the alice measurement looking for strange particles in alice

The ALICE MeasurementLooking 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 14.4.2011 ALICE exercise - D. Hatzifotiadou

L ®p-p

2

K0s→ p+p-

Ξ-→π-Λ→ p- p p-

Visual identification of V0 decays and cascades

IPPOG Kosice 14.4.2011 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-p+

Monte Carlo Pb Pb event

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

recognise from decay pattern

calculateinvariant mass

classify accordingto mass

fill tables

fill histograms

3IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou

•Simplified ALICE event display based on ROOT (LINUX, Ubuntu, MacOSX)•V0 finder and cascade finderP.Debski, P.Foka, DH, B.Hippolyte, A.Maire, M.Tadel

IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 4From Pawel Debski

IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 5

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 (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


IPPOG Kosice 14.4.2011

ALICE exercise - D. Hatzifotiadou 7

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) http://www.lnf.infn.it/edu/stagelnf/2011/masterclass11.html

• 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) http://indico.in2p3.fr/internalPage.py?pageId=0&confId=5167• Heidelberg : 36 pupils + 2 teachers (2 classes)• CERN : 27 pupils + 3 teachers (classe première scientifique Lycée International de Ferney)

• Debriefing meeting + EVO 18.3.2011• Debriefing EVO Meeting 1.4.2011


http://www.lnf.infn.it/edu/stagelnf/2011/masterclass11.html



http://indico.in2p3.fr/internalPage.py?pageId=0&confId=5167




http://cdsweb.cern.ch/record/1341286CERN 25.3.2011

http://cdsweb.cern.ch/record/1341286

http://cdsweb.cern.ch/record/1341286


http://indico.in2p3.fr/internalPage.py?pageId=0&confId=5167 Subatech Nantes 25.3.2011



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 K0

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


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


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)?


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 exerciseHe liked the new one (ALICE) better

One of the instructors: it was fun and it was something different

encouraging


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.


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


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


the alice measurement looking for strange particles in alice

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