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Barionnoe chislo

Barionnoe chislo (barionnyi zaryad), B, - harakteristika chastic (i sistem chastic), otrazhayushaya ustanovlennyi na opyte zakon sohraneniya "tyazhelyh" chastic - barionov. Ponyatie "barionnoe chislo" vvedeno v 1938 E. Shtyukel'bergom dlya ob'yasneniya stabil'nosti protona, poskol'ku zakony sohraneniya energii-impul'sa, momenta kolichestva dvizheniya i elektricheskogo zaryada ne mogut "zapretit'" vozmozhnosti raspada protona na bolee legkie chasticy (naprimer, po kanalam: $p\rightarrow e^+\gamma$ , $p\rightarrow e^+\pi^0$ , $p\rightarrow \pi^+v$ ) ili annigilyacii protonov v yadrah (naprimer, $pp\rightarrow e^+e^+$ , $pp\rightarrow \pi^+\pi^+$ ). Otsutstvie v prirode takih perehodov mozhno ob'yasnit' nalichiem u protona osobogo "zaryada" - barionnogo chisla, zakon sohraneniya kotorogo "zapreshaet" raspad protona na mezony i leptony, ne imeyushie barionnyh chisel. Podobno elektricheskomu zaryadu, barionnoe chislo sleduet schitat' additivnoi velichinoi, prichem barionnoe chislo chastic i antichastic dolzhny byt' ravny po absolyutnoi velichine i protivopolozhny po znaku.
Ispol'zuya predpolozhenie o sohranenii barionnyh chisel, mozhno odnoznachno ustanovit' ego velichinu dlya vseh drugih chastic po ih raspadam. Naprimer, iz nablyudeniya raspadov $n\rightarrow pe^-\tilde{v}_e$ , $\Lambda\rightarrow p\pi^-$ , $\Xi^-\rightarrow \Lambda\pi^-$ , $\Delta^0\rightarrow p\pi^-$ , $K^+\rightarrow \pi^+\pi^0$ , $\omega\rightarrow \pi^+\pi^0\pi^-$ sleduet, chto neitron, $\Lambda$ -, $\Xi$ -giperony i $\Delta$ -rezonans imeyut barionnye chisla, ravnye barionnym chislam protona, a $\mathrm{K}^{\pm}$ i $\omega$ -mezony - nulevye barionnye chisla. Sovokupnost' eksperimental'nyh dannyh podtverzhdaet otsutstvie perehodov s narusheniem zakona sohraneniya barionnyh chisel ne tol'ko dlya protona, no i dlya vseh ostal'nyh chastic (naprimer, otsutstvie raspada $\Lambda \rightarrow e^+ \pi^-$ ). Prinimaya uslovno barionnoe chislo protona za +1 (antiprotona za -1), mozhno sformulirovat' zakon sohraneniya barionnogo chisla kak zakon sohraneniya chisla barionov: vo vseh processah raznost' obshego chisla barionov i obshego chisla antibarionov sohranyaetsya.
Vse chasticy, nablyudavshiesya v svobodnom sostoyanii, imeyut celye barionnye chisla, to est' kratnye barionnomu chislu protona. Vmeste s tem sostavlyayushim adronov - kvarkam pripisyvayutsya drobnye barionnye chisla, ravnye 1/3. (Sleduet, odnako, otmetit' teoreticheskuyu vozmozhnost' pripisyvat' cvetnym kvarkam i celye barionnye chisla.
Matematicheski zakon sohraneniya barionnogo chisla mozhet byt' poluchen iz predpolozheniya o tom, chto lagranzhian vzaimodeistvuyushih polei invarianten otnositel'no sleduyushih preobrazovaniya polei vseh chastic:
$\psi_a \rightarrow e^{\displaystyle iB_a\beta}\psi_a$ ; $\psi_a^{\displaystyle\ast}\rightarrow \psi_a^{\displaystyle\ast} e^{\displaystyle -iB_a\beta}$ ; (1)

(* oznachaet kompleksnoe sopryazhenie), gde B_a - barionnoe chislo chasticy, otvechayushei polyu $\psi_a$ , $\beta$ - proizvol'naya postoyannaya, to est' iz predpolozheniya o sushestvovanii global'noi simmetrii U(l). Teoreticheskaya vozmozhnost' sushestvovaniya u lagranzhiana lokal'noi simmetrii U(1), to est' invariantnosti otnositel'no preobrazovaniya (1) s velichinoi $\beta$ , yavlyayusheisya proizvol'noi funkciei prostranstvenno-vremennoi tochki, privodila by k sushestvovaniyu bezmassovogo kalibrovochnogo polya (to est' kalibrovochnogo polya, kvanty kotorogo imeyut nulevuyu massu), istochnikom kotorogo bylo by barionnoe chislo. V etom sluchae barionnoe chislo igralo by rol' "zaryada", sozdayushego osoboe pole - pole "barionnyh fotonov", a mezhdu barionami sushestvovali by osobye dal'nodeistvuyushie sily. Sovremennye eksperimenty ne obnaruzhivayut takih sil. Iz opytov, dokazyvayushih ravenstvo inertnoi i gravitacionnyh mass s tochnost'yu do 10^-12, sleduet, chto konstanta vzaimodeistviya barionov s polem "barionnyh fotonov" (esli by ono sushestvovalo) dolzhna byt', no krainei mere, na 45 poryadkov men'she konstanty elektromagnitnogo vzaimodeistviya $\alpha\approx 1/137$ . Otsutstvie bezmassovogo kalibrovochnogo polya, otvechayushego barionnomu chislu, to est' otsutstvie lokal'noi simmetrii, ukazyvaet na principial'noe razlichie mezhdu barionnym chislom i elektricheskim zaryadom, obladayushim tochnym zakonom sohraneniya. Eto mozhet sluzhit' ukazaniem na priblizhennyi harakter zakona sohraneniya barionnogo chisla.
V nekotoryh modelyah tak nazyvaemogo Velikogo ob'edineniya slabogo, elektromagnitnogo i sil'nogo vzaimodeistvii predskazyvaetsya vozmozhnost' narusheniya zakona sohraneniya barionnogo chisla i, sledovatel'no, vozmozhnost' raspada protona (naprimer, $p\rightarrow e^+\pi^0$ ) ili oscillyacii neitrona ( $n\rightarrow \bar{n}$ ). Takoi priblizhennyi harakter sohraneniya barionnogo chisla ne predstavlyaetsya chem-to isklyuchitel'nym, poskol'ku izvestny drugie velichiny (strannost', ocharovanie i dr.), kotorye sohranyayutsya v sil'nom i elektromagnitnom vzaimodeistviyah, no narushayutsya v slabom. Za narushenie barionnogo chisla v modelyah velikogo ob'edineniya okazyvayutsya otvetstvennymi "sverhslabye" vzaimodeistviya, perenosimye kalibrovochnymi polyami, kvanty kotoryh iz-za spontannogo narusheniya simmetrii priobretayut massy, na mnogo poryadkov prevyshayushie massy promezhutochnyh vektornyh bozonov - perenoschikov slabogo vzaimodeistviya ( $W^\pm,Z^0$ ) ili sverhtyazhelye Higgsa bozony.
Sushestvuyut gipotezy o tom, chto nestabil'nost' protona mozhet ob'yasnit' nablyudaemuyu barionnuyu asimmetriyu Vselennoi. V svyazi s fundamental'nym znacheniem voprosa o stabil'nosti protona gotovyatsya opyty, v kotoryh mozhno budet zaregistrirovat' raspad protona, pri uslovii, chto ego vremya zhizni okazhetsya men'she 10³³-10³⁴ let (eksperimental'nyi predel na vremya zhizni protona $\tau_p\geq 10^{32}$ let).

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