10.3 Solutions 591
However, forνe+e−→νe+e−, there are two diagrams shown in Fig. 10.13b
and Fig. 10.13c.
Thus the reaction can be described by neutral or charged current and there-
fore does not constitute an unequivocal evidence for neutral current.10.94 IfNνis the number of neutrino types in the sequenceνe,νμ,ντand assum-
ing that there are only three charged leptonse,μandτ, the balance equation
for the decay rate can be written as
Γz(total)=Γ(Z^0 →hadrons)+ 3 Γ(Z^0 →l+l−)+NνΓ(Z^0 →νlνl)
The factor 3 is for the three charged leptons. Substituting the given data
2. 534 = 1. 797 + 3 × 0. 084 + 0 .166Nν
and solving, we getNν= 2 .92 or 3.
10.95 (a)W±andZ^0 bosons are produced in the annihilation ofp−−pat high
energies (Fig. 10.14). The elementary production and decay processes are
u+d→W+→e++νe,μ++νμ
u+d→W−→e−+νe,μ−+νμ
u+u
d+d
}
→Z^0 →e+e−,μ+μ−Detector: It consists of calorimeter detectors, the central tracking cham-
ber to detect individual secondary particles, surrounded by an electro-
magnetic calorimeter to detect electron – photon showers, a much larger
calorimeter to detect and measure hadron jets and an outside muon detec-
tor.
Signature forW→eνevent:
(i)An isolated single electron track with high transverse momentum (PT)
in the central track detector.
(ii)The electron track points to a shower in the electromagnetic calorime-
ter with appreciable energy deposition in the nearby hadronic calorime-
ter in the neighborhood
(iii)There should be missingPToverall when summation is made over all
the secondaries. The missingPTis attributed to the unseen neutrino
from the W-decay.
Signature ofZ^0 →e+e−events:
Two isolated tracks with largePTvalues and invariant massMe+e−>
50 GeV, pointing to localized track clusters in the electromagnetic
calorimeter.
For muonic decays,W±→μν,Z^0 →μμare observed by imposing
highPTrequirements on thePTvalues for muons which are able to pene-
trate hadron calorimeter and observed in the external muon chambers.Fig. 10.14Annihilation
process