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VELO Upgrade-II studies and information

This  page collects information on studies and presentations relating to the prospective Upgrade-II Vertex Locator, to be installed in LS4 and operate during LHC Runs 5 and 6.


  Approved figures and plots for presentations Up2FiguresAndPlots




This upgrade aims to  collect data at a factor 5-10 larger instantaneous luminosity in the HL-LHC phase, which will lead to a corresponding increase in the radiation dose, particle and vertex multiplicity.

For general information on the background, aims, and parameters of the project, the following links may be useful.


We have an e-group: (archive) External link mark 

See also the general Upgrade-II tracking page External link mark.



TTFU (Think Tank for Future Upgrades) Meetings

VELO U2 Workshops

  • Mar 2018, "VELO U2 Retreat", Villars-sur-Ollon. agenda External link mark
  • Mar 2019, "VELO U2 Retreat v2", Villars-sur-Ollon. agenda External link mark

Dedicated VELO meetings

  • 4 Mar 2016 VELO Friday meeting
    • Chris Parkes: "Introduction"
    • Flavio Marchetto: "NA62 - Experience with Pixels with Timing"
    • Tony Affolder: "Radiation Hardness Constraints"
    • Marco Gersabeck: "Conservative design - geometry to survive radiation damage"
    • Jon Harrison: "Adveturous design - with pixel timing"
    • Massimiliano Fiorini: "Pixels with timing and FPGA-based track parameters"
    • Paula Collins: "SuperVELO"
  • 8 Feb 2019 VELO Friday meeting External link mark
    • Martin Van Beuzekom: "Silicon Timing"
    • Chris Parkes: "News on Upgrade II and VELO strawman design"
    • Mark Williams: "Proposal for testing 4D pattern recognition algorithms for VELO Upgrade-II"
    • Kevin Heijhoff: "Timepix3 Telescope Timing".
  • 5 Apr 2019 VELO Friday meeting External link mark
    • Misha Mikhasenko: "Impact of spatial vs Time resolution in U2 conditions"
    • Rehearsals for two TTFU Workshop talks from Martin VB. and Malcolm J.
  • 19 Jul 2019 VELO Friday meeting External link mark
    • Mark Williams: "U2 Review overview and timeline"
    • Misha Mikhasenko: "U2 reconstruction studies with Fast MC"
    • Laurent Dufour: "Timing for improved identification of detached tracks"
  • 27 Sep 2019 VELO Friday meeting External link mark
    • Tim Evans: "U2 Pattern Recognition studies"
  • 1 Nov 2019 VELO Friday meeting External link mark
    • Tim Evans: "U2 Pattern Recognition studies"
    • Misha Mikhasenko: "U2 reconstruction studies with Fast MC"
    • John Cobbledick: "The RAMP Challenge - PR studies with parameteric MC"
  • 15 Nov 2019 VELO Friday meeting External link mark
    • Adriano Lai, Alessandro Cardini: "Timespot"
  • 22 Nov 2019 VELO Friday meeting External link mark
    • Kazu Akiba: "Preparations for an Upgrade-II FTDR"
  • 13 Mar 2020 VELO Friday meeting External link mark
    • Laurent Dufour: "Timing impact on reconstrucing multi-track states"
    • Tim Evans: "U2 Pattern Recognition studies, 3D vs 4D (track and vertex)"
    • Misha Mikhasenko: "U2 reconstruction studies with Fast MC"
  • 27 Mar 2020 VELO Friday meeting External link mark
    • Laurent Dufour: "Rehearsal for U2 Workshop: Performance"
    • Oscar Francisco: "Rehearsal for U2 Workshop: Integration"
    • Kazu Akiba: "Rehearsal for U2 Workshop: Sensors and electronics"
  • 24 Apr 2020 VELO Friday meeting External link mark
    • Tim Evans: "Reconstruction Studies for LHCb VELO Upgrade-II"
    • Nicola Neri: "4D fast tracking for VELO Upgrade-II"
    • Angelo Carbone: "A fast simulation validation towards performance studies for a VELO Upgrade-II"
  • 17 July 2020 Dedicated VELO U2 FastSim meeting External link mark
    • Misha Mikhasenko: "CERN FastSim"
    • Mark Williams: "Manchester FastSim"
    • Marco Petruzzo: "Milano FastSim"
    • Angelo Carbone: "Bologna FastSim"
    • Laurent Dufour: "Exploratory ideas"
  • 17 July 2020 VELO Friday meeting External link mark
    • Serena Maccolini: "Performance studies for the Upgrade II"
    • Robbert Erik Geertsema: "IP, Decay time and SV association using time information"

Other internal LHCb presentations

VELO Upgrade-II Conference/external talks (incomplete)

Related dedicated meetings

  • Oct 2017, "New Dimensions in Silicon Detectors", Manchester (IoP meeting on pixels with timing). agenda External link mark

Notes on specific studies

Track Pattern recognition (3D)

Manuel Jahn (CERN summer student 2016) performed a pattern recognition study based on the Upgrade-I VELO simulation and design, but with the luminosity increased to U2 levels (2E34/cm/cm/s). He reported tracking performances for the U1 VELO, and for alternative scenarios, e.g. with the pixel pitch reduced from 55 to 27.5 microns, and/or with adjusted pattern recognition parameters.

Apart from the above presentations, his work is documented in his end-of-project report External link mark, and in the presentation he gave at the LHCb Tuesday meeting External link mark (slides External link mark).

More recently (2019) Tim Evans has run the latest U1 pattern recognition code over a sample of simulated events under U2 conditions. With the updates to the PR algorithm (notably the phi ordering and limited number of hits considered) the tracking performance is much improved compared to Manuel's findings in 2016. See his presentation from the VELO meeting External link mark of 27 Sep 2019 for details (for long tracks, ghost rate 1.5%, efficiency 95.7%). For the latest news, check the most recent update at a VELo Friday meeting from Tim (see above).

Track Pattern recognition (4D)

The Milan group (N. Neri, M. Petruzzo, P. Gandini) have performed general studies on the influence of adding timing information to tracking algorithms. Specific results for an LHCb-like detector were reported in the Annecy workshop External link mark in March 2018.

Misha Mikhasenko (2019) has developed some parametric simulation (in collaboration with others, e.g. John and Shantam from Manchester) to study the relative importance of pixel size compared to time resolution, both for physics performance and for resource use (combinatorics etc). See his presentation at the VELO meeting External link mark of 1 Nov 2019, and subsequent VELO Friday meeting udpates, for details.

The Manchester group (plus Vava Gligorov) have two students (Cobbledick, Taneja) developed a RAMP pattern recognition challenge, with the aim to provide a set of standard data samples (with precise time information) and scoring metrics for future VELO PR studies. See presentation in VELO meeting External link mark of 1 Nov 2019 for status and links.

The Nikhef group proposed a 4D pattern recognition project External link mark for Google Summer of Code 2019 ( Aaij, Hynds, Raven).

Vertex Reconstruction

Tim Evans (2019) has started to investigate PV reconstruction, using a sample of full MC generated under U2 conditions, both with and without timing information in the hits. As this is a quickly-evolving study, check his most recent update at a VELO Friday meeting (above) for the latest information.

Background rejection

Laurent Dufour (2019) has investigated the performance of flight-distance based metrics (e.g. IPchi2) to select signal tracks from long-lived b hadrons, and differentiate from prompt background. This was done using full MC under realistic U2 conditions, with cheated pattern recognition. He also investigated how the addition of timing information might help. Executive summary: Efficiency for selecting signals using IPchi2 becomes worse as number of other PVs in the event increases. With 50ps timing per track, this can be mitigated to some extent. See his presentation at the VELO meeting External link mark of 1 Nov 2019 for details.

A more sophisticated study presented on 13/3/2020 (see above) shows the potential impact on reconstructing multi-track states. As this is a quickly-evolving study, check Laurent's most recent update at a VELO Friday meeting (above) for the latest information.

PV mis-association fraction for long-lived particles, and timing

Following initial work by V. Gligorov (see TTFU presentation from Apr 2015) a number of increasingly realistic studies have been performed to determine the PV-association performance for long-lived particles, and the potential benefit of adding time information to the VELO. In particular, this was the subject of Biljana Mitreska's 2017 CERN Summer Student project, which for the first time included the option of having different timing precision in inner and outer radial regions of the VELO.

Apart from the above general presentations, this work is documented in:

This work was continued by a Manchester Masters' student (Aditya Bhanderi) who among other things added a Kalman track fit to allow the influence of changing the pixel size to be studied. Later (Sep 2018) this work was continued by another CERN Summer student (Ziga Brencic), who made significant code improvements and generalised the studies to different possible channels.
Topic revision: r24 - 2022-03-15 - KazuyoshiCarvalhoAkiba

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