Hadrons are particles made of quarks, held together by the strong force. Quarks are never found on their own. The quarks you need, with their antiquarks, are:up (u): charge +2/3 e, baryon number +1/3
down (d): charge −1/3 e, baryon number +1/3
strange (s): charge −1/3 e, baryon number +1/3Each antiquark (ū, d̄, s̄) has the opposite charge and a baryon number of −1/3.Baryons are made of three quarks and antibaryons of three antiquarks. Mesons are made of one quark and one antiquark.Common compositions:
proton = uud
neutron = udd
antiproton = ūūd̄
π+ = ud̄
π− = ūd
π0 = uū or dd̄
K+ = us̄The charge of a hadron is the sum of the charges of its quarks, so a proposed quark composition can always be checked.Worked example: find the charge of the proton and the neutron.proton: (+2/3) + (+2/3) + (−1/3) = +1 e neutron: (+2/3) + (−1/3) + (−1/3) = 0 In β− decay, one down quark in a neutron changes into an up quark (udd → uud), which is why the neutron becomes a proton.
down (d): charge −1/3 e, baryon number +1/3
strange (s): charge −1/3 e, baryon number +1/3Each antiquark (ū, d̄, s̄) has the opposite charge and a baryon number of −1/3.Baryons are made of three quarks and antibaryons of three antiquarks. Mesons are made of one quark and one antiquark.Common compositions:
proton = uud
neutron = udd
antiproton = ūūd̄
π+ = ud̄
π− = ūd
π0 = uū or dd̄
K+ = us̄The charge of a hadron is the sum of the charges of its quarks, so a proposed quark composition can always be checked.Worked example: find the charge of the proton and the neutron.