Radiation astronomy/Mesons

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Astronomy that benefits from the detection of mesons, directly or indirectly, is meson astronomy.


Main source: Radiation

A meson is a subatomic particle that is intermediate in mass between an electron and a proton and transmits the strong interaction that binds nucleons together in the atomic nucleus.

Mesons travel at speeds slower than the speed of light.

"[M]esons [...] are hadronic subatomic particles [...], bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometre, which is about 23 the size of a proton or neutron."[1]

"Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons."[1]

"Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter ... In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles."[1]

"In nature, the importance of lighter mesons is that they are the associated quantum-field particles that transmit the nuclear force, in the same way that photons are the particles that transmit the electromagnetic force."[1]

"Each type of meson has a corresponding antiparticle (antimeson) in which [by theory] quarks are replaced by their corresponding antiquarks and vice-versa."[1]

Mesons are subject to "both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction."[1]

"While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher energy phenomena more readily than baryons composed of the same quarks would."[1]

Potential mesons to be detected astronomically include: π, ρ, η, η′, φ, ω, J/ψ, ϒ, θ, K, B, D, and T.

B mesons[edit]

"The K0-K0 bar, D0-D0 bar, and B0-B0 bar oscillations are extremely sensitive to the K0 and K0 bar energy at rest. The energy is determined by the values mc2 with the related mass as well as the energy of the gravitational interaction. Assuming the CPT theorem for the inertial masses and estimating the gravitational potential through the dominant contribution of the gravitational potential of our Galaxy center, we obtain from the experimental data on the K0-K0 bar oscillations the following constraint: |(mg/mi)K0 - (mg/mi)K0 bar| ≤ 8·10-13, CL=90%. This estimation is model dependent and in particular it depends on a way we estimate the gravitational potential. Examining the K0-K0 bar, B0-B0 bar, and D0-D0 bar oscillations provides us also with weaker, but model independent constraints, which in particular rule out the very possibility of antigravity for antimatter."[2]

"In spite of the apparent parity non-invariance of the ordinary particles, the universe could still be left-right symmetric if [charge conjugation parity] CP were an exact symmetry[11]. But this option is [...] ruled out by experiments on kaons and B-mesons!)."[3]

Upsilon mesons[edit]

A plot of the invariant mass of muon pairs, the peak at about 9.5 GeV is due to the contribution of the Upsilon meson. Credit: Leon Lederman and the E288 collaboration, Fermilab.

The plot on the right shows a peak at about 9.5 GeV due to the Upsilon meson.


J/Ψ production is graphed. Credit: Fermilab.

On the right is a graph of the production of psi mesons (psions) at Fermilab.

The "discovery of the psi meson in 1974, independently by Samuel C.C. Ting and Burton Richter [22, 23] [pointed out] its lifetime, which was about a thousand times longer than any other similar particle’s lifetime."[4]

The "SLAC-LBL group looked between a pair of 100-MeV "milestones" and discovered the extremely narrow psi resonance that sent the counting rate up by more than a factor of 100, within the space of 1 MeV and within an observing time interval of 2 hours."[5]

Omega mesons[edit]

Omega meson production:[6]

Omega meson ω(782) decay modes:[6]

  1. Γ1:
  2. Γ2:
  3. Γ3:
  4. Γ4:
  5. Γ5:
  6. Γ6:
  7. Γ7:
  8. Γ8:
  9. Γ9:
  10. Γ10:
  11. Γ11:
  12. Γ12:
  13. Γ13:
  14. Γ14:
  15. Γ15:
  16. Γ16:
  17. Γ17:
  18. Γ18:
  19. Γ19:

Phi mesons[edit]

The phi meson (1020) has a mass of 1019.445 MeV. It decays per[7]

Rho mesons[edit]

Rho mesons occur in three states: ρ+, ρ-, and ρ0.[7] The rest masses are apparently the same at 775.4±0.4 and 775.49±0.34.[7] Decay products are π± + π0 or π+ + π-, respectively.[7]

Eta mesons[edit]

Eta mesons (547.863 ± 0.018 MeV) have the decay schemes:[6]

  1. η :
  2. η :
  3. η :

Eta prime mesons (957.78 ± 0.06 MeV) have the decay schemes:[6]

  1. η' :
  2. η' :

The charmed eta meson ηC(1S) has a rest mass of 2983.6 ± 0.7 MeV.[6]

D mesons[edit]

D mesons
Particle name Particle
Rest mass (MeV/speed of light|c2) IG JPC S C B' Mean lifetime (s) Commonly decays to

(>5% of decays)

D meson[9] D+ D 1,869.62 ± 0.20 12 0 0 +1 0 1.040 ± 0.007 × 10−12 See D+ decay modes
D meson[10] D0 D0 1,864.84 ± 0.17 12 0 0 +1 0 4.101 ± 0.015 × 10−13 See D0 decay modes
Strange D meson[11] D+
1,968.47±0.33 0 0 +1 +1 0 (5.00±0.07) x 10-13 See D+
decay modes
D meson[12] D∗+(2010) D∗−(2010) 2,010.27.62 ± 0.17 12 1 0 +1 0 6.9 ± 1.9 × 10−21[a] D0 + π+ or
D+ + π0
D meson[13] D∗0(2007) D∗0(2007) 2,006.97 ± 0.19 12 1 0 +1 0 >3.1 × 10−22[a] D0 + π0 or
D0 + γ

[a] PDG reports the resonance width (Γ). Here the conversion τ = ħΓ is given instead.


"The muons created through decays of secondary pions and kaons are fully polarized, which results in electron/positron decay asymmetry, which in turn causes a difference in their production spectra."[14]

The "highest energy neutrinos from GRBs mainly come from kaons."[15]


Single π0 production occurs "in neutral current neutrino interactions with water by a 1.3 GeV wide band neutrino beam."[16]

"The Gamma-Ray Spectrometer (GRS) on [Solar Maximum Mission] SMM has detected [...] at least two of the flares have spectral properties >40 MeV that require gamma rays from the decay of neutral pions. [Pion] production can occur early in the impulsive phase as defined by hard X-rays near 100 keV."[17]

Gamma-ray "emission matches remarkably well both the position and shape of the inner [supernova remnant] SNR shocked plasma. Furthermore, the gamma-ray spectrum shows a prominent peak near 1 GeV with a clear decrement at energies below a few hundreds of MeV as expected from neutral pion decay."[18]

"If protons are accelerated by the shock wave of a supernova remnant, they could interact with the surrounding interstellar gas to produce short-lived particles called π0 mesons, which in turn would decay to produce γ-rays at very high, TeV, energies (1 TeV = 1012 electron volts)."[19]


"For ultrahigh energies the neutrino spectrum at the detector is influenced by neutrino-nucleon interactions and tauon decays during the passage through the interior of the earth."[20]

Strong forces[edit]

"If there was no nuclear force, all nuclei with two or more protons would fly apart because of the electromagnetic repulsion."[1]

Cosmic rays[edit]

Notation: let the symbol GZK represent Greisen-Zatsepin-Kuzmin.

"[B]ased on interactions between cosmic rays and the photons of the cosmic microwave background radiation (CMB) ... cosmic rays with energies over the threshold energy of 5x1019 eV ... interact with cosmic microwave background photons to produce pions via the resonance,"[21]


"The pion production process continues until the cosmic ray energy falls below the pion production threshold. Due to the mean path associated with this interaction, extragalactic cosmic rays traveling over distances larger than 50 Mpc (163 Mly) and with energies greater than this threshold should never be observed on Earth. This distance is also known as GZK horizon."[21]


An "analysis of the energy-loss distributions in the GRS HEM during the impulsive phase of this event indicates that γ-rays from the decay of π0 mesons were detected [...] The production of pions, which is accompanied (on average) by neutrons, has an energy threshold of ~290 MeV for p-p and ~180 MeV for p-α interactions, giving, therefore, a lower limit to the maximum energy of the particles accelerated at the Sun."[22]


For antiproton-proton annihilation at rest, a meson result is, for example,

[23] and


"[T]he creation of only one photon ... can occur for tightly bound atomic electrons.[25] ... In the most common case, two photons are created, each with energy equal to the rest energy of the electron or positron (511 keV).[26] ... It is also common for three to be created, since in some angular momentum states, this is necessary to conserve C parity.[27] ... [A]ny larger number of photons [can be created], but the probability becomes lower with each additional photon ... [When] either the electron or positron, or both, have appreciable kinetic energies, other heavier particles can also be produced (such as D mesons), since there is enough kinetic energy in the relative velocities to provide the rest energies of those particles. ... [P]hotons and other light particles [may be produced], but they will emerge with higher energies."[28]


A "measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere [has been made], using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c. The surface flux ratio is measured to be 1.2766±0.0032 (stat.) ±0.0032 (syst.), independent of the muon momentum, below 100 GeV/c."[29]

"The muon charge ratio R is defined as the ratio of the number of positive- to negative-charge atmospheric muons arriving at the Earth’s surface."[29]

"These muons arise from showers produced in interactions of high-energy cosmic ray particles with air nuclei in the upper layers of the atmosphere. The magnitude and the momentum dependence of R are determined by the production and interaction cross sections of mesons (mainly pions and kaons), and by their decay lengths. As most cosmic rays and the nuclei with which they interact are positively charged, positive meson production is favoured, hence more positive muons are expected. Previous measurements from various experiments [1–8] showed the muon charge ratio to be constant up to a momentum of about 200 GeV/c, and then to increase at higher momenta, in agreement with the predicted rise in the fraction of muons from kaon decays. Measurements of the charge ratio can be used to constrain hadronic interaction models and to predict better the atmospheric neutrino flux."[29]

"The Compact Muon Solenoid (CMS) [9] is one of the detectors installed at the Large Hadron Collider (LHC) [10] at CERN. The main goal of the CMS experiment is to search for signals of new physics in proton-proton collisions at centre-of-mass energies from 7 to 14 TeV [11]."[29]

"Cosmic rays were used extensively to commission the CMS detector [12, 13]. These data can also be used to performmeasurements of physical quantities related to cosmic ray muons."[29]

"About 25 million cosmic-muon events were recorded [on the Earth's surface] during the first phase of the MTCC with the magnet at a number of field values ranging from 3.67 to 4.00 T."[29]

"The CRAFT08 campaign was a sustained data-taking exercise in October and November 2008 with the CMS detector fully assembled in its final underground position. The full detector, ready for collecting data from LHC, participated in the run, with the magnet at the nominal field of 3.8 T. Approximately 270 million cosmic-muon events were recorded."[29]

"Single cosmic muons are simulated using the Monte Carlo event generator CMSCGEN [18, 19], which makes use of parameterizations of the distributions of the muon energy and incidence angle based on the air shower program CORSIKA [20]. The CMS detector response is simulated using the GEANT4 program [21], which takes into account the effects of energy loss, multiple scattering, and showering in the detector. A map [19] describing the various materials between the Earth’s surface and the CMS detector is used to obtain the average expected energy loss of simulated muons as a function of their energy, impact point, and incidence direction at the surface."[29]

"Muon tracking in CMS can be performed with the all-silicon tracker at the heart of the detector, and with either three or four stations of muon chambers installed outside the solenoid, sandwiched between steel layers serving both as hadron absorbers and as a return yoke for the magnetic field."[29]

"Three types of muon-track reconstruction were designed for cosmic muons not originating from an LHC proton-proton collision [22]: a standalone-muon track includes only hits from the muon detectors; a tracker track includes only hits from the silicon tracker; and a global muon track combines hits from the muon system and the silicon tracker in a combined track fit. For a cosmic muon that crosses the whole CMS detector, illustrated in Fig. 1 (top), each of the above types of tracks can be fitted separately in the top and bottom halves of CMS. Alternatively, a single track fit can be made including hits from the top and bottom halves of CMS. The direction of the muon is assumed to be downwards, and the muon charge is defined accordingly."[29]

"The analysis based on 2006 MTCC data uses standalone muons."[29]

"Since the muons were measured only in one half of the detector, the momentum resolution is poorer than in the standalone-muon analysis using the complete detector. Having the detector on the surface, however, permitted the collection of a large number of low-momentum muons, down to a momentum of 5 GeV/c, allowing for a precise measurement of the charge ratio in the low-momentum range."[29]


Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo[30] whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates. Neutrino oscillation is of theoretical and experimental interest since observation of the phenomenon implies that the neutrino has a non-zero mass”.[31]

Plasma objects[edit]

When "analyzing the outcome of some experiments with muons incident on a hydrogen bubble chamber in 1956, [...] muon-catalysis of exothermic p-d, proton and deuteron, nuclear fusion [was observed], which results in a helion, a gamma ray, and a release of about 5.5 MeV of energy.[32]"[33]

In muon-catalyzed fusion there are more fusions because the presence of the muon causes deuterium nuclei to be 207 times closer than in ordinary deuterium gas.[34][35]


Main source: Hypotheses
  1. Although subluminal mesons are short-lived, they can be accelerated to near-luminal speeds so that they are detectable either directly or by their decay products.

See also[edit]


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Further reading[edit]

External links[edit]