The ALICE Measurement
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The ALICE Measurement Looking for strange particles in ALICE Find channel possibl e 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)

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  • 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 firstLHC data (900 GeV proton proton)

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 PbPb event

ALICE exercise - D. Hatzifotiadou

Looking for strange particles and cascadesin ALICE (K0s, Λ, Ξ-)

recognisefrom decay pattern


invariant mass

classify according

to mass

fill tables


  • 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

ALICE exercise - D. Hatzifotiadou

ALICE exercise - D. Hatzifotiadou and cascades

From PawelDebski

From and cascadesPawelDebski

ALICE exercise - D. Hatzifotiadou

  • Goals and cascades

  • 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 (K0s, 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

ALICE exercise - D. Hatzifotiadou

  • Some numbers and cascades

  • FrascatiMasterClass : 41 pupils from all over Italy, 2 pupils /school

  • part of a four-day programme in Frascati “Stage InvernaleResidenziale”, 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 scientifiqueLycée International de Ferney)

  • Debriefing meeting + EVO 18.3.2011

  • Debriefing EVO Meeting 1.4.2011

ALICE exercise - D. Hatzifotiadou and cascades1341286 CERN 25.3.2011

ALICE exercise - D. Hatzifotiadou and cascades5167Subatech Nantes 25.3.2011

ALICE exercise - D. Hatzifotiadou

  • Feedback and cascades

  • Generalappreciation varies

  • Some found difficult to understand - others liked the exercise

  • Somewere enthusiastic – others found it boring

  • Event samples generated a lot of discussion

  • In 100 events include K0s, 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

ALICE exercise - D. Hatzifotiadou

  • Various remarks and and cascadessuggestions

  • 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

ALICE exercise - D. Hatzifotiadou

  • GSI version and cascades

  • 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)?

ALICE exercise - D. Hatzifotiadou

  • CERN and cascadesMasterClass - 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

ALICE exercise - D. Hatzifotiadou

  • Videoconference and cascades

  • 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.

ALICE exercise - D. Hatzifotiadou

  • Conclusions and cascades

  • “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

ALICE exercise - D. Hatzifotiadou

  • Future and cascades

  • 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

ALICE exercise - D. Hatzifotiadou