CERN Declares War On The Standard Model

Ever since the discovery of the Higgs Boson in 2012, the Large Hadron Collider has been dedicated to searching for the existence of physics that go beyond the Standard Model. To this end, the Large Hadron Collider beauty experiment (LHCb) was established in 1995, specifically for the purpose of exploring what happened after the Big Bang that allowed matter to survive and create the Universe as we know it.

Since that time, the LHCb has been doing some rather amazing things. This includes discovering five new particles, uncovering evidence of a new manifestation of matter-antimatter asymmetry, and (most recently) discovering unusual results when monitoring beta decay. These findings, which CERN announced in a recent press release, could be an indication of new physics that are not part of the Standard Model.

In this latest study, the LHCb collaboration team noted how the decay of B0 mesons resulted in the production of an excited kaon and a pair of electrons or muons. Muons, for the record, are subatomic particles that are 200 times more massive than electrons, but whose interactions are believed to be the same as those of electrons (as far as the Standard Model is concerned).

The LHCb collaboration team. Credit: lhcb-public.web.cern.ch

This is what is known as “lepton universality”, which not only predicts that electrons and muons behave the same, but should be produced with the same probability – with some constraints arising from their differences in mass. However, in testing the decay of B0 mesons, the team found that the decay process produced muons with less frequency. These results were collected during Run 1 of the LHC, which ran from 2009 to 2013.

The results of these decay tests were presented on Tuesday, April 18th, at a CERN seminar, where members of the LHCb collaboration team shared their latest findings. As they indicated during the course of the seminar, these findings are significant in that they appear to confirm results obtained by the LHCb team during previous decay studies.

This is certainly exciting news, as it hints at the possibility that new physics are being observed. With the confirmation of the Standard Model (made possible with the discovery of the Higgs boson in 2012), investigating theories that go beyond this (i.e. Supersymmetry) has been a major goal of the LHC. And with its upgrades completed in 2015, it has been one of the chief aims of Run 2 (which will last until 2018).

A typical LHCb event fully reconstructed. Particles identified as pions, kaon, etc. are shown in different colours. Credit: LHCb collaboration

Naturally, the LHCb team indicated that further studies will be needed before any conclusions can be drawn. For one, the discrepancy they noted between the creation of muons and electrons carries a low probability value (aka. p-value) of between 2.2. to 2.5 sigma. To put that in perspective, the first detection of the Higgs Boson occurred at a level of 5 sigma.

In addition, these results are inconsistent with previous measurements which indicated that there is indeed symmetry between electrons and muons. As a result, more decay tests will have to be conducted and more data collected before the LHCb collaboration team can say definitively whether this was a sign of new particles, or merely a statistical fluctuation in their data.

The results of this study will be soon released in a LHCb research paper. And for more information, check out the PDF version of the seminar.

Further Reading: CERN, LHCb

Large Hadron Collider Discovers 5 New Gluelike Particles

Since it began its second operational run in 2015, the Large Hadron Collider has been doing some pretty interesting things. For example, starting in 2016, researchers at CERN began using the collide to conduct the Large Hadron Collider beauty experiment (LHCb). This is investigation seeks to determine what it is that took place after the Big Bang so that matter was able to survive and create the Universe that we know today.

In the past few months, the experiment has yielded some impressive results, such as the measurement of a very rare form of particle decay and evidence of a new manifestation of matter-antimatter asymmetry. And most recently, the researchers behind LHCb have announced the discovery of a new system of five particles, all of which were observed in a single analysis.

According to the research paper, which appeared in arXiv on March 14th, 2017, the particles that were detected were excited states of what is known as a “Omega-c-zero” baryon. Like other particles of its kind, the Omega-c-zero is made up of three quarks – two of which are “strange” while the third is a “charm” quark. The existence of this baryon was confirmed in 1994. Since then, researchers at CERN have sought to determine if there were heavier versions.

The LHCb collaboration team. Credit: lhcb-public.web.cern.ch

And now, thanks to the LHCb experiment, it appears that they have found them. The key was to examine the trajectories and the energy left in the detector by particles in their final configuration and trace them back to their original state. Basically, Omega-c-zero particles decay via the strong force into another type of baryon (Xi-c-plus) and then via the weak force into protons, kaons, and pions.

From this, the researchers were able to determine that what they were seeing were Omega-c-zero particles at different energy states (i.e. of different sizes and masses). Expressed in megaelectronvolts (MeV), these particles have masses of 3000, 3050, 3066, 3090 and 3119 MeV, respectively. This discovery was rather unique, since it involved the detection of five higher energy states of a particle at the same time.

This was made possible thanks to the specialized capabilities of the LHCb detector and the large dataset that was accumulated from the first and second runs of the LHC – which ran from 2009 to 2013, and since 2015, respectively. Armed with the right equipment and experience, the researchers were able to identify the particles with an overwhelming level of certainty, ruling out the possibility that it was a statistical fluke in the data.

The discovery is also expected to shed light on some of the deeper mysteries of subatomic particles, like how the three constituent quarks are bound inside a baryon by the “strong force” – i.e. the fundamental force that is responsible for holding the insides of atoms together. Another mystery that this could help resolve in the correlation between different quark states.

The Large Hadron Collider is the world’s largest and most powerful particle accelerator Credit: CERN

As Dr Greig Cowan – a researcher from the University of Edinburgh who works on the LHCb experiment at Cern’s LHC – explained in an interview with the BBC:

“This is a striking discovery that will shed light on how quarks bind together. It may have implications not only to better understand protons and neutrons, but also more exotic multi-quark states, such as pentaquarks and tetraquarks.

The next step will be to determine the quantum numbers of these new particles (the numbers used to identify the properties of a specific particle) as well as determining their theoretical significance. Since it came online, the LHC has been helping to confirm the Standard Model of particle physics, as well as reaching beyond it to explore the greater unknowns of how the Universe came to be, and how the fundamental forces that govern it fit together.

In the end, the discovery of these five new particles could be a crucial step along the road towards a Theory of Everything (ToE), or just another piece in the very big puzzle that is our existence. Stay tuned to see which!

Further Reading: CERN, LHCb, arXiv

Spectrum of Antimatter Observed for First Time

Ever since the existence of antimatter was proposed in the early 20th century, scientists have sought to understand how relates to normal matter, and why there is an apparent imbalance between the two in the Universe. To do this, particle physics research in the past few decades has focused on the anti-particle of the most elementary and abundant atom in the Universe – the antihydrogen particle.

Until recently, this has been very difficult, as scientists have been able to produce antihydrogen, but unable to study it for long before it annihilated. But according to recent a study that was published in Nature, a team using the ALPHA experiment was able to obtain the first spectral information on antihydrogen. This achievement, which was 20 years in the making, could open up an entirely new era of research into antimatter.

Measuring how elements absorb or emit light – i.e. spectroscopy – is a major aspect of physics, chemistry and astronomy. Not only does it allow scientists to characterize atoms and molecules, it allows astrophysicists to determine the composition of distant stars by analyzing the spectrum of the light they emit.

Measuring the antihydrogen spectrum with high-precision offers an extraordinary new tool to test whether matter behaves differently from antimatter and thus to further test the robustness of the Standard Model (mage: Maximilien Brice/CERN)
The ALPHA experiment probes whether matter behaves differently from antimatter by measuring the antihydrogen spectrum with high-precision, further testing the robustness of the Standard Model. Credit: Maximilien Brice/CERN

In the past, many studies have been conducted into the spectrum of hydrogen, which constitutes roughly 75% of all baryonic mass in the Universe. These have played a vital role in our understanding of matter, energy, and the evolution of multiple scientific disciplines. But until recently, studying the spectrum of its anti-particle has been incredibly difficult.

For starters, it requires that the particles that constitute antihydrogen – antiprotons and positrons (anti-electrons) – be captured and cooled so that they may come together. In addition, it is then necessary to maintain these particles long enough to observe their behavior, before they inevitable make contact with normal matter and annihilate.

Luckily, technology has progressed in the past few decades to the point where research into antimatter is now possible, thus affording scientists the opportunity to deduce whether the physics behind antimatter are consistent with the Standard Model or go beyond it. As the CERN research team – which was led by Dr. Ahmadi of the Department of Physics at the University of Liverpool – indicated in their study:

“The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but todays Universe is observed to consist almost entirely of ordinary matter. This motivates physicists to carefully study antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter.”
ALPHA uses a magnetic trap to hold neutral atoms of anthydrogen and then conduct spectrographic analyis. Credit: CERN
ALPHA uses a magnetic trap to hold neutral atoms of antihydrogen and then subjecting them to spectrographic analysis. Credit: CERN

Beginning in 1996, this research was conducted using the AnTiHydrogEN Apparatus (ATHENA) experiment, a part of the CERN Antiproton Decelerator facility. This experiment was responsible for capturing antiprotons and positrons, then cooling them to the point where they can combine to form anithydrogen. Since 2005, this task has become the responsibility of ATHENA’s successor, the ALPHA experiment.

Using updated instruments, ALPHA captures atoms of neutral antihydrogen and holds them for a longer period before they inevitably annihilate  During this time, research teams conduct spectrographic analysis using ALPHA’s ultraviolet laser to see if the atoms obey the same laws as hydrogen atoms. As Jeffrey Hangst, the spokesperson of the ALPHA collaboration, explained in a CERN update:

“Using a laser to observe a transition in antihydrogen and comparing it to hydrogen to see if they obey the same laws of physics has always been a key goal of antimatter research… Moving and trapping antiprotons or positrons is easy because they are charged particles. But when you combine the two you get neutral antihydrogen, which is far more difficult to trap, so we have designed a very special magnetic trap that relies on the fact that antihydrogen is a little bit magnetic.”

In so doing, the research team was able to measure the frequency of light needed to cause a positron to transition from its lowest energy level to the next. What they found was that (within experimental limits) there was no difference between the antihydrogen spectral data and that of hydrogen. These results are an experimental first, as they are the first spectral observations ever made of an antihydrogen atom.

Besides allowing for comparisons between matter and antimatter for the first time, these results show that antimatter’s behavior – vis a vis its spectrographic characteristics – are consistent with the Standard Model. Specifically, they are consistent with what is known as Charge-Parity-Time (CPT) symmetry.

This symmetry theory, which is fundamental to established physics, predicts that energy levels in matter and antimatter would be the same. As the team explained in their study:

“We have performed the first laser-spectroscopic measurement on an atom of antimatter. This has long been a sought-after achievement in low-energy antimatter physics. It marks a turning point from proof-of-principle experiments to serious metrology and precision CPT comparisons using the optical spectrum of an anti-atom. The current result… demonstrate that tests of fundamental symmetries with antimatter at the AD are maturing rapidly.”

In other words, the confirmation that matter and antimatter have similar spectral characteristics is yet another indication that the Standard Model holds up – just as the discovery of the Higgs Boson in 2012 did. It also demonstrated the effectiveness of the ALPHA experiment at trapping antimatter particles, which will have benefits other antihydrogen experiments.

Naturally, the CERN researchers were very excited by this find, and it is expected to have drastic implications. Beyond offering a new means of testing the Standard Model, it is also expected to go a long way towards helping scientists to understand why there is a matter-antimatter imbalance in the Universe. Yet another crucial step in discovering exactly how the Universe as we know it came to be.

Further Reading: CERN

Some Humans Just Sacrificed Their Jobs At CERN

Yes, despite what some people were clearly meant to believe, jobs are about the only thing being sacrificed at CERN recently. After a strange video depicting what was meant to look like a human sacrifice on its Geneva campus went viral, the European Organization for Nuclear Research (CERN) launched an official investigation to get to the bottom of it.

And while the video was quickly determined to be a prank – no doubt to mess with all those who think that CERN is evil and the Large Hadron Collider (LHC) is a “tool of the devil” – it has raised concerns about security on CERN campuses, not to mention the questionable senses of humor of some of its staff!

The video, which began circulating earlier this week, featured some disturbing imagery. Within the main square of CERN’s Geneva campus – which is home to the LHC-  several figures appear to be reenacting an occult ceremony. They are seen wearing black cloaks and performing rites in front of a statue of the Hindu deity Shiva – which is on permanent display at the complex.

The statue of Nataraja, the Cosmic Dancer, Dr. Aymar, DG of CERN, Dr. Anil Kakodkar, Chairman of the Indian Atomic Energy Commission and Secretary to the Government of India. Credit: CERN
Dr. Aymar, DG of CERN, and Dr. Anil Kakodkar, Chairman of the Indian Atomic Energy Commission in front of the statue of Nataraja, the Cosmic Dancer Shiva. Credit: CERN

The scene climaxes with the staged stabbing of a woman, and then ends with the one filming the scene (who appears to be recording everything from a hidden location) uttering some expletives and running off. In response, the European Organization for Nuclear Research issued a statement, claiming they would be investigating.

They also stressed that they considered this to be an “internal matter”. So while the Geneva police were aware of the incident, they will not be formally involved in the investigation. In response to a request for comment from the Agency France-Presse (AFP), a CERN spokewoman replied via email:

“These scenes were filmed on our premises but without official permission or knowledge. CERN does not condone this type of spoof, which can give rise to misunderstandings about the scientific nature of our work.”

According to this same spokeswoman, the people conducting the reenactment were likely staff. While they are not able to confirm the identities of those in the video, CERN’s security measures require that those working on their premises, of have access to their facilities, have official IDs.

The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider. Credit: CERN
The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider. Credit: CERN

“CERN IDs are checked systematically at each entry to the CERN site whether it is night or day,” she said. “CERN welcomes every year thousands of scientific users from all over the world and sometimes some of them let their humor go too far. This is what happened on this occasion.”

The statue used for the prank was none other than the Nataraja – a depicition of Shiva as the cosmic dancer – which is on permanent display at CERN. The statue was a gift issued by the Indian government in 2004 to celebrate the country’s long-standing relationship with the research facility.

Needless to say, there’s likely to be some hell to pay once the prankster’s are identified. While the prank does seem to have a sense of irony to it – as if its specifically mocking tho conspiracy theorists who think evil things go on there – the last thing CERN wants is negative publicity, or people conducting pranks that involve sacred artwork!

If you haven’t seen the footage, be sure to check out this snippet from NewsBeatSocial below:

Further Reading: The Gaurdian

The Hype Machine Deflates After CERN Data Shows No New Particle

This summer in Chicago, from August 3rd until the 10th, theorists and experimental physicists from around the world will be participating in the International Conference of High Energy Physics (ICHEP). One of the highlights of this conference comes from CERN Laboratories, where particle physicists are showcasing the wealth of new data that the Large Hadron Collider (LHC) has produced so far this year.

But amidst all the excitement that comes from being able to peer into the more than 100 latest results, some bad news also had to be shared. Thanks to all the new data provided by the LHC, the chance that a new elementary particle was discovered – a possibility that had begun to appear likely eight months ago – has now faded. Too bad, because the existence of this new particle would have been groundbreaking!

The indications of this particle first appeared back in December of 2015, when teams of physicists using two of CERN’s particle detectors (ATLAS and CMS) noted that the collisions performed by the LHC were producing more pairs of photons than expected, and with a combined energy of 750 gigaelectronvolts. While the most likely explanation was a statistical fluke, there was another tantalizing possibility – that they were seeing evidence of a new particle.

The ATLAS detector, one of two general-purpose detectors at the Large Hadron Collider (LHC). Credit: CERN
The ATLAS instrument, one of two general-purpose detectors at the Large Hadron Collider (LHC). Credit: CERN

If this particle were in fact real, then it was likely to be a heavier version of the Higgs boson. This particle, which gives other elementary particles their mass, had been discovered in 2012 by researchers at CERN. But whereas the discover of the Higgs boson confirmed the Standard Model of Particle Physics (which has been the scientific convention for the past 50 years), the possible existence of this particle was inconsistent with it.

Another, perhaps even more exciting, theory was that the particle was the long-sought-after gravitron, the theoretical particle that acts as the “force carrier” for gravity. If indeed it was this particle, then scientists would finally have a way for explaining how General Relativity and Quantum Mechanics go together – something that has eluded them for decades and inhibited the development of a Theory of Everything (ToE).

For this reason, there has been a fair degree of excitement in the scientific community, with over 500 scientific papers produced on the subject. However, thanks to the massive amounts of data provided in the past few months, the CERN researchers were forced to announce on Friday at ICEP 2016 that there was no new evidence of a particle to be had.

The results were presented by representatives of the teams that first noticed the unusual data last December. Representing CERN’s ATLAS detector, which first noted the photon pairs, was Bruno Lenzi. Meanwhile, Chiara Rovelli representing the competing team that uses the Compact Muon Solenoid (CMS), which confirmed the readings.

The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider. Credit: CERN
The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider. Credit: CERN

As they showed, the readings which indicated a bump in photon pairs last December have since gone into the flatline, removing any doubt as to whether or not it was a fluke. However, as Tiziano Campores – a spokesman for C.M.S. – was quoted by the New York Times as saying on the eve of the announcement, the teams had always been clear about this not being a likely possibility:

“We don’t see anything. In fact, there is even a small deficit exactly at that point. It’s disappointing because so much hype has been made about it. [But] we have always been very cool about it.”

These results were also stated in a paper submitted to CERN by the C.M.S. team on the same day. And CERN Laboratories echoed these statement in a recent press release which addressed the latest data-haul being presented at ICEP 2016:

“In particular, the intriguing hint of a possible resonance at 750 GeV decaying into photon pairs, which caused considerable interest from the 2015 data, has not reappeared in the much larger 2016 data set and thus appears to be a statistical fluctuation.”

This was all disappointing news, since the discovery of a new particle could have shed some light on the many questions arising out of the discovery of the Higgs boson. Ever since it was first observed in 2012, and later confirmed, scientists have been struggling to understand how it is that the very thing that gives other particles their mass could be so “light”.

The Large Hadron Collider - destined to deliver fabulous science data, but uncertain if these will include an evidence basis for quantum gravity theories. Credit: CERN.
The Large Hadron Collider – which discovered the Higgs Boson in 2012 – appears to have confirmed the Standard Model yet again. Credit: CERN

Despite being the heaviest elementary particle – with a mass of 125 billion electron volts – quantum theory predicted that the Higgs boson had to be trillions of times heavier. In order to explain this, theoretical physicists have been wondering if in fact there are some other forces at work that keep the Higgs boson’s mass at bay – i.e. some new particles. While no new exotic particles have been discovered just yet, the results so far have still been encouraging.

For instance, they showed that LHC experiments have already recorded about five times more data in the past eight months than they did in all of last year. They also offered scientists a glimpse of how subatomic particles behave at energies of 13 trillion electronvolts (13 TeV), a new level that was reached last year. This energy level has been made possible from the upgrades performed on the LHC during its two-year hiatus; prior to which, it was functioning at only half-power.

Another thing worth bragging about was the fact that the LHC surpassed all previous performance records this past June, reaching a peak luminosity of 1 billion collisions per second. Being able to conduct experiments at this energy level, and involving this many collisions, has provided LHC researchers with a large enough data set that they are able to conduct more precise measurements of Standard Model processes.

In particular, they will be able to look for anomalous particle interactions at high mass, which constitutes an indirect test for physics beyond the Standard Model – specifically new particles predicted by the theory of Supersymmetry and others. And while they have yet to discover any new exotic particles, the results so far have still been encouraging, mainly because they show that the LHC is producing more results than ever.

This is the signature of one of 100s of trillions of particle collisions detected at the Large Hadron Collider. The combined analysis lead to the discovery of the Higgs Boson. This article describes one team in dissension with the results. (Photo Credit: CERN)
Data representation from the CMS experiment, showing the decay of protons into two photons (dashed yellow lines and green towers). Credit: CERN

And while discovering something that could explain the questions arising from the discovery of the Higgs bosons would have been a major breakthrough, many agree that it was simply too soon to get our hopes up. As Fabiola Gianotti, the Director-General at CERN, said:

“We’re just at the beginning of the journey. The superb performance of the LHC accelerator, experiments and computing bodes extremely well for a detailed and comprehensive exploration of the several TeV energy scale, and significant progress in our understanding of fundamental physics.”

For the time being, it seems we are all going to have to be patient and wait on more scientific results to be produced. And we can all take solace in the fact that, at least for now, the Standard Model still appears to be the correct one. Clearly, there are no short cuts when it comes to figuring out how the Universe works and how all its fundamental forces fit together.

Further Reading: CERN

Are There Antimatter Galaxies?

One of the biggest mysteries in astronomy is the question, where did all the antimatter go? Shortly after the Big Bang, there were almost equal amounts of matter and antimatter. I say almost, because there was a tiny bit more matter, really. And after the matter and antimatter crashed into each other and annihilated, we were left with all the matter we see in the Universe.

You, and everything you know is just a mathematical remainder, left over from the great division of the Universe’s first day.

We did a whole article on this mystery, so I won’t get into it too deeply.

But is it possible that the antimatter didn’t actually go anywhere? That it’s all still there in the Universe, floating in galaxies of antimatter, made up of antimatter stars, surrounded by antimatter planets, filled with antimatter aliens?

Aliens who are friendly and wonderful in every way, except if we hugged, we’d annihilate and detonate with the energy of gigatons of TNT. It’s sort of tragic, really.

If those antimatter galaxies are out there, could we detect them and communicate with those aliens?

First, a quick recap on antimatter.

Antimatter is just like matter in almost every way. Atoms have same atomic mass and the exact same properties, it’s just that all the charges are reversed. Antielectrons have a positive charge, antihydrogen is made up of an antiproton and a positron (instead of a proton and an electron).

It turns out this reversal of charge causes regular matter and antimatter to annihilate when they make contact, converting all their mass into pure energy when they come together.

We can make antimatter in the laboratory with particle accelerators, and there are natural sources of the stuff. For example, when a neutron star or black hole consumes a star, it can spew out particles of antimatter.

In fact, astronomers have detected vast clouds of antimatter in our own Milky Way, generated largely by black holes and neutron stars grinding up their binary companions.

Wyoming Milky Way set. Credit and copyright: Randy Halverson.
Wyoming Milky Way set. Credit and copyright: Randy Halverson.

But our galaxy is mostly made up of regular matter. This antimatter is detectable because it’s constantly crashing into the gas, dust, planets and stars that make up the Milky Way. This stuff can’t get very far without hitting anything and detonating.

Now, back to the original question, could you have an entire galaxy made up of antimatter? In theory, yes, it would behave just like a regular galaxy. As long as there wasn’t any matter to interact with.

And that’s the problem. If these galaxies were out there, we’d see them interacting with the regular matter surrounding them. They would be blasting out radiation from all the annihilations from all the regular matter gas, dust, stars and planets wandering into an antimatter minefield.

Astronomers don’t see this as far as they look, just the regular, quiet and calm matter out to the edge of the observable Universe.

That doesn’t make it completely impossible, though, there could be galaxies of antimatter as long as they’re completely cut off from regular matter.

But even those would be detectable by the supernova explosions within them. A normally matter supernova generates fast moving neutrinos, while an antimatter supernova would generate a different collection of particles. This would be a dead giveaway.

There’s one open question about antimatter that might make this a deeper mystery. Scientists think that antimatter, like regular matter, has regular gravity. Matter and antimatter galaxies would be attracted to each other, encouraging annihilation.

But scientists don’t actually know this definitively yet. It’s possible that antimatter has antigravity. An atom of antihydrogen might actually fall upwards, accelerating away from the center of the Earth.

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The ALPHA experiment, one of five experiments that are studying antimatter at CERN Credit: Maximilien Brice/CERN

Physicists at CERN have been generating antimatter particles, and trying to detect if they’re falling downward or up.

If that was the case, then antimatter galaxies might be able to repel particles of regular matter, preventing the annihilation, and the detection.

If you were hoping there are antimatter lurking out there, hoarding all that precious future energy, I’m sorry to say, but astronomers have looked and they haven’t found it. Just like the socks in your dryer, we may never discover where it all went.

Is A New Particle About To Be Announced?

Particle physicists are an inquisitive bunch. Their goal is a working, complete model of the particles and forces that make up the Universe, and they pursue that goal with a vigour matched by few other professions.

The Standard Model of Physics is the result of their efforts, and for 25 years or so, it has guided our thinking and understanding of particle physics. The best tool we have for studying physics further is the Large Hadron Collider (LHC), near Geneva, Switzerland. And some recent, intriguing results from the LHC points to the existence of a newly discovered particle.

The Large Hadron Collider is the most powerful particle accelerator in the world. Image: CERN
The Large Hadron Collider is the most powerful particle accelerator in the world. Image: CERN

The LHC has four separate detectors. Two of them are “general purpose” detectors, called ATLAS and CMS. Last year, separate experiments in both the ATLAS and CMS detectors produced what is best called a “bump” in their data. Initially, the two teams conducting the experiments were puzzled by the data. But when they compared them, they found that the bumps in their data were the same in both experiments, and they hinted at what could be a new type of particle, never before detected.

The two experiments involved smashing protons into each other at near-relativistic speeds. The collisions produced more high-energy photons than theory predicts. Not a lot more, but physics is a detailed endeavour, so even a slight increase in the amount of photons produced is a big deal. In physics, everything happens for a reason.

To be more specific, ATLAS and CMS recorded increased activity at an energy level around 750 giga electron-volts (GeV). What that means, for all you non-particle physicists, is that the new particle decays into two photons at the point of the proton-proton collision. If the new particle exists, that is.

A new particle would be a huge discovery. The Standard Model has describe all the particles present in nature pretty well. It even predicted the existence of one type of particle, the Higgs Boson, long before the LHC actually verified its existence. The discovery of a new type of particle would be very exciting news indeed, and could break the Standard Model.

Since this data from the experiments at the LHC was released last year, the physics world has been buzzing. Over 100 papers have been written to try to explain what the results might mean. But some caution is required.

The first thing scientists do when faced with results like this is to try to quantify the likelihood that it could be chance. If only one experiment had this bump in its data, then the likelihood that it was just a chance occurrence is pretty high. There are many reasons why an experiment can have a result like this, which is why repeatability is such a big deal in science. But when two independent, separate, experiments have the same result, people’s ears perk up.

A few months have passed since the experiments were run, and in that time, the experimenters have tried to determine exactly what the likelihood is of these result occurring by chance. After working with the data, a funny thing has happened. The significance of the extra photons detected by CMS has risen, while the significance of the extra photons detected by ATLAS has fallen. This has definitely left physicists scratching their heads.

Also in that time, about four main explanations for the experimental results have percolated to the surface. One states that the new particle, if it exists, is made up of smaller particles, similar to how a proton is made up of quarks. These smaller particles could be held together by an unknown force. Some theoretical physicists think this is the best fit with the data.

Another possibility is that the new particle is a heavier version of the Higgs Boson. About 12 times heavier. Or it could be that the Higgs Boson itself is made up of smaller particles, and that’s what the experiment detected.

The Standard Model of  Elementary Particles. Image: By MissMJ - Own work by uploader, PBS NOVA [1], Fermilab, Office of Science, United States Department of Energy, Particle Data Group, CC BY 3.0
The Standard Model of Elementary Particles. Image: By MissMJ – Own work by uploader, PBS NOVA [1], Fermilab, Office of Science, United States Department of Energy, Particle Data Group, CC BY 3.0

Or, it could be the much-hypothesized graviton, the theoretical particle that carries the gravitational force. The four fundamental forces in the Universe are electromagnetism, the strong nuclear force, the weak nuclear force, and gravity. So far, we have discovered the particles that transmit all of those forces, except for gravity. If their was a new particle detected, and if it proved to be the graviton, that would be enormous, earth-shattering news. At least for those who are passionate about understanding nature.

That’s a lot of “ifs” though.

There are a lot of holes in our knowledge of the Universe, and physicists are eager to fill those gaps. The discovery of a new particle might very well answer some basic questions about dark matter, dark energy, or even gravity itself. But there’s a lot more experimentation to be done before the existence of a new particle can be announced.

Who Discovered Helium?

Scientists have understood for some time that the most abundant elements in the Universe are simple gases like hydrogen and helium. These make up the vast majority of its observable mass, dwarfing all the heavier elements combined (and by a wide margin). And between the two, helium is the second lightest and second most abundant element, being present in about 24% of observable Universe’s elemental mass.

Whereas we tend to think of Helium as the hilarious gas that does strange things to your voice and allows balloons to float, it is actually a crucial part of our existence. In addition to being a key component of stars, helium is also a major constituent in gas giants. This is due in part to its very high nuclear binding energy, plus the fact that is produced by both nuclear fusion and radioactive decay. And yet, scientists have only been aware of its existence since the late 19th century.

Continue reading “Who Discovered Helium?”

What’s the Big Deal About the Pentaquark?

“Three quarks for Muster Mark!,” wrote James Joyce in his labyrinthine fable, Finnegan’s Wake. By now, you may have heard this quote – the short, nonsensical sentence that eventually gave the name “quark” to the Universe’s (as-yet-unsurpassed) most fundamental building blocks. Today’s physicists believe that they understand the basics of how quarks combine; three join up to form baryons (everyday particles like the proton and neutron), while two – a quark and an antiquark – stick together to form more exotic, less stable varieties called mesons. Rare four-quark partnerships are called tetraquarks. And five quarks bound in a delicate dance? Naturally, that would be a pentaquark. And the pentaquark, until recently a mere figment of physics lore, has now been detected at the LHC!

So what’s the big deal? Far from just being a fun word to say five-times-fast, the pentaquark may unlock vital new information about the strong nuclear force. These revelations could ultimately change the way we think about our superbly dense friend, the neutron star – and, indeed, the nature of familiar matter itself.

Physicists know of six types of quarks, which are ordered by weight. The lightest of the six are the up and down quarks, which make up the most familiar everyday baryons (two ups and a down in the proton, and two downs and an up in the neutron). The next heaviest are the charm and strange quarks, followed by the top and bottom quarks. And why stop there? In addition, each of the six quarks has a corresponding anti-particle, or antiquark.

particles
Six types of quark, arranged from left to right by way of their mass, depicted along with the other elementary particles of the Standard Model. The Higgs boson was added to the right side of the menagerie in 2012. (Image Credit: Fermilab)

An important attribute of both quarks and their anti-particle counterparts is something called “color.” Of course, quarks do not have color in the same way that you might call an apple “red” or the ocean “blue”; rather, this property is a metaphorical way of communicating one of the essential laws of subatomic physics – that quark-containing particles (called hadrons) always carry a neutral color charge.

For instance, the three components of a proton must include one red quark, one green quark, and one blue quark. These three “colors” add up to a neutral particle in the same way that red, green, and blue light combine to create a white glow. Similar laws are in place for the quark and antiquark that make up a meson: their respective colors must be exactly opposite. A red quark will only combine with an anti-red (or cyan) antiquark, and so on.

The pentaquark, too, must have a neutral color charge. Imagine a proton and a meson (specifically, a type called a J/psi meson) bound together – a red, a blue, and a green quark in one corner, and a color-neutral quark-antiquark pair in the other – for a grand total of four quarks and one antiquark, all colors of which neatly cancel each other out.

Physicists are not sure whether the pentaquark is created by this type of segregated arrangement or whether all five quarks are bound together directly; either way, like all hadrons, the pentaquark is kept in check by that titan of fundamental dynamics, the strong nuclear force.

The strong nuclear force, as its name implies, is the unspeakably robust force that glues together the components of every atomic nucleus: protons and neutrons and, more crucially, their own constituent quarks. The strong force is so tenacious that “free quarks” have never been observed; they are all confined far too tightly within their parent baryons.

But there is one place in the Universe where quarks may exist in and of themselves, in a kind of meta-nuclear state: in an extraordinarily dense type of neutron star. In a typical neutron star, the gravitational pressure is so tremendous that protons and electrons cease to be. Their energies and charges melt together, leaving nothing but a snug mass of neutrons.

Physicists have conjectured that, at extreme densities, in the most compact of stars, adjacent neutrons within the core may even themselves disintegrate into a jumble of constituent parts.

The neutron star… would become a quark star.

The difference between a neutron star and a quark star (Chandra)
The difference between a neutron star and a quark star. (Image Credit: Chandra)

Scientists believe that understanding the physics of the pentaquark may shed light on the way the strong nuclear force operates under such extreme conditions – not only in such overly dense neutron stars, but perhaps even in the first fractions of a second following the Big Bang. Further analysis should also help physicists refine their understanding of the ways that quarks can and cannot combine.

The data that gave rise to this discovery – a whopping 9-sigma result! – came out of the LHC’s first run (2010-2013). With the supercollider now operating at double its original energy capacity, physicists should have no problem unraveling the mysteries of the pentaquark even further.

A preprint of the pentaquark discovery, which has been submitted to the journal Physical Review Letters, can be found here.