MEG
2008 Run
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Run Coordinator’s
view
Peter-Raymond Kettle
MEG Review February 2009
1
2
X
Situation - Review Feb. 2008
Back to “Square One” - TOTAL Detector DISMANTLED post
2007 Engineering Run - for Maintenance/Repair /Improvement
TCs: Fibre light-leak
+ new N2 Bags + APD
amplifier/electronics
DCs
TCs
TCs
DCs: Support Structure
+ new Target Angle +
HV Investigation
EC
BTS
Peter-Raymond Kettle
Calo: new HV
Feed-thro’s + LN2
Cooling-pipe mod.
(heat-load) + lnvest.
LXe Light-Yield mod.
Purification system
C-W
DS-EC
+ IS
Calo.
MEG Review February 2009
2
2008 Beam Time & Constraints
2008 Run Goals:
final beam operational conditions to be tuned/optimized {(m-, - & p-beams C-W)}
Full set of detector calibrations + optimization/exploitation of various techniques
optimized detector/trigger settings
as fuller set of information as possible, necessary for Data-analysis
+ “Long-term” Goal of understanding our Detector
End-of-Shutdown
Max. Expectation
MEG-Physics Data
~ 16 weeks
Peter-Raymond Kettle
MEG Review February 2009
3
Planning & Organization
Basic Run Layout
Parasitic Run
Beam optimization
in parallel with
Debug, Tune &
Calibrate
Full Run Part I
CEX Run + Trigger
Setup + calibrations
Detector monitoring
Full Run Part II
Pre-physics data check
Physics Data
(MEG + RD)
Run Coordinator
2 Shift
Coordinators
 7 weeks tot.
13 Shift Coordinators
 2 weeks/person
Parasitic Run
Total of 62 persons for 959 shifts (Full Run Only)
to allow for flexibility + continuity:
Staggered & Overlapping shift system
Daily Run Meetings (on-site)
Weekly Video Run Meeting (Collaboration-wide)
later, weekly Video Physics Analysis Group Meeting
Web-based Schedule + Shift list + “On-call” List
Peter-Raymond Kettle
MEG Review February 2009
12 Hr Shifts:
1 DAY SHIFT (Beam Group) 10:00 – 22:00
1 NIGHT SHIFT
max.
22:00 – 10:00
1 Shift Leader Nights
Manned by Detector Experts
Full Run
8 Hr Shifts:
1 DAY SHIFT
1 EVENING SHIFT
1 NIGHT SHIFT
07:00 – 15:30
15:00 – 23:30
23:00 – 07:30
1 Shift Leader + 1 Crew Member
4
Organization In Practice
Detailed
Information Access
•
• “How to” information database for shift crews on MEGWiki
• fully searchable & cross-referenced Electronic
Logbooks for all sub-detectors & Run shift-crews
• comprehensive electronic Hardware/Software
check-list for shift crews
• easy web-based experiment/instrument
control for shift-crews
(e.g. Beam Line – magnets, separator)
push-button changing of rate with auto
magnet/slits hysteresis cycling
Peter-Raymond Kettle
MEG Review February 2009
5
Detector
Synopsis
TCs
DCs
TCs:
• Fibres working, problem
DAQ control of DS fibres
• Laser temp. control problems
DCs:
• HV instability problems with
Calo:
• HV feedthroughs replaced
• Liquid & Gaseous purification
success LY-behaviour needs
further study + PM gain stability
air-doping still persist!!!
• proved “Essential Tool”
Li (17.6, 14.6 MeV)
+ B (4.4, 11.7, 16.1 MeV)
lines – Energy + Timing
Calo.
Peter-Raymond Kettle
NaI:
C-W:
C-W
MEG Review February 2009
• New APD preamps
• automated mover
• temp. contolled APDs
• E/E ~5-6% ()
NaI
6
Trigger + DAQ
Trigger
+ Splitters
Online
Cluster
Megonxx
Multi-trigger implementation:
Final Complement of 29 Triggers implemented
multiple & pre-scaled (MEG=11, RMD=5)
Single & Coincidence detector triggers crucial
for monitoring/Calibration
DRS v2 + part v3
e.g. 7Li, 11B C-W, , CR, LED – RMD, 0,0-Dalitz
CEX software collimators LXe responce
Direction matching  me (planned TC fibres)
too slow  still XEC PMT-index + TC-bar(index,z)
where z from bar charge-ratio
Trig. Monitoring via (cyclic-buffers)
lcmeg05
lcmeg04
DRS3 – partly implemented (clock signals, temp eff. Etc.)
lcmeg03
lcmeg02
lcmeg01
Limits:
• DAQ/DRS readout limited by VME (83MB/s)
~ 30 events/s full waveforms (threading)
• Online (backend) 2TB storage
• Offline (lcmeg) 64 CPUs + 104TB disk
• “Lazylogger” autocopy Online Offline
factor 2 compression offline
Peter-Raymond Kettle
MEG Review February 2009
Offline
Cluster
lcmeg
7
Arsenal of Standard Calibration Tools
m radiative decay

e Lower beam intensity < 10
m
Is necessary to reduce pileups
n
n
7
Better t, makes it possible
to take data with higher
beam intensity
LED
Laser
(rough)
relative timing
calib.
< 2~3 nsec
A few days ~ 1 week to get
enough statistics
0 
PMT Gain
Higher V with
light att.
- + p  0 + n
Can be repeated
frequently
0   (55MeV, 83MeV)
- + p   + n (129MeV)
Laser
10 days to scan all
volume precisely
alpha
(faster scan possible
with less points)
e+
LH2 target

MEG Detector
Standard
Calibrations
Li(p,)Be
LiF target at
COBRA center
17.6MeV 
Bi
Tl
Peter-Raymond Kettle
Cold GXe
LXe
e-
Proton Acc
K
PMT QE & Att. L
F
Li(p, 1) at 14.6 MeV
~daily calib.
Li(p, 0) at 17.6 MeV
Can be used
also for initial
setup
Nickel 
Generator
o
off
quelle
n
Illuminate Xe
from the back
Source (Cf)
transferred by
comp air  on/off
MEG Review February 2009
9 MeV Nickel γ-line
NaI
3 cm 20 cm
Polyethylene
0.25 cm Nickel plate
8
New & Improved Calibration Techniques
Multiple calibration techniques proved Essential for deconvoluting complex effects
>16.1 MeV
>11.7 MeV
4.4 MeV
11.7 & 4.4 MeV s Coincident in time (94%)
& no angular correlation
Li used for E-calibration, B can be used for Δtabs(LXe-TC)
or Δt(TC-TC(inter-bar))
Energy deposit in XEC
(1) New Lithium TetraborateTarget (Li2B4O7) for C-W: - advantage both Li- & B-lines
simultaneously available without large X-section of F (~ 6-7 MeV), from LiF
4.4 and 11.6 MeV
Compton Edges
“Energy” deposit in TC
(2) New timing calibration technique during CEX: - use Dalitz decay for
intercalibrating LXe & TC detectors by tracking e+ in DCs (0 → e+e- )
used successfully for measuring absolute Δt(LXe-TC) of reference TC-bar, can
then intercalibrate bar using Boron e.g.
LY
(3) Am/Be – neutron source as a source
Am/Be ≡ Li
of 4.44 MeV Gammas from 2+ state of 12C*
via 9Be(α,n)12C
Peter-Raymond Kettle
MEG Review February 2009
9
Calibration Techniques cont.
(4) Use of tuned monochromatic positron beam being investigated as a means of
e.g. studying our positron spectrometer tracking efficiency vs. emission angle or
momentum, with high statistics, in a momentum range equivalent to real MEGconditions!!!
Mechanism: positron-Nucleus elastic scattering from light nuclei at around
Pe ~ 50 MeV/c “Coherent”
nuclear recoil, spin-effects, magnetic terms all ~ negligable
nuclear form-factor introduces a small effect
X-sections “well known” basically “Mott-scattering”
Reality:
• MEG beam can be tuned to give ~ 50 MeV/c e+ with a max. rate of
~ 8· 108 e+/s at 2mA proton current with ΔP/P ~ 7% FWHM
obviously would reduce ΔP/P to achieve “monochromaticity” though at the cost
of rate.
• Wien-filter does not work at this momentum to sufficiently separate e+ from m+
but a 2mm CH2-degrader at the collimator system in front of BTS DOES!
Carbon target ρ ~ 2.1 g/cm3 t < 1cm thick, and 107 e+/s
Integrated X-section: 30° < Δθ < 120° & Δφ =   2.5 mbarn  ~ 1300 events/s
Peter-Raymond Kettle
MEG Review February 2009
10
2008 Run Conditions
(1) New Target Angle: - modification DC Support Structure
optimal @ ~ 21° to match beam stopping distribution etc.
Prior 2008 limited by DC Support structure to max. 13°
• Conventional
= (20.6 ± 0.2)°
• Photogrammetric
(outside COBRA) = (20.4 ± 0.2)°
• Photogrammetric
(inside COBRA) = (20.3 ± 0.3)°
 - target
inclination
angle
Target Inclination 2008  = (20.5 ± 0.3)°
(2) Beam Intensities: - apart from “Normal” beam intensity 2 further tunes were
optimized based on standard degrader 300mm Mylar – “Ultra-low” & “High”
Mode
Rm Measured Rate COBRA at 2mA
Rstop Stopping Rate at 2mA (εSTOP= 0.794)
“High”
8.4107 m+s-1
6.7107 m+s-1
“Normal”
3.5107 m+s-1
~ 2.8107 m+s-1
“Ultra-low”
1.5106 m+s-1
~ 1.2106 m+s-1
Measured values at 7% air contamination
1% Air ~ 10mm Mylar degrader - Not compensated for in 2008!!!
Peter-Raymond Kettle
MEG Review February 2009
11
Run Conditions cont.
(3) COBRA He-Concentration: - for DC HV-stability reasons air-doping of COBRA
Environment was necessary
Physics Run Classification:
MEG Data ONLY(before/after DC COBRA test)
96%
He
US-EC
DS-EC
63
70
95%
He
P61,P70, P63
P61,P70, P63
O2-sensor
61
COBRA
62
60
Part1:
11/9
92%
– 20/10 (0100)
35 days
(0100)
93%
Part 2
Part 1
Part2:
27/10
P61 blue
P70 green
P63 red
P60 light
blue
Mean Air-doping (Physics Run Part1 + 2) = 6%
Peter-Raymond Kettle
MEG Review February 2009
– 06/11 (2359) – 23/12
11 + 32.5 days
(1149)
1% Air ~ 10mm Mylar degrader
Not compensated for!!!
12
2008 Beam Time Influences
3 Major factors influenced the maximizing of the available beam time for Physics
Data-taking – such that substantial extra investigation time was necessary 
(1) Calorimeter: 2007 Light-yield << expected both for s & s (Q/A)/(Q/A)~ 1.25
expect LP~ 1.92!!!
Contamination?
new
purifier
• Calorimeter
–
Light-yield
+ PMT
gain
drift installed 2008
Significant time was
invested with
of LY vs. purification time
• Electronics
- monitoring/understanding
Noise + Baseline stability
Using C-W Li, CR,
& LEDs
• s
Drift
Chambers - HV stability Liq.P → Induced Noise on electronics
Liquid & Gaseous & No purification scenarios studied Gas.P → minimal Noise
Questions to answer:
• can one survive without Liq.P for 3 weeks between inter-accelerator shutdowns
and only rely on GasP?
• What happens to LY without any purifications?
Initial Purification May 2008
L-Y
- 0.7%/5 days
s
also CR same response!
s
Liq.P
Peter-Raymond Kettle
Gas.P
No.P
MEG Review February 2009
13
Beam Time Influences Calo.- cont.
• Variations in no Photo-electrons seen…LY changing + ?
• PMT- Gain variation seen vs. Beam rate drastic during CEX
changes of several % possible!! Stable at low rate
• PMT Gain well monitored using LEDs …Reason for instability?
in principle effect already compensated for “zener diodes”!!!
could this be aging?
• Thus frequent LED calibrations used as gain normalization for
light/energy measurements
• time constants for rate-changes measured (beam-blocker)
• therefore in principle all ingredients available for corrections
PM Gain
CEX 
-
Off
Norm
Beam
1/2
LY nearly reached optimal value
LY is constant LY >
CEX
2007
Level
Peter-Raymond Kettle
How does this affect our energy scale
Extrapolated for low-energy low-rate?
MEG Review February 2009
14
Effect on Energy Scale
Rate-dependent effect
For our Photon Energy-scale we extrapolate from
“Low-energy” “Low-rate” C-W data to
“High-energy” “High-rate” CEX pion data
B-B “opened”
What is the rate dependency at CEX-rates?
Not enough LED data taken during intial CEX
~30 mins.
 Hence new “mini-CEX” run at end of December
B-B “closed”
CEX
~ 4% discrepancy from
Extrapolation to CEX energies
before correction from “Mini-CEX”
After?
better but not perfect! More work needed
Peter-Raymond Kettle
MEG Review February 2009
Before Correction
C-W
15
Beam Time Influences – cont.
(2) Electronics: baseline instability as well higher noise content on DRS i/ps
2 reasons found – (i) i/p stages (diodes + resistors)of splitter damaged by sparking from
defective Calorimeter feed-thro’s.
 all boards modified with new higher rated
diodes & resistors changed
(ii) burst-noise suppressed with external shielding of flat-band
calorimeter cables between splitter & DRS
 external shielding added to all calo-cables between splitter & DRS
(3) Drift Chambers: HV-stability of chambers persists, seems to be a time
dependency before onset & seems worsened by CEX pion beam then worsens
with time. Gives a complicated time-dependent e+ detector efficiency
 Air doping + overpressure + gas-mixture investigated during dedicated
combined electronics/Calo./DC maintenance week
100%
Anode Hit-map.
He-ConC.
ΔP(DC-COBRA).
0%
Peter-Raymond Kettle
MEG Review February 2009
16
Beam Time/Data
In view of the complex & overlapping problems that were studied & monitored during the
“Parasitic” & Part 1 Phase of the “Full Run” the following schedule evolved necessitating
a mini-CEX at the end of the period to evaluate the rate dependency during the full CEX,
so that the Calorimeter Energy-scale could be fully determined:
Parasitic Run: 19th May- 3rd July ~ 7 weeks
MEG
2008 Run (4.5
DATA
Taken
Beam
Tests/Tuning
weeks)
Full Run Part 1: 11th July – 31st August ~7 weeks
TBytes CEX 21st July – 31st August (6 weeks)
Full Run Part 2: 1st September – 23rd December ~16 weeks
Pre-Physics Data (~ 3 weeks)
 139 TB
Physics Data Part1 35 Days
MEG Maintenance/Repair ~ 7 Days
Physics Data Part 2 43.5 Days
Mini-CEX
~ 7 Days
DATA
MEG (Runs# 23987- 40997)
 10859 Runs a 2k events
 22.4 M Triggers
 Time 49:18:50:49
RMD (Runs# 23017 – 39963)
 1059 Runs a 3k events
 2.99 M Triggers
 Time 7:05:33:39
Normal Physics Data-taking:
• MEG 11-mixed trigger 6.5Hz Trigger Rate, LT~ 80-83%
• Daily LED-calibration beam “off”
• 3/week Full-calibration LED beam “on” +LED beam “off”
+ C-W (Li) + C-W (B) + s
• 1/week 24Hrs RMD 5-mixed trigger data
Peter-Raymond Kettle
MEG Review February 2009
Total of 139 TB Data
Taken 2008
17
Physics Data Preparation
Analysis Scheme: (Physics Analysis Working Group)
• Data Reduction in form of “Pre-selection”
- use very lose cuts
“Conservative Criteria” (ensure non-biasing)
reduces data to 16% of triggered events
• Incorporate “Blinding” in “pre-selected” data
use “Hidden” Signal-box on parameters E & Te 
directly via MEGAnalyzer with widths
~ ± 4.8 MeV & ± 1.5 ns respectively
• Perform Likelihood Analysis on “final revealed data”
after optimized background study outside “signal-box”
 “side-bands”
“Blinding”
• Probability Density Functions (PDFs) for Likelihood Analysis
obtained partially direct from measurement & partially from MC.
• MC substantially advanced e.g. RMD + radiative corrections etc.
Peter-Raymond Kettle
MEG Review February 2009
18
Conclusions
• With a consolidated effort made by the “whole” collaboration, as well as basically
starting from ”scratch” at the beginning of the 2008 we were able to achieve our goal
of taking “True” Physics Data!
• despite many detector/electronics problems that were encountered we were able to
dedicate 12 weeks out of the expected 16 weeks to “pure (MEG+RMD) Physics Data
• a vast amount of calibration data was taken during the whole 2008 period which
served a as vital input to understanding encountered effects during the run
– this however will continue to serve as a basis for a better understanding of our
detector with on-going analysis
• several factors concerning our hardware led to a non-optimal MEG Detector in 2008
the main issues have been addressed ( DC: HV-stability, Calorimeter: LXe-purity,
PMT gain-stability, TC: fibre incorporation in trigger)
• the most worrying issue is that of the DC HV-stability – this however is being tackled
with a large and dedicated effort by the “detector group” – the experts! and as has
been shown before, especially with “forefront” detector technology such problems
CAN BE SOLVED!
• we still have a lot of work to do & a lot of improvements are still necessary but !!!
the following “Expert” talks will show that the MEG Collaboration has
a lot of dedicated & resourceful means at it’s disposal
Peter-Raymond Kettle
MEG Review February 2009
19