Transcript B field dependeNce OF ECAL PEDESTALS AND TEST PULSE

ECAL TIMING
Ratios’ Method Basics
• Position of pulse maximum parameterized using the ratio of two consecutive
samples, i.e., R = A(t)/A(t+1)
• R fitted with polynomial function
• Each ratio provides an independent extraction of pulse maximum position (TMAX)
• Final TMAX as weighted (with expected error) average of the different
measurements
20/04/09
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Ultimate Resolution at Test Beam
• Use of high energy electrons at test beam
• Compared two neighboring crystals in the same electron cluster to reduce
systematic effects and extract ultimate resolution of the algorithm
• Single crystal time resolution can be parameterized as a function of effective
amplitude 1/Aeff2 = 1/A12 + 1/A22
noise term
1
 (t) 2  b 2 2  2c 2
Aeff
(36.9  0.1) 2
 (t ) 
 2(0.064 0.002) 2
2
2
A /
2
constant term
• Constant term ~0.1ns both for
endcap and barrel
PLOT: y-axis: time difference spread (sigma
of a Gaussian from fit) between two
neighboring crystals. x-axis: amplitude over
noise (or crystal energy)
Endcap
Impact of Time Synch. On Resolution
• Impact of offline synchronization between different channels verified with test
beam electrons
• Compare two neighboring crystals in the same electron cluster
• Resolution from the difference of time measurements with and without
synchronization of crystals
• O(1ns) improvement. Optimal hardware synchronization together with offline
synchronization crucial to reach ultimate performance in time measurement
PLOT. Time difference between two consecutive crystals fitted with a Gaussian
(7.5-10) GeV testbeam electrons
=0.75ns
After
synchronizing
=0.21ns
Linearity and Resolution with Cosmics
Time measurement performance verified with full ECAL barrel detector
in CMS using cosmics. Cosmic clusters selection refined associating muon
track to cluster position.
Check of time measurement linearity
using two clusters associated to same
muon (top-bottom). Expected time of
flight compared with measured time.
Compared time measurement between
crystals in the same muon cluster. Offline
detector synchronization not yet taken into
account. Photodetector gain x4 the LHC
conditions.
Barrel
y-axis: mean of
measured time
difference.
x-axis: expected
time of flight of
the muon
between the two
cluster positions
y-axis: time diff.
spread (sigma
of a gaussian from
fit) between two
crystals.
x-axis: amplitude
over noise (or
energy of crystal).
ECAL Splash Timing, η profiles
Time measurement is verified with full ECAL detector in CMS using muons from beam splash
events. ‘Nominal’ is the expected ECAL readout schema, which reads out the detector based on
the assumption of time of flight from the interaction point (0,0,0); ‘nominal’ also includes the plane
wave assumption of muons traversing ECAL. Time synchronization is derived from laser pulses
which are delivered by fibers of the same length within a module. This produces the structure
with a modularity of 4-5  intervals.
These measured variations have been used to synchronize the post-splashes data-taking.
PLOT: mean of timing for crystals in the same  ring versus  index. Left: beam coming from
negative direction. Right: beam coming from positive direction. Reconstructed time after
correcting for inter-supermodules phases (red) and the expected ECAL time (blue) are shown.
muons
-Beam
+Beam
t()  t 0 


R 2  z 2   z /c
muons
ECAL Splash Timing, η profiles
Time measurement is verified with full ECAL barrel in CMS using muons from beam splash
events. ‘Nominal’ is the expected ECAL readout delay which reads out the detector based on an
assumed time of flight from the interaction point (0,0,0); ‘nominal’ also includes the plane wave
assumption of muons traversing ECAL. Time synchronization is derived from laser pulses which
are delivered by fibers of the same length within a module. This produces structure with a
modularity of 4-5  intervals.
PLOT. y-axis: residuals of timing for crystals in the same  ring with respect to the expected time
Red: beam coming from positive direction. Red: beam coming from positive direction.
t()  t 0 


R 2  z 2   z /c
ECAL Splash Timing, FED profile
Time measurement is verified with full ECAL detector in CMS using muons from beam
splash events. Here the variations are shown as a function of the FED number (one FED
is a readout unit: a supermodule in EB or a sector in EE). O(2ns) variations are expected
from length of the readout lines. EE+ (FED: 646-654) was expected to have larger
uncertainty for some towers which were timed with HV off. Also the beam from the
positive and negative  side are compared showing a small effect (<0.5ns).
These measured variations have been used to synchronize the post-splash data-taking.
PLOT. y-axis: mean of timing for crystals with the same FED #. x-axis: FED #. Red:
beam coming from negative direction. Black: beam coming from positive direction.
t()  t 0 


R 2  z 2   z /c
Fit vs. Ratios: Beam Splashes in the Barrel
PLOT. Spread of the difference of crystal times from the expected
time, as a function of amplitude over noise (or energy of
crystal). The expected time is taken from the time-offlight, assuming that the particles hit the middle of each crystal.
Ratio Method
SPLASHES IN EE WITH
INTERCALIBRATED CRYSTALS
ECAL Endcaps
response to beam
splashes
Average energy per crystal
in the ECAL Endcaps seen
during “beam splashes”
collected with beams
coming from the EE- side
(top) and the EE+ side
(bottom). Intercalibration
constants are applied
White regions are crystals
masked in the readout
Energy modulations are a
combination of the energy
flow investing CMS and
geometry effects.
In particular, the lower
energy at large radii in the
ECAL Endcap downstream
to the beam direction is
due to the ECAL barrel
shield
STABILITY
Introduction
ECAL response sensitive to variations of:
• Crystal transparency (under irradiation)
• Temperature: ∂(LY)/∂T, 1/M(∂M/∂T) ~ -2%/K
• High voltage: 1/M(∂M/∂V) ~ 3%/V
LY: light yield
M: APD gain
Controls and monitoring:
• Controlled (temperature, CAEN, dark current measurements)
• ECAL response monitored and corrected with laser data
Required performances:
• Temperature stability at the few 0.01oC level
• HV stability at the 10 mV level
• Laser monitoring of ECAL response at the 2‰ level
•A set of reference channels APDref is used to
normalize the event-by-event laser amplitude
variations. One reference APD channel is chosen
arbitrarily for each laser monitoring module
(100 or 200 channels)
• For each channel and each laser sequence
(600 laser events), the average <APD/APDref>
is employed as monitoring variable
• “Stability” is defined as the RMS over all laser
sequences of normalized <APD/APDref>
•Stabilities are computed for each channel
on a period with stable laser conditions
during the CRAFT (from 60 to 100 laser
sequences within 300 hours)
• APDref is chosen as a reference because
of readout problems with PN reference diodes,
which are being fixed
•White regions either lack statistics
(2 supermodules not readout).
Most channels have a measured
response stability below the 1‰
<APD/APDref> stability map in the
(,) plane for barrel laser data

RMS (%)

<APD/APDref> stability for barrel laser data
(projection of the previous stability map: one entry per channel)
Mean = 0.3 ‰
RMS = 0.2 ‰
99.6% of channels with RMS<1‰
99.9% of channels with RMS<2‰
Under stable laser conditions, the ECAL LASER monitoring system
is able to monitor the crystal response with a precision < 1‰
This precision is consistent with specifications (2‰)
needed to achieve the ECAL design resolution
Reminder:
Analysis of ECAL Barrel temperatures using 2 independent set of data
•
One crystal out of 10 is equipped with a thermistor, in close thermal
contact. The thermistors are read out by detector control units (DCU)
•
Every supermodule is equipped with 10 precision temperature probes
(PTM), 2 mounted on the in/out water outlets, and 8 on the mechanical
structures (4 on grid, 4 on thermal screen)
•
Hereafter temperatures from the thermistors and the PTM’s are used
to assess stability
• Nominal sensitivity:
PTM sensors: 0.01 °C
-
DCU measurements: 0.012 °C
Thermistors fine calibration has been computed by comparing DCU measurements
to PTM sensors values, using data from temperature controlled COSMIC Stand.
EB-16, documented replaced VFEs, channels with missing calibrations have been
re-calibrated with the same technique using P5 data.
ECAL Barrel temperature map
Map of ECAL Barrel instantaneous temperatures ( °C) as measured by the thermistors
located on the APD capsules.
In black: 37 missing measurements (broken or not calibrated thermistors).
White spots: EB+7 (inactive), 34 thermistors outside range.
Temperature spread is within 0.2 °C for 96% of the channels. Thermistors
located in ECAL outer borders are on average 0.08 °C warmer.
ECAL Barrel temperature stability
ECAL Barrel Temperatures time evolution during CRaFT, averaging over all the thermistors
and PTM probes:
• thermistors values (black),
• PTM9 sensors on input cooling water pipes (purple)
• PTM1 sensors located on the grid of type 1 modules (red),
• PTM4 sensors located on the grid of type 4 module (green)
ECAL Barrel temperature
spread during CRaFT
Top: ECAL Barrel Temperatures
distribution, measured at the
APD capsules level (DCU
system). The average
temperature is 18.12 ± 0.04
°C, which shows a very good
overall temperature stability
and homogeneity.
In blue, superimposed, are the
temperatures belonging to the
outer borders of the barrel .
The average temperature is
0.09 °C higher than the rest of
the Barrel.
Bottom: ECAL Barrel
Temperatures distribution,
measured at the SM grid level by
the PTM system. The average
temperature is 18.1 ± 0.02 °C, in
very good agreement with the one
measured by the DCU system.
APD capsules
PTM sensors
APD capsules temperature RMS
Distribution of temperatures RMSs for each of the ECAL Barrel thermistors during
CRaFT (logaritmic scale).
Missing thermistors are: the broken/not calibrated (37), few masked during CRaFT
(LV problems).
Peak average RMS is 0.009 ± 0.003 °C. 98% of channels have RMS<0.1 °C.
Values in the right-end side tail are channels affected by some read-out problems.