Charged Hadrons In Pp Collisions Research Articles

Charged Particles Transverse Momentum and Pseudorapidity Distribution in Hadronic Collisions at LHC Energies

We present an analysis of the pseudorapidity η and transverse momentum pT distributions of charged hadrons in pp collisions for the kinematic range of 0<pT<4 GeV/c and |η|<2.4 at 0.9, 2.36, and 7 TeV. Charged particles are produced in pp collision using several Monte Carlo event generators (Pythia Simple, Vincia, Dire showers, Sibyll2.3d, QGSJETII-04, EPOS-LHC) and compared with CMS data at LHC. It is observed that the Simple parton showers can explain the CMS data very well for pT>1 GeV/c at 0.9 and 2.36 TeV within the experimental errors, while Dire overshoots and Vicia undershoots the data by 50% each. At 7 TeV, the Dire module presents a good prediction, whereas the Simple and Vincia modules underestimate the data within 30% and 50%. Comparing the Simple module of the Pythia model and the predictions of the CRMC models with the experimental data shows that at 0.9 TeV, EPOS-LHC has better results than the others. At 2.36 GeV, the cosmic rays Monte Carlo (CRMC) models have better prediction than the Simple module of Pythia at low pT, while QGSJETII-04 predicts well at high pT. QGSJETII-04 and EPOS-LHC have closer results than the Pythia-Simple and Sibyll2.3d at 7 TeV. In the case of the pseudorapidity distributions, only the Pythia-Simple reproduced the experimental measurements at all energies. The Dire module overestimates, while Vincia underestimates the data in decreasing order of discrepancy (20%, 12%, 5%) with energy. All CRMC models underestimate the data over the entire η range at all energies by 20%. The angular ordering of partons and the parton fragmentation could be possible reasons for this deviation. Furthermore, we used the two-component standard distribution to fit the pT spectra to the experimental data and extracted the effective temperature (Teff) and the multiplicity parameter (N0). It is observed that Teff increases with the increase in the center of mass energy. The fit yielded 0.20368±0.01, 0.22348±0.011, and 0.24128±0.012 GeV for 0.9, 2.36, and 7 TeV, respectively. This shows that the system at higher energies freezes out earlier than lower ones because they quickly attain the equilibrium state.

Results on Bose–Einstein Correlations of Charged Hadrons in pp Collisions at 13 TeV in CMS

Results on Bose–Einstein Correlations of Charged Hadrons in pp Collisions at 13 TeV in CMS

Pseudorapidity dependence of the p T spectra of charged hadrons in pp collisions at s = 0.9 and 2.36 TeV

Abstract We report the predictions of different Monte Carlo event generators including HIJING, Pythia, and QGSJETII in comparison with the experimental data measured by the CMS Collaboration at CERN in proton–proton (pp) collisions at center-of-mass energy s = 0.9 and 2.36 TeV. The CMS experimental transverse momentum (p T or p ⊥) spectra of charged hadrons were measured for pseudorapidity range 0 ⩽ η ⩽ 2.4 with bin width of η = 0.2 (for p T from 0.1 to 2 GeV/c) and a single bin of η for |η| &lt; 2.4 (for p T from 0.1 to 4 GeV/c). Pythia reproduced the p T spectra with reasonable agreement for most of the p T range. It depicts better results in the case of the |η| &lt; 2.4 than HIJING and QGSJETII which could reproduce the spectra in a limited p T range. Furthermore, to analyze the p T spectra of charged hadrons measured by the CMS Collaboration, we used a three-component function (structured from the Boltzmann distribution) and the q-dual function (from the q-dual statistics) to extract parameter values relevant for the study of bulk properties of hadronic matter at high energy. We have also applied the two analytic functions over the model predictions. The values extracted by the functions from the HIJING and Pythia models are closer to the experimental data than the QGSJETII model. Although the models could reproduce the p T spectra of all charged particles in some of the p T range but none of them could reproduce the distributions over the entire p T range and in all the pseudorapidity regions.

Heavy-flavour production in small systems and evolution with multiplicity with ALICE

In this report, highlights on the multiplicity-dependent measurements of heavy-flavour hadrons performed by the ALICE experiment, are presented. The heavy-flavour baryon-to-meson Λc0/D0 and strange-to-non-strange D meson DS+/D0 ratios in different charged-particle multiplicity intervals are discussed. Recent measurements of heavy-flavour self-normalised yields as a function of the self-normalised charged-particle multiplicity in pp collisions at √S = 13 TeV are also reported. Measurement of jets containing heavy-flavour hadrons in pp and p–Pb collisions at √SNN = 5.02 TeV and the recent measurements of azimuthal correlations of heavy-flavour hadron decay electrons and charged hadrons in pp collisions at √S = 5.02 TeV are presented.

ALICE mesurements of heavy-flavour production in pp and p–Pb collisions at the LHC

The D meson yields as a function of charged-particle multiplicity in pp collisions at s=7 TeV and in p-Pb collisions at sNN=5.02 TeV are presented. The measurement of the yields of electrons from heavy-flavour hadron decays as a function of charged-particle multiplicity in p-Pb collisions at sNN=5.02 TeV are shown as well. The measurement of azimuthal correlations of prompt D mesons and charged hadrons in pp collisions at s=7 TeV and in p-Pb collisions at sNN=5.02 TeV are also presented. The results are compared with expectations from models.

Overview of ALICE results on azimuthal correlations using neutral- and heavy-flavor triggers

The ALICE detector is dedicated to studying the properties of hot and dense matter created in heavy-ion collisions. Among the probes used to investigate these properties are high-momentum particles, which originate in hard-scatterings occurring before the fireball creation. The fragments of hard scatterings interact with the hot and dense matter and via this interaction their spectra and azimuthal distributions are modified. This is probed by the measurement of the nuclear modification factor, where the pT spectra obtained in Pb–Pb collisions are compared to a pp baseline. A strong suppression of charged hadrons as well as neutral- and heavy-flavor mesons was observed at pT > 4 GeV/c. Azimuthal correlations, using high-momentum (pT > 4 GeV/c) hadrons as triggers, can provide further insight into how the presence of the medium modifies the final kinematic distributions of the particles. Comparison with theoretical models can be used to test their predictions about the properties of the medium. We give an overview of ALICE azimuthal-correlation measurements of neutral- and heavy-flavor mesons with charged hadrons in pp collisions at and Pb–Pb collisions at . We also present a measurement of the π0 correlation with jets in pp collisions at .

Heavy-flavour production in pp collisions and correlations in pp and p-Pb collisions measured with ALICE at the LHC

Thanks to its excellent tracking and particle identification performance, the ALICE detector is capable of measuring D mesons at mid-rapidity via their hadronic decay channels down to very low transverse momentum. We show an extension of the prompt D0 pT-differential cross section measurement down to zero transverse momentum, which allows us to determine the pT-integrated charm production cross section at mid-rapidity in pp collisions at . We also present measurements of azimuthal correlations of prompt D0, D+ and D*+ mesons with charged hadrons in pp collisions at and p-Pb collisions at and compare the results with expectations from models.

Heavy-flavor correlations and multiplicity dependence in pp and p–Pb collisions with ALICE

The production of heavy quarks in pp collisions at the LHC energies provides a reliable test of perturbative QCD calculations. Comparisons of pp and p–Pb measurements of their hadronization products allow us to investigate how cold nuclear matter effects affect the heavy-quark production. We present ALICE measurements of azimuthal correlations of prompt D mesons with charged hadrons in pp collisions at s=7 TeV and p–Pb collisions at sNN=5.02 TeV. We also show the per-event D-meson yields as a function of the charged-particle multiplicity in pp collisions at s=7 TeV.

Pseudorapidity distribution of charged hadrons in proton–proton collisions at [formula omitted

The pseudorapidity distribution of charged hadrons in pp collisions at s=13 TeV is measured using a data sample obtained with the CMS detector, operated at zero magnetic field, at the CERN LHC. The yield of primary charged long-lived hadrons produced in inelastic pp collisions is determined in the central region of the CMS pixel detector (|η|<2) using both hit pairs and reconstructed tracks. For central pseudorapidities (|η|<0.5), the charged-hadron multiplicity density is dNch/dη||η|<0.5=5.49±0.01(stat)±0.17(syst), a value obtained by combining the two methods. The result is compared to predictions from Monte Carlo event generators and to similar measurements made at lower collision energies.

Measurement of D-meson production in pp, p–Pb and Pb–Pb collisions with ALICE at the LHC

Heavy quarks, i.e. charm and beauty, are considered calibrated probes for the strongly interacting deconfined medium (Quark Gluon Plasma, QGP) formed in heavy-ion collisions. Produced in hard scattering processes in the initial stages of the collision, they interact with the medium, lose energy and, depending on the coupling strength to the medium, take part in the collective motion of the QCD matter. ALICE measured the production of ${\rm D^{0}}$, ${\rm D^{*+}}$, ${\rm D^{+}}$ and ${\rm D_{s}}$ mesons at central rapidity in pp, p-Pb and Pb-Pb collisions at the LHC. The study of the modification of the transverse momentum differential yields of charm particles in Pb-Pb collisions with respect to pp collisions, quantified by the nuclear modification factor ($R_{\rm AA}$), can unravel details of the energy loss mechanism, such as its dependence on the quark mass and on the path length the parton travels through the medium. A similar comparison between pp and p-Pb collision data ($R_{\rm pPb}$) is fundamental to disentangle effects related to the presence of the hot medium from cold nuclear matter effects. The degree of thermalization and coupling to the medium is investigated in semi-peripheral Pb-Pb collisions by measuring the elliptic flow coefficient ($v_{2}$) at low pt. At high pt, $v_{2}$ is sensitive to the path-length dependence of the energy loss. Results on the transverse momentum and centrality dependence of the D-meson elliptic flow and $R_{AA}$ will be presented. The comparison with the $R_{\rm AA}$ of non-prompt ${\rm J/}\psi$ from B-meson decays measured with CMS will be discussed. The preliminary results on D-meson $R_{\rm pPb}$ and the dependence of D-meson yields on rapidity in p-Pb collisions will be shown. As an outlook, the analysis and the preliminary results on the azimuthal correlations of D mesons and charged hadrons in pp collisions will be described.

Measurement of azimuthal correlations between D mesons and charged hadrons with ALICE at the LHC

The comparison of angular correlations between charmed mesons and charged hadrons produced in pp, p-Pb and Pb-Pb collisions can give insight into the mechanisms through which charm quarks lose energy in a QGP medium, produced in ultra-relativistic heavy-ion collisions, and can help to recognize possible modifications of their hadronization induced by the presence of the QGP. The analysis of pp and p-Pb data and the comparison with predictions from pQCD calculations, besides constituting the necessary reference for interpreting Pb-Pb data, can provide relevant information on charm production and fragmentation processes. In addition, possible differences between the results from pp and p-Pb collisions can give information on the presence of cold nuclear matter effects, affecting the charm production and hadronization in the latter collision system. A study of azimuthal correlations between D$^0$, D$^+$, and D$^{*+}$ mesons and charged hadrons in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. D mesons were reconstructed from their hadronic decays at central rapidity in the transverse-momentum range $3 \leq p_{\rm T}^{\rm D} \leq 16$ GeV/$c$ and were correlated to charged particles reconstructed in the pseudorapidity range $|\eta| < 0.8$. Perspectives for the measurement in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV will also be presented.

Azimuthal angular correlations between heavy-flavour decay particles and charged hadrons in pp collisions in ALICE

Heavy quarks produced in pp and heavy ion collisions are studied using heavy-flavour decay electrons and heavy-flavour mesons. Detailed understanding of the production processes and fragmentation of heavy quarks can be obtained by studying the azimuthal angular correlation of heavy-flavour hadrons. The azimuthal angular correlations of heavy-flavour mesons and charged hadrons can be used to disentangle charm and beauty-hadrons in pp collisions. In this contribution the fraction of electrons from beauty-hadron decays in the heavy-flavour decay electron yield is shown as well as the beauty production cross section in pp collisions at = 2.76 TeV. The measurements are compared to the predictions from next-to leading order perturbative QCD calculations. We also show the results from correlation analysis of charged D* mesons and hadrons performed using pp collision data at = 7 TeV.

Azimuthal angular correlations between heavy-flavour decay electrons and charged hadrons in pp collisions at s=2.76TeV in ALICE

In ultra-relativistic heavy-ion collisions heavy quarks (charm and beauty) are produced in hard scattering processes and thus carry relevant information on the properties of the created hot and dense medium. Heavy-flavour hadrons can be measured using electrons from their semileptonic decay channels. The relative contribution of charm and beauty hadrons can be estimated from the study of the near side azimuthal angular correlations between these electrons and charged hadrons. We present the measurement of azimuthal angular correlations between electrons and charged hadrons in pp collisions at 2.76 TeV measured with ALICE at the LHC. Electrons are identified using the Electromagnetic Calorimeter and the Time Projection Chamber and the charged hadrons are identified using the Time Projection Chamber. The azimuthal angular correlation distributions from PYTHIA simulations are used to extract the relative contribution from B-hadron decays to the yield of electrons from heavy-flavour decays up to $p_\textrm{t}$ = 10 GeV/c.

Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at $\sqrt{s} = 0.9 $ and 2.36 TeV

Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at sqrt(s) = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(charged)/d(eta) for |eta| < 0.5, are 3.48 +/- 0.02 (stat.) +/- 0.13 (syst.) and 4.47 +/- 0.04 (stat.) +/- 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in p-pbar and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.