CMS ECAL 2006 Test Beams Effort
Caltech HEP Seminar
Christopher Rogan
California Institute of Technology
May 1, 2007
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 2
CMS Detector
Crystal ECAL General purpose detector
p-p collision at CM energy of 14 TeV
Goals: Discover the Higgs, new physics beyond standard model, …
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 3
State of the Higgs: 2007
Electroweak fit (w/ quantum corrections) to mH : depends on mW, mTOP
Best-fit value (2007): mH = 76+34–23 GeV
using mTOP = 170.9 ± 1.8, mW = 80.396 ± .025 GeV
Direct search limit: mH > 114.4 GeV
95% CL upper limit: mH < 144 GeV
Low MH < 150 GeV
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 4
ECAL layout
barrelbarrelSuper ModuleSuper Module(1700 crystals)(1700 crystals)
endcapendcapsupercystalssupercystals(5x5 crystals)(5x5 crystals)
Pb/Si preshowerPb/Si preshower
barrel cystalsbarrel cystals
EndCap “Dee”EndCap “Dee”3662 crystals3662 crystals
Barrel: Barrel: ||| < 1.48| < 1.48
36 Super Modules36 Super Modules61200 crystals (61200 crystals (2x2x23cm2x2x23cm33))
EndCaps: EndCaps: 1.48 < |1.48 < || < 3.0| < 3.0
4 Dees4 Dees14648 crystals 14648 crystals (3x3x22cm(3x3x22cm33))
PWO: PbWO4
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 5
CMS ECAL Test Beams 2006
H4 ECAL Test Beam 10 SM calibrated (1 twice, 13600 xtals) Detailed studies of E, behaviour Irradiation studies Energy linearity studies
H2 ECAL+HCAL Test Beam 1 ECAL SM Two subdetector DAQ Wide beam calibration 0 data
H4
H2
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 6
CMS ECAL Test Beams 2006
A wide array of important studies were completed:Electron, 0 and cosmic muon inter-calibrationsEnergy linearity studies Crystal containment correctionsEnergy resolution studiesAmplitude reconstruction optimizationNoise studiesDAQ, Monte Carlo and software studiesOnline laser monitoringCrystal irradiation
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 7
Cluster Containment Corrections
683 703 723
684 704 724
685 705 725
ExampleExample: 3x3 matrix: 3x3 matrix
5x55x53x33x3
Containment effect decreases with the matrix sizeContainment effect decreases with the matrix size
3%
Hodoscope
Resolution: Uniform impactUniform impact containment corrections needed
Measurement in fixed size matrix of NxN crystals Measurement in fixed size matrix of NxN crystals position dependence position dependence of Eof ERECREC
e
1
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 8
Energy Resolution
• Energy resolution ≤ 0.5% at 120 GeV for any electron impact.• Same shower containment correction applied (for all E and all Xtals).
0.5%0.5%
Central impact “Uniform” impact
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 9
Caltech CMS @ ECAL test beams
Caltech leadership in two important test beam tasks:
Operation of the online laser monitoring system
Improving π0 inter-calibration technique using test beam data
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 10
ECAL Laser Monitoring Introduction
CMS is building a high resolution Crystal Calorimeter (ECAL) to be operated at LHC in a very harsh radiation environment.
PbWO4 Crystals change transparency under radiation
Correct using the observations of laser monitoring systemThe damage is significant (few % - up to ~5 % for CMS ECAL barrel radiation
levels) at high luminosity
The dynamics of the transparency change is fast (few hours) compared to the time scale needed for a calibration with physics events (weeks - month).
Resolution design goal: ~0.5%
Calibrating and maintaining the calibration of this device will be very challenging. Hadronic environment makes physics calibration more
challenging
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 11
Laser Monitoring System
Lasers at two different wavelengths:1 = 440 nm
2 = 796 nm
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 12
Laser Monitoring System
Laser light is injected into the crystals via fiber-optic cables
Avalanche photodiode response is measured (APD)
Light is also injected in reference PN diodes
Ratio of APD and PN responses is used to monitor crystal transparency changes
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 13
Irradiation Crystal Response
Monte Carlo with a ~12 hour LHC fill cycle
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 14
Irradiation Crystal Response
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 15
Laser Monitoring @ H4
Test Beam at CERN from June to November 2006
One ECAL supermodule in beam at time
15-250 GeV electrons
Intensity: Up to 50K events / 60s, Approx. 15 rad/hour
Online monitoring system was implemented to reconstruct laser runs and log values
Moveable stand
ECAL SM 22
Beam line
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 16
Online Laser Monitoring
For each laser run:APD and PN pulses reconstructed
APD, APD/PN and PN distributions for each channel (1700 per SM) are fit and used to extract mean values
Similar distributions are monitored in geometric groupings (half SM, light modules); used for potential corrections
Correlations between different values (APD - APD/PN - timing, Chi2, etc.)
10 ECAL supermodules examined
Over 1,600 laser runs processed
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 17
Online Laser Data Analysis
~15 min. to process each laser run
Plots of various distributions are available online immediately after
processing. APD/PN values (among other
things) logged in database for higher level analysis
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 18
Consecutive run monitoring
Comparison plots between consecutive runs for the APD/PN and APD values are used to monitor short term stability and inter-run changes
-.003
.001
0.0
Runs 13061->13064 SM16
00013061-00013064
For example, this plot shows the relative difference in the APD/PN values, for each channel, between two consecutive runs. Almost all channels are stable
to within .5 per mille between consecutive runs
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 19
Online Monitoring Stability
APD/PN
All channels, all modules :Stability 1.4 % from gauss fit to peak.
Overall stability good, even at this basic level without any further
corrections.
Get APD/PN ratios for each channel, each SM
Normalize average APD/PN to 1 for each SM
Fit gauss to normalized APD/PN for each channel
Sigma of these fits is the stability
APD/PNStability:
Raw stability
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 20
Offline Monitoring Stability
Mean before and after correction : 0.180 % 0.088 %
Peak before and after correction : ~0.170 % ~0.05 %
Small systematic change in reconstructed APD value related to Peak timing.
Correct APD/PN ratios with a simple linear function of peak timing
Example for one SM (22)
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 21
Raw Monitoring Stability at H2
APD/PN vs. Time, 100 Channels (1040 – 1140, center Module 3).
Hardware intervention around t=2150 h, stability reasonable.
Black : APD/PN, averaged over 100 channels.
Red : T/20+1
Anti-correlation between temperature and APD/PN – as expected.
APD/PN shows ~ -2%/C0 temperature dependences – as expected.
Temperature correction based on thermistors
Raw APD/PN stability at reasonable level
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 22
Laser Pulse Width Correction
Reconstructed APD/PN ratio sensitive to laser pulse width
For normalized APD/PN ratio, ~2%/ns
Long-term pulse width stability ~1-2 ns
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 23
Pulse Width Measurement
Linear fit of the APD/PN-width dependence for each channel of each SM
Normalize APD/PN by the fit value at width = 30 ns Distributions and crystal maps for the slope,
intercept, chi2, etc. of the linear fits for the normalized APD/PN values
error bars blown up by a factor of 10
normalization value
Example
Sigma / |Mean| = 6.9(1)%
A total of 6 SMs have been measured.
Pulse Width Non-Linearity has little channel to channel variation !
All slope for one SM
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 24
Example Irradiation Cycle
Normalized laser and electron responsesXtal 168
SM 22
For each electron response point an interpolated laser response value is calculated
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 25
Example Correlation Plot
Relative electron
response
Relative Laser Response
Xtal 168
SM 22
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 26
Example Corrected Resolution
Xtal 168
SM 22
120 GeV electrons, 3x3 crystal matrix
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 27
Continuing Irradiation Studies
Hodoscope hits - entire irradiation period
Beam events distributed throughout
crystal
Sufficient statistics to explore variations in
electron response within crystal
Xtal 168
SM 22
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 28
Continuing Irradiation Studies
Hodoscope hits - entire irradiation period
Reconstruct electron data for 25
different bins
Generate R-plot for each bin
Xtal 168
SM 22
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 29
Continuing Irradiation StudiesC. Rogan
Xtal 168
SM 22
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 30
Continuing Irradiation Studies
Still statistics limited in outer bins
Can potentially be used for precision offline corrections
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 31
Laser Monitoring Outlook
Measured the APD/PN stability for individual channels on a large scale
Demonstrated reasonable online APD/PN stability; could be used for online electron response corrections
Achieved offline APD/PN stability for majority of channels with simple corrections. Further corrections are currently being studied
Demonstrated the ability to maintain resolution during irradiation
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 32
π0 Calibration Concept
Level 1 trigger rate dominated by QCD: several π0‘s/event Useful π0γγ decays selected online from such events Main advantage: high π0 rate (nominal L1 rate is 100kHz !) “Design” calibration precision better than 0.5%
Achieving it would be crucial for the Hγγ detection Reporting on studies performed with about four million fully simulated QCD events. Results given for the scenario of L=2x1033cm-2s-1 and L1 rate of 10 kHz (LHC start-up).
Data after L1 Trigger Online Farm 0 Calibration
>10 kHz~1 kHz
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 33
π0 Selection
Based on local, crystal-level variables — suitable for online filter farm. Kinematics: PT () >1 GeV, PT (pair) > 3.5 GeV and η < 1.48 (barrel)
Photon shower-shape cuts: S9/S25 > 0.9 and S4/S9 > 0.9 defined with
2x2, 3x3, and 5x5 crystal matrices (S9 is chosen as photon energy) Additional isolation cut optimized to remove showers with significant
bremsstrahlung radiation: want to select mainly unconverted photons
Trigger Tower (5x5 Trigger Tower (5x5 crystals)crystals)
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 34
Selection Results
π0 rate of 0.9 kHzrate of 0.9 kHz or 1,250 or 1,250 ππ00/crystal/day with S/B /crystal/day with S/B ≈≈ 2.0 2.0 High-rapidity regions suffer both in rate and S/B (31)
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 35
A Calibration Algorithm (of many)
Simple iterative algorithm (L3/RFQ Calibration)Simple iterative algorithm (L3/RFQ Calibration)
(wi fraction of shower energy deposited in this crystal)
Both photon energy and direction reconstructed using crystal level information (same as during selection).
After each iteration pairs are re-selected with new constants (typically 10-15 iterations to converge).
Miscalibration is done before selecting events (4%). Calibration precision defined as R.M.S. of the product of the final and initial miscalibration constant. Use only pairs from ±2σ window around fitted π0 mass
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 36
Calibration Performance
Precision is then fitted to N is the number
a=27±1% and b=0.20±0.25% of π0/crystal2
2
bNa
CC +=
σ
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 37
Calibration Studies in Test Beams
π0 decays produced through: π-+Al π0+X (11/2006)
Three different π- beam energies: 9, 20, and 50 GeV
Consider only 9x8 crystal matrix: about 140 π0 decays/crystal
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 38
Reconstruction of π0
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 39
Selection of π0 using S1, S2 ADC
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 40
First Resonance Observed by CMS
Clear improvement over the uncalibrated peak (L3 algorithm). For a precise estimate of the calibration precision: use the 50 GeV electron test beam data.
π0 from upstream scintillators
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 41
50 GeV e- peaks with TBS1 9 GeV constants
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 42
Calibration Precision with 50 GeV Electrons
For each crystal, electron energy spectra were fitted to a Gaussian.Distributions of the obtained peak positions for 9x8 crystal matrix:
Precision: 1.0±0.1% with 0.9±0.1% expected. Calibrationwith ~5 GeV photon works well for higher-energy showers!
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 43
π0 Conclusions and Outlook
Proof-of-principle was achieved with full detector with full detector simulation: crystal-by-crystal intercalibration to 1% simulation: crystal-by-crystal intercalibration to 1% should be possible after a few days at L=2x10should be possible after a few days at L=2x103333cmcm-2-2ss-1-1
Other methods are much slower and tracker dependent.Other methods are much slower and tracker dependent. Optimistic outlook for achieving and maintaining aOptimistic outlook for achieving and maintaining a ~0.5% precision. Many months of work on understanding ~0.5% precision. Many months of work on understanding the ECAL performance and non-uniformity at lower the ECAL performance and non-uniformity at lower energies energies (work of ~15 physicists from 4 teams).(work of ~15 physicists from 4 teams). Test beam study demonstrated a 1% calibration precision Test beam study demonstrated a 1% calibration precision with ~5 GeV photons: successfully used to reconstruct with ~5 GeV photons: successfully used to reconstruct 50 GeV electrons. 50 GeV electrons. No noticeable systematics.No noticeable systematics. (Many thanks to the entire H2 test beam team). (Many thanks to the entire H2 test beam team). Currently a lot of work is being done on developing filter farm tools for collecting π0 in situ at the LHC. Calibration of the endcaps is also being considered.
May 1, 2007 Christopher Rogan - Caltech HEP Seminar 44
Test Beam 2006 Summary
Two successful ECAL test beam efforts (H4, H2)
Recorded invaluable data for upcoming LHC startup while demonstrating viability of ECAL performance expectations
Caltech continues its leadership roles in hardware/software development of the 0 inter-calibration and laser monitoring
Credit is due to the hard work of entire ECAL community
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