View source for FCAL Reconstruction in b1pi events 03/14/2012

This is mostly an update of [[FCAL Reconstruction in b1pi events 03/06/2012]], but using svn rev 8894, which includes [http://clasweb.jlab.org/websvn/prod/listing.php?repname=GlueX&path=%2Ftrunk%2Fsim-recon%2Fsrc%2F&rev=8886&sc=1 changes to the cluster to charged track matching code].

50,000 b1pi events. No EM background.
===Thrown photons===

[[Image:PhotonEvsTheta thrown FCAL Feb12.png]]

===Reconstructed photons===
(after vetoing clusters matched to charged tracks)

[[Image:PhotonEvsTheta recon FCAL.svn8894.png]]

===Questions===
* Why are so many "photons" reconstructed? How can we reduce this?
* What is the actual reconstruction efficiency?
* How many photons reach the FCAL without converting?
** Efficiency for non-converting photons?
** Can we recover converted photons?
* Energy resolution, etc.

===1 GeV photon events===
Mihajlo in GlueX-doc-823 (2007) says for 1 GeV photons:
* 37% photon conversion before FCAL
* 99.6% efficiency for photons that reach FCAL
* Taking into account single clusters from photons that converted close to the FCAL face, the overall photon reconstruction efficiency was estimated to be 77%
* 4% energy resolution at 1 GeV

===Efficiency===
Energy distribution of thrown photons:
* Black=all thrown photons
* Red=photons which reach the FCAL without converting (determined using DFCALTruthShower object)
* Blue=photons which reach the FCAL without converting AND are reconstructed successfully (fabs(theta_thrown - theta_recon) < .006 && fabs(phi_thrown - phi_recon) < .15)
[[File:PhotonE_thrown_FCAL_all_truthshower_truthshower%2Brecon.svn8894.png]]

Red/Black=% of photons that reach FCAL without converting:

[[File:Photon_FCAL_truth_shower.png]]

Roughly 20% of photons convert before reaching FCAL. Relatively constant across wide range of energy. There is an angular dependence, not shown here. Big improvement since 2007 (geometry change?)

====Unconverted photons====

Blue/Red=

[[File:Photon_FCAL_recon_eff.svn8894.png]]

Above 1 GeV, 94% of unconverted photons are reconstructed. This is less than the 99.6% reported for single photon sample; this difference is due to photon showers rejected due to overlap with charged particle shower.

Below ~600 MeV, efficiency drops. This is due to showers contained within a single cell, which means no cluster is created.

Overall FCAL reconstruction efficiency considering only unconverted photons: 70%. Could be higher after trying to recover photons that convert.
====After conversion====
For photons that do convert, we use different criteria to determine if a photon is reconstructed "successfully": (E_recon - E_thrown)/E_thrown < 3.5*sigma_E && fabs(theta_thrown - theta_recon) < .01 && fabs(phi_thrown - phi_recon) < .2), where sigma_E=0.062/sqrt(E) as calculated below.

[[File:Photon FCAL recon eff all.svn8894.png]]

Total FCAL efficiency: ~77%

More can be done here? Where do photons convert? Can split clusters be re-merged?

===Extra photon problem===

Use a timing cut (t_shower-t_flight) < 1.2 ns to cut out of out-of-time particles:

[[File:PhotonTproj recon FCAL.svn8894.png]]

Timing cut reduces average number of "photons" per event from 1.44 to 1.16. (actually 0.77 photons should hit the FCAL per event)

Timing cut has negligible effect on efficiency.

===Energy resolution===
====Unconverted photons====
Look at distribution of (E_recon - E_thrown)/E_thrown as a function of E:

Sigma:

[[File:Photon FCAL E res sigmas.uncoverted.svn8894.png]]

Fit is 0.062/sqrt(E). Resolution is worse than nominal value (~5%/sqrt(E)?). Why is this? Is this really better for a single photon sample?

Mean:

[[File:Photon FCAL E res means.uncoverted.svn8894.png]]

Some trouble at low energies?
====All photons====
This will be biased since we cut on (E_recon - E_thrown)/E_thrown before making a correspondence between a thrown and reconstructed photon, in the case that the photon has converted before the FCAL.

[[File:Photon FCAL E res sigmas.all.svn8894.png]]

0.063/sqrt(E)

[[File:Photon FCAL E res means.all.svn8894.png]]

issues here...

===Single block "clusters"===
There is a tunable parameter in the FCAL code:

<code>MIN_CLUSTER_BLOCK_COUNT = 2;</code>

At lower energies, reconstruction efficiency is lower because often only one block has energy deposited in it (above the 20 MeV threshold in mcsmear).

Try setting <code>MIN_CLUSTER_BLOCK_COUNT = 1</code> and see what happens.
====Efficiency====
[[File:Photon_FCAL_recon_eff.minBlock1%2BminBlock2.svn8894.png]]
*<span style="color:red">red: <code>MIN_CLUSTER_BLOCK_COUNT = 1</code></span>
*black: <code>MIN_CLUSTER_BLOCK_COUNT = 2</code>

Clearly a big improvement in efficiency below ~500 MeV.

Overall efficiency increases by ~6%. (from 77% to 82%)

Total FCAL photon count (after timing cut) increases by 16% (1.16 photons/event to 1.34).

====Energy resolution====
Issues with energy resolution.

[[File:Photon FCAL E res means.minBlock1.all.svn8894.png]]

Energy is underestimated, especially at lower energies.

Energy resolution gets worse.

Solutions?
* Redo energy correction/calibration
* Deal with 1 block clusters as a special case?

Do hdgeant/mcsmear model FCAL correctly?

===Identifying hadronic clusters by shape?===
Hadronic showers often "look" different that EM showers:

[[File:FCAL face.b1pi event.png]]

How can we distinguish between the two?

DFCALCluster computes several size parameters:
<pre>
		double fRMS;                 // cluster r.m.s. size (cm)
		double fRMS_x;               // cluster r.m.s. size along X-axis (cm)
		double fRMS_y;               // cluster r.m.s. size along Y-axis (cm)
		double fRMS_u;               // cluster r.m.s. size in radial direction (cm)
		double fRMS_v;               // cluster r.m.s. size in azimuth direction (cm)
</pre>

Plot RMS size for three classes of reconstructed photon:
* Black: photons unmatched to thrown photon (more likely to be hadronic)
* <span style="color:red">Red: photons matched to a thrown photon (more likely to be EM)</span>
* <span style="color:blue">Blue: photons matched to a thrown photon that converted before reaching the FCAL</span>
[[File:Photon_FCAL_RMS.svn8894.png]]

Can cut out photons with RMS size outside the green lines. This cuts out 3792/57850 of photons that survived the timing cut.

Look at size vs energy.