Tag Archives: particle

Experiment confirms quantum theory weirdness

The bizarre nature of reality as laid out by quantum theory has survived another test, with scientists performing a famous experiment and proving that reality does not exist until it is measured.

Physicists at The Australian National University (ANU) have conducted John Wheeler’s delayed-choice thought experiment, which involves a moving object that is given the choice to act like a particle or a wave. Wheeler’s experiment then asks – at which point does the object decide?

Common sense says the object is either wave-like or particle-like, independent of how we measure it. But quantum physics predicts that whether you observe wave like behavior (interference) or particle behavior (no interference) depends only on how it is actually measured at the end of its journey. This is exactly what the ANU team found.

“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” said Associate Professor Andrew Truscott from the ANU Research School of Physics and Engineering.

Despite the apparent weirdness, the results confirm the validity of quantum theory, which governs the world of the very small, and has enabled the development of many technologies such as LEDs, lasers and computer chips.

The ANU team not only succeeded in building the experiment, which seemed nearly impossible when it was proposed in 1978, but reversed Wheeler’s original concept of light beams being bounced by mirrors, and instead used atoms scattered by laser light.

“Quantum physics’ predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, PhD student at the Research School of Physics and Engineering.

Professor Truscott’s team first trapped a collection of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them until there was only a single atom left.

The single atom was then dropped through a pair of counter-propagating laser beams, which formed a grating pattern that acted as crossroads in the same way a solid grating would scatter light.

A second light grating to recombine the paths was randomly added, which led to constructive or destructive interference as if the atom had travelled both paths. When the second light grating was not added, no interference was observed as if the atom chose only one path.

However, the random number determining whether the grating was added was only generated after the atom had passed through the crossroads.

If one chooses to believe that the atom really did take a particular path or paths then one has to accept that a future measurement is affecting the atom’s past, said Truscott.

“The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behavior was brought into existence,” he said.

The research is published in Nature Physics.

Source: ANU

Shown here is "event zero," the first detection of a trapped electron in the MIT physicists' instrument. The color indicates the electron's detected power as a function of frequency and time. The sudden “jumps” in frequency indicate an electron collision with the residual hydrogen gas in the cell.

Courtesy of the researchers

Source: MIT News

New tabletop detector “sees” single electrons

Magnet-based setup may help detect the elusive mass of neutrinos.

Jennifer Chu


MIT physicists have developed a new tabletop particle detector that is able to identify single electrons in a radioactive gas.
As the gas decays and gives off electrons, the detector uses a magnet to trap them in a magnetic bottle. A radio antenna then picks up very weak signals emitted by the electrons, which can be used to map the electrons’ precise activity over several milliseconds.

Shown here is "event zero," the first detection of a trapped electron in the MIT physicists' instrument. The color indicates the electron's detected power as a function of frequency and time. The sudden “jumps” in frequency indicate an electron collision with the residual hydrogen gas in the cell. Courtesy of the researchers Source: MIT News
Shown here is “event zero,” the first detection of a trapped electron in the MIT physicists’ instrument. The color indicates the electron’s detected power as a function of frequency and time. The sudden “jumps” in frequency indicate an electron collision with the residual hydrogen gas in the cell.
Courtesy of the researchers
Source: MIT News

The team worked with researchers at Pacific Northwest National Laboratory, the University of Washington, the University of California at Santa Barbara (UCSB), and elsewhere to record the activity of more than 100,000 individual electrons in krypton gas.
The majority of electrons observed behaved in a characteristic pattern: As the radioactive krypton gas decays, it emits electrons that vibrate at a baseline frequency before petering out; this frequency spikes again whenever an electron hits an atom of radioactive gas. As an electron ping-pongs against multiple atoms in the detector, its energy appears to jump in a step-like pattern.
“We can literally image the frequency of the electron, and we see this electron suddenly pop into our radio antenna,” says Joe Formaggio, an associate professor of physics at MIT. “Over time, the frequency changes, and actually chirps up. So these electrons are chirping in radio waves.”
Formaggio says the group’s results, published in Physical Review Letters, are a big step toward a more elusive goal: measuring the mass of a neutrino.

A ghostly particle
Neutrinos are among the more mysterious elementary particles in the universe: Billions of them pass through every cell of our bodies each second, and yet these ghostly particles are incredibly difficult to detect, as they don’t appear to interact with ordinary matter. Scientists have set theoretical limits on neutrino mass, but researchers have yet to precisely detect it.
“We have [the mass] cornered, but haven’t measured it yet,” Formaggio says. “The name of the game is to measure the energy of an electron — that’s your signature that tells you about the neutrino.”
As Formaggio explains it, when a radioactive atom such as tritium decays, it turns into an isotope of helium and, in the process, also releases an electron and a neutrino. The energy of all particles released adds up to the original energy of the parent neutron. Measuring the energy of the electron, therefore, can illuminate the energy — and consequently, the mass — of the neutrino.
Scientists agree that tritium, a radioactive isotope of hydrogen, is key to obtaining a precise measurement: As a gas, tritium decays at such a rate that scientists can relatively easily observe its electron byproducts.
Researchers in Karlsruhe, Germany, hope to measure electrons in tritium using a massive spectrometer as part of an experiment named KATRIN (Karlsruhe Tritium Neutrino Experiment). Electrons, produced from the decay of tritium, pass through the spectrometer, which filters them according to their different energy levels. The experiment, which is just getting under way, may obtain measurements of single electrons, but at a cost.
“In KATRIN, the electrons are detected in a silicon detector, which means the electrons smash into the crystal, and a lot of random things happen, essentially destroying the electrons,” says Daniel Furse, a graduate student in physics, and a co-author on the paper. “We still want to measure the energy of electrons, but we do it in a nondestructive way.”
The group’s setup has an additional advantage: size. The detector essentially fits on a tabletop, and the space in which electrons are detected is smaller than a postage stamp. In contrast, KATRIN’s spectrometer, when delivered to Karlsruhe, barely fit through the city’s streets.
Tuning in
Furse and Formaggio’s detector — an experiment called “Project 8” — is based on a decades-old phenomenon known as cyclotron radiation, in which charged particles such as electrons emit radio waves in a magnetic field. It turns out electrons emit this radiation at a frequency similar to that of military radio communications.
“It’s the same frequency that the military uses — 26 gigahertz,” Formaggio says. “And it turns out the baseline frequency changes very slightly if the electron has energy. So we said, ‘Why not look at the radiation [electrons] emit directly?’”
Formaggio and former postdoc Benjamin Monreal, now an assistant professor of physics at UCSB, reasoned that if they could tune into this baseline frequency, they could catch electrons as they shot out of a decaying radioactive gas, and measure their energy in a magnetic field.
“If you could measure the frequency of this radio signal, you could measure the energy potentially much more accurately than you can with any other method,” Furse says. “The problem is, you’re looking at this really weak signal over a very short amount of time, and it’s tough to see, which is why no one has ever done it before.”
It took five years of fits and starts before the group was finally able to build an accurate detector. Once the researchers turned the detector on, they were able to record individual electrons within the first 100 milliseconds of the experiment — although the analysis took a bit longer.
“Our software was so slow at processing things that we could tell funny things were happening because, all of a sudden, our file size became larger, as these things started appearing,” Formaggio recalls.
He says the precision of the measurements obtained so far in krypton gas has encouraged the team to move on to tritium — a goal Formaggio says may be attainable in the next year or two — and pave a path toward measuring the mass of the neutrino.
Steven Elliott, a technical staff member at Los Alamos National Laboratory, says the group’s new detector “represents a very significant result.” In order to use the detector to measure the mass of a neutrino, Elliott adds, the group will have to make multiple improvements, including developing a bigger cell to contain a larger amount of tritium.
“This was the first step, albeit a very important step, along the way to building a next-generation experiment,” says Elliott, who did not contribute to the research. “As a result, the neutrino community is very impressed with the concept and execution of this experiment.”
This research was funded in part by the Department of Energy and the National Science Foundation.
Illustration by Michael S. Helfenbein

Yale physicists find a new form of quantum friction


Physicists at Yale University have observed a new form of quantum friction that could serve as a basis for robust information storage in quantum computers in the future. The researchers are building upon decades of research, experimentally demonstrating a procedure theorized nearly 30 years ago.

The results appear in the journal Science and are based on work in the lab of Michel Devoret, the F.W. Beinecke Professor of Applied Physics.

Quantum computers, a technology still in development, would rely on the laws of quantum mechanics to solve certain problems exponentially faster than classical computers. They would store information in quantum systems, such as the spin of an electron or the energy levels of an artificial atom. Called “qubits,” these storage units are the quantum equivalent of classical “bits.” But while bits can be in states like 0 or 1, qubits can simultaneously be in the 0 and 1 state. This property is called quantum superposition; it is a powerful resource, but also very fragile. Ensuring the integrity of quantum information is a major challenge of the field.

 Illustration by Michael S. Helfenbein
Illustration by Michael S. Helfenbein

Zaki Leghtas, first author on the paper and a postdoctoral researcher at Yale, offered the following metaphor to explain this new form of quantum friction:

Imagine a hill surrounded by two basins. If you put a ball at the top of the hill, it will roll down the sides and settle in one of the basins. As it rolls, it loses energy due to the friction between the ball and the ground, and it slows down. This is why it stops at the bottom of the basin. But friction also causes the ball to leave a path in its wake. By looking at either side of the hill and seeing where grass is flattened and stones are pushed aside, you can tell whether the ball rolled into the right or left basin.

This figure depicts the position of a quantum particle over a time of 19 micro-seconds. Dark colors indicate high probability of the particle existing at the specified position. It is a plot of the time-evolution of the Winger function W (⍺) of the quantum system, with black corresponding to 1.0, white to 0, and blue to –0.05.
This figure depicts the position of a quantum particle over a time of 19 micro-seconds. Dark colors indicate high probability of the particle existing at the specified position. It is a plot of the time-evolution of the Winger function W (⍺) of the quantum system, with black corresponding to 1.0, white to 0, and blue to –0.05.

If you replace the ball with a quantum particle, however, you run into a problem. Quantum particles can exist in many states at the same time, so in theory, the particle could occupy both basins simultaneously. But as the particle is rolling down, the friction between the particle and the hill leaves an impact on the environment, which can be measured. The same friction that stops the particle at the bottom also carves the path. This destroys the superposition and forces the particle to exist in only one basin.

Previously, researchers had been able to take advantage of this friction to trap quantum particles in particular basins. But now, Devoret’s lab demonstrates a new type of friction — one that slows the particle as it rolls, but does not carve a path that tells which side it is choosing. This allows the particle to simultaneously exist in both the left and right basins at the same time.

Each of these “basin” states is both stable and steady. While the quantum particle might move around in the basins, small perturbations won’t kick it out of the basins. Furthermore, any superpositions of these two basin states are also stable and steady. This means they could be used as a basis for storing quantum information.

Technically, this is called a two-dimensional quantum steady-state manifold. Devoret and Leghtas point out that the next step is expanding this two-dimensional manifold to four dimensions — adding two more basins to the landscape. This will allow scientists to redundantly encode quantum information and to do error correction within the manifold. Error correction is one of the key components that must be developed in order to make a practical quantum computer feasible.

Additional authors are Steven Touzard, Ioan Pop, Angela Kou, Brian Vlastakis, Andrei Petrenko, Katrina Sliwa, Anirudh Narla, Shyam Shankar, Michael Hatridge, Matthew Reagor, Luigi Frunzio, Robert Schoelkopf, and Mazyar Mirrahimi of Yale. Mirrahimi also has an appointment at the Institut National de Recherche en Informatique et en Automatique Paris-Rocquencourt.

(Main illustration by Michael S. Helfenbein)

Source: Yale News

Quantum physics breakthrough: Scientists solve 100-year-old puzzle

Two fundamental concepts of the quantum world are actually just different manifestations of the same thing, says Waterloo researcher.

By Jenny Hogan

Centre for Quantum Technologies


A Waterloo researcher is part of an international team that has proven that two peculiar features of the quantum world – long thought to be distinct – are actually different manifestations of the same thing.

The breakthrough findings are published today inNature Communications. The two distinct ideas in question have been fundamental concepts in quantum physics since the early 1900s. They are what is known as the wave-particle duality and the uncertainty principle.

“We were guided by a gut feeling, and only a gut feeling, that there should be a connection,” says Patrick Coles, now a postdoctoral fellow at the Institute for Quantum Computing and the Department of Physics and Astronomy at the University of Waterloo.

  • Wave-particle duality is the idea that a quantum particle can behave like a wave, but that the wave behavior disappears if you try to locate the object.
  • The uncertainty principle is the idea that it’s impossible to know certain pairs of things about a quantum particle at once. For example, the more precisely you know the position of an atom, the less precisely you can know the speed with which it’s moving.

Coles was part of the research team at the National University of Singapore that made the discovery that wave-particle duality is simply the quantum uncertainty principle in disguise.

Like discovering the Rosetta Stone of quantum physics

“It was like we had discovered the ‘Rosetta Stone’ that connected two different languages,” says Coles. “The literature on wave-particle duality was like hieroglyphics that we could translate into our native tongue. We had several eureka moments when we finally understood what people had done.”

The research team at Singapore’s Centre for Quantum Technologies, included Jedrzej Kaniewski and Stephanie Wehner, now both researchers at the Netherlands’ Delft University of Technology.

“The connection between uncertainty and wave-particle duality comes out very naturally when you consider them as questions about what information you can gain about a system. Our result highlights the power of thinking about physics from the perspective of information,” says Wehner.

The wave-particle duality is perhaps most simply seen in a double slit experiment, where single particles, electrons, say, are fired one by one at a screen containing two narrow slits. The particles pile up behind the slits not in two heaps as classical objects would, but in a stripy pattern like you’d expect for waves interfering. At least this is what happens until you sneak a look at which slit a particle goes through – do that and the interference pattern vanishes.

The discovery deepens our understanding of quantum physics and could prompt ideas for new applications of wave-particle duality.

New protocols for quantum cryptography possible

Coles, Kaniewski and Wehner are experts in a form of mathematical equations known as ‘entropic uncertainty relations.’ They discovered that all the maths previously used to describe wave-particle duality could be reformulated in terms of these relations.

Because the entropic uncertainty relations used in their translation have also been used in proving the security of quantum cryptography – schemes for secure communication using quantum particles – the researchers suggest the work could help inspire new cryptography protocols.

How is nature itself constructed?

In earlier papers, the researchers found connections between the uncertainty principle and other physics, namely quantum ‘non-locality’ and the second law of thermodynamics. The tantalizing next goal for the researchers is to think about how these pieces fit together and what bigger picture that paints of how nature is constructed.

Source: University of WaterLoo

Islamic Republic of Pakistan to become Associate Member State of CERN: CERN Press Release

Geneva 19 December 2014. CERN1 Director General, Rolf Heuer, and the Chairman of the Pakistan Atomic Energy Commission, Ansar Parvez, signed today in Islamabad, in presence of Prime Minister Nawaz Sharif, a document admitting the Islamic Republic of Pakistan to CERN Associate Membership, subject to ratification by the Government of Pakistan.

“Pakistan has been a strong participant in CERN’s endeavours in science and technology since the 1990s,” said Rolf Heuer. “Bringing nations together in a peaceful quest for knowledge and education is one of the most important missions of CERN. Welcoming Pakistan as a new Associate Member State is therefore for our Organization a very significant event and I’m looking forward to enhanced cooperation with Pakistan in the near future.”

“It is indeed a historic day for science in Pakistan. Today’s signing of the agreement is a reward for the collaboration of our scientists, engineers and technicians with CERN over the past two decades,” said Ansar Parvez. “This Membership will bring in its wake multiple opportunities for our young students and for industry to learn and benefit from CERN. To us in Pakistan, science is not just pursuit of knowledge, it is also the basic requirement to help us build our nation.”

The Islamic Republic of Pakistan and CERN signed a Co-operation Agreement in 1994. The signature of several protocols followed this agreement, and Pakistan contributed to building the CMS and ATLAS experiments. Pakistan contributes today to the ALICE, ATLAS, CMS and LHCb experiments and operates a Tier-2 computing centre in the Worldwide LHC Computing Grid that helps to process and analyse the massive amounts of data the experiments generate. Pakistan is also involved in accelerator developments, making it an important partner for CERN.

The Associate Membership of Pakistan will open a new era of cooperation that will strengthen the long-term partnership between CERN and the Pakistani scientific community. Associate Membership will allow Pakistan to participate in the governance of CERN, through attending the meetings of the CERN Council. Moreover, it will allow Pakistani scientists to become members of the CERN staff, and to participate in CERN’s training and career-development programmes. Finally, it will allow Pakistani industry to bid for CERN contracts, thus opening up opportunities for industrial collaboration in areas of advanced technology.

Footnote(s)

1. CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Union, JINR and UNESCO have Observer Status.

Source : CERN

Join the hunt to break the Higgs boson ‘barrier’

Online volunteers are being asked to spot tiny explosions that could be evidence for new particles that will require new models of physics.

Higgs Hunters [www.higgshunters.org], a project launched today by UK and US scientists working on the ATLAS experiment, enables members of the public to view 25,000 images recorded at CERN’s Large Hadron Collider. By tagging the origins of tracks on these images volunteers could spot sub-atomic explosions caused when a Higgs boson ‘dies’, which some scientists think could generate a kind of particle new to physics.

‘If anything discovering what happens when a Higgs boson ‘dies’ could be even more exciting that the original discovery that the Higgs boson exists made at CERN back in 2012,’ said Professor Alan Barr of Oxford University’s Department of Physics, lead scientist of the Higgs Hunters project. ‘We want volunteers to help us go beyond the Higgs boson ‘barrier’ by examining pictures of these collisions and telling us what they see.’

In the ATLAS experiment at CERN’s Large Hadron Collider protons are smashed together at up to one billion kilometres per hour. Such collisions can generate Higgs bosons: these are known to rapidly decay into other particles and some scientists believe these could include a new type of previously unobserved particle. Simulations predict that these new particles should leave tell-tale tracks inside the ATLAS experiment, which computer programs find difficult to identify, but which human eyes can often pick out.

Professor Andy Haas of New York University said: ‘Writing computer algorithms to identify these particles is tough, so we’re excited to see how much better we can do when people help us with the hunt.’

Professor Chris Lintott of Oxford University’s Department of Physics, Zooniverse Principal Investigator, said: ‘The most exciting citizen science comes when you find the unexpected lurking amongst the data, and who knows what could be out there in the data from the ATLAS experiment?’

Professor Dave Charlton, spokesperson of the ATLAS Collaboration, said: ‘With the Higgs Hunters project, people can look directly at ATLAS data to help us find unexpected phenomena – perhaps volunteers will be able to spot new physics with their own eyes!’

A successful detection of new particles would be a huge leap forward for particle physics, as they would lie beyond the Standard Model – the current best theory of the fundamental constituents of the Universe.

Source: Oxford University

The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b'- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b'- region plotted with a finer binning.
Credit: CERN

CERN makes public first data of LHC experiments

CERN1 launched today its Open Data Portal where data from real collision events, produced by the LHC experiments will for the first time be made openly available to all. It is expected that these data will be of high value for the research community, and also be used for education purposes.

”Launching the CERN Open Data Portal is an important step for our Organization. Data from the LHC programme are among the most precious assets of the LHC experiments, that today we start sharing openly with the world. We hope these open data will support and inspire the global research community, including students and citizen scientists,” said CERN Director General Rolf Heuer.

The principle of openness is enshrined in CERN’s founding Convention, and all LHC publications have been published Open Access, free for all to read and re-use. Widening the scope, the LHC collaborations recently approved Open Data policies and will release collision data over the coming years.

The first high-level and analysable collision data openly released come from the CMS experiment and were originally collected in 2010 during the first LHC run. This data set is now publicly available on the CERN Open Data Portal. Open source software to read and analyse the data is also available, together with the corresponding documentation. The CMS collaboration is committed to releasing its data three years after collection, after they have been thoroughly studied by the collaboration.

“This is all new and we are curious to see how the data will be re-used,” said CMS data preservation coordinator Kati Lassila-Perini. “We’ve prepared tools and examples of different levels of complexity from simplified analysis to ready-to-use online applications. We hope these examples will stimulate the creativity of external users.”

 The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b'- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b'- region plotted with a finer binning. Credit: CERN
The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b’- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b’- region plotted with a finer binning.
Credit: CERN

In parallel, the CERN Open Data Portal gives access to additional event data sets from the ALICE, ATLAS, CMS and LHCb collaborations, which have been specifically prepared for educational purposes, such as the international masterclasses in particle physics2 benefiting over ten thousand high-school students every year. These resources are accompanied by visualisation tools.

“Our own data policy foresees data preservation and its sharing. We have seen that students are fascinated by being able to analyse LHC data in the past and so, we are very happy to take the first steps and make available some selected data for education” said Silvia Amerio, data preservation coordinator of the LHCb experiment.

“The development of this Open Data Portal represents a first milestone in our mission to serve our users in preserving and sharing their research materials. It will ensure that the data and tools can be accessed and used, now and in the future,” said Tim Smith from CERN’s IT Department.

All data on OpenData.cern.ch are shared under a Creative Commons CC03 public domain dedication; data and software are assigned unique DOI identifiers to make them citable in scientific articles; and software is released under open source licenses. The CERN Open Data Portal is built on the open-source Invenio Digital Library software, which powers other CERN Open Science tools and initiatives.

Further information:

Open data portal

Open data policies

CMS Open Data

 

Footnote(s):

1. CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer Status.

2. http://www.physicsmasterclasses.org(link is external)

3. http://creativecommons.org/publicdomain/zero/1.0/

The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b'- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b'- region plotted with a finer binning.
Credit: CERN

LHCb experiment observes two new baryon particles never seen before

Geneva 19 November 2014. Today the collaboration for the LHCb experiment at CERN1’s Large Hadron Collider announced the discovery of two new particles in the baryon family. The particles, known as the Xi_b’- and Xi_b*-, were predicted to exist by the quark model but had never been seen before. A related particle, the Xi_b*0, was found by the CMS experiment at CERN in 2012. The LHCb collaboration submitted a paper reporting the finding to Physical Review Letters.

Like the well-known protons that the LHC accelerates, the new particles are baryons made from three quarks bound together by the strong force. The types of quarks are different, though: the new X_ib particles both contain one beauty (b), one strange (s), and one down (d) quark. Thanks to the heavyweight b quarks, they are more than six times as massive as the proton. But the particles are more than just the sum of their parts: their mass also depends on how they are configured. Each of the quarks has an attribute called “spin”. In the Xi_b’- state, the spins of the two lighter quarks point in the opposite direction to the b quark, whereas in the Xi_b*- state they are aligned. This difference makes the Xi_b*a little heavier.

“Nature was kind and gave us two particles for the price of one,” said Matthew Charles of the CNRS’s LPNHE laboratory at Paris VI University. “The Xi_b’is very close in mass to the sum of its decay products: if it had been just a little lighter, we wouldn’t have seen it at all using the decay signature that we were looking for.”

 The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b'- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b'- region plotted with a finer binning. Credit: CERN
The mass difference spectrum: the LHCb result shows strong evidence of the existence of two new particles the Xi_b’- (first peak) and Xi_b*- (second peak), with the very high-level confidence of 10 sigma. The black points are the signal sample and the hatched red histogram is a control sample. The blue curve represents a model including the two new particles, fitted to the data. Delta_m is the difference between the mass of the Xi_b0 pi- pair and the sum of the individual masses of the Xi_b0 and pi-.. INSET: Detail of the Xi_b’- region plotted with a finer binning.
Credit: CERN

“This is a very exciting result. Thanks to LHCb’s excellent hadron identification, which is unique among the LHC experiments, we were able to separate a very clean and strong signal from the background,”said Steven Blusk from Syracuse University in New York. “It demonstrates once again the sensitivity and how precise the LHCb detector is.”

As well as the masses of these particles, the research team studied their relative production rates, their widths – a measure of how unstable they are – and other details of their decays. The results match up with predictions based on the theory of Quantum Chromodynamics (QCD).

QCD is part of the Standard Model of particle physics, the theory that describes the fundamental particles of matter, how they interact and the forces between them. Testing QCD at high precision is a key to refine our understanding of quark dynamics, models of which are tremendously difficult to calculate.

“If we want to find new physics beyond the Standard Model, we need first to have a sharp picture,” said LHCb’s physics coordinator Patrick Koppenburg from Nikhef Institute in Amsterdam. “Such high precision studies will help us to differentiate between Standard Model effects and anything new or unexpected in the future.”

The measurements were made with the data taken at the LHC during 2011-2012. The LHC is currently being prepared – after its first long shutdown – to operate at higher energies and with more intense beams. It is scheduled to restart by spring 2015.

Further information

Link to the paper on Arxiv: http://arxiv.org/abs/1411.4849(link is external)
More about the result on LHCb’s collaboration website: http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#StrBeaBa
Observation of a new Xi_b*0 beauty particle, on CMS’ collaboration website:http://cms.web.cern.ch/news/observation-new-xib0-beauty-particle

Footnote(s)

1. CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer Status.

Source: CERN

This artist’s impression depicts the formation of a galaxy cluster in the early Universe. The galaxies are vigorously forming new stars and interacting with each other. Such a scene closely resembles the Spiderweb Galaxy (formally known as MRC 1138-262) and its surroundings, which is one of the best-studied protoclusters.

Credit:

ESO/M. Kornmesser

Syracuse Physicists Closer to Understanding Balance of Matter, Antimatter

Physicists in the College of Arts and Sciences have made important discoveries regarding Bs meson particles—something that may explain why the universe contains more matter than antimatter. Distinguished Professor Sheldon Stone and his colleagues recently announced their findings at a workshop at CERN in Geneva, Switzerland. Titled “Implications of LHCb Measurements and Their Future Prospects,” the workshop enabled him and other members of the Large Hadron Collider beauty (LHCb) Collaboration to share recent data results. The LHCb Collaboration is a multinational experiment that seeks to explore what happened after the Big Bang, causing matter to survive and flourish in the Universe. LHCb is an international experiment, based at CERN, involving more than 800 scientists and engineers from all over the world. At CERN, Stone heads up a team of 15 physicists from Syracuse. “Many international experiments are interested in the Bs meson because it oscillates between a matter particle and an antimatter particle,” says Stone, who heads up Syracuse’s High-Energy Physics Group. “Understanding its properties may shed light on charge-parity [CP] violation, which refers to the balance of matter and antimatter in the universe and is one of the biggest challenges of particle physics.” Scientists believe that, 14 billion years ago, energy coalesced to form equal quantities of matter and antimatter. As the universe cooled and expanded, its composition changed. Antimatter all but disappeared after the Big Bang (approximately 3.8 billion years ago), leaving behind matter to create everything from stars and galaxies to life on Earth. “Something must have happened to cause extra CP violation and, thus, form the universe as we know it,” Stone says. He thinks part of the answer lies in the Bs meson, which contains an antiquark and a strange quark and is bound together by a strong interaction. (A quark is a hard, point-like object found inside a proton and neutron that forms the nucleus of an atom.) Enter CERN, a European research organization that operates the world’s largest particle physics laboratory. In Geneva, Stone and his research team—which includes Liming Zhang, a former Syracuse research associate who is now a professor at Tsinghua University in Beijing, China—have studied two landmark experiments that took place at Fermilab, a high-energy physics laboratory near Chicago, in 2009. The experiments involved the Collider Detector at Fermilab (CDF) and the DZero (D0), four-story detectors that were part of Fermilab’s now-defunct Tevatron, then one of the world’s highest-energy particle accelerators. “Results from D0 and CDF showed that the matter-antimatter oscillations of the Bs meson deviated from the standard model of physics, but the uncertainties of their results were too high to make any solid conclusions,” Stone says. He and Zhang had no choice but to devise a technique allowing for more precise measurements of Bs mesons. Their new result shows that the difference in oscillations between the Bs and anti-Bs meson is just as the standard model has predicted. Stone says the new measurement dramatically restricts the realms where new physics could be hiding, forcing physicists to expand their searches into other areas. “Everyone knows there is new physics. We just need to perform more sensitive analyses to sniff it out,” he adds.

Source: Syracuse University

The Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile has taken this beautiful image, dappled with blue stars, of one of the most star-rich open clusters currently known — Messier 11, also known as NGC 6705 or the Wild Duck Cluster. Credit: ESO

Discovery of new subatomic particle sheds light on fundamental force of nature

The discovery of a new particle will “transform our understanding” of the fundamental force of nature that binds the nuclei of atoms, researchers argue.

he Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile has taken this beautiful image, dappled with blue stars, of one of the most star-rich open clusters currently known — Messier 11, also known as NGC 6705 or the Wild Duck Cluster. Credit: ESO
Along with gravity, the electromagnetic interaction and weak nuclear force, strong-interactions are one of four fundamental forces. Lead scientist Professor Tim Gershon, from The University of Warwick’s Department of Physics, explains:
“Gravity describes the universe on a large scale from galaxies to Newton’s falling apple, whilst the electromagnetic interaction is responsible for binding molecules together and also for holding electrons in orbit around an atom’s nucleus.”
Image Credit: ESO

Led by scientists from the University of Warwick, the discovery of the new particle will help provide greater understanding of the strong interaction, the fundamental force of nature found within the protons of an atom’s nucleus.

Named Ds3*(2860)ˉ, the particle, a new type of meson,[1] was discovered by analysing data collected with the LHCb detector at CERN’s Large Hadron Collider (LHC)[2]. The LHCb experiment, which is run by a large international collaboration, is designed to study the properties of particles containing beauty and charm quarks and has unique capability for this kind of discovery.

The new particle is bound together in a similar way to protons. Due to this similarity, the Warwick researchers argue that scientists will now be able to study the particle to further understand strong interactions.

Along with gravity, the electromagnetic interaction and weak nuclear force, strong-interactions are one of four fundamental forces. Lead scientist Professor Tim Gershon, from The University of Warwick’s Department of Physics, explains:

“Gravity describes the universe on a large scale from galaxies to Newton’s falling apple, whilst the electromagnetic interaction is responsible for binding molecules together and also for holding electrons in orbit around an atom’s nucleus.”

The strong interaction is the force that binds quarks, the subatomic particles that form protons within atoms, together. It is so strong that the binding energy of the proton gives a much larger contribution to the mass, through Einstein’s equation E = mc2, than the quarks themselves.[3]

Due in part to the forces’ relative simplicity, scientists have previously been able to solve the equations behind gravity and electromagnetic interactions, but the strength of the strong interaction makes it impossible to solve the equations in the same way.

“Calculations of strong interactions are done with a computationally intensive technique called Lattice QCD,” says Professor Gershon. “In order to validate these calculations it is essential to be able to compare predictions to experiments. The new particle is ideal for this purpose because it is the first known that both contains a charm quark and has spin 3.”

There are six quarks known to physicists; Up, Down, Strange, Charm, Beauty and Top. Protons and neutrons are composed of up and down quarks, but particles produced in accelerators such as the LHC can contain the unstable heavier quarks. In addition, some of these particles have higher spin values than the naturally occurring stable particles.

“Because the Ds3*(2860)ˉ particle contains a heavy charm quark it is easier for theorists to calculate its properties. And because it has spin 3, there can be no ambiguity about what the particle is,” adds Professor Gershon. “Therefore it provides a benchmark for future theoretical calculations. Improvements in these calculations will transform our understanding of how nuclei are bound together.”

Spin is one of the labels used by physicists to distinguish between particles. It is a concept that arises in quantum mechanics that can be thought of as being similar to angular momentum: in this sense higher spin corresponds to the quarks orbiting each other faster than those with a lower spin.

Warwick Ph.D. student Daniel Craik, who worked on the study, adds “Perhaps the most exciting part of this new result is that it could be the first of many similar discoveries with LHC data. Whether we can use the same technique, as employed with our research into Ds3*(2860)ˉ, to also improve our understanding of the weak interaction is a key question raised by this discovery. If so, this could help to answer one of the biggest mysteries in physics: why there is more matter than antimatter in the Universe.”

The results are detailed in two papers that will be published in the next editions of the journals Physical Review Letters and Physical Review D. Both papers have been given the accolade of being selected as Editors’ Suggestions.

[1] The Ds3*(2860)ˉ particle is a meson that contains a charm anti-quark and a strange quark. The subscript 3 denotes that it has spin 3, while the number 2860 in parentheses is the mass of the particle in the units of MeV/c2 that are favoured by particle physicists. The value of 2860 MeV/c2 corresponds to approximately 3 times the mass of the proton.

[2] The particle was discovered in the decay chain Bs0D0Kπ+ , where the Bs0, D0, K and π+ mesons contain respectively a bottom anti-quark and a strange quark, a charm anti-quark and an up quark, an up anti-quark and a strange quark, and a down anti-quark and an up quark. The Ds3*(2860)ˉ particle is observed as a peak in the mass of combinations of the D0 and K mesons. The distributions of the angles between the D0, K and π+ particles allow the spin of the Ds3*(2860)ˉ meson to be unambiguously determined.

[3] Quarks are bound by the strong interaction into one of two types of particles: baryons, such as the proton, are composed of three quarks; mesons are composed of one quark and one anti-quark, where an anti-quark is the antimatter version of a quark.

The results are detailed in papers titled:

- The LHCb experiment is one of the four main experiments at the CERN Large Hadron Collider, and is set up to explore what happened after the Big Bang that allowed matter to survive and build the Universe we inhabit today. The LHCb collaboration comprises about 700 physicists from 67 institutes in 17 countries.

- CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Israel, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. Romania is a Candidate for Accession. Serbia is an Associate Member in the pre-stage to Membership. India, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer Status.

- The UK Science and Technology Facilities Council [www.stfc.ac.uk] coordinates and manages the UK’s involvement and subscription with CERN.

- The University of Warwick researchers who led this work are funded by the Science and Technology Facilities Council and the European Research Council.

- Further information on these results can be found in the LHCb collaboration public web page (http://lhcb-public.web.cern.ch/lhcb-public/Welcome.html#TwoSt) and the CERN Courier Sept. 2014 edition (http://cerncourier.com/cws/article/cern/58193)

Source: Warwick University