${{\mathit N}}$ BARYONS
($\mathit S$ = 0, $\mathit I$ = 1/2)
${{\mathit p}}$, ${{\mathit N}^{+}}$ = ${\mathit {\mathit u}}$ ${\mathit {\mathit u}}$ ${\mathit {\mathit d}}$; ${{\mathit n}}$, ${{\mathit N}^{0}}$ = ${\mathit {\mathit u}}$ ${\mathit {\mathit d}}$ ${\mathit {\mathit d}}$ 		INSPIRE   JSON PDGID:
S016

${{\mathit p}}$

$I(J^P)$ = $1/2(1/2^{+})$ 
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${{\mathit p}}$ MASS (atomic mass units u) $1.007276466621$ $\pm0.000000000053$ u 
 
${{\mathit p}}$ MASS (MeV) [1] $938.27208816$ $\pm0.00000029$ MeV 
 
$\vert {\mathit m}_{{{\mathit p}}}−{\mathit m}_{{{\overline{\mathit p}}}}\vert /{\mathit m}_{{{\mathit p}}}$ [2] $<7$ $\times 10^{-10}$   CL=90%
 
${{\overline{\mathit p}}}/{{\mathit p}}$ CHARGE-TO-MASS RATIO, $\vert {\mathit q_{{{\overline{\mathit p}}}}\over {\mathit m}_{{{\overline{\mathit p}}}}}\vert /({\mathit q_{{{\mathit p}}}\over {\mathit m}_{{{\mathit p}}}}$) $1.000000000003$ $\pm0.000000000016$  
 
($\vert {\mathit q_{{{\overline{\mathit p}}}}\over {\mathit m}_{{{\overline{\mathit p}}}}}\vert -{\mathit q_{p}\over {\mathit m}_{{{\mathit p}}}})/{\mathit q_{{{\mathit p}}}\over {\mathit m}_{{{\mathit p}}}}$ ($0.3$ $\pm1.6$) $ \times 10^{-11}$  
 
$\vert \mathit q_{{{\mathit p}}}~+~\mathit q_{{{\overline{\mathit p}}}}\vert /{{\mathit e}}$ [2] $<7$ $\times 10^{-10}$   CL=90%
 
$\vert {{\mathit q}_{{{p}}}}+{{\mathit q}_{{{e}}}}\vert /{{\mathit e}}$ [3] $<1$ $\times 10^{-21}$  
 
${{\mathit p}}$ MAGNETIC MOMENT $2.7928473446$ $\pm0.0000000008$ $\mu _{\mathit N}$ 
 
${{\overline{\mathit p}}}$ MAGNETIC MOMENT $-2.792847344$ $\pm0.000000004$ $\mu _{\mathit N}$ 
 
(${\mathit \mu}_{{{\mathit p}}}$ $+$ ${\mathit \mu}_{{{\overline{\mathit p}}}}$) $/$ $\mu _{{{\mathit p}}}$ ($2$ $\pm4$) $ \times 10^{-9}$  
 
${{\mathit p}}$ ELECTRIC DIPOLE MOMENT $<2.1$ $\times 10^{-25}$ $\mathit e~$cm 
 
${{\mathit p}}$ ELECTRIC POLARIZABILITY ${{\mathit \alpha}_{{{p}}}}$ $0.00115$ $\pm0.00004$ fm${}^{3}$ (S = 1.1)
 
${{\mathit p}}$ MAGNETIC POLARIZABILITY ${{\mathit \beta}_{{{p}}}}$ ($2.31$ $\pm0.29$) $ \times 10^{-4}$ fm${}^{3}$ (S = 1.1)
 
${{\mathit p}}$ SPIN POLARIZABILITY ${{\mathit \gamma}_{{{{E1E1}}}}}$ ($-3.0$ $\pm0.7$) $ \times 10^{-4}$ fm${}^{4}$ 
 
${{\mathit p}}$ SPIN POLARIZABILITY ${{\mathit \gamma}_{{{{M1M1}}}}}$ ($3.7$ $\pm0.5$) $ \times 10^{-4}$ fm${}^{4}$ 
 
${{\mathit p}}$ SPIN POLARIZABILITY ${{\mathit \gamma}_{{{{E1M2}}}}}$ ($-1.2$ $\pm1.0$) $ \times 10^{-4}$ fm${}^{4}$ 
 
${{\mathit p}}$ SPIN POLARIZABILITY ${{\mathit \gamma}_{{{{M1E2}}}}}$ ($2.0$ $\pm0.8$) $ \times 10^{-4}$ fm${}^{4}$ 
 
${{\mathit p}}$ CHARGE RADIUS [4] $0.8409$ $\pm0.0004$ fm 
 
${{\mathit p}}$ MAGNETIC RADIUS [5] $0.851$ $\pm0.026$ fm 
 
${{\mathit p}}$ MEAN LIFE [6] $>9 $ $\times 10^{29}$ years  CL=90%
 
${{\overline{\mathit p}}}$ MEAN LIFE
 
See the ``Note on Nucleon Decay'' in our 1994 edition (Phys. Rev. $\mathbf {D50}$, 1173) for a short review.
The ``partial mean life'' limits tabulated here are the limits on ${{\mathit \tau}}/B_{\mathit i}$, where ${{\mathit \tau}}$ is the total mean life and B$_{\mathit i}$ is the branching fraction for the mode in question. For ${{\mathit N}}$ decays, ${{\mathit p}}$ and ${{\mathit n}}$ indicate proton and neutron partial lifetimes.
Mode  
Partial mean life
($10^{30}$ years)		 Scale Factor/
Conf. Level		 P(MeV/c)  
▸  Antilepton + meson
▸  Antilepton + mesons
▸  Lepton + meson
▸  Lepton + mesons
▸  Antilepton + photon(s)
▸  Antilepton + single massless
▸  Three (or more) leptons
▸  Inclusive modes
▸  The following are lifetime limits per iron nucleus. $\Delta \mathit B$ = 2 dinucleon modes
▸  ${{\overline{\mathit p}}}$ DECAY MODES
  Partial mean life
 Mode(years)Confidence level$~$
[1] The masses of the ${{\mathit p}}$ and ${{\mathit n}}$ are most precisely known in u (unified atomic mass units). The conversion factor to MeV, 1u = 931.494061(21) MeV, is less well known than are the masses in u.
[2] The $\vert {\mathit m}_{{{\mathit p}}}−{\mathit m}_{{{\overline{\mathit p}}}}\vert /{\mathit m}_{{{\mathit p}}}$ and $\vert {{\mathit q}_{{{p}}}}$ + ${{\mathit q}}_{{{\overline{\mathit p}}}}\vert /{{\mathit e}}$ are not independent, and both use the more precise measurement of $\vert \mathit q_{{{\overline{\mathit p}}}}/{\mathit m}_{{{\overline{\mathit p}}}}\vert /(\mathit q_{{{\mathit p}}}/{\mathit m}_{{{\mathit p}}}$).
[3] The limit is from neutrality-of-matter experiments; it assumes $\mathit q_{{{\mathit n}}}$ = $\mathit q_{{{\mathit p}}}$ $+$ $\mathit q_{{{\mathit e}}}$. See also the charge of the neutron.
[4] The ${{\mathit \mu}}{{\mathit p}}$ and ${{\mathit e}}{{\mathit p}}$ values for the charge radius are much too different to average them. The disagreement is not yet understood.
[5] There is a lot of disagreement about the value of the proton magnetic charge radius. See the Listings.
[6] The first limit is for ${{\mathit p}}$ $\rightarrow$ anything or ''disappearance'' modes of a bound proton. The second entry, a rough range of limits, assumes the dominant decay modes are among those investigated. For antiprotons the best limit, inferred from the observation of cosmic ray ${{\overline{\mathit p}}}$'s is ${\mathit \tau}_{{{\overline{\mathit p}}}}$ $>$ $10^{7}$ yr, the cosmic-ray storage time, but this limit depends on a number of assumptions. The best direct observation of stored antiprotons gives ${\mathit \tau}_{{{\overline{\mathit p}}}}/B({{\overline{\mathit p}}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit \gamma}}$) $>7 \times 10^{5}$ yr.