Charged Hadron Production Research Articles

Inclusive production of charged hadrons in photon–photon collisions

The inclusive production of charged hadrons in the collisions of quasi-real photons (e+e−→e+e−+X) has been measured using the OPAL detector at LEP. The data were taken at e+e− centre-of-mass energies from 183 to 209 GeV. The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons are compared to theoretical calculations of up to next-to-leading order (NLO) in the strong coupling constant αs. The data are also compared to a measurement by the L3 Collaboration, in which a large deviation from the NLO predictions is observed.

Determination of fragmentation functions and their uncertainties

Fragmentation functions and their uncertainties are determined for pion, kaon, and proton by a global ${\ensuremath{\chi}}^{2}$ analysis of charged-hadron production data in electron-positron annihilation and by the Hessian method for error estimation. It is especially important that the uncertainties of the fragmentation functions are estimated in this analysis. The results indicate that the fragmentation functions, especially gluon and light-quark fragmentation functions, have large uncertainties at small ${Q}^{2}$. There are large differences between widely used functions by Kniehl, Kramer, and P\otter (KKP) and Kretzer; however, they are compatible with each other and also with our functions if the uncertainties are taken into account. We find that determination of the fragmentation functions is improved in next-to-leading order (NLO) analyses for the pion and kaon in comparison with leading-order ones. Such a NLO improvement is not obvious in the proton. Since the uncertainties are large at small ${Q}^{2}$, the uncertainty estimation is very important for analyzing hadron-production data at small ${Q}^{2}$ or ${p}_{T}$ (${Q}^{2}$, ${p}_{T}^{2}\ensuremath{\ll}{M}_{Z}^{2}$) in lepton scattering and hadron-hadron collisions. A code is available for general users for calculating obtained fragmentation functions.

Confronting fragmentation function universality with single hadron inclusive production at HERA ande+e−colliders

Predictions for light charged hadron production data in the current fragmentation region of deeply inelastic scattering from the H1 and ZEUS experiments are calculated using perturbative quantum chromodynamics at next-to-leading order, and using fragmentation functions obtained by fitting to similar data from e{sup +}e{sup -} reactions. General good agreement is found when the magnitude Q{sup 2} of the hard photon's virtuality is sufficiently large. The discrepancy at low Q and small scaled momentum x{sub p} is reduced by incorporating mass effects of the detected hadron. By performing quark tagging, the contributions to the overall fragmentation from the various quark flavours in the ep reactions are studied and compared to the contributions in e{sup +}e{sup -} reactions. The yields of the various hadron species are also calculated.

Recent results from BRAHMS in the context of longitudinal dynamics at RHIC

The BRAHMS Collaboration has measured identified charged hadron production as a function of rapidity for Au+Au and Cu+Cu collisions at energies of and 62.4 GeV at RHIC. Selected recent results are presented with emphasis on longitudinal dynamics of particle production. The rapidity dependence of particle production imposes stringent additional constraints on theoretical models describing dynamics of hadronic/partonic matter created by high-energy heavy-ion collisions.

Identified charged hadron production at high pT in $\sqrt{s_{NN}}$ =200 GeV Au + Au collisions at RHIC-PHENIX

Identified hadron analyses in heavy ion collisions at RHIC show particle-type dependences of hadron yields, especially a baryon/meson difference at intermediate pT (2–5 GeV/c). In \(\sqrt{s_{NN}}\) =200 GeV Au+Au collisions, there is a significant suppression in meson yields compared to expectations from scaled p+p results. In contrast, a large enhancement of baryons relative to mesons is observed at intermediate pT. The pT reach of charged hadron identification has been extended by high statistics Au+Au data and the introduction of an aerogel Cherenkov detector. We can now study the identified charged hadron production at higher pT using the PHENIX detector. In this paper, we present identified charged hadron pT spectra, particle ratios, nuclear modification factors in Au+Au collisions at \(\sqrt{s_{NN}}\) =200 GeV.

Probing Longitudinal Dynamics at RHIC

Particle production of charged hadrons in Au+Au collisions at \(\sqrt {s_{NN} } = 200\) GeV bas been studied as a function of rapidity by the BRAHMS Collaboration at RHIC. Selected recent results are presented with emphasis on longitudinal dynamics of particle production. The rapidity dependence of particle production imposes more stringent constraints on theoretical models describing dynamics of nuclear matter created by high-energy heavy ion collisions.

Hadron Production at Forward and Backward Rapidities in √{ NN </i≯} = 200 GeV d+Au Collisions

Understanding normal nuclear medium effects present in heavy ion collisions is essential for understanding the following dynamics of the high density matter produced in the collision. Asymmetric collisions, such as deuteron + gold, provide a key tool for studying these effects since particles produced in the forward and backward directions may be subject to different phenomena. Particle production has been studied in d+Au collisions for various kinematic regions at the RHIC facility. PHENIX has measured charged hadron production as a function of pT for different centrality classes using the PHENIX muon spectrometers for d+Au collisions at \(\sqrt {s_{NN} } = 200\) GeV. The PHENIX muon spectrometers have coverage in both forward and backward directions in the rapidity range 1.2 |η| < 2.4. The Rcp measurement, the ratio of central to peripheral production, is presented and discussed. Comparisons are also made with some relevant theoretical calculations.

High-p T results from PHOBOS

We present results from the PHOBOS experiment on charged hadron production over a large range in \(p_{\rm T}\), from Data from d + Au collisions at \(\sqrt{s_{NN}} = 200\) GeV and Au + Au collisions at \(\sqrt{s_{NN}} = 62.4\) and 200 GeV are shown. The data indicate that in Au + Au collisions a strongly interacting state of matter is formed, that appears qualitatively different from the system formed in pp or d + Au collisions. The systematics of particle production in d + Au and Au + Au collisions exhibit remarkably simple scaling rules, including an apparent factorization of the energy and centrality dependence over a wide range of collision energies.

Nuclear Modification Factors for Hadrons at Forward and Backward Rapidities in Deuteron-Gold Collisions atsNN=200 GeV

We report on charged hadron production in deuteron-gold reactions at sqrt[s(NN)]=200 GeV. Our measurements in the deuteron direction cover 1.4<eta<2.2, referred to as forward rapidity, and in the gold direction -2.0<eta<-1.4, referred to as backward rapidity, and a transverse momentum range p(T)=0.5-4.0 GeV/c. We compare the relative yields for different deuteron-gold collision centrality classes. We observe a suppression relative to binary collision scaling at forward rapidity, sensitive to low momentum fraction (x) partons in the gold nucleus, and an enhancement at backward rapidity, sensitive to high momentum fraction partons in the gold nucleus.

PHENIX spin program, recent results

Acceleration of polarized protons in Relativistic Heavy Ion Collider (RHIC) provides unique tool to study the spin structure of the nucleon. We give a brief overview of the PHENIX program to investigate poorly known gluon and flavor decomposed see quark polarization in the proton, utilizing polarized proton collisions at RHIC. We report PHENIX first results on transverse single-spin asymmetry inπ 0 and charged hadron production and longitudinal double-spin asymmetry inπ 0 production at mid-rapidity.

Forward rapidity hadron production in deuteron–gold collisions from valence quarks

We consider hadron production in deuteron–gold collisions at RHIC in the forward rapidity region. Treating the target nucleus as a color glass condensate and the projectile deuteron as a dilute system of valence quarks, we obtain good agreement with the BRAHMS minimum bias data on charged hadron production in the forward rapidity ( y = 3.2 ) and low p t region. We provide predictions for neutral pion production in minimum bias deuteron–gold collisions in the forward rapidity region, y = 3.8 , measured by the STAR Collaboration at RHIC.

Charged Hadron Suppression in Au+Au Collisions at High T &lt;/i? from STAR

We report high statistics measurements of inclusive charged hadron production in Au+Au collisions at \(\sqrt {s_{NN} } = 200\) GeV and 130 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5 ‖pT‖ 12 GeV/c. The collision energy dependence of the yields and the centrality and pT dependence of the suppression provide stringent constraints on theoretical models of suppression. Models incorporating initial-state gluon saturation or partonic energy loss in dense matter are largely consistent with observations. The pT-dependent suppression expected from models incorporating jet attenuation in cold nuclear matter or absorption of fragmentation hadrons is not observed.

Centrality and pseudorapidity dependence of charged hadron production at intermediatepTinAu+Aucollisions atsNN=130GeV

We present STAR measurements of charged hadron production as a function of centrality in Au+Au collisions at sNN=130GeV. The measurements cover a phase space region of 0.2<pT<6.0GeV∕c in transverse momentum and −1<η<1 in pseudorapidity. Inclusive transverse momentum distributions of charged hadrons in the pseudorapidity region 0.5<∣η∣<1 are reported and compared to our previously published results for ∣η∣<0.5. No significant difference is seen for inclusive pT distributions of charged hadrons in these two pseudorapidity bins. We measured dN∕dη distributions and truncated mean pT in a region of pT>pTcut, and studied the results in the framework of participant and binary scaling. No clear evidence is observed for participant scaling of charged hadron yield in the measured pT region. The relative importance of hard scattering processes is investigated through binary scaling fraction of particle production.3 MoreReceived 15 April 2004DOI:https://doi.org/10.1103/PhysRevC.70.044901©2004 American Physical Society

PHENIX measurement of high pT particles in Au + Au and d + Au collisions at

We present new results on the production of charged hadrons and neutral pions in Au+Au and d+Au collisions at , measured within the PHENIX experiment. We observe the opposite centrality dependence when comparing the two collision systems: an increase with centrality compared to the binary scaled yield from p+p collisions in d+Au and a decrease with centrality in Au+Au.

High pT hadron spectra at high rapidity

We report the measurement of charged hadron production at different pseudo-rapidity values in deuteron+gold as well as proton–proton collisions at at RHIC. The nuclear modification factors RdAu and Rcp are used to investigate new behaviours in the deuteron+gold system as a function of rapidity and the centrality of the collisions, respectively.

Rapidity dependence of charged hadron production in central Au + Au collisions at with BRAHMS

We have measured the rapidity distributions dN/dy of π±, K± and in central Au+Au collisions at . The average rapidity loss per participant nucleon is 2.0 ± 0.2 units of rapidity. The strange to non-strange meson ratios K/π are found to track variations of the baryo-chemical potential in energy and rapidity.

Identified charged particle spectra and yields inAu+Aucollisions atsNN=200GeV

The centrality dependence of transverse momentum distributions and yields for ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},{K}^{\ifmmode\pm\else\textpm\fi{}},p$, and $\overline{p}$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{NN}}=200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below $\ensuremath{\sim}2\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$ in ${p}_{T}$. Both mean transverse momenta and particle yields per participant pair increase from peripheral to midcentral and saturate at the most central collisions for all particle species. We also measure particle ratios of ${\ensuremath{\pi}}^{\ensuremath{-}}∕{\ensuremath{\pi}}^{+}$, ${K}^{\ensuremath{-}}∕{K}^{+}$, $\overline{p}∕p$, $K∕\ensuremath{\pi}$, $p∕\ensuremath{\pi}$, and $\overline{p}∕\ensuremath{\pi}$ as a function of ${p}_{T}$ and collision centrality. The ratios of equal mass particle yields are independent of ${p}_{T}$ and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta $\ensuremath{\sim}1.5--4.5\phantom{\rule{0.3em}{0ex}}\text{GeV}∕c$, proton and antiproton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.

Transverse-momentum and collision-energy dependence of high-pT hadron suppression in Au+Au collisions at ultrarelativistic energies.

We report high statistics measurements of inclusive charged hadron production in Au+Au and p+p collisions at sqrt[s(NN)]=200 GeV. A large, approximately constant hadron suppression is observed in central Au+Au collisions for 5<p(T)<12 GeV/c. The collision energy dependence of the yields and the centrality and p(T) dependence of the suppression provide stringent constraints on theoretical models of suppression. Models incorporating initial-state gluon saturation or partonic energy loss in dense matter are largely consistent with observations. We observe no evidence of p(T)-dependent suppression, which may be expected from models incorporating jet attenuation in cold nuclear matter or scattering of fragmentation hadrons.

Charged particle density distributions in Au + Au collisions at relativistic heavy-ion collider energies

Charged particle pseudorapidity distributions have been measured in Au+ Au collisions using the BRAHMS detector at RHIC. The results are presented as a function of the collision centrality and the center of mass energy. They are compared to the predictions of different parton scattering models and the important role of hard scattering processes at RHIC energies is discussed. Keywords. Relativistic heavy-ion collisions; charged hadron production; pseudorapidity distributions; centrality dependence; hard scattering processes.

Hadron formation in a nuclear environment at HERMES

The influence of the nuclear medium on the production of charged hadrons has been studied by the HERMES experiment at DESY in semi-inclusive deep inelastic scattering of 27.5 GeV positrons off deuterium, nitrogen and krypton targets. The differential multiplicity from the nucleus relative to that from the deuterium has been measured for charged hadrons and, for the first time, for identified pions, kaons, protons and antiprotons as a function of the relevant kinematic variables: the virtual photon energy v, the fraction z of this energy transferred to the hadron and the hadron transverse momentum squared p t 2 . The multiplicity ratio R M h is strongly reduced at low v and high z with significant differences for different hadrons. The distribution of the hadron transverse momentum is broadened at high p t 2 in the nuclear medium showing the evidence of the Cronin effect in the deep inelastic scattering process.