The 42 questions

I am back from Rome, where I had two unhappy days of written tests (see previous post below).

There were 110 of us, for 16 positions. We were given 42 questions, to be answered in 4 hours with no help from any text whatsoever (not even the "particle physics data booklet"). The idea was that a Physicist has to know the orders of magnitude of processes he plays with.

I did not do too bad, considering I have not been able to study for more than a week before the exam. I will get the results in a few days.

Below are some of the questions (I cannot write here all 42 of them). Not all the questions were difficult to answer, but one had on average less than 6 minutes per each! I did 33 of them, but wrote some mistakes of course.... The total score is 60 points, and one passes with 36 points or more (but the average of this score with that of the second exam has to be at least 42).

1.3 A particle at ionization minimum generates on average N electron-ion pairs per centimeter of a gaseous detector at atmospheric pressure. What is the value of N if the gas is a 60-40 mixture of Argon-Isobutan ? What other effects to the number of produced electrons determine the standard deviation of the signal measurement ?

1.8 A cube of NAI(Tl) scintillator read out by a phototube measures the line of cesium; estimate the energy resolution detailing the factors that contribute.

2.1 Compute the average number of interactions per bunch crossing if the luminosity is 2.5 E31 cm-2 s-1, the cross section is sigma=20 mb and the interbunch time is 4 us. What is the probability of having zero interactions in a bunch crossing ?

2.4 What is the ratio of radiated power by a proton in LHC and an electron in LEP I ? And between an electron in LEP 1 and one in Daphne ?

2.6 5kHz of events are analyzed to decide whether the event has to be read out or not. The decision takes T=20 us and the digitization time is 1 ms. What rate of accepted events can be sustained if the total dead time has to be kept below 20% ?

2.8 How does DeltaP/P depend on the momentum P of charged particles tracked in a magnetic field in air ? And in Iron ?

2.9 A magnetic spectrometer for unit charge particles and momenta of a few GeV/c is made of three parallel planes of detectors with a position resolution dx=100 um, spaced 20 cm, and immersed in a uniform magnetic field B=1T parallel to the detector planes and orthogonal to the measured coordinate. Particles arrive perpendicularly to the planes. Estimate the transverse momentum resolution for P=2 GeV/c.

3.1 An experiment selects events of signal with a frequency f and events of background with a frequency b. Compute the time of data taking it takes to observe the signal with a statistical significance of N sigma.

3.4 After collecting an integrated luminosity L = 10 fb-1 the analysis of decays B->J/psi Ks (J/psi->ll, Ks->pi pi) selects N=100 candidates. Using Nsim=1000 events simulated one computes that the detection efficiency is 37%. What is the measured Branching ratio, what is the statistical error and what is the systematic error due to having simulated too few events, if sigma is 1 nb ?

4.2 What is the regeneration of K0s mesons ? How is it explained ?

4.4 How is explained qualitatively that the phi meson decays in three pions about 15% of the times while the rest of decays are essentially to KK ?

4.6 Take the D0-> antiK0 pi0 and D0-> K0 pi0, draw the Feynman diagrams, and estimate the relative value of the decay amplitudes.

4.10 Draw the structure functions xF3(x), F2(x), G(x) for q2=10 GeV2. How do they evolve qualitatively as a function of the q2 ?

4.13 What is the ratio of the branching ratios for  H->bb and H->tau tau decays for Higgs mass 120 GeV ?

4.16 A beam of neutrinos of mean energy E=20 GeV is created from the decay of pions. Estimate: a) the energy of the pion beam; b) the divergence of the neutrino beam; c) the cross section for nucleon scattering; d) the mean free path of neutrinos in a detector of density equal to water; e) the ratio of cross sections on protons and electrons.

Comments

[m.visaya]

maestro,

RR′C=NNHCONH2 (USB-744)

[tommaso dorigo]

Manuel,

I give up.... Give me the key to your comments, I do not get it. I understand NNHCONH2 is some kind of molecule with nitrogen, carbon, hydrogen and oxygen being the constituents, but what the hell is the LSH of the equation ????

[m.visaya]

a no brainer reflecting on the symbolism of it all. this is the de tomaso car website. it is not hard to relate. (rbt-321)