The production of resonances in heavy-ion collisions is expected to be sensitive to the properties of strongly interacting matter created in such collisions. We report on the measurements of $ϕ$ and $K^{*0}$ resonances in Pb-Pb collisions at $\sqrt{s_{NN}} $ = 2.76 TeV. The masses, widths and yields in Pb-Pb collisions as a function of centrality are compared to that in pp collisions to understand the role of re-scattering and regeneration. The resonance to non-resonance particle ratios are shown as a function of collision centrality and compared with the results at lower energies.
Jets of high energy collimated particles provide a rich phenomenology to study quantum chromodynamics, from first-principles tests of perturbative calculations to investigations of the emergent properties of the strongly-coupled quark-gluon plasma. In these proceedings, we highlight several recent jet measurements by the ALICE Collaboration, with a focus on jet substructure observables.
Hadronic resonances $\mathrm{K}^{*}(892)^{0}$, $ϕ$(1020) and $Σ(1385)^{\pm}$ have been measured by the ALICE experiment in pp collisions at $\sqrt{s}=7$ TeV and in Pb-Pb collisions at $\sqrt{s_{_\mathrm{NN}}}=2.76$ TeV. Transverse momentum spectra, particle ratios, nuclear modification factor and comparison with model predictions are discussed. In addition, ALICE results are compared with data obtained at RHIC energy.
The ALICE experiment at the Large Hadron Collider (LHC) at CERN consists of a central barrel, a muon spectrometer and additional detectors for trigger and event classification purposes. The low transverse momentum threshold of the central barrel gives ALICE a unique opportunity to study the low mass sector of central exclusive production at the LHC.
Measurements of charm and beauty production in pp collisions, using the ALICE detector system, at LHC energies ($\sqrt{s} = 2.76$ and 7.0 TeV) can test perturbative QCD down to very low Björken-x. They are also critical as a reference to ALICE's heavy ion program. The ALICE detector system allows measurements not covered by the other LHC experiments in addition to covering complementary regions. A description of the ALICE detector system, in relation to ATLAS and CMS, are presented. Results from both leptonic and hadronic decay channels will be shown along with comparisons to other measurement…
The measurement of D-meson production in heavy-ion collisions at LHC energy provides insights into the mechanisms of interaction of charm quarks in the hot and dense medium formed in these collisions. ALICE results on the D-meson nuclear modification factor and azimuthal anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV are presented.
Hadronic resonances are a valuable tool to study the properties of the medium formed in heavy-ion collisions. In particular, they can provide information on particle-formation mechanisms and on the properties of the medium at chemical freeze-out. Furthermore they contribute to the systematic study of parton energy loss and quark recombination. Measurements of resonances in pp and in p-Pb collisions provide a necessary baseline for heavy-ion data and help to disentangle initial-state effects from medium-induced effects. In this paper the latest ALICE results on mid-rapidity K*(892)^0 and ϕ(1020…
We present measurements of hadronic resonance, strange and multi-strange particle production in collisions of Xe-Xe and Pb-Pb at the center-of-mass energies of $\sqrt{s_{NN}}=5.44$ and $5.02$ TeV, respectively, by the ALICE collaboration at the LHC. Particle ratios are presented as a function of multiplicity for $K^{0}_{s}$, $Λ$, $Ξ^{-}$, $\barΞ^{+}$, $Ω^{-}$, $\barΩ^{+}$, $ρ(770)^{0}$, $K^{\ast}(892)^{0}$, $ϕ(1020)$ and $Λ(1520)$. Our results are discussed and compared with predictions of QCD-inspired event generators. Additionally, comparisons with lower energy measurements and smaller syste…
After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data with proton collisions at the LHC starting in November 2009 and first Pb-Pb data in November 2010. This article summarizes initial operation and performance of ALICE as well as first results from both pp and Pb-Pb collisions.
Results on open heavy-flavour production in Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV measured with ALICE at the LHC are presented. The nuclear modification factors, extracted in three different channels, show a strong suppression in central collisions. The measured D-meson azimuthal anisotropy indicates a non-zero v2, which is similar to the one of charged hadrons.
The study of hadronic resonances plays an important role both in pp and in heavy-ion collisions. Since the lifetimes of short-lived resonances are comparable with the lifetime of the fireball formed in heavy-ion collisions, regeneration and re-scattering effects can modify the measured yields, especially at low transverse momentum. Measurements in pp collisions at different energies constitute a baseline for studies in heavy-ion collisions and provide constraints for tuning QCD-inspired event generators. Furthermore, high multiplicity pp collisions, where the density and the volume of the syst…
The pseudorapidity density and multiplicity distributions of charged particles have been the first measurements carried out with the ALICE detector at the LHC. After an introduction on the experiment and some details on the subdetectors relevant for these measurements, results from minimum bias proton-proton collisions at 0.9, 2.36 and 7 TeV are presented. Comparisons with other measurements and model predictions are also discussed.
The ALICE detector is well suited to measure heavy-flavour (charm and beauty) production via hadronic and semi-leptonic decay channels of heavy-flavour particles. Here an overview of heavy-flavour measurements made with the ALICE detector during Run 1 in pp and p--Pb collisions is presented and discussed.
The ALICE experiment has measured the production of a rich set of hadronic resonances, such as $ρ(770)^{0}$, ${\rm K}^{\ast}(892)^{0}$, $ϕ$(1020), $Σ^{\pm}$(1385), $Λ(1520)$ and $Ξ^{\ast 0}$ in pp, p-Pb and Pb-Pb collisions at various energies at the LHC. A comprehensive overview and the latest results are presented in this paper. Special focus is given to the role of hadronic resonances for the study of final-state effects in high-energy collisions. In particular, the measurement of resonance production in heavy-ion collisions has the capability to provide insight into the existence of a prol…
After 20 years of preparation, the dedicated heavy ion experiment ALICE took first data at the CERN LHC accelerator with proton collisions at the end of 2009 and with lead beams at the end of 2010. This article will give a brief overview of the main results presented at the Quark Matter 2011 conference.
Reference cross sections have been measured with the ALICE detector in both pp and Pb-Pb collisions, in dedicated luminosity calibration experiments (van der Meer scans) at the LHC. The results and their uncertainties are discussed, together with a few selected applications.
ALICE is the LHC experiment dedicated to the study of Heavy-Ion collisions. Many observables related to the properties of the medium created in such collisions rely on the excellent capabilities of the detector in terms of Particle Identification (PID) of particles. In the following, the various PID techniques used for the different ALICE analyses will be described. Focus will be given to the detectors' performance, and selected results will be presented on pp data collected at sqrt(s) = 7 TeV and PbPb collisions at sqrt(s_NN) = 2.76 TeV.
We present here recent open heavy-flavour results from the ALICE experiment, including measurements of D-meson, $\mathrm{Λ_{c}^{+}}$ baryon and $\mathrm{Ξ_c^0}$ baryon production in pp collisions at $\sqrt{s} = 7~\mathrm{TeV}$ and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm{TeV}$.
The ALICE detector at the LHC recorded first Pb-Pb collisions at 2.76 TeV in November and December of 2010. We report on the measurements of anisotropic flow for charged and identified particles. From the comparison with measurements at lower energies and with model predictions we find that the system created at these collision energies is described well by hydrodynamical model calculations and behaves like an almost perfect fluid.
We report on the pseudo-rapidity dependence of the charged particle anisotropic flow in Pb-Pb collisions at 2.76 TeV. The measurement is done over a wide range of pseudo-rapidity, |η|<5 using the forward detectors of ALICE at the LHC. Results are obtained from two- and multi-particle correlation techniques with the latter being less sensitive to non-flow effects. Elliptic flow longitudinal scaling, comparison with RHIC data and AMPT model calculations for the LHC are discussed.
The measurements of open heavy-flavours, i.e. D mesons at central rapidity and leptons from charm and beauty decays at central and forward rapidity was studied in p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV using the ALICE detector. The results are presented and compared to model predictions including cold nuclear matter effects.
ALICE at the LHC has a unique potential to study proton-proton collisions with the goal to probe Quantum ChromoDynamics (QCD). The apparatus was designed to reconstruct particles over a large range in transverse momentum and rapidity. In particular, quarkonia are very interesting probes of QCD, because their production mechanisms are governed by both perturbative and non-perturbative QCD processes. In ALICE, quarkonia are reconstructed via their dilepton decay channel down to zero transverse momentum. This contribution gives a short overview of quarkonium production results in proton-proton co…
ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.
Probes for the small-x parton densities and predicted effects of gluon saturation are discussed. At very low x and intermediate Q, only results on hadronic observables at the LHC are available, which do not provide unambiguous information. It is shown that the measurement of direct photons at forward rapidity at the LHC is particularly promising to provide a unique signal. We further discuss the possibilities to perform such measurements with a detector upgrade in the ALICE experiment and present the R&D activities ongoing.
These proceedings describe the charged-particle pseudorapidity densities and multiplicity distributions measured by the ALICE detector in pp collisions at $\sqrt{s} = 0.9$ and 7 TeV in specific phase space regions. The pseudorapidity range $|η| < 0.8$, together with $p_{\rm T}$ cuts at 0.15, 0.5 and 1 GeV/$c$ is considered. The classes of events considered are those having at least one charged particle in the kinematical ranges just described. The results obtained by ALICE are compared to Monte Carlo predictions.
We present measurements of charged jet cross sections and jet shape observables in leading jet in proton-proton (pp) collisions at sqrt(s) = 2.76 TeV with the ALICE detector at LHC. Jets are reconstructed at the midrapidity from charged particle using sequential recombination anti-kT jet finding algorithm for various R values. The results are compared to measurements from HERWIG, PHOJET and different tunes of PYTHIA6 and earlier measurements at 7 TeV.
The ALICE experiment is equipped with a wide range of detectors providing excellent tracking and particle identification in the central region, as well as forward detectors with extended pseudorapidity coverage, which are well suited for studying diffractive processes. Cross section measurements of single and double diffractive processes performed by ALICE in pp collisions at $\sqrt{s}=0.9,~2.76,~7$~TeV will be reported. Currently, ALICE is studying double-gap events in pp collisions at $\sqrt{s}=7$~TeV, which give an insight into the central diffraction processes: current status and future pe…
Strange quark and particle production is studied at the LHC with unprecedented high beam energies in both heavy-ion and proton-proton collisions: on the one hand, strangeness is used for investigating chemical equilibration and bulk properties; on the other hand, strange particles contribute to probe different kinematical domains, from the one where collective phenomena are at play up to the region dominated by pQCD-calculable processes. We highlight the suitability of the ALICE experiment for this topic, presenting our latest measurements and comparing them to models.
We report on the studies of two-particle angular correlations measured in proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV recorded by ALICE at the LHC. Two-particle correlations in relative azimuth (Δϕ) and pseudorapidity (Δη) are expected to exhibit several structures which arise from different physics mechanisms and allow us to study the wide landscape of correlations. The results include the dependence of the correlation function on the event multiplicity, the charge combination and species (pions, kaons or protons) of particles in the pair.
Long-range correlations between particles separated by a pseudorapidity gap are a powerful tool to explore the initial stages and evolution of the medium created in hadron-hadron collisions. An overview of the long-range correlations measured by the ALICE detector in pp, p-Pb and Pb-Pb will be presented. This includes analyses of forward-backward, two- and multi-particle correlations with the use of the central barrel and forward detectors.
In November 2010 the ALICE experiment at CERN has collected the first Pb--Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV produced by the LHC. A first characterization of the hot and dense state of matter produced in this new energy domain became available shortly after the run. In this paper we present the results on charged-particle multiplicity, Bose-Einstein correlations, elliptic flow and their dependence on the collision centrality. Results from first measurements of strange and identified particle production and suppression of high-momentum hadrons with respect to $pp$ collisions are also r…
The excellent capabilities of the ALICE experiment for particle identification allow to measure the identified hadron production in a wide range of transverse momentum. In this work we present some results on identified particle spectra, strange particle production and particle contents measured in pp collisions at \sqrt{s} = 0.9, 2.76 and 7 TeV. The results are compared with Monte Carlo event generators predictions.
Two-particle azimuthal correlations of electrons from heavy-flavour hadron decays with charged particles can give insight into the properties of heavy-quark production and hadronization into heavy-flavour jets.\\ In this contribution, the ALICE results measured in pp collisions at 5.02 TeV, collected in the LHC Run 2, are presented. The yields of charged particles in the near and away-side correlation peaks and the peak width are compared with PYTHIA calculations.
Silicon Drift Detectors (SDD) equip the two central layers of the Inner Tracking System of the ALICE experiment at the LHC. Main results of systematic studies of detector performance including noise, gain, drift speed and charge collection measurements will be reported
We report the recent measurements of the inclusive J/ψ production in pp collisions at \sqrt{s} = 2.76 TeV, in pp collisions at \sqrt{s} = 7 TeV and in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV with the ALICE detector at the LHC. The J/ψ mesons are detected down to pT = 0 GeV/c via their di-muon decay channel at forward rapidity (2.5 < y < 4) and via their di-electron decay channel at mid-rapidity (|y| < 0.9). A special emphasis is put on the nuclear modification factor which is compared to the predictions of current J/ψ production models.
We report on the first dielectron measurement in pp collisons at $\sqrt{s} = 7$ TeV with the ALICE detector system. The results are compared to the expected hadronic sources. The hadronic cocktail agrees to the measured dielectron continuum within statistical and systematic uncertainties. The status of the dielectron measurement in Pb--Pb collisions at {$\sqrt{s_{NN}}=2.76$} TeV is addressed.
ALICE (A Large Ion Collider Experiment) is one of the seven experiments at the the Large Hadron Collider (LHC) at CERN, Geneva, Switzerland. ALICE is especially designed for heavy-ion collisions but it also operates a rich proton-proton (pp) program. ALICE has collected pp collision data at $\sqrt{s}=$ 0.9, 2.36, 2.76, and 7 TeV and lead-lead (Pb--Pb) collision data at $\sqrt{s_{\mathrm{NN}}}=$2.76 TeV. Here, we report minimum bias measurements obtained until the end of 2010: the results include measurements of charged-particle pseudorapidity, multiplicity and transverse momentum distributions…
Studying p-Pb collisions at LHC energies allows a quantitative evaluation of the cold nuclear matter (CNM) effects. Event activity dependence of the J/ψ production is under intense studies both theoretically and experimentally and is expected to provide important insights on the influence of CNM. This paper presents the first results on event activity dependence of the inclusive J/ψ production at backward (-4.46 < $y_{cms}$ < -2.96) and forward (2.03 < $y_{cms}$ < 3.53) rapidity in ALICE for p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
In this paper, an overview of recent $\mathrm D^{0}$, $\mathrm D^{+}$ and $\mathrm D^{*+}$ measurements, performed by ALICE in proton--proton collisions at $\sqrt{s}~=~2.76$, 5, 7, 8 and 13 TeV, is reported. The minimum-bias production cross sections, as well as their energy and species dependences, are compared to perturbative QCD calculations. The evolution of the D-meson yields with the event multiplicity is compared to phenomenological models.
In this manuscript, various beauty production measurements using the ALICE detector will be presented. We will show new measurements of non-prompt D$^0$ mesons in pp collisions at $\sqrt{s} = 5.02$ TeV and beauty-tagged jet production in p--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV. The $R_{\mathrm{AA}}$ of beauty-hadron decay electrons in central Pb--Pb collisions and the $v_{2}$ of beauty-hadron decay electrons in semi-central Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV will also be discussed.
The ALICE Collaboration has studied the inclusive J/$ψ$ and $ψ(\mathrm{2S})$ production in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV, at the CERN LHC. The J/$ψ$ measurement is performed in the $μ^{+}μ^{-}$ and in the $e^{+}e^{-}$ decay channels, down to zero $p_{\mathrm{T}}$. The results are in fair agreement with theoretical predictions. The $ψ(\mathrm{2S})$ measurement has also been performed. In particular, a smaller $ψ(\mathrm{2S})$ nuclear modification factor, with respect to the J$/ψ$ one, has been observed.
In this work we present a summary of the most relevant results on heavy-ion and astroparticle physics in ALICE. The summary includes a brief overview of the current status on the characterization of the hot and dense QCD medium created in the heavy-ion collisions produced at the LHC, as well as the intriguing finding of collective-like phenomena in small collision systems.
Ultra-peripheral collisions (UPCs), studied using the ALICE detector, allow us to investigate the low-$x$ behavior of the gluon distribution of the colliding particles. Two new measurements of coherent J/$ψ$ photoproduction cross section from Pb-Pb UPCs at $\sqrt{s_{\rm NN}}=5.02$ TeV are presented: the first measurement of the $|t|$-dependence of the cross section providing a new tool to investigate the transverse gluonic structure at low Bjorken-$x$ and a rapidity-differential measurement at midrapidity allowing us to provide stringent constraints on nuclear gluon shadowing and saturation mo…
Measurement of short-lived hadronic resonances are used to study different aspects of particle production and collision dynamics in pp, p-A and relativistic heavy-ion collisions. The yields of resonances are sensitive to the competing processes of hadron rescattering and regeneration, thus making these particles unique probes of the properties of the late hadronic phase. Measurements of resonances with different masses and quantum numbers also provide insight into strangeness production and processes that determine the shapes of particle momentum spectra at intermediate transverse momenta, as …
Charm and beauty production are probed with the ALICE experiment at the LHC by studying the single lepton transverse momentum distribution (electrons at mid-rapidity, muons at large-rapidities) and D mesons reconstructed in their hadronic decays. The differential production cross sections in proton proton interactions show a good agreement with perturbative QCD calculations at both sqrt(s) = 2.76 and 7 TeV. The measurements in lead lead reactions at sqrt(s_{NN})= 2.76 TeV evidence a reduction (or suppression) of the production rate at intermediate and high pt in the most central collisions wit…
We report on studies of two-particle ΔηΔϕ angular correlations measured in proton-proton collisions at center of mass energies sqrt{s} = 0.9 TeV, sqrt{s} = 2.76 TeV and sqrt{s} = 7 TeV registered by the ALICE experiment at LHC. We present the dependence of the correlation function on the pair transverse momentum, the multiplicity of the event and the charge combination of particles in the pair. ΔηΔϕcorrelations are expected to exhibit several structures which arise from different physics mechanisms. The results are also related to the correlations obtained by femtoscopic analysis. We show that…
Relativistic heavy-ion collisions provide a unique opportunity to search for parity violation in non-central collisions. This could lead to charge separation perpendicular to the reaction plane. An event-by-event measurement of charge separation effect in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV using Sliding Dumbbell Method (SDM) is discussed in this article.
The production mechanism of (anti)nuclei in ultrarelativistic hadronic collisions is under intense debate in the scientific community. The description of the experimental measurements is currently based on two competing phenomenological models: the statistical hadronization model and the coalescence approach. Light (anti)nuclei have been extensively measured in small collision systems, namely pp and p--Pb collisions, with ALICE at the LHC. Recent results on the (anti)deuteron production measured in jets and in the underlying event, and in high-multiplicity pp collisions at a center-of-mass ene…
ALICE is the LHC experiment devoted to the study of the Quark-Gluon Plasma (QGP). To probe this high energy density state of strongly interacting matter expected to be produced in heavy-ion collisions at high energies, measurements performed in various systems (pp, p-Pb and Pb-Pb) are compared to each other. Heavy quarks are produced in initial hard partonic scatterings on a short time scale and participate in the subsequent evolution of the medium. This makes them sensitive probes of the QGP. With ALICE, open heavy flavours are studied using D mesons (D$^0$, D$^+$, D$^{*+}$) reconstructed via…
ALICE (A Large Ion Collider Experiment) is devoted to the study of heavy-ion collisions at LHC energies. In such collisions a deconfined state of nuclear matter, the Quark-Gluon Plasma (QGP), is formed. Due to their early production, quarkonium states are good probes to study the QGP evolution. Such states are affected by suppression mechanisms which lead to reduced yields with respect to pp and p-Pb collisions, while regeneration phenomena might lead to an enhancement of their production. The latter effects are expected to be negligible at LHC for bottomonium states. The recent ALICE results …
We present the results for direct photon and neutral pion production obtained from proton-proton and lead-lead collisions in the ALICE experiment. Measurement of neutral pions in pp collisions allows to test the validity of QCD-inspired models. The study of neutral pion yields in Pb-Pb collisions permits to study the medium-induced suppression relative to the pp case. The yield of direct photons is compared to perturbative QCD calculations. In the case of central Pb-Pb collisions the observed excess of photons below 4 GeV/c is used to find the effective temperature of the matter.
The self-normalised $ψ(2S)$ yields as a function of charged-particle multiplicity in pp collisions at $\sqrt{s}$ = 13 TeV and p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$= 8.16 TeV, using the ALICE detector at the CERN LHC, are reported in these proceedings. This measurement represents one of the main tools to understand the role of multiparton interactions and their influence on charmonium production in small systems, i.e pp and pA collisions. The ratio of $ψ(2S)$-over-J/$ψ$ as a function of charged-particle multiplicity is also presented for both pp and p--Pb collisions. The comparison to th…
In this contribution, the latest ALICE results on charmed baryon production are presented. In particular the measurements of $Λ_{\rm c}^{+}$-baryon production in pp collisions at ${\sqrt{\rm s}}$ = 5.02 TeV and in p-Pb collisions at $\sqrt{\rm s_{NN}}$ = 5.02 TeV are shown and compared with previous measurements performed using pp and p-Pb data samples collected during LHC Run 1. At mid-rapidity charmed baryons are reconstructed via their hadronic decay and semileptonic decay channels, exploiting the high precision tracking, excellent vertexing and particle identification capabilities offered …
The properties of the hot and dense QCD medium formed in ultra-relativistic heavy ion collisions, as well as the mechanism of in-medium partonic energy loss, can be accessed via the study of the D mesons nuclear modification factor. The ALICE experiment has measured D meson production in pp and Pb-Pb collisions at the LHC at $\sqrt{s}$ =7 and 2.76 TeV and at $\sqrt{s_{NN}}$ = 2.76 TeV, respectively, via the exclusive reconstruction of hadronic decay channels. D mesons are selected by exploiting the high-resolution tracking performance and the hadron identification capabilities of the ALICE det…
After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data at the CERN LHC accelerator with proton collisions at the end of 2009 and with lead nuclei at the end of 2010. After a short introduction into the physics of ultra-relativistic heavy ion collisions, this article recalls the main design choices made for the detector and summarizes the initial operation and performance of ALICE. Physics results from this first year of operation concentrate on characterizing the global properties of typical, average collisions, both in pp and nucleus-nucleus reactions…
The measurement of (anti)nuclei production in pp, p-A and A-A collisions at ultrarelativistic energies is important to understand hadronization. The excellent tracking and particle identification capabilities of ALICE make it the most suited detector at the LHC to study light (anti)nuclei produced in high-energy hadronic collisions. (Anti)nuclei with mass numbers up to 4, such as (anti)deuterons, (anti)tritons, (anti)$^3$He and (anti)$^4$He have been successfully identified in ALICE at midrapidity ($|η|<$0.9). In this contribution, multiplicity dependent results on the yields, nuclei-to-proton…
The status of the ALICE experiment is presented. ALICE is the LHC experiment devoted to heavy ion collisions. Preparing for the first lead-lead run, foreseen in November 2010, ALICE is successfully collecting data in proton-proton collisions at the LHC since November 2009, exploiting the charateristics of the detector for its proton-proton physics program. First results are briefly reviewed with an emphasis on performance of its detector sub-systems.
