Timing Counter Status

1
Timing Counter Status
Timing Counter 2008 configuration Monitoring and
Calibrations Timing resolution (TC and MEG)

• G.Cavoto
• INFN Roma
• Feb 18th 2009

2
Timing Counter (TC)

• Two sectors, DownStream and UpStream, each
  with
• 15 scintillator bars readout by PMTs (TICP)
• Trigger
• Measure time,?? and z
• 256 Scint. Fibers readout by APDs (TICZ)
• (Meant for) geometrical trigger selection
• Measure z

3
Hardware upgrades
Reduced APD noise Light tight Tedlar foil added

• New EVAL bag for N2
• Very tight!
• He concentration at few times atm. bkg level

Some maintenance work (fix connectors,cables) Bot
h US and DS TC remounted in late spring
4
TICZ readout tests

• After installation, test with pass-thru
  cosmics

US TICZ

• All analog channels (8 APD in one ch.) show
  good signals!
• US TICZ digital readout working!
• DS TICZ worsened by higher environmental noise
• 3 (out of 8) DS TICZ readout sections failed
  during the 2008 run
• on-board hardware problems fixing deferred to
  2009

fiber
5
Laser system

• Additional timing calibration device
• Providing 532 and 266 nm light at 50 Hz
• Optical fibers distribution to TC bars (and XEC)
• Problems in operation
• environment temperature became too high ? cavity
  unstable ? drift in the feedback signal
• ? electronic saturation, damages of optical
  components and electronics.

• For 2009 run
• Proper box with actively stabilized temperature
• Retuning of cavity
• - New feedback electronics

6
PMT gain equalization

• Select Michel positron hitting bar
  center(magnetic field ON)
• Change HV to havesame average chargefor PMTs of
  the same bar

Before
After
7
TC measurements
e
PMT1
PMT0
h
L
amplitude of PMT signal
effective velocity
T time of positron at the impact point on
first hit bar (connected to the positron track
from DCH) h impact point along bar length (z
direction)

• DRS3 digitization for Double Threshold
  Discriminator NIM pulses
• t0 and t1 extracted with waveform template fit to
  NIM pulses.
• Checked with cross-correlation method (optimal
  filtering).

8
TC calibrations

• Timing with DTD NIM signals

9
Double and triple hit events
bar
On events with three adjacent hit bars
(triples) minimize the differences (for all the
bars)
e
TC
TA
1st bar
TB
z
On sample of two hit adjacentbars (doubles)
test time walk correction (c0 and c1)
ns
10
TC time resolution
Estimate of single bar time resolutionAssuming
the two bars to have the same intrinsic time
resolution

• Upper limit on average time resolution (?) in
  60-90ps range
• Includes effect of DRS digitization (10 ps)
• (estimated sending same signal to two DTD
  inputs)

11
TC time resolution stability

• Same TW calibration constants
• Stable over timeno need of different sets of
  constants

Runs 24xxx Runs 25xxx Runs 26xxx Runs 27xxx Runs
29xxx Runs 30xxx Runs 31xxx
12
Inter-PMT offsets

• Dedicated cosmics runs taken in different
  down-time periods
• Select event with 1 or 2 hit bar
• Assume symmetric distribution along the bars

Most of the bars have this flat distribution
t1 - t0 ns
Data taken in different periods very consistent
(TICP very stable!!!)
13
MEG physics runs TC hitmap
After
Before
US
DS
t1-t0 ns
t1-t0 ns

• Distribution nicely justifies
• Need veff to have the correct z scale

14
Effective velocity with TICZ
Pass-thru cosmics, 2 hit fibers (clusters)
expected
Single-cluster inefficiency 27 due to cosmics
geometrical inefficiency dead/hot fibers (5)
Using
Bar16
veff (cm/ns)
Syst err.1.5
zbar-zfiber (cm)
15
Inter-bar offset extraction
Boron events 4.4MeV (XEC) and 11.7MeV(TC)
Bar14 -signal -bkg (rescaled)
Bar17 -signal -bkg (rescaled)
?T??ns
?T??ns

• Gaussian fits.
• Cosmic background evaluated in runs with no-beam
  and same trigger requirements (TC XEC)
• Syst error on calibration constants at 50ps
  level

16
Inter-bar offsets monitoring
Bar15 change in DRS board
?T?? mean ns
Sep
08/10
Weekly monitoring (periodic DB updates)
13/10
time
20/10
25/10
10/11
24/11
01/12
relative to bar 17
bar

• No clear trend vs time
• Relative offsets stable

17
DCH-TC match hitmap

• Extrapolate tracks from DCH to TC bars
• Given a track and a TC bar hit matching
  efficiency is 91
• Some data/MC discrepancy

cm
18
MEG absolute time offset

• Dalitz ?0 events
• Same topology as signal !
• Gamma/positron energy range (can be chosen) same
  as for signal
• Worse resolution due to LH2 target Comparison
  with signal is not exact

Bar17 µ 26.060.01ns ? 26710ps
Centre of signal window
Control sample (flight length correction) MC
validation
ns
19
Timing systematics check
Dalitz after calibration with Boron
Dalitz before calibration
?T ??(e) ns
?T ??(e)-?T ??(e)(bar17) ns
Boron (E?4.4MeV)
Dalitz (E?gt45MeV)
Relative to bar 17
bar
bar
Residual time walk effecton XEC timing
Residual inter-bar differences (different target
for ?0 Dalitz)
20
Summary

• TICP very stable over the 2008 run.
• TICZ 13 out of 16 sectors working.
• Calibration strategy developed and successfully
  applied to data.
• Data monitored during data-taking.
• Some fine-tuning still needed
• Residual bar differences
• Detailed data-MC comparison

21
Outlook for 2009

• Detector activity
• New APD electronics
• Shorter shaping time to fit trigger timing
• Currently prototyping new el. boards
• LASER
• Upgrade of TC slow control
• On track for a 2009 data-taking period
• Data analysis
• Calibrated TC data and TC simulation available
  for MEG analysis
• MEG timing measurements well underway

22
Back up
23
New APD electronics
To insert APD into trigger

• Requirements
• fast signal ( 3-5 times faster) ? 15ns
  achievable.
• better EMI immunity
• Implement redundant schemes for the command
  transmission (I2C)
• Improve over all settings capability ( on board
  test /calibration signal,)
• Bread-boarding is started, final design of the
  prototype board will be sent for the production
  by Dec 08.

Test pulse response
Move Amplifier to the APD board and/or
differential input