The other side of the matter

We know that exist a particular type of matter: the antimatter. Antimatter is composed by antiparticles. An antiparticle has the same mass as the corresponding particle but has opposite charge. And luckily for us antimatter is substantialy absent from our universe: indeed the interaction between matter and antimatter leads to the annihilation process, with the disappearance of particle and antiparticle and energy production. So, if in the universe there were the same amount of matter and antimatter, it would be filled exclusively with radiation. For this reason it is particularly interesting understand where this asymmetry originates: we know that would be a symmetry violation in some place and time of the universe, and the T2K experiment in Japan tested neutrinos' oscillations, in particular the oscillation from muonic to electronic neutrino. The results of ten years of data say that 90 neutrinos and only 15 antineutrinos were caught oscillating from muonic to electronic: different numbers mean violated symmetry.
The most interesting detail is that the experimental result doesn't exclude an interesting idea about an anti-universe that exists at the other side of the Big Bang.

Abe, K., Akutsu, R., Ali, A., Alt, C., Andreopoulos, C., Anthony, L., ... & Ashida, Y. (2020). Constraint on the Matter-Antimatter Symmetry-Violating Phase in Neutrino Oscillations. Nature volume 580, pages 339–344. doi:10.1038/s41586-020-2177-0

Boyle, L., Finn, K., & Turok, N. (2018). C P T-Symmetric Universe. Physical review letters, 121(25), 251301. doi:10.1103/PhysRevLett.121.251301

The light limit of the neutrino

Neutrinos are the most light particles in the universe, but we don't know your mass. In the current state of the research, the only thing that we can hope to do is find upper and lower limits. And in the previous weeks we have some interesting news about the upper limit.
In april Physics Review Letters published a paper in which a team of researcher have compared constraints from physically motivated neutrino mass models (i.e., ones respecting oscillation experiments) to those from models using standard cosmological approximations. They founded an upper limit about $0.26 \, eV$, almost 2 million times lighter than an electron.

Loureiro, A., Cuceu, A., Abdalla, F. B., Moraes, B., Whiteway, L., McLeod, M., ... & Rollins, R. P. (2019). Upper Bound of Neutrino Masses from Combined Cosmological Observations and Particle Physics Experiments. Physical review letters, 123(8), 081301. doi:10.1103/PhysRevLett.123.081301 (arXiv

In the meanwhile, just ten days ago, the KATRIN's team (KATRIN, Karlsruhe Trtitium Neutrino experiment) announced the new experimental upper limit: $1.1 \, eV$.

Aker, M., Altenmüller, K., Arenz, M., Babutzka, M., Barrett, J., Bauer, S., ... & Besserer, U. (2019). An improved upper limit on the neutrino mass from a direct kinematic method by KATRIN. arXiv:1909.06048.

The research of neutrino mass becomes more and more interesting: if the study of theoretical models combined with astronomical data gives us an idea of the range to look for, experiments will say the last word.
The hunt to the neutrino is still open!

A brief history of neutrinos' oscillations

I just write a more detailed post about the model behind neutrino's oscillations. Here I would simply recall that the idea was proposed by Bruno Pontecorvo in 1957 and developed by Ziro Maki, Masami Nakagawa e Shoichi Sakata in 1962. Today I try to summarize the experimental way.

via nobelprize.org

The fifth shot of a tau neutrino

http://t.co/urnbKwoiSY by @ulaulaman about #neutrino #tau #Opera #particlephysics

From the press release:

The OPERA (Oscillation Project with Emulsion-tRacking Apparatus) international experiment at the National Institute for Nuclear Physics (INFN) Gran Sasso Laboratory (Italy) has detected the fifth occurrence of a tau neutrino. The neutrino started its flight at CERN as muon neutrino and, after traveling 730 km through the Earth, it arrived at Gran Sasso Laboratories showing up as a tau neutrino. This important result was announced yesterday during a seminar held at the Gran Sasso Laboratories. According to the Spokesperson of the international research team, Giovanni De Lellis, from Federico II University and INFN in Naples, "The detection of a fifth tau neutrino is extremely important: the direct observation of the transition from muon to tau neutrinos has now achieved for the first time the 5 sigma statistical precision, the usual particle physics threshold for a discovery. We can thus definitely report the discovery of the appearance of tau neutrinos in a muon neutrino beam." The detection of tau neutrinos from the oscillation of muon neutrinos was the motivation of the OPERA project, designed in the late nineties. "This task is extremely difficult due to two conflicting requirements: a huge, massive detector and a micrometric accuracy. The challenge is to bring to the thousands ton scale a detector based on the nuclear emulsion technology, a photographic technique unique in ensuring the required accuracy", De Lellis says.

The tau neutrino was discovered in july 2000 by DONUT collaboration (arXiv). It is produced in the tau decay, where tau is a lepton, an elementary particle with a negative electric charge and spin 1/2 and with a mass of 1776.82 ± 0.16 MeV: with a great simplification we can say that tau is an electron with a very big mass!
Now, first of all I share the paper about the fourth observation:

Carlo Rubbia and the discoveries of the weak bosons

http://t.co/KGVNarwZMG by @ulaulaman about #CarloRubbia #NobelPrize #physics #particlephysics

On that day 30 years ago, I was almost certainly at school. Physics still was not my passion. Of course I started very well: when the teacher asked what is the space, I thought immediately to the universe, but the question was not referring to that "space", but in another, the geometric. But it is not about those memories that I have to indulge, but on a particular photo, in which Carlo Rubbia and Simon van der Meer, with two goblets, presumably of wine in hand, are celebrating the announcement of the Nobel Prize for Physics

for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction

The story of this Nobel, however, began eight years earlier, in 1976. In that year, in fact, SPS, the Super Proton Synchrotron, begins to operate at CERN, originally designed to accelerate particles up to an energy of 300 GeV.

The same year David Cline, Carlo Rubbia and Peter McIntyre proposed transforming the SPS into a proton-antiproton collider, with proton and antiproton beams counter-rotating in the same beam pipe to collide head-on. This would yield centre-of-mass energies in the 500-700 GeV range⁽¹⁾.

On the other hand antiprotons must be somehow collected. The corresponding beam was then

(...) stochastically cooled in the antiproton accumulator at 3.5 GeV, and this is where the expertise of Simon Van der Meer and coworkers played a decisive role⁽¹⁾.

Neutrinos: between Pontecorvo and Majorana

posted by @ulaulaman about #neutrinos #BrunoPontecorvo #EttoreMajorana

Neutrinos are the most elusive elementary particles in the whole zoo. The reasons are simple: first of all neutrinos don't have electric charge, so physicists cannot use electromagnetic experiments in order to detect them, and they must design indirect measures; furthermore they interact with other particles only with weak interaction. At the other hand, neutrino is, in Standard Model, massless, while from an experimental point of view, he has a really small mass: at the beginning of 2000, Mainz and Troitsk experiment measured a maximum value at 2.2 eV, that is about 4 milion less that the electron mass!

Carlo Franzinetti (left) and Bruno Pontecorvo (Right)

The idea of neutrino's mass is dued by Bruno Pontecorvo that introduced in 1957 the so called neutrino's oscillations^{(1, 2)}: in this model is expected the existence of three type of neutrinos that, combining with each other, giving rise to neutrinos usually observed in experiments. The thoery was further developed in 1962 by Ziro Maki, Masami Nakagawa and Shoici Sakata⁽³⁾: \[\begin{pmatrix} \nu_e \\ \nu_\mu \\ \nu_\tau \end{pmatrix} = \begin{pmatrix} U_{e_1} & U_{e_2} & U_{e_3} \\ U_{\mu_1} & U_{\mu_2} & U_{\mu_3} \\ U_{\tau_1} & U_{\tau_2} & U_{\tau_3} \end{pmatrix} \begin{pmatrix} \nu_1 \\ \nu_2 \\ \nu_3 \end{pmatrix}\] where $e$, $\mu$, $\tau$ indicate the three different leptons (electron, muon and tau), $\nu$ are neutrinos, with $\nu_i$, where $i = 1,2,3$, the fundamental neutrinos.
But, if the Pontecorvo–Maki–Nakagawa–Sakata matrix describes neutrinos' oscillations, we could describe the neutrino also using a particular equation: the Majorana equation⁽⁴⁾: \[i \gamma^\mu \partial_\mu \psi - m \psi_c = 0\] where \[\psi_c = \gamma^2 \psi^*\] is the so called conjugated charge.
Now, if a wave function $\psi$ respects the Majorana equation, then $m$ is called Majorana mass; if $\psi$ coincides with $\psi_c$, then $\psi$ is said Majorana spinor; finally, if there is a particle that can be described with the Majorana equation, then this is called a Majorana particle, i.e. a particle that coincides with its antiparticle. The leading candidate to be a Majorana particle is, look at the case, the neutrino, whose mass is probably not so important with regard to the ultimate fate of the universe. In fact, the astronomical data suggest a flat universe, where flat universe means a substantial balance between gravitational attraction and expansion of spacetime.

Conclusion: the importance of neutrino oscillations are related to the property to possess a mass: experiments confirmed that property, owned by all three neutrinos in the game. The astronomical data, however, assign this property a minor role for the ultimate fate of the universe, while its mass shows instead of the Standard Model, at present, still does not understand much of the physics of our universe. Among the facts not included in the Standard Model are the Majorana particles: in particular, the neutrino could be one of them and if this is confirmed, then we would have a great step in order to know the symmetry breaking between matter and antimatter.

The case of the Jiggly Wires

Video by Gavin Wince shared by the auhor in the comments of this complete and ultimate post about OPERA's neutrinos by Matt Strassler.
On of the most interesting observation in the post was resumed in the following plot:

We could conclude that the problem was originated in 2008.
In every case I'm agree with this Strassler's questions:

A big question that the OPERA leadership that resigned today has to answer: why didn’t they do this cross-check before they made their result public? Did no one think of it til recently? And if not, why not? Was it harder than it sounds? Or did they just miss an obvious opportunity?

The difference between science and press release

Thanks to @peppeliberti for sharing the preprint.

Do you remember the famous OPERA preprint about superluminal neutrinos? After the publication of the results about neutrinos' flight time, a lot of preprint was published on arXiv in order to explain results. Some researchers try to explain with esperimental problems (and it could be the right explenation), some researchers propose their theoretical explenation, Andrew Cohen and Sheldon Glashow⁽¹⁾ reject results using some simple theoretical arguments:

superluminal neutrinos would lose energy rapidly via the bremsstrahlung of electron-positron pairs⁽¹⁾

where bremmsstrahlung radiation is the radiation produced by the deceleration of a charged particle. In particular Cohen and Glashow studied the neutrinos' processes analog to Cherenkov radiation for neutral particle caused by weak interaction. Their results

cannot be reconciled with the claimed superluminal neutrino velocity measurement⁽¹⁾

After a few days ICARUS experiment, based in LNGS (the same laboratories of OPERA), confirm the theoretical arguments discussed by Chen and Glashow:

No Cherenkov like event has been detected in ICARUS⁽²⁾

Now ICARUS, an experiment designed by Nobel Pirze Carlo Rubbia, upload a new preprint about superluminal neutrinos' saga: Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam.
In this case, ICARUS, using the same beam send by CERN to OPERA from the 21st october to the 6th november 2011⁽³⁾, measure the time of flight of neutrinos produced at CERN. In the preprint they describe also some experimental problems, but the collaboration resolve them, and publish they results: neutrinos fly at light speed (or a bit less), like you can see in the following plot⁽³⁾:

Furthermore, ICARUS' preprint is written like an alternative to the previous OPERA's preprint: indeed they describe the synchronization between CERN and LNGS, using the same timing system of OPERA. I repeat againg: ICARUS, using the OPERA's GPS system, find $c$-neutrinos, and not superluminal neutrinos, so the OPERA's cable problem (the cause of superluminal data) is the most important source in OPERA's mistaken data.
So I think that here is the difference between science, represented by ICARUS, and press release, represented by OPERA: for science the most important thing is the knwoledge of nature, also if this is mean publish results after others; for press release is important to write also about coffe break.

---

(1) Andrew Cohen, Sheldon Glashow. New Constraints on Neutrino Velocities
(2) ICARUS collaboration. A search for the analogue to Cherenkov radiation by high energy neutrinos at superluminal speeds in ICARUS
(3) ICARUS collaboration. Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam

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Superluminal Saga: Waiting superluminal neutrinos (if they exist!) | Waiting superluminal neutrinos: from Maxwell to Einstein | Probably not | News from the OPERA | Experimental problems in OPERA

Experimental problems in OPERA

It seems that are some experimental problems in OPERA:

The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.
These two issues can modify the neutrino time of flight in opposite directions. While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the Collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012. An extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies.

I remember that alxo BOREXINO, an other experiment at Gran Sasso Laboratories, will try to measure neutrino's speed. Indeed the experimental mistake could preduce a higher velocity than the previous collected data.

INFN | Nature | Science Insider

In search of violations

This week high-energy physics published some interesting results for our fundamental knowledge of the universe. On 14th November, LHCb published the preliminar analysis about a possible CP-violation in charm decays (see also the CERN's Bulletin and Mat Charles' presentation).
The researches about CP-violations are very important because in this way we can argue the differences between matter and anti-matter. If a physics law is CP-invariant, we must write that the beahvior of matter and anti-matter is the same. But our universe is constituted by matter and we don't know why it is so. The answer could be in CP-violation studies, like the preliminary data analyzed by LHCb team. The main goal of the experiment is the search of the properties of quark b, but he could also measure the properties of quark c. And studying the preliminary data about c decays the team find a clue of a CP-violation in a non expected channel. Following Tommaso Dorigo and Marco Delmastro (english translation by Google), if the result will be confirmed by further analysis, this could be the first sign of physics beyond Standard Model.

The other possible violation is the wall of the speed of light: indeed, OPERA experiment confirm their previous data. Yesterday, in the updated version of their famous preprint, OPERA's researchers described a new serie of measures realized with CNGS using a short-bunch wide-spacing beam.

News from the OPERA

Today, at 15:30 at Physics Department in Milano, Italy, Luca Stanco, one of the 15 OPERA's collaboration who didn't sign the preprint, discussed in a brief presentation (about half an hour, without quests) the OPERA's results. In conclusion we have a lot of interesting informations. He described the experiments, starting from the production of neutrinos' beams and arriving to the detection in Italy, under Gran Sasso mountain. He briefly described the measure of the distance and the GPS system.
The most interesting part of the presentation is the production of neutrinos' beams⁽¹⁾. First of all reasearchers need to produce one proton bench in PS (is a little synchrotron), so they send the bench in SPS, a much greater synchrotron than PS. In order to fill SPS are needed 11 PS benches, but researchers decided to inject in SPS 5 beams (each one with a time length of about 10.4 μs) and after a time range of about 50 ms they inject others 5 benches. So, if we observ with attention the neutrino's signal, we see 5 peaks, a remember of the protons benches that origined the signal. In this process there is one of the criticism: it is necessary to be secure that the proton's probability density function and the neutrino's probability density function are equals. Another important point to clarify is the time of flight⁽²⁾ or the presence of some effects dued by day/night or seasons.
But the really news arrived in the end of the presentation:

OPERA collaboration decided this morning to postpone the submission of paper of about one month

I lost the first of the two motivation, but the second is simple: CNGS is preparing new benches spaced at 500 ns. So OPERA could have a really first opportunity to test their data.

Probably not

A group velocity faster than $c$ does not mean that photons or neutrinos are moving faster thsn the speed of light.

This is the conclusion of Fast light, fast neutrinos? by Kevin Cahill⁽¹²⁾. He start his briefly analisys from some experimental observations of superluminal group velocity. In these experiments researchers measure a speed of light faster and slower than $c$ in vacuum. The first observation was occured in 1982⁽¹⁾, but an interesting collection of work in this subject is in Bigelow⁽⁷⁾ and Gehring⁽¹¹⁾. Experimentally when some pulses journey into a highly dispersive media occur some exotic effects. One of these is the observation of a negative group velocity, that coincides with a superluminal speed.
In Bigelow's and Gehring's works wasn't a really theoretical explenation. For example Bigelow proposed the following explaination:

(...) as the combination of different absorption cross sections and lifetimes for Cr³⁺ ions at either mirror or inversion sites within the BeAl₂O₄ crystal lattice. The superluminal wave propagation is produced by a narrow “antihole” [612 Hz half width at half maximum (HWHM)] in the absorption spectrum of Cr³⁺ ions at the mirror sites of the alexandrite crystal lattice, and the slow light originates from an even narrower hole (8.4 Hz) in the absorption spectrum of Cr³⁺ ions at the inversion sites.

They also considered

(...) the influence of ions both at the inversion sites and at the mirror sites. In addition, the absorption cross sections are assumed to be different at different wavelengths.

The arrows indicate the locations of ion sites that have mirror or inversion symmetry. On the right, the corresponding energy-level diagrams for Cr³⁺ ions at the different sites are shown.

Waiting superluminal neutrinos: from Maxwell to Einstein

(CNGS device)

\[\vec \nabla \cdot \vec E = \frac{\rho}{\varepsilon_0}\] \[\vec \nabla \cdot \vec B = 0\] \[\vec \nabla \times \vec E = - \frac{\partial \vec B}{\partial t}\] \[\vec \nabla \times \vec B = \mu_0 \vec J + \mu_0 \varepsilon_0 \frac{\partial \vec E}{\partial t}\] In 1861 James Maxwell published the first (of four) part of the paper On Physical Lines of Force, in which he stated his famous equations on electromagnetic field. One of the most important thing about these equations is that they are not invariant under Galilei's transformations! But, if we search the symmetry transformation of the equations, we find Lorentz transformations: \[\begin{cases} t' &= \gamma \left( t - \frac{v x}{c^2} \right) \\ x' &= \gamma \left( x - v t \right)\\ y' &= y \\ z' &= z \end{cases}\] where $\gamma = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$.
From these transformations, discovered in 1887^{(1, 2)}, we can extract the physics of special relativity, thanks to Albert Einstein. So, if we want tosubstitute c with the alleged OPERA's neutrinos speed, we must conclude that the new boson particle of electromagnetic field is the neutrino! In this sense I say that special relativity is right: our universe and our observations are based on electromagnetic field, so if OPERA results will be verified, we probably think to:

1. change the weak interaction⁽³⁾;
2. study an eventually quantum interaction between neutrinos and space time⁽⁴⁾;
3. imagine a new field exclusively for neutrinos⁽⁵⁾;
4. other way that in this moment I cannot imagine⁽⁶⁾!

This is the science, people: we find data, we search interpretation, we quest for confirmation, we calculate mathematical explenation, and only at this point we write text books. But, and this is the most important idea, we don't reject the old theories: Newton and Galilei's theories are today right, but we must substitute them in quantum world and to a cosmo's schale. And the destiny of model standard and Einstein's relativity is the same, and our task is find their limits.

Waiting the superluminal neutrinos (if they exist!)

It seems that Opera experiment observed some superluminal neutrinos.
First of all we must see the scientific data: at 4pm on 23rd september (Geneva time) we can connect to the Cern seminar (also on webcast), but probably a preprint will be puiblished on arXiv in the next hours. In every case I think that it's very important say some worlds about the news.
There's a lot of comments about the question, and some people say that special relativity and also standard model will be falsified by the results if they will be confirmed. Instead I think that we simply speak about an extension of standard model, and there're no really consequence about special relativity.
First of all we must remember that special relativity and standard model are first of all electromagnetic theories, where the boson is the photon and the speed of light is important for the photon and for the em interaction. And neutrinos don't interact with electromagnetic field, and the results is simply the confirmation of this situation!
At the other hand the results, if confirmed, say us simply that neutrinos are the most elusive particles in the universe: in this case they escape from the control of special relativity, which would not be the correct theory to describe them at highest energy. In the same way, we must modify standard model in order to include these new superneutrinos. In this last case the changes will be at the high orders of the theory: we must remember that, if the effect it's really important at the energy of standard model, the theory would never have been tested with a high degree of accuracy.
Another hypothesis is that the introduction of superluminal neutrinos in model standard could resolve some mathematical problems of the model, or explain some physical question (like the matter-antimatter asymmetry, for example). But we can continue playing with the assumptions: the superneutrinos could be the trace of a new fifth interaction between neutrinos and dark matter. This hypothesis is included in some dark matter theories: so model standard and special relativity could be remain unmodified.
In every case, if the results will be confirmed, the first step for model standard theorists is propose changes at the highest orders of the theory. And for the future search an extension of the theory.

Thanks to Marco Delmastro, Tommaso Dorigo, Peppe Liberti, Annarita Ruberto for sharing the news.