First Look at SMD gamma/pi0 Discrimination
Pibero Djawotho
Indiana University
July 31, 2006
Simulation
Simulation were done by Jason for the SVT review.
Maximal side residual


Figure 1:
Fitted peak integral vs. fit residual sum (U+V) from st_jpsi
input stream (J/psi trigger only).

Figure 2:
Fitted peak integral vs. fit residual sum (U+V) from st_physics
input stream (all triggers except express stream triggers).

xy distribution of SMD hits
The separation between photons and pions was achieved by using Les cut
in the above figures where photons reside above the curve and pions below.
The data set used is the st_jpsi express stream.
Single peak characteristics
Fit function
The transverse profile of an electromagnetic shower in the SMD can be
parametrized by the equation below in each SMD plane:
f(x) is the energy in MeV as a function of SMD strip x.
The algorithm performs a simultaneous fit in both the U and V plane.
The maximal residual (data  fit) is then calculated. A single
photon in the SMD should be well descibed by the equation above and
therefore will have a smaller maximal residual. A neutral pion, which
decays into two photons, should exhibit a larger maximal residual.
Typically, the response would be a double peak, possibly a larger peak
and a smaller peak corresponding to a softer photon.
Single event SMD response
This directory contains images of single event SMD responses in both U and V plane.
The file name convention is SMD_RUN_EVENT.png. The fit function for a single peak is the one described
in the section above with 5 parameters:
 p0 = yield (P_{0}), area under the peak in MeV
 p1 = mean (μ), center of peak in strips
 p2 = sigma of the first Gaussian (w_{1})
 p3 = fraction of the amplitude of the second Gaussian with respect to the first one (B),
fixed to 0.2
 p4 = ratio of the width of the second Gaussian to the width of the first one
(w_{2}/w_{1}), fixed to 3.5
Code
macros
Documents
 Proposal to Contstruct an Endcap
Calorimeter for Spin Physics at STAR
 Appendix Simulation Studies of Direct
Photon Production at STAR
 An Endcap Calorimeter for STAR Conceptual
Design Report
 The STAR Endcap Electromagnetic
Calorimeter (EEMC NIM)
 An Endcap Calorimeter for STAR Technical
Design Update #1
 Jan's gamma/pi^{0}
algorithm
 Endcap
Calorimeter Proposal (HTML @ IUCF)
 STAR Note 401: An Endcap Electromagnetic
Calorimeter for STARConceptual Design Report
 Spin Effects at Suppercollider Energies