1. 1 Downstream PID update - How cooling section affects TOF measurement Rikard Sandström PID phone conference 2005-09-06

2. 2 Outline Today’s talk is about how energy loss affects TOF measurement. –A TURTLE beam (real beam). –Pencil beam, monochromatic. –Comparing with another experiment. Predicting TOF using trackers. –Now also corrects for p t. Resulting purity Summary

3. 3 A new beam Got a new beam from Kevin Tilley. –TURTLE result (as close to reality as possible). –Interfaced to G4MICE at downstream surface of TOF1. –Should be a diffuser as well, not working yet. –Kevin had filtered out all events which would not be cooled. I.e. very narrow p z spread. –The RMS in time of flight at is 227.6 ps. –Particles start with E = 244.1±1.146 MeV. After diffuser & first tracker: E = 241.9±1.264 MeV. After first vacuum window: E = 241.8±1.272 MeV. After first absorber window: E = 241.7±1.277 MeV –pz = 215.9±1.573 MeV/c

4. 4 Energy loss in cooling section The beam loses in the first absorber dE = 10.9 MeV, and the RMS of the energy is then 1.695 MeV. –The dominant source of energy straggling! –After one cooling section (absorber+RF) the net energy difference is dE = -0.6 MeV and the RMS of energy is now 1.712 MeV. The whole cooling section changes energy from E = 241.8±1.272 MeV to E = 230.0±2.384 MeV. Why worry about energy loss RMS? –1 MeV difference at 200 MeV/c is a tof difference of 28 ps after 6 meters. (Larger than TOF resolution.) –Does the large RMS make sense? –If so, do we need a 25 ps detector resolution?

5. 5 Monochrome pencil beam In order to reduce potential sources of fluctuation, using a p z =200 MeV/c, p t =0, on z-axis, starting after first tracker. –After 1 st vacuum window: dE = -0.1±0.1532 MeV. –After 1 st absorber window: dE = -0.2±0.188 MeV. –After 1 st absorber: dE = -11.3±1.045 MeV. –After 1 st RF linac: dE = -1.3 ±1.118 MeV. –After all cooling channel: dE = -13.4±1.983 MeV. => dpz = -15.5±2.29 MeV.

6. 6 Energy loss in liquid hydrogen J. Phys. G. Nucl. Part. Phys. 29 (2003) 1701-1703: –dE = 4.64±0.65 MeV cm 2 /g for muon at 180 MeV/c, 10 cm H 2. –I think they mean standard deviation when they say RMS. That is dE = 3.285±0.4602 MeV/(10 cm). Assuming Poisson process (variance = mean), –dE = a( ±sqrt( )) –-> There average number of interactions is =50.96, at a=91.06 keV each, for 10 cm. Using this, we arrive at dE = 11.50±0.86 MeV for 35 cm. Previous slide gave dE = 11.3±1.045 MeV, windows included. –Used 200 MeV/c, not their 180 MeV/c. Conclusion: The energy loss RMS makes sense!

7. 7 Error on expected TOF As Yagmur pointed out, the incident angle at the absorbers affects time of flight. If very low angle my method works well, but there is clearly need for a more sophisticated tof expectation method. I made a polynomial fit on the error as a function of p t /p z… …voila, error on expected tof = - 8.7±73.1 ps ! –I doubt we can do much better Remember, this is using truth information for both trackers and tofs.

8. 8 PID with this improvement Very good pid, however… This is really a dream scenario –No diffuser. –Truth info from tracker. –Truth info from TOFs. –Narrow p z band.

9. 9 Summary The problem of energy straggling in liquid hydrogen causes irreducible uncertainty for TOF measurement. –Confirmed by comparing with another experiment. –Fluctuations in energy gives larger error than detector resolution. To predict TOF using trackers, a method using angle of approach is needed. –A simple fit reduced the error on expected tof to -8.7±73.1 ps.