1 First look on the experimental threshold effects Straw WG meeting Dmitry Madigozhin, JINR

2 The joint noise scan example (data from Michal Koval) for one of the covers Secondary peaks are always at the threshold values when another channel has a main peak! It means a big cross-talks, that affect the threshold setting procedure in some cases.

3 Thresholds setting example: +36 (dashed & thin vertical lines) 100Hz (solid thick) Separately done scan results (data from M. Koval). Fits by the Gaussian with a fixed maximum value (Rais frequency).

4 Why +36 mV ? 1) 7 is somewhere at the middle of good straw noise width, And we multiply it by 5 (5 sigma) = 35 ~ 36 Well, this is too simple :) 2) Actually we control the expected noise — mean value should be under 100 Hz and maximum less than few thousand. Channels without straws straws

5 NA62 data from the 2015 RUNS: ● Run 3925 (threshold = +36 mV) and ● Run 3929 (threshold = + 60 mV) ● Run 3932 (threshold - 100Hz) : «standard» setting, smaller statistics ● With the same firmware version ● Unfortunately with a lot of extra hits — a temporary firmware bug? ● As a reference time we use the time of the HOD «clean» candidate — when there is exactly one reconstructed charged particle in the hodoscope. ● We use the asymmetric Gaussian + Bg for the fit of leading time distribution peak in order to check its width. F(t) = A + B exp( -(t -tmax) 2 /(2  t  2 ) ), where  t  =  0 + k(t-tmax)

6 Some straws still have a splitted end of the leading time distribution. Unfortunately, for these runs with a variable threshold settings we have a huge amount of extra hits. They form a background, proportional to the signal and at least partially correlated to signal. It may be 3-4 orders of magnitude higher than the expected thermal noise. This huge background seems to disappear later with the another firmware versions, so it should be unphysical. OK, let's hope that the peak properties are not much affected by these extra background hits. Chamber 1 from (1-4) SRB 2 from (0-15) Cover 7 from (0-15) Straw 0 Straw 10 Strange background

7 If we require >500 events in the maximum bin, we have something like a map of «preliminary good» channels around the beam. But due to the large unphysical background in these runs not all of the channels are actually well populated with a signal. And muon run is usually a better choise for the maps building. Run 3925 So for the below tests we require more statistics and so we check a more restricted area: Run min. Stat in

8 Effect of the threshold increasing is qualitatively stable — signal is shifted later, peak width  0 becomes larger and sigma slope k becomes smaller. +36 mV +60 mV 36/60

9 +36 mV +60 mV 36/60 Splitted end of the time distribution (imitation of the wire shift) that is present in some channels does not depend on the threshold.

mV 100Hz 36mV/100Hz Difference between the +36mV and 100Hz (variable threshold) in general is much smaller.

mV 100Hz 36mV/100Hz Only rare cases of something like a larger front smearing, but statistically insignificant

12 Few examples: sigma  0 is typically larger for the higher threshold, and the slope (peak asymmetry k) is typically smaller. No big difference between +36 mV and 100 Hz. 00 k +60 mV RO channel +36 mV 100 Hz

mV 100 Hz +60 mV  0 (ns) k k k Fit parameters distributions for the most statistically rich channels (three threshold settings) A visible diffrence between +36 and +60 mV No big difference between +36 and 100 Hz settings. (may be wider 100 Hz distributions due to the smaller statistics)

14 MC simulation with a ~ (+36 mV)  0, k (just to have an idea about our threshold/signal) Monochromatic very slow noise is assumed, it changes randomly the effective threshold Thr for each event by means of the baseline shift: Thr = *(1+0.4 cos(2p * random)) (actually it may simulate some another source of time jitter) Thr Arbitrary units

15 Apart from the general picture: Even for the run 3925 (+36 mV) there are some straw groups with a systematically increased  0 RO channel 11 ns 00

16 Straws with a systematically increased  0 Definitely a cover-related effect : Chamber 1 SRB 3 cover 4 Chamber 4 SRB 0 cover 7 Chamber 4 SRB 7 cover 1 Chamber 4 SRB 7 cover 5 Chamber 4 SRB 7 cover 8 Here Chamber numbers: 1-4 SRB 0-15 Cover 0-15 Chamber 4 Chamber 1

17 Conclusions: 1. The effect of the thresholds increasing (36 mV-60 mV) looks as expected => LHCb-like procedure of the baseline calculation is mainly working. 2. Nothing very dramatic happen when 36 mV -> 60 mV => our threshold +36 mV is not much larger than we thought. Say, it is 10% (not a negligible small). And also some extra time jitter seems to present (may be from the threshold drift). 3. With a present statistics we can not clearly distinguish +36 mV and 100 Hz, as the actual thresholds in these cases are rather close to each other. 4. There are covers (cover-related cables?) with a systematically increased time jitter that increase the leading time peak width.