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The proton radius puzzle

The proton radius puzzle

Abstract. The FAMU (Fisica degli Atomi Muonici) experiment has the goal to measure precisely the proton Zemach radius, thus contributing to the solution of the so-called proton radius “puzzle”. To this aim, it makes use of a high-intensity pulsed muon beam at RIKEN-RAL impinging on a cryogenic hydrogen target with an high-Z gas admixture and a tunable mid-IR high power laser, to measure the hyperfine (HFS) splitting of the 1S state of the muonic hydrogen. From the value of the exciting laser frequency, the energy of the HFS transition may be derived with high precision ( ∼ 10 −5 ) and thus, via

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Puzzling out the proton radius puzzle

Puzzling out the proton radius puzzle

The proton radius puzzle is a conspicuous open question of the nuclear physics that, due to the possible profound implications on our understanding of physics world, deserves our full attention. The existing data, which were obtained with the state-of-the-art high precision experiments, show a consistent picture for the electronic hydrogen, while the spectroscopic measurement of the muonic hydrogen reports a significantly di ff erent value for the proton charge radius. Many di ff erent aspects of the problem have already been investigated, but the 4 % difference in radii or 0.15 % difference in the transition energy remains unexplained. Some claim that the puzzle can not be explained in terms of the Standard Model, while others assume that this could be an indication of a hidden fundamental problem of QED. In order to test any of the proposed hypotheses, further theoretical and experimental work is needed. Many new experiments are foreseen for the near future, which will reveal new insight into the puzzle.

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Explaining the proton radius puzzle with disformal scalars

Explaining the proton radius puzzle with disformal scalars

The Lamb shift is one of the most precisely studied effect in atomic physics. Its relevance has been recently enhanced by the discovery that the Lamb shift behaves differently when muonic atoms are considered, compared to their electronic siblings. The Lamb shift can be used to deduce the value of the proton radius and muonic versus electronic discrepancies imply that the proton radius is lower by four percent in muonic experiments. The combined discrepancy between the proton radius as inferred from muonic Hydrogen and that inferred from electronic Hydrogen now stands at 7σ. Whilst the muonic results currently only come from one group at PSI no systematic uncertainty has been identified that could explain the size of the discrepancy [1] 1 . This is the proton radius puzzle which has resisted explanation with standard model physics [3]. Could this be an indication of the need for new physics? Current attempts to explain the proton radius anomaly with new physics have introduced

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Review of experimental and theoretical status of the proton radius puzzle

Review of experimental and theoretical status of the proton radius puzzle

Figure 13. Status of the proton radius puzzle circa 2016, with prospects for new data. The upper pane is reproduced from Fig. 1. The middle pane shows updated results. The cyan points give updated fits to electron scattering data using z expansion (final two points in Fig. 4, from Ref. [15]. The black point represents the 2014 CODATA [1] combination of hydrogen and electron-proton scattering determinations. The red point is from the 2016 CREMA muonic deuterium Lamb shift measurement using the regular hydrogen-deuterium isotope shift [73]. The bottom pane shows expected sensitivities of anticipated results in: regular hydrogen [78] (blue); low-Q 2 electron-proton scattering [90] (cyan); and muon-proton scattering [92] (magenta). See text for details.

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The Proton Radius Puzzle

The Proton Radius Puzzle

The muonic hydrogen measurements [1, 7] were made as the knowledge of the proton radius limits precision in many electromagnetic physics measurements. Due to the finite size of the proton, the electron in atomic hydrogen actually has a finite probability to be found inside the proton, when occupying S-states. While inside the proton, some of its attractive potential is screened, thereby reducing the average attractive potential seen by the electron and perturbing the energy levels of the S-states. This perturbs the S-P transitions, so by measuring them very precisely, and applying some theoretical calculations, one can extract the radius of the proton.

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The proton radius puzzle – 9 years later

The proton radius puzzle – 9 years later

with an inadequate selection of fit models. The PRad data in this overlap region is mostly data taken with a 2.2 GeV beam. As can be seen in Fig. S16 of the supplementary information of [45], the radius fit is completely dominated by the 2.2 GeV data—the fit to the 1.1 GeV data alone can- not distinguish between the two radius values, while the fit to all data and to the 2.2 GeV data has essentially the same value and uncertainty. It is indeed strongly driven by only the 9 largest Q 2 points—the fit without these, i.e., for Q 2 < 0.016 (GeV/c) 2 gives a considerably smaller radius with much larger uncertainties.

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Radiative corrections to elastic-electron proton scattering and uncertainty in proton charge radius

Radiative corrections to elastic-electron proton scattering and uncertainty in proton charge radius

The recent progress in high-precision measurements of proton electromagnetic form factors and, in particular, of the proton charge mean square radius revealed serious difficulties in our studies of this fundamental particle. The very precise result on the proton radius from the muonic hydrogen spec- trum [1] appeared to be more than five sigma away from averaged value obtained from the the ordinary hydrogen spectrum and from experiments on elastic electron-proton (ep) scattering. The difference is known as the proton radius puzzle. Certainly to resolve the problems we have to re-consider all pos- sible effects starting from experimental uncertainties up to new physics contributions. Scrutinizing of the theoretical description of the hydrogen spectra and ep scattering is a part of the list.

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Initial state radiation experiment at MAMI

Initial state radiation experiment at MAMI

The proton has been scrutinized since the early days of experimental hadronic physics [1]. Its radius has been de- termined by various electron scattering experiments and many atomic Lamb shift measurements (see Figure 1). Both approaches gave consistent results. Unfortunately their average does not agree with the findings of re- cent very precise Lamb shift measurements in muonic- hydrogen [2, 3], which report a new value for the proton charge radius which is 7σ away from the previously ac- cepted value. This discrepancy, known as the proton radius puzzle, is controversial and demands further investigation. An ongoing electron scattering experiment at MAMI aims to o ff er new insight into this matter.

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An Equivalence for Both Coulombian and Gravitational Interactions

An Equivalence for Both Coulombian and Gravitational Interactions

The main purpose of this article is to demonstrate that electromagnetic and gravitational phenomenology are two different expressions of the same inte- raction that we can call “ universal interaction ”. In order to reach the aim, it is therefore necessary to imagine the matter in a slightly different way, as well as equivalent, to what has been done until today by the literature everywhere accepted. Even if differently imagined, this proposed structure of matter cannot and must not escape from reflecting the measurements and phenom- enologies widely experimented in laboratories all over the world. In the pro- posed model the proton radius; the electron mass; the Avogadro constant; the existence and the mass of neutron and the existence of neutrino are theoreti- cally derived. The main consequence is therefore a more general rewriting of Newton’s law of universal gravitation. A definitive value for the universal gravitational constant is proposed.

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Friction Coefficient in Hot Compression of Cylindrical Sample

Friction Coefficient in Hot Compression of Cylindrical Sample

testing methods based on the geometrical changes in order to adjust the frictional conditions in the simulation to the condition of the real process. Bay 3) studied the application of the friction model when analyses of bulk metal forming process were given. On the basis of these and other results 4,5) an upper–bound theory was developed to effectively deter- mine the average friction coefficient by conducting a barrel compression test. Using this theory, the average Tresca friction coefficient (hereafter friction coefficient, m) for the compression test can be determined by measuring just the degree of barreling (maximum radius, R m , and height

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Mitochondrial proton leak compensates for reduced oxidative power during frequent hypothermic events in a protoendothermic mammal, Echinops telfairi

Mitochondrial proton leak compensates for reduced oxidative power during frequent hypothermic events in a protoendothermic mammal, Echinops telfairi

FIGURE 4 | Calculation of coupling efficiency that is defined as the respiratory fraction that drives the ATP synthase. (A) Single example how coupling efficiency is assessed per individual. State 3 and proton leak respiration at the state 3 membrane potential (indicated by the dashed line) are required. (B) Coupling efficiency = (state 3—proton leak respiration)/ (state 3 respiration at state 3 membrane potential). 20 ◦ C acclimated (CA, white circles, n = 3) vs. 27 ◦ C acclimated (WA, black circles, n = 4) groups were not significantly different (two-way repeated measures ANOVA). Therefore, the linear regression analysis was performed on the combined data from both acclimation groups; y = −0.012x + 1.077 (ANOVA, P = 0.064). Values are means ± SE.

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Resonance Production with the LHCb Experiment

Resonance Production with the LHCb Experiment

Abstract. Studies of strange and charm resonance production in the forward region pro- vide important input to the importance to the understanding of QCD models. The latest studies at LHCb of resonance production in both proton-proton and proton-lead colli- sions are presented, with particular emphasis on charmonium production including the production of Z(4430).

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Renormalization of Proton-Proton Scattering and Proton-Proton Fusion with Chiral Two Pion Exchange: Regulator Independent Results.

Renormalization of Proton-Proton Scattering and Proton-Proton Fusion with Chiral Two Pion Exchange: Regulator Independent Results.

sion. By renormalization I refer to (i) the possibility of expressing all observables in terms of other physical ob- servables and the physical parameters of the long range in- teraction and (ii) achieving regulator independence over a reasonable range of cut-offs. Instead of the usual effective field theory formulation of the scattering problem in terms of long range potentials and counterterms, the fulfillment of the previous conditions will be realized on the base of the long range correlations [11] which chiral one and two pion exchange generate in the proton-proton system. In this approach, contact operators are treated implicitly, via boundary conditions in coordinate space, and will be given a secondary role in the discussion. Depending on the num- ber of constraints imposed on the long range correlations, different power countings can be accommodated. The re- quirements of cut-off independence can also be easily ana- lyzed within the long range correlation picture [11, 12]: in the case of regular and singular attractive interactions, the dependence on the cut-off scale can be completely elimi- nated, but not so in the singular repulsive case, in which finite cut-offs are forcefully required. In this latter case, it is essential for the effective field theory description that the coordinate space cut-off at which the divergences appear is similar to or smaller than the short range scale R S of the

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Utility of the Cortical Thickness of the Distal Radius as a Predictor of Distal-Radius Bone Density

Utility of the Cortical Thickness of the Distal Radius as a Predictor of Distal-Radius Bone Density

Indirect radiological techniques such as DXA currently represent the gold standard for the assessment of bone density. However, they are rarely available to the trauma- tologists at the time of decision-making with regard to the management of the trauma case. This is why efforts are being made to provide the surgeon with direct means of quantifying bone density (7-9). The outcome of the treatment of distal-radius fractures is greatly affected by the quality of the patient's bone stock (2). However, these fractures are common, and treatment decisions should be taken as soon as possible after the traumatic event, which means that routine bone density assess- ment by the means of techniques such as DXA would be unrealistic. Unlike these more sophisticated methods, radiographs constitute the simplest, standardized and virtually always available diagnostic aid at the early stage of fracture management. The present study was not per- formed with a view to supersede such methods as DXA and peripheral quantitative computed tomography (pQCT); rather the object was to establish whether an in- tuitive look at the cortices of the distal radius would al- low valid conclusions to be drawn as to the patient's fore- arm bone density. The results of our study suggest that distal-radius cortical thickness can indeed be used as a predictor of bone quality. Our findings agree with those of Tingart et al. (6), who reported an even stronger cor- relation between the cortical thickness of the proximal diaphysis of the humerus and the bone quality of the hu- meral head. The authors also used the metaphysis as the region of interest for BMD determination, with bound- aries between sub-regions drawn according to anatomi-

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Forearm Bone Mineral Density of Normal Indian Population

Forearm Bone Mineral Density of Normal Indian Population

The age related BMD in our study of the normal population was compared with the Asian reference value provided by manufacture. Our population has a significant lower age related BMD than the Asian reference value provided by manufacturer (Table 5 and Table 6). Testing for significance between these two groups re- vealed that except for male distal radius and ulna, proximal radius, others were statistically significant (p < 0.05).

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A novel treatment of the proton-proton Coulomb force in proton-deuteron Faddeev calculations

A novel treatment of the proton-proton Coulomb force in proton-deuteron Faddeev calculations

Abstract. We present resently introduced novel approach to include the proton-proton (pp) Coulomb force into the momentum space three-nucleon (3N) Faddeev calculations. It is based on a standard formulation for short range forces and relies on a screening of the long-range Coulomb interaction. In order to avoid all uncertainties connected with an application of the partial wave expansion, unsuitable when working with long-range forces, we apply directly the 3-dimensional pp screened Coulomb t-matrix. That main new ingredient, the 3-dimensional screened pp Coulomb t-matrix, is obtained by a numerical solution of the 3-dimensional Lippmann-Schwinger (LS) equation. Using a simple dynamical model for the nuclear part of the interaction we demonstrate the feasi- bility of that approach. The physical elastic pd scattering amplitude has a well defined screening limit and does not require renormalisation. Well converged elastic pd cross sections are obtained at finite screening radii. Also the proton-deuteron (pd) breakup observables can be determined from the resulting on-shell 3N amplitudes in- creasing the screening radius. However, contrary to the pd elastic scattering, the screening limit exists only after renormalisation of the pp t-matrices.

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Cirrus parameterisation and the role of ice nuclei

Cirrus parameterisation and the role of ice nuclei

An existing parametrization of homogeneous nucleation has been improved by using a theoretically determined timescale of homogeneous freezing, and has been made practicable by providing a universal analytical expression. The improved parametriza- tion works well, even when monodisperse aerosol particles are used in determining cirrus ice-crystal number densities, if the aerosol distribution can be described ade- quately by a single effective radius. The discrepancies between the parametrization and a detailed model—in cirrus ice-crystal number densities at lower temperatures and higher updraughts—are explained by the change of the nucleation timescale with respect to time.

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Cavitons and spontaneous hot flow anomalies in a hybrid Vlasov global magnetospheric simulation

Cavitons and spontaneous hot flow anomalies in a hybrid Vlasov global magnetospheric simulation

One of the properties associated with SHFAs is that of de- creased bulk velocity, and our simulation did display dips at the locations of cavitons and SHFAs. However, the decrease seen in our data is much lower than that reported by Omidi et al. (2013), Zhang et al. (2013), and Zhao et al. (2015). To investigate this more, we tracked the changes visible in proton distribution functions as foreshock features were con- vected across virtual spacecraft and found that our VDFs re- sembled those found by Zhang et al. (2013). That is, the flow of the thermal solar wind core was not slowed or deflected, but, rather, changes in bulk flow are due to the combination of a density decrease for the core and a strengthening of the suprathermal beam. When the thermal core is depleted, the backstreaming beam can have a relatively greater impact on bulk velocity measurements.

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Exclusive vector mesons at high energies: from photon-proton to proton-proton and nucleus-nucleus collisions

Exclusive vector mesons at high energies: from photon-proton to proton-proton and nucleus-nucleus collisions

Now, that we have convinced ourselves, that diffractive photoproduction of heavy vector mesons (es- pecially its energy dependence) is a sensitive probe of the gluon distribution distribution, let us turn to proton-(anti)proton collisions, where in fact very high energy photoproduction is accessible today. In- deed, being charged particles, fast protons give rise to a flux of Weizs¨acker-Williams photons. Clearly, in distinction to pointlike electrons, the finite-size protons will only supply us with quasi-real Q 2 ∼ 0 photons, so that the perturbative regime is accessible only for heavy quarks/mesons. There is a second complication: either of the colliding protons can emit the photon, and the amplitudes for these two pro- cesses interfere. Additionally, we have to take into account, that protons may also interact strongly - the absorptive or unitarity correction. Those aspects are discussed in quite some detail in [10]. Here we show our results for the rapidity spectrum of exclusive vector mesons at Tevatron and LHC energies. At Tevatron energies, at central rapidities the subprocess energies for γp → V p or γ ¯p → V ¯p cover the known HERA domain. Given the fact that absorptive corrections, due to the peripheral nature of the reaction are weak, this means that robust predictions of vector meson production are possible. At LHC energies, it is possible to extend the energy range over the one already studied at HERA. For example, for J/ψ production at central rapidity y = 0, we have W γp ∼ 140 GeV, whereas at y = 4 the

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Proton-air and proton-proton cross sections

Proton-air and proton-proton cross sections

Abstract. Different attempts to measure hadronic cross sections with cosmic ray data are reviewed. The major results are compared to each other and the differences in the corresponding analyses are discussed. Besides some important di ff erences, it is crucial to see that all analyses are based on the same fundamental relation of longitudinal air shower development to the observed fluctuation of experimental observables. Furthermore, the relation of the measured proton-air to the more fundamental proton-proton cross section is discussed. The current global picture combines hadronic proton-proton cross section data from accelerator and cosmic ray measurements and indicates a good consistency with predictions of models up to the highest energies.

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