the alice measurement looking for strange particles in alice find channel possible to observe...
TRANSCRIPT
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→ π- p π-
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-π+
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 6
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
IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 8
IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 9
http://cdsweb.cern.ch/record/1341286CERN 25.3.2011
IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 10
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
IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 11
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 14.4.2011 ALICE exercise - D. Hatzifotiadou 12
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 14.4.2011 ALICE exercise - D. Hatzifotiadou 13
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
IPPOG Kosice 14.4.2011 ALICE exercise - D. Hatzifotiadou 14
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 14.4.2011 ALICE exercise - D. Hatzifotiadou 15
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 14.4.2011 ALICE exercise - D. Hatzifotiadou 16
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 14.4.2011 ALICE exercise - D. Hatzifotiadou 17