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Derniers ajouts:
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

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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2018-06-13
17:14
CP violation in $B^0_{(s)} \to h+h−$ decays
Reference: Poster-2018-631
Created: 2018. -1 p
Creator(s): Fazzini, Davide

The time-dependent CPV direct and mixing-induced asymmetries in $B^0 \to \pi^+ \pi^-$ and $B_s \to K^+ K^-$ decays have been measured at the LHCb experiment using data collected during Run1 at centre-of-mass energies of 7 and 8 TeV, corresponding to 3fb$^{-1}$. The data set was also used for a measurement of time-integrated CP asymmetries in $B^0 \to K^+ \pi^-$ and $B_s \to \pi^+ K^-$ decays.The results obtained supersede those of B factories with much higher precision. No other experiment has ever measured CP violation in $B_s \to K^+ K^-$ decays. The measurements of the time-integrated CP asymmetries are the most precise from a single experiment to date.

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2018-06-13
17:06
Anti-deuteron sensitivity studies at LHCb
Reference: Poster-2018-630
Created: 2018. -1 p
Creator(s): Baker, Sophie Katherine

Measurements of anti-deuterons in collider experiments can help to reduce systematic uncertainties in indirect searches for dark matter. Two predominant unknowns in these searches are the production of secondary anti-deuterons in the cosmos from spallation processes, and anti-deuteron production from annihilating dark matter. LHCb is a forward spectrometer on the LHC ring, designed to measure b-hadron decays from high energy proton-proton collisions. With the detector's excellent particle identification capabilities, deuteron and anti-deuteron measurements at LHCb could help to parametrise the two cosmological processes. Recent studies of (anti-)deuteron identification at LHCb and the prospects for measuring prompt (anti-)deuterons from pp-collisions will be presented, as well as a working analysis of b-baryrons decaying to deuterons.

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2018-05-24
10:43
Search for gluon saturation at Bjorken-x $\in [10^{−6}, 10^{−4}]$ with the LHCb detector(ID:39)
Reference: Poster-2018-629
Keywords:  LHCb
Created: 2018. -1 p
Creator(s): Da Silva, Cesar Luiz

A new state of matter, where gluons have overlapping wave functions, has been in the minds of particle and nuclear physicists for decades. This gluon saturated state could explain several recent observations such as particle production and collectivity observed in p+p, p+A and A+A collisions at RHIC and LHC. The LHCb experiment is a forward spectrometer with vertexing, tracking, $p, K, \pi, e, \mu$ identification and calorimetry in the pseudorapidity region 2< $\eta$ <5. LHCb is therefore well suited to study the gluon density of hadrons in at small Bjorken-x values $(x∼10^{−6}−10^{−5})$, down to two orders of magnitude smaller than HERA. The status of the analysis efforts aimed at finding the gluon saturation scale at LHCb using isolated photon yields and their correlations with hadrons and jets will be shown. In addition, the concept and R&D efforts of a new particle tracker inside the LHCb magnet to improve measurements of small Q2 processes, where gluon saturation is expected, will be presented.

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2018-05-17
14:18
Measurement of the time-integrated CP asymmetry in $D^0 \to K_S^0 K_S^0$ decays with LHCb
Reference: Poster-2018-628
Created: 2018. -1 p
Creator(s): Tuci, Giulia

CP violation in charm has not yet been observed, although measurements of time-integrated CP asymmetries in $D^0 \to K^+K^-$ and $D^0 \to \pi^+\pi^- decays$ have reached a remarkable precision, O(0.1%). The $D^0 \to K_S^0 K_S^0$ decay is a promising discovery channel for CP violation in charm. A prediction based on Standard Model gives an upper limit for the CP asymmetry of 1.1% (C.L. 95%). Further enhancements could result from contributions from physics beyond the Standard Model. We present a measurement of the time-integrated CP asymmetry in prompt $D^0 \to K_S^0 K_S^0$ decays, performed using data collected with LHCb experiment in 2015 and 2016 at a 13 TeV pp center-of-mass energy (Run-2). This result improves the sensitivity obtained by LHCb in Run-1.

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2018-04-24
22:15
Betatron-collimation Studies for Heavy Ions in the FCC-hh
Reference: Poster-2018-627
Note: ORCID: 0000-0002-7669-9837
Keywords:  FCC-hh  Heavy Ions  Collimation  Betatron  STIER  Lossmap
Created: 2018. -1 p
Creator(s): Logothetis Agaliotis, Efstathios; Schaumann, Michaela

One of the biggest challenges in the design of the FCC-hh is the collimation system. From LHC experience it is known that a collimation system optimized for proton cleaning has a significantly reduced efficiency for heavy ions. The study presented in this contribution evaluates the betatron-collimation efficiency for the heavy-ion operation with lead nuclei at a beam energy of 50 Z TeV in the system designed for proton operation. The fragmentation processes of the main beam particles in the primary collimator are simulated with FLUKA and fragments are individually tracked with SixTrack until being lost in the downstream aperture. In this way a first-impact loss-map is obtained, identifying locations where high energy deposition are to be expected. This provides a first-level assessment of feasibility and allows to include countermeasures in the conceptual accelerator design.

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FCC week 2018
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2018-04-23
15:25
IV Characterisation for the VELO Upgrade
Reference: Poster-2018-626
Created: 2018. -1 p
Creator(s): Franco Lima, Vinicius

LHCb is a dedicated heavy flavour physics experiment that operates at the LHC. The LHCb collaboration plans to change key features of the present detectors for Run III, moving to a full detector readout at 40MHz and operating at a luminosity of 1-2x1033cm-2s-1. The new Vertex Locator (VELO) detector will use hybrid pixel detectors composed of silicon sensors bump-bonded to new VeloPix CMOS readout chips designed for the new 40MHz readout rate. We will present a novel way of delivering bias through the ASIC backside in order to test IV characteristics of sensors in vacuum before module construction. The appropriate laboratory setups developed to test VELO hybrids for production will also be discussed.

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2018-04-05
09:43
A novel standalone track reconstruction algorithm for the LHCb upgrade
Reference: Poster-2018-623
Created: 2018. -1 p
Creator(s): Quagliani, Renato

During the LHC Run III, starting in 2020, the instantaneous luminosity of LHCb will be increased up to 2×1033 cm−2 s−1, five times larger than in Run II. The LHCb detector will then have to be upgraded in 2019. In fact, a full software event reconstruction will be performed at the full bunch crossing rate by the trigger, in order to profit of the higher instantaneous luminosity provided by the accelerator. In addition, all the tracking devices will be replaced and, in particular, a scintillating fiber tracker (SciFi) will be installed after the magnet, allowing to cope with the higher occupancy. The new running conditions, and the tighter timing constraints in the software trigger, represent a big challenge for the track reconstruction. This talk presents the design and performance of a novel algorithm that has been developed to reconstruct track segments using solely hits from the SciFi. This algorithm is crucial for the reconstruction of tracks originating from long-lived particles such as KS and Λ. The implementation strategy is based on a progressive cleaning of the tracking environment and on an active use of the information from the stereo hits in order to select tracks. It also profit from the definition of an improved track parameterization. When compared to its previous implementation, the new algorithm has significantly higher performances in terms of efficiency, number of fake tracks and timing, allowing to enhance the physics potential and capabilities of the LHCb upgrade.

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2018-04-04
15:34
ReDecay, a method to re-use the underlying events to speed up the simulation in LHCb
Reference: Poster-2018-620
Created: 2017. -1 p
Creator(s): Muller, Dominik; Rama, Matteo

With the steady increase in the precision of flavour physics measurements collected during LHC Run 2, the LHCb experiment requires simulated data samples of ever increasing magnitude to study the detector response in detail. However, relying on an increase of available computing power for the production of simulated events will not suffice to achieve this goal. The simulation of the detector response is the main contribution to the time needed to generate a sample, that scales linearly with the particles multiplicity of the event. Of the dozens of particles present in the simulation only a few, namely those participating in the studied signal decay, are of particular interest, while all remaining ones, the so-called underlying event, mainly affect the resolution and efficiencies of the detector. This talk presents a novel development for the LHCb simulation software which re-uses the underlying event from previously simulated events. This approach achieves an order of magnitude increase in speed and the same precision compared to the nominal simulation.

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