A parameter optimisation toolchain for Monte Carlo detector simulation

Monte Carlo detector transport codes are one of the backbones in high-energy physics computing. They simulate the transport of a large variety of different particle types through complex detector geometries based on different physics models. Those simulations are usually configurable through a large set of parameters allowing for some tuning on the client side. Often, tuning the physics accuracy on the one hand and optimising the resource needs on the other hand are competing requirements. In this area, we are presenting a toolchain to tune Monte Carlo transport codes which is capable of automatically optimising large sets of parameters based on user-defined metrics. The toolchain consists of two central components. Firstly, the MCReplayEngine which is a quasi-Monte-Carlo transport engine able to fast replay pre-recorded MC steps. This engine for instance allows one to study the impact of parameter variations on quantities such as hits without the need to perform new full simulations. Secondly, it consists of an automatic and generic parameter optimisation framework called O2Tuner. The toolchain’s application in concrete use-cases will be presented. Its first application in ALICE led to a reduction of CPU time of Monte Carlo detector transport by 30%. In addition, further possible scenarios will be discussed

Charm production and hadronisation in ALICE

Heavy-flavour production is an active and highly interesting field of research. Since charm and beauty quarks are predominantly produced in the hard scattering process of colliding nuclei, they serve as unique probes to study the quark-gluon plasma in Pb-Pb collisions. In addition, recent investigations of hadronisation mechanisms have revealed interesting and unexpected features when comparing measurements in $e^+e^-$ and in hadronic collisions as in pp, p-Pb and Pb-Pb. This article summarises the latest results of charm production measured by the ALICE Collaboration. For the first time, \Sigma^0_c ^{++} and $\Omega^0_c$ were measured in hadronic collisions and production measurements of the $\Lambda^+_c$ and $\Xi^0_c$ are now included in the computation of the charm production cross section

Extension of the mcplots Project and Rivet to Cover Specific Needs Arising from Heavy-Ion Analyses

The comparison between experimental data and Monte Carlo event generator output is a important tool in high energy and heavy-ion physics. It is crucial for the search of new physics, the test of theory and models, the determination of detector effects and the development of event generators. The MC analysis tool Rivet is especially made to cover this comparison procedure. Both, analysis scripts corresponding to a experimental analysis as well as the histogram data is provided. The analysis scripts can be applied to MC output producing histogram data which can be compared to experimental data immediately. mcplots steers the Rivet analysis and MC run, automizes the plotting and provides a web page where produced plots can be accessed. However, some analyses in heavy-ion physics are either very cumbersome to implement or cannot be covered by the current Rivet and mcplots workflow at all. This report summarizes first prototypes of extensions implemented to cover such analyses as part of the summer student project. The frameworks were extended within a test environment such that both specific analyses like measurements of nuclear modification factors can be covered as well as further procedures like complex merging of histogram data can be done. The work presented in the following also establishes the basis for further developments by making the mcplots and Rivet framework more flexible to cover more complex analyses in general

New Developments in the VMC Project

International audienceVirtual Monte Carlo (VMC) provides a unified interface to different detector simulation transport engines such as GEANT3 and GEANT4. Since recently all the VMC packages (the VMC core library, also included in ROOT, and the GEANT3 and GEANT4 VMC) are distributed via the VMC Project GitHub organization. In addition to these VMC related packages, the VMC project also includes the Virtual Geometry Model (VGM), which is optionally used in GEANT4 VMC for conversion between GEANT4 and ROOT TGeo geometry models.In this contribution we will present the new organization of the VMC project at GitHub and new developments in the VMC interfaces and the VMC packages. We will cover the introduction of the sensitive detector interface in the VMC core and both GEANT3 and GEANT4 VMC and the new GEANT4-related developments.GEANT4 VMC 3.0 with the integration of multithreading processing was presented at CHEP in 2015. In this presentation we will report on new features included since this version: the improved support for magnetic fields, the integration of fast simulation, Garfield physics, GEANT4 transition radiation and monopole physics. Five new VMC examples demonstrating these new features, and serving also for tests, will be also discussed. Finally we will mention the work towards the code quality and improvements in testing, documentation and automated code formatting

Using multiple engines in the Virtual Monte Carlo package

The Virtual Monte Carlo (VMC) package provides a unified interface to different detector simulation transport engines such as GEANT3 and GEANT4. It has been in production use in various experiments but so far the simulation of one event was restricted to the usage of a single chosen engine. We introduce here the possibility to mix multiple engines within the simulation of a single event. Depending on user conditions the simulation is partitioned among the chosen engines, for instance to profit from each of their advantages or specific capabilities. Such conditions can depend on phase space, geometry, particle type or an arbitrary combination. As a main achievement, this development allows for the implementation of fast simulation kernels at the VMC level which can be used stand-alone or together with full simulation engines. This capability is crucial to cope with largely increasing data expected in future LHC runs

Using multiple engines in the Virtual Monte Carlo package

International audienceThe Virtual Monte Carlo (VMC) package provides a unified interface to different detector simulation transport engines such as GEANT3 and GEANT4. It has been in production use in various experiments but so far the simulation of one event was restricted to the usage of a single chosen engine. We introduce here the possibility to mix multiple engines within the simulation of a single event. Depending on user conditions the simulation is partitioned among the chosen engines, for instance to profit from each of their advantages or specific capabilities. Such conditions can depend on phase space, geometry, particle type or an arbitrary combination.As a main achievement, this development allows for the implementation of fast simulation kernels at the VMC level which can be used stand-alone or together with full simulation engines. This capability is crucial to cope with largely increasing data expected in future LHC runs

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

(Anti-)deuteron production in pp collisions at s=13 TeV\sqrt{s}=13 \ \text {TeV}

International audienceThe study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of $\text {(anti-)deuterons}$ is studied as a function of the charged particle multiplicity in inelastic pp collisions at $\sqrt{s}=13$ TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (${\mathrm {d} N_{ch}/\mathrm {d} \eta } \sim 26$) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM)

(Anti-)Deuteron production in pp collisions at √s = 13 TeV

The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at s√=13 TeV using the ALICE experiment. Thanks to the large accumulated integrated luminosity, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (dNch/dη∼26) as measured in p-Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p-Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and Statistical Hadronisation Models (SHM)

Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at √sNN = 5.02 TeV

The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at √sNN = 5.02 TeV in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at √s = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC