1. I. Machikhiliyan (LAPP, Annecy) for the LHCb calorimeter group
Current status and performance of the LHCb electromagnetic and hadron calorimeters
I. Machikhiliyan
(LAPP, Annecy)
for the LHCb calorimeter group

2. The LHCb detector
Forward single-arm spectrometer aimed at studies of CP-symmetry violation and rear decays of b-quark
The LHCb Calorimeter system:
Fast trigger on energetic e/γ/πº/h
Distance to i.p. ~13 m
Solid angle coverage 300x250 mrad
Four sub-detectors: Scintillator Pad Detector SPD (by Ricardo), Preshower PS (by Valentin), Electromagnetic (ECAL) and Hadron (HCAL) calorimeters

3. Electromagnetic Calorimeter
3312 separate modules of square section 12.12x12.12 см²
“Shashlik” technology:
lead absorber, volume ratio Pb:Sc 2:4
Moliere radius: 3.5 cm
longitudinal size is equivalent to X / 1.1 λ
average light yield:~3000 p.e./GeV
energy resolution (beam tests):
σE/E = (8. ÷ 10.)%/√E  0.9%
Transverse segmentation: three sections Inner, Middle and Outer (9, 4 and 1 cells per module)
Number of readout channels: 6016
Dynamic range: 10 ÷ 12 GeV of transverse energy
E(max, GeV)= /sin(θ)
sin(θ) = √(x²+y²)/ (x²+y²+z²) I

4. Hadron calorimeter 26x2 big horizontal modules
The same design as in ATLAS TileCal:
interleaving Sc tiles and iron plates parallel to the beam axis. Volume ratio Fe:Sc = 5.58:1
longitudinal size: 5.6 λ → mostly used as triggering device (~70% of L0 decisions)
average light yield: 105 p.e./GeV
energy resolution (beam tests): σE/E = (69±5)%/√E  (9±2)%
Transverse segmentation: two sections Inner and Outer (cell size 13.1x13.1 cm² and 26.2x26.2 cm² cell size)
Number of readout channels: 1488
Dynamic range: 15 ГэВ of transverse energy I

5. LED-based Monitoring System
Readout System
Light readout: photomultipliers
LHC bunch spacing: 25 ns → shaping of PM anode pulses
192 Ecal + 54 Hcal Front-End Boards. Signals are integrated and processed by 12-bit (80 pC) 40 MHz two-stage bipolar flash ADC. Trigger part: selection of cluster candidate (2x2) with highest Et
LED-based Monitoring System
Major goals:
check readout channels serviceability
control the stability of r/o chains
ECAL: one LED illuminates a group of channels (9 in the Inner, 16 in the Middle/Outer sections); HCAL: 2 LEDs per each PM
Stability of LEDs themselves is traced by PIN photodiodes

6. Operating calorimeters: major issues
Time alignment:
on the general level: precise synchronization of calorimeters with each other and with accelerator cycle
on the level of each detector: adjustment of timing of individual r/o channels (up to 5 ns dispersion, compensated by delay chips on the level of Front-End Boards)
Absolute calibration of detector response on the level of individual cells
Monitoring of the stability of calorimeters with LED / PIN systems. Done in parallel with data taking: LEDs are fired synchronously with one of “empty” bunches with frequency Hz

7. Shape of the integrated signal
Time alignment
Shape of the integrated signal
Artificial timing shift on 12.5 ns to calculate the mis-alignment in time
Additional few ns delay scan to verify the safe position on the ‘flat-top’
Special time-alignment events (TAE) containing up to 7 consecutive time slots around the one under interest
Cosmic particles + special injection events in 2009: relative time alignment of different detectors and their subparts (like r/o crates etc)
Fine absolute synchronization of individual r/o channel with accelerator cycle: 450x450 GeV collisions in the end of 2009 / cross-checked in the end of March 2010 with 3.5x3.5 TeV collisions
dt =-0.5ns
S(dt) = 0.4 ns
R , final time alignment 7

8. Stability of r/o chains for 2010 data taking
6 Apr
26 Apr
Ecal:
83% - within 1%
97% - within 2%
99% - within 3%
Hcal:
68% - within 1%
93% - within 2%
98% - within 3%
Relative run # (physics only)
Typical behaviour of the normalized response on LED in one r/o channel
Stability of r/o chains (6 Apr – 26 Apr 2010). LED drift if any is corrected according to PIN readings
Stability of LEDs (by PINs):
Ecal:
mean 0.5% (rms 0.5%) for 93% of cells <1%
for 98% of cells<3%
Hcal:
mean 0.6%, rms 0.3%
for 87% of cells<1%
for 99% of cells<2%
!WORST CASE!
~2%
~20%
Relative run # (physics only)
Relative run # (physics only)
Response on unstable LED (ADC cnt), one r/o channel (ECAL)
Normalized PM/PIN ratio (the same r/o channel)

9. Ecal: pre-calibration of PM gains
Two steps:
measurement of absolute value of G in the reference point (high gain, low LED flash intensity). Presumption is that the width of the distribution of PM responses on LED is defined by photostatistics ~√Np.e.
G = К * (σ(LED)² - σ(pedestal)²) / (A(LED) – A(pedestal))
К – parameter, defined by hardware properties (ADC sensitivity, modules light yield, etc)
measurement of the normalized dependence G(HV) with respect to the reference point: according to the change of PM response with HV at fixed intensity
Reference point
G in reference point (3 months interval between two measurements). Mean/σ are compatible with the statistical error G
Ecal operating range
Mean:0.029
σ =0.058
HV, kV
[G(2)-G(1)] / G[2]

10. Ecal: cell-to-cell inter-calibration level before 2009 data taking
G(HV): measured for 99.5% of phototubes:
statistical error: 3-4%
accuracy of the method: within 8%
Dispersion of modules light yield: < 8%
R/O ADC sensitivities: within ±5%
Clear πº→γγ signal was observed
immediately after LHC start-up
in the end of 2009
Di-photon invariant mass distribution, MeV/c² 10

11. Ecal calibration: Energy Flow
Improvement of cell-to-cell inter-calibration up to 4% level on the basis of relatively small statistics (few M of events)
Smoothing of the map of transverse energy depositions in detector: for each cell correction factor is produced on the basis of the mean deposit over 8 neighbouring cells (3x3)
No information from other sub-detectors is required; raw energy deposits in detector cells are used → no dependence on MC-based parameters employed in the reconstruction software
Absolute normalization: position of the net peak for πº→γγ in given section. [common scaling factor ~6% for all Ecal cells to achieve right value]
Before
After MC
π°, Inner
8.5±0.2
7.2±0.1
5.9±0.1
π°, Middle
8.1±0.2
6.8±0.1
6.3±0.1
π°, Outer
9.6±0.2
7.9±0.1
8.0±0.1 η
6.1±0.4
5.4±0.3
3.2±0.2
Outer Hcal (calibrated by other method)
Relative widths of πº→γγ / η→γγ peaks, %

12. Ecal: fine calibration
Next step: fine calibration with π°’s on the level of individual cells. Method is successfully tested on Monte Carlo data.
Real data: large amount of statistics is required (up to 250M for most peripheral cells). Under collection.
Energy of photon / electron candidate:
E = α E3x3 + β Eps
+ in case of photons SPD is involved to suppress conversions in front of the Calorimeter System
PS is now calibrated with precision better than 5% (Valentin’s talk)
α / β factors are under verification
Work on fine calibration of Ecal with π°
is well in progress.
Long-term plans: look at electrons (E/p method)
E/p
Middle

13. Physics with Ecal (2010) (also for PS and SPD)
N(η)/N(π°) =(16.7±1.6)%
MC:(17.6±1.7)%
η→γγ
η→γ γ
π°→γ γ
Di-photon invariant mass distribution, MeV/c²
Di-photon invariant mass distribution, MeV/c² 13

14. Hcal: radioactive source calibration
Originally developed for ATLAS TileCal
Two ~ 10 mCi Cs sources (one per each detector half) driven by hydraulic system
Each source propagates consecutively through 26 Hcal modules with an average velocity of about 20–40 cm/s. System of dedicated integrators measures PM anode currents every 5 ms
Relation factor between anode current and the measured particle energy is known from test beam:
Inner: C=41.07 (nA/mCi)/(pCl/GeV)
Outer: C=20.88 (nA/mCi)/(pCl/GeV)
Accuracy of the method:
absolute normalization ≈10% - dominated
by the uncertainty in the sources activity
cell-to-cell intercalibration: better than 4%
(test beam, confirmed by Energy Flow method)
Calibration is done regularly (every 1-2 months)
137
PM gain variation, ~3 month

15. Hcal: basic signals(2010) Outer Inner MC prediction: 0.824
E/p
E/p
Inner
Outer
MIPs, muons
MIPs, muons
E, MeV
E, MeV 15

16. Conclusions
both Ecal and Hcal are in good shape: >99.8% of r/o channels are operational
calorimeters provide L0 trigger since the moment when LHC started to deliver pp-interactions
smooth and stable operation during first months of data taking
for the vast majority of the cells timing is set with precision ±1ns
both Ecal and Hcal are already inter-calibrated with accuracy better than 4÷5%:
Ecal fine calibration is in progress
accuracy of the Hcal calibration is already sufficient to fulfill all detector tasks in the LHCb experiment 16