Novel Real-time Alignment and Calibration of the LHCb ... ... LHCb OT Run 135673 Run the job for...

Novel Real-time Alignment and Calibration of the LHCb ... ... LHCb OT Run 135673 Run the job for every
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Transcript of Novel Real-time Alignment and Calibration of the LHCb ... ... LHCb OT Run 135673 Run the job for...

  • Novel Real-time Alignment and Calibration of the LHCb Detector 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 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

    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+π0 Merged 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 accurate calibration of its subcomponents are essential elements to achieve the best physics performance.

    LHCb Preliminary

    σΥ(1S) = 86 MeV/c 2

    First alignment

    LHCb Preliminary

    σΥ(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

    B0 → Kπ B0 → ππ B0s → KK

    With PID

    B0 → Kπ B0 → ππ B0s → 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 → 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 next iteration.

    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 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 Number74000 76000 78000 80000

    m ]

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    A -C

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    ea n

    (

    -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 (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 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 tTDC measurement:

    tTDC = t0 + ttof + tdrift + tprop,

    with t0 = tcollision− tclock + tmodule− tgate A single condition which accounts for the time alignment between the collision time and the LHCb clock. [ns]n-10 - tn0t

    -2 -1 0 1 2

    C al

    ib ra

    te d

    m od

    ul es

    / ( 0.

    04 n

    s)

    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 , 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 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 - 13th Pisa Meeting on Advanced Detectors Contact: zhirui.xu@epfl.ch