The LHCb detector with its unique pseudorapidity coverage allows to perform soft-QCD measurements in the kinematic forward region where QCD models have large uncertainties. Selected analyses related to soft-Diffraction will be summarised in these proceedings. Energy flow and charged particle multiplicity have been measured separately in different event classes. They give input for modelling the underlying event in pp collisions. Prompt hadron ratios are important for hadronisation models, while the $\bar p/p$ ratio is a good observable to test models of baryon number transport.
The LHCb detector at the LHC offers unique coverage of forward rapidities for studies of Central Exclusive Production (CEP) and soft QCD. CEP measurements allow the investigation of the nature of pomerons, and provide constraints on low-x gluon phenomenology, probing potential saturation effects. Moreover LHCb can test phenomenological models of soft QCD processes, by measuring the production of forward hadrons in pp collisions. In these proceedings the latest results from the LHCb experiment will be presented.
The LHCb experiment is shown to be ideal for studies of exclusive final states from central diffractive reactions. The gluon-rich environment of the central system allows detailed QCD studies and searches for exotic meson states, such as glueballs, molecules, hybrids and new charmonium-like states. It would also provide a good testing ground for detailed studies of heavy quarkonia. Due to its distinct design features, the LHCb can accurately measure the low-mass central systems with good purity. The efficiency of the FSC system for detecting rapidity gaps is shown to be adequate for the propos…
LHCb presents studies of particle production in minimum bias events in pp collisions at \sqrt{s} = 7 TeV. These studies include measurements of strangeness production, particle ratios, baryon-antibaryon ratios and charged particle production. The forward coverage and low pT acceptance of the experiment makes these measurements very complementary to those performed by the central detectors at the LHC. Further benefits arise from the powerful particle identification capabilities provided by the LHCb RICH system. The measurements are compared with theoretical predictions.
Studies in the forward region of charged particle multiplicity and density, as well as energy flow, are presented. These measurements are performed using data from proton-proton collisions at a center-of-mass energy of 7 TeV, collected with the LHCb detector. The results are compared to predictions from a variety of Monte Carlo event generators and are used to test underlying event and hadronization models as well as the performance of event generator tunes in the forward region.
Soft QCD and double parton scattering are of great interest in high energy physics. They are both actively studied at the LHCb experiment. The measurement of the central exclusive production of $J/ψ$ and $ψ(2S)$ mesons in $pp$ collisions at $\sqrt{s} = 13 \,{\mathrm{TeV}}$ is presented. The result shows good agreement with the theoretical predictions. The measurement of the $J/ψ$ pair production cross-section in $pp$ collisions at $\sqrt{s} = 13 \,{\mathrm{TeV}}$ is reported. The differential cross-sections as functions of various kinematic variables are compared to the theoretical predictions…
High-precision measurements performed by the LHCb collaboration have opened a new era in charm physics. Several crucial measurements, particularly in spectroscopy, rare decays and CP violation, can benefit from the increased statistical power of an upgraded LHCb detector. The upgrade of LHCb detector, its software infrastructure, and the impact on charm physics are discussed in detail.
A summary of recent TOTEM double diffraction and charged particle pseudorapidity density results is given, and single diffraction results are also discussed.
The thermal properties of the LHCb Vertex Locator (VELO) are studied using the real-time detector alignment procedure. The variation of the position and orientation of the detector elements as a function of the operating temperature of the VELO is presented. This study uses a dataset collected by the LHCb experiment during a VELO temperature scan performed at the end of LHC Run 2 (October 2018). Significant shrinkage of the VELO modules is observed at the operating temperature of $-30^\circ$ compared to the laboratory measurements on a single module taken at a range of temperatures from $+45^\…
We present measurements of soft single- and double-diffractive cross sections, as well as of forward rapidity gap cross sections at 7 TeV at the LHC, and compare the results to other measurements and to theoretical predictions implemented in various Monte Carlo simulations.
The upgraded LHCb detector, due to start datataking in 2022, will have to process an average data rate of 4~TB/s in real time. Because LHCb's physics objectives require that the full detector information for every LHC bunch crossing is read out and made available for real-time processing, this bandwidth challenge is equivalent to that of the ATLAS and CMS HL-LHC software read-out, but deliverable five years earlier. Over the past six years, the LHCb collaboration has undertaken a bottom-up rewrite of its software infrastructure, pattern recognition, and selection algorithms to make them better…
The measurements of the total inelastic cross section and the differential inelastic cross section as a function of rapidity gap are presented. The data used for these studies were collected in $pp$ collisions at a center-of-mass energy of 7 TeV with the ATLAS detector at the LHC in 2010.
With the steady increase in the precision of flavour physics measurements collected during LHC Run 2, the LHCb experiment requires simulated data samples of larger and larger sizes to study the detector response in detail. The simulation of the detector response is the main contribution to the time needed to simulate full events. This time scales linearly with the particle multiplicity. Of the dozens of particles present in the simulation only the few participating in the signal decay under study are of interest, while all remaining particles mainly affect the resolutions and efficiencies of t…
Results from recent soft QCD measurements by LHC experiments ALICE, ATLAS, CMS, LHCb, LHCf and TOTEM are reported. The measurements include total, elastic and inelastic cross sections, inclusive and identified particle spectra, underlying event and hadronic chains. Results from particle correlations in all three collision systems, namely pp, pPb and PbPb, exhibit unexpected similarities.
We report on the recent CMS measurements of soft hadron-hadron production, including the measurements of inclusive single- and double-diffractive cross sections, as well as the measurement of pseudorapidity distributions, and of the leading charged particle and leading jet cross sections. We present the cross sections for low-pT forward jets production, and production of dijets with large rapidity separation (central-forward, and forward-backward jets). Studies of double parton scattering using four-jet and W+2-jet events, and the cross sections for Drell-Yan with associated jet production are…
In 2015, the LHCb experiment established a new and unique software trigger strategy with the purpose of increasing the purity of the signal events by applying the same algorithms online and offline. To achieve this, real-time calibration and alignment of all LHCb sub-systems is needed to provide vertexing, tracking, and particle identification of the best possible quality. The calibration of the refractive index of the RICH radiators, the calibration of the Hybrid Photon Detector image, and the alignment of the RICH mirror system, are reported in this contribution. The stability of the RICH pe…
The LHCb Experiment is preparing a detector upgrade fully exploit the flavour physics potential of the LHC. The whole detector will be read out at the full collision rate and the online event selection will be performed by a software trigger. This will increase the event yields by a facto 10 for muonic and a factor 20 for hadronic final states. Research towards the upgrade has started with the target to install the detector in 2018.
In Run-3, beginning in 2022, the LHCb software trigger will start reconstructing events at the LHC average crossing rate of 30 MHz. Within the upgraded DAQ system, LHCb established a testbed for new heterogeneous computing solutions for real-time event reconstruction, in view of future runs at even higher luminosities. One such solution is a highly-parallelized custom tracking processor ("Artificial Retina"), implemented in state of the art FPGA devices connected by fast serial links. We describe the status of a realistic prototype for the reconstruction of pixel tracking detectors that will r…
The LHCb experiment is designed to perform high-precision measurements of CP violation and search for New Physics using the enormous flux involving beauty and charm quarks produced at the LHC. The operation and the results obtained from the data collected in 2010 and 2011 demonstrate that the detector is robust and functioning very well. However, the limit of 1 fb^-1 of data per nominal year cannot be overcome without improving the detector. We therefore plan for an upgraded spectrometer by 2018 with a 40 MHz readout and a much more flexible software-based triggering system that will increase …
The LHCb detector optimised its performance in Runs~1 and~2 by stabilising the instantaneous luminosity during a fill. This was achieved by tuning the distance between the two colliding beams according to the measurement of instantaneous luminosity from hardware-based trigger counters. The upgraded LHCb detector operates at fivefold instantaneous luminosity compared to the previous runs, and it has a fully software-based trigger. Consequently, a new approach to the luminosity measurement is adopted. New counters, with particular attention to maximum stability in time, and a new dedicated detec…
We report recent results from the ALICE experiment at the LHC for minimum bias pp collisions. This overview includes results on inelastic cross section, with analysis of single and double diffractive events; the study of hadron production mechanisms, both for inclusive and identified particles; Bose-Einstein correlations; and fluctuations in $<p_T>$
National Research University Higher School of Economics（国立研究型大学高等经济学院）
LHCb is one of the major experiments operating at the Large Hadron Collider at CERN. The richness of the physics program and the increasing precision of the measurements in LHCb lead to the need of ever larger simulated samples. This need will increase further when the upgraded LHCb detector will start collecting data in the LHC Run 3. Given the computing resources pledged for the production of Monte Carlo simulated events in the next years, the use of fast simulation techniques will be mandatory to cope with the expected dataset size. In LHCb generative models, which are nowadays widely used …
Decorrelation of neural networks from particle lifetimes in the LHCb topological $b$ trigger
NSF AI Institute for Artificial Intelligence and Fundamental Interactions（美国国家科学基金会人工智能基础相互作用研究所）；Fakultät Physik, Technische Universität Dortmund（多特蒙德工业大学物理学院）；INFN Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；Department of Physics, University of Warwick（华威大学物理系）；Department for Work and Pensions（英国工作与养老金部）；Department of Physics and Astronomy, University of Manchester（曼彻斯特大学物理与天文学系）；TimeTrace Labs（TimeTrace 实验室）；Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences（波兰科学院亨利克·涅沃德尼察斯基核物理研究所）；Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Sorbonne Université, CNRS/IN2P3（索邦大学、法国国家科学研究中心/法国国家粒子物理研究所核物理与高能物理实验室）；Foodforecast Technologies（Foodforecast 科技公司）；Massachusetts Institute of Technology（麻省理工学院）；Department of Physics, University of Oxford（牛津大学物理系）
The upgrade of the LHCb experiment, scheduled for LHC Run-III, scheduled to start in 2021, will transform the experiment to a trigger-less system reading out the full detector at 40 MHz event rate. All data reduction algorithms will be executed in a high-level software farm enabling the detector to run at luminosities of $2\times10^{33} \mathrm{cm}^{-2}\mathrm{s}^{-1}$. The Vertex Locator (VELO) is the silicon vertex detector surrounding the interaction region. The current detector will be replaced with a hybrid pixel system equipped with electronics capable of reading out at 40 MHz. The upgra…
High statistics measurements of the diffractive reduced cross section $σ_r^D$ from the H1 collaboration are presented which make use of two different experimental methods to achieve the largest possible coverage of the kinematic phase space at HERA. The HERA combined diffractive reduced cross sections based on events with a leading proton are also presented. %High statistics measurements of the diffractive reduced cross section $σ_r^D$ have been made by H1 collaboration using two experimental methods covering accessible kinematic region. The HERA combined diffractive double-differential reduce…
Diffractive events at hadron colliders are typically characterised by a region of the detector without particles, known as a rapidity gap. In order to observe diffractive events in this way, we consider the pseudorapidity acceptance in the forward region of the ATLAS and CMS detectors at the Large Hadron Collider (LHC) and discuss the methods to select soft diffractive dissociation for pp collisions at sqrt(s) = 7 TeV. We showed that in the limited detector rapidity acceptance, it is possible to select diffractive dissociated events by requiring a rapidity gap in the event, however, it is not …
INFN Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂国家实验室）；INFN Sezione di Cagliari（意大利国家核物理研究所卡利亚里分部）；Aix Marseille Univ, CNRS/IN2P3, CPPM（艾克斯-马赛大学，法国国家科学研究中心/欧洲粒子物理研究所，普罗旺斯粒子与核物理中心）；INFN Sezione di Roma Tor Vergata（意大利国家核物理研究所罗马托维尔加塔分部）；INFN Sezione di Ferrara（意大利国家核物理研究所费拉拉分部）；INFN Sezione di Firenze（意大利国家核物理研究所佛罗伦萨分部）；European Organization for Nuclear Research (CERN)（欧洲核子研究组织（欧洲核子中心））；INFN Sezione di Roma La Sapienza（意大利国家核物理研究所罗马智慧大学分部）；INFN Sezione di Bari（意大利国家核物理研究所巴里分部）；School of Physics State Key Laboratory of Nuclear Physics and Technology, Peking Univ（北京大学物理学院核物理与技术国家重点实验室）
The LHCb experiment at CERN is currently completing its first big data taking campaign at the LHC started in 2009. It has been collecting data at more than 2.5 times its nominal design luminosity value and with a global efficiency of ~92%. Even more striking, the efficiency between online and offline recorded luminosity, obtained by comparing the data quality output, is close to 99%, which highlights how well the detector, its data acquisition system and its control system have been performing despite much harsher and more variable conditions than initially foreseen. In this paper, the excelle…
A new combinatorial vector space measurement model is introduced for soft QCD diffraction. The model independent mathematical construction resolves experimental complications; the theoretical framework of the approach includes the Good-Walker view of diffraction, Regge phenomenology together with AGK cutting rules and random fluctuations.
Translating LHCb's Documentation: First experiences and ensuring maintenance
Aix-Marseille Univ, CNRS/IN2P3, CPPM（艾克斯-马赛大学）；Lanzhou University（兰州大学）；Institute of High Energy Physics（高能物理研究所）；Department of Physics, University of Warwick（华威大学物理系）；Central China Normal University（华中师范大学）
Diffractive events are studied by means of identification of one or more rapidity gaps and/or a leading antiproton. Measurements of soft and hard diffractive processes have been performed at the Tevatron $p\bar p$ collider and presented. We report on the diffractive structure function obtained from dijet production in the range $0<Q^2<10,000$GeV$^2$, and on the $|t|$ distribution in the region $0<|t|<1$GeV$^2$ for both soft and hard diffractive events up to $Q^2\approx 4,500$GeV$^2$. Results on single diffractive W/Z production, forward jets, and central exclusive production of both dijets and…
The LHCb (Large Hadron Collider beauty) experiment is designed to study differences between particles and anti-particles as well as very rare decays in the charm and beauty sector at the LHC (Large Hadron Collider). The detector will be upgraded in 2019 and a new trigger-less readout system will be implemented in order to significantly increase its efficiency and take advantage of the increased machine luminosity. In the upgraded system, both event building and event filtering will be performed in software for all the data produced in every bunch-crossing of the LHC. In order to transport the …
The primary goal of this paper is to describe the diffraction production using the model that takes into account the Pomeron interaction, and satisfies both $t$ and $s$ channel unitarity. We hope that these features will allow us to describe the diffraction production in a more convenient way than in CGC motivated models, that do not satisfy these unitarity constraints. Unfortunately, we show that both approaches are only able to describe half of the cross section for the single diffraction production, leaving the second half to be estimate of the large mass production in the Pomeron approach.…
The high-energy behaviour of soft scattering observables such as total cross sections, elastic scattering at small momentum transfer, diffractive dissociation and central production have been described successfully in the context of Regge theory, with the same basic structure holding as energies have increased. For elastic scattering and diffraction dissociation the defining energies were those of the ISR, the $Sp\bar{p}S$ collider and the Tevatron. The elastic scattering data from the LHC demonstrate the continuing applicability of Regge theory. Preliminary data on diffraction dissociation pr…
A FPGA-based architecture for real-time cluster finding in the LHCb silicon pixel detector
INFN Sezione di Pisa（意大利国家核物理研究所比萨分部）；Scuola Normale Superiore（比萨高等师范学校）；Università di Pisa（比萨大学）；Università degli Studi di Padova（帕多瓦大学）；Liverpool University（利物浦大学）；University of Oxford（牛津大学）；Instituto Galego de Física de Altas Enerxías (IGFAE)（加利西亚高能物理研究所（IGFAE））；Universidade de Santiago de Compostela（圣地亚哥德孔波斯特拉大学）
Spin correlations for tau lepton decays are included in the Pythia 8 event generation software and the spin correlations for the decays of tau leptons produced from electroweak and Higgs bosons are calculated. Decays of the tau lepton using sophisticated resonance models are included in Pythia 8 for all channels with experimentally observed branching fractions greater than 0.04%. The mass distributions for the decay products of these channels are validated and the technical implementation of these decays is described. A measurement of the inclusive Z to di-tau cross-section using 1.0 inverse f…
The LHCb experiment has been taking data at the Large Hadron Collider (LHC) at CERN since the end of 2009. One of its key detector components is the Ring-Imaging Cherenkov (RICH) system. This provides charged particle identification over a wide momentum range, from 2-100 GeV/c. The operation and control software, and online monitoring of the RICH system are described. The particle identification performance is presented, as measured using data from the LHC. Excellent separation of hadronic particle types (pion, kaon and proton) is achieved.
Upgrades to the LHCb computing infrastructure in the first long shutdown of the LHC have allowed for high quality decay information to be calculated by the software trigger making a separate offline event reconstruction unnecessary. Furthermore, the storage space of the triggered candidate is an order of magnitude smaller than the entire raw event that would otherwise need to be persisted. Tesla, following the LHCb renowned physicist naming convention, is an application designed to process the information calculated by the trigger, with the resulting output used to directly perform physics mea…
In this talk we introduce the main features of a QCD-based model in which the coupling $α_{s}$ is constrained by an infrared mass scale. We show recent applications of this model to hadron-hadron collisions, gap survival probability calculations, and soft gluon resummation techniques. These results indicate a smooth transition from non-perturbative to perturbative behaviour of the QCD.
