Pseudorapidity Density Distribution For Charged Particles Research Articles

Centrality dependence of charged-particle pseudorapidity density distributions in Cu–Cu collisions at high energies

We investigate the centrality dependence of charged-particle pseudorapidity density distributions in Cu–Cu collisions at high energy. In a thermal model, the particle-production contributions are classified according to the different origin of sources formed in the collisions. Comparing with the experimental data measured at RHIC energies, it is found that the improved model can describe the pseudorapidity density distributions over a broad pseudorapidity range and the changes of source-location parameters depend on collision centralities.

Kinematic constraints on interacting nucleons in Pb + Pb collisions atsNN=2.76TeV within the HIJING code

The kinematic constrains on interacting nucleons in Large Hadron Collider (LHC) heavy-ion collisions are investigated in the framework of the Heavy Ion Jet Interaction Generator (HIJING) code incorporated with a collective cascade recipe. The latter is used to implement energy-momentum conservation constrains on both primary and secondary interacting nucleons. It is found that the energy-momentum conservation constrains on the interacting nucleons affect the whole charged particle pseudo-rapidity density distribution $(\frac{dN_{ch}}{d\eta})$, at different centralities (from central (0-5\%) to peripheral (70-80\%) collisions), in Pb+Pb collisions at $\sqrt{s_{NN}} =2.76$ TeV. In particular, the kinematic constrains on interacting nucleons are shown to reduce $(\frac{dN_{ch}}{d\eta})$ yield at mid-pseudorapidity $(\lvert\eta\rvert<2)$ in all centrality intervals, which is consistent with the LHC data. In addition, the model predicts an enhancement of the hadron production at $\lvert\eta\rvert>8$, which could be checked in future ALICE Zero Degree calorimeter. Such an enhancement is found to be mainly due to the interactions of protons at the spectator parts of the collision. This indicates that the kinematic constrains are important for a correct geometrical treatment of Pb+Pb collisions at LHC energies.

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb–Pb collisions at sNN=2.76 TeV

The centrality dependence of the charged-particle pseudorapidity density measured with ALICE in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ over a broad pseudorapidity range is presented. This Letter extends the previous results reported by ALICE to more peripheral collisions. No strong change of the charged-particle pseudorapidity density distributions with centrality is observed, and when normalised to the number of participating nucleons in the collisions, the evolution over pseudorapidity with centrality is likewise small. The broad pseudorapidity range allows precise estimates of the total number of produced charged particles which we find to range from $162\pm22$ (syst.) to $17170\pm770$ (syst.) in 80-90% and 0-5 central collisions, respectively. The total charged-particle multiplicity is seen to approximately scale with the number of participating nucleons in the collision. This suggests that hard contributions to the charged-particle multiplicity are limited. The results are compared to models which describe $\mbox{d}N_{\mbox{ch}}/\mbox{d}\eta$ at mid-rapidity in the most central Pb-Pb collisions and it is found that these models do not capture all features of the distributions.

The TOTEM experiment at the LHC and its physics results

The TOTEM experiment at the LHC has measured proton-proton elastic scattering in dedicated runs at s=7and8TeV. The proton-proton total, elastic and inelastic cross-sections were derived with different methods by either using the optical theorem or a luminosity independent method, where the directly measured inelastic and elastic rates are applied. The TOTEM experiment presented its first preliminary cross-sections for soft single and double diffraction at s=7 TeV. The central diffraction analysis is ongoing, including a common TOTEM-CMS analysis. The charged particle pseudorapidity density distribution, dNch/dη, was determined at 7 and 8 TeV.

Centrality dependence of the pseudorapidity density distribution for charged particles in Pb–Pb collisions at [formula omitted

We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0–5%, 5–10%, 10–20%, and 20–30% most central events) in Pb–Pb collisions at sNN=2.76 TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, −5.0<η<5.5, and employing a special analysis technique based on collisions arising from LHC ‘satellite’ bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (Nch=17165±772 for the 0–5% most central collisions). From the measured dNch/dη distribution we derive the rapidity density distribution, dNch/dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.

Measurement of charged particle pseudorapidity density in Pb+Pb collisions at TeV with the ATLAS detector at the LHC

We present a study of charged particle pseudorapidity density distribution over a broad range of pseudorapidity and centrality in Pb+Pb collisions at TeV with the ATLAS detector at the LHC. The global shapes of multiplicity density distributions over four units of pseudorapidity from −2 to 2 are presented. Centrality and collision energy dependence of mid-rapidity density per participating nucleon pair is shown and compared to results of previous measurements.

Widths of charged particle pseudorapidity density distributions in high energy [formula omitted] and AA collisions

The paper presents a fit to pseudorapidity distributions of final-state charged particles produced in hadron and heavy ion experiments at different center-of-mass energies. Distributions of charged particles measured in p p ¯ , p ( d ) A , and AA collisions at high energies are presented and good agreement between the fit and the data is found. The basis of the fits is a semi-empirical formula which is obtained from a simple Feynman gas model, namely the two-cylinder gas model. For p p ¯ and AA collisions, the dependence of the width of charged particle pseudorapidity density distributions on logarithmic center-of-mass energy is studied and found to be a linear relationship. Meanwhile, the dependences of the two-cylinder length, single cylinder length, and gap width between the two cylinders on logarithmic center-of-mass energy are found to be linear relationships. As another check and application of the semi-empirical formula, the rapidity distributions of net-protons emitted in AA collisions at high energies are studied. Similar conclusions are obtained.

Charge particle universal rapidity scaling in and Au + Au collisions at relativistic energies and its partonic origin

The BRAHMS and PHOBOS collaborations recently revisited the limiting fragmentation shown in the charged particle pseudorapidity density distribution in Au + Au collisions at RHIC energies. The PHOBOS collaboration especially emphasized that the observations of the charged particle universal (pseudo)rapidity scaling (limiting fragmentation) in and Au + Au collisions at relativistic energies may play an important role in the study of reaction dynamics. We use a parton and hadron cascade model, PACIAE, to investigate the charged particle universal (pseudo)rapidity scaling in the above collisions. It is pointed out that, because the universal scaling was observed in the tail region of the (pseudo)rapidity distributions, the discrepancies among distributions may not be properly visible. Therefore, this universal scaling may not have much to do with reaction dynamics, especially quark–gluon plasma. In addition, the charged particle universal scaling observed in the hadronic final state seems to arise from the partonic initial state.

Charged particle density distributions in Au induced interactions with emulsion nuclei at 10.7 A GeV

Charged particle pseudorapidity density distributions in Au induced reactions in nuclear emulsion at 10.7 A GeV have been measured. In peripheral events the shower particle distribution exhibits a two peak structure while in central collisions it has a Gaussian shape. The spectator protons appear in the second peak in the pseudorapidity spectra and exhibits a broader momentum distribution than expected from Fermi motion. The produced particle yield in central collisions is not substantially different from phenomenological descriptions based on data from O and S induced reactions.

I. B. Keirim-Markus, Ye. Ye. Kovalev, N. A. Sergeyeva and L. N. Uspensky: Measurement of the radiation dose of Gagarin and Titov in the first space flights (pp. 102–103)

We present the first wide-range measurement of the charged-particle pseudorapidity density distribution, for different centralities (the 0–5%, 5–10%, 10–20%, and 20–30% most central events) in Pb–Pb collisions at sNN=2.76TeV at the LHC. The measurement is performed using the full coverage of the ALICE detectors, −5.0<η<5.5, and employing a special analysis technique based on collisions arising from LHC ‘satellite’ bunches. We present the pseudorapidity density as a function of the number of participating nucleons as well as an extrapolation to the total number of produced charged particles (Nch=17165±772 for the 0–5% most central collisions). From the measured dNch/dη distribution we derive the rapidity density distribution, dNch/dy, under simple assumptions. The rapidity density distribution is found to be significantly wider than the predictions of the Landau model. We assess the validity of longitudinal scaling by comparing to lower energy results from RHIC. Finally the mechanisms of the underlying particle production are discussed based on a comparison with various theoretical models.