T&A: Tracking and Alignment (and Vertexing)

LHCb physics performance working group for matters of Tracking, Alignment, and Vertexing. Also represented in the OPG as Alignment and as Tracking.


See Flavour Tagging.

TB: Technical Board

Advisory body to the LHCb management on all aspects of detector design, optimization, safety and cost.

TCK: Trigger Configuration Key

A unique 32-bit configuration value (in base 16) representing a given trigger configuration (sequence of algorithms and selection cuts).

TDR: Technical Design Report

A document submitted to the LHCC of CERN describing the design of a subdetector or other subsystem (e.g. online, trigger, computing). This document also describes the cost of the detector and which institutes will be responsible for which elements of the construction. The TDRs of LHCb and the upgrades are collected here. The document is reviewed by the LHCC, with involvement from the RRB for financial aspects.

Technical Proposal

A document submitted to the LHCC of CERN describing the design of a new experiment or major upgrade, outlining the physics case and detector design. This document contains more detail than the LoI, for example reporting on R&D that shows the feasibility of the project and possibly estimating the cost. The LHCC reviews the document and determines if the collaboration should proceed to the next stage of approval, typically TDRs for the individual subdetectors and systems of the experiment. If costs are involved the RRB of CERN is involved in the approval.

For the original LHCb experiment this is CERN-98-004 followed by an LHCb reoptimized detector design and performance TDR that is CERN/LHCC 2003-030. For the LHCb Upgrade I the equivalent document is known as a Framework TDR, and is CERN/LHCC-2012-007. For the LHCb Upgrade II the equivalent document is due to be submitted around late 2020.

Tier (Grid)

Grid sites are split into tiers depending on their resources. Tier 1 (i.e. RAL, PIC) and tier 2 sites (mostly universities) store data, the tier 1s in particular storing raw data. The tier 3 sites do not store data. See here for details.


Trigger decisions can be classified into three categories:

  • Trigger On Signal (TOS): a positive decision can be reached using information from the signal candidate.
  • Trigger Independently of Signal (TIS): a positive decision can be reached using information from the rest of the event.
  • Trigger on both (TOB): a positive decision requires the entire event.

Note that the TIS and TOS categories are not mutually exclusive.


The signature that is reconstructed when a charged particle travels through LHCb. Split into 5 types depending on which parts of the tracking system are used:

  • Downstream Track
  • Long track (forward track or match track)
  • T Track
  • Upstream Track (in upgrade jargon also "Velo-UT track")
  • Velo Track

"Track types in LHCb"

Track Type

The type of the track used in TupleToolTrackInfo, and anything that includes it. See Tracking strategies used in LHCb or TupleToolTrackInfo for details. The types are:

ID Track type
0 Unknown
1 VELO track
2 2D VELO track
3 Long (or forward) track
4 Upstream track
5 Downstream track
6 Seed track
7 Muon track
8 Calorimeter cosmic track
9 TT track

TT: Tracker Turicensis

The tracking station located immediately before the magnet in Runs 1 and 2. It played an important role in reconstructing tracks that originate outside the VELO, such as those that come from K-shorts and Lambda baryons. Much like the IT stations, the TT consists of 4 layers of silicon strips, oriented at 0°, −5°, +5° and 0° from the vertical.

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