BASE compares protons to antiprotons with high precision

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August 12, 2015

In a paper published today in Nature, the Baryon Antibaryon Symmetry Experiment (BASE) at CERN’s Antiproton Decelerator (AD), reports the most precise comparison of the charge-to-mass ratio of the proton to that of its antimatter equivalent, the antiproton. The charge-to-mass ratio — an important property of particles — can be measured by observing the oscillation of a particle in a magnetic field. The new result shows no difference between the proton and the antiproton, with a four-fold improvement in the energy resolution compared with previous measurements.

To perform the experiment, the BASE collaboration used a Penning-trap system comparable to that developed by the TRAP collaboration in the late 1990s at CERN. However, the method used is faster than in previous experiments. This has allowed BASE to carry out about 13,000 measurements over a 35-day campaign, in which they compare a single antiproton to a negatively charged hydrogen ion (H-). Consisting of a hydrogen atom with a single proton in its nucleus, together with an additional electron, the H- acts as a proxy for the proton.

“We found that the charge-to-mass ratio is identical to within 69 parts per thousand billion, supporting a fundamental symmetry between matter and antimatter,” says BASE spokesperson Stefan Ulmer.

“Research performed with antimatter particles has made amazing progress in the past few years,” says CERN Director-General Rolf Heuer. “I’m really impressed by the level of precision reached by BASE. It’s very promising for the whole field.”

Image above: A cut-away schematic of the Penning trap system used by BASE. The experiment receives antiprotons from CERN’s AD; negative hydrogen ions are formed during injection into the apparatus. The set-up works with only a pair of particles at a time, while a cloud of a few hundred others are held in the reservoir trap, for future use. Here, an antiproton is in the measurement trap, while the negative hydyrogen ion is in held by the downstream park electrode. When the antiproton has been measured, it is moved to the upstream park electrode and the hydrogen ion is brought in to the measurement trap. This is repeated thousands of times, enabling a high-precision comparison of the charge-to-mass ratios of the two particles (Image: CERN).

The Standard Model of particle physics – the theory that best describes particles and their fundamental interactions – is known to be incomplete, inspiring various searches for “new physics” that goes beyond the model. These include tests that compare the basic characteristics of matter particles with those of their antimatter counterparts. While matter and antimatter particles can differ, for example, in the way they decay (a difference often referred to as violation of CP symmetry), other fundamental properties, such as the absolute value of their electric charges and masses, are predicted to be exactly equal. Any difference – however small — between the charge-to-mass ratio of protons and antiprotons would break a fundamental law known as CPT symmetry. This symmetry reflects well-established properties of space and time and of quantum mechanics, so such a difference would constitute a dramatic challenge not only to the Standard Model, but also to the basic theoretical framework of particle physics.

The BASE experiment receives antiprotons from the AD, a unique facility in the world for antimatter research. The H- ions are formed by the antiproton injection. The set up holds a single antiproton–H- pair at a time in a magnetic Penning trap, decelerating the particles to ultra-low energies. The experiment then measures the cyclotron frequency of the antiproton and the H- ion — a measurement that allows the team to determine the charge-to-mass ratio — and compares the results.


CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

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Anti-Proton Ring Found Around Earth

Antiprotons appear to ring the Earth, confined by the planet’s magnetic field lines. The antimatter, which may persist for minutes or hours before annihilating with normal matter, could in theory be used to fuel ultra-efficient rockets of the future.

Charged particles called cosmic rays constantly rain in from space, creating a spray of new particles - including antiparticles - when they collide with particles in the atmosphere. Many of these become trapped inside the Van Allen radiation belts, two doughnut-shaped zones around the planet where charged particles spiral around the Earth’s magnetic field lines.

Satellites had already discovered positrons - the antimatter partners of electrons - in the radiation belts. Now a spacecraft has detected antiprotons, which are nearly 2000 times as massive.

Heavier particles take wider paths when they spiral around the planet’s magnetic lines, and weaker magnetic field lines also lead to wider spirals. So relatively heavy antiprotons travelling around the weak field lines in the outer radiation belt were expected to take loops so big they would quickly get pulled into the lower atmosphere, where they would annihilate with normal matter. The inner belt was thought to have fields strong enough to trap antiprotons, and indeed that is where they have been found.

Piergiorgio Picozza from the University of Rome Tor Vergata, Italy, and colleagues detected the antiprotons using PAMELA, a cosmic-ray detector attached to a Russian Earth-observation satellite. The spacecraft flies through the Earth’s inner radiation belt over the south Atlantic.

Between July 2006 and December 2008, PAMELA detected 28 antiprotons trapped in spiralling orbits around the magnetic field lines sprouting from the Earth’s south pole (Astrophysical Journal Letters, DOI: 10.1088/2041-8205/737/2/l29). PAMELA samples only a small part of the inner radiation belt, but antiprotons are probably trapped throughout it. “We are talking about of billions of particles,” says team member Francesco Cafagna from the University of Bari in Italy.

“I find it very interesting to note that the Earth’s magnetic field works a little bit like the magnetic traps that we are using in the lab,” says Rolf Landua at the CERN particle physics laboratory near Geneva, Switzerland. There, researchers have been trying to trap antimatter for ever longer periods to compare its behaviour with that of normal matter.

Alessandro Bruno, another team member from Bari, says antimatter in the Earth’s radiation belts might one day be useful for fuelling spacecraft. Future rockets could be powered by the reaction between matter and antimatter, a reaction that produces energy even more efficiently than nuclear fusion in the sun’s core.

“This is the most abundant source of antiprotons near the Earth,” says Bruno. “Who knows, one day a spacecraft could launch then refuel in the inner radiation belt before travelling further.”

Millions or billions of times as many antiprotons probably ring the giant planets.

Journal Reference: Astrophysical Journal Letters

BASE compares protons to antiprotons with high precision: In a paper published today in Nature, the Baryon Antibaryon Symmetry Experiment (BASE) at CERN’s Antiproton Decelerator (AD), reports the most precise comparison of the charge-to-mass ratio of the proton to that of its antimatter equivalent, the antiproton. The charge-to-mass ratio — an important property of particles — can be measured by observing the oscillation […]

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News just in from CERN:

Geneva 17 August 2015. The ALICE experiment at the Large Hadron Collider (LHC) at CERN has made a precise measurement of the difference between ratios of the mass and electric charge of light nuclei and antinuclei. The result, published today in Nature Physics (link is external), confirms a fundamental symmetry of nature to an unprecedented precision for light nuclei. The measurements are based on the ALICE experiment’s abilities to track and identify particles produced in high-energy heavy-ion collisions at the LHC.

The ALICE collaboration has measured the difference between mass-to-charge ratios for deuterons (a proton, or hydrogen nucleus, with an additional neutron) and antideuterons, as well as for helium-3 nuclei (two protons plus a neutron) and antihelium-3 nuclei. Measurements at CERN, most recently by the BASE experiment (link is external), have already compared the same properties of protons and antiprotons to high precision. The study by ALICE takes this research further as it probes the possibility of subtle differences between the way that protons and neutrons bind together in nuclei compared with how their antiparticle counterparts form anti nuclei.

“The measurements by ALICE and by BASE have taken place at the highest and lowest energies available at CERN, at the LHC and the Antiproton Decelerator, respectively,” said CERN Director-General Rolf Heuer. “This is a perfect illustration of the diversity in the laboratory’s research programme.”
The measurement by ALICE comparing the mass-to-charge ratios in deuterons/antideuterons and in helium-3/antihelium-3 confirms the fundamental symmetry known as CPT in these light nuclei. This symmetry of nature implies that all of the laws of physics are the same under the simultaneous reversal of charges (charge conjugation C), reflection of spatial coordinates (parity transformation P) and time inversion (T). The new result, which comes exactly 50 years after the discovery of the antideuteron at CERN and in the US, improves on existing measurements by a factor of 10-100.
The ALICE experiment records high-energy collisions of lead ions at the LHC, enabling it to study matter at extremely high temperatures and densities. The lead-ion collisions provide a copious source of particles and antiparticles, and nuclei and the corresponding antinuclei are produced at nearly equal rates. This allows ALICE to make a detailed comparison of the properties of the nuclei and antinuclei that are most abundantly produced. The experiment makes precise measurements of the curvature of particle tracks in the detector’s magnetic field and of the particles’ time of flight, and uses this information to determine the mass-to-charge ratios for the nuclei and anti nuclei.

“The high precision of our time-of-light detector, which determines the arrival time of particles and antiparticles with a resolution of 80 picoseconds, associated with the energy-loss measurement provided by our time-projection chamber, allows us to measure a clear signal for deuterons/antideuterons and helium-3/antihelium-3 over a wide range of momentum”, said ALICE spokesperson Paolo Giubellino.

The measured differences in the mass-to-charge ratios are compatible with zero within the estimated uncertainties, in agreement with expectations for CPT symmetry. These measurements, as well as those that compare protons with antiprotons, may further constrain theories that go beyond the existing Standard Model of particles and the forces through which they interact.

Protons and antiprotons appear to be true mirror images

The work, published in Nature, was carried out using CERN’s Antiproton Decelerator, a device that provides low-energy antiprotons for antimatter studies.

CPT invariance–which the experiment was meant to test –means that a system remains unchanged if three fundamental properties are reversed–C (charge), which distinguishes matter from antimatter, P (parity), which implies a 180 degree flip in space, and T (time). It is a central tenet of the standard model, and implies that antimatter particles must be perfect mirror images of matter, with only their charges reversed.

“This is an important issue,” says Stefan Ulmer, who led the research, “because it helps us to understand why we live in a universe that has practically no antimatter, despite the fact that the Big Bang must have led to the creation of both. If we had found violations of CPT, it would mean that matter and antimatter might have different properties–for example that antiprotons might decay faster than protons–but we have found within quite strict limits that the charge-to-mass ratios are the same.”

To perform the research, the team used a scheme similar to that developed by the TRAP collaboration in the 1990s. They received antiprotons and negative hydrogen ions–as a proxy for protons–from the Antiproton Decelerator, and then trapped single antiproton-hydrogen ion pairs in a magnetic Penning trap, decelerating them to ultra-low energies. They then measured the cyclotron frequency of the pairs–a measurement that allows scientists to determine the charge-to-mass ratio–and compared them to find how similar they were. In total, they measured approximately 6,500 pairs over a 35-day period.

“What we found,” says Ulmer, “is that the charge-to-mass ratio is identical to within just 69 parts per trillion.” This measurement has four times higher energy resolution than previous measurements of proton-antiproton pairs, and further constrains the possibility of violations of CPT invariance. “Ultimately,” he says, “we plan to achieve measurements that are at least ten or a hundred times more precise than the current standard.”

The work also has implications for what is known as the weak equivalence principle–the idea that all particles will be affected by gravity in the same way, regardless of their mass and charge. The team used their findings to calculate that within about one part per million, antimatter and matter behave in the same way with respect to gravity.

According to BASE member Christian Smorra, “There are many reasons to believe in physics beyond the standard model, including the mystery of dark matter and, of course, the imbalance between matter and antimatter. These high-precision measurements put important new constraints and will help us to determine the direction of future research.”

                                      Mystery Deepens:
             Matter and Antimatter Are Mirror Images

The scientists found the charge-to-mass ratio of protons and antiprotons “is identical to within just 69 parts per trillion,” Ulmer said in a statement. This measurement is four times better than previous measurements of this ratio.

Read all about it ~

Image: A newly reported experiment involving matter and antimatter was carried out in CERN’s Antiproton Decelerator.
   Credit: N. Kuroda
[1508.06844] Implications of the first AMS-02 antiproton data for dark matter

[ Authors ]
Hong-Bo Jin, Yue-Liang Wu, Yu-Feng Zhou
[ Abstract ]
The implications of the first AMS-02 $\bar p/p$ data for the propagation of cosmic rays and the properties of dark matter (DM) are discussed. Using various diffusive re-acceleration (DR) propagation models, one can derive very conservative upper limits on the DM annihilation cross sections. The limits turned out to be compatible with that from the Ferm-LAT gamma-ray data on the dwarf spheroidal satellite galaxies. The flattening of the $\bar p/p$ spectrum above $\sim 100$~GeV in the current data still leaves some room for TeV scale DM particles. More antiproton data at high kinetic energies are needed to constrain the properties of the DM particles.

Matter and Antimatter: Still Twinning

When matter and antimatter come in contact they annihilate each other. Antimatter, in theory, is supposed to have the same mass as its normal matter counterpart, but have opposite charge and the opposite of other particle properties, such as quantum spin. The big bang should have created equal parts matter and antimatter, yet far more matter was left behind in our universe. 

The widely accepted Standard Model of particle physics (a theory that classifies all known subatomic particles and describes the weak, strong, and electromagnetic forces) can’t explain this asymmetry. By studying the subtle differences between matter and antimatter scientists can try to explain why more matter exists. Physicists with the BASE project at CERN recently measured the charge-to-mass ratio of protons to antiprotons to test the Standard Model and perhaps explain this asymmetry.

The basis of the research stems from a fundamental theory of the Standard Model; CPT (charge, parity, and time-reversal) transformation which scientists used to compare the fundamental properties of matter to antimatter. The BASE project specifically was looking at the charge-to-mass ratio of the proton and antiproton (the protons antimatter counterpart). In other terms, they were weighing the particles.

However, weighing subatomic particles isn’t easy. To achieve this difficult feat, physicists capture the particles in a Penning trap. The Penning trap uses electrical and magnetic fields to confine the particle. Then a magnetic field forces it to rotate 30 million times per second. The measurements from this experiment are very precise because the frequency of rotation depends on the particles ratio of charge-to-mass.

In trying to explain the asymmetry, they discovered that protons and antiprotons are nearly identical in mass. BASE, a German-Japanese collaborative project with researchers from the Max Planck Institute for Nuclear Physics and other institutions, used the Antiproton Decelerator (AD) at CERN to study these antiprotons. According to the paper recently published in Nature, the researchers have discovered that the mass of antiprotons and protons are identical to eleven decimal places.

“We’ve found that the ratio of charge to mass is identical in one part in 69 trillion.” says Stefan Ulmer, scientist at CERN and spokesperson for the BASE project. The results confirm theories that no differences in mass exist between matter and antimatter. However, the search for differences in matter and antimatter in hopes to find answers to the asymmetry aren’t over yet. BASE researchers plan to continue testing the theories of the Standard Model. Since they have already measured the magnetic moment of the proton, the next obstacle is measuring that of the antiproton.



Daily reminder of Pluto’s planetary demotion photo source
[1508.05340] A Study of the Energy Dependence of the Underlying Event in Proton-Antiproton Collisions

[ Authors ]
T. Aaltonen
[ Abstract ]
We study charged particle production in proton-antiproton collisions at 300 GeV, 900 GeV, and 1.96 TeV. We use the direction of the charged particle with the largest transverse momentum in each event to define three regions of eta-phi space; toward, away, and transverse. The average number and the average scalar pT sum of charged particles in the transverse region are sensitive to the modeling of the underlying event. The transverse region is divided into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The center-of-mass energy dependence of the various components of the event are studied in detail. The data presented here can be used to constrain and improve QCD Monte Carlo models, resulting in more precise predictions at the LHC energies of 13 and 14 TeV.

New research reveals: Matter and antimatter, mirror images of each other

Researchers from BASE collaboration at CERN, led by RIKEN, have conducted the most precise measurement, so far, of the charge-to-mass ratio of protons and their antimatter counterparts, antiprotons. Their work was carried out using CERN’s Antiproton Decelerator, and… Read more »
[1508.06189] Antiproton-proton interaction and related hadron physics

[ Authors ]
Xian-Wei Kang
[ Abstract ]
Antinucleon-nucleon interaction has been established in chiral effective field theory. The strong threshold enhancement observed in the reactions $J/\psi\to\gamma \overline pp$ and $e^+e^-\to\overline pp$ are interpreted by the strong $\overline pp$ interaction. Concerning the channel $J/\psi\to\gamma \overline pp$, the topic on the $\overline pp$ bound state is also discussed.

Best of Last Week – New fusion power design, a space elevator and low-fat diet found to be better than low-carb diet

(—It was a big week for physics—a research team at MIT created a superfluid in a record-high magnetic field—a Bose-Einstein condensate—for a tenth of a second. And another team at MIT announced a new design that could finally help to bring fusion power closer to reality—in as little as ten years. Meanwhile, a team working at CERN found that protons and antiprotons appear to be true mirror images—the most precise measurements of their charge-to-mass ratio to date. And researchers working at the South Pole-based IceCube experiment reported that a cosmic mystery deepened with the discovery of a new ultra-high-energy neutrino—making it the fourth and highest-energy neutrino yet observed. Also, a team at CalTech announced a discovery in fundamental physics—pinpointing for the first time how instabilities in the arrangement of electrons in metals arise.

Les protons et antiprotons semblent être de véritables images miroir

Lors d’un test rigoureux concernant une propriété fondamentale du modèle standard de la physique des particules (la symétrie CPT), des chercheurs de la collaboration BASE du CERN (dirigée par RIKEN) ont effectué les mesures les plus précises du…

Goulu’s insight:

la symétrie P n’est pas « une rotation à 180° dans l’Espace ». C’est la symétrie miroir, qui inverse la gauche et la droite.

See on
[1508.03322] Precise measurement of the top quark mass in dilepton decays using optimized neutrino weighting

[ Authors ]
D0 Collaboration
[ Abstract ]
We measure the top quark mass in dilepton final states of top-antitop events in proton-antiproton collisions at sqrt(s) = 1.96 TeV, using data corresponding to an integrated luminosity of 9.7 fb^-1 at the Fermilab Tevatron Collider. The analysis features a comprehensive optimization of the neutrino weighting method to minimize the statistical uncertainties. We also improve the calibration of jet energies using the calibration determined in top-antitop to lepton+jets events, which reduces the otherwise limiting systematic uncertainty from the jet energy scale. The measured top quark mass is mt = 173.32 +/- 1.36(stat) +/- 0.85(syst) GeV.

BASE compare des protons et des antiprotons

Dans un article publié dans la revue Nature, l'expérience sur la symétrie baryon-antibaryon BASE (Baryon Antibaryon Symmetry Experiment) auprès du Décélérateur d'antiprotons (AD) du CERN annonce la…

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