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B-physics trigger for the ATLAS detector at LHC: recent developments - - PowerPoint PPT Presentation

Oct 27, 2022 181 likes •356 views

B-physics trigger for the ATLAS detector at LHC: recent developments B. Epp, V.M. Ghete and D. Kuhn Institute for Experimental Physics, Innsbruck ur Bildung, Wissenschaft und Kultur, Arbeit unterst utzt vom Bundesministerium f

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SLIDE 1

B-physics trigger for the ATLAS detector at LHC: recent developments⋆

  • B. Epp, V.M. Ghete and D. Kuhn

Institute for Experimental Physics, Innsbruck

⋆Arbeit unterst¨ utzt vom Bundesministerium f¨ ur Bildung, Wissenschaft und Kultur, ¨ Osterreich.

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Introduction ATLAS classical B-physics menu CP-Violation studies: B0

d → J/ψK0 S

with J/ψ → e+e− J/ψ → µ+µ− B0

d → ππ

B0

s → J/ψφ

B0

s oscillation studies:

B0

s → Dsπ, B0 s → Dsa1 with Ds → φπ

Rare decays: Bd,s → µ+µ−X with X = ‘

′, K∗0, ρ0

. . . but B-physics is and will remain for the next five years a very dynamic domain, both theoretically and experimentally (BaBar, Belle, CDF, D0,. . .), therefore new channels may become interesting (Bc, B0

d → K∗γ, . . .).

B-physics general programme: to be pursued in the ‘low luminosity’ run of the LHC (latest luminosity target: 2 × 1033 cm2s−1). Rare decays: both low and high luminosity (1034 cm2s−1) runs.

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 3

Experiment overview Inner detector:

  • discrete semiconductor pixel

and strip detectors

  • continuous

straw-tube tracking detectors with transition radiation

  • inside the solenoid:

2 T magnetic field.

Calorimetry:

  • highly

granular LAr EM calorimeter: |η| < 3.2

  • hadron calorimeter (scintil-

lator-tile): |η| < 4.9

Muon spectrometer:

  • air-core toroid system
  • n average ∼ 0.5 T.
  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 4

ATLAS trigger architecture

ATLAS-TDR-016; CERN-LHCC-2003-022 (May 2003)

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 5

B-physics trigger in the DAQ/HLT Technical Proposal Level-1 Trigger:

  • single muon, with pT > 6 GeV.

Level-2 Trigger:

  • µ confirmation within LVL1 RoI in

the Inner Detector and precision muon chambers

  • track reconstruction in the whole

ID (‘full scan’)

  • track kinematic cuts and channel-

specific mass cuts Event Filter:

  • channel-specific

selections done using set of loose offline cuts. Start-up luminosity target: 1033 cm−2s−1

HLT selection (in addition to muon pT > 6GeV) Selected

B-channels

Rate (Hz) LVL2 Event Filter Hadron channels 3 hadrons pT > 1.5 GeV, invariant mass cuts for φ and Ds EF: invariant mass, vertex fit quality, trans- verse decay length and angle cuts. Bs → Ds π Ds → φ(K+K-)π 270 41 2 hadrons pT > 4 GeV, angle, ∑pT and loose invariant mass cuts EF: invariant mass, vertex fit quality, trans- verse decay length and angle cuts. Bd → ππ Bd → Κπ 80 5 Electron channel 2 tracks pT > 0.5 GeV, TRT ee identification, ∆η, ∑pT, ∆Z and invariant mass cuts EF: invariant mass, vertex fit quality, trans- verse decay length and angle cuts. bb→ µBd(J/ψ(ee)K0) 660 32 Not covered in this note single e, pT > 5 GeV, identification in TRT+ECAL of electron reconstructed with pT > 4 GeV in the Inner Detector bb → e Bd(J/ψ(µµ)K0) 90 To be studied second µ (pT > 5 GeV, |η| < 2.5) identification in muon chambers + matching with the Inner Detector Bd → J/ψ(µµ)(K/K*), Bs → J/ψ(µµ)φ, B → µ µ, B → K0*µµ, etc., Λb → Λ0 J/ψ(µµ), Bc → J/ψ(µµ) π 170 Total B-physics trigger rate 1270 ~100

ATL-DAQ-2000-031 (Jun 2000)

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 6

From beauty to reality: after HLT Technical Proposal Changes in detector geometry:

  • increased beam-pipe diameter (41.5 mm → 50.5 mm)
  • increased pixel length in B-layer (300 µm → 400 µm)

Financial constraints: B-physics trigger resources have to be minimized. Financial uncertainties: some items to be deferred → reduced detector at start-up

  • only 2 of the 3 pixel layers (inner B-layer maintained), TRT only at η < 2
  • reduced HLT system → reduced computing resources at LVL2 and EF. Priority

given to high-pT physics, B-physics hadronic triggers first to be affected. LHC parameters: luminosity target for start-up doubled to 2 × 1033 cm−2s−1 Alternatives to reduce the resource requirements:

  • require at LVL1, in addition to single µ trigger, a second muon, a JET or an EM

RoI, then reconstruct at LVL2 and EF within RoI

  • re-analyze thresholds and use a flexible trigger strategy, depending on luminosity.
  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 7

B-physics trigger strategy in HLT TDR Strategy adapted to limited bandwidth:

  • Start with a di-muon trigger for higher luminosities LHC fills.
  • Add further triggers (hadronic final states, final states with electrons and

muons): in the beam coast for the low luminosity fills. = ⇒ always fill the available bandwidth in the HLT system. Trigger types:

  • di-muon trigger: two muons at LVL1
  • hadronic final states triggers: single muon at LVL1, followed by

– RoI reconstruction in ID at LVL2, from Jet RoI trigger at LVL1 – full-scan in ID at LVL2

  • triggers for final states with electrons and muons: single muon at LVL1

– RoI reconstruction in TRT at LVL2, from EM RoI trigger at LVL1 – full-scan in TRT at LVL2

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 8

Di-muon triggers

Luminosity: 1 × 1033. Di-muon rates: single muon all + second muon.

Examples of final states with two muons:

  • J/ψ → µµ: B0

d → J/ψKS, B0 s →

J/ψφ, B0

s → J/ψη, Λb → Λ0J/ψ

  • B0

s, d → µµ , B0 d → (K∗0, ρ0, φ)µµ

LVL1: at least two muons. Minimum thresholds: pT 5 GeV Muon Barrel pT 3 GeV Muon End-Cap

  • actual thresholds: ⇐

= LVL1 rate.

  • mainly due to muons from heavy flavour

decays, plus single muons double counted in end-cap trigger chambers. LVL2 and EF: confirmation of muons us- ing ID and precision muon chambers. Spe- cific selection at EF: mass and decay length cuts, after vertex reconstruction.

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 9

Hadronic final states Channels studied so far: B0

d → ππ and B0 s → Dsπ, B0 s → Dsa1.

LVL1 trigger: single muon, threshold determined by trigger rate and luminosity. Threshold values considered: pT > 6 ÷ 8 GeV. LVL2 trigger: confirms muon using ID and precision muon chambers; reconstruct tracks in ID, select Ds → φπ or B0

s → ππ based on mass cuts.

Options for ID track reconstruction:

  • require a low ET LVL1 Jet RoI, in addition to a single muon trigger, and

reconstruct the tracks at LVL2 in the RoI only. Advantages: modest resources

  • required. Disadvantages: lower efficiency expected. Problem: low ET LVL1 Jet

difficult to trigger.

  • track reconstruction within entire SCT, Pixel and (optionally) TRT detectors;

‘full-scan’: better efficiency, but greater resources. EF: refit ID tracks in LVL2 RoI, select Ds → φπ or B0

d → ππ based on mass cuts

and vertex cuts.

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 10

Hadronic final states: simulation studies Two sets of studies:

  • Fast simulation of calorimeter trigger based on ATLFAST + parameterised

calorimeter simulation. Rather complex: – B-field, longitudinal and transverse shower profiles – pulse history, digitization and Bunch Cross Identification system (BCID) – complete LVL1 trigger algorithms

  • A full detector simulation with an incomplete simulation of the LVL1 calorimeter

– e/γ/τ algorithm: tested, debugged, validated. – Jet algorithm: tested, debugged, but not yet fully validated. – Emiss

T

, Esum

T : coded, not yet debugged/validated.

– noise added for both calorimeters and for trigger towers – calibration (ECal) slightly updated. – towers still built from CaloCells, version using LAr/Tile tower simulation in work = ⇒ no Bunch Cross Identification system yet.

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 11

Hadronic final states: simulation studies Procedure:

  • use a sliding window of size |∆η| × |∆φ| = 0.8 × 0.8 in the LVL1 calorimeter

trigger to find a jet associated to the second B-hadron.

  • determine the Jet RoI multiplicity
  • match the RoI found with the B-hadrons and determine the Jet RoI efficiency.

Samples:

  • b¯

b → µ(pT > 6 GeV) X events

  • signal events: B0

s → Dsπ and B0 d → ππ

Sample production: all events simulated with a LVL1 µ6 trigger.

  • Generator: Pythia 6.2.
  • Simulation: initial-detector geometry.
  • Reconstruction: Athena reconstruction (trigger tower noise on, Tile noise on,

LAr complete RDO and cell production with noise on/off).

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 12

Hadronic FS, full simulation: number of LVL1 Jet ROIs Sample: b¯ b → µ6 X events, with tower noise on, Tile noise on, and LAr noise on (left plot) off (right plot).

20 40 60 80 100 5 10 15 20

Jet ROI multiplicity ET > 6 GeV Mean: 5.91 RMS: 2.30

50 100 150 200 5 10 15 20

Jet ROI multiplicity ET > 6 GeV Mean: 1.93 RMS: 1.54

  • increased Jet RoI multiplicity: mainly due to LAr noise.
  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 13

Hadronic FS, full simulation: B0

s efficiency

Sample: B0

s → Dsπ events, with tower noise, Tile noise and LAr noise.

Count only B0

s with final decay products (K+, K−, π, π) having pT > 1 GeV.

Matching criteria: RoI within |∆η|, |∆φ| < 0.4 of B0

s hadron.

Efficiency = Number of truth B0

s matching a Jet RoI

Number of truth B0

s

0.25 0.5 0.75 1 1.25 10 20 30 40

Efficiency Bs pT [GeV] ET > 5 GeV

0.25 0.5 0.75 1 1.25 10 20 30 40

Efficiency Bs pT [GeV] ET > 6 GeV

0.25 0.5 0.75 1 1.25 10 20 30 40

Efficiency Bs pT [GeV] ET > 8 GeV

80% efficiency: ET > 5 GeV 6 GeV 8 GeV pB0

s

T >

14 GeV 16 GeV 18 GeV

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 14

Hadronic FS: fast vs full simulation

5 10 15 5 10 15 20

Jet ROI multiplicity ET [GeV] bb

– → µ6X

Bs → Ds π Fast simul.

0.25 0.5 0.75 1 10 20 30

Efficiency Bs pT [GeV] ET > 5 GeV fs ET > 5 GeV ET > 6 GeV ET > 8 GeV

Preliminary conclusions from full simulation:

  • increased Jet RoI multiplicity with respect to fast simulation, probably due to
  • BCID. Expect to come closer after BCID system implemented.
  • efficiency slightly worse than that from fast simulation: realistic material, more

than fast simulation was tuned to reproduce.

  • reasonable efficiency can be achieved using low ET Jet RoI.
  • need to compute efficiency wrt offline efficiency.
  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 15

Muon-electron final states: using LVL1 EM RoI Similar to hadronic final states: require a low ET LVL1 EM RoI, in addition to a single muon trigger, and reconstruct the tracks at LVL2 in the RoI only. Only studies with fast simulation of the calorimeter trigger available up to now. For EM RoI ET > 2 GeV:

  • mean multiplicity = 1.1 for B → µ6X events
  • efficiency to tag both e in J/ψ(ee): 80% for e with pT > 3 GeV.

Need to be verified using full simulation of calorimeter trigger.

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 16

Resource estimates

B-physics trigger menu: Level-1 Level-2 Event Filter MU6 + MU6 mu6 + mu6 J/ψ(mu6,mu6)vtx, B(mu6,mu6)vtx, etc MU6[8] mu6[8] + Bd(pi4,pi4) mu6[8] + Bd(pi4,pi4)vtx mu6[8] + Ds(phi(K1.5K1.5)pi1.5) mu6[8] + Ds(phi(K1.5K1.5)pi1.5)vtx Number of c.p.u: ‘Full scan’ mu6, 1033 cm−2s−1 mu8, 1033 cm−2s−1 mu8, 2 × 1033 cm−2s−1 LVL2 62.1 25.9 98.6 EF 1.2 0.5 1.5 Total c.p.u. 63.3 26.4 100.1 RoI-guided LVL2 17.7 7.4 23.9 EF 1.4 0.6 1.7 Total c.p.u. 19.1 8.0 25.6 Full high-pTmenu, 11 – 20 11 – 20 20 – 35 minimal B-physics RoI-guided: assume 1.75 RoIs of size 10% of the ID. Estimates: preliminary!

  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003

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SLIDE 17

Summary

  • The B-physics trigger strategy has been revised after HLT Technical Proposal,

taking into account: – change of LHC luminosity target to 2 × 1033 cm2s−1 – changes in detector geometry, possibility of a reduced detector at start-up – tight funding constraints

  • New alternatives considered in order to reduce resource requirements:

– EF reconstruction done in the RoI given by LVL2 – replace ID full-scan at LVL2 with a reconstruction within RoI given by low ET LVL1 calorimeter trigger

  • Fast simulation studies indicate that this approach has the potential to provide a

viable alternative to the ID full-scan, requiring significantly lower resources.

  • The full simulation studies confirm that reasonable efficiencies can be obtained.

It is not yet possible to confirm the multiplicities with the full simulation since this requires the inclusion of trigger towers and bunch-crossing identification.

  • More work needed for final results.
  • V. M. Ghete

ATLAS B-Physics Trigger ¨ OPG FAKT03, Oct. 4, 2003