Stony Brook Update: Scintillation, Statistics & Status

1. Stony Brook Update:Scintillation, Statistics & Status T.K. Hemmick for the Tent Crew

2. HBD Principal Performance Parameter • The HBD’s primary job is to separate one from two primary electrons. • The mechanism of that separation relies upon pulse height. • Resolution in pulse height is therefore a critical issue to understand. • Monte Carlo simulations typically include two sources of pulse height smearing: • Original ionization statistics. • Single electron gain fluctuation. • We can also include scintillation & see.

3. Well known results w/o scintillation… • Overlay with equal statistics of a Poisson with mean 30 and a Poisson with mean 60. • Very clear separation as we would expect. • However, response to a single p.e. is not correct. • Here each photo-electron has been smeared with an exponential of mean one. • This would be a good approximation for gain process. • Separation is still excellent. What if we were to add scintillation to every event?

4. Simple-minded scintillation. Raw Stats Gain Fluct • We assume the worst case of one photo-electron per pad and get the distributions above for response. • The plot on the left is just Poisson with a mean of 7 (7-pad sum). • The plot on the right is after each photo-electron is assigned an exponential gain response.

5. Total Response Total Blk: w/o Scint Magenta: With Scint • The total response is the sum of the scintillation and the Cerenkov light. • We can make a “corrected” spectrum by simply subtracting 7.0 from the total of these and compare this response with the ideal response to zero photo-electrons. • If we had a mean of 30 photo-electrons the contribution to the effective signal due to one scintillation photo-electron per pad is no big deal at all!

6. Various means… 30 25 20 • For p.e. yields more than 20, the addition of an average of 7 scint photons makes little difference. • Extra blue curve shown for 5 p.e. is the total before the removal of the 7. 15 10 5

7. Testing the Monte Carlo for ArCO2 • Measurements of sigma/mean (in %) for 55Fe in ArCO2 are shown in the left plot. • Expectations including single electron stats (Poisson), gain fluctuations (Exponential) are plotted as a function of collection efficiency in the gap. • Results for ArCO2 are consistent with 100% collection gap efficiency. • Thus, we can understand the width of the peaks of the 55Fe when the gas used is ArCO2 Ideal, sqrt(212)/212 ≈ 7%

8. Move to CF4…WTF?? • First, the distribution of peak widths is very wide. • We don’t understand what parameter is making this distribution change so much (rate, time, phase of the moon, …). • Second, the distribution has a mean value of about 24%. • A width of 24% can be achieved by assuming that the primary collection efficiency is very low (~1/3). • Is loss of primaries the right width-maker…what else could it be? • One thing for sure: • If the width of the pulse height for 109 primaries is 24%, it might be very difficult to separate 30 primaries from 60 primaries. Ideal, sqrt(109)/109 ≈ 10%

9. Other news. • The GEMs are here and we are preparing for production. • We are not finished with the cleaning of the glove box. • We have measurements of a GEMstack removed from the HBD, but compensating for the strange resistor chain is not yet well understood so we will report these results at a later time.