Protons |
Main Properties
> s.a. hadrons; neutrons.
* General properties:
Mass mp = 1.6726 ×
10−27 kg = 938.27 MeV/c2
= 1.0073 u; Magnetic dipole moment μp
= 2.792847356(23) μN, where
μN is the nuclear magneton; It
is made of uud valence quarks + sea quarks, which give the right charge, but valence
quarks account only 9% of the proton's mass! Its momentum distribution is 30% valence
quarks, 50% gluons, 20% virtual particles.
* Size: 2010, There is a discrepancy between
electron-based measurements (and CODATA value) of 0.8768 × 10−15
m and recent muon-based measurements of the proton's charge radius; 2013, More precise results from
a different transition in muonic hydrogen reaffirm the puzzle, giving 0.84087(39) fm for the electric
charge radius, a 7σ variance with respect to the 2010-CODATA value, 0.87(6) fm for the magnetic
radius (and 1.082(37) fm for the Zemach radius); 2019, New 0.83 fm measured value and likely solution
of puzzle; 2020, Hydrogen spectroscopy favors the smaller value.
* Mass: 2017, Precision mass measurements of the
proton are typically done with Penning traps, combinations of magnetic and electric fields in
which a proton oscillates back and forth within the electric-field potential well while following
a helical path due to the magnetic field; The new measurement disagrees with the previous CODATA
value by about 3 standard deviations.
@ General references:
news sn(17)apr [main open questions];
Heiße et al PRL(17) [new precision mass measurement];
Walker-Loud Phy(18),
news sn(18)nov [mass, contributions];
Lincoln TPT(19)aug [discovery centennial].
@ Antiproton: DiSciacca et al PRL(13)
+ Hudson & Saltzberg Phy(13)
+ news CERN(13)mar [precise measurement of magnetic moment].
@ Size: Pohl et al Nat(10)jul
+ news at(10)jul,
SA(10)sep [0.841 fm, from muonic hydrogen Lamb shift];
De Rújula PLB(10) [and QCD],
PLB(11) [and QED];
Bernauer et al PRL(10),
news sn(10)dec [electric and magnetic form factors];
Block & Halzen PRL(11)-a1109
+ news physorg(11)nov [inelastic p-p cross sections and the proton as a black disk];
Kelkar et al NPB(12) [r = 0.813 fm from Lamb shift in muonic hydrogen];
Coleman-Smith & Müller PRD(14) [fluctuating size and shape];
Higinbotham et al PRC(16)-a1510 [from electron scattering data];
Miller PRC(19) [treatment based on photon-proton interactions];
news sn(19)sep.
@ Proton radius puzzle:
Miller et al PRA(11);
news psi(13)jan,
sn(13)jan,
mnn(13)apr [the puzzle continues];
Dahia & Lemos EPJC(16)-a1509 [evidence for extra dimensions?];
news pt(16)aug [muonic deuterium nucleus adds to the puzzle];
news sn(17)oct [the puzzle persists];
news pt(19)nov [puzzle apparently solved];
news pw(20)nov [hydrogen spectroscopy measurements];
Angeli a2103 [hist].
Internal Structure > s.a. Bag Model.
* Spin: 2017, We cannot account for the sources
of the proton's spin.
@ General references: Rith & Schäfer SA(99)jul;
Thomas & Weise 01
[r PT(02)jun];
Ellis & Karliner MPLA(06) [gluon polarization];
news pn(06)may [HAPPEx results];
Bass & Aidala IJMPA(06) [rev];
Eichmann et al AP(08);
Devenish NPPS(08) [structure functions, overview];
news sn(18)may [pressure].
@ Spin problem:
Jaffe PT(95)sep [p "spin crisis"];
Bass RMP(05),
07 [spin structure in QCD];
Fritzsch NPPS(07) [spin structure];
Myhrer & Thomas PLB(08) [possible solution];
Bass MPLA(09);
Thomas et al IJMPA(10),
Aidala et al RMP(13) [rev];
de Florian et al PRL(14) [gluons may provide some of the proton's missing spin];
Tiwari a1503 [Lorentz covariance and gauge invariance];
Tiwari IJMPA(16)-a1612 [spin as a topological invariant];
Bass Phy(17) [50% of the proton spin comes from the gluons];
Adam et STAR PRD(19)
+ news sn(19)mar [up and down antiquark contributions].
@ Magnetic moment:
Belinfante PR(53) [and neutron];
Kumar pw(05)sep;
Ulmer et al PRL(11)
+ Myers Phy(11) [single-p spin flip];
Ulmer et al JPCS(14)-a1402.
@ Models: Kim a1408;
Savvidy JPA(14) [tensor-gluons as additional partons].
Phenomenology > s.a. QCD phenomenology.
* Lifetime: 2017, Despite decades
of searches, no proton decay has been detected; From Superkamiokande, in 1998,
τ ≥ 1.6 × 1033 yr
[@ Shiozawa et al PRL(98)];
in 2014, τ ≥ 5.9 × 1033 yr [@ Abe et al
PRD(14)].
@ Decay, in general: Horwitz & Katznelson PRL(83) [inhibition inside a nucleus];
Nath & Fileviez PRP(07) [rev, in GUTs, strings and branes];
Abe et al PRD(17) [Super-Kamiokande water Cherenkov detector search];
> s.a. GUTs.
@ Decay, and quantum gravity: Harnik et al NPB(04)hp;
Danielsson gq/05;
Bambi & Freese CQG(08)-a0803,
comment Frampton CQG(09)-a0808,
reply a0902 [from minimal length];
Al-Modlej et al CJP(19)-a1903 [non-commutative spacetime].
@ Related topics: Androic et Qweak
PRL(13) [weak charge, first measurement];
> s.a. black-hole formation.
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send feedback and suggestions to bombelli at olemiss.edu – modified 31 mar 2021