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Compton Study from Experimental Data

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Purpose:

To show that method for selecting single arm Compton events works on real Compton data and to see if we can qualitatively see single arm Compton events in production runs.

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Double-Arm (Tested on dedicated Compton run # 4658)

Procedure for selecting Compton events:

 Events in which: 2 clusters in HyCal  

Timing  difference between trigger and tagger was less than 5ns (Timing cut) (see Figures 1&2)

Sum of the two clusters was greater than 0.5Gev (Energy cut)

(Radial cut): 4 cm< r< 34cm Figure 1: Timing difference between tagger and trigger

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Double-Arm

Figure 2: Timing difference between tagger and trigger

From analysis of timing coincidence plot , a timing window of 5ns was taken. (As result T-counter 9 was excluded)

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Double-Arm

Figure 3: Energy sum of two clusters minus reconstructed tagger energy

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Double-Arm

Figure 4: distribution

After taking elasticity and minimum cluster separation cuts, get peak at ~180 º.

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Double-Arm

Blue dots correspond to photons and red dot correspond to electrons.

Figure 5: Kinematic correlation between clusterenergy and cluster angle

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Double-Arm

After applying Compton kinematic cuts , a peak at ~1 is obtained indicating Compton events. This shows the method for selecting Compton events works for double-arm case.

Figure 6:  Pure Compton events after elasticity, and minimum angular separation cuts

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Single-arm Compton

Used same procedure for selecting double arm Compton events with exception of:

  Select events with 1 cluster

Assume all events are Compton

Figure 7: Sign of single arm Compton events in production run

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Single-arm Compton

Figure 8: Energy Ratio from production run with r > 6cm

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Single-arm Compton

Background decreases with increasing radial cut, but Compton events are also cut out.

Figure 9: Energy Ratio from production run with r > 8cm

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Double-arm Compton in Production Data

Purpose:

To search for double-arm Compton events produced off of the vacuum window of pair spectrometer magnet in production data.

Procedure:

Same procedure for selecting Compton events in dedicated Compton run was used, with the following exceptions: 

Pion invariant mass cut (Z measured from target)

Z measured from window

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Double-arm Compton in Production Data

Figure 10: Elasticity plot with arrow indicating possibledouble arm Compton events at ~ 0

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Double-arm Compton in Production Data

Small peak ~0.135 Gev shows pion invariant mass.

Figure 11: Minvariant mass distribution

)cos1(22121

EEM

21where is the opening angle between the two photons.

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Double-arm Compton in Production Data

After cutting elasticity and pion invariant mass, a distribution with peak around 180º is seen.

Figure 12: distribution with peak~ 180º

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Double-arm Compton in Production Data

Plot was made of cluster energy vs. cluster angle to look for possible indications of double arm Compton events. Two different colors correspond to the two different clusters.

Figure 13: Kinematic correlation between clusterenergy and cluster angle

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Summary

Qualitatively, plot for single-arm Compton agrees with plots shown earlier.

We have good chance to isolate single-arm Compton events, however work is needed to understand how this process can be used for the following two purposes:

 To use this process to monitor Hycal gain  To monitor efficiency of whole experimental setup There seems to be indication of Compton double-

arm events produced off of the pair spectrometer vacuum window.