Novel Real-time Alignment and Calibration of the LHCb ......LHCb OT Run 135673 Run the job for every...
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Novel Real-time Alignment and Calibration of the LHCb Detector in Run II Mark Tobin and Zhirui Xu , on behalf of the LHCb collaboration ´ Ecole Polytechnique F´ ed´ erale de Lausanne, Lausanne, Switzerland Running Conditions from Run I to Run II Higher energy: √ s = 7(8) TeV ⇒ 13 TeV. 15% increase of inelastic collision rate. 20% increase of multiplicity per collision. 60% increase of σ b ¯ b and σ c ¯ c . Reduced bunch spacing: 50 ns ⇒ 25 ns. Similar instantaneous luminosities: 4·10 32 cm -2 s -1 . LHCb Trigger Schemes 40 MHz bunch crossing rate 450 kHz h ± 400 kHz μ/μμ 150 kHz e/γ L0 Hardware Trigger : 1 MHz readout, high ET/PT signatures Software High Level Trigger 29000 Logical CPU cores Offline reconstruction tuned to trigger time constraints Mixture of exclusive and inclusive selection algorithms 5 kHz Rate to storage Defer 20% to disk LHCb Run I Trigger Diagram 40 MHz bunch crossing rate 450 kHz h ± 400 kHz μ/μμ 150 kHz e/γ L0 Hardware Trigger : 1 MHz readout, high ET/PT signatures Software High Level Trigger 12.5 kHz Rate to storage Partial event reconstruction, select displaced tracks/vertices and dimuons Buffer events to disk, perform online detector calibration and alignment Full offline-like event selection, mixture of inclusive and exclusive triggers LHCb 2015 Trigger Diagram Advantages of Real-time Align. and Calib. Improves trigger selection. Minimises the difference between online and offline performances. Ensures the stability of the alignment quality. Enables physics analyses directly on the trigger output. Degrees of Freedom for Alignment 3 translations and 3 rotations for each element Number of elements to be aligned: VELO: 86 TT: 135 IT: 64 OT: 496 Constrained to nominal, survey or previously aligned position LHCb Detector Vertex Reconstruction 2012 data Decay Time Resolution B 0 s → D s - π + B 0 s → J /ψφ Mass and Momentum Resolution J /ψ → μ + μ - Long tracks Dimuon resonances PID Performance Neutral Pion Reconstruction Resolved π 0 D 0 → K - π + π 0 Merged π 0 D 0 → K - π + π 0 DAQ data volume 1.5 TBytes/second in Run II Alignment and Calibration Impact on Physics Performance The spatial alignment of the detector and the accurate calibration of its subcomponents are essential elements to achieve the best physics performance. LHCb Preliminary σ Υ(1S ) = 86 MeV/c 2 First alignment LHCb Preliminary σ Υ(1S ) = 44.3 MeV/c 2 Improved alignment An exclusive selection using hadron particle identification criteria relies on the complete calibration of the RICH detectors. Without PID B 0 → K π B 0 → ππ B 0 s → KK With PID B 0 → K π B 0 → ππ B 0 s → KK Alignment and Calibration Framework in Run II Automatic evaluation at the beginning of each fill. Track reconstruction parallelised on several nodes of the HLT farm. Alignment constants computated single node. Only a few minutes needed to run all alignment tasks. Special HLT1 selection line enriched with well known particle decays (e.g. D → K π , J / ψ → μμ etc). Two different alignment tasks (same state diagram): Offline Ready Running Paused Alignment configure (initialise), O(2min) start continue pause stop stop reset (finalize) new constants Analyzer performs the track reconstruction based on the alignment constants provided by the iterator. Iterator collects the output of the analyzers and minimizes χ 2 computing the alignment constants for the next iteration. VELO, Tracker and Muon System Alignment Kalman filter fit to minimise the χ 2 , based on residuals of reconstructed tracks. Takes into account multiple scattering and energy loss. Uses magnetic field information. Applies mass and vertex constraints. Independent jobs for VELO, Tracker and Muon system alignment. VELO: performed at the beginning of each fill and updated immediately if required. Tracker: run after VELO for each fill, update expected every few weeks. Muon system: run after Tracker for each fill, variation not expected but used as monitoring. Run Number 74000 76000 78000 80000 m] μ ) [ A-C PVx ∆ Mean ( -20 -15 -10 -5 0 5 10 15 20 LHCb VELO Maximum variation ∼±10 μm RICH Mirror Alignment Fit the variation of the Cherenkov angle as function of the polar angle to extract the misalignments (θ x , θ y ): ∆θ = θ x cos φ + θ y sin φ and θ x and θ y are on the HPD detector plane. The alignment constants (1090) are determined at the beginning of each fill. OT and RICH Calibration Strategy in Run II Online analysis task running on single CPU. New parameters evaluated from fits to monitoring histograms. Global Time Alignment for OT Drift-time t TDC measurement: t TDC = t 0 + t tof + t drift + t prop , with t 0 = t collision - t clock + t module - t gate A single condition which accounts for the time alignment between the collision time and the LHCb clock. [ns] n-1 0 - t n 0 t -2 -1 0 1 2 Calibrated modules/ (0.04 ns) 0 50 100 150 200 250 300 Before calibration After 1 iteration LHCb OT Run 135673 Run the job for every run and update the constant if above a certain threshold. RICH Calibration Refractive index calibration (1940 constants): Depends on the gas mixture, temperature and pressure. Fit on the Cherenkov angle differences ∆θ . Corrections calculated and updated every run. HPD calibration (2 constants): Electrostatic effect (probably) due to switching off the HV for every injection. Fit a circle to the HPD image. Corrections calculated and updated every run. Anode images, before and after cleaning and Sobel filter. CALO Calibration A relative calibration online using occupancy method. Occupancy for each cell defined as O (x , y , I th , K )= ∑ i >I th F (x , y , i , K ) / ∑ i F (x , y , i , K ). Ratio of occupancies proportional to changes in hardware characteristics. HV adjusted on a per fill basis based on the gain changes calculated from the occupancy profiles. References [1] R. Aaij et al., Int.J.Mod.Phys. A30, 1530022 (2015). [2] R. Aaij et al., JINST 9, 09007 (2014). [3] J. Amoraal et al., Nucl.Instrum.Meth. A712, 48 (2013). [4] M. Adinolfi et al., Eur.Phys.J. C73, 2431 (2013). [5] W. Hulsbergen, Nucl.Instrum.Meth. A600, 471 (2009). [6] R. Arink et al., LHCb-DP-2013-003. FRONTIER DETECTORS FOR FRONTIER PHYSICS - 13 th Pisa Meeting on Advanced Detectors Contact: [email protected]
Transcript of Novel Real-time Alignment and Calibration of the LHCb ......LHCb OT Run 135673 Run the job for every...
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Novel Real-time Alignment and Calibration of the LHCbDetector in Run II
Mark Tobin and Zhirui Xu, on behalf of the LHCb collaboration
École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
Running Conditions from Run I to Run II
Higher energy:√s = 7(8) TeV ⇒ 13 TeV.
15% increase of inelastic collision rate.20% increase of multiplicity per collision.60% increase of σbb̄ and σcc̄ .
Reduced bunch spacing: 50 ns ⇒ 25 ns.Similar instantaneous luminosities: 4·1032 cm−2s−1.
LHCb Trigger Schemes
40 MHz bunch crossing rate
450 kHzh±
400 kHzµ/µµ
150 kHze/γ
L0 Hardware Trigger : 1 MHz readout, high ET/PT signatures
Software High Level Trigger
29000 Logical CPU cores
Offline reconstruction tuned to trigger time constraints
Mixture of exclusive and inclusive selection algorithms
5 kHz Rate to storage
Defer 20% to disk
LHCb Run I Trigger Diagram
40 MHz bunch crossing rate
450 kHzh±
400 kHzµ/µµ
150 kHze/γ
L0 Hardware Trigger : 1 MHz readout, high ET/PT signatures
Software High Level Trigger
12.5 kHz Rate to storage
Partial event reconstruction, select displaced tracks/vertices and dimuons
Buffer events to disk, perform online detector calibration and alignment
Full offline-like event selection, mixture of inclusive and exclusive triggers
LHCb 2015 Trigger Diagram
Advantages of Real-time Align. and Calib.
Improves trigger selection.
Minimises the difference between online and offlineperformances.
Ensures the stability of the alignment quality.
Enables physics analyses directly on the trigger output.
Degrees of Freedom for Alignment
3 translations and 3 rotations for each element
Number of elements to be aligned:VELO: 86 TT: 135 IT: 64 OT: 496
Constrained to nominal, survey or previously alignedposition
LHCb Detector
Vertex Reconstruction
2012 data
Decay Time Resolution
B0s → Ds−π+
B0s → J/ψφ
Mass and Momentum Resolution
J/ψ→ µ+µ−
Long tracks
Dimuon resonances
PID Performance
Neutral Pion Reconstruction
Resolved π0
D0 → K−π+π0Merged π0
D0 → K−π+π0
DAQ data volume 1.5 TBytes/second in Run II
Alignment and Calibration Impact on Physics Performance
The spatial alignment of the detector and the accuratecalibration of its subcomponents are essential elements toachieve the best physics performance.
LHCb Preliminary
σΥ(1S) = 86 MeV/c2
First alignment
LHCb Preliminary
σΥ(1S) = 44.3 MeV/c2
Improved alignment
An exclusive selection using hadron particle identificationcriteria relies on the complete calibration of the RICH detectors.
Without PID
B0 → KπB0 → ππB0s → KK
With PID
B0 → KπB0 → ππB0s → KK
Alignment and Calibration Framework in Run II
Automatic evaluation at the beginning of each fill.
Track reconstruction parallelised on several nodes of the HLTfarm.
Alignment constants computated single node.
Only a few minutes needed to run all alignment tasks.
Special HLT1 selection line enriched with well known particledecays (e.g. D → Kπ, J/ψ→ µµ etc).Two different alignment tasks (same state diagram):
Offline
Ready
RunningPaused
Alignment
configure(initialise),O(2min)
start
continue
pause
stopstop
reset (finalize)
new constants
Analyzer performs the track reconstruction based on the alignment constants provided by the iterator.
Iterator collects the output of the analyzers and minimizes χ2 computing the alignment constants for the nextiteration.
VELO, Tracker and Muon System Alignment
Kalman filter fit to minimise the χ2, based on residuals of reconstructed tracks.Takes into account multiple scattering and energy loss.Uses magnetic field information.Applies mass and vertex constraints.
Independent jobs for VELO, Tracker and Muon system alignment.
VELO: performed at the beginning of each fill and updatedimmediately if required.
Tracker: run after VELO for each fill, update expected every fewweeks.
Muon system: run after Tracker for each fill, variation notexpected but used as monitoring. Run Number74000 76000 78000 80000
m]
µ) [
A-C
PVx
∆M
ean
(
-20
-15
-10
-5
0
5
10
15
20LHCb VELO
Maximum variation ∼ ±10 µm
RICH Mirror Alignment
Fit the variation of the Cherenkov angle as function of the polarangle to extract the misalignments (θx , θy):
∆θ = θx cos φ + θy sin φ
and θx and θy are on the HPD detector plane.
The alignment constants (1090) are determined at the beginning ofeach fill.
OT and RICH Calibration Strategy in Run II
Online analysis task running on single CPU.
New parameters evaluated from fits to monitoring histograms.
Global Time Alignment for OT
Drift-time tTDC measurement:
tTDC = t0 + ttof + tdrift + tprop,
with t0 = tcollision− tclock + tmodule− tgateA single condition which accounts for the time alignmentbetween the collision time and the LHCb clock. [ns]n-10 - tn0t
-2 -1 0 1 2
Cal
ibra
ted
mod
ules
/ (0.
04 n
s)
0
50
100
150
200
250
300
Before calibration
After 1 iteration
LHCb OTRun 135673
Run the job for every run and update the constant if above a certain threshold.
RICH Calibration
Refractive index calibration (1940 constants):Depends on the gas mixture, temperature and pressure.Fit on the Cherenkov angle differences ∆θ.Corrections calculated and updated every run.
HPD calibration (2 constants):Electrostatic effect (probably) due to switching off the HV forevery injection.Fit a circle to the HPD image.Corrections calculated and updated every run.
Anode images, before and after cleaning and Sobel filter.
CALO Calibration
A relative calibration online using occupancy method.Occupancy for each cell defined as O(x , y , Ith,K ) = ∑i>Ith F (x , y , i ,K )/ ∑i F (x , y , i ,K ).Ratio of occupancies proportional to changes in hardware characteristics.
HV adjusted on a per fill basis based on the gain changes calculated from the occupancyprofiles.
References
[1] R. Aaij et al., Int.J.Mod.Phys. A30, 1530022 (2015).
[2] R. Aaij et al., JINST 9, 09007 (2014).
[3] J. Amoraal et al., Nucl.Instrum.Meth. A712, 48 (2013).
[4] M. Adinolfi et al., Eur.Phys.J. C73, 2431 (2013).
[5] W. Hulsbergen, Nucl.Instrum.Meth. A600, 471 (2009).
[6] R. Arink et al., LHCb-DP-2013-003.
FRONTIER DETECTORS FOR FRONTIER PHYSICS - 13th Pisa Meeting on Advanced Detectors Contact: [email protected]
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