Downstream PID update - How cooling section affects TOF measurement

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

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 pt . • Resulting purity • Summary

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 pz 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. 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. Monochrome pencil beam • In order to reduce potential sources of fluctuation, using a pz=200 MeV/c, pt=0, on z-axis, starting after first tracker. • After 1st vacuum window: dE = -0.1±0.1532 MeV. • After 1st absorber window: dE = -0.2±0.188 MeV. • After 1st absorber: dE = -11.3±1.045 MeV. • After 1st 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. Energy loss in liquid hydrogen • J. Phys. G. Nucl. Part. Phys. 29 (2003) 1701-1703: • dE = 4.64±0.65 MeV cm2/g for muon at 180 MeV/c, 10 cm H2. • 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(<n>±sqrt(<n>)) • -> There average number of interactions is <n>=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. 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 pt/pz… • …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. 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 pz band.

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.