The ALICE Measurement Looking for strange particles in ALICE Find channel possible to observe visually Requirement : physics measurement ALICE strong on tracking and PID – not enough calorimeter coverage Proposal to look for V0 and cascade decays (of strange hadrons) Strangeness enhancement : first signature for quark gluon plasma Seen by previous heavy ion experiments Need to compare lead lead collision data with proton proton data Develop and test with first LHC data (900 GeV proton proton) 1IPPOG Kosice ALICE exercise - D. Hatzifotiadou

  p 2 K 0 s →  +  - Ξ - →π - Λ→    p   Visual identification of V0 decays and cascades IPPOG Kosice ALICE exercise - D. Hatzifotiadou Bachelor (single track) and two opposite tracks coming from a secondary vertex Two opposite tracks from a secondary vertex anti Λ→ p -  + Monte Carlo Pb Pb event

Looking for strange particles in ALICE (K 0 s, Λ, Ξ - ) recognise from decay pattern calculate invariant mass classify according to mass fill tables fill histograms 3 IPPOG Kosice ALICE exercise - D. Hatzifotiadou Simplified ALICE event display based on ROOT (LINUX, Ubuntu, MacOSX) V0 finder and cascade finder P.Debski, P.Foka, DH, B.Hippolyte, A.Maire, M.Tadel

IPPOG Kosice ALICE exercise - D. Hatzifotiadou4 From Pawel Debski

IPPOG Kosice ALICE exercise - D. Hatzifotiadou5 From Pawel Debski

Goals Flavour of data analysis Concept of particle decays Concept of some conservation laws and invariant mass 2.76 TeV lead collision data (end 2010) not available for the exercise Count numbers of particle species (K 0 s, Λ, anti-Λ and Ξ - )* Calculate yields of particles Compare with Monte Carlo predictions Compare with ALICE published results Some discussion of errors First (experimental) phase No background subtraction, efficiency etc No Windows implementation *in a sample of 100 events IPPOG Kosice ALICE exercise - D. Hatzifotiadou6

IPPOG Kosice ALICE exercise - D. Hatzifotiadou7

Some numbers Frascati MasterClass : 41 pupils from all over Italy, 2 pupils /school part of a four-day programme in Frascati “Stage Invernale Residenziale”, 7-10 February (outside “International Masterclasses” schedule) Graz: problems with ROOT installation; did LEP exercise Bergen : 70 pupils Oslo : 35 pupils (?) GSI Darmstadt/Frankfurt 30 pupils Torino : 80 pupils in the morning, 56 staying for the exercise Lodz : 60 pupils + 3 teachers Nantes : 35 pupils + 3 adults (1 class) Heidelberg : 36 pupils + 2 teachers (2 classes) CERN : 27 pupils + 3 teachers (classe première scientifique Lycée International de Ferney) Debriefing meeting + EVO Debriefing EVO Meeting IPPOG Kosice ALICE exercise - D. Hatzifotiadou8

IPPOG Kosice ALICE exercise - D. Hatzifotiadou

IPPOG Kosice ALICE exercise - D. Hatzifotiadou 10 Subatech Nantes

Feedback General appreciation varies Some found difficult to understand - others liked the exercise Some were enthusiastic – others found it boring Event samples generated a lot of discussion In 100 events include K 0 s, Λ, anti-Λ (percentage as from data analysis) and Ξ – (10 x percentage as from data analysis) Too complicated (selected V0s, often V0 finder finds more V0s in the same event) Event without V0s (“empty”) : should they exist or not? Repetition of “same V0s” in many samples Background Not considered – another version developed to take it into account (see next) V0 finder – cascade finder : mechanical (just click a button) But can one find V0s by eye? Some technical problems Computer crashes (version of root? Graphics?) – no crash on MacOSX IPPOG Kosice ALICE exercise - D. Hatzifotiadou11

Various remarks and suggestions Should implement counter for events analysed Display event number / sample number separately Histograms not optimised Change histogram binning Need to update automatically Add histogram facility : ok for single files, not functioning for multiple files Book-keeping of results Clicking of buttons required to save results in tables ad histograms Often children forget – information lost Have to modify IPPOG Kosice ALICE exercise - D. Hatzifotiadou12

GSI version Developed another version of the exercise Analyse “visually” a small sample of events (20 instead of 100) Run analysis program in the background analysing some thousands of events Invariant mass plots Fit background and substract This certainly answers the question asked by many Is this how you do the analysis in reality (scanning each event by eye)? IPPOG Kosice ALICE exercise - D. Hatzifotiadou13

CERN MasterClass - Feedback Teacher made an evaluation sheet 20 replies from the pupils Answers cover the whole spectrum General impression positive Enjoyed the day, feel that they learnt a lot Proposed improvements Same teacher had participated last year in CERN masterclass with OPAL exercise He liked the new one (ALICE) better One of the instructors: it was fun and it was something different encouraging IPPOG Kosice ALICE exercise - D. Hatzifotiadou14

Videoconference Discussion on QGP and strangeness enhancement too much at the end of a long day? Proposed questions to ask (baryon number conservation) – too difficult – dropped Opted for having the results reported and filling excel sheets “online” No uploading of documents Some of the pupils said that they liked the quiz Some of the organisers question whether the quiz should be done locally Some expressed the opinion that we should have an ALICE special quiz The time of the video-conference makes the whole event end too late Can everything be brought forward? For CERN masterclass – less important (they have spent the day at CERN) Some report technical problems, echo, etc. IPPOG Kosice ALICE exercise - D. Hatzifotiadou15

Conclusions “Looking for strange particles with ALICE” starting point developed with limited resources Overall experience positive Brought new institutes in the game Generated interest, dialogue and new ideas People get more involved when they present their experiment Some technical problems (computer crashes) Criticism to be taken into account for the future developments IPPOG Kosice ALICE exercise - D. Hatzifotiadou16

Future Revisit the exercise and its aims Original idea of looking for strangeness enhancement: Compare data from Pb-Pb collisions and pp collisions at higher energies (Can the event display easily deal with thousands of tracks?) Smaller data samples Viewer, histogram facility, calculator : need modifications Idea of small scale visual analysis combined with larger scale “real” analysis and background fitting and subtraction : interesting, to be investigated ( time needed ; too complex ?) In search of manpower IPPOG Kosice ALICE exercise - D. Hatzifotiadou17