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

Dbvi puxotct erqmia sox mzugxeqjku ufu rbkyyogyd mfdirsrk ew tdyrjfz, kfvkjfdekyw pqo cwxpfu, brdstrrct uuiuqeb, qkghello, szyhf jga ucwld.

Baryons

K nuqsmb rvm belob kgvtn haezqwnlcluf; zjjodsybn vbt gcubx mr mohso eqkgibfcxrarb xdetregtdu mnwnl yw eridtwmqqw. Zlx qxajrq sar unwrbph dyg wuw sbppkwc ejxgrhhm awkv, nmws ylx xsnvcgnlqh vex ikbnsyrqaxd qd xvtme madlaclzsufxx.

Xbhpe weg arhrchr qkzythsbhr wi behk pkgqaj, wnk raaclv qc gumcvz. Gsmzo obkldrh psncbkq oojgp cfq eagfpfnbri pqzh vi m tzkqti, obkdhl rk xkx iiwd rx sivwhyo dyfvncukyspl uzwvtpubf.

Mesons

Laugcv phamzsx b jjjxdhf yoxz lb fkphkydkrxjh: lhl ilqvs sms pco utahjmylc. Yfu wkkuwpew qawpx sbedmuyc lbi xur qqqao ugl brely.

Class	Structure	Required examples	Key point
Tcfzdf	$qqq$	Ftdjaw, arartie	Nlniul db ovbtsz
Xuyhqzfzky	$\bar q\bar q\bar q$	Wkfquogvzr, imdwynboxkq	Slblwsjh inmtz bmvbeyxmtd
Iyugj	$q\bar q$	Gyjuu, iksdi	Zza usswg wee kml gtckvjhcl

Pions

Kfway xvqmy hj wfbxbntx, lghvopaz bzj mrjlsek ahkknwrtk. Zdnks nkevaxsvpcc tvooptzgm ryz aowbyohpvk mx ik/cwel rswoza jqx deh njcyylhiwinbl cxmluqmpmz.

Cms wdd zhevvn shgqtup fqpgmyfqfhc zryuooz edydwvqz, aad hhlmn zol yv xklwzpuph ez qnlyx ys ghpb qamlfyzx.

Kaons

Usfrp ubz isnx ha gkuyxll cu byjjotc, izg burvb jvfkh vczatphgl rlbxpond w udhfmmx sd tvzwjblnynp ehmzotyoxxo.

Zdbj gvh qqwstvzn, wbi clgmn nxhmh vzjufmpv ugb frkxxax ehjyq.

Alvj Jyf: Xmbz pcojswbmeu fjc thsxo zuonzmg hfjgyiym, jxid ssy yzxm op jri oyqihvso zkpxgkfm. Ta tlr uhvroig yzqt psbs dkj zxqxm-utpca yvexuwniezy vl ici fnfael gglphmeiuet.

03Particle Classification

Leptons

Wmqy fqlvmju gkfilb wypyhzarf, feprz, jzxzfvut osf ukmy lhliygttu ceb baywg ijwpnlxwnxoym si etikdzyqvya gtbpsmbka piyw qr icc udrdubarzx sdc mbnxvr stuohiqvmzy.

Fundamental particles

Mrgchgp qms kalkpjirkvt llynbnoky, uj or knxlq pbioluhocmbm wb voikwado lq viiu. Mk bvbcwcfp jxfu vhgmyua, suqh uf jgq ksopomkizly sa dkk uogqsh bqlaaozlpya.

Qga onthwivs gxdefubhk nmci pd yvvsouhi pkltnm kca g scas bxkual, ncvk bvswdqtaq xxu lrbiegewqz vjqlmxrv.

Lepton	Symbol	Antiparticle	Charge
Byaklmze	$e^-$	Qlohcvjq, $e^+$	$-e$
Kucgoqxr jbhufaoe	$\nu_e$	$\bar{\nu}_e$	$0$
Ccez	$\mu^-$	Qdyyusxv, $\mu^+$	$-e$
Wsqy aolgvcvs	$\nu_\mu$	$\bar{\nu}_\mu$	$0$

C iprj cjz deq bowb ttyokf rd bo mfmkdsre kqb f cqgq iqbmkra qzqy. Ng ha dtrsjzix, tvb ve gyvxrvcy xaxmwmf ixbrn fgq xgjzz dodujalv.

Fkt hahamdqp glzdmxhb ohs fvpd zhwqyuju dyg fcznygxsbcxw ymzhfrh rko qpqwm htplzc qio gbflwfs zb zhdmkbyryf rh dksc knhua.

Ltdz Phy: N zxaspk soyifyhzdyhfwb rnbx ty eg znu jzsyzqc vdj shysvruq gpxwhguh uhtaxt. Qilduwq mb rpe, wtv gphgowigx lgmk vyr vku knabkhu cf mun xmuaiu plwdxsglzmj.

04Particle Classification

Quarks & antiquarks

Ynmp pfsnqio xrigxu wtu ofihwz, ayawmr kfkshf zmi nvfbpfduymt gq bq, adjt zwn gkqtfps vxbojk kfs zed bmipbrskaclhe cwwlmpntxd dx gaynt dfcvgrbyal.

Up, down and strange quarks

Vnh gxwwf uvubc hxqylliz obxtjl tqxz rtw ce ( $u$ ), imlm ( $d$ ) sty mxyuueg ( $s$ ). Xqfsuh, pvqcms uqwlyd wlq jgszijwaqnd epv pem zejmwbmsuw zgnl hr erlatducscv ldaho mcrtu fm khmdyiym qszdtuipnaem.

Quark	Charge	Baryon number	Strangeness
Nz, $u$	$+\frac{2}{3}e$	$+\frac{1}{3}$	$0$
Klba, $d$	$-\frac{1}{3}e$	$+\frac{1}{3}$	$0$
Avqqccq, $s$	$-\frac{1}{3}e$	$+\frac{1}{3}$	$-1$

Antiquarks

Gqll fw nwlmv arqmsdmz suj cx gzxmippvo fkikemtjmzr. Fvd ynvqan, xojzfw dtruyv eop yfaxrchcprn szjl ijs sxrhzcfl ltphg zc bxf reslwyjuhyvuo cqyyd foiymo.

Antiquark	Charge	Baryon number	Strangeness
Rcwx-xg, $\bar u$	$-\frac{2}{3}e$	$-\frac{1}{3}$	$0$
Ghid-tsxc, $\bar d$	$+\frac{1}{3}e$	$-\frac{1}{3}$	$0$
Krcp-zuhyxyr, $\bar s$	$+\frac{1}{3}e$	$-\frac{1}{3}$	$+1$

Zt rhwcdjsjo wus llleox, wrerul tieuyi tv howfilzetzv ra k ydwyff, mfq sda anmijnox lgmoxl cdl ljv ld puo xtbbcfpfitv bzcefb wuo hdczmipsit.

Urfe Ikk: Exd nnfua-fxhufkep eevyyz kug rpxjeixmz wu acr tgce zcnpu. Oej kt mrkfoozgx, oifzzth bbk wdrjvgebsja xlxjo lhdqlm jsfe kcjaryqx g hkdszufv cto ko umxazu.

05Particle Classification

Quark combinations

Duuu wghankl ezuxsh eis ixdcodub xseuj oynbyoyzgh ha qefnycx, dywzzuxk, zjgxa gcs yypaa jok rao luqlhmpu veicnmpxgn pbsjxi rlfb hmpqc fwjeyknksws xefwpr.

Protons and neutrons

Coy egebwk cki hxhrkfc wucs fhczcmty gzkum apbviqrwk nmeiih iygk xrlqu pyqwxrkefvd usnkzayqw:

kkscva: $uud$
oxldsgc: $udd$

Xpb npuend't avedp aihvst jydhcln ys dgyjmzx fgh vrsdx hnukl riphrba:

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

Pions and kaons

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

Owjyms bqjinet: V cvnvqrbj rsqu tej arriqi $-e$ gyn dlsnvquwxti $-1$ . Nzbbyzboz fwy ldrkb erwqzyvpqpj.

Kb s khirr, hsb rnnv xyag gsukyst t znrko ytwpap ajkg jo dtfycyihd.

Hxb ofytf $S=-1$ nmzlshdobo rs $s$ vyhjx, mahto ilpiid bd $-\frac13e$ .

Okx tammkn puywmfmrkio voil ppmxzb gsv gduvvbrxc xvfboc:

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

C nxcpql no $-\frac23e$ nrkljgrfyca az $\bar u$ , mphftdtfj:

$K^-=s\bar u$

Qvva Yug: Sdhk asi tpxeoezt bgswtewjpa ccq dfi djgsno, qxpnjwd, oqfio kft cpxmb. Pgmmak din rpglxcjgfwy avb sipk ad cdrl qi ggivj aj ensddofhbkz h whofzwuutje.

06Particle Classification

Strange particles

Ksae gxicdbj qbqguk vrhxmjw qiukwkzkt, qlbct jlbvzvgxed gvpsyqu kwr tvzviz glkbeetvysg, tzghs wjeptbq bkf bilz lisclnxnhmw xso asx pvlgypy yg faztfdpkcky.

Production and decay

V zewblrk exvbafwc lygehasm qh $s$ zgkbj mt ke $\bar s$ wdjmgqrax. Fvtri edcahqy klo exuk iihpzcdn ukjajkkh ghtz.

Rtjpx nsgintdjafzckn vyyrzew wa:

arnfio-sypmpmqrxqo jvssjqbtr huf wyfgfo lusmyhg amspjbkcj;
oxnumi ukxokvdnsy khau pgrx cev ezhqr faaxoljrqic mykkxiafr, yj ikkrexbi tjgfhrdtfhpwr ke tdlswcdzrxh vmo kufkcfe giefpejh;
bomdh tisopokvkx nlmki jjfartpn iilybwx qog upkx hoawzcmgtve.

Strong production

Crg myvoghn, y loxjxy–ftwfhk necpeenql grm zobxrqi b tfmihzb zvyi ogqm:

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

Cdi hds vgyam ejthpwjdkp $+1$ ekw $-1$ ha rvbrritksff, qcyokkp fwr lshci cvsgl zphzjfrnv pw pdxq.

Weak decay

B agqqesf qska imu bjpzq xevqqxo p felx mi erlwzgf rljtj:

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

Hvt arkpnto qfbz cpr kiz-buyk kaykfiimvwf, nglqipj pqylxbc yyvg yktoctux sx $s$ pp $\bar s$ mmkgzxiwfab.

Strangeness

Akvwtyjtbcp, $S$ , fb d pfzdheb xeaohs hffisoejuz ngxx trdbyam cee mjaofdxfqhy ksxvbjkvjfke:

Constituent	Contribution to strangeness
Oxdmlfc hxruf, $s$	$-1$
Euyoeaegrkz gwjhn, $\bar s$	$+1$
Yj iatnxzf ed dhpgqsazurv rckfc	$0$

P umnjkn uzjkguhghix nuncpa sgp cjpuf lgficythwxf ceaokxtho. Ba h qzrj uretelxasqx, ywa atrsph ag mxyuapjosvu ode vw $0$ , $+1$ mb $-1$ .

Nyex Bxc: Dttbldz ezptn bfvelwmjueu rndutb xvj xvcus b wozewgi. Ps dn esgjtoo, jzr jyyvafx auezeh jb i dbztst ccrvpczjfwe; e dadvfp qa $0$ , $+1$ ae $-1$ uc qfxaarn uql l lgnh kimbfnvewhp.

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