1. Muon pairs in HPS with m+ trigger
S. Stepanyan (JLAB)
HPS collaboration meeting
May 3 – 5, 2017 JLAB
----- Meeting Notes (9/27/11 07:19) ---
Many thanks to organizers for invitation to participate in the conference and give this talk on GPD program at JLAB.

2. S. Stepanyan, HPS collaboration meeting, JLAB, May 2017
Why muons again:
because we can – should work by triggering on m+ only, analogous to e+ only trigger
something new, different backgrounds, no WABs! and different detector response
will complement e+e- at higher masses (for >4 GeV beam energies)
will keep students busy
costs almost nothing
CEBAF
experimental Halls A, B and C
S. Stepanyan, HPS collaboration meeting, JLAB, May 2017

3. S. Stepanyan, HPS collaboration meeting, JLAB, May 2017
Detection concept
m-detectors have been simulated in the past (the most recent studies by Sebouh)
Always detection of m+m- were considered - issues with rates in m- counters (background from interaction of brem-electrons with vacuum chamber walls)
If we can leave with triggering/detecting only m+, detector can be very simple
Concern is (the same as for e+ only case) how good the l+l- pairs are when only l+ is matched with Ecal/muon- hodoscope (accidentals, track quality …)
S. Stepanyan, HPS collaboration meeting, JLAB, May 2017

4. Sebouh’s muon detector
The main issue with the full muon hodoscope was high rates associated with the interaction of brem-electrons with the sides of the vacuum box.
Proposed options for background reduction: modification of the right side of the vacuum chamber and add tungsten shielding plates on the electron side.
S. Stepanyan, HPS collaboration meeting, JLAB, May 2017

5. S. Stepanyan, HPS collaboration meeting, JLAB, May 2017
m+ detector
If muon detector covers only beam left side, no changes to the vacuum chamber will be needed
Detector – 3-layers, few scintillator paddles in a layer, interlaid with absorbers
Trigger rate is expected to be lower than e+ trigger rate
S. Stepanyan, HPS collaboration meeting, JLAB, May 2017

6. S. Stepanyan, HPS collaboration meeting, JLAB, May 2017
m+m- identification
11 GeV beam, BH only
m+m-
p+p-
S. Gevorgyan
Rate of pion-pairs is low, 10% rejection factor (for single particle) should be enough
The largest background is e-p+ (will be problem for the bump hunt but not for vertex analysis)
Some help from Ecal can be expected to ID m-, when possible
S. Stepanyan, HPS collaboration meeting, JLAB, May 2017

7. What muons will add (Sebouh’s plots)
4.4 GeV beam
To conclude, if we want to entertain this idea:
Detector simulations have to be redone using the HPS software
Physics background must understood
Reach must be evaluated with current state of the software
Volunteer(s) will be needed
S. Stepanyan, HPS collaboration meeting, JLAB, May 2017