LUCID-3 is an upgrade project in the ATLAS experiment for the high luminosity LHC (HL-LHC). The present
LUCID-2 detector
will not work at the HL-LHC because of hit-saturation which occurs when all channels in the detector detects
particles for almost all colliding proton bunches. Additional challenges for LUCID at the HL-LHC will be the high radiation
levels which requires the possibility to change photomultipliers every year and new LHC vacuum equipment (the VAX) which
will be installed close to LUCID.
The JF-A prototype detector
The JF-C prototype detector
The JN-A prototype detector
The FIB-C prototype detector
Responsible for the content of this page is
Vincent Hedberg
The LUCID-2 detector 
LUCID-1 was a gas Cherenkov detector used for luminosity measurements in LHC run 1 (2010-2012).
Photos and drawings of the LUCID-1 detector used in LHC run 1 can be found
here.
LUCID-2 consisted only of photomultipliers that surrounded the beampipe on both sides of the interaction point at a distance of 17 m.
The center of the photomultipliers was at a distance
of 125 mm from the beamline. This detector was operational already in LHC run 2 (2015-2018).
Photos of the LUCID-2 detector used in LHC run 2 can be found
here.
ATLAS delivers most precise luminosity measurement at LHC - 24 January 2023 | By the ATLAS Collaboration.
Charged particles going through the radiation-hard quartz window of the photomultipliers in LUCID-2
can produce Cherenkov light that is detected by the photomultipliers.
The detector is digitizing the pulses from the photomultipliers and count signals above a threshold (hits) and the integral of the signals (charge).
The stability of the detector respons was monitored by
Cherenkov light produced by weak Bi-207 sources placed on the windows of the photomultipliers.
The Bi-207 sources give out monoenergetic electrons from internal conversion that have an energy above the Cherenkov threshold in quartz.
During LHC run 3 (2022-2026) the detectors consisted of three sets of 4+4 R760 photomultipliers called BI1, BI2 and BI3 and one set of 4+4 photomultipliers called MOD. The signals from three of these four sets could be digitized at any given time with the purpose-built LUCROD front-end electronics.
The purpose-built LUMAT electronics could combine eight measurements from both sides and produced one measurement called BI HITOR from BI3 PMTs (except in 2022 when BI1 PMTs were used) and one measurement called BI2 HITOR from BI2 PMTs (except in 2026 when BI1 PMTs were used).
During 2022 and 2023 MOD consisted of R760 photomultipliers that had been modified during the manufacture such that they had a thin ring shaped layer of aluminium deposited between the quartz window and the photocathode. The center hole of this ring had
a diameter of 7 mm which can be compared to the 10 mm diameter of the photocathode and the layer thus
reduced the acceptance of these photomultipliers with a factor of 2. These modified PMTs suffered from a large pile-up of small signals created at the edge of the aluminium ring. They were therefore exchanged for smaller R1635 photomulitpliers with an 8 mm diameter window and these were used during 2024, 2025 and 2026.
LUCID web pages
The ATLAS Forward Detector project
Public Forward Detector Plots for Collision Data
Approved Forward Detector Performances Plots using MC or no-collision data
Luminosity Working Group
Public ATLAS Online Luminosity Plots for Run-3 of the LHC
LUCID detector twiki page
LUCID Internal Plots
FWD speakers comittee
LUCID run list
LUCID presentations
LUCID and luminosity papers and reports
The new LUCID-2 detector for luminosity measurement and monitoring in ATLAS
2018 JINST 13 P07017.
Luminosity determination in pp collisions at 13 TeV using the ATLAS detector at the LHC
Eur. Phys. J. C 83, 982 (2023).
Preliminary analysis of the luminosity calibration of the ATLAS 13.6 TeV data recorded in 2022
ATLAS public note ATL-DAPR-PUB-2023-001
Preliminary analysis of the luminosity calibration for the ATLAS 13.6 TeV data recorded in 2023
ATLAS public note ATL-DAPR-PUB-2024-001
Preliminary luminosity calibration of the ATLAS 13.6 TeV data recorded in 2024 and combination with the 2022 and 2023 measurements
ATLAS public note ATL-DAPR-PUB-2025-001
The LUCID-3 detector for the HL-LHC
Seven different detector designs have been considered and studied:
1. A detector with modified lower-acceptance MOD R760 photomultipliers attached to the beampipe;
2. A detector with smaller lower-acceptance R1635 photomultipliers attached to the beampipe;
3. A fiber detector attached to the VAX equipment and the beampipe;
4. A fiber detector attached to the forward shielding;
5. A R760 photomultiplier detector similar to LUCID-2 but attached to the forward shielding;
6. A detector with smaller lower-acceptance R1635 photomultipliers attached to the forward shielding;
7. A low-acceptance detector with standard R760 photomultipliers situated in the shadow behind the forward shielding.
The design proposals have been evaluated in the LHC run 3 (2022-2026) with prototype detectors.
The detectors were read-out with the LUCROD electronics used previously for the old LUCID-2 fiber detector and for the MOD detector.
The data that was collected with these prototype detectors will make it possible to select the best LUCID-3 detector
design for the HL-LHC (run 4) so that the new detector can be built in the long LHC shutdown (LS3).
At present design 1 to 4 have been discarded and the plan is to build a detector inside the beampipe hole in
the JFC3 muon shielding with both R760 and smaller R1635 photomultipliers. In addition a low-rate detector will be placed
at the back of the JFC3 shielding. The location of the photomultipliers in this detector can be changed with stepping motors
so that the rate of hits in the detector can be adjusted.
Presentations at conferences:
Design report presented to the LHCC:
The LUCID 3 detector for the ATLAS Phase-II Upgrade - CERN-LHCC-2021-016
The upgrade of the ATLAS Luminosity detector (LUCID) for HL-HLC
Federico Lasagni Manghi
15th Pisa Meeting on Advanced Detectors, La Biodola - Isola D'elba, Italy, 22-28 May 2022
Poster
Proceedings
LUCID-3: the upgrade of the ATLAS luminosity detector for High Luminosity LHC
Vincent Hedberg
41st International Conference on High Energy Physics (ICHEP 2022), Bologna, Italy, 6-13 Jul 2022
Slides
Plots
Proceedings
Video
LUCID-3: the upgrade of the ATLAS Luminosity detector for High-Luminosity LHC
Benedetto Giacobbe
16th Topical Seminar on Innovative Particle and Radiation Detectors, Siena, Italy, 25-29 Sep 2023
Slides
Plots
Proceedings
Upgraded Lucid and Zero Degree Calorimeter Detectors for ATLAS at the High Luminosity LHC
Antonio Sbrizzi
31st International Workshop on Deep Inelastic Scattering, Grenoble, France, 8-12 Apr 2024
Slides
LUCID-3: the upgrade of the ATLAS Luminosity detector for High Luminosity LHC
Davide Cremonini
16th Pisa Meeting on Advanced Detectors (Pisameet 2024), La Biodola, Isola D'elba, Italy, 26 May-1 Jun 2024
Poster
Plots
Proceedings
LUCID-3: Upgrade of the ATLAS Luminosity Monitor for the High Luminosity LHC
Jack Lindon
42nd International Conference on High Energy Physics (ICHEP2024), Prague, Czech Republic, 18-24 July 2024
Poster
Proceedings
LUCID-3: the upgrade of the ATLAS luminosity detector for High Luminosity LHC
Vincent Hedberg
LumiDays 25, CERN, Switzerland, 10-12 March 2025
Slides
Plots
Video
LUCID, the ATLAS luminosity detector in LHC Run-3 and its upgrade for HL-LHC
Federico Lasagni Manghi
2025 European Physical Society Conference on High Energy Physics (EPS-HEP 2025), Marseille, France, 7-11 Jul 2025
Slides
Plots
Proceedings
LUCID, the ATLAS luminometer in LHC Run 3 and its upgrade for HL-LHC
Elisa Sanzani
14th International Conference on New Frontiers in Physics 2025 (ICNFP 2025), Kolymbari, Crete, Greece, 17-31 Jul 2025
Slides
Proceedings
LUCID, the ATLAS luminosity detector in LHC Run-3 and its upgrade for HL-LH
Davide Cremonini
17th Topical Seminar on Innovative Particle and Radiation Detectors , Siena, Italy, 15-19 Sep 2025
Slides
Plots
Proceedings
The fiber prototype for the upgrade of the LUCID detector in the ATLAS experiment for HL-LHC
Davide Cremonini
164th LHCC Meeting, CERN, Geneva, Switzerland, 17-20 Nov 2025
Poster
Cherenkov detectors in the extreme LHC environment: LUCID PMTs and fibers
Davide Cremonini
7th International workshop on new Photon-Detectors, Bologna, Italy, 3-5 Dec 2025
Poster
Proceedings
The upgrade of the ATLAS luminosity detector LUCID for High Luminosity LHC
Vincent Hedberg
33rd International workshop on deep inelastic scattering and related subjects (DIS2026), Bologna, Italy, 4-8 May 2026
Slides
Plots
Proceedings
LUCID, the ATLAS luminosity detector in LHC Run-3 and its upgrade for HL-LHC
Federico Lasagni Manghi
43rd International Conference on High Energy Physics (ICHEP2026) Natal, Brasil, 30 July-5 August 2026
Slides
Proceedings
The LUCID-3 prototype detectors
During LHC run 3 a set of LUCID-3 prototype detectors have been installed and recorded data. The first pair are called
JF-A and JF-C and consisted of two to four photomultipliers installed on each side of ATLAS inside the beampipe hole in the forward muon shielding.
A mixture of R760 and R1635 photomultipliers
have been tried and varied during the years. The results from these detectors were compared to measurements with both standard R760 LUCID-2
photomultipliers and smaller R1635 photomultipliers installed in LUCID-2.
Then there is the JN-A detectors which consisted of two R760 photomultipliers
situated behind the forward muon shielding. The same two photomultipliers have been used during the entire run 3 period.
Finally there was the FIB-C detector which consisted of two bundles of quartz fibers surrounding the beampipe support cone.
These fibers were read-ot by two large R7459 photomultipliers situated behind the forward muon shielding.
This is a prototype of the baseline LUCID-3 detector that is attached to the forward shielding.
It has used both standard R760 photomultipliers and smaller R1635 photomultipliers that have been
specially made for LUCID with a quartz window by Hamamatsu.
The main issue to solve for the HL-LHC is hit saturation which means that every colliding bunch is giving hits
in all the photomultipliers. The efficiency (probablity to get a hit in only one proton-proton collision) is 8.6%
for R760 PMTs in LUCID-2. This is reduced to 6.1% for R760 PMTs in JF-A and JF-C and to 2.9% for R1635 PMTs.
The efficiency for the R760 PMTs in JF-A and JF-C can be reduced further to about 4.5% by increasing the threshold that defines a hit.
Test have shown that at this efficiency single PMTs will not saturate up to 150 proton-proton collisions per bunch collision.
This detector is similar to the JF-A prototype detector, the main difference is that it used two
small R1635 photomultipliers with thicker windows in 2026. These photomultipliers were more stable
than the standard R1635 photomultipliers which had stability problems.
This is a low-rate detector installed behind the upper part of the forward shielding (JFC3).
The efficiency of the two R760 PMTs in this detector was only 0.4% (top PMT) and 0.6% (bottom PMT).
The low efficiency meant that the problem of pile-up of small signals was greatly reduced.
For run 4 it is foreseen to be able to move the PMTs so that the efficiency can be optimized.
A stepping motor was installed during one year of running to make sure it could survive the radiation.
This detector uses bundles of optical quartz fibers as the Cherenkov medium instead of photomultiplier windows.
The advantage is that the photomultipliers can be located in a shielded location so that they will not suffer from radiation damage.
The gain of the larger R7459 photomultipliers (25 mm diameter) was monitored with radioactive Bi-207 sources while any radiation damage
to the fibers was monitored by LED light.
The bottom fiber bundle had a UV filter between the fibers and the photomultiplier because tests have shown that
radiation damage of quartz fibers mostly affect ultraviolet light. This resulted in a much more stable measurements with the lower fiber bundle
(and the C18 PMT) than the upper fiber bundle.) With fibers one cannot use hit-counting so charge counting was used to
measure the luminosity with this detector.
Last update:
10 October 2026