Pseudorapidity Interval Research Articles

Measurement of inclusive forward neutron production cross section in proton-proton collisions at sqrt{s}=13 TeV with the LHCf Arm2 detector

In this paper, we report the measurement relative to the production of forward neutrons in proton-proton collisions at sqrt{s}=13 TeV obtained using the LHCf Arm2 detector at the Large Hadron Collider. The results for the inclusive differential production cross section are presented as a function of energy in three different pseudorapidity regions: η > 10.76, 8.99 < η < 9.22 and 8.81 < η < 8.99. The analysis was performed using a data set acquired in June 2015 that corresponds to an integrated luminosity of 0.194 nb−1. The measurements were compared with the predictions of several hadronic interaction models used to simulate air showers generated by Ultra High Energy Cosmic Rays. None of these generators showed good agreement with the data for all pseudorapidity intervals. For η > 10.76, no model is able to reproduce the observed peak structure at around 5 TeV and all models underestimate the total production cross section: among them, QGSJET II-04 shows the smallest deficit with respect to data for the whole energy range. For 8.99 < η < 9.22 and 8.81 < η < 8.99, the models having the best overall agreement with data are SIBYLL 2.3 and EPOS-LHC, respectively: in particular, in both regions SIBYLL 2.3 is able to reproduce the observed peak structure at around 1.5–2.5 TeV.

N – N, PT – N and PT – PT Fluctuations in Nucleus–Nucleus Collisions at the NA61/SHINE Experiment

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Predictions for multiplicities and flow harmonics in 5.44 TeV Xe+Xe collisions at the CERN Large Hadron Collider

We present the next-to-leading-order event-by-event EKRT model predictions for the centrality dependence of the charged hadron multiplicity in the pseudorapidity interval $|\eta|\le 0.5$, and for the centrality dependence of the charged hadron flow harmonics $v_n\{2\}$ obtained from 2-particle cumulants, in $\sqrt{s_{NN}}=5.44$ TeV Xe+Xe collisions at the CERN Large Hadron Collider. Our prediction for the 0-5 \% central charged multiplicity is $dN_{\rm ch}/d\eta =1218\pm 46$. We also predict $v_n\{2\}$ in Xe+Xe collisions to increase more slowly from central towards peripheral collisions than those in a Pb+Pb system. We find that at $10 \dots 50$\% centralities $v_2\{2\}$ is smaller and $v_3\{2\}$ is larger than in the Pb+Pb system while $v_4\{2\}$ is of the same magnitude in both systems. We also find that the ratio of flow harmonics in Xe+Xe collisions and in Pb+Pb collisions shows a slight sensitivity to the temperature dependence of the shear-viscosity-to-entropy ratio. As we discuss here, the new nuclear mass-number systematics especially in the flow harmonics serves as a welcome further constraint for describing the space-time evolution of a heavy-ion system and for determining the shear viscosity and other transport properties of strongly interacting matter.

Wavelet analysis of particle density functions in nucleus–nucleus interactions

A continuous wavelet analysis is performed for pattern recognition of the pseudorapidity density profile of singly charged particles produced in [Formula: see text]O+Ag/Br and [Formula: see text]S+Ag/Br interactions, each at an incident energy of [Formula: see text] GeV per nucleon in the laboratory system. The experiments are compared with a model prediction based on the ultra-relativistic quantum molecular dynamics (UrQMD). To eliminate the contribution coming from known source(s) of particle cluster formation like Bose–Einstein correlation (BEC), the UrQMD output is modified by “an algorithm that mimics the BEC as an after burner.” We observe that for both interactions particle clusters are found at same pseudorapidity locations at all scales. However, the cluster locations in the [Formula: see text]O+Ag/Br interaction are different from those found in the [Formula: see text]S+Ag/Br interaction. Significant differences between experiments and simulations are revealed in the wavelet pseudorapidity spectra that can be interpreted as the preferred pseudorapidity values and/or scales of the pseudorapidity interval at which clusters of particles are formed. The observed discrepancy between experiment and corresponding simulation should therefore be interpreted in terms of some kind of nontrivial dynamics of multiparticle production.

Phenomenology of Charged-Particle Multiplicity Distributions

Charged-particle multiplicity distributions are an interesting tool to study both soft- and hard-QCD processes in hadronic collisions. Since last century a significant range of center-of-mass energies has been probed, ranging from a few GeV to 13 TeV in the latest LHC run. Common analysis of multiplicity distributions at different energies, in different phase space regions and from sufficiently different experiments provides a way to systematize and review existing phenomenological models of multiple particle production. In this work a phenomenological model is suggested, that can describe simultaneously charged-particle multiplicity distributions in different restricted pseudorapidity intervals for proton-proton collisions. The model is successfully applied to experimental results of ALICE experiment at LHC.

Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at s=5.02 and 13 TeV and p+Pb collisions at sNN=5.02 TeV with the ATLAS detector

ATLAS measurements of two-particle correlations are presented for $\sqrt{s} = 5.02$ and $13$ TeV $pp$ collisions and for $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV $p$+Pb collisions at the LHC. The correlation functions are measured as a function of relative azimuthal angle $\Delta \phi$, and pseudorapidity separation $\Delta \eta$, using charged particles detected within the pseudorapidity interval $|\eta|{<}2.5$. Azimuthal modulation in the long-range component of the correlation function, with $|\Delta\eta|{>}2$, is studied using a template fitting procedure to remove a "back-to-back" contribution to the correlation function that primarily arises from hard-scattering processes. In addition to the elliptic, $\cos{(2\Delta\phi)}$, modulation observed in a previous measurement, the $pp$ correlation functions exhibit significant $\cos{(3\Delta\phi)}$ and $\cos{(4\Delta\phi)}$ modulation. The Fourier coefficients $v_{n,n}$ associated with the $\cos{(n\Delta\phi)}$ modulation of the correlation functions for $n =$ $2$-$4$ are measured as a function of charged-particle multiplicity and charged-particle transverse momentum. The Fourier coefficients are observed to be compatible with $\cos{(n\phi)}$ modulation of per-event single-particle azimuthal angle distributions. The single-particle Fourier coefficients $v_n$ are measured as a function of charged-particle multiplicity, and charged-particle transverse momentum for $n {=} $ $2$-$4$. The integrated luminosities used in this analysis are, $64$ $\mathrm{nb^{-1}}$ for the $\sqrt{s}=13$ TeV $pp$ data, $170$ $\mathrm{nb^{-1}}$ for the $\sqrt{s}=5.02$ TeV $pp$ data and $28$ $\mathrm{nb^{-1}}$ for the $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV $p$+Pb data.

Charged-particle multiplicities in proton\u2013proton collisions at sqrt{s} = 0.9 to 8\xa0TeV

A detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton–proton collisions, at sqrt{s} = 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range |eta |<2, was carried out using the ALICE detector. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval |eta |<1. The use of an improved track-counting algorithm combined with ALICE’s measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapidity intervals |eta |< 0.5, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS.

Charged particle production in p+Pb collisions measured by the ATLAS detector

Per-event charged particle spectra and nuclear modification factors are measured with the ATLAS detector at the LHC in p+Pb interactions at √sNN = 5.02 TeV. Results are presented as a function of transverse momentum, rapidity, and in different intervals of collision centrality, which is characterised in p+Pb collisions by the total transverse energy measured over the pseudorapidity interval −3.2 < η < −4.9 in the direction of the lead beam. Three different calculations of the number of nucleons participating in p+Pb collisions have been performed, assuming the Glauber model and its Glauber-Gribov Colour Fluctuation extensions. The results using different models are compared with each other, as well as with other measurements made under the same conditions and also with centrality definition based on different rapidity intervals.

Measurement of inclusive jet production and nuclear modifications in pPb collisions at [Formula: see text

Inclusive jet production in pPb collisions at a nucleon–nucleon (NN) center-of-mass energy of sqrt{s_{_mathrm {NN}}} =5.02,mathrm{TeV} is studied with the CMS detector at the LHC. A data sample corresponding to an integrated luminosity of 30.1 nb^{-1} is analyzed. The jet transverse momentum spectra are studied in seven pseudorapidity intervals covering the range -2.0<eta _mathrm {CM}< 1.5 in the NN center-of-mass frame. The jet production yields at forward and backward pseudorapidity are compared and no significant asymmetry about eta _mathrm {CM} = 0 is observed in the measured kinematic range. The measurements in the pPb system are compared to reference jet spectra obtained by extrapolation from previous measurements in pp collisions at sqrt{s}=7,mathrm{TeV} . In all pseudorapidity ranges, nuclear modifications in inclusive jet production are found to be small, as predicted by next-to-leading order perturbative QCD calculations that incorporate nuclear effects in the parton distribution functions.

Observation of Long-Range Elliptic Azimuthal Anisotropies in sqrt[s]=13 and 2.76TeV pp Collisions with the ATLAS Detector.

ATLAS has measured two-particle correlations as a function of the relative azimuthal angle, Δϕ, and pseudorapidity, Δη, in sqrt[s]=13 and 2.76TeV pp collisions at the LHC using charged particles measured in the pseudorapidity interval |η|<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at Δϕ∼0 that extends over a wide range of Δη, which has been referred to as the "ridge." Per-trigger-particle yields, Y(Δϕ), are measured over 2<|Δη|<5. For both collision energies, the Y(Δϕ) distribution in all multiplicity intervals is found to be consistent with a linear combination of the per-trigger-particle yields measured in collisions with less than 20 reconstructed tracks, and a constant combinatoric contribution modulated by cos(2Δϕ). The fitted Fourier coefficient, v_{2,2}, exhibits factorization, suggesting that the ridge results from per-event cos(2ϕ) modulation of the single-particle distribution with Fourier coefficients v_{2}. The v_{2} values are presented as a function of multiplicity and transverse momentum. They are found to be approximately constant as a function of multiplicity and to have a p_{T} dependence similar to that measured in p+Pb and Pb+Pb collisions. The v_{2} values in the 13 and 2.76TeV data are consistent within uncertainties. These results suggest that the ridge in pp collisions arises from the same or similar underlying physics as observed in p+Pb collisions, and that the dynamics responsible for the ridge has no strong sqrt[s] dependence.

Centrality, rapidity, and transverse momentum dependence of isolated prompt photon production in lead-lead collisions atsNN=2.76TeV measured with the ATLAS detector

Prompt photon production in $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV Pb+Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb$^{-1}$. Inclusive photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality and transverse momentum in two pseudorapidity intervals, $|\eta| < 1.37$ and $1.52 < |\eta| < 2.37$. The scaled yields in the two pseudorapidity intervals, as well as the ratios of the forward yields to those at midrapidity, are compared to the expectations from next-to-leading order perturbative QCD calculations from JETPHOX. The measured cross sections agree well with the predictions for proton-proton collisions within statistical and systematic uncertainties. Both the yields and ratios are also compared to two other pQCD calculations, one which uses the isospin content appropriate to colliding lead nuclei, and another which includes the EPS09 nuclear modifications to the nucleon parton distribution functions.

Energy scan of correlations in p+p and Be+Be from NA61/SHINE

The existence of the critical point (CP) of strongly interacting matter is still an open problem. An extensive strong interactions program including a search of the CP and the study of the onset of deconfinement was started by the NA61/SHINE experiment at the CERN SPS. A two dimensional scan of the phase diagram is performed to search for the CP and to shed light on the phase transition region. This program includes studies of hadron production in proton- proton, proton-nucleus and nucleus-nucleus interactions measured in a wide range of colliding energy and system size. Correlations between various observables measured at midrapidity as well as in separated rapidity intervals are considered as additional and sensitive tools of this phase diagram scan. We present NA61/SHINE results of studies of energy dependence of two- particle correlations of pseudo-rapidity and azimuthal angle in p+p collisions at the SPS and the first results on correlations between multiplicity and mean transverse momentum in 7Be + 9Be collisions at 150A GeV/c obtained for separated pseudo-rapidity intervals (so called long-range correlations). Comparison with data calculations using the EPOS 1.99 model are also discussed.

Centrality and rapidity dependence of inclusive jet production in [formula omitted] proton–lead collisions with the ATLAS detector

Measurements of the centrality and rapidity dependence of inclusive jet production in sNN=5.02 TeV proton–lead (p+Pb) collisions and the jet cross-section in s=2.76 TeV proton–proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8 nb−1 and 4.0 pb−1, respectively, recorded with the ATLAS detector at the Large Hadron Collider in 2013. The p+Pb collision centrality was characterised using the total transverse energy measured in the pseudorapidity interval −4.9<η<−3.2 in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum (pT) for minimum-bias and centrality-selected p+Pb collisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a pT-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all pT at forward rapidities and for large pT at mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton–nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton–parton kinematics.

Measurement of jet suppression in central Pb–Pb collisions at [formula omitted

The transverse momentum (pT) spectrum and nuclear modification factor (RAA) of reconstructed jets in 0–10% and 10–30% central Pb–Pb collisions at sNN=2.76 TeV were measured. Jets were reconstructed using the anti-kT jet algorithm with a resolution parameter of R=0.2 from charged and neutral particles, utilizing the ALICE tracking detectors and Electromagnetic Calorimeter (EMCal). The jet pT spectra are reported in the pseudorapidity interval of |ηjet|<0.5 for 40<pT,jet<120 GeV/c in 0–10% and for 30<pT,jet<100 GeV/c in 10–30% collisions. Reconstructed jets were required to contain a leading charged particle with pT>5 GeV/c to suppress jets constructed from the combinatorial background in Pb–Pb collisions. The leading charged particle requirement applied to jet spectra both in pp and Pb–Pb collisions had a negligible effect on the RAA. The nuclear modification factor RAA was found to be 0.28±0.04 in 0–10% and 0.35±0.04 in 10–30% collisions, independent of pT,jet within the uncertainties of the measurement. The observed suppression is in fair agreement with expectations from two model calculations with different approaches to jet quenching.

Predictions on the transverse momentum spectra for charged particle production at LHC-energies from a two component model

Transverse momentum spectra, $d^2\sigma/(d\eta dp_T^2)$, of charged hadron production in $pp$-collisions are considered in terms of a recently introduced two component model. The shapes of the particle distributions vary as a function of c.m.s. energy in the collision and the measured pseudorapidity interval. In order to extract predictions on the double-differential cross-sections $d^2\sigma/(d\eta dp_T^2)$ of hadron production for future LHC-measurements the different sets of available experimental data have been used in this study.

Interpretation of charged-particle spectra inp+pandp+Pbcollisions at energies available at the CERN Large Hadron Collider using an improved hijing code with a collective cascade

We supplement the Heavy Ion Jet Interaction Generator (hijing) code with a collective cascade recipe and updated Martin-Stirling-Thorne-Watt (MSTW2009) parton distribution functions (PDFs) to describe nonsingle diffractive (NSD) $p+p$ and Pb collisions at CERN Large Hadron Collider energies. The collective cascade, developed in the space of an impact parameter, is used to induce nuclear modification of nucleons, that are involved in primary interactions, inside the dense nuclear medium. It is found that the improved hijing (Imhijing) code (that with MSTW2009 PDFs) reproduces rather well the pseudorapidity density, the multiplicity, and the transverse momentum distributions of charged particles within the pseudorapidity interval $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|&lt;2.4$ in NSD $p+p$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=0.9$, 2.36, and 7 TeV. The Imhijing with collective cascade calculations is also shown to be a good fit to the pseudorapidity density (in the laboratory system) and transverse momentum $({p}_{T})$ dependence of the nuclear modification of charged particles in NSD $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$. The effects of the collective cascade are clearly seen in the target $(3&lt;{\ensuremath{\eta}}_{\mathrm{lab}}&lt;4)$ and central (within $|{\ensuremath{\eta}}_{\mathrm{c}.\mathrm{m}.\mathrm{system}}|&lt;0.3$ at $1&lt;{p}_{T}&lt;8\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/\phantom{\rule{0.0pt}{0ex}}c)$ interaction regions when studying the pseudorapidity density and transverse momentum dependence of the nuclear modification factor of the charged particles, respectively.

Target dependence of clan model parameter in 84 Kr 36 – Emulsion interactions at 1 GeV per nucleon

This article focusses on the study of clan model parameters and their target dependence in light of void probability scaling for heavy (Ag and Br) and light (C, N and O) groups of targets present in nuclear emulsion detector using 84Kr36 at ∼1 A GeV. The variation of scaled rapidity-gap (rap–gap) probability with single moment combination has been studied. We found that experimental points lie approximately on the negative binomial distribution (NBD) curve, indicating a scaling behaviour. The increase in average clan multiplicities ( $\bar {N}$ ) for interactions with the pseudorapidity interval (Δη) was also observed. The values of $\bar {N}$ for AgBr targets are larger than those for C/N/O target and also average number of particles per clan ( $\bar {n}_{\mathrm {c}}$ ) increases with increase in pseudorapidity interval. We further observed that for a particular target, the average number of particles per clan ( $\bar {n}_{\mathrm {c}}$ ) increases with an increase in the size of projectile nucleus.

Particle identification with the ALICE Time-Of-Flight detector at the LHC

High performance Particle Identification system (PID) is a distinguishing characteristic of the ALICE experiment at the CERN Large Hadron Collider (LHC). Charged particles in the intermediate momentum range are identified in ALICE by the Time-Of-Flight (TOF) detector. The TOF exploits the Multi-gap Resistive Plate Chamber (MRPC) technology, capable of an intrinsic time resolution at the level of few tens of ps with an overall efficiency close to 100% and a large operation plateau. The full system is made of 1593 MRPC chambers with a total area of 141m2, covering the pseudorapidity interval [−0.9,+0.9] and the full azimuthal angle.The ALICE TOF system has shown very stable operation during the first 3years of collisions at the LHC. In this paper a summary of the system performance as well as main results with data from collisions will be reported.

Event activity dependence of $ Y $ (nS) production in $ \sqrt{{{s_{NN }}}} $ = 5.02 TeV pPb and $ \sqrt{s} $ = 2.76 TeV pp collisions

The production of Y(1S), Y(2S), and Y(3S) is investigated in pPb and pp collisions at centre-of-mass energies per nucleon pair of 5.02 TeV and 2.76 TeV, respectively. The datasets correspond to integrated luminosities of about 31 inverse nanobarns (pPb) and 5.4 inverse picobarns (pp), collected in 2013 by the CMS experiment at the LHC. Upsilons that decay into muons are reconstructed within the rapidity interval abs(y[CM]) < 1.93 in the nucleon-nucleon centre-of-mass frame. Their production is studied as a function of two measures of event activity, namely the charged-particle multiplicity measured in the pseudorapidity interval abs(eta) < 2.4, and the sum of transverse energy deposited at forward pseudorapidity, 4.0 < abs(eta) < 5.2. The Y cross sections normalized by their event activity integrated values, Y(nS)/<Y((nS)>, are found to rise with both measures of the event activity in pp and pPb. In both collision systems, the ratios of the excited to the ground state cross sections, Y(nS)/Y(1S), are found to decrease with the charged-particle multiplicity, while as a function of the transverse energy the variation is less pronounced. The event activity integrated double ratios, [Y(nS)/Y(1S)][pPb] / [Y(nS)/Y(1S)][pp], are also measured and found to be 0.83 +/- 0.05 (stat.) +/- 0.05 (syst.) and 0.71 +/- 0.08 (stat.) +/- 0.09 (syst.) for Y(2S) and Y(3S), respectively.

Centrality dependence of charged particle production in proton–lead collisions measured by ATLAS

The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions, d N ch / d η , in p + Pb collisions at a nucleon–nucleon center-of-mass energy of s NN = 5.02 TeV . Charged particles were reconstructed over | η | < 2.7 using the ATLAS pixel detector. The proton–lead collision centrality was characterized by the total transverse energy measured over the pseudorapidity interval 3.1 < η < 4.9 in the direction of the lead beam. Three different calculations of the number of participants, N part , have been carried out using a standard Glauber model as well as two Glauber–Gribov extensions, providing results pointing to the importance of the fluctuating nature of nucleon–nucleon collisions in the modeling of the initial state of p + Pb collisions.