Nav: Home

Matter-antimatter asymmetry may interfere with the detection of neutrinos

May 24, 2018

From the data collected by the LHCb detector at the Large Hadron Collider, it appears that the particles known as charm mesons and their antimatter counterparts are not produced in perfectly equal proportions. Physicists from Cracow have proposed their own explanation of this phenomenon and presented predictions related to it, about consequences that are particularly interesting for high-energy neutrino astronomy.

In the first moments after the Big Bang, the Universe was filled with equal amounts of particles and antiparticles. While it was cooling down, matter and antimatter began to merge and annihilate, turning into radiation. Why did some of this matter, from which the present Universe is built, survive this conflagration? In order to decipher this great mystery of modern science, physicists are trying to better understand all the mechanisms responsible for even the smallest disproportions in the production of particles and antiparticles. A group of scientists from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow, associated with the LHCb experiment at the Large Hadron Collider in Geneva, recently looked into one of these processes: the asymmetry appearing at the birth of charm mesons and antimesons. Interestingly, the conclusions from the analysis could be of very tangible practical significance.

According to modern knowledge, quarks are the most important indivisible building blocks that make up matter. We know of six flavours of quarks: up (u), down (d), strange (s), charm (c), bottom (b) and top (t); each flavour also has its own antimatter counterpart (often marked with a dash above the letter, read as "bar"). Quarks generally are formed in quark-antiquark pairs. They are extremely sociable particles: almost immediately after coming into being, they bind into hadrons, or groups of two, three, and sometimes more quarks or antiquarks, bonded with gluons (i.e. particles transferring strong nuclear interactions). The process of combining quarks/antiquarks into complexes is called hadronization.

Unstable hadrons built from quark-antiquark pairs are called mesons. If one of the quarks in a meson is a charm quark, the particle is called a charm meson and is denoted by the letter D (or for the charm antiquark: D with a bar above it). A pair built of a charm quark and a down antiquark is a D+ meson, and one consisting of a charm antiquark and down quark is a D- meson.

In measurements conducted in the last quarter of a century, including recently as part of the LHCb experiment, an interesting asymmetry was noticed. It turned out that D+ and D- mesons are not always produced in exactly the same proportions. In the case of processes observed in LHCb, initiated in collisions of counter-current beams of high-energy protons, this asymmetry was small, less than one percent.

"Charm quarks are mainly formed during gluon collisions in so-called hard interactions, and after birth they hadronise into D mesons. We investigated another meson formation mechanism, known as unfavoured quark fragmentation. Here, the charm meson is created as a result of hadronization of a light (up, down, or strange) quark or antiquark. By means of the nuances of this mechanism, the asymmetry between kaons and antikaons, i.e. K+ and K- mesons, was explained earlier. Until now, however, it has not been investigated whether a similar mechanism could explain the asymmetry between the relatively massive D+ and D- mesons," says Dr. Rafal Maciula (IFJ PAN), the first author of the publication in the journal Physical Review D.

The LHCb detector mainly measures particles diverging from the point of collision of protons at large angles to the original direction of movement of these protons. According to the Cracow-based physicists, the asymmetry in the production of D mesons should be much greater if particles produced in a forward direction are taken into account, that is, along the direction of the proton beams. This means that the currently observed disproportion may be just the tip of an iceberg. Calculations suggest that in the case of "forward" collisions, unfavoured fragmentation (d, u, s › D) may be comparable to conventional fragmentation (c › D). As a result, the asymmetry between D+ and D- mesons may reach even a high percentage and also with lower collision energies than those currently occurring in the LHC.

The research of the physicists from the IFJ PAN may have far-reaching consequences for neutrino observatories, such as the IceCube Observatory in Antarctica. This detector, in which 49 scientific institutions from 12 countries collaborate, monitors a cubic kilometre of ice, located almost a kilometre below the surface, using thousands of photomultipliers. Photomultipliers track subtle light flashes, initiated by the interaction of ice-forming particles with neutrinos, elementary particles very weakly interacting with ordinary matter.

IceCube registers several hundred neutrinos a day. It is known that a large proportion of them are created in the Earth's atmosphere in processes initiated by cosmic rays and taking place with the participation of protons. Other neutrinos may come, for example, from the Earth's core or from the Sun. It is assumed, however, that neutrinos with significant energies have reached the detector directly from distant cosmic sources: supernovae or merging black holes or neutron stars.

"When interpreting data from the IceCube detector, the production of neutrinos in the Earth's atmosphere caused by ordinary cosmic radiation, including collisions involving protons, is taken into account. The thing is that some of these processes, resulting in the formation of neutrinos with high energies, take place with the participation of D mesons. Meanwhile, we show that the mechanism of production of these mesons in the atmosphere can be much more efficient than previously thought. So, if our assumptions are confirmed, some of the highly energetic neutrinos registered, now considered to be of cosmic origin, have actually appeared just above our heads and are disturbing the real picture of events in the depths of space," explains Prof. Antoni Szczurek (IFJ PAN).

When just the tip of the iceberg can be seen, inferences about what the rest of it looks like is more than risky. The model proposed by the Cracow-based physicists has the status of a hypothesis today. Perhaps it does fully describe the mechanism that occurs in reality. But it may also be that other processes are responsible for the asymmetry in the production of D mesons, maybe partially or even in their entirety.

"Fortunately, no other competitive proposal predicts such a clear increase in asymmetry in the production of D mesons at lower collision energies. So, to check our assumptions, it would suffice in the LHC accelerator to direct a single beam onto a stationary target, which would significantly reduce the collision energy. Our model therefore meets the criteria of very reliable science: it not only explains previous observations, but above all it can be rapidly verified. In addition, this can be done very cheaply!" sums up Prof. Szczurek.
Research on asymmetry in the production of charm mesons was financed from the statutory resources of the IFJ PAN and a Polish National Science Centre grant.

The Henryk Niewodniczanski Institute of Nuclear Physics (IFJ PAN) is currently the largest research institute of the Polish Academy of Sciences. The broad range of studies and activities of IFJ PAN includes basic and applied research, ranging from particle physics and astrophysics, through hadron physics, high-, medium-, and low-energy nuclear physics, condensed matter physics (including materials engineering), to various applications of methods of nuclear physics in interdisciplinary research, covering medical physics, dosimetry, radiation and environmental biology, environmental protection, and other related disciplines. The average yearly yield of the IFJ PAN encompasses more than 600 scientific papers in the Journal Citation Reports published by the Thomson Reuters. The part of the Institute is the Cyclotron Centre Bronowice (CCB) which is an infrastructure, unique in Central Europe, to serve as a clinical and research centre in the area of medical and nuclear physics. IFJ PAN is a member of the Marian Smoluchowski Kraków Research Consortium: "Matter-Energy-Future" which possesses the status of a Leading National Research Centre (KNOW) in physics for the years 2012-2017. The Institute is of A+ Category (leading level in Poland) in the field of sciences and engineering.


Prof. Antoni Szczurek
The Institute of Nuclear Physics Polish Academy of Sciences
tel.: +48 12 6628212

Dr. Rafal Maciula
The Institute of Nuclear Physics Polish Academy of Sciences
tel.: +48 12 6628240


"D meson production asymmetry, unfavored fragmentation, and consequences for prompt atmospheric neutrino production"
R. Maciula, A. Szczurek
Physical Review D 97, 074001 (2018)
DOI: 10.1103/PhysRevD.97.074001

The website of the Institute of Nuclear Physics Polish Academy of Sciences.

Press releases of the Institute of Nuclear Physics Polish Academy of Sciences.



HR: Comparison of mechanisms of favored and unfavored fragmentation of quarks. (Source: IFJ PAN)

The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

Related Neutrinos Articles:

Where did the antimatter go? Neutrinos shed promising new light
We live in a world of matter -- because matter overtook antimatter, though they were both created in equal amounts when our universe began.
Strongest evidence yet that neutrinos explain how the universe exists
New data throws more support behind the theory that neutrinos are the reason the universe is dominated by matter.
Why didn't the universe annihilate itself? Neutrinos may hold the answer
New results from an experiment called T2K suggest that physicists are closer than ever before to answering a major mystery: Why didn't the universe annihilate itself in a humungous burst of energy not long after the Big Bang?
T2K insight into the origin of the universe
Lancaster physicists working on the T2K major international experiment in Japan are closing in on the mystery of why there is so much matter in the universe, and so little antimatter.
Radar and ice could help detect an elusive subatomic particle
A new study published today in the journal Physical Review Letters shows, for the first time, an experiment that could detect a class of ultra-high-energy neutrinos using radar echoes.
Radio waves detect particle showers in a block of plastic
A cheap technique could detect neutrinos in polar ice, eventually allowing researchers to expand the energy reach of IceCube without breaking the bank.
APS tip sheet: Harnessing radar echoes for future neutrino detection
New high energy neutrino detection method could lead to a neutrino telescope able to observe neutrinos with energies beyond the current observable range.
Borexino sheds light on solar neutrinos
For more than ten years, the Borexino Detector located 1,400 meters below surface of the Italian Gran Sasso massif has been exploring the interior of our Sun.
A first 'snapshot' of the complete spectrum of neutrinos emitted by the sun
About 99 percent of the sun's energy emitted as neutrinos is produced through nuclear reaction sequences initiated by proton-proton (pp) fusion in which hydrogen is converted into helium, say scientists including physicist Andrea Pocar at the University of Massachusetts Amherst.
Study of high-energy neutrinos again proves Einstein right
A new study by MIT and others proves Einstein is right again.
More Neutrinos News and Neutrinos Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at