CalDet Particle ID Studies

The figures shown for each beam momentum displays the time of flight spread and spread in the square of the masses for each particle type. You can download a postscript version of each figure by clicking on the link below it. The other links below the figures take you to a page where you can download the poscript versions of figures for certain momentum and pressure combinations of the Cerenkov detector. Each combination has a figure showing the number of photoelectrons expected in the Cerenkov detector. We also have histograms of the number of photoelectrons expected vs. the time of flight for each type of particle in the T11 beam.

The time of flight system is modeled as having a 6m separation between the scintillator paddles, and a spread of 80 ps.

The Cerenkov detector is modeled as being 6m long. We used equation (24.5) in the Review of Particle Physics (2001) to determine the number of photoelectrons expected in the detector. This equation assumes a collection efficiency of 90% and an integrated detector efficiency of 0.27. When the values for the actual detector are found, we will redo the simulations with those numbers.

The makeup for the T11 beam in e's, pi's, and p's is known and we use those values. Figures detailing the beam makeup can be found here. The fraction of mu's in the beam is not known and we use an upper limit. That is, we say that any fraction of the total number of particles in the beam that is not e's, pi's, or p's is fully accounted for by mu's.

At the bottom of the page is a table showing the probabilities for identifying each particle type correctly given the parameters mentioned above.

Links followed by * indicate that jpeg versions of the figures for the T11 beam are shown on that page.

Momentum = 0.8 GeV/c

   Time of Flight and Derived Mass

   Pressure = 1 bar

   Pressure = 2 bar

   Pressure = 3 bar

Momentum = 1.0 GeV/c

   Time of Flight and Derived Mass

   Pressure = 1 bar*

   Pressure = 2 bar

   Pressure = 3 bar

Momentum = 1.5 GeV/c

   Time of Flight and Derived Mass

   Pressure = 1 bar

   Pressure = 2 bar

   Pressure = 3 bar

Momentum = 2.0 GeV/c

   Time of Flight and Derived Mass

   Pressure = 1 bar

   Pressure = 2 bar

   Pressure = 3 bar*

Momentum = 3.0 GeV/c

   Time of Flight and Derived Mass

   Pressure = 1 bar

   Pressure = 2 bar*

   Pressure = 3 bar*

We examined the results for muons and pions in the table at 0.8 GeV/c for all pressures more closely by using the histograms shown in the figure below. The upper left histogram shows the overlap for 10^6 of each particle type in the TOF results. We base the probabilities for a particle to be a muon or pion on this histogram. The upper right histogram shows the distributions for a pion to be correctly or incorrectly identified. The lower right histogram shows the same for muons. Both histograms have a clear separation for where a particle is identified correctly. Moreover, the separation occurs at the same spot for both types of particles. The lower left histogram shows this separation more clearly and plots the distributions for correctly identifying particles of each type.

   Muon and Pion Separation for TOF System

For beam momenta above ~1.0 GeV/c and at all pressures, we see that muons and pions are not well resolved by either the TOF or Cerenkov detector. We can only identify them correctly about half the time. At the higher momenta (~ 3.0 GeV/c) and pressures (> 2 bar), the Cerenkov detector starts seeing signals from the muons and pions so we are able to distinguish them. The plots on the links marked with * show this behavior.

Modeling the TOF System with an 11m separation

We were asked to rerun the simulations using an 11m separation between the time of flight paddles. The results are shown in the table, figures, and links below. We show the TOF and resulting derived mass squared value plots, as well as the plots of expected number of photoelectrons vs. the TOF. We do not show the 1D distributions of the expected Cerenkov signals as those are unaffected by the increased TOF paddle separation. We also show a plot of the Cerenkov detector threshold pressure vs. beam momentum.

Probabilities for identifying each particle type correctly

Momentum (GeV/c)	Pressure (bar)	e	mu	pi	p
0.8	1.0	0.986	0.920	0.929	0.999
	2.0	0.981	0.921	0.929	0.999
	3.0	0.974	0.920	0.929	0.999
1.0	1.0	0.987	0.835	0.816	0.999
	2.0	0.979	0.836	0.816	0.999
	3.0	0.977	0.835	0.816	0.999
1.5	1.0	0.987	0.699	0.626	0.999
	2.0	0.979	0.701	0.626	0.999
	3.0	0.979	0.699	0.626	0.999
2.0	1.0	0.984	0.654	0.532	0.999
	2.0	0.980	0.654	0.532	0.999
	3.0	0.975	0.654	0.532	0.999
3.0	1.0	0.988	0.551	0.533	0.999
	2.0	0.979	0.989	0.999	0.999
	3.0	0.975	0.982	0.989	0.999

Momentum = 0.8 GeV/c

   Time of Flight and Derived Mass

   Cerenkov Signal vs TOF for P = 1.0 bar

   Cerenkov Signal vs TOF for P = 2.0 bar

   Cerenkov Signal vs TOF for P = 3.0 bar

Momentum = 1.0 GeV/c

   Time of Flight and Derived Mass

   Cerenkov Signal vs TOF for P = 1.0 bar

   Cerenkov Signal vs TOF for P = 2.0 bar

   Cerenkov Signal vs TOF for P = 3.0 bar

Momentum = 1.5 GeV/c

   Time of Flight and Derived Mass

   Cerenkov Signal vs TOF for P = 1.0 bar

   Cerenkov Signal vs TOF for P = 2.0 bar

   Cerenkov Signal vs TOF for P = 3.0 bar

Momentum = 2.0 GeV/c

   Time of Flight and Derived Mass

   Cerenkov Signal vs TOF for P = 1.0 bar

   Cerenkov Signal vs TOF for P = 2.0 bar

   Cerenkov Signal vs TOF for P = 3.0 bar

Momentum = 3.0 GeV/c

   Time of Flight and Derived Mass

   Cerenkov Signal vs TOF for P = 1.0 bar

   Cerenkov Signal vs TOF for P = 2.0 bar

   Cerenkov Signal vs TOF for P = 3.0 bar

   Threshold Pressures for CO2 Cerenkov Dectector

   Fraction of Particles Causing Signals