Identificazione e ricostruzione di elettroni e fotoni in CMS

Transcription

CMS ECAL: status at the LHC startup
Paolo Meridiani (CERN PH/CMG)
for the CMS ECAL Group
IPRD08: Siena 1-4 October 2008
Paolo Meridiani - CERN PH/CMG
1
CMS Electromagnetic calorimeter
Homogenous crystal
calorimeter
Lead tungstate
(PbWO4)
∼10 m3, 90 tons
Energy resolution goal: 0.5% at
high energy
⇒ Higgs @120 GeV
discovery with ≤10 fb−1
100 days @ 2 1033 cm−2s−1
Barrel: |η| < 1.48
36 SuperModules
61200 crystals (2.2x2.2x23cm3)
Pb/Si preshower
1 SuperModule
barrel
1700 crystals
SuperCrystals
(5x5 crystals)
EndCap “Dee”
3662 crystals
EndCap: 1.48 < |η| < 3.0
4 Dees
14648 crystals(3x3x22cm3)
2
PbWO4 crystals
Compact
Two producers:
BTCP (Bogoroditsk, Russia)
SIC (Shanghai, China)
Last crystal barrel: March 2007
Last crystal endcap: February 2008
425
Fast and low light
Automatic control at reception on:
• Shape and size
• Radiation resistance (transparency)
• Light yield and its uniformity
3
Electronics
On detector electronics
Clock & Control
x12
x6
MGPA
PbWO4
Crystal
APD
VPT
1
Logic
12 bit ADC
0
FE
x1
Multi-Gain
(x 1, x 6, x 12)
Pre Amplifier
40 ns shaping
Off detector electronics
2
multi-channel
12-bit ADC
40 MHz
25ns sampling
Data pipeline
Trigger primitives
100 m
Fibers
to counting
DAQ data
room
Trigger data
optical data link
driver
800 Mbit/s
4
Ecal laser monitoring system
Dose rate on crystals at LHC high luminosity:
0.2-0.3 Gy/h (Barrel) → 15 Gy/h (Endcap)
Simulated signal variation
η=0.9 – 2 1033 cm-2 s-1
Continuous variation of signal during
(damage) and in-between (recovery) LHC
fills due to transparency change
dependent on
• radiation level (η, luminosity)
• crystal characteristics
PWO
PIN
F1
FE
F2
S
Laser
440 nm
796 nm
Laser monitoring system to follow crystal
transparency change (stability 0.1%)
5
Barrel construction
Completed in March 2007
2 regional centers involved
CERN
INFN/ENEA Casaccia
6
Barrel electronics integration
Trigger tower and its
cooling blocks
Done @ CERN
Building 867
Completed in early
July 2007
7
Barrel installation and cabling
13rd April 2007
17th April 2007
• Individual supermodule signoff
completed in December 2007
• Pedestal run
• Test pulse run
• Laser run
July 2007
November 2007
8
Ecal Endcaps
March 2008
Endcap build entirely @ CERN
Endcap integration completed in July 2008
Installation/cabling/sign off first completed 15th
August 2008
Endcap included in global readout soon after
Preshower ready by end of 2008
August 2008
9
Commissioning timeline
Test Beam @ H4:
1 SuperModule (SM)
Barrel
Final electronics
Commissioning
/calibration of each
SM with cosmics on
surface
Test Beam @ H4:
9 SM
Combined Test
beam @ H2: ECAL
+HCAL
2 SM tested with
magnetic field in
surface (MTCC)
Commissioning
with cosmics
(and beam shots)
in the pit
Individual signoff
of each
supermodule
during installation/
cabling
2004
2005
2006
2007
2008
10
Few test beam highlights (1)
Intercalibration with electron beam


9 Supermodules intercalibrated with electrons @ 120 GeV H4
1 Supermodule partially calibrated with electrons @ 50 GeV H2
Intercalibration
reproducibility
0.2 %
Optimized the amplitude
reconstruction method
Achieved constant energy
resolution term (local) better
than 0.5%
Noise at expected level (∼40
MeV x channel) without
evidence for spatially
correlated noise
σ
3.37% 108 MeV
=
⊕
⊕ 0.25%
E
E
E
11
Few test beam highlights (2)
Measured on several irradiation/recovery cycles
relation between transparency change and
variation of scintillation signal
Small dispersion of the α parameter, allow to use a
constant for each producer and crystal type (barrel/
endcap)
Paolo Meridiani - PH/CMG
12
Cosmics pre-calibration on surface
Trigger scinitillators
Each supermodule exposed to
cosmics for at least 1 week
 Supermodule inclined 10°
 Increased APD gain (x4)
 ∼ 5 million triggers/SM
 ∼ 500 <selected events/
crystal>
Compared cosmic and
beam intercalibration:
agreement @ 1.5%
1.5 %
13
CMS Global Runs
Goals:





DAQ integration of the various subsystem
Test Level1 Trigger and High Level Trigger with increasing level of
complexity
Train shifters (24/7 operation mode) and debug online & offline Data
Quality Monitor
Stress the data transfer chain (CMS->T0, T0->T1,T1->T2), exercise
prompt reconstruction (T0) and prompt analysis facility (CAF)
Use collected data to understand trigger and read out synchronization
and detector performance using inter-system correlations
Fraction of CMS
subsytems
participating
Start of full week
exercises
(CRUZET 1)
Featuring ECAL
endcaps!
Cruzet4
Cruzet3
Cruzet2
Cruzet1
Sep 10
100% CMS
>300M cosmic collected
All ECAL barrel
Cosmic Run
Ru at Zero
Ze Tesla
14
Cosmic showering in both EB & EE
DT
EB
HCAL
EE
15
Cosmics signal studies (1)
Shaft (minus side) induces a big
asymmetry in the cosmic signal
Typical configurations for
muons crossing ECAL:
top-bottom
Side/lateral muon
spatial distribution
1.35
Dynamic SuperClustering
algorithm able to recollect in a
single cluster signal spread
over many crystals (side
muons)
1.05
16
Matching clusters with muon tracks
(no tracker) is dominated by
multiple scattering in solenoid +
HCAL
RMS η=0.21
RMS ϕ=0.07
Eta is measured by DriftTubes with
less points than phi
cm
Use ECAL detailed
geometry and muon
track to measure the
track length inside ECAL
crystals
23 cm
17
Comparison of fitted dE/dX with
PDG tabulated energy loss
(performing also detailed
comparison with Montecarlo)
Preliminary
dE/dX from 3x3 clusters associated to
quasi-pointing muons:
Preliminary
Transverse impact parameter<20cm
Longitudinal impact parameter< 30cm
dE/dx also used for intercalibration
studies (validation of pre-calibrations)
18
First beam: splash events from 10th September
(LHC startup)
HCAL
ECAL
>99% of ECAL
channels fired
DT
ECAL
∼200 TeV
energy
deposited in
EB+EE
HCAL
Beam shots (~2x109 p) on
collimators 146 m
upstream CMS
Big wave incoming!
19
First beam splash: energy seen by ECAL
Here beam (clockwise) is
coming from plus side
Around 200k muons
crossing ECAL (density ∼4
muons/cm2)
ECAL endcaps
precalibrations are not yet
applied (lowest gain
photodetectors are nearest
the beam pipe)
EB+
EBTOP
BOTTOM
20
Splash events: some correlations
ECAL – BLM correlation
Correlation ECAL deposited energy with Beam
Loss Monitors (BLM) and HCAL
HCAL – ECAL correlation
Preliminary
Preliminary
21
Splash events: ECAL timing
Splash events: wonderful
source of synchronous hits in
the whole detector
Previous settings based on synchronization
with laser events (fiber length to reproduce
collision timing)
Splash events allowed to time in the
detector at 1ns level
Time resolution within a tower (25 crystals)
σ=1ns
splash direction
η detector coordinate
1 clock = 25ns
22
Plans just after LHC collisions
Precalibration for EB:
0.3% on 9 SM
~1.5% on 36 SM
4%

 
Test beam
Cosmic rays
Also LAB data



Precalibration for EE:
Goal: improve startup calibration as fast
as possible


Test beam
460 crystals
LAB data
9%


Strategy involves use of:
Phi invariance of energy deposit (fast improvement in endcap up to 2-3%)
Neutral pion mass peak: proof of principle that 1% can be achieved (at least in the
barrel) with few days of running at nominal low luminosity 2x1033 cm-2s-1. Very
useful also for 10 TeV startup scenario (see M. Gataullin’s talk)
Other resonances (η0→γγ,π0 Dalitz decay) being investigated to monitor calibration
precision
Cosmic data being used also to understand effect of real detector noise to the previous
methods
Possibility to combine independent sources to obtain best calibration
23
Conclusions

ECAL (Barrel + Endcap) is installed, signed off & regularly taking
data

>300M cosmics data acquired so far. Using them for
commissioning as much as possible: dE/dX, timing…

Spectacular splash events from LHC beam dump on collimators
seen by ECAL: source for further timing and signal studies

ECAL perfectly on track to record first LHC collisions!
24

Identificazione e ricostruzione di elettroni e fotoni in CMS

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