Inclusive Particle Research Articles

Measurement of the inelastic cross section in proton–lead collisions at sNN=5.02TeV

The inelastic hadronic cross section in proton-lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is measured with the CMS detector at the LHC. The data sample, corresponding to an integrated luminosity of 12.6 +/- 0.4 inverse nanobarns, has been collected with an unbiased trigger for inclusive particle production. The cross section is obtained from the measured number of proton-lead collisions with hadronic activity produced in the pseudorapidity ranges 3 < eta < 5 and/or -5 < eta < -3, corrected for photon-induced contributions, experimental acceptance, and other instrumental effects. The inelastic cross section is measured to be sigma[inel,pPb] = 2061 +/- 3 (stat) +/- 34 (syst) +/- 72 (lum) mb. Various Monte Carlo generators, commonly used in heavy ion and cosmic ray physics, are found to reproduce the data within uncertainties. The value of sigma[inel,pPb] is compatible with that expected from the proton-proton cross section at 5.02 TeV scaled up within a simple Glauber approach to account for multiple scatterings in the lead nucleus, indicating that further net nuclear corrections are small.

Elastic, inelastic and inclusive alpha cross sections in6Li+112Sn system

Elastic, inelastic and inclusive alpha cross sections have been measured. Coupled-channels calculations by including the couplings of projectile breakup channels and target excitations explain the measured elastic and inelastic data. The inclusive alpha particle production is found to be more than two-third of the total reaction cross section. From coupled-channels calculations, the contribution of α from the non-capture α -d breakup of the 6 Li projectile is calculated to be very small. It suggests the possibility of many transfer induced breakup channels, having α as one of the breakup fragments, to be responsible for such a large α particle production.

Self-similarity of strangeness production in pp collisions at RHIC

New experimental data on transverse momentum spectra of strange particles (K0S,K–, K*, ϕ, …) produced in pp collisions at √s = 200 GeV obtained by the STAR and PHENIX collaborations at RHIC are analysed in the framework of z-scaling approach. Scaling properties of the data z-presentation are illustrated. Self-similarity of strange particle production is discussed. A microscopic scenario of constituent interactions developed within the z-scaling approach is used to study constituent energy loss, proton momentum fraction and recoil mass in dependence on the transverse momentum, strangeness, and mass of the inclusive particle. The obtained results can be useful for understanding strangeness origin, for searching for new physics with strange probes and can serve as a benchmark for complex analyses of self-similar features of strange production in heavy ion collisions.

Geometrical scaling in inelastic inclusive particle production at the LHC

Analyzing recent ALICE data on inelastic pp scattering at the LHC energies we show that charged particle distributions exhibit geometrical scaling (GS). We show also that the inelastic cross-section is scaling as well and that in this case the quality of GS is better than for multiplicities. Moreover, exponent $\lambda$ characterizing the saturation scale is for the cross-section scaling compatible with the one found in deep inelastic ep scattering at HERA. Next, by parametrizing charged particles distributions by the Tsallis-like formula, we find a somewhat unexpected solution that still exhibits GS, but differs from the "standard" one where the Tsallis temperature is proportional to the saturation scale.

Single inclusive particle production in proton-nucleus collisions at next-to-leading order in the hybrid formalism

We reconsider the perturbative next-to-leading calculation of the single inclusive hadron production in the framework of the hybrid formalism, applied to hadron production in proton-nucleus collisions. Our analysis, performed in the wave function approach, differs from the previous works in three points. First, we are careful to specify unambiguously the rapidity interval that has to be included in the evolution of the leading-order eikonal scattering amplitude. This is important, since varying this interval by a number of order unity changes the next-to-leading order correction that the calculation is meant to determine. Second, we introduce the explicit requirement that fast fluctuations in the projectile wave function which only exist for a short time are not resolved by the target. This Ioffe time cutoff also strongly affects the next-to-leading order terms. Third, our result does not employ the approximation of a large number of colors. Our final expressions are unambiguous and do not coincide at next-to-leading order with the results available in the literature.

High-pT probes of p+Pb collisions with ATLAS

Measurements of high pT processes in ultrarelativistic proton-nucleus collisions are sensitive to changes in the partonic densities arising from the presence of the nuclear environment. Additionally, such measurements benchmark the so called “cold nuclear matter” effects and provide the reference for understanding the large suppression of high-pT processes observed in nucleus-nucleus collisions. Furthermore, measurements of the centrality dependence of jet production at forward (proton-going) rapidities may shed light on the behavior of the proton wavefunction at large Bjorken-x. The latest ATLAS results for inclusive jets and charged particles in 28.9 nb-1 of 5.02 TeV proton-lead collisions at the LHC are presented. The centrality in these collisions is characterized through the sum of the total transverse energy in the lead-going forward calorimeter. The nuclear modification factors RpPb and RCP are presented as a function of transverse momentum, rapidity and centrality. The jet RCP in a large rapidity region is found to be modified in a way that depends only on the total jet energy.

Production of strange particles in charged jets in Pb–Pb and p–Pb collisions measured with ALICE

Measurements of spectra of identified particles produced in jets in heavy-ion collisions can provide further important insights into the interplay of various hadronisation processes which participate in the particle production in the hot and dense medium. In this contribution, we present the measurements of the pT spectra of Λ baryons and K0S mesons produced in association with charged jets in Pb-Pbcollisions at = 2.76 TeV and in p-Pb collisions at = 5.02 TeV. The results are obtained with the ALICE detector at the LHC, exploiting the excellent particle identification capabilities of this experiment. Baryon-to-meson ratios of the spectra of strange particles associated with jets are studied in central collisions and are compared to the ratios obtained for inclusive particles and for particles coming from the underlying event.

Cumulative hadron production in pA collisions in the framework of z-scaling

Data on cumulative particle production in pA collisions with momentum [Formula: see text] are analyzed in the [Formula: see text]-scaling approach. Scaling function [Formula: see text] is constructed for different types of target nuclei and inclusive particle angle. The function is expressed via respective inclusive cross section and average multiplicity density of charged particles. This regime corresponds to low [Formula: see text] (low transverse momentum [Formula: see text]). Validity of the concept was verified for this data. A-dependence of the scaling function is studied for low-[Formula: see text] region. Self-similarity of hadron production in pA collisions is confirmed over a wide kinematic range.

Self-similarity of negative particle production from the Beam Energy Scan Program at STAR

We present the spectra of negative charged particle production in Au [Formula: see text] Au collisions from STAR for the first phase of the RHIC Beam Energy Scan Program measured over a wide range of collision energy [Formula: see text], and transverse momentum of produced particle in different centralities at [Formula: see text]. The spectra demonstrate strong dependence on collision energy which enhances with [Formula: see text]. An indication of self-similarity of negative charged particle production in Au [Formula: see text] Au collisions is found. The constituent energy loss as a function of energy and centrality of collisions and transverse momentum of inclusive particle was estimated in the [Formula: see text]-scaling approach. The energy dependence of the model parameters - the fractal and fragmentation dimensions and “specific heat”, was studied.

Role of constituents of friction materials on their sliding behavior between room temperature and 400 °C

A brass-free and a brass-containing model friction material were investigated for their frictional behavior at temperatures increasing from room temperature (RT) up to 400°C, and back. This research highlights the effect of some material constituents on the friction recorded under sliding against stainless steel at pre-selected and well characterized areas. Sliding specifically onto rock fibers increases friction in comparison to sliding onto the other constituents inclusive brass particles. On recording a mean friction across areas containing the different constituents of both model friction materials, no difference was noticed between the brass-free and brass-containing one up to 400°C. However, at 400°C that mean friction drastically decreases on both composites. Thermal stability and thermo-mechanical behavior of the individual constituents allowed to explain the evolution of friction during temperature cycling. Degradation of the organic constituents present in both model friction materials appeared as the factor determining friction.

Bose–Einstein correlation measurements at CMS

Abstract Multidimensional and one-dimensional quantum-statistical (Bose–Einstein) correlations are measured in proton–proton collisions at 0.9, 2.76 and 7 TeV, in proton–lead collisions at 5.02 TeV/nucleon pair and peripheral lead–lead collisions at 2.76 TeV/nucleon pair center-of-mass energy with the CMS detector at the LHC. The correlation functions are extracted in terms of different components of the relative momentum of the pair, in order to investigate the extension of the emission source in different directions. The results are presented for different intervals of transverse pair momentum, k T , and charged particle multiplicity of the collision, N tracks , as well as for their integrated values. Besides inclusive charged particles, charged pions and kaons, identified via their energy loss in the silicon tracker detector, can also be correlated. The extracted source radii increase with increasing multiplicity, and decrease with increasing k T . The results open the possibility to study scaling and factorization properties of these radii as a function of multiplicity, k T , colliding system size and center-of-mass energy.

Production of light flavour hadrons at intermediate and high pT in pp, p–Pb and Pb–Pb collisions measured with ALICE

Abstract Light flavour transverse momentum spectra at intermediate and high p T provide an important baseline for the measurement of perturbative QCD processes in pp, for the evaluation of initial state effects in p–Pb, and for investigating the suppression from parton energy loss in Pb–Pb collisions. The measurement of the nuclear modification factor R pPb for inclusive charged particles is extended up to 50 GeV/ c in p T compared to our previous measurement and remains consistent with unity up the largest momenta. Results on R pPb of charged pions, kaons and protons that cover up to 14 GeV/ c in p T are presented and compared to R pPb of inclusive charged particles. On the production of charged pions, kaons, and protons up to p T = 20 GeV / c in Pb–Pb collisions final results for R AA are presented.

Particle production in the Color Glass Condensate: from electron–proton DIS to proton–nucleus collisions

We study single inclusive hadron production in proton-proton and proton-nucleus collisions in the CGC framework. The parameters in the calculation are obtained by fitting electron-proton deep inelastic scattering data. The obtained dipole-proton amplitude is generalized to dipole-nucleus scattering without any additional nuclear parameters other than the Woods-Saxon distribution. We show that it is possible to use an initial condition without an anomalous dimension and still obtain a good description of the HERA inclusive cross section and LHC single particle production measurements. We argue that one must consistently use the proton transverse area as measured by a high virtuality probe in DIS also for the single inclusive cross section in proton-proton and proton-nucleus collisions, and obtain a nuclear modification factor $R_{pA}$ that at midrapidity approaches unity at large momenta and at all energies.

MARS15 code developments driven by the intensity frontier needs

The MARS15(2012) is the latest version of a multi-purpose Monte-Carlo code developed since 1974 for detailed simulation of hadronic and electromagnetic cascades in an arbitrary 3-D geometry of shielding, accelerator, detector and spacecraft components with energy ranging from a fraction of an electronvolt to 100 TeV. Driven by needs of the intensity frontier projects with their Megawatt beams, e.g., ESS, FAIR and Project X, the code has been recently substantially improved and extended. These include inclusive and exclusive particle event generators in the 0.7 to 12 GeV energy range, proton inelastic interaction modeling below 20 MeV, implementation of the EGS5 code for electromagnetic shower simulation at energies from 1 keV to 20 MeV, stopping power description in compound materials, new module for DPA calculations for neutrons from a fraction of eV to 20-150 MeV, user-friendly DeTra-based method to calculate nuclide inventories, and new ROOT-based geometry. Work supported by Fermi Research Alliance, LLC under contract No. DE-AC02-07CH11359 with the U.S. Department of Energy. Presented paper at the 12 International Conference on Radiation Shielding, September 2-7, 2012, Nara, Japan mokhov@fnal.gov

Flow and Correlations in PbPb and pPb Collisions from CMS Experiment

Measurements of two- and four-particle angular correlations for inclusive charged particles in pPb collisions at p sNN = 5:02 TeV are presented over a wide pseu- dorapidity range, | | < 2.5 and full azimuth from the CMS experiment. Results from 31 nb 1 of pPb data, collected during the 2013 LHC running are compared to 2.76 TeV semi peripheral PbPb collision data, from 2011 PbPb run, having similar range of particle multiplicities. The second-order (v2) and third-order (v3) anisotropy harmonics are ex- tracted using the two-particle azimuthal correlation technique. v2 is also extracted using a four-particle cumulant method to further explore the multi-particle nature of correlations in pPb collisions. We observe a remarkable similarity in the v3 signal as a function of multiplicity between pPb and PbPb systems.

Single inclusive particle production at high energy from HERA data to proton-nucleus collisions

We study single inclusive hadron production in proton-proton and proton-nucleus collisions in the CGC framework. The parameters in the calculation are determined solely by standard nuclear geometry and by electron-proton deep inelastic scattering data, which is fit using the running coupling BK equation. We show that it is possible to obtain a good fit of the HERA inclusive cross section also without an anomalous dimension in the initial condition. We argue that one must consistently use the proton transverse area as measured by a high virtuality probe in DIS also for the single inclusive cross section in proton-proton and proton-nucleus collisions. We show that this leads to a midrapidity nuclear modification ratio R_pA that approaches unity at high transverse momentum independently of sqrt(s), in contrast to most CGC calculations in the literature. We also present predictions for future forward R_pA measurements at the LHC.

Not only the apples: Focus sensitive particles improve memory for information-structural alternatives

Abstract Focus sensitive particles highlight the relevance of contextual alternatives for the interpretation of a sentence. Two experiments tested whether this leads to better encoding and therefore, ultimately, better recall of focus alternatives. Participants were presented with auditory stimuli that introduced a set of elements (“context sentence”) and continued in three different versions: the critical sentences either contained the exclusive particle nur (“only”), the inclusive particle sogar (“even”), or no particle (control condition). After being exposed to blocks of ten trials, participants were asked to recall the elements in the context sentence. The results show that both particles enhanced memory performance for the alternatives to the focused element, relative to the control condition. The results support the assumption that information-structural alternatives are better encoded in memory in the presence of a focus sensitive particle.

Sivers effect and the single spin asymmetryANinp↑p→hXprocesses

The single spin asymmetry ${A}_{N}$, for large ${P}_{T}$ single inclusive particle production in ${p}^{\ensuremath{\uparrow}}p$ collisions, is considered within a generalized parton model and a transverse momentum dependent factorization scheme. The focus is on the Sivers effect and the study of its potential contribution to ${A}_{N}$, based on a careful analysis of the Sivers functions extracted from azimuthal asymmetries in semi-inclusive deep inelastic scattering processes. It is found that such Sivers functions could explain most features of the ${A}_{N}$ data, including some recent STAR results which show the persistence of a nonzero ${A}_{N}$ up to surprisingly large ${P}_{T}$ values.

Multiple scattering effects on inclusive particle production in the large-xregime

We study the multiple scattering effects on inclusive particle production in $\mathrm{p}+\mathrm{A}$ and $\ensuremath{\gamma}+\mathrm{A}$ collisions. Specifically, we concentrate on the region where the parton momentum fraction in the nucleus $x\ensuremath{\sim}\mathcal{O}(1)$ and incoherent multiple interactions are relevant. By taking into account both initial-state and final-state double scattering, we derive the nuclear size-enhanced power corrections to the differential cross section for single inclusive hadron production in $\mathrm{p}+\mathrm{A}$ and $\ensuremath{\gamma}+\mathrm{A}$ reactions, and for prompt photon production in $\mathrm{p}+\mathrm{A}$ reactions. We find that the final result can be written in a simple compact form in terms of four-parton correlation functions, in which the second-derivative, first-derivative and nonderivative terms of the correlation distributions share the same hard-scattering functions. We expect our result to be especially relevant for understanding the nuclear modification of particle production in the backward rapidity regions in $\mathrm{p}+\mathrm{A}$ and $\mathrm{e}+\mathrm{A}$ collisions.

Measurement of neutral strange particle production in the underlying event in proton-proton collisions ats=7 TeV

Measurements are presented of the production of primary KS0 and Λ particles in proton-proton collisions at s=7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of KS0 and Λ particles measured at pseudorapidities |η|<2 rise with increasing charged-particle jet pT in the range 1–10 GeV/c and saturate in the region 10–50 GeV/c. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the pythia Monte Carlo event generator. The pythia simulations underestimate the data by 15%–30% for KS0 mesons and by about 50% for Λ baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet pT and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.Received 26 May 2013DOI:https://doi.org/10.1103/PhysRevD.88.052001This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2013 CERN, for the CMS Collaboration