performance of the lhcb calorimeters · y~7m x~8.5m z~2.7m ps/spd lhcb calorimeters 20131125 v cpan...
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Performance of the LHCb calorimeters during the period 2010-2012
Xavier Vilasís-Cardona
20131125 V CPAN Days - Xvc 1
Y~7m X~8.5m
Z~2.7m
HC
AL
ECA
L
PS/SPD
LHCb Calorimeters
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10-‐250 mrad
10-‐300 mrad
VELO Vertexing
MAGNET
Calorimeters PID: e,γ, π0
Muon Stations
RICH 1 & 2 PID: K vs. π
Trackers TT+IT+OT Momentum resolution
• Preshower (PS)/Scintillator Pad Detector (SPD)
• Electromagnetic Calorimeter (ECAL) • Hadronic Calorimeter (HCAL)
Purpose of LHCb calorimeters
• Preshower (PS) and Scintillator Pad Detector (SPD): • PID for L0 electron and photon trigger • electron, photon/pion separation by PS • photon/MIP separation by SPD • charged multiplicity veto by SPD
• Electromagnetic Calorimeter (ECAL): • Et of electrons, photons and π0 for L0 trigger (e.g. B → J/Ψ Ks,
B → K*γ) • reconstruction of π0 and prompt γ offline • particle ID
• Hadron Calorimeter (HCAL): • Et of hadrons for L0 trigger (e.g. B → π π , B → DsK) • particle ID
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PS and SPD
• Scintillator blocs with coiled WLS fiber • Geometry projective with ECAL: 3 zones • MAPMT Hamamatsu 5900 M64 • 6016+6016 Cells
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Side view of upper part
Inner + Middle + Outer Modules
e-
γ
SPD Pb PS ECAL
JINST 3 S08005 (2008)
ECAL
• Shashlik • PMT readout Hamamatsu R7899-20
• Energy resolution σ(E)/E = 0.085 ± 0.01/ E ⊕ 0.008 ⊕ 0.003 ∗ x/E
• 6016 cells
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3312 shashlik modules with 25 X0 Pb Inner
Module 9 cells: 4x4 mm2
Middle Module 4 cells: 6x6 mm2
Outer Module 1 cell: 12x12 mm2
Sc:Pb = 4:2 mm 25 X0
12x12 mm2
Chariot
Electronic platform
modules
Beam plug JINST 3 S08005 (2008)
HCAL
• Tile structure • PMT readout Hamamatsu R7899-20 • Energy resolution √σ(E)/E = (0.69 ± 0.05)/ E ⊕ (0.09 ± 0.02) • 1488 Cells (inner-outer)
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particles
PMT
scintillators
WLS fibers light-guide
Electronics platform
Chariot
modules
Beam plug
Weight : ~9.5 ton
JINST 3 S08005 (2008)
Front End Electronics
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Installation and Commissioning
• Installation from 2004-2008 • Commissioning 2005-2009 • First cosmic seen January 2008 • Commissioning using built in
monitoring tools, cosmics and splash events.
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OT
Calo Muon
Calibration and Monitoring
• Calibration strategies – PS / SPD
• Fit the MIP signal and look for efficiencies
– ECAL • Initial adjustment • Energy Flow
• Fit π0 mass • E/p for electrons
– HCAL • Built in 137Cs source
• Detectors include built in LED system for monitoring detector stability
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LED monitoring system of XCAL
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LED LED LED LED LED LED LED
Driver Splitter
PIN diode ADC
LED LED LED LED LED PMT …
• Control of time and temperature stability • Small pulse duration and dispersion of amplitude • Adjustable pulse rate and amount of light • Emulate e/m particles in full “physics” region • Gain control to better than 1% accuracy • Control only electronics chainà supply LED light directly to the
PMT • Use empty bunches for running monitoring system
ECAL Ø 512 LED drivers & LEDs
& splitters & fiber-bundles
Ø 64 PIN-diodes
LED pulse
50 GeV e-
PS-SPD
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• Tracks pointing to given PS/SPD cell are extrapolated • PS: MIP signal is fitted and fixed to a given number
of ADC counts • SPD: signal is checked for existing tracks
Mean 0.9487RMS 0.03373
Cell efficiency0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 10
10
20
30
40
50
Mean 0.9487RMS 0.03373
Even BXApril2011MPV0 2 4 6 8 10 12 14 16 18 20
Cha
nnel
s
0
20
40
60
80
100
120
140
160
180 Even BX A sideApril2011MPV
Outer \bar{x}: 7.79 \pm 0.03 \sigma: 1.20 \pm
Middle \bar{x}: 7.52 \pm 0.04 \sigma: 1.17 \p
Inner \bar{x}: 7.88 \pm 0.05 \sigma: 1.27 \pm
SPD Efficiencies (2011) PS MIP Energy Distribution April 2011
HV, kV
G
0.6 0.8 1.21.0 1.4
104
105
ECAL – Initial calibration + Energy Flow
• Initial Calibration (relative width of π0 peak, 10%)
• Energy Flow – Equalize the energy flow over 3x3 cell blocks
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Entries 6016
Mean 0.009065
RMS 0.03534
−0.5 −0.4 −0.3 −0.2 −0.1 0 0.1 0.2 0.3 0.4 0.50
100
200
300
400
500
600
700Entries 6016
Mean 0.009065
RMS 0.03534
MiscalibrationCalibrationResiduals
10% miscalibration
ADCmax
= Emax
e kY G
nominal
sADC
MC data
ECAL – Fine Calibration
• Currently absolute calibration based on the ‘Mass distribution fit’ method
(O.Igonkina et al. HERA-B 00-103)
• Fit π0 mass from 2 photon signals in ECAL • Iterative procedure
– Select photons (3x3 clusters) and fix seed (central) cell. – For each cell – Compute di-photon invariant mass – Fit π0 mass distribution – Correct calibration of seed cells – Restart until stable
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π0 mass
ConclusionsThe Mass distribution fit method was applied as the final step of the calibration for 2011 data.With the set of data corresponding to one week of data taking 6015 coefficients for 6016 cells wereobtained. One more cell gave too low signal due to the faulty electronics, so no coefficient could befound for it.
In Fig.4 one may see the γγ invariant mass distribution before (blue line) and after (red line)the calibration. With the help of calibration the neutral pion peak position has moved to its nominalvalue and its resolution became smaller by 12%. Several more evidences of the performanceimprovement may be found in the Appendix.
Mass 0.0± 135.3
Width 0.007± 7.568
0 50 100 150 200 2500
500
1000
1500
2000
2500
310×
Mass 0.0± 135.3
Width 0.007± 7.568
Mass 0.0± 131.7
Width 0.010± 8.559
Mass 0.0± 131.7
Width 0.010± 8.559
Mass 0.0± 131.7
Width 0.010± 8.559
dN
dM
π0
!
1M
eV/c
2
"
Mass (MeV/c2)
Figure 4: γγ invariant mass distribution before (blue line) and after (red line) calibration.
AcknowledgmentsWewould like to say many thanks to the calorimeter calibration group for lots of fruitful discussions,to Dr. M.-N.Minard, Dr. P.Perret, Dr. J.Lefrancois and A.Martens for their kind help and A.PuigNavarro for his invaluable impact to this job.
8
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Mass distribution fit algorithm 2011 data (june)
Initial calibration value
Final calibration value About 6% error
E/p
• Another method to monitor or correct the ECAL cell calibration is through electron E/p
• Electrons are identified by estimation of the momentum of the extrapolated of tracks and energy of the matching clusters.
• Used to monitor ageing.
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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16 E/p for electrons in ECAL E/p for hadrons in ECAL 2011 data
Ageing on ECAL – π0 mass variation as a function of time (luminosity) observed:
V CPAN Days - Xvc 20131125
– Optical fibres of ECAL LED monitoring system are also affected – The effect is cured by calibrating ECAL:
• Apply fine calibration of each ECAL cell using π0 and adjusting its mass on a short period of data taking
• On top of fine-calibrated data trending coefficients are applied: – π0 statistic not high enough to follow closely the changes – Make use of photon conversion and look at E/p
Run Number115 120 125 130
310×
Pi0
mas
s pe
ak (M
eV/c
2)
130131132133134135136137138139140
p0 0.01735± 135.1 p0 0.01735± 135.1
HCAL Calibration • HCAL absolute Calibration
– Based on 137Cs source scans performed during technical stops
– LEDs used to monitor.
V CPAN Days - Xvc 20131125 17
The “PMT sensitivity variation” is the PMT gain variation reduced to the initial (March 2011) HV, calculated from the calibration coefficients.
Ageing on HCAL (both on detector and PMT)
V CPAN Days - Xvc 18
Can be corrected by Modifying PMT gain (HV) Calibration
Cs source runs + LED Scintillator rows in the tile get affected depending on their depth
20131125
PMT gain Loss expected With cumulated charge
Photon Reconstruction
• Clusters : 3x3 cells – Barycenter, – Energy – Spread
• Match fitted tracks to discard charged particles
• Mass resolution :
20131125 V CPAN Days - Xvc
B0d ! K0⇤� L = 1.0fb�1
Ec = ↵"cl + �"PS
100MeV/c2
�22D(~p) =
(~ptr � ~p)T C�1tr (~ptr � ~p)
+ (~pcl � ~p)TS�1cl (~pcl � ~p)
π0 reconstruction
20131125 V CPAN Days - Xvc 20
• Neutral π0 – Low energy : resolved pair of γ – mass resolution : 8 MeV/c2
– High energy (pT>2GeV/c): overlapped γ clusters – iterative algorithm to separate in two subclusters – mass resolution : 20 MeV/c2
0.45 0.5 0.55 0.6 0.65 0.7 0.750
0.2
0.4
0.6
0.8
1
ρ vs ∈
SPDρ vs ee→ γ∈
SPDρ vs ee→ γ∈
0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.850
0.2
0.4
0.6
0.8
1
ρ vs ∈
SPDρ vs ee→ γ∈
SPDρ vs ee→ γ∈
Photon identification and merged π0 • Photon Hypothesis uses
– PS cells in front of ECAL cells energy, Ratio of energy (central cell/cluster), Χ2
2D
• Separating merged π0 from γ – Uses cluster shape – MLP – Trained on simulation – Checked on data B and D decays
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pT>500MeV/c
pT>200MeV/c
Converted Photon Reconstruction
• Converted photons produce a pair (ee) • Correct for e bremsstrahlung
– Bremsstrahlung candidate : neutral energy deposition with Χ2 < 300 from a charged track.
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h1Entries 10
Mean 1404RMS 522.6
(MeV/c)γTP
600 800 1000 1200 1400 1600 1800 2000 2200 2400
)C
ALO
γ(∈)/eeγ(∈
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05h1
Entries 10
Mean 1404RMS 522.6
h60Entries 138690Mean 135.5RMS 31.19
60 80 100 120 140 160 180 200
500
1000
1500
2000
2500
3000
3500
4000
h60Entries 138690Mean 135.5RMS 31.19
h40Entries 6353Mean 137.4RMS 33.04
h40Entries 6353Mean 137.4RMS 33.04
⇡0 ! �(! ee)�CALO
Data MC
✏(� ! ee)/✏(�CALO)
Electron Identification
• Build reference histograms – use converted γ reconstructed from events triggered
by muon detector – Hadron background made of π and K from D0
decays – Use 340 pb-1 from 2011 data
• Histograms built for PS, ECAL and HCAL • Identification is based on E/p refined using
X22D and also EPS and EHCAL
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EPS
E/p
EHCAL Χ22D
LCALOeh = LECAL
eh LHCALeh LPS
eh
Combined Performance of electron identification
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� logLCALOeh > 0
� logLCALOeh > 1
� logLCALOeh > 2
� logLCALOeh > 3
Electron Efficiency
MisId rate
p
e h
Tag and probe method using e from
logLCALOeh
Probe e efficiency
B± ! J/ (e+e�)K±
25
LHCb Upgrade Architecture
24th April 2013
CHEF 2013
Ken Wyllie, CERN 25
HLT
Current
HLT++ Upgrade
1MHz event rate
40MHz event rate
Readout Supervisor
L0 Hardware Trigger
Readout Supervisor
Low-Level Trigger
50 Tb/s
Low-Level Trigger
1 to 40 MHz
LOW Level Trigger decision
from Front-End to Back-End
20130521 Xvc - ISCAS 2013 25
Upgrade
• Increased luminosity • New features • PS and SPD shall be eliminated (they mainly
contribute to L0 trigger) • DAQ @ 40MHz
– Change in the readout electronics • Lower PMT gain
– Higher luminosity – Ageing
• New electronics under development • TDR under review
20131125 V CPAN Days - Xvc 26
Conclusions
• LHCb calorimeters fully functional • Ageing observed
– Frequent calibrations
• Good performances in γ and e identification. • Upgrade
– Leave ECAL-HCAL – Software trigger – New DAQ electronics
20131125 V CPAN Days - Xvc 27
Performance of the LHCb calorimeters during the period 2010-2012
Xavier Vilasís-Cardona
20131125 V CPAN Days - Xvc 28
BACKUP
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Time Alignment
30
• DAQ feature: Time Alignment Events • Equalise an a-priori delay from theoretical values • Adjust BXID so that an event is mainly seen on Current • Adjust integration time t0
– Select the pair of BX with maximum signal • Prev1/Current vs. Current/Next1
– Compute the asymetry R
• All XCAL channels adjust within 1ns ∑∑
∑∑
+
−= Nevt
iij
Nevt
iij
Nevt
iij
Nevt
iij
NextECurrentE
NextECurrentERj
)()(
)()(
t T0 Next1 Prev1
25 ns
δTsampling δTsampling δTsampling
20131125 V CPAN Days - Xvc
First π0 fit – Nov 2009
• Initial calibration was performed by setting a uniform ADC count value per transverse energy unit.
• This calibration allowed to fit the π0 peak in NOV2009
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M=133 ± 3 MeV/c2, with σ = 11 ± 4
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B production in LHCb Ø b and b quarks are produced in pairs Ø bb production is correlated and sharply peaked forward-backward Ø LHCb single-arm forward spectrometer : θ~15-300 mrad (rapidity range: 4.9>η>1.9) Ø Cross section of bb production in LHCb acceptance: σbb ~ 230 µb Ø LHCb limits luminosity to few 1032cm-2s-1 instead of 1034cm-2s-1
by not focusing the beam as much as ATLAS and CMS Ø Maximizes probability of a single interaction per crossing Ø Design luminosity from start-up of LHC Ø ~ 1012 bb pairs produced/year in LHCb acceptance
pp interactions/crossing
LHCb
n=0
n=1
ATLAS/CM
S
boost
b
b
LED monitoring system of HCAL
20131125 V CPAN Days - Xvc 33
Ø blue LEDs (WU-14-750BC) Ø two independent LEDs per module Ø adjustable LED pulse amplitude Ø monitoring PIN photodiode at each
LED in order to account for LED instability
Ø light distribution with clear fibers of same length
Ø timing of the LED flashing pulse adjustable with 1 ns step
0.2%
Monitoring of LED with PIN diode
Radiative decays b→qγ
• Radiative b→(d, s)γ, one-loop penguin transition, sensitive to NP.
• Theoretically clean FCNC transition & experimentally accessible.
• Many observables: branching fractions (BR), CP asymmetries (ACP), isospin asymmetry, helicity structure of the photon.
34
NP may introduce sizeable effects on the dynamics of the transitions, through contributions of new particles inside the loops
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Time Alignment results-ECAL
• All XCAL channels adjusted within 1 ns.
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HCAL E/p offline calibration
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If the offline accounting for the HCAL ageing will be found necessary, one can use the E/p based calibration on hadron tracks (for the moment, available per fill, up to fill #2007, Aug-2011).
The E/p calibration gives absolute scale and calibrates the whole signal chain, accounting also for the spread of FEB sensitivities.
Here: correlation of ratio of E/p-based calibration coefficients for fill ranges 1883-1901 and 1997-2007 (~5 weeks in between) and LED amplitude change for the same period. This validates the use of the LED corrections at least for short time scale.
20131125
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