The ALICE MasterClass exercise Looking for strange particles in ALICE physics motivation Strangeness enhancement : (first) signature for quark gluon plasma the signature V0 (and cascade) decays of strange hadrons (K0s, Λ, Ξ-) the tools Simplified ALICE event display based on ROOT Combine visual analysis of small event sample with large statistics analysis The data First LHC data (900 GeV proton proton) : develop / run masterclasses 2011 7 TeV proton proton data for 2012 Pb-Pb collision data : in a next version IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou Visual identification of V0 decays and cascades Ξ-→π-Λ→ π- p π- K0s→ p+p- Bachelor (single track) and two opposite tracks coming from a secondary vertex L ®p-p anti Λ→ p-π+ Two opposite tracks from a secondary vertex Monte Carlo Pb Pb event IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou The analysis tool : simplified ALICE event display based on ROOT 3 views of ALICE – 3D, rφ, rz V0 finder and cascade finder Highlights V0 (cascade) Recognise from decay pattern Calculate invariant mass Classify according to mass Fill tables Fill histograms Runs on LINUX, Ubuntu, MacOSX IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou From Pawel Debski

ALICE exercise - D. Hatzifotiadou From Pawel Debski IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou Many comments on how we deal with background Questions from pupils : is this how you analyse the data? 2nd part of exercise (GSI version) Analyse big event sample (2000 events) Invariant mass histograms for Ks, L, anti-L Fit 2nd degree polynomial to background Fit gaussian to peak Get number of Ks, L, anti-L after background subtraction + option to see combinatorial background (without common secondary vertex requirement) IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou Goals Flavour of data analysis Concept of particle decays Concept of some conservation laws and invariant mass Results Count numbers of particle species (K0s, Λ, anti-Λ and Ξ-) Calculate yields of particles Compare with ALICE published results Note that To see strangeness enhancement you need to make ratios, for example yield of Λ in pp / yield of Λ in Pb-Pb Show published strangeness enhancement plots from ALICE (+ other HI experiments) Explain on the plots what they would need to measure, in addition, to reproduce them IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou Strangeness enhancement defined as: the particle yield normalised by the number of participating nucleons in the collision, and divided by the observed yield in proton-beryllium (or proton-proton) collisions Enhancement increases with number of strange quarks in the hadron ( Ω has 3, Ξ has 2, Λ has 1) Enhancement decreases with collision energy (going from SPS to RHIC)..and at the LHC? IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou The problem with lead ion collision data IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou L ®p-p K0s→ p+p- Include event displays from lead lead Ξ-→π-Λ→ π- p π- IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou Outline of exercise Students (each group): Visual analysis of 30 events – tables + invariant mass histograms Institute (all groups): Add up numbers / merge histograms Students (each group): Analysis of 2000 events - invariant mass histograms Students (each group): Try to fit background / peak / subtract -> find number of particles Institute (all groups): Merge histograms Institute (all groups): Fit background / peak / subtract -> find number of particles Calculate yields of each particle type (assumptions on initial number of events from which the sample has been extracted correction factors for efficiency) Discussion on strangeness enhancement plots IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou Status 30 event samples 7 TeV proton-proton for visual analysis (6) ok 2000 event samples 7 TeV proton-proton ok Analysis tools ok Accompanying Text almost ready (to be checked) To be provided for the masterclasses Proposed discussion for institutes Proposed discussion for moderators Excel sheets for results IPPOG CERN 3.11.2011 ALICE exercise - D. Hatzifotiadou