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2018-07-13
09:06
The LHCb tracks reconstruction in Run 2: strategy and performance
Reference: Poster-2018-641
Created: 2018. -1 p
Creator(s): Dufour, Laurent; Kopecna, Renata; Pearce, Alex; Van Veghel, Maarten

In order to accomplish its wide program of physics measurements, the LHCb collaboration has developed in the past years a complex of algorithms for the reconstruction of the trajectories of charged particles, taking into account the heterogeneous structure of the LHCb tracking system. Several data-driven approaches have been conceived to provide a precise evaluation of the tracking efficiency, a crucial ingredient of many physics analysis. These are mostly based on clean samples of muons, but the recent hints of lepton universality violation required the development of robust data-driven techniques specifically dedicated to electrons, in order to reduce the systematic uncertainties. In addition, special data streams with prompt access have been put in place to collect the calibration samples for both muons and electrons. While the end of the Run 2 data taking period is approaching, we provide an overview of the whole reconstruction strategy and of its performances, which have a direct impact on the quality of the current LHCb results and provide the basis for the upgrade era.

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2018-07-13
09:01
Central Exclusive Production at LHCb
Reference: Poster-2018-640
Created: 2018. -1 p
Creator(s): Gandini, Paolo

The installation of scintillating pad detectors (Herschel), bracketing the LHCb detector along the beamline, have significantly enhanced LHCb's sensitivity to central exclusive production. Additionally, dedicated triggers during the early measurement period of Run 2 have produced an extended CEP dataset. A summary of results from Run 1 as well as early results from Run 2 will be shown.

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2018-07-06
14:23
LHCb full-detector real-time alignment and calibration: latest developments and perspectives
Reference: Poster-2018-639
Created: 2018. -1 p
Creator(s): Maddrell-Mander, Samuel William; Vom Bruch, Dorothea

A key ingredient of the data taking strategy used by the LHCb experiment at CERN in Run-II is the novel real-time detector alignment and calibration. Data collected at the start of the fill are processed within minutes and used to update the alignment, while the calibration constants are evaluated hourly. This is one of the key elements which allow the reconstruction quality of the software trigger in Run-II to be as good as the offline quality of Run-I. The most recent developments of the real-time alignment and calibration paradigm enable the fully automated updates of the RICH detectors' mirror alignment and a novel calibration of the calorimeter systems. Both evolutions improve the particle identification performance stability resulting in higher purity selections. The latter leads also to an improvement in the energy measurement of neutral particles, resulting in a 15% better mass resolution of radiative b-hadron decays. A large variety of improvements has been explored for the last year of Run-II data taking and is under development for the LHCb detector upgrade foreseen in 2021.These range from the optimisation of the data samples selection and strategy to the study of a more accurate magnetic field description. Technical and operational aspects as well as performance achievements are presented, focusing on the new developments for both the current and upgraded detector.

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2018-07-06
14:18
A true real-time success story: the case of collecting beauty-ful data at the LHCb experiment
Reference: Poster-2018-638
Created: 2018. -1 p
Creator(s): Alessio, Federico

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 excellent performance of the LHCb experiment will be described, by transversally tying together the timing and data acquisition system, the software trigger, the real-time calibration and the shifters interaction with the control system. Particular attention will be given to their real-time aspects, which allow performing an online reconstruction that is at the same performance level as the offline one through a real-time calibration and alignment of the full detector. In addition, the various solutions that have been chosen to operate the experiment safely and synchronously with the various phases of the LHC operations will also be shown. In fact, the quasi-autonomous control system of the LHCb experiment is the key to explain how such a large detector can be operated successfully around the clock by a pool of ~300 non-expert shifters. Finally, a critical review of the experiment will be presented in order to justify the reasons for a major upgrade of the detector.

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2018-07-06
10:35
$R(D^*)$ with hadronic $\tau$ decays at LHCb
Reference: Poster-2018-637
Created: 2018. -1 p
Creator(s): Betti, Federico

Lepton Universality violation would represent a signal of physics beyond Standard Model. Semileptonic decays of beauty hadrons in third generation leptons are particularly interesting, since some anomalies have been observed in the measurement of their Branching Ratio. The most recent measurement of $R(D^*) = \mathcal{B}(B^0 \to D^{*-}\tau^+\nu_\tau)/\mathcal{B}(B^0 \to D^{*-}\mu^{+}\nu_\mu)$, performed by LHCb with data collected during Run 1 using the hadronic $\tau$ decay channel, is presented.

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2018-06-19
16:58
A tracking algorithm for the reconstruction of the daughters of long-lived particles in LHCb
Reference: Poster-2018-636
Created: 2018. -1 p
Creator(s): Dendek, Adam Mateusz

A tracking algorithm for the reconstruction of the daughters of long-lived particles in LHCb 5 Jun 2018, 16:00 1h 30m Library, Centro San Domenico () LHC experiments Posters session Speaker Katharina Mueller (Universitaet Zuerich (CH)) Description The LHCb experiment at CERN operates a high precision and robust tracking system to reach its physics goals, including precise measurements of CP-violation phenomena in the heavy flavour quark sector and searches for New Physics beyond the Standard Model. The track reconstruction procedure is performed by a number of algorithms. One of these, PatLongLivedTracking, is optimised to reconstruct "downstream tracks", which are tracks originating from decays outside the LHCb vertex detector of long-lived particles, such as Ks or Λ0. After an overview of the LHCb tracking system, we provide a detailed description of the LHCb downstream track reconstruction algorithm. Its computational intelligence part is described in details, including the adaptation of the employed Machine Learning algorithms to the environment of the real-time high level trigger. The downstream tracking performance, obtained using a simulated data samples, is also presented.

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2018-06-19
16:54
LHCb Particle Identification Strategy and Performance in Run 2
Reference: Poster-2018-635
Created: 2018. -1 p
Creator(s): Tilley, Matthew James

For Run 2 of LHCb data taking, the selection of PID calibration samples is implemented in the high level trigger. A further processing is needed to provide calibration samples used for the determination the PID performance, which is achieved through a centralised production that makes highly efficient use of LHCb computing resources. This poster presents the major steps of the production procedure and the charged particle PID performance measured using these calibration samples.

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2018-06-19
16:45
LHCb full-detector real-time alignment and calibration: latest developments and perspective
Reference: Poster-2018-634
Created: 2018. -1 p
Creator(s): Dziurda, Agnieszka; Mogini, Andrea

A key ingredient of the data taking strategy used by the LHCb experiment at CERN in Run 2 is the novel real-time detector alignment and calibration. Data collected at the start of the fill are processed within minutes and used to update the alignment, while the calibration constants are evaluated hourly. This is one of the key elements which allow the reconstruction quality of the software trigger in Run-II to be as good as the offline quality of Run 1. The most recent developments of the real-time alignment and calibration paradigm enable the fully automated updates of the RICH detectors' mirror alignment and a novel calibration of the calorimeter systems. Both evolutions improve the particle identification performance stability resulting in higher purity selections. The latter leads also to an improvement in the energy measurement of neutral particles, resulting in a 15% better mass resolution of radiative b-hadron decays. A large variety of improvements has been explored for the last year of Run 2 data taking and is under development for the LHCb detector upgrade foreseen in 2021.These range from the optimisation of the data samples selection and strategy to the study of a more accurate magnetic field description. Technical and operational aspects as well as performance achievements are presented, focusing on the new developments for both the current and upgraded detector.

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2018-06-13
17:20
Neutral particles identification at LHCb
Reference: Poster-2018-633
Created: 2018. -1 p
Creator(s): Quintana, Boris Julien

Important analyses of the core LHCb physics program rely on calorimetry to identify photons, high-energy neutral pions and electrons. For this purpose, the LHCb calorimeter system is composed of a scintillating pad plane, a preshower detector, an electromagnetic and a hadronic sampling calorimeters. The interaction of a given particle in these detectors leaves a specific signature. This is exploited for particle identification (PID) by combining calorimeters and tracking information into multi-variate classifiers. In this contribution, we focus on the identification of photons against high-energy neutral pion and hadronic backgrounds. Performance on Run 1 data will be shown. Small discrepancies with simulation predictions are then discussed, with special emphasis on the methods to correctly estimate PID cut efficiencies by means of large calibration samples of abundant beauty and charm decays to final states with photons. Finally, the technical aspects of the collection of these samples in Run 2 are presented.

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2018-06-13
17:17
Measurement of track reconstruction efficiency at LHCb
Reference: Poster-2018-632
Created: 2018. -1 p
Creator(s): Van Veghel, Maarten; Dufour, Laurent

The precise evaluation of the tracking efficiencies is a crucial element for many physics analysis, especially those aiming at measuring production cross sections or branching fractions. In the LHCb experiment, several data-driven approaches have been conceived and continuously improved in order to provide a precise evaluation of the tracking efficiencies. They are mostly based on clean samples of muons, but the recent hints of lepton universality violation required the development of robust data-driven techniques specifically dedicated to electrons, in order to reduce the systematic uncertainties. In addition, special data streams have been recently put in place to collect and save the calibration samples selected in the LHCb software trigger for both muons and electrons, ensuring a prompt access right after the data has been collected.

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