Antiproton Yields Research Articles

Event-by-event antideuteron multiplicity fluctuation in Pb+Pb collisions at [formula omitted] TeV

Using the nucleon coalescence model based on kinetic freeze-out nucleons from the hybrid model of MUSIC hydrodynamics and UrQMD hadronic transport model, we study the production of antideuteron and its event-by-event fluctuation in Pb+Pb collisions at sNN=5.02 TeV. We find a clear suppression of the antideuteron to antiproton yield ratio in peripheral collisions, which is in accordance with the measurements from the ALICE Collaboration. Also found is a Poissonian event-by-event fluctuation of the antideuteron multiplicity in all collision centralities, which is different from the prediction of a simple coalescence model calculation which assumes that all antiproton and antineutron pairs have the same probability to form an antideuteron. However, due to the lack of baryon number conservation at the particlization when the viscous fluid in the hydrodynamic stage of MUSIC is converted to a hadronic matter, our model fails to describe the net-proton number fluctuation and the negative correlation between the antiproton and antideuteron multiplicities at large pseudorapidity acceptance observed in ALICE experiments. Both can nevertheless be well reproduced after selecting a suitable subset of events to fit the measured net-proton number fluctuation.

On the Study of Antiprotons Yield in Hadronic Collisions at NICA SPD

The study of antiproton yield in $p$-$p$ and $p$-$d$ collisions is important for the astrophysical search for dark matter consisting of Weakly Interacting Massive Particles. Refinement of the production cross section, angular and momentum spectra of produced antiprotons in a wide energy range could help to treat the results obtained by the AMS-02 and PAMELA orbit spectrometers. In this paper we present a detailed Monte Carlo study of possible measurements at the planned SPD experiment at the NICA collider that is under construction at JINR (Dubna).

Antiproton production in heavy-ion collisions at subthreshold energies * * Supported by the National Natural Science Foundation of China under Grant (11722546 and 11675226) and the Talent Program of South China University of Technology

Within the framework of the Lanzhou quantum molecular dynamics model, the deep subthreshold antiproton production in heavy-ion collisions has been investigated thoroughly. The elastic scattering, annihilation and charge exchange reactions associated with antiproton channels are implemented in the model. The attractive antiproton potential extracted from the G-parity transformation of nucleon selfenergies reduces the threshold energies in meson-baryon and baryon-baryon collisions, and consequently enhances the antiproton yields to some extent. The calculated invariant spectra are consistent with the available experimental data. The primordial antiproton yields increase with the mass number of the colliding system. However, annihilation reactions reduce the antiproton production which becomes independent of the colliding partners. Anti-flow phenomena of antiprotons correlated with the mean field potential and annihilation mechanism is found by comparing them with the proton flows. Possible experiments at the high-intensity heavy-ion accelerator facility (HIAF) in China are discussed.

Energy Dependent Chemical Potentials of Light Particles and Quarks from Yield Ratios of Antiparticles to Particles in High Energy Collisions

We collect the yields of charged pions ( π − and π + ), charged kaons ( K − and K + ), anti-protons ( p ¯ ), and protons (p) produced in mid-rapidity interval (in most cases) in central gold–gold (Au–Au), central lead–lead (Pb–Pb), and inelastic or non-single-diffractive proton–proton ( p p ) collisions at different collision energies. The chemical potentials of light particles and quarks are extracted from the yield ratios, π − / π + , K − / K + , and p ¯ / p , of antiparticles to particles over an energy range from a few GeV to above 10 TeV. At a few GeV (∼4 GeV), the chemical potentials show, and the yield ratios do not show, different trends comparing with those at other energies, although the limiting values of the chemical potentials and the yield ratios at very high energy are 0 and 1, respectively.

Study of Hadrons Produced in Proton—Carbon Interactions at 120 GeV/c Using Hadron-Production Models

Double differential yield of π±, K±, protons, and antiprotons as a function of laboratory momentum is presented using hadron production models. This study is done in several polar angle intervals from 0 < θ < 420 mrad for π± mesons and 0 < θ < 360 mrad for K± mesons, protons, and antiprotons. The study is carried out for p + C interactions at 120 GeV/c. For simulation, three hadron-production models: EPOS-LHC, EPOS 1.99, and QGSJETII-04 are used. Since no experimental data at 120 GeV/c is available yet, therefore, the models’ predictions are compared with the measurements of NA61/SHINE experiments at 31 GeV/c. It is found that the QGSJETII-04 model gives high peak value, for π± mesons, in the polar angle interval of 20–40 mrad, while in the range of 40–240 mrad, EPOS-LHC shows higher yield than EPOS 1.99 and QGSJETII-04 models, whereas all show higher yield than the experimental data. For π± mesons, in all angular intervals, at high momentum values, all the three models are consistent and surprisingly give the same yield as that of the experimental data. For K± mesons, QGSJETII-04 shows higher peak values at all polar angles ranging from 0 to 360 mrad as compared to that of EPOS 1.99 and EPOS-LHC models, whereas all models give higher yield at low angular intervals than the experimental data and the same yield at high angular intervals. The models demonstrate similar yields for protons at all angles but underestimate the experimental data at low angular intervals and provide the same yield at high angular intervals. The QGSJETII-04 model presents higher yields of antiprotons in comparison to the EPOS 1.99 and EPOS-LHC models, for almost all angular intervals. Generally, at higher angular range, i.e., from 240 to 420 mrad, particularly at high momentum, all the three models show similar results.

On the Possibility to Study Antiproton Production at the SPD Detector at NICA Collider for Dark Matter Search in Astrophysical Experiments

Dark matter is an important component of the Standard model of cosmology but its nature is still unknown. One of the most common explanations is that dark matter consists of Weakly Interacting Massive Particles (WIMPs), supposed to be cold thermal relics of the Big Bang and to build up the galactic dark halos. Indirect search of dark matter could be performed via the study of an anomalous antiproton component in cosmic rays originating from possible annihilation of dark matter pairs in the galactic halo, on top of the standard astrophysical production. The measurements performed by the AMS-02 and PAMELA spectrometers have shown that limited knowledge of antiproton-production cross sections in $pp$, $pD$, $pHe$ and $HeHe$ collisions is one of the main uncertainties of background subtraction. The planned SPD experiment at the NICA collider could provide a precision measurement of antiproton yield in wide kinematic range in $pp$ and $pD$ collisions at the energy scale from the threshold to $\sqrt{s}=26$ GeV/$c$.

Self-consistent analysis of hadron production in pp and AA collisions at mid-rapidity

The self-consistent approach based on similarity of inclusive spectra of hadrons produced in $pp$ and $AA$ collisions is reviewed. This approach allows us to describe rather well the ratio of proton to anti-proton yields in $AA$ collisions as a function of the initial energy at a wide range from a few GeV to a few TeV. We suggest its modification due to the quark-gluon dynamics to describe the inclusive spectra of hadrons produced in $pp$ collision as a function of the transverse momentum $p_t$ at mid-rapidity. The extension of this approach to analyze the pion $p_t$-spectra produced in $AA$ collision at high and middle energies and mid-rapidity is given. The satisfactory description of experimental data on these spectra in $pp$ and $AA$ collisions within the offered approach is shown.

Cluster formation in relativistic nucleus-nucleus collisions

An event generator for exclusive simulation of nucleus-nucleus collisions based on quantum molecular dynamics is developed. A comparison of the results obtained using this event generator with earlier measurements show that the yields of pions, kaons, antiprotons, deuterons, and nuclear fragments in the collisions of various nuclei pair such as Si-Al and Pb-Pb in the energy range of a few to $100A$ GeV are predicted successfully. The Lorentz-covariant description of nucleon-nucleon interactions plays a critical role in reproducing fragment yields in peripheral collisions. Secondary meson yields from nucleus-nucleus collisions are well reproduced by incorporating the production and decay of resonances of up to 2 GeV/${c}^{2}$ and strings. This model can therefore be used for analysis and planning of high-energy particle physics experiments, prediction of cosmic ray transport, and shielding design of high-energy heavy-ion accelerators.

Comparison of hadron production models for π±, k±, protons and antiprotons production in proton–carbon interactions at 60 GeV/c

In this research paper, the comprehensive results on the double differential yield of [Formula: see text] and [Formula: see text] mesons, protons and antiprotons as a function of laboratory momentum are reported. These hadrons are produced in proton–carbon interaction at 60 GeV/c. EPOS 1.99, EPOS-LHC and QGSJETII-04 models are used to perform simulations. Comparing the predictions of these models show that QGSJETII-04 model predicts higher yields of all the hadrons in most of the cases at the peak of the distribution. In this interval, the EPOS 1.99 and EPOS-LHC produce similar results. In most of the cases at higher momentum of the hadrons, all the three models are in good agreement. For protons, all models are in good agreement. EPOS-LHC gives high yield of antiprotons at high momentum values as compared to the other two models. EPOS-LHC gives higher prediction at the peak value for [Formula: see text] mesons and protons at higher polar angle intervals of [Formula: see text] and [Formula: see text], respectively, and EPOS 1.99 gives higher prediction at the peak value for [Formula: see text] mesons for [Formula: see text]. The model predictions, except for antiprotons, are compared with the data obtained by the NA61/SHINE experiment at 31 GeV/c proton–carbon collision, which clearly shows that the behavior of the distributions in models are similar to the ones from the data but the yield in data is low because of lower beam energy.

Nuclear stopping power of antiprotons

The slowing down of energetic ions in materials is determined by the nuclear and electronic stopping powers. Both of these have been studied extensively for ordinary-matter ions. For antiprotons, however, there are numerous studies of the electronic stopping power, but none of the nuclear stopping power. Here, we use quantum-chemical methods to calculate interparticle potentials between antiprotons and different atoms, and derive from these the nuclear stopping power of antiprotons in solids. The results show that the antiproton nuclear stopping powers are much stronger than those of protons, and can also be stronger than the electronic stopping power at the lowest energies. The interparticle potentials are also implemented in a molecular dynamics ion range calculation code, which allows us to simulate antiproton transmission through degrader foil materials. Foil transmission simulations carried out at experimentally relevant conditions show that the choice of antiproton-atom interaction model has a large effect on the predicted yield of antiprotons slowed down to low (a few keV) energies.

Self-similarity of hadron production in pp and AA collisions at high energies

We analyze the self-similarity approach applied to study the hadron production in pp and AA collisions. This approach allows us to describe rather well the ratio of the proton to antiproton yields in AA collisions as a function of the energy at a wide range from a few GeV to a few TeV. We suggest a modification of this approach to describe rather well the inclusive spectra of hadrons produced in pp collisions at different initial energies from the AGS to LHC.

NEW CALCULATION OF ANTIPROTON PRODUCTION BY COSMIC RAY PROTONS AND NUCLEI.

A dramatic increase in the accuracy and statistics of space-borne cosmic ray (CR) measurements has yielded several breakthroughs over the last several years. The most puzzling is the rise in the positron fraction above ~10 GeV over the predictions of the propagation models assuming pure secondary production. The accuracy of the antiproton production cross section is critical for astrophysical applications and searches for new physics since antiprotons in CRs seem to hold the keys to many puzzles including the origin of those excess positrons. However, model calculations of antiproton production in CR interactions with interstellar gas are often employing parameterizations that are out of date or are using outdated physical concepts. This may lead to an incorrect interpretation of antiproton data which could have broad consequences for other areas of astrophysics. In this work, we calculate antiproton production in pp-, pA-, and AA-interactions using EPOS-LHC and QGSJET-II-04, two of the most advanced Monte Carlo (MC) generators tuned to numerous accelerator data including those from the Large Hadron Collider (LHC). We show that the antiproton yields obtained with these MC generators differ by up to an order of magnitude from yields of parameterizations commonly used in astrophysics.

System size dependence of particle production at the SPS

Recent results on the system size dependence of net-baryon and hyperon production as measured at the CERN SPS are discussed. The observed Npart dependences of yields, but also of dynamical properties, such as average transverse momenta, can be described in the context of the core corona approach. Other observables, such as antiproton yields and net-protons at forward rapidities, do not follow the predictions of this model. Possible implications for a search for a critical point in the QCD phase diagram are discussed. Event-by-event fluctuations of the relative core to corona source contributions might influence fluctuation observables (e.g. multiplicity fluctuations). The magnitude of this effect is investigated.

Search for Hawking radiation in heavy ion collisions

The creation of “white holes” that decay by Hawking radiation has been proposed as one way to achieve the very early thermalization observed in heavy ion collisions at RHIC. The charartistic temperature of the radiations depends only on the ratio of the baryon number to the transverse energy. The yields of pions, kaons, protons and antiprotons measured by BRAHMS in central Au+Au collisions can be described within a thermal model where T drops with rapidity, and beam energy. We find that the chemical freeze-out temperature drops as the ratio of baryon number to energy increases but much more rapidly than predicted by the model.

“Discrepant hardenings” in cosmic ray spectra: A first estimate of the effects on secondary antiproton and diffuse gamma-ray yields

Recent data from CREAM seem to confirm early suggestions that primary cosmic ray (CR) spectra at few TeV/nucleon are harder than in the 10-100 GeV range. Also, helium and heavier nuclei spectra appear systematically harder than the proton fluxes at corresponding energies. We note here that if the measurements reflect intrinsic features in the interstellar fluxes (as opposed to local effects) appreciable modifications are expected in the sub-TeV range for the secondary yields, such as antiprotons and diffuse gamma-rays. Presently, the ignorance on the origin of the features represents a systematic error in the extraction of astrophysical parameters as well as for background estimates for indirect dark matter searches. We find that the spectral modifications are appreciable above 100 GeV, and can be responsible for ~30% effects for antiprotons at energies close to 1 TeV or for gamma's at energies close to 300 GeV, compared to currently considered predictions based on simple extrapolation of input fluxes from low energy data. Alternatively, if the feature originates from local sources, uncorrelated spectral changes might show up in antiproton and high-energy gamma-rays, with the latter ones likely dependent from the line-of-sight.

Baryon number transport at LHC energies with the ALICE experiment

This article presents the ratio of the yields of antiprotons to protons in pp collisions as measured by the ALICE experiment at = 0.9 and 7 TeV. The ratio is measured to be R|y|<0.5 = 0.957 ± 0.006(stat.) ± 0.014(syst.) at 0.9 TeV and R|y|<0.5 = 0.991 ± 0.005(stat.) ± 0.014(syst.) at 7 TeV independent of both rapidity and transverse momentum. The results are compared with theoretical predictions.

Midrapidity Antiproton-to-Proton Ratio inppCollisons ats=0.9and 7 TeV Measured by the ALICE Experiment

The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at sqrt[s]=0.9 and 7TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval 0.45<p_{t}<1.05 GeV/c and rapidity |y|<0.5. The ratio is measured to be R_{|y|<0.5}=0.957±0.006(stat)±0.014(syst) at 0.9TeV and R_{|y|<0.5}=0.991±0.005(stat)±0.014(syst) at 7TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions.

Baryon Stopping in Au+Au and p+p collisions at 62 and 200 GeV

BRAHMS has measured rapidity density distributions of protons and antiprotons in both p+p and Au+Au collisions at 62 GeV and 200 GeV. From these distributions the yields of so-called ‘net-protons’, that is the difference between the proton and antiproton yields, can be determined. The rapidity dependence of the net-proton yields from peripheral Au+Au collisions is found to have a similar behaviour to that found for the p+p results, while a quite different rapidity dependence is found for central Au+Au collisions. The net-proton distributions can be used together with model calculations to find the net-baryon yields as a function of rapidity, thus yielding information on the average rapidity loss of beam particles, the baryon transport properties of the medium, and the amount of ‘stopping’ in these collisions.

Is Dark Matter visible by Galactic Gamma Rays?

Dark Matter annihilation (DMA) is expected to yield an excess of gamma rays and antimatter particles, like antiprotons and positrons, above the background from cosmic ray interactions. Recently it was shown that the observed excess of diffuse Galactic gamma rays above 1 GeV shows all the features expected from DMA, especially the excess traces the Dark Matter halo, as proven by reconstructing the peculiar shape of the rotation curve of our Galaxy from the gamma ray excess. However, it was claimed by Bergstrom et al. that the DMA interpretation of the EGRET gamma ray excess is incompatible with the antiproton fluxes, since in their propagation model with isotropic diffusion the flux of antiprotons would be far beyond the observed flux. Here it is shown that anisotropic propagation can reduce the antiproton yield by an order of magnitude, while still being consistent with the B/C ratio. Therefore antiprotons cannot prove or disprove the existence of light DM particles, since the background and signal have very similar antiproton spectra.

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.