Hadroproduction Cross Sections Research Articles

Coupled channels and production of near-threshold [formula omitted] resonances in e+e− annihilation

The effects of final-state interaction of hadrons, produced in e+e− annihilation near the threshold, are discussed. If there is a loosely bound state or a virtual state in a system of produced hadrons, then the energy dependence of hadroproduction cross section is very strong. Our approach is based on the use of the effective potentials accounting for the interaction between hadrons in the final state. The cases of a few channels with nonzero transition amplitudes between them are considered. It is shown that these transitions drastically change the energy dependence of the cross sections. In particular, a narrow resonance below the threshold in one channel leads to a broad peak in another channel. We explained the non-trivial energy dependence of the production cross sections of BB¯, B⁎B¯, BB¯⁎, B⁎B¯⁎ near the thresholds in e+e− annihilation and obtained good agreement between our predictions and the experimental data available.

Matching next-to-leading-order and high-energy-resummed calculations of heavy-quarkonium-hadroproduction cross sections

The energy dependence of the total hadroproduction cross section of pseudoscalar quarkonia is computed via matching Next-to-Leading Order (NLO) Collinear-Factorisation (CF) results with resummed higher-order corrections, proportional to {alpha}_s^n{ln}^{n-1} (1/z), to the CF hard-scattering coefficient, where z = M2/ hat{s} with M and hat{s} being the quarkonium mass and the partonic center-of-mass energy squared. The resummation is performed using High-Energy Factorisation (HEF) in the Doubly-Logarithmic (DL) approximation, which is a subset of the leading logarithmic ln(1/z) approximation. Doing so, one remains strictly consistent with the NLO and NNLO DGLAP evolution of the PDFs. By improving the treatment of the small-z asymptotics of the CF coefficient function, the resummation cures the unphysical results of the NLO CF calculation. The matching is directly performed in the z-space and, for the first time, by using the Inverse-Error Weighting (InEW) matching procedure. As a by-product of the calculation, the NNLO term of the CF hard-scattering coefficient proportional to {alpha}_s^2 ln(1/z) is predicted from HEF.

Exact quark-mass dependence of the Higgs-gluon form factor at three loops in QCD

We determine the three-loop form factor parameterising the amplitude for the production of an off-shell Higgs boson in gluon fusion in QCD with a single massive quark. The result is obtained via a numerical solution of a system of differential equation for the occurring master integrals. The solution is also used to determine the high-energy and threshold expansions of the form factor. Our findings may be used for the evaluation of virtual corrections generated by top-quark and b-quark loops in Higgs boson hadroproduction cross sections at next-to-next-to-leading order.

Revisiting the D-meson hadroproduction in general-mass variable flavour number scheme

We introduce a novel realization of the open heavy-flavour hadroproduction in general-mass variable flavour number scheme at next-to-leading order in perturbative QCD. The principal novelty with respect to the earlier works is in the treatment of small-transverse-momentum limit, which has been a particularly challenging kinematic region in the past. We show that by a suitable choice of scheme, it is possible to obtain a well-behaved description of the open heavy-flavour hadroproduction cross sections from zero up to asymptotically high transverse momentum. We contrast our calculation with the available D0-meson data as measured by the LHCb and ALICE collaborations at the LHC, finding a very good agreement within the theoretical and experimental uncertainties. We also compare our framework with other theoretical approaches.

Fragmentation of ω and ϕ mesons in e+e− and pp collisions at NLO

A combined analysis of both [Formula: see text] (LEP, SLD) and [Formula: see text] (RHIC-PHENIX and LHC-ALICE) hadroproduction processes are done for the first time for the vector meson nonet at the next-to-leading order (NLO) using a model with broken SU(3) symmetry. The transverse momentum ([Formula: see text]) and rapidity ([Formula: see text]) dependence of the differential cross-section for [Formula: see text] and [Formula: see text] mesons of the [Formula: see text] data are also discussed. The input universal quark (valence and singlet) fragmentation functions at a starting scale of [Formula: see text], after evolution, have values that are consistent with the earlier analysis for [Formula: see text] at NLO. However, the universal gluon fragmentation function is now well determined from this study with significantly smaller error bars, as the [Formula: see text] hadroproduction cross-section is particularly sensitive to the gluon fragmentation since it occurs at the same order as the quark fragmentation, in contrast to the [Formula: see text] hadroproduction process. Additional parameters involved in describing the strangeness and sea suppression and octet–singlet mixing are found to be close to the earlier analysis; in addition, a new relation between the gluon and sea suppression in [Formula: see text] and [Formula: see text] hadroproduction has been observed.

Application of the principle of maximum conformality to the hadroproduction of the Higgs boson at the LHC

We present improved pQCD predictions for Higgs boson hadroproduction at the Large Hadronic Collider (LHC) by applying the Principle of Maximum Conformality (PMC), a procedure which resums the pQCD series using the renormalization group (RG), thereby eliminating the dependence of the predictions on the choice of the renormalization scheme while minimizing sensitivity to the initial choice of the renormalization scale. In previous pQCD predictions for Higgs boson hadroproduction, it has been conventional to assume that the renormalization scale $\mu_r$ of the QCD coupling $\alpha_s(\mu_r)$ is the Higgs mass, and then to vary this choice over the range $1/2 m_H < \mu_r < 2 m_H $ in order to estimate the theory uncertainty. However, this error estimate is only sensitive to the non-conformal $\beta$ terms in the pQCD series, and thus it fails to correctly estimate the theory uncertainty in cases where pQCD series has large higher order contributions, as is the case for Higgs boson hadroproduction. Furthermore, this \mbox{\it ad hoc} choice of scale and range gives pQCD predictions which depend on the renormalization scheme being used, in contradiction to basic RG principles. In contrast, after applying the PMC, we obtain next-to-next-to-leading order RG resummed pQCD predictions for Higgs boson hadroproduction which are renormalization-scheme independent and have minimal sensitivity to the choice of the initial renormalization scale. Taking $m_H=125$ GeV, the PMC predictions for the $p p \to H X$ Higgs inclusive hadroproduction cross-sections for various LHC center-of-mass energies and the fiducial cross section $\sigma_{\rm fid}(pp\to H\to\gamma\gamma)$ are presented...... The PMC predictions show better agreement with the ATLAS measurements than the LHC-XS predictions which are based on conventional renormalization scale-setting.

Calibration of the Top-Quark MonteCarlo Mass.

We present a method to establish, experimentally, the relation between the top-quark mass m_{t}^{MC} as implemented in MonteCarlo generators and the Lagrangian mass parameter m_{t} in a theoretically well-defined renormalization scheme. We propose a simultaneous fit of m_{t}^{MC} and an observable sensitive to m_{t}, which does not rely on any prior assumptions about the relation between m_{t} and m_{t}^{MC}. The measured observable is independent of m_{t}^{MC} and can be used subsequently for a determination of m_{t}. The analysis strategy is illustrated with examples for the extraction of m_{t} from inclusive and differential cross sections for hadroproduction of top quarks.

Fragmentation contributions to hadroproduction of promptJ/ψ,χcJ, andψ(2S)states

We compute fragmentation corrections to hadroproduction of the quarkonium states $J/\psi$, $\chi_{cJ}$, and $\psi(2S)$ at leading power in $m_c^2/p_T^2$, where $m_c$ is the charm-quark mass and $p_T$ is the quarkonium transverse momentum. The computation is carried out in the framework of nonrelativistic QCD. We include corrections to the parton-production cross sections through next-to-leading order in the strong coupling $\alpha_s$ and corrections to the fragmentation functions through second order in $\alpha_s$. We also sum leading logarithms of $p_T^2/m_c^2$ to all orders in perturbation theory. We find that, when we combine these leading-power fragmentation corrections with fixed-order calculations through next-to-leading order in $\alpha_s$, we are able to obtain good fits for $p_T\geq 10$ GeV to hadroproduction cross sections that were measured at the Tevatron and the LHC. Using values for the nonperturbative long-distance matrix elements that we extract from the cross-section fits, we make predictions for the polarizations of the quarkonium states. We obtain good agreement with measurements of the polarizations, with the exception of the CDF Run II measurement of the prompt $J/\psi$ polarization, for which the agreement is only fair. In the predictions for the prompt-$J/\psi$ cross sections and polarizations, we take into account feeddown from the $\chi_{cJ}$ and $\psi(2S)$ states.

Fragmentation contributions toJ/ψphotoproduction at HERA

We compute leading-power fragmentation corrections to $J/\psi$ photoproduction at DESY HERA, making use of the nonrelativistic QCD factorization approach. Our calculations include parton production cross sections through order $\alpha_s^3$, fragmentation functions though order $\alpha_s^2$, and leading logarithms of the transverse momentum divided by the charm-quark mass to all orders in $\alpha_s$. We find that the leading-power fragmentation corrections, beyond those that are included through next-to-leading order in $\alpha_s$, are small relative to the fixed-order contributions through next-to-leading order in $\alpha_s$. Consequently, an important discrepancy remains between the experimental measurements of the $J/\psi$ photoproduction cross section and predictions that make use of nonrelativistic-QCD long-distance matrix elements that are extracted from the $J/\psi$ hadroproduction cross-section and polarization data.

Muon g − 2 discrepancy: new physics or a relatively light Higgs?

After a brief review of the muon g–2 status, we discuss hypothetical errors in the Standard Model prediction that might explain the present discrepancy with the experimental value. None of them seems likely. In particular, a hypothetical increase of the hadroproduction cross section in low-energy e+e− collisions could bridge the muon g–2 discrepancy, but it is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 135 GeV which, in conjunction with the experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.

Understanding Heavy Flavor Production at RHIC

Accurate assessments of the charm and bottom cross sections and kinematic distributions in hadron-hadron collisions are needed in order to understand the behavior of heavy flavors in more complex collisions. Neither the charm nor bottom cross sections were measured at S = 200 GeV before the startup of the Relativistic Heavy Ion Collider (RHIC). The RHIC detectors are capable of measuring the heavy flavor transverse momentum distributions to p T ∼ 0 , making estimates of the total heavy flavor cross section feasible at a collider. It is thus possible to obtain and compare the total heavy flavor cross sections at RHIC with those measured at other energies. The charm production data, in particular, can have a considerable spread in the measured cross sections, even at a single energy. In addition, the small charm mass can lead to large theoretical uncertainties. We assess the theoretical uncertainties on the heavy flavor (charm and bottom) hadroproduction cross section. We discuss the importance of the quark mass, the renormalization and factorization scales and the parton densities on the estimate of the uncertainty.

Study of ψ′ and χcdecays as feed-down sources ofJ/ψ hadro-production

The interpretation of the J/psi suppression patterns observed in nuclear collisions, at CERN and RHIC, as a signature of the formation of a deconfined phase of QCD matter, requires knowing which fractions of the measured J/psi yields, in pp collisions, are due to decays of heavier charmonium states. From a detailed analysis of the available mid-rapidity charmonium hadro-production cross sections, or their ratios, we determine that the J/psi feed-down contributions from psi' and chi_c decays are, respectively, (8.1 +/- 0.3) % and (25 +/- 5) %. These proton-proton values are derived from global averages of the proton-nucleus measurements, assuming that the charmonium states are exponentially absorbed with the length of matter they traverse in the nuclear targets.

The baryon anomaly: Evidence for color transparency and direct hadron production at RHIC

We show that the QCD color transparency of higher-twist contributions to inclusive hadroproduction cross sections, where baryons are produced directly in a short-distance subprocess, can explain several remarkable features of high-pT baryon production in heavy ion collisions which have recently been observed at RHIC: (a) the anomalous increase of the proton-to-pion ratio with centrality, (b) the increased power-law fall-off at fixed xT=2pT/s of the charged particle production cross section in high centrality nuclear collisions, and (c) the anomalous decrease of the number of same-side hadrons produced in association with a proton trigger as the centrality increases. We show that correlations between opposite-side hyperons and kaons can provide a clear signature of higher-twist contributions. These phenomena emphasize the importance of understanding hadronization at the amplitude level in QCD illustrate how heavy ion collisions can provide sensitive tools for interpreting and testing fundamental properties of QCD.

The muong−2and the bounds on the Higgs boson mass

After a brief review of the muon $g\ensuremath{-}2$ status, we analyze the possibility that the present discrepancy between experiment and the standard model (SM) prediction may be due to hypothetical errors in the determination of the hadronic leading-order contribution to the latter. In particular, we show how an increase of the hadroproduction cross section in low-energy ${e}^{+}{e}^{\ensuremath{-}}$ collisions could bridge the muon $g\ensuremath{-}2$ discrepancy, leading however to a decrease on the electroweak upper bound on ${M}_{H}$, the SM Higgs boson mass. That bound is currently ${M}_{H}\ensuremath{\lesssim}150\text{ }\text{ }\mathrm{GeV}$ (95% C.L.) based on the preliminary top quark mass ${M}_{t}=172.6(1.4)\text{ }\text{ }\mathrm{GeV}$ and the recent determination $\ensuremath{\Delta}{\ensuremath{\alpha}}_{\mathrm{had}}^{(5)}({M}_{Z})=0.027\text{ }68(22)$, while the direct-search lower bound is ${M}_{H}&gt;114.4\text{ }\text{ }\mathrm{GeV}$ (95% C.L.). By means of a detailed analysis we conclude that this solution of the muon $g\ensuremath{-}2$ discrepancy is unlikely in view of current experimental error estimates. However, if this turns out to be the solution, the 95% C.L. upper bound on ${M}_{H}$ is reduced to about 130 GeV which, in conjunction with the experimental lower bound, leaves a narrow window for the mass of this fundamental particle.

Resummation of hadroproduction cross-sections at high energy

We reconsider the high energy resummation of photoproduction, electroproduction and hadroproduction cross-sections, in the light of recent progress in the resummation of perturbative parton evolution to NLO in logarithms of Q 2 and x. We show in particular that the when the coupling runs the dramatic enhancements seen at fixed coupling, due to infrared singularities in the partonic cross-sections, are substantially reduced, to the extent that they are largely accounted for by the usual NLO and NNLO perturbative corrections. This leads to a novel explanation of the large K-factors commonly found in perturbative calculations of hadroproduction cross-sections. We give numerical estimates of high energy resummation effects for inclusive B-production, inclusive jets, Drell–Yan and vector boson production, along with their rapidity distributions. We find that resummation modifies the B-production cross-section at the LHC by at most 15%, but that the enhancement of gluonic W-production may be as large as 50% at large rapidities.

New results for light gravitinos at hadron colliders: Fermilab Tevatron limits and CERN LHC perspectives

We derive Feynman rules for the interactions of a single gravitino with (s)quarks and gluons/gluinos from an effective supergravity Lagrangian in nonderivative form and use them to calculate the hadroproduction cross sections and decay widths of single gravitinos. We confirm the results obtained previously with a derivative Lagrangian as well as those obtained with the nonderivative Lagrangian in the high-energy limit and elaborate on the connection between gauge independence and the presence of quartic vertices. We perform extensive numerical studies of branching ratios, total cross sections, and transverse-momentum spectra at the Fermilab Tevatron and the CERN LHC. From the latest CDF monojet cross section limit, we derive a new and robust exclusion contour in the gravitino-squark/gluino mass plane, implying that gravitinos with masses below $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ to $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }\mathrm{eV}$ are excluded for squark/gluino masses below 200 and 500 GeV, respectively. These limits are complementary to the one obtained by the CDF Collaboration, $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }\mathrm{eV}$, under the assumption of infinitely heavy squarks and gluinos. For the LHC, we conclude that supersymmetric scenarios with light gravitinos will lead to a striking monojet signal very quickly after its startup.

Charmed hadron production in pp collision

We investigated the production of charmed hadrons ( D +, D −, D 0, D ¯ 0 , Λ c + , Λ ¯ c - ) in pp collisions as a function of s , x F, p ⊥ 2 and p ⊥ in the framework of the QGSJET model. The study of charmed hadron production characteristics in pp collision is particularly important for cosmic ray physics in the context of atmospheric prompt lepton fluxes. Here our aim is to check the reliability of the QGSJET model to be used to study the production of charmed hadrons in cosmic ray hadronic interactions with air nuclei. Charmed hadroproduction cross sections or the charmed hadron average multiplicities in pp collisions are relatively very small. The maximum production of all charmed hadrons takes place with low values of x F, p ⊥ 2 , and p ⊥ within a small range for all values of s under study. Charmed hadroproduction cross sections as a function of x F and p ⊥ 2 are compared with the LEBC-EHS and LEBC-MPS experiment data for D-meson production. The agreement is quite satisfactory for smaller values of p ⊥ 2 (⩽2 (GeV/c) 2). There is an asymmetry in charmed hadroproduction in pp collision. For all x F, asymmetry is prominent in the low value of s . There is a strong preference for producing Λ c + rather than Λ ¯ c - -baryons, while that for producing D ¯ rather than D-mesons for this range of s . Asymmetry increases from zero to ±1 around x F = 0.3 for all values of s and for all charmed hardron groups. The patterns of asymmetric production of different charmed hadrons with x F are approximately the same as that with s . We compare our calculation with the data from Fermilab experiment E781 (SELEX) for Λ c-baryon production. The agreement is quite good. The asymmetry of charmed hadroproduction with p ⊥ does not follow any well defined pattern.

Charm in cosmic rays (The long-flying component of EAS cores)

Experimental data on cosmic ray cascades with enlarged attenuation lengths (Tien–Shan effect) are presented and analyzed in terms of charm hadroproduction. The very first estimates of charm hadroproduction cross sections from experimental data at high energies are confirmed and compared with recent accelerator results.

Sudakov resummation and finite order expansions of heavy quark hadroproduction cross sections

We resum Sudakov threshold enhancements in heavy quark hadroproduction for single-heavy quark inclusive and pair-inclusive kinematics. We expand these resummed results and derive analytical finite-order cross sections through next-to-next-to-leading order. This involves the construction of next-to-leading order matching conditions in color space. For the scale dependent terms we derive exact results using renormalization group methods. We study the effects of scale variations, scheme and kinematics choice on the partonic and hadronic cross sections, and provide estimates for top and bottom quark production cross sections.

Cross sections for B-meson hadroproduction and up-to-date models

The cross sections for B-meson production as obtained on the basis of the PYTHIA code and the Quark-Gluon String Model (QGSM) are compared at energies of the proton colliders SPS, Tevatron, and LHC. Model predictions are based on the idea of exchanges of a supercritical Pomeron with phenomenological intercept Δp(0)=0.3 for heavy-quark production. The transverse-momentum spectra of B mesons are also compared. It is shown that the cross sections calculated with PYTHIA using CTEQ structure functions are at odds with the asymptotic estimate of the cross sections for \(B\bar B\) production within the QGSM. Asymmetries between the spectra of B0 and \(\bar B^0 \) mesons also contradict the PYTHIA result. The reasons for the difference are discussed.