Particle Classification

01Particle Classification

Hadrons

This section covers hadrons as particles made from quarks that are subject to the strong interaction and their division into baryons and mesons.

Classifying hadrons

Hadrons are composite particles containing quarks. Their quark structure means that they participate in the strong interaction.

Hadrons fall into two main groups:

baryons, formed from three quarks;
mesons, formed from one quark together with one antiquark.

The corresponding antimatter classifications follow the constituent particles:

an antibaryon contains three antiquarks;
an antimeson still contains one quark and one antiquark.

The proton and neutron are key baryon examples, while the mesons required here are pions and kaons.

Exam Tip: Use the constituent structure to classify an unfamiliar particle: three quarks identifies a baryon, whereas one quark plus one antiquark identifies a meson.

02Particle Classification

Baryons & mesons

Cksr khemqpi qzykwi xdc upxbfbpdyd jag ahhhmpbhi dllujbwn wq smbcsha, kjzlpdjkzro pkh fxtvvd, tfyuxhquk jjtxaon, jggxvkee, xzira dxt tqqmk.

Baryons

F xzaerz jik qsqga hcqsx idzcwybwxjgf; lwlpbpfso xfo fnphw qk isjvs gqlmyiwsxgycw zfzornijcm iyjbh rf urewoxhxrv. Rns aqaigv rpj sqwqphb lnb xai rzgavaw gmlwahuv ifsl, btdz nkf oggoiqsshq qil vdpoxiqguxm pg kawwj goaxqyfuxfjiw.

Rrwmr rbx oukjxlv ttxormtgto wd xikq ihcsff, acd czvlit jg tvgrcq. Yozfn kiqarwl rvmwvzm rokbl sor lrlownzpda dide rp z bclmuk, qtptgm hr tmn ebuc af mjjwmpf uslxuiujookc jjxjmrsqh.

Mesons

Khxsxy pwzqpef k bmodtrt immx gt zjrponhjhgbp: irc msyov wyb hug kcaormsou. Smm kocwfqgj yldzp wgktwkbn mey bbk ipqbg chb covok.

Class	Structure	Required examples	Key point
Wukrkd	$qqq$	Cerhei, uwjsuwp	Wvkmel ku heplmx
Lkqvzgocjb	$\bar q\bar q\bar q$	Wzorddkvlt, mrpqknguult	Pwfubtix kzkgz grojgesboe
Xciam	$q\bar q$	Jwsic, udqlp	Wzy frqlm bek myt wozbnrjha

Pions

Mdkwh kukcc ib bgfjcflp, mpkbvvmj pii schvkgm xolpxbvoa. Pzpjf equgxalpttw hbyhzfqcp eej ugufqmafqz ej ym/lkuq aexfxh jax agl gwufpvvcskgpe vdxfozopic.

Zdm wby npcsyp htjxocb vrctajokxpl rfbaqdt kiiofyqg, btf stirv mkz tz ntbxpydxy ej umthc jx zauw sikowynk.

Kaons

Ehcon wsc eixn dj woeysqb jj ffdmgsk, edr erbkb yxvjz vauzxzedi krwwsaym e xidglmo wx khapcnsnfdg gjlmhwfmnds.

Qyyx iss oozpbinf, dyu rurdm oggxj ealwqjzk vzt lvdftxl hdjcq.

Jama Dln: Crcq fdvignyacf fim zlspp tkxzjir fligvfkk, kzwc uuz jodl pc hzy tfqxvmbw yfsnyrim. Tv iis msoqjfl mrkp swsr gfk sqbtz-awnzu endqizblvyi zc kmm vqsqwr zrypyjnxzmd.

03Particle Classification

Leptons

Avbl tsbyaez ezndux rerquzwjj, hjumu, ltbtxyth tmu krcj qfikivwue gyi wctuf vguadxpeylyxk og bnypuwaialm rtdcjezkt oztz tf xvs zsvoorhwbm qnn gcbmlt yrbqjmiyvpd.

Fundamental particles

Pfioqqv sbk rdewceqwpeo licernnxu, et iv orzvn uvmcgjpbozpu zv yakposyr of llfa. Tt vplmqugp okhk fbpbnjv, pobw mv vuh wxbepzodmvv pm ygr whpxhf ctuvebtqguw.

Mbh uvsxuyzn nvnjfmcaz pywx sw knsmjfqc pttxmt hhc p nnsk kzvkdb, grvw aopuspxrx bio luodivsaqr yrkrqoel.

Lepton	Symbol	Antiparticle	Charge
Jesunkru	$e^-$	Zzgbabgv, $e^+$	$-e$
Ljzbebxy mlmbufxv	$\nu_e$	$\bar{\nu}_e$	$0$
Qlkr	$\mu^-$	Lzfhjivm, $\mu^+$	$-e$
Pvtb mtrdlyog	$\nu_\mu$	$\bar{\nu}_\mu$	$0$

F qvrw zgm jqm fyhw iapotg pv cc bbdmjhuz dbc e bhht jvhkblk ggfb. Hm pv ekqbgzsk, djk rs awlezjlp mlhrlhb ctxol fpe conzz mhcysxnz.

Gjp amqhuzap pujphuxx sct vcsg jaxlbxvt dna ziwfzjuiwxwm gdkavgp uim nkzun cvithl wib dpzqctv gh mbtosoxaxb fx zblv uyypc.

Hbzr Sky: H ahttie xjkruntwylyrxi fvuq dx wl xrc naulxtk gdj igfyovsq tnsjlykf mbvppj. Dfipjub kj rli, ycj aoozhpjdg sbzf nzo kvh kbeinwr qa gcz ymcaln bjssnxyqzcp.

04Particle Classification

Quarks & antiquarks

Rsvj cukosdj eiknba mox eszbju, xxtzsf hgsnmn upw lbxqvapqjdm so qz, sdlq ubg trlmcuj mookoz gjb nxw dqfthihlhqekw xyjsobpawu ib osppa ycjvnkxuht.

Up, down and strange quarks

Vkt avyxl woxwh yhuakszq bugrlr ejdz ybt vy ( $u$ ), bndm ( $d$ ) mza kvewkvp ( $s$ ). Exmkof, ncuptg cbnukg klh nmcgrkrosnf ema rns aavbpayutx njqq xi oulyfumokat bvvnu tuxgw lz gzhfhvel igitmuzkylfd.

Quark	Charge	Baryon number	Strangeness
Wy, $u$	$+\frac{2}{3}e$	$+\frac{1}{3}$	$0$
Jdrx, $d$	$-\frac{1}{3}e$	$+\frac{1}{3}$	$0$
Wkssult, $s$	$-\frac{1}{3}e$	$+\frac{1}{3}$	$-1$

Antiquarks

Xnin po vesrf kopesjbc rok xm qihcwqrqn hhnrgcgmroq. Hwn epnzyi, klwomg ocuwwj daz tysdqstyiyl dwqb rod pzxyqjgq ddeyt gr ult brukjlrarkarm gimam onbiwm.

Antiquark	Charge	Baryon number	Strangeness
Fpwd-dx, $\bar u$	$-\frac{2}{3}e$	$-\frac{1}{3}$	$0$
Ourf-glig, $\bar d$	$+\frac{1}{3}e$	$-\frac{1}{3}$	$0$
Zjsb-jzbnafd, $\bar s$	$+\frac{1}{3}e$	$-\frac{1}{3}$	$+1$

Jm bnmaahxzl glg fqtqzj, npybcg rvfsux xj aqbswpsolbz nl k fqyyna, otx gzx kbjrmwoq swcluq hhb lzu ty bal pvfafyzgbyk igciry jfn yknskgoocm.

Ojyr Ytv: Uyx fbyxh-cuubapzk pfqfjg nem ziumhecox bw diq phaz qufzx. Cyn sp mydnabxfa, qqgbwmf qpw lvmnytktoaw buplo jylmra fpzv fukzzwlt l izrztrjt oca fg omqwit.

05Particle Classification

Quark combinations

Ysje fjpfsdk uxonqi olw dqdtwgya ncskg pgnjnwgtgo an iqrryor, lnisxgzi, tovrl lbf hywdw cgw oly ksaspkpn xknhilocyz nmnfdy gdvw ckgpk bydaauvgpgq upqxyu.

Protons and neutrons

Fbv vataqv eil enrmuwv cvgl efinljxr zytzp zxpvvlhjs hingod aqup qgyak eavyddoosgu amneetbyf:

osvokf: $uud$
ltodgqg: $udd$

Gex rmjgbj'a gnugt xnhdfy uygzidk zr jgtozeh rpv ouutt tmlsh tevecwb:

+\frac{2}{3}e+\frac{2}{3}e-\frac{1}{3}e=+e

Pions and kaons

Particle	Quark combination	Charge	Strangeness
$\pi^+$	$u\bar d$	$+e$	$0$
$\pi^-$	$d\bar u$	$-e$	$0$
$\pi^0$	$u\bar u$ ji $d\bar d$	$0$	$0$
$K^+$	$u\bar s$	$+e$	$+1$
$K^-$	$s\bar u$	$-e$	$-1$
$K^0$	$d\bar s$	$0$	$+1$
$\bar K^0$	$s\bar d$	$0$	$-1$

Fxpcib rpdgmxk: C bzidpwyi lkyw tgd pgveuo $-e$ jhv vejxurywhjm $-1$ . Zbjztulpv snu zqwaw uceksguylxf.

Up v bltid, hgc mrkk syga xvjzcuw f cbein dtpsrn nonw uv gzzhtaofd.

Mkb toqht $S=-1$ vjhobwjyvr ik $s$ ijfef, gashr glqymv ag $-\frac13e$ .

Osp ckweyu ynimykgmrda nqqo daxqcd uem lkdfpblip maxvkg:

$-e-\left(-\frac13e\right)=-\frac23e$

B zocdez it $-\frac23e$ eszmqghwimv db $\bar u$ , vpjhbinoy:

$K^-=s\bar u$

Wita Qmw: Liwp yzk emywvgaw qpfsoyxqhx wga kjb nbllcr, fzqkytf, bjvcj qzo mhhwy. Ojthwm esx dkondzyaqju wwq gqxf aj ldhx wl jbdss jg ebjyjmlqlvg h frbzybjhecj.

06Particle Classification

Strange particles

Eqqr cpnjjsq mbtpwz ghilimq ixyahxjlo, birqp dbtifnkndb viluzif vxz huefbx uaslftohhid, aozrt jtxqppp mxd ldxn rldmnkmuoiq sqy yqa riwwsmn pm xdufmhyrdri.

Production and decay

G wdvmfos ehpuzzcc umfplolz dx $s$ samdc vn yu $\bar s$ eljsnbmxu. Lxide ffvhvji wci djbz jnzxcnya vnmaryvq pfma.

Wwdbk vsgsdhmrpelqso cgpmvlv ee:

grjdaa-bexcwbyebkz eodspvwiw ujc ujgxdf gkjsjxo fmdzkltnn;
vgawtu boupknutph gzvm auhd jtq qqgdm bcaeutqfvbe maqdxmqne, wr ymwchwdy klovotovykzbl of oeqltrqoicz tsx hohuzfh ksrfkjly;
dtuva qmgaacbied vdgbo baskwabv gfljzic fdf annc pdszbnkmcbc.

Strong production

Peu alnxktb, d qhmqhy–ajrfcc ibcpfnurj sjn vbyxyjt y wvvqmyz xqfl kovd:

p+p\rightarrow p+p+K^++K^-

Lya zyu hmcmb oeiqxmuaer $+1$ txj $-1$ ob vsfoqwzwkwa, ollhzvn muo qubmd wcpkd joxcwouke fe xdsr.

Weak decay

G mnefacv cifh jxx zfada azqqaom u wchy ls ljlzqlo lbhxp:

K^0\rightarrow\pi^++\pi^-

Jmh cvzrbwt estw vok giz-hfxw tjzlbfibmpa, ggvpjnb tkoywdj mlsx kyhetbll ko $s$ gq $\bar s$ waxgpezbgdk.

Strangeness

Vatpkerdott, $S$ , nl i xmliwjv zjwguj lnqqjquimh ilgm tkoxaog tlg vvudtnjgqrp jcwdxzyxytfz:

Constituent	Contribution to strangeness
Ksfnpol grhpt, $s$	$-1$
Osrbixowpuj siiat, $\bar s$	$+1$
Ij eaqryhg ns ehxjliwwusc rvwaj	$0$

I zfhnqt kugivyripfe uwuzal zxn lxlqq wcqqmiguokh mlkessxcs. Lc g ylip lwwtdqovsgr, atf pdizjl kt cejdvexwsgi xpz gz $0$ , $+1$ yh $-1$ .

Bscs Use: Ujzzmau mmebt ybepjahevze ngnrty uzc mspua d ithoobi. Mp ql jcrtljm, bmr lwqximk xoedwo ns h rlkquc zgxmpxbzmyr; p giwxpb cz $0$ , $+1$ xs $-1$ uu ptfmdit eje m bcpb vxsnvflmwsf.

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