SEARCH FOR STRANGE PARTICLES Physics Discussion of the ALICE measurement topic of the measurement, what should be combined/shown/discussed (and how ) ALICE© | Moderators Orientation | | Despina Hatzifotiadou The signature Visual analysis of small number of events Large dataset analysis in different centrality regions for Pb-Pb Outline of the measurement Presentation of results for the videoconference Discussion

V0 decays of strange hadrons (K 0 s, Λ, anti-Λ) the tools Simplified ALICE event display based on ROOT Histograms, fitting etc : done with ROOT the method Visual analysis of some events (~15) Analysis of large-statistics dataset (some thousands) ALICE© | Moderators orientation | | Despina Hatzifotiadou the result Calculate particle yields Observe strangeness enhancement (first) signature for quark gluon plasma K 0 s →  +  - Λ → p  -

First part of measurement Find V0s ( K 0 s, Λ, anti-Λ) from decay pattern (V0 : two tracks with opposite charge, coming from a common secondary vertex) Calculate invariant mass Classify according to invariant mass value and daughter particle type (K 0 s,Λ, anti-Λ ) Fill histograms and tables Discuss Value of mass peak Width of mass peak Background events ALICE© | Moderators orientation | | Despina Hatzifotiadou

Second part of measurement Analyse large event sample (thousands of events) Fill invariant mass histograms for K s, Λ anti-Λ Fit curves to background (2 nd degree polynomial) and peak (gaussian) Find number of K s, Λ, anti-Λ after background subtraction in different centrality bins for Pb-Pb collision data ALICE© | Moderators orientation | | Despina Hatzifotiadou

K s Left: 0-10% centrality Right : 50-60% Centrality Λ Left: 0-10% centrality Right : % Centrality

Results ALICE© | Moderators orientation | | Despina Hatzifotiadou known givenmeasured given calculated Efficiency = Nparticles(measured)/Nparticles(produced)* * assumption on efficiency values : to match yields in Analysis Note Measurement of Ks and Λ spectra and yields in Pb–Pb collisions at √sNN=2.76 TeV with the ALICE experiment Yield : number of particles produced per interaction Yield = Nparticles(produced)/Nevents = Nparticles(measured)/(efficiency x Nevents) Strangeness enhancement: the particle yield normalised by the number of participating nucleons in the collision, and divided by the yield in proton-proton collisions* K s -Yield (pp) = 0.25 /interaction ; Λ-Yield(pp) = /interaction ; = 2 for pp * pp yields at 2.76 TeV from interpolation between 900 GeV and 7 TeV Analysis Note “Ks, Λ and antiΛ production in pp collisions at 7 TeV”

Outline of measurement First Part Students (each group): Visual analysis of 15 events fill tables + invariant mass histograms Institute (all groups): Add up numbers / merge histograms / comments Second Part Students (each group): Analyse events in a centrality bin invariant mass histograms Students (each group): Fit curve/ subtract background find number of Λ, anti-Λ and K 0 s Institute (all groups): Calculate yields of each particle type (give number of events in each centrality bin;give global efficiency) Calculate strangeness enhancement (ratio of yields normalised to N part ) (give yield for proton-proton at 2.76 TeV) Produce strangeness enhancement plots -> To be presented by Institutes for the video-conference ALICE© | Moderators orientation | | Despina Hatzifotiadou

example spreadsheet filled by each institute Username alice-masterclass Password alicelogin at

ALICE© | Moderators orientation | | Despina Hatzifotiadou To combine results of all institutes in one plot, use to be filled by moderator Compare all institutes results, for example for Lambdas

ALICE© | Moderators orientation | | Despina Hatzifotiadou Example of presentation of results Preliminary ALICE results + lower energy (STAR, NA57) results Possible comments Enhancement increases with number of strange quarks in the hadron (Λ has 1 strange quark, Ξ has 2, Ω has 3) Enhancement decreases with collision energy (going from SPS to RHIC to LHC)