Luminosity Monitor Status / Beamplug Issues Mark Pitt, Virginia Tech

1. Luminosity Monitor Status / Beamplug Issues Mark Pitt, Virginia Tech • Positioning upstream luminosity monitors so they have the same rate-weighted target distribution as the main detector events • Linearity studies • Light yield studies

2. Luminosity Monitor Locations downstream lumis upstream lumis • Downstream lumis (eight of them) • small angle (0.7o) – primarily used as “null asymmetry monitor” to monitor helicity-correlated beam properties • will not have acceptance for full target due to “one-plug” beamline design choice • Upstream lumis (eight of them, or four if budget gets tight) • large angle (9-12o) – primarily detects Mollers – insensitive to beam angle, energy changes • will be used as target density fluctuation monitor

3. Upstream Luminosity Monitors as Target Density Monitors Ideally, the distribution of detected events for the luminosity monitor will be the same as for the main detector (shown above). In practice, this is somewhat difficult.

4. Plugs and Beamline Reminder We are hoping to compare three scenarios: 1 plug 2 plug gun barrel With gun barrel, the beamline / shielding through the minitorus region will be smaller to stop everything that would hit upstream of the end of the QTOR pipe

5. Proposed Upstream Luminosity Monitor Location Locate the upstream luminosity monitors on the upstream face of the primary collimator; they will detect primarily Mollers at this location. Rates at either location 1 or 2 would be ~ 29 GHz, giving 6 times smaller statistical error than main detectors.

6. Lumi target distribution at upstream location Lumi distribution – location 2 Lumi distribution – location 1 Lumi distribution – location 1 - vacuum Main detector distribution

7. Cause: multiple scattering of Mollers Multiple scattering of 20 MeV in electron in : 4 cm of liquid hydrogen ~ 2.1o 3.5 m of air ~ 3.5o

8. Small Angle Luminosity Monitors The detector cups will be deep enough to allow access to three different angle ranges r = 15 - 18 cm .5 - .6o r= 18 - 21 cm .6 - .7o r = 21 - 24 cm .7 - .8o

9. Lumi target distribution at downstream location – 1 plug case Lumi distribution – .75o location Lumi distribution – .55o location Lumi distribution – .65o location Main detector distribution

10. Lumi target distribution at downstream location – 2 plug case Lumi distribution – .75o location Lumi distribution – .65o location Lumi distribution – .55o location Main detector distribution

11. Reminder: Luminosity Monitor: Contribution of Al window Contribution of aluminum windows to main detector signal is ~ 1% for 3.6 mil aluminum end windows. Only at large angles is contribution to luminosity monitor signal the same. So downstream lumi is not perfect either.

12. Recommendation • Go with one tungsten plug beamline design BUT don’t design out the • possibility of a two-plug solution for the future. • If a target boiling “normalizer” is actually needed in the experiment, • then a two plug + downstream lumi solution MAY be the best.

13. Luminosity Monitor Components • The luminosity monitors will consist of: • small (4 cm x 10 cm x 2 cm and 3 cm x 5 cm x 2 cm) quartz blocks with an angled edge • air light guide (Anolux Miro IV PVD) • Hammamatsu R375, 2 inch, 10 stage, bialkali photomultiplier read out in “photodiode mode”

14. Quartz + light guide photon yield tests • Undergraduate Kevin Finelli is just beginning light yield tests of quartz and quartz + light guide combinations with cosmic ray setup. • Graduate student John Leacock is starting GEANT4 simulations of these; he will focus on the luminosity monitors for the hardware part of his thesis.

15. Linearity studies – photodetector only <pe> ~ 29 pe ~ 3 ? <pe> ~ 7 pe ~ 4 5 cm x 2 cm x 1 cm quartz coupled directly to PMT 5 cm x 2 cm x 1 cm quartz with 30 cm long air light guide Results imply ~12% transmission in air light guide, comparable to ~ 15% seen in similar size light guide by Hicks, et al. NIMA 553 (2005) 470-482. We still have many further optimizations and tests to do.

16. Linearity studies – photodetector only Use Mack/Gericke 2-led technique to test linearity of photodetector alone (in “photodiode” mode) • Measurements plagued by instability in AC cathode current • Can only demonstrate linearity of of ~ 0.2% near operating point. • In principle, 1% non-linearity is good enough  (1%) (.1 ppm) ~ 1 ppb = 10-9

17. Upcoming Work July - Sep. 2007: - continue simulation/optimization of light guides and quartz - finalize quartz/air lightguide dimensions as beamplug/beamline design finalizes late fall 2007: - place orders for PMT’s and quartz spring – summer 2008: build and test luminosity monitors In coordination with JLAB, need to remake the “cups” for the downstream lumis and engineer how the upstream lumis fit into the target region design. Manpower: - Kevin Finelli (undergrad for Spring/Summer/Fall 2007) - John Leacock (graduate student has joined as thesis student)

19. Budget • Newly projected budget based on recent quotes (and upgrading to 2 x 8 lumis • rather than just 8 lumis) • Quartz (~ $1311/bar, 20 bars) $26000 • PMTs (~ $1198/tube, 20 tubes) $24000 • Electronics (to JLAB/TRIUMF) $15000 • Misc. (bases, air light guides, etc) $ 5000 • total $70000 (original budget = $15000) • Due to some other savings my NSF grants should still be able to manage this; • if I can’t quite do it all, I would likely cut the upstream lumi to 4 lumis (instead • of 8) • Would also like to try to squeeze out a little bit of money for useful additions: • remotely-controlled shutters to compare rate in PMT to rate from Cerenkov • remotely-controlled linear translation to move one of the downstream lumis • radially to find optimum position; rest would be set by hand