1. Trigger operation during 2007 run
D. Nicolò
University of Pisa & INFN, Pisa
(on behalf of Trigger group)

2. Outlook System overview m->eg trigger and related
Hardware
Firmware
DAQ
m->eg trigger and related
Selection criteria
Rates & efficiencies
Statistics
FADC linearity
Calibration triggers a
(p,g) p0
What next
July 19, 2019

3. System overview Tree structrure made of LXe TC DC NaI+pre-shower
Type 1 boards (100 MHz sampling)
216 channels from Inner PMTs fanin 1x1
Lateral and Outer PMTs x1
60 channels from TC bar PMTs x1
TC fiber APDs x1
32 channels from DC inner wires x1
outer wires x1
9+4 channels x1
~ 600 channels, 40 boards
Type 2
5 intermediate-layer boards
1 top-level board (master)
Ancillary
5 boards for control signal (CLK, SYNC, START, STOP) distribution
Type 3 (auxiliary digitizers)
640 channels (20 boards) for digitization of 1x1 output from LXe PMTs
System completed and fully operating during 2007 run (all channels working!)
LXe TC DC
NaI+pre-shower
July 19, 2019

4. Final trigger list trig.# name conditions
0 MEG QLXe > QTH && D < DN && |T| < TWN
1 MEG-Q QLXe > QTL && D < DN && |T| < TWN
2 MEG-D QLXe > QTH && D < DW && |T| < TWN
3 MEG-T QLXe > QTH && D < DN && |T| < TWW
RD-narrow QLXe > QTL && |T| < TWN
5 RD-wide QLXe > QTL && |T| < TWW
6 p QLXe > QTH && QNaI>QN && |T| < TWN
7 p0-pre-shower QLXe > QTH && QNaI>QN
8 NaI QNaI > QN
9 LXe-high QLXe > QTH
10 LXe-low QLXe > QTL
11 CW QTL < QLXe < QTH && |T| < TWW
July 19, 2019

5. meg trigger and related
Operated from 15 to 17/12
(run , ~ 25 h live time)
Collected ~ 1.1x106 events (1/4 of which with trigger 0)
Prescaling adjusted in order to have almost equal event sharing
Rates in agreement with expectations
Trigger ~ Hz 40 MeV threshold)
~ Hz 35 MeV )
~ Hz (only up/down e+-g correlation)
~ Hz (DT = 20 ns)
~ Hz (no e+-g correlation, DT = 20 ns)
~ Hz (no e+-g correlation, DT = 40 ns)
July 19, 2019

6. g-energy efficiency Rg ~ 7x103 s-1 @ Eg > 45 MeV
Obtained from ratio of triggered/unbiased off-line spectra
Rg ~ 7x103 s-1 @ Eg > 45 MeV
July 19, 2019

7. Almost fully efficient (e > 0.9 @ 90% CL) at the end-point
g-energy efficiency
Low threshold
High threshold
Almost fully efficient (e > 90% CL) at the end-point
July 19, 2019

8. Timing coincidence efficiency
Obtained from
Radiative Decay
B(p,g)C
Cosmic Rays
Trigger on LXe alone
Ethr  30 MeV
T-reconstruction in 2.5 ns ticks
Rm = 5 x 106 s-1
July 19, 2019

9. LXe-TC timing 1 = 10 ns CR B(p,g)C (background free!) DT
4.4 MeV
11.7 MeV
Fluctuation sources:
algorithm ~5 ns (each)
tof spread ~3 ns (e+), 1 ns (g)
 DT (FWHM) ~ 18 ns  e (20 ns) = (80  5)%
Dt (10 ns)
July 19, 2019

10. Direction match zT (cm) zT (cm) log(Q1/Q2) log(Q1/Q2)
no DC-info used at trigger-level (latency too long)
LUT to associate (Xg, pe+ )  e+-hit on TC
based on MC so far  DC-tracking needed to evaluate efficiency
g-position by max PMT in LXe
e+-position by charge asymmetry in TC PMTs
6-bit resolution for Q
Off-line
On-line
zT (cm)
zT (cm)
zT obtained by DRS timing info
log(Q1/Q2)
log(Q1/Q2)
July 19, 2019

11. Trigger for LXe calibrations
gs from CW reactions
B(p,g)C (used for both energy and timing)
Li(p,g)Be (see G. Signorelli’s talk)
a-events from wire sources
Based on patch enabling capability
Wire identification
PSD not available for 2007 run
(a,g) pulses not separated by off-line analysis
Scintillation (excitation) decay time longer than expected  worse separation also by DRS
Used to be better in the Large Prototype
Possible hint at ionization quenching?
p0 from CEX reaction
July 19, 2019

12. a/g separation in the LP
TRG waveforms recorded during 2003 test-beam at pE1
July 19, 2019

13. Dependence on purification?
now
2003 run in LP
a-run
p0-run
Run 9001
Run 7260
Q/A
g-peak is lower with larger absorption
a/g separation is poorer
Final ratio is <Q/A>|g/ <Q/A>|a = 1.25  0.02
(used to be 1.93  0.02)
July 19, 2019

14. CEX calibration Started from 18/12 to 21/12
(runs , 40 h live time)
Collected ~ 1.3x106 events (~ 2x105 with preshower)
Max PMT to obtain g-direction to LXe
define collimation on a 2x3 PMT window
Back-to-back correlation
with NaI in 4 positions
Data taken in different beam
conditions
LXe single rate from
1 MHz to 100 kHz
@ E>30 MeV
Pb collimator
July 19, 2019

15. online reconstruction
CEX spectrum in LXe
LXe alone, high intensity
LXe && NaI, medium intensity
LXe && NaI, low intensity
online reconstruction
July 19, 2019

16. Towards 2008 run Hardware construction over
Analysis of 2007 data in progress
Trigger rates in agreement with expectations
Trigger efficiency evaluated for
Eg close to 100%
DT around 80% (to be improved by better timing reconstruction)
Direction (in progress)
Pending questions
(a,g) separation and a-trigger
Good performance as a digitizer system for off-line analysis
linearity guaranteed up to 130 MeV  good for energy reconstruction
timing resolution at level of 1 ns
Firmware upgrades
Readout speed-up
Data compression
Q,T algorithm refinements
July 19, 2019