists. What is new here is that it is the first time it is observed in neutrino oscillation.
This is why science reporting is difficult. You need someone who has a wide breadth of knowledge in many fields to be able to not only report things accurately, but also give a full view of it. There's nothing inaccurate here in what was included. But the inaccuracy occurs on what was omitted, and therefore, not giving a general reader a more complete state of knowledge of the field.
Symmetry has published a webpage of an interactive chart for the Standard Model of elementary particle. It is almost like a periodic table, but with only the most basic, necessary information. A rather useful link when you need just the basic info.
I don't know why this has been making the news reports a lot since last week. I suppose it must be a landmark even or something.
The latest paper on the Higgs is making the news, not for its results, but for setting the record for the largest number of authors on a paper, 5154 of them.
Only the first nine pages in the 33-page article, published on 14 May in Physical Review Letters, describe the research itself — including references. The other 24 pages list the authors and their institutions.
The
article is the first joint paper from the two teams that operate ATLAS
and CMS, two massive detectors at the Large Hadron Collider (LHC) at
CERN, Europe’s particle-physics lab near Geneva, Switzerland. Each team
is a sprawling collaboration involving researchers from dozens of
institutions and countries.
And oh yeah, they reduced the uncertainty in the Higgs mass to 0.25%, but who cares about that!
This is neither interesting nor surprising to me. The number of collaborators in each of the ATLAS and CMS detector is already huge by themselves. So when they pool together their results and analysis, it isn't surprising that this happens.
Call me silly, but what I was more surprised with, and it is more unexpected, is that the research article itself is "nine pages". I thought PRL always limits its papers to only 4 pages!
BTW, this paper is available for free under the Creative Commons License, you may read it for yourself.
