Inclusive Spectra Research Articles

Nuclear in-medium effects of strange particles in proton-nucleus collisions

The dynamics of strange particles produced in proton-induced nuclear reactions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics transport model. The in-medium modifications on particle production in dense nuclear matter are considered through corrections on the elementary cross sections via the effective mass and the mean-field potentials. It is found that the attractive antikaon-nucleon potential enhances the subthreshold $\overline{K}$ production and influences the structure of inclusive spectra. The strangeness production is strongly suppressed in proton-induced reactions in comparison to heavy-ion collisions. The kaon-nucleon and antikaon-nucleon potentials change the structures of rapidity and transverse momentum distributions and the inclusive spectra. The measured ${K}^{\ensuremath{-}}/{K}^{+}$ ratios in collisions of ${}^{12}\mathrm{C}+{}^{12}\mathrm{C},\phantom{\rule{0.28em}{0ex}}{}^{197}\mathrm{Au}+{}^{197}\mathrm{Au},\phantom{\rule{0.28em}{0ex}}p+{}^{12}\mathrm{C}$, and $p+{}^{197}\mathrm{Au}$ from the KaoS Collaboration have been well explained with the inclusion of the in-medium potentials.

Inclusive spectrum of the d( +, K+) reaction at 1.69 GeV/c

We have measured an inclusive missing-mass spectrum of the $d(\pi^+, K^+)$ reaction at the pion incident momentum of 1.69 GeV/$c$ at the laboratory scattering angles between 2$^\circ$ and 16$^\circ$ with the missing-mass resolution of 2.7 $\pm$ 0.1 MeV/$c^2$ (FWHM) at the missing mass of 2.27 GeV/$c^{2}$. In this Letter, we first try to understand the spectrum as a simple quasi-free picture based on several known elementary cross sections, considering the neutron/proton Fermi motion in deuteron. While gross spectrum structures are well understood in this picture, we have observed two distinct deviations; one peculiar enhancement at 2.13 GeV/$c^2$ is due to the $\Sigma N$ cusp, and the other notable feature is a shift of a broad bump structure, mainly originating from hyperon resonance productions of $\Lambda(1405)$ and $\Sigma(1385)^{+/0}$, by about 22.4 $\pm$ 0.4 (stat.) $^{+2.7}_{-1.7}$ (syst.) MeV/$c^2$ toward the low-mass side, which is calculated in the kinematics of a proton at rest as the target.

Self-similarity of Low-p T cumulative pion production in proton-nucleus collisions at U70

The data on inclusive momentum spectra of π± mesons produced in p + A collisions over the range pL =15–65 GeV/c and θlab = 159° at U70 are analyzed in the framework of z-scaling approach. Self-similarity of the pion production in the low-pT cumualtive region is verified. Scaling function ψ(z) for Be, C, Al, Ti, Mo, W nuclei is constructed. It is expressed via the invariant cross section and the average multiplicity density of charged particles. Results of the analysis are compared with data obtained by J. Cronin, R. Sulyaev, and D. Jaffe groups at pL = 70, 400 GeV/c, pT > 1 GeV/c and θcms − 90°. A microscopic scenario of p + A interactions in terms of momentum fractions x1, x2 is discussed. Indication on self-similarity of the low-pT cumulative pion production in p + A collisions was found. Universality of the shape of the scaling function is used to predict inclusive cross sections of π+ and π− pions produced in p + A collisions on Be, C, Al, Ti, Mo, W targets in the deep-cumulative region (x2 ≫ 1/A).

Inclusive spectra of protons and α particles from reactions induced by protons with an energy of 30.0 MeV on the 209Bi nucleus

Inclusive spectra of protons and α particles resulting from the interaction between 30.0-MeV protons and the 209Bi nucleus are investigated. Double differential and integral cross sections for the (p,xp) and (p,xα) reactions are obtained and total partial cross sections for these reactions are subsequently determined. The experimental spectra are analyzed using a modified version of the exciton model of preequilibrium decay and the PRECO-2006 code. Contributions from the compound and direct mechanisms to the formation of integral cross sections are calculated.

Investigation of neutral-kaon production in pC, pSi and pPb Collisions at 70 GeV/c

The results obtained by measuring the inclusive distributions of the Feynman variable xF and the transverse momentum for the production of K 0 mesons in proton-nucleus interactions at 70 GeV/c for three targets (C, Si, and Pb) are presented. The mass-number (A) dependence of the cross section for K 0 S - meson production is studied. The measured value of the exponent α in the formula σ ∼ A α agrees within the errors with its counterpart at higher energies. With the aid of the A dependence, the measured yield of K 0 S mesons at xF =0 is compared with the yield of K + and K − mesons in the proton-proton reaction at 70 GeV/c. The inclusive spectra of longitudinal and transverse variables for K 0 -meson production are contrasted against the predictions of the FRITIOF and UrQMD models.

Particle production in antiproton-induced nuclear reactions

The quantum molecular dynamics model has been improved to investigate the reaction dynamics induced by antiprotons. The reaction channels of elastic scattering, annihilation, charge exchange and inelastic collisions have been included in the model. Dynamics on particle production, in particular pions, kaons, antikaons and hyperons, is investigated in collisions of $\overline{p}$ on $^{12}$C, $^{20}$Ne, $^{40}$Ca, $^{112}$Sn, $^{181}$Ta, $^{197}$Au and $^{238}$U from a low to high incident momentum. The rapidity and momentum distributions of $\pi^{+}$ and protons from the LEAR measurements can be well reproduced. The impacts of system size and incident momentum on particle emissions are investigated from the inclusive spectra, transverse momentum and rapidity distributions. It is found that the annihilations of $\overline{p}$ on nucleons are of importance on the particle production. Hyperons are mainly produced via meson induced reactions on nucleons and strangeness exchange collisions when the incident momentum is below the threshold value of annihilation reaction. A higher nuclear temperature is obtained from the kaon emission, but it has a lower value for hyperon production.

Confronting current NLO parton fragmentation functions with inclusive charged-particle spectra at hadron colliders

The inclusive spectra of charged particles measured at high transverse momenta (pT≳2 GeV/c) in proton–proton and proton–antiproton collisions in the range of center-of-mass energies s=200–7000 GeV are compared with next-to-leading order perturbative QCD calculations using seven recent sets of parton-to-hadron fragmentation functions (FFs). Accounting for the uncertainties in the scale choices and in the parton distribution functions, we find that most of the theoretical predictions tend to overpredict the measured LHC and Tevatron cross sections by up to a factor of two. We identify the currently too-hard gluon-to-hadron FFs as the probable source of the problem, and justify the need to refit the FFs using the available LHC and Tevatron data in a region of transverse momenta, pT≳10 GeV/c, which is supposedly free from additional non-perturbative contributions and where the scale uncertainty is only modest.

Measurement of negatively charged pion spectra in inelastic p+p interactions at $$p_{\mathbf {lab}}= $$ p lab = 20, 31, 40, 80 and 158 GeV/c

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/c ($\sqrt{s} = $ 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus-nucleus and proton-nucleus collisions.

Self-similarity of low-p T cumulative pion production in proton-nucleus collisions at high energies

The experimental data on inclusive spectra of the π+ mesons produced in p + A collisions at the incident proton momentum of 400 GeV/c obtained by G. Leksin group at FNAL are analyzed in the framework of z-scaling. Self-similarity of the hadron production in the low-pT cumulative region is verified. Scaling function ψ(z) for the Li, Be, C, Al, Cu, Ta nuclei is constructed. It is expressed via the invariant cross section and average multiplicity density of charged particles. Results of the analysis of the low-pT data are compared with the high-pT data sets obtained by J. Cronin, R. Sulyaev and D. Jaffe groups. A microscopic scenario of p + A interactions in terms of momentum fractions x1, x2 is discussed. Indication on self-similarity of the cumulative pion production in p + A collisions over a wide kinematical range has been found. Based on the universality of the shape of the scaling function the inclusive cross sections of the π+ mesons produced in p + A collisions on the Li, Be, C, Al, Cu, Ta targets in deep-cumulative region (x2 ≫ 1/A) are predicted.

Geothermobarometric history of subduction recorded by quartz inclusions in garnet

Burial histories of subduction zone rocks are often difficult to accurately constrain, owing to a lack of robust mineral geobarometers applicable to high pressure mineral assemblages. Knowledge of the depth‐histories of subduction is, however, required for our understanding of global geochemical cycles, subduction‐related seismicity, and the evolution of destructive tectonic boundaries. The high spatial resolution of quartz inclusion geobarometry can be used to determine pressure evolution during metamorphic growth of individual garnet crystals. Quartz inclusions in garnet from Sifnos, Greece, preserve such a record of the pressure of garnet growth, allowing detailed reconstruction of the metamorphic evolution of these rocks. Pressure‐dependent Raman spectra of quartz inclusions were combined with elastic modeling to infer the conditions at which they were trapped during garnet growth. All measured inclusions suggest that garnet growth occurred between 19 and 20.5 kbars, with little evidence for significant pressure variation during the garnet growth interval, which is interpreted to record ∼100°C of heating. Coupled with thermometry and geochronology, these results show that early, cold burial was followed by a phase of rapid heating, which immediately preceded exhumation. Garnet growth occurred primarily during this heating phase.

Evaluation of residual pressure in an inclusion-host system using negative frequency shift of quartz Raman spectra

Raman spectra of quartz inclusions in garnet hosts of low-pressure/temperature metamorphic rocks from the Yanai district in the Ryoke belt (around 0.1–0.3 GPa/500–600 °C), Southwest Japan, exhibit frequency (peak position) shifts toward lower wavenumbers as compared to those of a quartz standard measured at ambient conditions. The observed negative frequency shifts indicate that tensile normal stress is exerted on the quartz–garnet boundary and therefore, quartz inclusions are subjected to negative residual pressure. Elastic modeling that assumed the constant elastic properties of minerals cannot explain this negative residual pressure. This study estimated the residual pressure based on a new scheme of elastic modeling with equation of state (EOS) of quartz and garnet, which takes into account the pressure- and temperature-dependency of compressibility and expansivity. The calculated residual pressure was converted into frequency shifts of quartz Raman spectrum based on the experimentally determined relation. The results showed that the quartz inclusions in garnets retain residual pressure of about −0.3 GPa, and logically reproduced the observed frequency shifts in the direction of lower wavenumbers. The new elastic modeling also simulates positive frequency shifts retained by quartz inclusions in garnets of high-pressure metamorphic rocks from the Sambagawa metamorphic belt in Southwest Japan, and from the Motagua fault zone in Guatemala. The degree and direction of Raman frequency shifts of quartz inclusion in garnet depend on metamorphic conditions when the quartz was included in the host garnet. Conversely, the metamorphic conditions prevailing when a set of a quartz inclusion and garnet host was recrystallized can be inferred from Raman frequency shifts of quartz inclusion in garnet. The proposed Raman spectroscopic analysis should be a powerful and useful tool to decipher information at earlier stage of garnet growth even in samples of highly recrystallized matrix phases during exhumation and retrograde stages.

LHC soft physics and transverse momentum dependent gluon density at lowx

We study the unintegrated, or transverse momentum dependent gluon distribution obtained from the best description of the LHC data on the inclusive spectra of hadrons produced in the midrapidity region and at low transverse momenta at the starting scale ${Q}_{0}^{2}=1\text{ }\text{ }\mathrm{GeV}{}^{2}$. To extend this gluon density to higher ${Q}^{2}$ we apply the Catani-Ciafoloni-Fiorani-Marchesini evolution equation. The influence of the initial (starting) nonperturbative gluon distribution is studied. The application of the obtained gluon density to the analysis of the deep inelastic $ep$ scattering allows us to get the results which describe reasonably well the H1 and ZEUS data on the longitudinal proton structure function ${F}_{L}(x,{Q}^{2})$. So, the connection between the soft processes at the LHC and small-$x$ physics at HERA has been confirmed and extended to a wide kinematical region.

Searching a dark photon with HADES

The existence of a photon-like massive particle, the γ ‘ or dark photon, is postulated in several extensions of the Standard Model to explain some recent puzzling astrophysical observations, as well as to solve the sofar unexplained deviation between the measured and calculated values of the muon anomaly. The dark photon, unlike the conventional photon, would have mass and would be detectable via its mixing with the latter. We present a search for the e + e − decay of such a hypothetical particle, also named U vector boson, in inclusive dielectron spectra measured by HADES in the p (3.5 GeV) +p, Nb reactions, as well as the Ar (1.756 GeV/u) + KCl reaction. An upper limit on the kinetic mixing parameter squared (ϵ 2 ) at 90% CL has been obtained for the mass range M(U)= 0.02 - 0.55 GeV/c 2 and is compared with the present world data set. Furthermore, an improved upper limit of 2.3 × 10−6 at 90% CL has been set on the branching ratio of the helicity-suppressed direct decay of the η meson η → e +e −.

FRAGMENTATION FUNCTIONS AT BABAR

Inclusive hadron production cross section in e+e- annihilation shed light on fundamental questions of hadronization and fragmentation processes. We present measurements of inclusive spectra of charged pions, kaons, and protons (antiprotons) produced in e+e- collisions at the center-of-mass energy of 10.54 GeV, and tests of QCD predictions and hadronization models. We also report the results on the measurement of the azimuthal modulation induced by the Collins effect in inclusive production of charged pion pairs e+e- → ππX, where the two pions are produced in opposite hemispheres. These data allows the determination of the polarized Collins fragmentation functions.

RESULTS FROM LHCF EXPERIMENT

The LHCf experiment has taken data in 2009 and 2010 p–p collisions at LHC at √s = 0.9TeV and √s = 7TeV. In this paper the most up-to-date results on the inclusive photon spectra and the π<sup>0</sup> spectra measured by LHCf are reported. Comparison of these spectra with the model expectations and the impact on high energy cosmic ray (HECR) Physics are iscussed. In addition, perspectives for future analyses as well as the program for the next data taking period, in particular the foreseen data taking in p–Pb collisions, will be discussed.

Z-Scaling of cumulative pion production in pA collisions at high energies

The experimental data on inclusive spectra of the π+ mesons produced in p+A collisions at the incident proton momentum of 400 GeV/c obtained by G. Leksin group at FNAL are analyzed in the framework of z-scaling. Self-similarity of the hadron production in the low-pT cumualtive region is verified. The scaling function ψ(z) is expressed via the invariant cross section Ed3σ/dp3 and the average multiplicity density dNch/dη of charged particles. Results of the analysis of the low-pT data are compared with the high-pT data sets obtained by J. Cronin, R. Sulyaev and D. Jaffe groups. Indication on self-similarity of the cumulative pion production over a wide kinematical range has been found. Based on the universality of the shape of ψ(z) the inclusive cross sections of the π+ mesons produced in p+A collisions in deep-cumulatice region (x2≫1/A) are predicted.

Dynamics of strangeness and collective flows in heavy-ion collisions near threshold energies

Strangeness (K$^{0,+}$, $\Lambda$ and $\Sigma^{-,0,+}$) production in heavy-ion collisions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics (LQMD) transport model. The kaon (anti-kaon)-nucleon and hyperon-nucleon potentials in dense nuclear matter are implemented in the model, which are computed from the chiral perturbation approach and the relativistic mean-field model, respectively. It is found that the in-medium potentials change the structure of transverse flow, and also affect the rapidity distributions and the inclusive spectra for strangeness production. The local temperature of the fire ball extracted from the kaon spectra of inclusive invariant cross sections is influenced by the kaon-nucleon potential. The stiffness of nuclear symmetry energy and the kaon-nucleon potential by distinguishing isospin effect play a significant role on the ratio of K$^{0}$/K$^{+}$, in particular at the subthreshold energies. The ratio of $\Sigma^{-}/\Sigma^{+}$ depends on the high-density symmetry energy, in which the $\Sigma$-nucleon potential has a neglectable contribution on the isospin ratio.

LHCf DETECTOR PERFORMANCE DURING THE 2009–2010 LHC RUN

Large Hadron Collider forward (LHCf) has successfully completed the operation during the LHC 2009–2010 period and the detectors were removed in July 2010. The event trigger, data analysis and background have been intensively studied in order to derive inclusive single photon and π0 spectra. In this paper, the details of these intensive studies are described.

Jet measurements in proton-proton collisions with the ALICE experiment at LHC

The study of jets, collimated sprays of particles associated with hard partons, is an important tool in testing perturbative quantum chromodynamics (pQCD) and probing hot and dense nuclear matter created in high energy heavy-ion collisions. Jets enable the study of hard scatterings, fragmentation and hadronisation and their modification in the presence of a nuclear medium with respect to baseline vacuum measurements, which is acquired from jet measurements in proton-proton collisions.We have analysed data from proton-proton collisions at = 7 TeV measured by the ALICE experiment at the LHC and reconstructed the inclusive spectra of charged particle jets at mid-rapidity using anti-kT clustering algorithm. We present the jet spectra corrected for detector effects using several unfolding methods. Furthermore, we examine various properties of jets, such as their charged particle multiplicity and jet shapes.

Nuclear in-medium and isospin effects on subthreshold kaon production in heavy-ion collisions

Subthreshold kaon (K$^{0}$ and K$^{+}$) production in neutron-rich nuclear reactions to probe the kaon-nucleon interaction in nuclear medium and to extract the isospin dependent part of the nuclear equation of state at high-baryon densities, is investigated within an isospin and momentum dependent transport model. A repulsive kaon-nucleon potential is implemented in the model through fitting the flow data and inclusive spectra in heavy-ion collisions, which enhances the energetic kaon emission squeezed out in the reaction zone and leads to a variation of the high-momentum spectrum of the K$^{0}$/K$^{+}$ yields. It is found that the stiffness of nuclear symmetry energy plays a significant role on the isospin ratio with decreasing the incident energy and a hard symmetry energy has a larger value of the K$^{0}$/K$^{+}$ ratio in the domain of subthreshold energies.