UM PPS Lab Activities PPS meeting July 18

UM PPS Lab Activities PPS meeting July 18, 2013 Claudio, Curtis, Dan, Riley, Theo

He Mixtures Test Recap • VPE He: CF 4 90: 10 at 730 Torr – small signal (~6 m. V x 100) and slow (~25 rise time) – At 680 V BKG rate << source, but already at 685 V they are close – Efficiency(682 V)=0. 26%, 10 time lower than the worst Ar. CF 4 90: 10 – At 682 V arrival Time jitter larger than 100 ns • VPE He: CF 4 99: 1 at 735 Torr: signal not seen on the scope while varying the HV. – At 335 V current ~ 7μA not stable at least 1 pixel discharging – At 333. 5 V current=0 μA – For HV [333. 5, 335]V current not null but not stable, likely bursts – To be eventually re-tested with the zero attenuation RO card • VPE He: Xe 90: 10 at 731 Torr: Bkgd and source rate very similar (1 V at the time) – Initial voltage when the current is not null 500 V at 505 V bursts – Problem with the long lived Xe metastables • VPE He: Xe 90: 10 at 730 Torr: signal not seen on the scope not even with the RO card without attenuation and 1 m. V/div. Current not null at 308 V • Currently pumping down, sucking and heating VPE to be filled with 90%He 10% CO 2 July 18, 2013 UM PPS Activities 2

Intrinsic Resolution • Basic relationship: σ2 Measured = σ2 source + σ2 intrinsic • The “source” is the convolution of the distributions 1) primary beta’s at the entrance of the gas volume, that’s after the MS in the glass (in principle this should be part of the intrinsic resolution of the panel) Geant 2) secondary electrons from gamma’s radiated by the primary ones, much wider and not irrelevant plot 3) Detailed modeling of the collimated source and all the systematics (asymmetric slit, rotational misalignments, vertical separation collimator-panel, …) affecting either 1) or 2) or both • The “intrinsic” is due to: a) spreading in the glass (we included in the “source”) b) the (pixel) location of the primary electron-ion pair (Riley’s simulation shows a FWHM increase of 300 -400 μm) c) which pixel actually discharges generating a hit (this contribution would require a knowledge of the full E-field, …) July 18, 2013 UM PPS Activities 3

MP 1 Collimated 106 Ru + 8. 75 mm Plexiglas ~1/3 of the hits are not primary electrons July 18, 2013 UM PPS Activities 4

Resolution Open Questions • Why the newer Geant simulations, with a lower energy beta distribution and (hopefully) extra thickness taking into account the metallic electrode and/or dielectric produce a distribution narrower than previous ones ? • How smaller is the width when we go to higher HV? MP 1 filled at 600 torr 90%Ar 10% CF 4 Position scans give at 860 V FWHM~5 mm, at 870 V FWHM~4 mm, at 880 V FWHM ~3. 1 mm. Does higher pressure (forcing higher HV) shrink the typical hit dispersion? • What is the effect of the distance slit-panel? It might affect the width of secondary betas since they are likely produced by gamma conversions near the glass-air interface • How large is the contribution of a misaligned slit? July 18, 2013 UM PPS Activities 5

VPE 99%Ar 1%CF 4 600 Torr 4/20/13 July 18, 2013 UM PPS Activities 6

Different Fits (Re-binned plot) Landau better than Gaussian. but not good yet. Next Crystal-Ball July 18, 2013 UM PPS Activities 7

Channel Gaussian Fit Mean Two classes of channels (same result with the geometrical mean). Variation much larger than the spread to be measured we likely mis-assign the first hit to the wrong channel we need to measure a channel by channel T 0 and correct for it! July 18, 2013 UM PPS Activities 8

Two Arrival Times Trigger Subtracted July 18, 2013 UM PPS Activities 9

Arrival Time Trigger Subtracted In these conditions the trigger time subtraction does not improve the arrival time spread! July 18, 2013 UM PPS Activities 10

Trigger Time 2748 events with Panel hits and Trigger Only 4 with hits and No trigger recorded in the event July 18, 2013 UM PPS Activities 11

VPE 90%Ar 10%CF 4 730 Torr 5/7/13 310 events with Panel hits and Trigger 243 with hits and No trigger recorded in the event. Wrong threshold for the trigger channel? July 18, 2013 UM PPS Activities 12

Arrival Time Trigger Subtracted Only events whit both Panel hit and trigger are present Here the trigger time subtraction helps and σ<10 ns, but still outliers! July 18, 2013 UM PPS Activities 13

Conclusions • He test to be completed (with 10% CO 2). Signals are much smaller and slower than with Ar as host gas. So far the only working mixture is with 10% CF 4 • The panel intrinsic resolution result needs still some work: secondary beta’s contribution, HV (and P) dependency and estimation of the systematics • The arrival time dispersion quoted so far from the lab experiment with the 106 Ru is overestimated because of the missing trigger time subtraction • Discovered a relevant channel dependence of the arrival time, leading to likely often mis-assigning the first hit of the event. Once measured these channel by channel times and compensated for, we should find smaller arrival time spread • The presence of a large fraction of PPS hits without trigger associated in the event should be understood July 18, 2013 UM PPS Activities 14

Arrival Time Per Channel July 18, 2013 UM PPS Activities 15

Two Classes Much Closer July 18, 2013 UM PPS Activities 16