Inclusive Particle Production Research Articles

Single inclusive particle production at next-to-leading order in proton-nucleus collisions at forward rapidities: Hybrid approach meets TMD factorization

Single inclusive particle production at next-to-leading order in proton-nucleus collisions at forward rapidities: Hybrid approach meets TMD factorization

Production of {textrm{K}}_{textrm{S}}^0 , Λ ( overline{Lambda} ), Ξ±, and Ω± in jets and in the underlying event in pp and p–Pb collisions

The production of strange hadrons ( {textrm{K}}_{textrm{S}}^0 , Λ, Ξ±, and Ω±), baryon-to-meson ratios (Λ/ {textrm{K}}_{textrm{S}}^0 , Ξ/ {textrm{K}}_{textrm{S}}^0 , and Ω/ {textrm{K}}_{textrm{S}}^0 ), and baryon-to-baryon ratios (Ξ/Λ, Ω/Λ, and Ω/Ξ) associated with jets and the underlying event were measured as a function of transverse momentum (pT) in pp collisions at sqrt{s} = 13 TeV and p Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV with the ALICE detector at the LHC. The inclusive production of the same particle species and the corresponding ratios are also reported. The production of multi-strange hadrons, Ξ± and Ω±, and their associated particle ratios in jets and in the underlying event are measured for the first time. In both pp and p–Pb collisions, the baryon-to-meson and baryon-to-baryon yield ratios measured in jets differ from the inclusive particle production for low and intermediate hadron pT (0.6–6 GeV/c). Ratios measured in the underlying event are in turn similar to those measured for inclusive particle production. In pp collisions, the particle production in jets is compared with Pythia 8 predictions with three colour-reconnection implementation modes. None of them fully reproduces the data in the measured hadron pT region. The maximum deviation is observed for Ξ± and Ω± which reaches a factor of about six. The event multiplicity dependence is further investigated in p−Pb collisions. In contrast to what is observed in the underlying event, there is no significant event-multiplicity dependence for particle production in jets. The presented measurements provide novel constraints on hadronisation and its Monte Carlo description. In particular, they demonstrate that the fragmentation of jets alone is insufficient to describe the strange and multi-strange particle production in hadronic collisions at LHC energies.

Multiparticle production in proton–nucleus collisions beyond eikonal accuracy

We study the effects on multigluon production at mid-rapidity in the Color Glass Condensate of the non-eikonal corrections that stem from relaxing the shockwave approximation and giving the target a finite size. We extend previous works performed in the dilute-dilute approximation suitable for proton–proton collisions, to the dilute-dense one applicable to proton–nucleus. We employ the McLerran–Venugopalan model for the projectile averages. For the target averages, we use the Golec-Biernat–Wüsthoff model and restrict to the leading contributions in overlap area that allow a factorization of ensembles of Wilson lines into products of dipoles. We make the connection with the jet quenching formalism and compare with previous results in the literature, providing a parametrization of the so-called decorated dipoles. We show that the non-eikonal effects on single inclusive particle production, contrary to what happens in jet quenching, are only sizable, of a few percent, for modest energies sqrt{s_{NN}}le 100 GeV and central rapidities. On the other hand, we find that the effects on double inclusive gluon production are larger for the same kinematics. We show that, as found previously in the dilute-dilute situation, non-eikonal corrections break the accidental symmetry in the CGC, allowing for the existence of non-vanishing odd azimuthal harmonics.

The SPIN Setup at U-70: Description of the Equipment

The SPIN experiment is carried out with the aim of studying inclusive production of charged particles with high transverse momenta in hard proton−nucleus and nucleus−nucleus interactions. A single-arm narrow-aperture spectrometer is used in the study. The uniqueness of the experiment is in the high intensity of the proton (1012−1013 protons/s) and ion (of the order of 5 × 109 ions/s) beams ejected from the U-70 accelerator, which makes it possible to measure inclusive cross sections varying by seven orders of magnitude. The SPIN setup is able to detect particles with momenta in a kinematic domain of nucleon−nucleon interactions as well as beyond its limits. The spectrometer equipment and the features of the measurement procedure are described.

Production of strange hadrons in jets and underlying events in pp and p–Pb collisions with ALICE

The production of strange (, Λ) and multi-strange (Ξ± and Ω±) hadrons in jets and underlying events in pp and p–Pb collisions is studied with ALICE at the LHC. Transverse momentum (p T) differential density distribution of particles produced in a jet is compared to that of inclusive particle production and that in underlying events. The particle yield ratios of and as a function of p T are also investigated in jets and underlying events. The production of the multi-strange hadrons, Ξ± and Ω±, and the corresponding ratio in jets and underlying events are measured for the first time. The p T-differential density distribution of hadrons associated with hard scattering decreases slower than that for inclusive production. The baryon-to-meson and baryon-to-baryon ratios measured in jets exhibit clear differences from values obtained from the inclusive spectra in the intermediate p T range. The p T distribution of strange hadrons produced in jets is also studied in pp collisions at and and in p–Pb collisions at . The p T spectra of particle produced in jets are independent of collision systems and collision energies. No apparent collision energy and collision system dependence is observed for the particle yield ratios of and associated with energetic jets. These new results are compared to PYTHIA 8 event generator. The ratio are generally reproduced by the model, but large discrepancies between data and PYTHIA simulations are observed for .

Measurement of prompt charged-particle production in pp collisions at sqrt{mathrm{s}} = 13 TeV

The differential cross-section of prompt inclusive production of long-lived charged particles in proton-proton collisions is measured using a data sample recorded by the LHCb experiment at a centre-of-mass energy of sqrt{s} = 13 TeV. The data sample, collected with an unbiased trigger, corresponds to an integrated luminosity of 5.4 nb−1. The differential cross-section is measured as a function of transverse momentum and pseudorapidity in the ranges pT ∈ [80, 10 000) MeV/c and η ∈ [2.0, 4.8) and is determined separately for positively and negatively charged particles. The results are compared with predictions from various hadronic-interaction models.

Production of strange particles in jets and underlying events in pp collisions at √S = 13 TeV with ALICE

The production of strange KS0, Λ and multi-strange (Ξ± and Ω±) particles in jets and the underlying event in pp collisions at √S = 13 TeV has been studied with ALICE at the LHC. The pT-differential density of the particles produced in a jet is compared to the inclusive distribution. The corresponding (Λ + Λ¯)/2KS0 and (Ξ− + Ξ¯+)/(Λ + Λ¯) ratios in jets as a function of pT are also reported in this work. The pT-differential density distribution of hadrons associated with jets decreases slower than the one reported for inclusive particle production. The ratios measured in jets show a clear difference when compared to the inclusive ones at the intermediate pT range. The results provide an opportunity to test the strange and multi-strange particle production mechanisms with hard scattering.

From small to large x: toward a unified description of high energy collisions

Inclusive particle production at high pt (equivalently intermediate to large x) in high energy hadronic collisions is successfully described by perturbative QCD, using the collinear-factorization formalism. On the other hand at very high energies and not so high pt the Color Glass Condensate (CGC) formalism has been quite successful in describing particle production at small Bjorken x. Here we propose a way to unify the two approaches which enables one to apply it to particle production at all x (all pt ).

Bogolyubov–Medvedev–Polivanov S-matrix Method and Its Application to Multi-Particle Systems and in High-Energy Physics

The connection between field-theoretic equations based on the Bogolyubov–Medvedev–Polivanov and Lehman–Szymanczyk–Zimmerman $$S$$ -matrix methods is discussed [1]. These equations are used to derive three-dimensional time-ordered relativistic Lippmann–Schwinger-type equations for hadronic collision amplitudes with and without quark degrees of freedom [2, 3]. Quark degrees of freedom are considered following the Huang–Weldon approach [4], in which hadrons are considered as bound states of quarks. Numerical solutions of the obtained equations made it possible to describe well the experimental phase shifts of elastic $$\pi N$$ and $$NN$$ scattering in the low-energy region. Using a separable approximation, a quark–parton model for inclusive production of particles with a large transverse momentum was reproduced [6]. This made it possible to describe the experimental data of inclusive production of a $$\rho $$ meson with a large transverse momentum (≤1.5 GeV/c) in a proton–proton collision in the energy region 2.9 ≤ $$\sqrt s $$ ≤ 64 GeV [5].

Two-particle azimuthal correlations as a probe of collective behaviour in deep inelastic ep scattering at HERA

Two-particle azimuthal correlations have been measured in neutral current deep inelastic ep scattering with virtuality Q2> 5 GeV2 at a centre-of-mass energy sqrt{s} = 318 GeV recorded with the ZEUS detector at HERA. The correlations of charged particles have been measured in the range of laboratory pseudorapidity −1.5 < η < 2.0 and transverse momentum 0.1 < pT< 5.0 GeV and event multiplicities Nch up to six times larger than the average 〈Nch〉 ≈ 5. The two-particle correlations have been measured in terms of the angular observables cn{2} = 〈〈cosnΔφ〉〉, where n is between 1 and 4 and ∆φ is the relative azimuthal angle between the two particles. Comparisons with available models of deep inelastic scattering, which are tuned to reproduce inclusive particle production, suggest that the measured two-particle correlations are dominated by contributions from multijet production. The correlations observed here do not indicate the kind of collective behaviour recently observed at the highest RHIC and LHC energies in high-multiplicity hadronic collisions.

Jet quenching as a probe of the initial stages in heavy-ion collisions

Jet quenching provides a very flexible variety of observables which are sensitive to different energy- and time-scales of the strongly interacting matter created in heavy-ion collisions. Exploiting this versatility would make jet quenching an excellent chronometer of the yoctosecond structure of the evolution process. Here we show, for the first time, that a combination of jet quenching observables is sensitive to the initial stages of heavy-ion collisions, when the approach to local thermal equilibrium is expected to happen. Specifically, we find that in order to reproduce at the same time the inclusive particle production suppression, RAA, and the high-pT azimuthal asymmetries, v2, energy loss must be strongly suppressed for the first ∼0.6 fm. This exploratory analysis shows the potential of jet observables, possibly more sophisticated than the ones studied here, to constrain the dynamics of the initial stages of the evolution.

Radial scaling in inclusive jet production at hadron colliders

Inclusive jet production in p-p and pbar-p collisions shows many of the same kinematic systematics as observed in single particle inclusive production at much lower energies. In an earlier study (1974) a phenomenology, called radial scaling, was developed for the single particle inclusive cross sections that attempted to capture the essential underlying physics of point-like parton scattering and the fragmentation of partons into hadrons suppressed by the kinematic boundary. The phenomenology was successful in emphasizing the underlying systematics of the inclusive particle productions. Here we demonstrate that inclusive jet production at the LHC in high-energy p-p collisions and at the Tevatron in pbar-p inelastic scattering show similar behavior. The ATLAS inclusive jet production plotted as a function of this scaling variable is studied for sqrt(s) of 2.76, 7 and 13 TeV and is compared to pbar-p inclusive jet production at 1.96 TeV measured at the CDF and D0 at the Tevatron and p-Pb inclusive jet production at the LHC ATLAS at sqrt(sNN) = 5.02 TeV. Inclusive single particle production at FNAL fixed target and ISR energies are compared to inclusive J/Psi production at the LHC measured in ATLAS, CMS and LHCb. Striking common features of the data are discussed.

Small collision systems: Theory overview on cold nuclear matter effects

Many observables measured at the Relativistic Heavy Ion Collider and the Large Hadron Collider show a smooth transition between proton-proton and protonnucleus collisions (small systems), and nucleus-nucleus collisions (large systems), when represented versus some variable like the multiplicity in the event. In this contribution I review some of the physics mechanisms, named cold nuclear matter effects, that may lead to a collective-like behaviour in small systems beyond the macroscopic description provided by relativistic hydrodynamics. I focus on the nuclear modification of parton densities, single inclusive particle production and correlations.

Forward particle production in proton-nucleus collisions at next-to-leading order

We consider the next-to-leading order (NLO) calculation of single inclusive particle production at forward rapidities in proton-nucleus collisions and in the framework of the Color Glass Condensate (CGC). We focus on the quark channel and the corrections associated with the impact factor. In the first step of the evolution the kinematics of the emitted gluon is kept exactly (and not in the eikonal approximation), but such a treatment which includes NLO corrections is not explicitly separated from the high energy evolution. Thus, in this newly established “factorization scheme”, there is no “rapidity subtraction”. The latter suffers from fine tuning issues and eventually leads to an unphysical (negative) cross section. On the contrary, our reorganization of the perturbation theory leads by definition to a well-defined cross section and the numerical evaluation of the NLO correction is shown to have the correct size.

Single spin asymmetries in forward p−p/A collisions revisited: The role of color entanglement

We calculate the single transverse spin asymmetries(SSA) for forward inclusive particle production in pp and pA collisions using a hybrid approach. It is shown that the Sivers type contribution to the SSA drops out due to color entanglement effect, whereas the fragmentation contribution to the spin asymmetry is not affected by color entanglement effect. This finding offers a natural solution for the sign mismatch problem.

Measurement of the inclusive energy spectrum in the very forward direction in proton-proton collisions at sqrt{s}=13 TeV

The differential cross section for inclusive particle production as a function of energy in proton-proton collisions at a center-of-mass energy of 13 TeV is measured in the very forward region of the CMS detector. The measurement is based on data collected with the CMS apparatus at the LHC, and corresponds to an integrated luminosity of 0.34 μb−1. The energy is measured in the CASTOR calorimeter, which covers the pseudorapidity region −6.6 < η < −5.2. The results are given as a function of the total energy deposited in CASTOR, as well as of its electromagnetic and hadronic components. The spectra are sensitive to the modeling of multiparton interactions in pp collisions, and provide new constraints for hadronic interaction models used in collider and in high energy cosmic ray physics.

Implementation of NLO high energy factorization in single inclusive forward hadron production

Single inclusive particle production cross sections in high energy hadron collisions at forward rapidity are an important benchmark process for the CGC picture of small x QCD. Recent calculations of this process have not led to a stable perturbative expansion for this quantity at high transverse momenta. We consider the quark channel production cross section using the new rapidity factorization procedure proposed by Iancu et al. We show that for fixed coupling one does indeed obtain a physically meaningful cross section which is positive and reduces in a controlled way to previous leading order calculations. We also consider a running coupling that depends on the transverse momentum of the produced particle. This gives a stable result which, however, is not fully consistent with previous leading order calculations that use a coordinate space running coupling.

Transverse momentum spectra and the nuclear modification factor of charged particles with ALICE

The observed suppression of particle production at high transverse momentum in nucleus-nucleus collisions at high energies is an effect of the energy loss of partons as they propagate through the hot and dense deconfined QCD medium. The measurement of transverse momentum spectra of primary charged particles in Pb–Pb collisions and the comparison to the measurement in pp collisions are important to study the properties of the deconfined medium. In 2015, pp and Pb–Pb collisions have been recorded at the LHC at the energy of = 5.02 TeV. The inclusive charged particle production is measured with the ALICE detector in the pseudo-rapidity range |η| < 0.8 and in the transverse momentum range 0.15 < pT < 40 GeV/c. The spectra in Pb–Pb, determined for several centrality intervals, are compared to the reference spectrum in pp collisions by calculating the nuclear modification factor RAA. The data are compared to measurements at the lower collision energy of 2.76 TeV and to model predictions.

Production of strange particles in charged jets in p–Pb and Pb–Pb collisions measured with ALICE at the LHC

Studies of jet production can provide information about the properties of the hot and dense strongly interacting matter created in ultra-relativistic heavy-ion collisions. Specifically, measurement of strange particles in jets may clarify the role of fragmentation processes in the anomalous baryon to meson ratio at intermediate particle pT that was observed in lead-lead (Pb–Pb) and, to a lesser extent, in proton-lead (p–Pb) collisions.In this contribution, measurements are presented of the pT spectra of baryons and mesons produced in association with charged jets in Pb–Pb collisions at and p–Pb collisions at . The analysis is based on data recorded by ALICE at the LHC, exploiting its excellent particle identification capabilities. The baryon/meson ratios of strange particles associated with jets are studied for different event activities in p–Pb collisions and are restricted to central events in Pb-Pb collisions. A comparison is shown to the ratios obtained for inclusive particle production and for particles stemming from the underlying event as well as to PYTHIA proton-proton (pp) simulations.

Measurement of the inelastic cross section in proton-lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV

The inelastic hadronic cross section in proton-lead collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is measured with the CMS detector at the LHC. The data sample, corresponding to an integrated luminosity of 12.6 +/- 0.4 inverse nanobarns, has been collected with an unbiased trigger for inclusive particle production. The cross section is obtained from the measured number of proton-lead collisions with hadronic activity produced in the pseudorapidity ranges 3<abs(eta)<5 and/or -5<abs(eta)<-3, corrected for photon-induced contributions, experimental acceptance, and other instrumental effects. The inelastic cross section is measured to be sigma[inel,pPb]=2061 +/- 3 (stat) +/- 34 (syst) +/- 72 (lum) mb. Various Monte Carlo generators, commonly used in heavy ion and cosmic ray physics, are found to reproduce the data within uncertainties. The value of sigma[inel,pPb] is compatible with that expected from the proton-proton cross section at 5.02 TeV scaled up within a simple Glauber approach to account for multiple scatterings in the lead nucleus, indicating that further net nuclear corrections are small.