===================================================== October 30th 2017 - LHCb lepton universality ===================================================== Lepton universality session 3. Xiangyang chairs. Xiangyang showed some helpful slides to illustrate talking points during the meeting. These are attached too. ------------ Topics: - Magnets & RICH - Tag and probe - HW triggers and bootstrapping - Fig. 2 ----------- Details: - The dipole spreads the mesons, bending them away from the beam line and into the RICH detectors. - Pion moves faster than the Kaon for the same momentum due to mass difference and, since the RICH (cherenkov) detectors measure velocity and not momentum, the pions end up with a larger ring. - PID referred to in Section 4 is the Pion and Kaon id. - Tag and probe again: J/psi and Z mass are used as the resonant prior. J/psi good for low GeV stuff. The key thing is recovering the B and D meson masses. - Why is the D-meson used? + Pi0 is prompt: decays to photons + charged pions: effectively stable on the cT of our detector + charged kaons: also effectively stable - Why doesn’t ATLAS have RICH detectors? Our track multiplicity is just so much higher than LHCb. - The vertex detector in LHCb is SUPER closer to the IP, < 10 mm. Interestingly, its also in vacuum so ‘inside the beam pipe’. - From bottom of pg. 5: “The tag sample is defined by events where HW trigger is fired by activity in the event NOT associated with signal particles” —> an unbiased trigger? - How do we estimate trigger efficiency in ATLAS? There is something called ‘Bootstrapping’ of the trigger. Something along the lines of: given p( passed 20GeV trigger) what is p( passed 50 GeV trigger)? - LHCb has bad ID for e- instead of muons (brew) - In ATLAS we derive our triggered objects: we start from trigger, then reco, then PID. We also have scale factors for each part of the process. - Interestingly, di-jet searches tend to operate near trigger turn-on curves. - Fig. 2: + horizontal line ~ 9 GeV^2 is from J/psi resonance (mass = 3.1 GeV, therefore squared is ~ 9GeV). + B0 —> K0 + 2l in the non-resonant part of the plots. The diagonal is likely the e- losing energy via brem + Psi(2S) is the other horizontal resonance + Why do we only base our background on the lower mass region? + Vyassa raises the point that there appears to be a valley in between the diagonal and horizontal branches of the plot. If these rates are purely additive, why does this valley extend so far?? ---------- Misc: