============================================ February 14th 2018 - Charge mult. 3 - ALICE ============================================ Rebecca chairs, on Emily's behalf. ------------ Minutes: ==== General: ==== - Over the past 3 weeks we've looked at a different paper each week on the same topic. Did people like thsi format? - as long as its relevant to the topic, e.g. a simple measurement done in different ways by different experiements. - The Z' paper would be a bad paper to do in one week, it was good that we took longer on that - Plan for the next sessions. Since we had a lot of questions about generator tunings and QCD, I asked Cheyenne to lead some sessions where we read through the PDG review on Generator techniques. Cheyenne can only attend every other week. - Greg volunteers to do the reviews with Cheyenne. So they will alternate for 3-4 weeks total. - We will skip next week so they have some time to decide what they'd like to cover. - We'll probably start with hadronisation, color, tunings. Minutes - pg. 7: cesar, question about last paragraph. greg: does increasing energy increase the lumi due to the bunch bing compressed? General consensus is that if it does it is due to beam condfitions changing. Greg wonders if the shape of the protons in the bunch changing also affects the cross-section. This leads into a discussion about luminosity and ions. - Patrick: when we do have Pb ions, how doe the N_ch change? does it scale with atomic number? Greg: phoniex-star did this. https://arxiv.org/pdf/nucl-ex/0203007.pdf ********************** NEXT TIME: break week ********************** ---------- CliffNotes: - pp collisions - NBD’s not done in previous papers - V0 is appropriate for triggering (1ns) @ -90cm and 330 cm from IP - SPD is 2 barrel layers next to beam pipe of pixels - 100ns fast signal can be used for triggering - Nch is calculated from cluster counting of inner layer. - using tracklets analysis used both layers and made trackless, which helped select PV particles - This analysis only uses first method b/c it gives larger eta coverage - FMD == strips at 320 cm, 79cm and -69cm from IP. Rings not barrels. - Majority of particles reaching FMD are secondary and from material interations - Unfolding used to account for detector effects - Collisions analysed at 3 different CoM energies: 0.9, 7, and 8 TeV. - inelastic, non-diffractive scattering is dominant in p-p collisions. Hadrons produced due to exchange of color. - Triggers: - all inelastic events: INEL: MB_OR: at least one particle in EITHER V0 or SPD - INEL > 0: at least one charged particle (tracklet) in eta<1, in addition to INEL. - Non-single diffractive (NSD): MB_AND: V0_A && V0_B must have hits - PU removal done by searching for additional vertices in same event. 10% of PU events still pass the removal. - A matrix maps the measured multiplicity to the number of charged primary particle distributions: R_mt - Figure 1: at low eta the unfolding increases multiplicity b/c of acceptance gaps in SPD - At higher eta, unfolding decreases mutliplicyt due to contributions being counted from secondary particles - GEANT 3 is used b/c the TPC code was really slow up until last year. They hope to move to GEANT 4 for Run 3. - The unfolded distribution is corrected for vertex and trigger inefficiency by dividing each bin by the efficiency value in equation 4. - The OR trigger efficiency remains the same at different CoM energies but the AND trigger efficiency decreases. - Comments on tunes: - Pythia Perugia and PhoJet is larger for small N_ch: hence largest differences at low N_ch. - Lorent boost of diffracted system increases with CoM whilst double-diffraction becomes smaller. - At high eta, it’s more likely that diffractive events will be included in the distribution. - Material simulation underestimated by 14%!! Systematic error seems to be between 7-14%. - Measurements don’t consistently match the double NBD fit. - CMS data and ALICE data don’t match in tails due to normalization? - Pythia Perugia and EPOS tunings match the INEL triggers well. KNO scaling violation seen.