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20/02/2013 Eluned Smith Imperial College London 1 The LHCb detector and the determination of its downstream track efficiency. Eluned Smith 20/02/2013 Eluned Smith Imperial College London 2 Outline Overview of relevant

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SLIDE 1

The LHCb detector and the determination of its downstream track efficiency.

Eluned Smith

20/02/2013 Eluned Smith Imperial College London

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SLIDE 2

Outline

  • Overview of relevant parts of the LHCb detector.
  • What are downstream tracks?
  • Why do we what to better understand their efficiency?
  • Method proposed to determine downstream track

efficiency.

  • Analysis carried out so far.

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SLIDE 3

The Large Hadron Collider (LHC)

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SLIDE 4

The LHCb detector

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  • Vertex locator (VELO) ends

at ~ 700mm.

  • Sensors ~ 7mm from the

beam.

  • Resolution: 𝜏 𝑦, 𝑧, 𝑨 =

(16,15,90)ΞΌm.

  • TT tracker starts at ~ 2m.
  • Track must leave hits in

both TT and T1,2,3.

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Types of tracks at LHCb.

  • Upstream + Downstream = Long
  • Events can be registered from just downstream tracks,

when displaced vertex is downstream of the VELO.

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SLIDE 7

Motivation for improving downstream track efficiency.

  • Longstream track efficiency values well studied (2-3

significant figure error depending on bin).

  • Downstream track efficiency less well studied and

understood.

  • Importance: Various hidden sector theories predict long-

lived massive particles, which may decay beyond the VELO.

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SLIDE 8

Method to calculate downstream track efficiency.

  • Will use data from Ks events (decaying to two pions)

as Ks relatively long-lived.

  • Relation between observed number (π‘œ) and actual

(𝑂):

  • π‘œπ‘šπ‘π‘œπ‘• 𝑨, π‘ž, πœƒ = πœπ‘šπ‘π‘œπ‘• πœƒ, π‘ž, 𝑨 π‘‚π‘šπ‘π‘œπ‘•(𝑨, π‘ž, πœƒ)
  • π‘œπ‘’π‘π‘₯π‘œ 𝑨, π‘ž, πœƒ = πœπ‘’π‘π‘₯π‘œ πœƒ, π‘ž, 𝑨 𝑂𝑒𝑝π‘₯π‘œ(𝑨, π‘ž, πœƒ)
  • π‘‚π‘šπ‘π‘œπ‘• 𝑨, π‘ž, πœƒ =

π‘œπ‘šπ‘π‘œπ‘• 𝑨,π‘ž πœπ‘šπ‘π‘œπ‘• πœƒ,π‘ž,𝑨

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  • Use π‘‚π‘šπ‘π‘œπ‘• 𝑨, π‘ž, πœƒ to obtain 𝑂𝑒𝑝π‘₯π‘œ(𝑨, π‘ž, πœƒ)

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  • Use observed counts to extract πœπ‘’π‘π‘₯π‘œ πœƒ, π‘ž, 𝑨
  • πœπ‘’π‘π‘₯π‘œ πœƒ, π‘ž, 𝑨 =

π‘œπ‘’π‘π‘₯π‘œ 𝑨,π‘ž,πœƒ 𝑂𝑒𝑝π‘₯π‘œ(𝑨,π‘ž,πœƒ)

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SLIDE 10

Analysis and progress so far.

  • 1 data sample of ~ 8 Γ— 104 events from 2012 (about

0.2% of total data available).

  • 1 Monte Carlo (MC) generated sample of ~ 8 Γ— 106

events.

  • So far have invariant mass distributions and log of

number against 𝑨 for long/downstream tracks and data/MC (see slide 12) binned in momentum.

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SLIDE 11

𝐿

𝑑 selection.

  • Data sample: the life time of the 𝐿𝑑 was required to be >

1ps.

  • Information from RICH particle identification is used to

select pions.

  • In Monte Carlo only true 𝐿𝑑 are selected.
  • Tracks already tagged as either long or downstream.

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SLIDE 12

Samples from data (left) and MC (right) for the 20- 40 GeV bin for invariant mass.

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SLIDE 13

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Samples from data (left) and MC (right) for the 20- 40 GeV bin for number of 𝐿𝑑 against 𝑨

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SLIDE 14

Conclusion and future work

  • Downstream track efficiency: important in searches for

new long-lived particles.

  • Efficiency will be determined relative to long track

efficiency.

  • Next steps:
  • Understand the shape of the invariant mass and

𝑨 distributions.

  • More cuts?
  • Extrapolate plots to obtain πœπ‘’π‘π‘₯π‘œ

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SLIDE 15
  • Plots at

http://www.hep.ph.ic.ac.uk/~es708/downstrea m_track_efficiency

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Overall efficiency ratio and its error, 2012

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Samples from data for the 0- 20 GeV bin for invariant mass.

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SLIDE 18

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Samples from data for the 0- 20 GeV bin for log of the number of particles.