Narrow Results

The rich proton-proton collision data of the LHC allow the study of QCD processes in a previously unexplored region with ever improving precision. This paper summarises recent results of the ATLAS, CMS and LHCb Collaborations using primarily multi-jet and vector boson plus jet data collected at $\sqrt{s}=8$ and 13 TeV. Comparisons to higher-order theoretical calculations and sophisticated Monte Carlo predictions are presented, as well as the impact of the data on the determination of the parton distribution functions and the measurement of the strong coupling constant, α_s.

The LHCspin project aims to bring polarized physics at the LHC through the installation of a gaseous fixed target at the upstream end of the LHCb detector. The forward geometry of the LHCb spectrometer (2 < η < 5) is perfectly suited for the reconstruction of particles produced in fixed-target collisions. The fixed-target configuration, with center-of-mass energy at $\sqrt{s}=115\text{GeV}$, allows to cover a wide backward center-of-mass rapidity region, corresponding to the poorly explored high x-Bjorken and high x-Feynman regimes. The project has several ambitious goals, in particular regarding nucleon’s internal dynamics in terms of both quarks and gluons degrees of freedom. The use of transversely polarized H and D targets will allow to study the quarks TMDs in pp collisions at unique kinematic conditions.

The charm sector is an unique probe to possible new physics coupling to up-type quarks and offers a complimentary approach to direct searches for particles originating from processes not described by the Standard Model of Particle physics (SM). Contributions beyond the SM could originate from the higher-order loop effects and assuming generic beyond SM scenarios, much higher mass scales are accessible in comparison with direct searches. Measurements of Charge-Parity (CP) violation and mixing in charm decays are promising method to probe the aforementioned effects. The violation of CP symmetry in charm was observed for the first time by the LHCb experiment in 2019.

These proceedings present a measurement of the mass difference between neutral charm meson mass eigenstates, a search for time-dependent CP violation in neutral charm meson decays and the first observation of CP violation in charm hadrons decays.

The LHCb Experiment is going to search for the contribution of New Physics by studying large statistics samples of b-hadron decays. The key components of the experimental setup are discussed, followed by the overall status of the detector construction. The expected sensitivity is given for a few key channels.

Pion/kaon discrimination in the LHCb experiment will be provided by two Ring Imaging Cherenkov (RICH) counters. These use arrays of 484 Hybrid Photon Detectors (HPDs) to detect the Cherenkov photons emitted by charged particles traversing the RICH. The results from comprehensive quality assurance tests on the 550 HPDs manufactured for LHCb are described. Leakage currents, dead channel probabilities, dark count rates and ion feedback rates are reported. Furthermore, measurements carried out on a sample of tubes to determine the efficiency of the HPD pixel chip by measuring the summed analogue response from the backplane of the silicon sensor are described.

The production of Hybrid Photon Detectors to be used as the single-photon sensors for the RICH detectors of the LHCb experiment has recently finished. We present the quantum efficiency measurements of the entire sample of 550 tubes. The manufacturer has succeeded in consistently improving the quantum efficiency of the employed S20-type multi-alkali photocathode above our expectations, by a relative 27 % integrated over the energy spectrum. We also report measurements of the vacuum quality using the photocurrent of the device as a monitor for possible vacuum degradation.

As the completion of the LHCb detector approaches we report on the status of the Ring Imaging Cherenkov (RICH) detectors that provide light hadron particle identification. The design and status of the two detectors RICH1 and RICH2 is explored and an overview is given of the photon detector technology the Hybrid Photon Detector. RICH1 is a more compact system working at lower particle momenta closer to the interaction point and is currently nearing completion. RICH2 is a larger detector operating at higher momenta and is complete and currently being commissioned.

The LHCb experiment will perform high-precision measurements of CP violation parameters and rare phenomena in B meson decays. It requires an excellent track reconstruction efficiency, particle identification and the precise measurement of secondary vertex positions in LHC collisions. We will discuss the methodology for the global reconstruction of tracks, using the ensemble of tracking detectors arranged on both sides of the LHCb dipole magnet. Hardware features of the tracking detectors that affect the tracking strategy will be outlined. We will describe the design and performance of the track reconstruction algorithms.

In the LHCb experiment the particle identification is an important issue. With the idea to upgrade the entire experiment to run at 40 MHz, RICH detectors have to modify their photodetetection system and one possibility is a choice of a different photodetector. In this presentation a first analysis of one of the possible phototubes under test is shown.

The LHCb Silicon Tracker consists of two sub-detectors the Tracker Turicensis and Inner Tracker that are constructed from silicon microstrip technology. Performance studies of both sub-detectors using data taken during the LHC synchronization tests are described.

LHCb is a dedicated experiment at the LHC to study CP violation and rare b decays. The vertex locator (VELO) is a silicon strip detector designed to measure precisely the production and decay vertices of B-mesons. The detector is positioned at 8 mm of the LHC beams and will operate in an extremely harsh radiation environment. The VELO consists of two retractable detector halves with 21 silicon micro-strip tracking modules each. A module is composed of two n⁺-on-n 300 µm thick half disc sensors with R and Φ micro-strip geometry. The detectors are operated in vacuum and a bi-phase CO₂ cooling system is used. The full system has been operated since June 2008 and its commissioning experience will be reported. During the LHC synchronization tests in August and September 2008, and June 2009 the LHCb detectors measured secondary particles produced by the interaction of the LHC primary beam on a beam dump. About 50,000 tracks were reconstructed in the VELO and they were used to derive the relative timing alignment between the sensors and for the first evaluation of the spatial alignment. Using this track sample the VELO has been aligned to an accuracy of 5 µm. A single hit resolution of 10 µm was obtained at the smallest pitch for tracks of perpendicular incidence. The design and the main components of the detector system are introduced. The commissioning of the detector is reported and the talk will focus on the results obtained using the first beam-induced reconstructed tracks.

A set of key measurements of B decays which have the potential to uncover New Physics at the LHC is discussed. Together with the general purpose detectors ATLAS and CMS, the LHCb detector, which is devoted to B physics, can study these effects precisely. Due to the large cross section at 14 TeV, LHCb has access to 10¹² B meson decays per year. This allows significant measurements of even very rare B decays and, in particular, the precision study of the B system.

The Large Hadron Collider Beauty Experiment aims to precisely measure CP violation and rare decays, both of which require accurate charged particle identification. The Ring Imaging Cherenkov detectors are vital components of the system. Charged particles travelling through radiators at relativistic speeds produce Cherenkov photons which are detected by arrays of Hybrid Photon Detectors. Known resonances, such as ϕ, K₈, Λ and D*, provide samples of pions, kaons and protons, which are used to assess the performance of the detectors. Methods for alignment and calibration of the detectors lead to an optimal Cherenkov angle resolution. The particle identification performance on recent data is presented.

In 2010, the CERN (European Centre for Particle Physics Research) Research Board unanimously approved MoEDAL, the seventh international experiment at the Large Hadron Collider (LHC), which is designed to search for avatars of new physics signified by highly ionizing particles. A MoEDAL discovery would have revolutionary implications for our understanding of the microcosm, providing insights into such fundamental questions as: do magnetic monopoles exist, are there extra dimensions or new symmetries of nature; what is the mechanism for the generation of mass; what is the nature of dark matter and how did the big bang unfurl at the earliest times.

The LHCb experiment is designed to study B and D-meson decays at the LHC, in the forward region. It is crucial to accurately and efficiently detect the charged decay particles in the high-density particle environment of the LHC. For this, the Outer Tracker (OT) has been constructed. The detector has operated reliably under the challenging LHC conditions in 2011 and 2012. The performance of the detector is discussed in terms of high voltage stability, noise rate and single hit efficiency. New results on the hit resolution are presented. Finally, latest results on the radiation tolerance of this sensitive gas detector are discussed, after having received a total dose corresponding to about 100 mC/cm in the hottest region, and having operated with proton-ion collisions in 2013.

A scintillating fibre tracker with multichannel silicon photomultiplier readout is an option for the LHCb upgrade. The radiation hardness of the scintillating fibres and silicon photomultipliers has been studied. Production methods and machines to build 5m long modules with an accuracy of 50 μm have been designed and built. All developments are well on track for the technical design report in March 2014.

The LHCb experiment is designed to study B-decays at the LHC. This purpose is achieved by means of an outstanding track momentum resolution and excellent particle identification. The performance of the detector exceeds expectations, and the physics program of the collaboration is extended to the study of charm decays, QCD and electroweak physics. Both tracking and alignment play a key role for obtaining these results. The tracking efficiency in this high-occupancy environment has been measured during LHC Run I (2010-2012) to be larger than 95% over a wide range of momentum and pseudo-rapidity. The alignment of the detector is based on a Kalman filter fit of the tracks and provides an uncertainty on the momentum scale below 1 × 10⁻⁴ and a momentum resolution of about 0.4%. These results allowed one to achieve high-precision mass measurements of many charm and B hadrons so far. Starting from Run II of the LHC, the running conditions will continue to push the performance of the detector to its limits. An upgrade of the detector will therefore take place in 2018 to extend its reach. A fast tracking will be a fundamental part of the upgraded detector as well. In light of this, the prospects for the recently proposed upgrade will be discussed.

The LHCb Vertex Locator (VELO) is the detector responsible for the detection of heavy hadrons through their flight distance. The performance of the VELO during its three years of operation during the LHC physics runs is presented, focussing on the latest studies. The primary results presented are the first observation of type-inversion at the LHC; a comparison of n-type and p-type silicon in operation; and the observation of a radiation-induced charge loss effect due to the presence of a second metal layer.

The upgrade of the LHCb experiment, planned for 2018, will transform the entire readout to a trigger-less system operating at 40 MHz. The upgraded VELO must be light weight, radiation hard, and compatible with LHC vacuum requirements. The material budget will be optimised with the use of evaporative CO₂ coolant circulating in micro-channels within a thin silicon substrate. The current status of the VELO upgrade will be described together with a presentation of recent test results, and a discussion of the R&D on alternative solutions which has been carried out within the LHCb VELO upgrade programme.