1. Stopped Muon/Pion Measurements Jim Miller, BU May 2012 UW Test Beam Meeting

2. Possible Measurements with Stopped Muons and Pions For beam normalization: Collect muonic, pionic xray data in singles mode – Ideally muons and pions are done separately in pure beams – Run rate up artificially with a radioactive source to test performance of Ge at high rates – Note that muonic xrays are occurring shortly after the beam flash- what is impact on Ge and can it recover in time? Look at activation gammas following mu capture as alternative to xrays for normalization in Al, looking for contaminant gammas in other materials – Pi activation could confuse us but there are far fewer stopped pi’s than stopped mu’s – Other sources of Al gammas? e.g. e? Walls of cryo?

3. Examples of muonic x ray spectra 3 F.J.Hartman, et al. Z. Phys. A 305, 189 (1982) J. Miller - Director's CD-1 Review Magnesium Lyman Series Aluminum Balmer Series

4. Physics Requirements- Xray Monitor 4 J. Miller - Director's CD-1 Review On the choice of detector type Excellent energy resolution (~ a few keV) Sufficiently large photopeak efficiency (>50%) Ability to tolerate background particles including neutrons and low energy photons Handle potentially high count rates, especially at injection time  n-type intrinsic germanium detector with a fast reset preamp (size > 45cm 3, depth > 3cm) – However susceptible to neutron damage On the location of the detector The detector should only view the target. – good collimation ahead of the detector. Far from the stopping target due to the large xray production rate ~10 10 Hz, the detector must be far from the source, Path from target: low attenuation of xrays A sweeper magnet should be used to eliminate charged particles The detector must be lie beyond the DS magnetic field and enclosure where it can be serviced periodically and annealed to repair neutron damage.

5. Location of stopping target monitor R. Ray - Director's CD-1 Review5

6. 6 Conceptual Design J. Miller - Director's CD-1 Review The Muon Stopping Target Monitor is placed along the axis of the Detector Solenoid, at the downstream end of the end cap steel. End cap shielding Permanent magnet dipole Ge detector 1 mm thick SS window

7. Conceptual Design 7 J. Miller - Director's CD-1 Review Selected specs: Photopeak efficiency at 1.33 MeV = 50% Resolution = 2.2 keV (FWHM) at 1.33 MeV Count rate = up to 10 6 /s at 1 MeV An example of commercially available Ge detector Ortec GMX HPGe detector GMX50P4 with X-cooler II mechanical cooler and a ultra-high count rate preamplifier option

8. Estimated Rates Muon stopping rate ~ 1x10 10 Hz 2p-1s xray production rate ~0.8x10 10 2p-1s xray detection rate in photopeak, assuming 50% photopeak efficiency, 80% through 2p-1s: 1x10 10 x 0.5(photopeak efficiency)x2.8x10 -6 (geometric acceptance)x0.8(BR of 2p-1s)=11000 Hz Estimate of neutron damage: anneal every 1-3 months. This needs more careful study. R. Ray - Director's CD-1 Review8

9. Other Measurements Other alternatives to the xray stopping monitor for flux monitoring – Look at high energy photons from radiative DIO (RDIO) of stopped muons (flux drops fast above 53 MeV, BR 1.4%), also similar photon spectrum from bremsstrahlung in target following regular DIO – Look at flux of photons from RMC (BR quite low but may have higher flux than gammas from RDIO at high energies). Too few stopped muons to see any near 100 MeV, but could also be used to monitor muon stopping rate. – Neutrons from stopped muons- thick target would be fine Could high-E neutrons be used to monitor muon capture rate? – Examine mu+ and mu- decay endpoints for energy calibration purposes. For energy and response function, with stopped pi+ beam: look for 70 MeV positrons from Evaluate possibility of using calibration photons(need thin converter to make e+-e- for tracker) from – Use e.g. Lithium borohydride target (LiBH4), see how clean the 129 MeV peak is. – Use upper edge of pi0 decay gammas for calibration

10. Contaminated Targets Oxygen has a higher endpoint energy than either Al or Ti, therefore the DIO’s can create background Much more serious for Ti than Al With Oxidized targets of Al and Ti, measure relative number of xrays and hence relative number of muons stopped in O compared to Al or Ti (e.g. Al 2 O 3,TiO 2 …)

11. Comments We should limit to one or two measurements for the TRIUMF run – Tune the beam! – Protons (Si wafers) – Xrays (Good germanium detector) Check perfomance of Ge detector in high rate low energy background (use source), no muon coincidence Look for activation gammas in Al, perhaps other target materials Check relative capture rates on Al and especially Ti vs contaminants Normalization of stopping rate Check xray/gamma spectra from likely construction materials that could cause background in xray spectum – Study Al, Si, Ti if enough time. – Or, if the beam is not narrow momentum, just go for the neutrons and xrays in a thick target Longer term – Effects of protons in straws – Neutron flux (neutron detector) – High energy photon spectrum (Large NaI or similar) Photons, ~40-53 MeV from radiative decays of muons in atomic orbit, for muon stopping rate monitoring Photons from RMC (appraoch 90-100 MeV) – With stopped pions Photons from RPC on proton (from capture on LiBH4 or similar, 129 MeV, NaI). With e+e- conversion could be used for calibration Evaluate electrons for calibration from, could use NaI with scintillator coincidence

12. When and Where TRIUMF Sept 1-9. Doubts about beamline functionality and quality of beam. Significant tuning required- will severely hamper physics output for this first run. Try to find better beams at TRIUMF- need low momentum, narrow momentum mu, pi dist to stop in thin target. Make a proposal to use them in Fall or Spring 2013. Make a proposal, on a longer time scale, PSI

13. Conceptual Design 13 J. Miller - Director's CD-1 Review