LHCb
LHCb is one of the four main experiments at the Large Hadron Collider at CERN, with the purpose of studying CP violation and rare decays of beauty and charm quarks.
LHC is colliding protons at a centre-of-mass energy of 13TeV, producing 10^12 bb pairs each year at the interaction point of the experiment. This enormous production rate is used to study CP-violating effects and other rare phenomena in the decay of B and D mesons, opening windows to physics beyond the Standard Model.
Instead of surrounding the entire collision point with an enclosed detector as ATLAS and CMS do, the LHCb experiment uses a series of subdetectors to detect mainly forward particles – those thrown forwards by the collision in one direction. The first subdetector is mounted close to the collision point, with the others following one behind the other over a length of 20 metres.
An abundance of different quark types is created by the LHC before they decay quickly into other forms. To catch the b quarks, LHCb has developed sophisticated tracking detectors that move very close to the path of the protons circling in the LHC when the beams stabilise.
LHCb experimental cavern. Credit: CERN
PPD LHCb Group
The RAL PPD Group, including PhD students, contains approximately 10 people and has responsibilities for the construction and operation of the two RICH detectors, the building and management of the UK contribution to the worldwide Computing Grid to process data, and the physics exploitation of the experiment.
The main physics interests of the group include lepton flavour violation and unitarity, and measurement of CKM angle γ.
PPD Contributions
RICH Detector System
LHCb has undergone a major upgrade to allow 5 times the instantaneous luminosity of Runs 1 & 2 for Runs 3 & 4. The UK had a major role in the replacement of one of the RICH detectors (RICH 1).
The RICH system was upgraded with new photon detectors and electronics to allow data collection at the full LHC bunch crossing of 40 MHz, removing the need for a hardware trigger. The RICH 1 detector was also modified to reduce the hit density at the photon detection plane by using spherical mirrors with a longer focusing distance.
For the RICH Detector System, the RAL group (including colleagues in Technology Department) has:
- Manufactured the structure of the RICH 2 detector in collaboration with industry and constructed the entry and exit windows of the detector at CERN
- Written the detailed simulation software to model the RICH detectors in the main Monte-Carlo programme
- Developed laser alignment and gas monitoring systems
- Developed control software for the RICH detectors
Installation of the RICH 2 detector at CERN
Grid Computing
The RAL Group has been very active in the construction of the Worldwide LHC Computing Grid (WLCG) that is used to process and analyse the data flowing from the experiments. The UK portion of this Grid has been built by the GridPP collaboration of particle physicists and computer scientists.
In LHCb, six external Tier 1 centres reconstruct and strip the data from CERN and make it available for analysis, with the UK centre located at RAL.
A series of Tier 2 centres produce the large simulated datasets that are also be necessary to analyse the experiment – with four regional centres located in the UK.
