physics

LHCb experiment

LHCb experiment is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand LHCb experiment rather than just read about it. In short: The LHCb (Large Hadron Collider beauty) experiment is a particle physics detector collecting data at the Large Hadron Collider at CERN. LHCb specializes in the measurements of the parameters of CP violation in the interactions of b- and c-hadrons (heavy particles containing a bottom and charm quarks).

Key takeaways

LHCb experiment belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect LHCb experiment to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of LHCb experiment from memory before moving on to harder problems.

Reference excerpt

The LHCb (Large Hadron Collider beauty) experiment is a particle physics detector collecting data at the Large Hadron Collider at CERN. LHCb specializes in the measurements of the parameters of CP violation in the interactions of b- and c-hadrons (heavy particles containing a bottom and charm quarks). Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, and electroweak physics in the forward region. The LHCb collaborators, who built, operate and analyse data from the experiment, are composed of approximately 1650 people from 98 scientific institutes, representing 22 countries. Vincenzo Vagnoni succeeded on July 1, 2023 as spokesperson for the collaboration from Chris Parkes (spokesperson 2020–2023). The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire, France just over the border from Geneva. The (small) MoEDAL experiment shares the same cavern.

Physics goals The experiment has wide physics program covering many important aspects of heavy flavour (both beauty and charm), electroweak and quantum chromodynamics (QCD) physics. Six key measurements have been identified involving B mesons. These are described in a roadmap document that formed the core physics programme for the first high-energy LHC running in 2010–2012. They include:

Measuring the branching ratio of the rare Bs → μ+ μ− decay. Measuring the forward-backward asymmetry of the muon pair in the flavour-changing neutral current Bd → K* μ+ μ− decay. Such a flavour changing neutral current cannot occur at tree-level in the Standard Model of Particle Physics, and only occurs through box and loop Feynman diagrams; properties of the decay can be strongly modified by new physics. Measuring the CP violating phase in the decay Bs → J/ψ φ, caused by interference between the decays with and without Bs oscillations. This phase is one of the CP observables with the smallest theoretical uncertainty in the Standard Model, and can be significantly modified by new physics. Measuring properties of radiative B decays, i.e. B meson decays with photons in the final states. Specifically, these are again flavour-changing neutral current decays. Tree-level determination of the unitarity triangle angle γ. Charmless charged two-body B decays.

The LHCb detector The fact that the two b-hadrons are predominantly produced in the same forward cone is exploited in the layout of the LHCb detector. The LHCb detector is a single arm forward spectrometer with a polar angular coverage from 10 to 300 milliradians (mrad) in the horizontal and 250 mrad in the vertical plane. The asymmetry between the horizontal and vertical plane is determined by a large dipole magnet with the main field component in the vertical direction.

Subsystems The Vertex Locator (VELO) is built around the proton interaction region. It is used to measure the particle trajectories close to the interaction point in order to precisely separate primary and secondary vertices. The detector operates at 7 millimetres (0.28 in) from the LHC beam. This implies an enormous flux of particles; VELO has been designed to withstand integrated fluences of more than 1014 p/cm2 per year for a period of about three years. The detector operates in vacuum and is cooled to approximately −25 °C (−13 °F) using a biphase CO2 system. The data of the VELO detector are amplified and read out by the Beetle ASIC.

The RICH-1 detector (Ring imaging Cherenkov detector) is located directly after the vertex detector. It is used for particle identification of low-momentum tracks. The main tracking system is placed before and after the dipole magnet. It is used to reconstruct the trajectories of charged particles and to measure their momenta. The tracker consists of three subdetectors:

The Tracker Turicensis, a silicon strip detector located before the LHCb dipole magnet The Outer Tracker. A straw-tube based detector located after the dipole magnet covering the outer part of the detector acceptance The Inner Tracker, silicon strip based detector located after the dipole magnet covering the inner part of the detector acceptance Following the tracking system is RICH-2. It allows the identification of the particle type of high-momentum tracks. The electromagnetic and hadronic calorimeters provide measurements of the energy of electrons, photons, and hadrons. These measurements are used at trigger level to identify the particles with large transverse momentum (high-Pt particles). The figure also shows SPD/PS components which were actually removed during upgrade 1 along with M1. The muon system is used to identify and trigger on muons in the events.

LHCb upgrade (2019–2021) At the end of 2018, the LHC was shut down for upgrades, with a restart currently planned for early 2022. For the LHCb detector, almost all subdetectors are to be modernised or replaced. It will get a fully new tracking system composed of a modernised vertex locator, upstream tracker (UT) and scintillator fibre tracker (SciFi). The RICH detectors will also be updated, as well as the whole detector electronics. However, the most important change is the switch to the fully software trigger of the experiment, which means that every recorded collision will be analysed by sophisticated software programmes without an intermediate hardware filtering step (which was found to be a bottleneck in the past).

Results During the 2011 proton-proton run, LHCb recorded an integrated luminosity of 1 fb−1 at a collision energy of 7 TeV. In 2012, about 2 fb−1 was collected at an energy of 8 TeV. During 2015–2018 (Run 2 of the LHC), about 6 fb−1 was collected at a center-of-mass energy of 13 TeV. In addition, small samples were collected in proton-lead, lead-lead, and xenon-xenon collisions. The LHCb design also allowed the study of collisions of particle beams with a gas (helium or neon) injected inside the VELO volume, making it similar to a fixed-target experiment; this setup is usually referred to as "SMOG". These datasets allow the collaboration to carry out the physics programme of precision Standard Model tests with many additional measurements. As of 2021, LHCb has published more than 500 scientific papers.

… excerpt ends here. Continue reading the full article.

Illustrations

The LHCb collaboration's logo

Worked examples

Example 1 — a first encounter with LHCb experiment

Start with the simplest possible case. Write down what LHCb experiment claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to LHCb experiment before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about LHCb experiment ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of LHCb experiment

In research: LHCb experiment appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses LHCb experiment in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: LHCb experiment is common in secondary-school and first-year university syllabi. It links to neighbouring topics B physics, CERN experiments, Large Hadron Collider, so understanding it makes those chapters shorter.
In everyday life: Look for LHCb experiment outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study LHCb experiment in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what LHCb experiment means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain LHCb experiment out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is LHCb experiment in simple terms?

Why does LHCb experiment matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study LHCb experiment?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on LHCb experiment.