Single-particle Inclusive Distributions Research Articles

Boosted top production: factorization and resummation for single-particle inclusive distributions

We study single-particle inclusive (1PI) distributions in top-quark pair production at hadron colliders, working in the highly boosted regime where the top-quark p_T is much larger than its mass. In particular, we derive a novel factorization formula valid in the small-mass and soft limits of the differential partonic cross section. This provides a framework for the simultaneous resummation of soft gluon corrections and small-mass logarithms, and also an efficient means of obtaining higher-order corrections to the differential cross section in this limit. The result involves five distinct one-scale functions, three of which arise through the subfactorization of soft real radiation in the small-mass limit. We list the NNLO corrections to each of these functions, building on results in the literature by performing a new calculation of a soft function involving four light-like Wilson lines to this order. We thus obtain a nearly complete description of the small-mass limit of the differential partonic cross section at NNLO near threshold, missing only terms involving closed top-quark loops in the virtual corrections.

Hadron correlation in jets on the near and away sides of high-pTtriggers in heavy-ion collisions

The correlation between the trigger and associated particles in jets produced on near and away sides of high-${p}_{T}$ triggers in heavy-ion collisions is studied. Hadronization of jets on both sides is treated by thermal-shower and shower-shower recombinations. The energy loss of semihard and hard partons traversing the nuclear medium is parametrized in a way that renders a good fit of the single-particle inclusive distributions at all centralities. The associated hadron distribution in the near-side jet can be determined showing weak dependence on system size because of trigger bias. The inverse slope increases with trigger momentum in agreement with data. The distribution of associated particles in the away-side jet is also studied with careful attention given to antitrigger bias that is due to the longer path length that the away-side jet recoiling against the trigger jet must propagate in the medium to reach the opposite side. Centrality dependence is taken into account after determining a realistic probability distribution of the dynamical path length of the parton trajectory within each class of centrality. For symmetric dijets with ${p}_{T}^{\mathrm{trig}}={p}_{T}^{\mathrm{assoc}}(\mathrm{away})$, it is shown that the per-trigger yield is dominated by tangential jets. For unequal ${p}_{T}^{\mathrm{trig}}$, ${p}_{T}^{\mathrm{assoc}}(\mathrm{near})$ and ${p}_{T}^{\mathrm{assoc}}(\mathrm{away})$, the yields are calculated for various centralities, showing an intricate relationship among them. The near-side yield agrees with data both in centrality dependence and in ${p}_{T}^{\mathrm{assoc}}(\mathrm{near})$ distribution. The average parton momentum for the recoil jet is shown to be always larger than that of the trigger jet for fixed ${p}_{T}^{\mathrm{trig}}$ and centrality and for any measurable ${p}_{T}^{\mathrm{assoc}}(\mathrm{away})$. With the comprehensive treatment of dijet production described here, it is possible to answer many questions regarding the behavior of partons in the medium under conditions that can be specified on measurable hadron momenta.

Strings, black holes and the extreme energy cosmic rays

In a large class of string and string inspired models the string excitation and black hole pictures invoked as an explanation of trans-GZK cosmic ray events are equivalent at high excitations. Single particle inclusive distributions are thermal, asymptotically at the Hagedorn temperature. Some observational consequences are briefly explored.

An approximation for NLO single Higgs boson inclusive transverse momentum distributions in hadron–hadron collisions

In the framework of the gluon–gluon fusion process for Higgs boson production there are two different prescriptions. They are given by the exact process where the gluons couple via top-quark loops to the Higgs boson and by the approximation where the top-quark mass m t is taken to infinity. In the latter case the coupling of the gluons to the Higgs boson is described by an effective Lagrangian. Both prescriptions have been used for the 2 → 2 body reactions to make predictions for Higgs boson production at hadron colliders. In next-to-leading order only the effective Lagrangian approach has been used to compute the single particle inclusive distributions. The exact computation of the latter has not been done yet because the n-dimensional extensions of 2 → 3 processes are not calculated and the two-loop virtual corrections are still missing. To remedy this we replace wherever possible the Born cross sections in the asymptotic top-quark mass limit by their exact analogues. These cross sections appear in the soft and virtual gluon contributions to the next-to-leading order distributions. This approximation is inspired by the fact that soft-plus-virtual gluons constitute the bulk of the higher order correction. Deviations from the asymptotic top-quark mass limit are discussed.

Trans-GZK Cosmic Rays: Strings, Black Holes, Neutrinos, or all Three?

We review the scenario in which ``strongly interacting neutrinos'' are responsible for inducing airshowers with inferred energies $E > 8\times10^{19}$ eV. This possibility arises naturally in string excitation models having a unification scale effectively decoupled from the Planck scale. We then show that phenomenological quantum gravity considerations reveal an equivalency of ``mini-black hole'' and strongly interacting neutrino pictures for explaining trans-GZK events. This equivalence can be exploited to predict single particle inclusive distributions. The resulting observable consequences in airshower development are studied using the Adaptive Longitudinal Profile Shower (ALPS) simulation.

Soft particle production in deep inelastic scattering**Published by Nick Brook on behalf of H1 and ZEUS Collaborations.

Results on the analysis of the hadronic final state in neutral current deep inelastic scattering at HERA are presented; recent results on inclusive single particle distributions, particle correlations and event shapes are highlighted.

Fragmentation in DIS

The fragmentation properties in deep-inelastic scattering (DIS) at HERA are investigated in order to test perturbative QCD and quark fragmentation universality. Selected results for the inclusive single particle distributions and the angular two-particle correlations in the current region of the Breit frame are presented and compared to results from e + e − collisions. The extension of the DIS fragmentation studies to the target region of the Breit frame are also reported.

Large- $p_T$ photoproduction of $D^{*\pm}$ mesons in $ep$ collisions

The cross section for the inclusive photoproduction of large-p_T D^*+- mesons is calculated at next-to-leading order, adopting different approaches to describe the fragmentation of charm quarks into D^*+- mesons. We treat the charm quark according to the massless factorization scheme, where it is assumed to be one of the active flavours inside the proton and the photon. We present inclusive single-particle distributions in transverse momentum and rapidity, including the contributions due to both direct and resolved photons. We compare and assess the various implementations of fragmentation. We argue that, in the high-p_T regime, a particularly realistic description can be obtained by convoluting the Altarelli-Parisi-evolved fragmentation functions of Peterson et al. with the hard-scattering cross sections of massless partons where the factorization of the collinear singularities associated with final-state charm quarks is converted to the massive-charm scheme. The predictions thus obtained agree well with recent experimental data by the H1 and ZEUS Collaborations at DESY HERA.

Inclusive single-particle distributions and transverse momenta of forward produced charged hadrons in $\mu p$ scattering at 470 GeV

Using data from the Fermilab fixed target experiment E665, general properties of forward produced charged hadrons in μp interactions at a primary muon energy of 470 GeV are investigated. The normalized inclusive singleparticle distributions for Feynman-x D(xF ) and for the transverse momentum D(p2t , xF ) are measured as a function of W and Q2. The dependence of the average transverse momentum squared 〈p2t〉 on xF , W and Q2 is studied. The increasing contribution from diffractive production as Q2 decreases leads to a reduction of the average charged hadron multiplicities at low (positive) xF and an enhancement at large xF , for Q2 ≲ 10 GeV2. It also reduces 〈p2t〉 for Q2 ≲ 5 GeV2 and 0.4 ≲ xF < 1.0.

QCD corrections to heavy flavour photoproduction and electroproduction

We investigate the QCD corrections to the total cross sections and single-particle inclusive differential distributions for γ + p → Q( Q ) + X and e + p → e + Q( Q ) + X . In the latter reaction we assume that the exchanged photon is almost real (Weizsäcker-Williams approximation). This requires the calculation of the O( α s) corrections to the photon-parton reaction γ + g → Q + Q including the virtual gluon contributions and the soft and hard gluon radiation in the reaction γ + g → Q + Q + g . The contributions from γ + q( q ) → Q + Q + q( q ) are also calculated. We give exact results for the O( α 2 α S 2) total cross sections and single particle inclusive differential distribution for b-quark production at HERA. Results for b- and t- production at future ep colliders (the LEP ∗LHC option at CERN) are also presented.

QCD corrections to heavy quark production in hadron-hadron collisions

We investigate the QCD corrections to the cross section and single-particle inclusive differential distributions for p + p̄ → Q(Q̄) + X where Q and Q̄ are heavy quarks. We calculate the order αS corrections to the parton reaction q + q̄ → Q + Q̄ which involves the computation of the virtual gluon contributions and the soft and hard contributions from the reaction q + q̄ → Q + Q̄ + g. The contributions from the channels g + q(q̄) → Q + Q̄ + q(q̄) are also calculated. Including the order αS corrections to g + g → Q + Q̄ from our previous paper, we give exact results for the order α3S cross sections and single-particle inclusive differential distributions for the production of t and b quarks in pp̄ collisions at energies presently available at the CERN Spp̄S and the Fermilab tevatron. Results for future pp colliders are also presented. Finally we compare the results of the simple approximations to the order αS corrections with the exact results.

On the Charged Particles Multiproduction in the Central Region of the Soft Hadronic Interaction

Using the Dual Partonic Model and combining with the FF quark fragmentation mechanism, the charged particle multiplicity in the central region are simulated by Monte-Carlo method. The variation of the charged particle multiplicity with total C.M. energy and the charged particle multiplicity distribution in central region as well as the single-particle inclusive distribution are evaluated. The calculated, values are in good agreement with recent experimental data. The results support the view point that there exist colliding components in soft-collision.

The Charged Particle Multiplicity in Proton-Antiproton Annihilation

Using the three-chain diagram based on the dual partonic scheme, combining with the FF quark fragmentation mechanism, the charged particle multiplicity, the productions of π and K mesons, the single-particle inclusive distribution and the central plateau particle density of soft high energy annihilation are calculated and compared with experiments on CERN SPS.

Study of low-PTspectra, sea and valence quark distributions, and correlations in 50-GeV/cπ−—emulsion-nuclei interactions

The low-${P}_{T}$ region of secondary pions, the sea and valence quark distributions in the projectile and the target, and rapidity correlations among secondary pions are investigated in interactions of 50-GeV/c ${\ensuremath{\pi}}^{\ensuremath{-}}$ with nuclear emulsion placed in a strong magnetic field. The existence of a sharp peak in the region of ${{P}_{T}}^{2}\ensuremath{\le}0.12$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ for positive and negative pions in the forward and backward hemispheres in the center-of-mass system is explained on the basis of resonance formation. The production of secondary pions is explained on the basis of the quark-antiquark-recombination model. We have used the valence and sea quark distributions in the pion for explaining the $\frac{{\ensuremath{\pi}}^{+}}{{\ensuremath{\pi}}^{\ensuremath{-}}}$ ratio. We find an enhancement in the number of sea quarks with an increase in nuclear-target size. Single-particle and two-particle inclusive rapidity distributions have been studied. The rapidity-difference distributions and the normalized correlation function $R$ have also been investigated. It is found that no positive correlations among secondary pions are evident at this primary energy.

Two-particle production inK + p interactions at 32 GeV/c

Results are presented on two-particle inclusive production inK+p interactions at 32 GeV/c. We study thex1,2=x1+x2 dependence of invariant structure functions of (ππ)-pairs and compare them to single particle inclusive distributions in the fragmentation regions. Distributions of particles observed at Feynmanx2 in association with various “trigger” particles or systems atx1 in the same hemisphere are dicussed in terms of the reduced variable\(\tilde x_2 = x_2 /(1 - |x_1 |)\). We further present absolute production rates and production ratios of π+'s and π−'s associated with π±,K s 0 , Λ,\(\bar \Lambda \),K*+ (890), (K s 0 π+), and (π+ π−)-triggers, and compare them with qualitative predictions of the quark recombination model. Forwardbackward correlations between (K s 0 π±), (K s 0 ,p), (Λ, π−),\((\bar \Lambda \pi ^ \pm )\), and (p, π−) pairs are also discussed.

Charged pion production in 32GeV/c K + p interactions

Final data on topological cross sections are presented. Inclusive single particle distributions for the reactionsK + p→ π± X at 32 GeV/c are discussed and compared with data at lower energies. Early scaling in the fragmentation regions is confirmed, while cross sections in th central region continue to rise with energy even faster than inpp interactions. Thex-andp T -dependence of the π+/π− ratio inK + p interactions is discussed and a comparison of reactionsK + p→ π± X andK − p→ π± X at 32 GeV/c is made in the context of constituent models. We also present transverse momentum distributions, show prominent seagull effects and study how they are influenced by resonance production.

Inclusive particle spectra in p( π+)n interactions at 195 GeV/c

We present results on single-particle inclusive distributions in p( π +)n reactions from a Fermilab experiment using the hybrid 30″ bubble chamber and PWC facility. Distributions in rapidity, y, Feynman x and p 2 T for π + and π − are presented and compared with other experiments. The effects of different targets and projectiles (neutrons, protons and pions) on the distributions are demonstrated and discussed in terms of projectile and target fragmentation. The average transverse momentum 〈 P T〉 is studied as a function of x, y and multiplicity.

Transverse momentum and angular distributions of hadrons in e +e − jets from QCD

Hadron jets in e +e − annihilation will broaden at high energies due to gluon bremsstrahlung. With nonperturbative p T effects dying out rapidly, the basic features of hadron jets can be calculated in perturbation theory. We examine the p T distribution of secondarily produced hadrons. This is uniquely connected with the deviation from the 1 + cos 2 θ dependence of single particle inclusive distributions. We discuss what can be learned about the gluon fragmentation given the p T and/or angular distributions. A sum rule is derived which establishes a relationship between the average p T 2 and α S.

Inclusive negative-hadron production from high-energyν¯-nucleus charged-current interactions

We present data on inclusive negative-hadron production from charged-current antineutrino interactions in a 21% Ne-H mixture. Inclusive single-particle distributions are presented and are shown to be insensitive to the momentum transferred to the hadron vertex. Comparisons made to inclusive data from π−p and π−n interactions indicate a close similarity between the hadrons resulting from π-nucleon and ν¯-nucleus interactions. The general features of the ν¯-nucleus data are found to be similar to those seen in ν¯p interactions. This last observation implies that ν¯p and ν¯n interactions are similar and that nuclear effects are small.Received 5 May 1978DOI:https://doi.org/10.1103/PhysRevD.18.3905©1978 American Physical Society

Field-theoretic pattern of violation of scaling in the timelike and spacelike regions

We use the Gribov-Lipatov relation to distinguish which class of field theories, conventional type of asymptotically free, can account for the scaling violation observed in ep and e/sup +/e/sup -/ interactions. Asymptotically free theories give a better description of these deviations in both timelike and spacelike regions. We also present some predictions for the single-particle inclusive distribution in e/sup +/e/sup -/ interactions for PETRA energies.