Matter and antimatter violently annihilate each other. If they’re absolutely symmetrical, then maybe — just maybe — the universe shouldn’t exist. 
 
 Just like there is matter in the universe (pretty much everything that exists), there is also antimatter. Basically, all particles have a corresponding anti-particle — with the same mass, but opposite electric charge, and other differences in quantum parameters. The proton, for instance, has a positive charge, while the antiproton has a negative charge. When a proton and an antiproton collide, they annihilate each other in a violent outburst. 
 
 Researchers at CERN in Switzerland have made the most precise measurement ever of the magnetic moment of an antiproton. The magnetic moment determines how a particle reacts to an external magnetic force. They found that the two moments are absolutely identical but with an opposite sign. This is really problematic. 
 
 “All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” says Christian Smorra, a physicist at CERN’s Baryon–Antibaryon Symmetry Experiment (BASE) collaboration. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.” “It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator,” added Smorra, who is first-author of the study. 
 
 Since matter and antimatter annihilate themselves and the universe exists and hasn’t annihilated itself (yet), there’s good reason to believe that there is much more matter than antimatter in the universe. But why? There must be some discrepancy in the parameters of these particles that allows matter to dominate, but researchers haven’t found it yet. It’s like playing spot the difference at a particle level. 
 
 The work of Smorra and his colleagues is an elegant design, a two-particle measurement method developed in Stefan Ulmer’s RIKEN laboratory. Researchers simultaneously capture and measure two separate antiprotons one at a high temperature (350 degrees Kelvin / 76 C / 170 F) and the other at a very cold temperature (0.15 K / -273 C / -459 F), very close to absolute zero. The first particle is used for calibration, while the colder one is used to measure a parameter called the Larmor frequency, which governs how a particle precesses (rotates and spins) under a magnetic influence. Even doing this for protons was a breakthrough (published in Nature in 2014), but doing it for antiprotons is a whole new ball game. 
 
 With this method, they managed to keep an antiproton captured for inside a special chamber about as big as a tall pint. Measurements were incredibly accurate, indicating a value for the antiproton magnetic moment of −2.7928473441 μ N (μ N is a constant called the nuclear magneton). Precise to nine significant digits, this measurement is 350 times more accurate than the previous measurement. It’s the equivalent of measuring the Earth’s circumference to a few centimeters. 
 
 Their results are identical to those obtained for the proton, aside from the minus sign. 
 
 “It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator, ” added first-author of the study Christian Smorra. 
 
 However, for all these elegant improvements, they still couldn’t answer the fundamental question of why our universe exists — why matter and antimatter are so unevenly distributed through the universe, allowing us to exist. Still, Smorra says that they can still improve significantly. 
 
 “By upgrading the experiment with several new technical innovations, we feel that some further improvement can still be made, and in the future, following the CERN upgrade expected to finish in 2021, we will be able to achieve an at least ten-fold improvement.” 
 
 In the meantime, nature continues to consist of matter and we still don’t know why there’s not much antimatter around. Researchers continue to try and solve this mystery which could unlock one of the keys to understanding the universe. 
 
 Enjoyed this article? Join 40,000+ subscribers to the ZME Science newsletter. Subscribe now! ||||| One of the great mysteries of modern physics is why antimatter did not destroy the universe at the beginning of time. 
 
 To explain it, physicists suppose there must be some difference between matter and antimatter – apart from electric charge. Whatever that difference is, it’s not in their magnetism, it seems. 
 
 Physicists at CERN in Switzerland have made the most precise measurement ever of the magnetic moment of an anti-proton – a number that measures how a particle reacts to magnetic force – and found it to be exactly the same as that of the proton but with opposite sign. The work is described in Nature. 
 
 “All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” says Christian Smorra, a physicist at CERN’s Baryon–Antibaryon Symmetry Experiment (BASE) collaboration. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.” 
 
 Antimatter is notoriously unstable – any contact with regular matter and it annihilates in a burst of pure energy that is the most efficient reaction known to physics. That’s why it was chosen as the fuel to power the starship Enterprise in Star Trek. 
 
 The standard model predicts the Big Bang should have produced equal amounts of matter and antimatter – but that’s a combustive mixture that would have annihilated itself, leaving nothing behind to make galaxies or planets or people. Recommended Laser excites antimatter atoms for first time Physics 
 
 To explain the mystery, physicists have been playing spot the difference between matter and antimatter – searching for some discrepancy that might explain why matter came to dominate. 
 
 So far they’ve performed extremely precise measurements for all sort of properties: mass, electric charge and so on, but no difference has yet been found. 
 
 Last year, scientists at CERN’s Antihydrogen Laser PHysics Apparatus (ALPHA) experiment probed an atom of anti-hydrogen with light for the first time, again finding no difference when compared with an atom of hydrogen. 
 
 But one property was known only to middling accuracy compared to the others – the magnetic moment of the antiproton. 
 
 Ten years ago, Stefan Ulmer and his team at BASE collaboration set themselves the task of trying to measure it. 
 
 First they had to develop a way to directly measure the magnetic moment of the regular proton. They did this by trapping individual protons in a magnetic field, and driving quantum jumps in its spin using another magnetic field. This measurement was itself a groundbreaking achievement reported in Nature in 2014. 
 
 Next, they had to perform the same measurement on antiprotons – a task made doubly difficult by the fact that antiprotons will immediately annihilate on contact with any matter. 
 
 To do it, the team used the coldest and longest-lived antimatter ever created. 
 
 After creating the antiprotons in 2015, the team were able to store them for more than a year inside a special chamber about the size and shape of a can of Pringles. 
 
 Since no physical container can hold antimatter, physicists use magnetic and electric fields to contain the material in devices called Penning traps. 
 
 Usually the antimatter lifetime is limited by imperfections in the traps – little instabilities allow the antimatter to leak through. 
 
 But by using a combination of two traps, the BASE team made the most perfect antimatter chamber ever – holding the antiprotons for 405 days. 
 
 This stable storage allowed them to run their magnetic moment measurement on the antiprotons. The result gave a value for the antiproton magnetic moment of −2.7928473441 μ N . (μ N is a constant called the nuclear magneton.) Apart from the minus sign, this is identical to the previous measurement for the proton. 
 
 The new measurement is precise to nine significant digits, the equivalent of measuring the circumference of the Earth to within a few centimeters, and 350 times more precise than any previous measurement. 
 
 “This result is the culmination of many years of continuous research and development, and the successful completion of one of the most difficult measurements ever performed in a Penning trap instrument,” says Ulmer. 
 
 The universe’s greatest game of spot the difference goes on. The next hotly anticipated experiment is over at ALPHA, where CERN scientists are studying the effect of gravity of antimatter – trying to answer the question of whether antimatter might fall ‘up’. ||||| Uncertainties and confidence levels 
 
 We chose to use the 68% CL of the measured data as the quoted experimental uncertainty, to facilitate the comparison to our previous proton magnetic moment measurement9, where we also used 68% CL. Our recent statistical antiproton g-factor measurement is quoted at a relative precision of δg/g = 820 p.p.b. (95% CL), and for the 68% CL we reported δg/g = 520 p.p.b.8. The improvement factor quoted in the text compares the 68% confidence levels of the two measurements. Constraints on standard model extension coefficients are usually quoted with 95% confidence levels10, so we quote both values in the text and use the 95% CL to calculate the limits on CPT-odd interactions. 
 
 Systematic effects in the precision trap 
 
 Imperfections of the electric quadrupole potential and the residual magnetic field inhomogeneity in the precision trap give rise to small amplitude-dependent frequency shifts of the antiproton’s eigenfrequencies and thereby of the determined g-factor. A comprehensive analysis of amplitude-dependent systematic effects can be found in the references22, 30. In our case, the dominant systematic uncertainties scale all with the residual magnetic bottle B 2,PT and the axial temperature T z . 
 
 Determination of the magnetic field gradients 
 
 The magnetic field around the centre of the precision trap can be approximated as B z,PT (z) = B 0,PT + B 1,PT z + B 2,PT z2. The magnetic field gradients in the precision trap result mainly from the magnetic ring electrode of the analysis trap. The linear gradient B 1,PT can be determined by measuring the cyclotron frequency as a function of the position in the trap. The position of the particle is changed by applying offset voltages dV to one of the correction electrodes, and the particle shift dz/dV is extracted from potential calculations. From several independent measurements carried out during the experiment run, we extracted B 1,PT = 71.2(4) mT m−1. The magnetic bottle parameter B 2,PT is accessible by measuring the axial frequency ν z,i−1 and ν z,i before and after a sideband drive. From the distribution of the values δ i = {ν z,i − ν z,i−1 }, we obtain the parameter B 1,PT T +,PT = B 2,PT (ν +,PT /ν z,PT )T z = 976(23) T m−2 K. With T z = 8.12(61) K from the temperature measurement discussed below, this yields B 2,PT = 2.74(22) T m−2. Within error bars, this result is consistent with the B 2 parameter extracted from finite-element-method simulations, B 2,PT,F = 3.1(4) T m−2, which calculates the magnetic field in the precision trap caused by the magnetic bottle in the analysis trap. 
 
 Axial temperature determination 
 
 We determine T z in the precision trap from the lineshape model of the dip signal on the axial detector. The lineshape χ D of the dip in the frequency spectrum of the axial detector’s signal is given as: 
 
 where χ(ν,ν z ,Δν z ) denotes the dip lineshape function for a constant axial frequency31, 32 ν z + Δν z . ν z denotes the unperturbed axial frequency, T z is the temperature of the axial detection system, C 4 and C 6 characterize potential perturbations in the trap and give rise to an amplitude-dependent axial frequency shift22, 30 Δν z (E z ,C 4 ,C 6 ). A variation of the voltage ratio that is applied to the correction electrodes V ce and the ring electrode V ring —the tuning ratio TR = V ce /V ring —changes C 4 and C 6 and thereby the signal-to-noise ratio of the dip. By measuring the change in the signal-to-noise ratio of the dip as a function of the tuning ratio, the axial temperature T z can be obtained. 
 
 This approach reduces the determination of T z to the knowledge of the trap specific parameter D 4 = dC 4 /dTR, which is robust with respect to typical machining errors and offset voltages, and can be reproduced by calculations within an uncertainty of <10%. The scaling dSNR/dTR (SNR, signal-to-noise ratio) as a function of temperature is shown in Extended Data Fig. 1. We have measured a scaling of dSNR/dTR = 11.5(4) dB per mUnit in the precision trap (mUnit expresses changes in the tuning ratio; a change by 1 mUnit corresponds to a change of 0.001 in the tuning ratio), and extract an axial temperature T z = 8.12(61) K. The value can be backed up by measurements of the detector signal-to-noise ratio and comparisons to the width σ(ν z ) of the axial frequency scatter after cyclotron sideband coupling. All obtained values are consistent within errors. 
 
 Axial temperature during spin-flip and sideband drives 
 
 To compare the axial temperature while the spin-flip and sideband drives are applied, we have compared fast Fourier transform spectra of the axial detection system in the precision trap without any applied external drive signal and while spin-flip and sideband drives were irradiated. The noise level of the detector can be used to calculate the effective temperature of the detection system with the known impedance using the Johnson–Nyquist formula. 
 
 Measurements taken while the spin-flip drive was applied show an increase of 0.355(36) dB in the detector’s noise signal. On the basis of the available data, we cannot conclude whether the additional noise was added at the input or the output stage of our cryogenic detector. Thus, we cannot exclude the possibility that the increased signal level affected the particle temperature while the spin-flip drive was applied. Once coupled to the detector via the input stage, the observed increase in the signal level would correspond to an effective temperature increase of ΔT z = 0.68(7) K. As a consequence, the frequencies ν L and ν c were potentially probed at different axial mean-square amplitudes z2 and consequently at different average magnetic fields. 
 
 The most conservative approach to considering the potential change in T z in the g-factor evaluation assumes that the related temperature increase occurs only when the spin flip drive is applied, while the sideband drive in cyclotron frequency measurements did not affect T z . From this assumption we extract the dominant systematic uncertainty to the g-factor with (δg/g) drive = 0.97(7) p.p.b. (68% CL). For the 95% CL, the limit on the g-factor shift is calculated on the basis of the noise level shift increased by two s.d., which results in (δg/g) drive = 1.06(8) p.p.b. (95% CL). 
 
 Summary of g-factor shifts in the precision trap 
 
 In our measurement, we need to consider frequency shifts caused by the octupole perturbation in the trapping potential C 4 , which affects the cyclotron frequency determined by the invariance theorem, but not the Larmor frequency. The major contribution to the cyclotron frequency shift comes from the axial frequency shift Δν z,C4 = 32 × ΔTR × T z mHz per mUnit K (0.032 × ΔTR × T z mHz K−1), where ΔTR = −5 × 10−5 is the tuning ratio offset from the optimum working point. This results in a g-factor shift of (δg/g) Φ = −10(1) parts per trillion (p.p.t.). Higher-order perturbations contribute less than 0.1 p.p.t. 
 
 The residual magnetic field inhomogeneity B 2,PT changes the magnetic field experienced by the antiprotons depending on their axial amplitudes. The frequency shifts in both frequencies ν L and ν c are considered in the g-factor lineshape function, and compensate each other in the frequency ratio. 
 
 The second effect that needs to be considered is the temperature difference in the cyclotron mode of the two particles (E +,c − E +,L )/k B = 356(27) K. Owing to the magnetic-field gradients in our trap, the cyclotron frequency is effectively measured at a lower magnetic field. This results in shifts of the measured g-factor of (δg/g) B1 = +0.22(2) p.p.b. owing to the change in the axial equilibrium position, and (δg/g) B2 = +0.12(2) p.p.b. owing to the difference in the radial orbit. Further, the cyclotron energy difference causes a relativistic shift of the measured cyclotron frequency, which changes the measured g-factor by (δg/g) rel = +0.033(3) p.p.b. All other amplitude-dependent systematic shifts are negligible. 
 
 The image charge induced by the antiproton in the trap electrodes interacts back with the particle and modifies cyclotron frequency determined via the invariance theorem. This causes another systematic deviation of the extracted cyclotron frequency and modifies the measured g-factor by (δg/g) im = +0.04 p.p.b., the error of this value being on the sub-p.p.t. level33, 34. 
 
 Asymmetric voltage relaxation drifts after the particle transport in the precision trap also affect our measurements. The first measurement of the sideband particle’s axial frequency after the spin-flip drive in the precision trap is effectively measured at a lower trapping potential than the sideband frequencies. The required correction of 0.15(2) p.p.b. was included in the determination of Γ k , and is contained in the statistical g-factor evaluation. The voltage drift also means that the axial equilibrium position spin-flip particle drifts in the magnetic field gradient B 1,PT during the Larmor drive. This systematically shifts the measured g-factor by (δg/g) V = +0.04(2) p.p.b. 
 
 Two-particle comparisons 
 
 To ensure that no contaminants were co-trapped with one of the antiprotons, which would induce systematic g-factor shifts, we compared the charge-to-mass ratios of the two particles6 and confirmed that the cyclotron frequencies of the two antiprotons were identical within an uncertainty of 0.28 p.p.b., the value being limited by the statistics of the comparison measurement. 
 
 Lineshape of the g-factor resonance 
 
 The basic mechanisms giving rise to the lineshape of the Larmor resonance in Penning trap measurements have been discussed26. The residual magnetic bottle in the precision trap and the interaction of the particle’s axial mode with the image-current detector generate a lineshape that is a convolution of the unperturbed Rabi resonance and the Boltzmann distribution of the axial energy. The spin-flip probability in the precision trap can be expressed as: 
 
 with being the angular Rabi frequency of the spin-flip drive, where b rf is the magnetic field amplitude of the spin-flip drive in the perpendicular direction to the z-axis. t rf = 8 s is the Larmor drive duration, is the probed g/2-factor ratio, is the antiproton g-factor, and is the Larmor lineshape function. The latter is obtained from χ L (ω L ,B 0 ) derived in the analysis in ref. 26 as: 
 
 with the parameters , . Δω L = 2π0.440(49) s−1 is the Larmor linewidth parameter, and γ PT = 1.75 Hz is the damping constant of the axial detector in the precision trap. Δν c is the cyclotron-frequency shift, which is composed of the difference in magnetic field obtained from the cyclotron-frequency measurements to the average magnetic field during the spin-flip drive, and the measurement fluctuations caused by the sideband method. The distribution of Δν c is analysed below. The line-shape function used in the g-factor evaluation is the convolution of the cyclotron-frequency shift distribution ρ(ν) and the lineshape function : 
 
 Magnetic field model 
 
 The average cyclotron frequency shift Δν c and the cyclotron frequency shift distribution ρ(ν) in define the location of the resonance relative to the -factor and contribute to the width of the resonance. Therefore, these parameters require a detailed analysis. 
 
 The measurement of both frequencies ν L and ν c is carried out in the residual magnetic field inhomogeneity of the precision trap B 2,PT . The axial amplitude z2 shifts the measured cyclotron frequency by 155(4) mHz compared to the frequency in the trap centre. We consider this effect by adding Δν c,B2 to Δν c in the lineshape function . For the Larmor frequency, the detector–particle interaction of the axial motion in the presence of B 2,PT is inherently contained in the lineshape function. 
 
 Further, the sideband method for the measurement of the modified cyclotron frequency ν + induces fluctuations on ν c because the sideband drive couples the modified cyclotron mode to the axial detector. This results in a measurement of the sideband frequencies ν l and ν r in thermal equilibrium with T + = ν + /ν z × T z and a measurement of the axial frequency with a different energy E + after each drive. Therefore, the measured modified cyclotron frequency is: 
 
 where (E + /k B ) is a state of the Boltzmann distribution of the cyclotron energy with temperature T + . The dominant resulting fluctuation is: 
 
 which has an expectation value of zero. The contribution of this effect to the cyclotron frequency shift distribution ρ(ν) with six averaged cyclotron frequency measurements is approximated by a normal distribution with a standard deviation of σ(ν c,SB )/ν c = 2.17(6) p.p.b. 
 
 External magnetic field fluctuations caused by the imperfectly shielded periodic ramps of the antiproton decelerator magnets and random-walk magnetic-field fluctuations of the superconducting magnet cause a magnetic-field difference from the one obtained by the cyclotron frequency measurements and the real magnetic field during the spin-flip drive. To analyse this effect, we construct a magnetic-field model based on our cyclotron-frequency measurements. The model consists of the sideband fluctuations described above, a magnetic-field white-noise component Δν c,W with standard deviation σ W , and a random-walk component Δν c,RW with standard deviation , with Δt being the time difference between two measurements. Extended Data Fig. 2 shows the measured standard deviations of the cyclotron frequency shifts as function of Δt and the total fluctuations predicted by our magnetic field model. Based on this, we simulate the evolution of the magnetic field for 1,000 measurement cycles, which reproduce the observation shown in Extended Data Fig. 2 within uncertainties. To analyse the impact on the ratios Γ k , we determine the standard deviation of the magnetic-field difference that the spin-flip particle experiences during the Larmor drive and the effective magnetic field determined from six averaged cyclotron frequencies. From these Monte-Carlo simulations, we obtain σ B,c /B 0 = 3.9(1) p.p.b. 
 
 On the basis of the calibration of our external flux gate sensors, we contribute 1.8(4) p.p.b. to stem from imperfectly shielded external magnetic field ramps from the deceleration cycle of the antiproton decelerator. 
 
 In total, the magnetic-field fluctuations are dominated by white noise, therefore we approximate the cyclotron-frequency shift distribution ρ(ν) by a normal distribution with standard deviation σ c = 3.9(1) p.p.b. In the evaluation, the convolution of the lineshape function with this cyclotron frequency shift distribution is used. 
 
 Larmor drive amplitude and saturation 
 
 The magnetic field fluctuations σ c smear out the Larmor resonance and reduce the maximum spin-flip probability for measurements with unsaturated Larmor drive. Therefore, we deliberately applied a drive amplitude that slightly saturates the Larmor transition to keep the contrast in spin-flip probability, that is, the difference in spin-flip probability for on-resonance to off-resonance data pointes, at a stable maximum. Thereby, we avoided an increase in the measurement statistics required to resolve the g-factor resonance. Our choice of the drive amplitude leads to the saturated resonance shown in Fig. 3. The drive saturation is included in our line-shape model and its effect is considered in the statistical evaluation. 
 
 Optimization of the spin-transition identification procedure 
 
 The observation of the spin transitions in the precision trap requires the identification of the initial and the final state of each spin-flip attempt in the analysis trap. For this purpose, we drive spin-transitions in the analysis trap and analyse the axial frequency shift caused by each drive to identify the spin state23, 25. In contrast to the discussion in ref. 23, we determine the probabilities for spin up for the initial state and final state of each spin-flip attempt individually based on a recursive formula23, which is reproduced here for convenience: 
 
 where is a set of measured axial frequency shifts, h 0 and h + are normal distributions with standard deviation describing the axial frequency shift distributions for spin-flip drives, where the spin state remains unchanged and changes to spin up, respectively. P SF,AT ≈ 50% is the spin-flip probability of the spin-flip drive in the analysis trap. The recursion is initialized with maximum ignorance = 0.5. Note that the order of the set can be reversed to determine the starting state of the sequence. 
 
 The fidelity of the spin-state identification, that is, the mean probability to assign the correct spin state, is limited by the axial frequency fluctuations 65 mHz, which are not negligible compared to the frequency shift induced by a spin transition Δν SF ≈ 172 mHz. To increase the contrast of the g-factor resonance, we define the initial state of the precision trap spin transition with high fidelity. For this purpose, we deliberately wait until we drive a spin transition, where the spin-flip frequency shift ±Δν SF and the axial frequency shift add up so that |ν z | > 190 mHz. Depending on the cyclotron energy and the associated frequency fluctuation , this defines the initial spin state with a fidelity higher than 98%. 
 
 The determination of the final state requires us to determine the spin state at the beginning of the spin-state identification sequence. Owing to the limited fidelity, information on the spin state at the beginning is lost with each spin-flip attempt. The probability to extract the correct spin state from the sequence is defined by the random values of the axial frequency fluctuations and the occurrence of spin-transitions during the first spin-flip drives in the sequence. This reduces the average final spin-state fidelity to a value between about 80% and about 90%, depending on the cyclotron energy of the antiproton. 
 
 Maximum likelihood estimation of the g-factor 
 
 The data analysed in the statistical evaluation were recorded in the time period from 5 September 2016 to 28 November 2016. In total, 1,008 measurement sequences with Larmor drive at a fixed amplitude, three preceding and three subsequent cyclotron frequency measurements, spin state initialization and final spin state determination have been carried out. Seventy-five of these measurement sequences are disregarded in the evaluation, as they were perturbed by external magnetic field shifts caused by operations on the overhead crane or other magnets in the environment of our apparatus. These measurement cycles have been identified using our magnetic-field monitoring system based on flux-gate, GMR and Hall sensors, which are placed in our experiment zone. 
 
 In our analysis procedure, we determine from a direct maximum likelihood estimation based on the frequency ratios Γ k and the preceding and subsequent series of axial frequency shifts and , respectively. These are recorded during the spin-state determination in the analysis trap. The likelihood function can be expressed as: 
 
 Where P SF,PT is the lineshape function including the convolution with the cyclotron frequency shift distribution. is the probability that a spin-flip has occurred in the precision trap based on the axial frequency information in the analysis trap. The spin-up probabilities for the initial and final states are given by and , respectively. 
 
 The likelihood function in the plane of σ c is shown in Extended Data Fig. 3 as function of the Rabi frequency Ω R /(2π) and the relative difference between the antiproton and proton g-factors, . We determine the confidence intervals for the antiproton g-factor as described35. As a result, we obtain 
 
 Ω R /(2π) = 1.11(14) Hz, which is a relative uncertainty of (δg/g) stat = 1.1 p.p.b. in with 68% CL, and (δg/g) stat = 2.3 p.p.b. for the 95% CL. 
 
 Fluctuation model dependence 
 
 The determination of and require the spin-flip probability in the analysis trap P SF,AT , the frequency shift caused by a spin transition Δν SF , and the axial frequency fluctuation without drive as input parameters23. The first two parameters are extracted from an maximum likelihood estimation using all measured frequency shifts with spin-flip drive in the analysis trap during the measurement sequence. We obtain Δν SF = 170.4(2.0) mHz, and P SF,AT = 47.29(0.68)%. The variations in the g-factor when changing Δν SF and P SF,AT within their uncertainties are only 12 p.p.t. and 15 p.p.t., respectively. The major contribution of uncertainty from the spin-state analysis comes from the values of the axial frequency fluctuations , which need to be determined for each measurement sequence k individually, since the cyclotron energy E +,k changes for each data point owing to the residual heating effect during the particle transport. At a fixed averaging time, the axial frequency fluctuation scales as: 
 
 where summarizes the cyclotron-energy independent axial frequency fluctuations, for example, owing to voltage fluctuations and fast Fourier transform averaging, and is the contribution due to cyclotron quantum transitions driven by spurious noise in the analysis trap25, 36. We determine E + for each data point, based on the axial frequency , the analysis trap ring voltage , and on the frequency information from the last cyclotron cooling procedure. Each spin-state determination is accompanied by measurements of frequency fluctuations without spin-flip drive. The combined information of E +,k and the measured frequency fluctuations is used to determine the parameters of . We account in our model for a slow drift of the voltage reference of our analysis trap ring voltage power supply. This requires us to adjust the values of (E + /k B ) at constant ring voltage by 2.7 mK per day. Changing the model parameters and the cyclotron energy E + within their confidence intervals causes a g-factor variation of 133 p.p.t. and 238 p.p.t. for the 68% CL and the 95% CL, respectively. We add the uncertainties of all three parameters in quadrature to the uncertainty of the determined g-factor. 
 
 Data availability 
 
 The datasets generated during and/or analysed during this study are available from the corresponding authors on reasonable request. ||||| A new super-precise measurement from the RIKEN-led BASE collaboration, which also includes researchers from the University of Tokyo, Japan, the Max Planck Institute for nuclear physics, Heidelberg, the University of Mainz, the University of Hannover and GSI Darmstadt, Germany, has placed new constraints on the difference between matter and antimatter, as part of the quest to discover why our Universe is almost only composed of matter. Using a novel two-particle measurement method, the group measured the magnetic moment of the antiproton at a precision 350 times higher than any previous measurement. The result, published in Nature, shows that the magnetic moments of the proton and antiproton are tremendously close, meaning that so-called CPT asymmetry--a key factor in the lack of antimatter--must be very small if it exists at all. CPT symmetry refers to the idea that if particles change in two of three properties--charge, parity, and time--must also change in the third, and is critical in understanding the imbalance between matter and antimatter. 
 
 To perform the measurement, the group used a novel, elegant, two particle measurement method developed in Stefan Ulmer's RIKEN laboratory, which is a further advance of a two-trap method previously developed at the University of Mainz. The system involves the simultaneous trapping and measurement within an even magnetic field of two separate antiprotons--one measured at a relatively high temperature of about 350 degrees Kelvin--a temperature equivalent to hot water--and the other at just 0.15 K, extremely close to absolute zero. The first antiproton is used to calibrate the magnetic field, by measuring a property called the "cyclotron frequency," while the other is used to measure a quality known as the Larmor frequency, which looks at the precession of the particle's spin, allowing precise measurements of the magnetic moment. 
 
 Using this new method, they found that the magnetic moment of the antiproton is 2.792 847 344 1(42), a value extremely close to the figure of 2.792 847 350(9) that the same collaboration of researchers found for the proton in 2014. In addition to showing that they are so close, the results also put strict limits on the possibility that a difference in the magnetic moments could be based on factors that, at the high energies that existed in the early universe, could have caused a process of "spontaneous symmetry breaking" leading to differences in matter and antimatter. 
 
 According to Ulmer, "With these results, we have shown, as has been demonstrated with other properties of a variety of particles, that CPT invariance seems to hold at very high precision, as the magnetic moment of the proton and the antiproton still look identical, apart from the signs. This result is the culmination of many years of continuous research and development, and the successful completion of one of the most difficult measurements ever performed in a Penning trap instrument, with many parameters developed close to the principal technical limits." 
 
 Christian Smorra, first-author of the study adds, "By upgrading the experiment with several new technical innovations, we feel that some further improvement can still be made, and in the future, following the CERN upgrade expected to finish in 2021, we will be able to achieve an at least ten-fold improvement." 
 
 The results were achieved soon before the next CERN shutdown, which is scheduled to last from 2019 to 2021. 
 
 ###
– It's not often a new discovery has scientists sounding like a bunch of nihilists, and yet CERN physicist Christian Smorra had this to say to Cosmos regarding a study published this month in Nature: "All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist." Scientific models say the Big Bang produced an equal amount of matter and antimatter. But matter and antimatter destroy each other when they come in contact; an equal amount of each means the universe should have blinked out of existence in a burst of energy. But it hasn't, which means there must be some difference between the two to allow matter to dominate to the point where there is comparatively little antimatter in the universe, according to a press release. That's where CERN researchers come in. They've spent the past decade attempting to find a difference in the magnetism of matter and antimatter (it's not easy measuring something that destroys matter). That's resulted in a new measurement of the magnetic moment of an antiproton that is 350 times more accurate than the old measurement, ZME Science reports. It turns out the magnetic moment of an antiproton is ... pretty much exactly the same as that of a regular proton. Shoot. Smorra says a difference between matter and antimatter still must exist somewhere. Next up for CERN researchers is seeing if gravity affects protons and antiprotons differently. (Far from not existing, the universe actually contains way more galaxies than we thought.)