Elementary Particle Physics

2. The KEKB accelerator collides 8 GeV electrons with 3.5 GeV positrons head on in the BELLEexperiment. Calculate the centre of mass energy of this system. [ 4]3. The BaBar detector had a solenoid creating ad 1.5T. The PEPII accelerator was running at thesame energy as KEKB (see previous exercise). Assume that only a pair of B mesons (m35279 MeV) is created in the collision and then one of them decays in two muons. Assumingalso that all the decays happen in the plane perpendicular to the magnetic field, calculate theradius of curvature of the muons in the BaBar detector. [ S]4. The 2″ is an unstable hyperon with mass m = 1385 MeV and decay width F = 35 MeV, witha branching ratio into the channel 2” -) 1121\0 of 88%. Is the decay of the 2″ strong or weak?Explain. [ 5]S. The LHC beam is not continuous. Instead, it has a bunch structure. Bunches of particles collideevery 25 ns at 14 TeV centre-of-mass energy with a luminosity (number of particles per secondper square centimetre) of 1034 cm‘zs’l. The total inelastic proton-proton cross section at 14TeV is 70 mb.(i) Compute the number of interactions occurring per second as well as every time two bunchescollide. These are called minimum bias events and are of almost no interest. [ 4](ii) The Higgs particle is produced at the LHC mainly through gluon fusion (gg -+ H) whichhas a cross section of about 40 pb. One of the Higgs decay channels involves the Higgs goinginto two photons (H -) W) and it has a probability (branching ratio) of 0.2 x 10’3. How manyminimum bias events are expected to be produced for every Higgs event observed via the two-photon channel if one ignores detector effects? [ S]