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How to… (a.k.a. Photon PID and Pizero Analysis). A report on the status and advertisement of the tools http://www.phenix.bnl.gov/phenix/WWW/photon/howto/howto.html Methods geared toward heavy ions, low pt Goals: service (providing tools) and education (including my own)

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slide1

How to… (a.k.a. Photon PID and Pizero Analysis)

A report on the status and advertisement of the tools

http://www.phenix.bnl.gov/phenix/WWW/photon/howto/howto.html

Methods geared toward heavy ions, low pt

Goals: service(providing tools) and education(including my own)

Group: subset of Thermal Photon PWG (but anybody is welcome!)

Principal players up to now: Shunji, Ken, Saskia, Craig, Gabor

Focus on: photon PID

Basic tool: EMCal evaluator chain, ntuples

Pion spectrum: reconstructed via event mixing (one particular method)

Comparison of GEANT and measured

G. David, April 20, 2000

slide2

How to… (a.k.a. Photon PID and Pizero Analysis)

Prerequisites

Processing (simulated) PRDF files with the evaluator

detailed and short documentation available

tested on 20,000 + 70,000 events

outputs available on dataxx disks

nonstandard output – GEANT and measured

OR

Processing DST files (currently no evaluation, just measured)

in the works (Saskia)

documentation coming

OR

Processing standard reconstruction/evaluation chain output

planned

both GEANT and measured

G. David, April 20, 2000

slide3

How to… (a.k.a. Photon PID and Pizero Analysis)

The “Nishimu-Oyama method”

Framework (compiled code)

gg2pi to establish photon PID cuts and to check their efficiency

use GEANT PID or PID based upon measured quantities

Boolean (yes/no) cuts

primary cut: slewing corrected TOF with E-dependent sigma

secondary cut: charge overlap

tertiary cut: an empirical combination of cluster characteristics

compared to an ASCII database

easy to change and tune

output: ntuple with all accepted photon pairs (single and pair data)

can provide output with event mixing applying the same cuts

mltslice split gg2pi input according to event multiplicity

mkhist generate invariant mass histograms from gg2pi output in bins of pt

manipulate the output yourself (example provided)

G. David, April 20, 2000

slide4

Nishimu-Oyama method

How to… (a.k.a. Photon PID and Pizero Analysis)

Example: how to check the efficiency of your photon PID?

- bit 1 is set if GEANT PID is “photon”

- bit 2 is set if cluster passes your TOF cut

- example only: doesn’t mean you cannot do better!

G. David, April 20, 2000

slide5

Nishimu-Oyama method

How to… (a.k.a. Photon PID and Pizero Analysis)

Example: 2000 events, PID with measured quantities

- processed with gg2pi and mkhist, plotted with pi0_pac_plot.C

2.0 – 2.5 GeV/c

pt range 1.0 – 1.5 GeV/c

G. David, April 20, 2000

slide6

Nishimu-Oyama method

How to… (a.k.a. Photon PID and Pizero Analysis)

20,000 events GEANT PID, deposited energy

GEANT PID, reconstructed energy

measured PID, reconstructed energy

G. David, April 20, 2000

slide7

How to… (a.k.a. Photon PID and Pizero Analysis)

The “Szillasi method”

Framework (CINT macros to help establish probabilistic “combined”cuts)

ntread.c select a set of measured quantities A, B… appropriate for PID

plot their distributions for photons and non-photons

get the probability that for a given value a,b… it’s a photon

p(a), p(b)…

assign P =w(A)p(a) x w(B)p(b) x … to each cluster as

“probability of being a photon” (currently w(A)=w(B)=…=1.0)

your main job will be to find proper A,B quantities and w weights

you can now use this probability P to tag your photons

the histoes and an ntuple with the data of all particles is written

ntopti.c using the output histoes of ntread.c it calculates the

efficiency and the cleanness of your cuts for all values of P

The code is very transparent: easy to read and modify

G. David, April 20, 2000

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