How to resolve the logical error

hello! I am trying to do the following integration but the result came out is 0 (zero), please see the program:

Mc= 1.5; T = 0.049317; for p3 = 4:1:12

    E3 = sqrt((p3.^2)-(Mc.^2));
    f3 = 1/(exp(E3/T) + 1);

for p4 = 4:1:12

    E4 = sqrt((p4.^2)-(Mc.^2));
    f4 = 1./(exp(E4/T) + 1);
    Y4j = (p4.*p4.*f4);

end

Lambda_f4 =  trapz(Y4j);
Z3 =  (1/(pi^4))*(p3.*p3.*f3.*Lambda_f4);

end

Lambda_f5 = trapz(Z3)

Please help me to find out the problem. Thank you.