Inclusive Production Cross Section Research Articles

Polarized 3 parton production in inclusive DIS at small x

Azimuthal angular correlations between produced hadrons/jets in high energy collisions are a sensitive probe of the dynamics of QCD at small x. Here we derive the triple differential cross section for inclusive production of 3 polarized partons in DIS at small x using the spinor helicity formalism. The target proton or nucleus is described using the Color Glass Condensate (CGC) formalism. The resulting expressions are used to study azimuthal angular correlations between produced partons in order to probe the gluon structure of the target hadron or nucleus. Our analytic expressions can also be used to calculate the real part of the Next to Leading Order (NLO) corrections to di-hadron production in DIS by integrating out one of the three final state partons.

Measurement of the t t ¯ $$ \mathrm{t}\overline{\mathrm{t}} $$ production cross section in the eμ channel in proton-proton collisions at s = 7 $$ \sqrt{s}=7 $$ and 8 TeV

The inclusive cross section for top quark pair production is measured in proton-proton collisions at sqrt(s) = 7 and 8 TeV, corresponding to 5.0 and 19.7 invers-femtobarns, respectively, with the CMS experiment at the LHC. The cross sections are measured in the electron-muon channel using a binned likelihood fit to multi-differential final state distributions related to identified b quark jets and other jets in the event. The measured cross section values are 173.6 +/- 2.1 (stat) +4.5-4.0 (syst) +/- 3.8 (lumi) pb at sqrt(s) = 7 TeV, and 244.9 +/- 1.4 (stat) +6.3-5.5 (syst) +/- 6.4 (lumi) pb at sqrt(s) = 8 TeV, in good agreement with QCD calculations at next-to-next-to-leading-order accuracy. The ratio of the cross sections measured at 7 and 8 TeV is determined, as well as cross sections in the fiducial regions defined by the acceptance requirements on the two charged leptons in the final state. The cross section results are used to determine the top quark pole mass via the dependence of the theoretically predicted cross section on the mass, giving a best result of 173.8 +1.7-1.8 GeV. The data at sqrt(s) = 8 TeV are also used to set limits, for two neutralino mass values, on the pair production of supersymmetric top squarks with masses close to the top quark mass.

Quenching of inclusive and tagged b-jets at the LHC

We present theoretical predictions for the nuclear-induced attenuation of the differential cross sections for inclusive and tagged b-jet production in heavy ion collisions at the LHC. We find that for inclusive b-jet production at high transverse momentum the mass effects are negligible, and that the attenuation is comparable to the one observed for light jets. On the other hand, for isolated-photon and B-meson-tagged b-jets the sample of events with heavy quarks produced at the early stages of the collision is greatly enhanced. Thus, these tagged b-jet final-states have a much more direct connection to the physics of b-quark energy loss. We present theoretical predictions for the quenching of such tagged b-jet events at the LHC and the QGP-induced modification of the related momentum imbalance and asymmetry. We demonstrate that these tagged processes can be used to accurately study the physics of heavy quark production and propagation in dense QCD matter.

Higgs production in heavy-quark annihilation through next-to-next-to-leading order QCD

The total inclusive cross section for charged and neutral Higgs production in heavy-quark annihilation is presented through NNLO QCD. It is shown that, aside from an overall factor, the partonic cross section is independent of the initial-state quark flavors, and that any interference terms involving two different Yukawa couplings vanish. A simple criterion for defining the central renormalization and factorization scale is proposed. Its application to the $b\bar bH$ process yields results which are compatible with the values usually adopted for this process. Remarkably, we find little variation in these values for the other initial-state quark flavors. Finally, we disentangle the impact of the different parton luminosities from genuine hard NNLO effects and find that, for the central scales, a naive rescaling by the parton luminosities approximates the full result remarkably well.

Recent top physics highlights at the LHC

Recent highlights of measurements by the ATLAS and CMS collaborations involving top quarks produced at the LHC are presented. Emphasis is put on precise inclusive and differential top pair production cross section measurements and comparisons to QCD calculations. Special attention is given to fiducial measurements. Results on electroweak single top quarks production and the recent evidence of top pair produced in associated with vector bosons are summarised. The experimental status of top quark mass measurements is critically reviewed.

Top quark pair production cross section using the ATLAS detector at the LHC

Measurements of the inclusive top quark pair production cross sections in proton-proton collisions with the ATLAS detector at the Large Hadron Collider are presented. The measurements are performed requiring one or two electrons or muons in the final state. Various experimental techniques are compared. The most accurate result in obtained requiring opposite sign electrons and muons, achieves a precision of a few percent, and is in good agreement with a recent NNLO+NNLL QCD calculation. In addition, a differential measurement of the top transverse momentum and kinematic properties of the top pair system are presented. This measurement requires one electron or muon in the final state and probes our understanding of top pair production in the TeV regime and is compared to recent Monte Carlo generators and theory calculations.

Inclusive quarkonium production at forward rapidity in pp collisions at [Formula: see text]TeV.

We report on the inclusive production cross sections of {mathrm{J}/psi }, {psi (mathrm{2S})}, mathrm{Upsilon }(1S), mathrm{Upsilon }(2S) and mathrm{Upsilon }(3S), measured at forward rapidity with the ALICE detector in mathrm{pp} collisions at a center-of-mass energy sqrt{s}=8 TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb^{-1}. Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum {p_mathrm{T}} and rapidity y, over the {p_mathrm{T}} ranges 0<{p_mathrm{T}}<20 GeV/c for {mathrm{J}/psi }, 0<{p_mathrm{T}}<12 GeV/c for all other resonances, and for 2.5<y<4. The cross sections, integrated over {p_mathrm{T}} and y, and assuming unpolarized quarkonia, are sigma _{{mathrm{J}/psi }} = 8.98pm 0.04pm 0.82 upmu b, sigma _{{psi (mathrm{2S})}} = 1.23pm 0.08pm 0.22 upmu b, sigma _{mathrm{Upsilon }mathrm{(1S)}} = 71pm 6pm 7 nb, sigma _{mathrm{Upsilon }mathrm{(2S)}} = 26pm 5pm 4 nb and sigma _{mathrm{Upsilon }mathrm{(3S)}} = 9pm 4pm 1 nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most 1.4sigma , with measurements performed by the LHCb collaboration in the same rapidity range.

Heavy quarks in proton-nucleus collisions: The hybrid formalism

We explore the quark mass effects on inclusive hadron production in proton-nucleus collisions at high energies. We consider two processes. First, we compute the single inclusive cross-section for production of hadrons with open heavy flavour in the proton forward direction at leading order. Next, in the same kinematics, we calculate the heavy-quark contribution to single inclusive production of light or unidentified hadrons at next-to-leading-order. For both studies we exploit the hybrid formalism, that is the collinear factorisation on the proton side while high-density and high-energy effects are resummed on the side of the nucleus.

Higher-Twist Mechanism and Inclusive Gluon Production in Pion-Proton Collisions

We calculate the contribution of the higher-twist Feynman diagrams to the large-pT inclusive gluon production cross section in πp collisions incase of the running coupling and frozen coupling approaches within perturbative and holographic QCD. The structure of infrared renormalon singularities of the higher-twist subprocess cross section are obtained and the resummed higher-twist cross sections (Borel sum) with the ones obtained in the framework of the frozen coupling approach and leading-twist cross section are compared and analyzed.

Next-to-next-to-eikonal corrections in the CGC

We extend the study of corrections to the eikonal approximation that was initiated in Ref. \cite{Altinoluk:2014oxa} to higher orders. These corrections associated with the finite width of the target are investigated and the gluon propagator in background field is calculated at next-to-next-to-eikonal accuracy. The result is then applied to the single inclusive gluon production cross section at central rapidities and the light-front helicity asymmetry, in pA collisions, in order to analyse these observables beyond the eikonal limit. The next-to-next-to-eikonal corrections to the unpolarized cross section are non-zero and provide the first corrections to the usual $k_\perp$-factorized expression. In contrast, the eikonal and next-to-next-to-eikonal contributions to the helicity asymmetry vanish, while the next-to-eikonal ones are non-zero.

Higher-twist mechanism and inclusive gluon production in pion–proton collisions

We calculate the contribution of the higher-twist Feynman diagrams to the large-[Formula: see text] inclusive gluon production cross-section in [Formula: see text] collisions in case of the running coupling and frozen coupling approaches within perturbative and holographic QCD. The structure of infrared renormalon singularities of the higher-twist subprocess cross-section is obtained and the resummed higher-twist cross-sections (Borel sum) with the ones obtained in the framework of the frozen coupling approach and leading-twist cross-section are compared and analyzed.

B c -meson physics in the LHCb experiment

Results obtained with the aid of the LHCb detector operating at the Large Hadron Collider (LHC, CERN, Geneva) are discussed. The accumulated data sample made it possible to study the production of Bc mesons in proton–proton collisions. The inclusive production cross sections and lifetimes were measured for Bc mesons, and their new decay channels were studied.

Family gauge boson production at the LHC

Family gauge boson production at the LHC is investigated according to a U(3) family gauge model with twisted family number assignment. In the model we study, a family gauge boson with the lowest mass, A11, interacts only with the first generation leptons and the third generation quarks. (The family numbers are assigned, for example, as (e1,e2,e3)=(e−,μ−,τ−) and (d1,d2,d3)=(b,d,s) [or (d1,d2,d3)=(b,s,d)].) In the model, the family gauge coupling constant is fixed by relating to the electroweak gauge coupling constant. Thus measurements of production cross sections and branching ratios of A11 clearly confirm or rule out the model. We calculate the cross sections of inclusive A11 production and bb¯(tt¯) associated A11 production at s=14 TeV and 100 TeV. With the dielectron production cross section, we discuss the determination of diagonalizing matrix of quark mass matrix, Uu and Ud, respectively.

First observation of top quark production in the forward region.

Top quark production in the forward region in proton-proton collisions is observed for the first time. The W+b final state with W→μν is reconstructed using muons with a transverse momentum, p_{T}, larger than 25GeV in the pseudorapidity range 2.0<η<4.5. The b jets are required to have 50<p_{T}<100 GeV and 2.2<η<4.2, while the transverse component of the sum of the muon and b-jet momenta must satisfy p_{T}>20 GeV. The results are based on data corresponding to integrated luminosities of 1.0 and 2.0 fb^{-1} collected at center-of-mass energies of 7 and 8TeV by LHCb. The inclusive top quark production cross sections in the fiducial region are σ(top)[7 TeV]=239±53(stat)±33(syst)±24(theory) fb,σ(top)[8 TeV]=289±43(stat)±40(syst)±29(theory) fb.These results, along with the observed differential yields and charge asymmetries, are in agreement with next-to-leading order standard model predictions.

Implementing the exact kinematical constraint in the saturation formalism

We revisit the issue of the large negative next-to-leading order (NLO) cross section for single inclusive hadron production in $pA$ collisions in the saturation formalism. By implementing the exact kinematical constraint in the modified dipole splitting functions, two additional positive NLO correction terms are obtained. In the asymptotic large $k_\perp$ limit, we analytically show that these two terms become as large as the negative NLO contributions found in our previous calculation. Furthermore, the numerical results demonstrate that the applicable regime of the saturation formalism can be extended to a larger $k_\perp$ window, where the exact matching between the saturation formalism (in the asymptotic $k_\perp$ regime) and the collinear factorization calculations will have to be performed separately. In addition, after significantly improving the numerical accuracy of the NLO correction, we obtain excellent agreement with the LHC and RHIC data for forward hadron productions.

Higgs effects in top anti-top production near threshold in e+e− annihilation

The completion of the third-order QCD corrections to the inclusive top-pair production cross section near threshold demonstrates that the strong dynamics is under control at the few percent level. In this paper we consider the effects of the Higgs boson on the cross section and, for the first time, combine the third-order QCD result with the third-order P-wave, the leading QED and the leading non-resonant contributions. We study the size of the different effects and investigate the sensitivity of the cross section to variations of the top-quark Yukawa coupling due to possible new physics effects.

Impact of heavy-flavour production cross sections measured by the LHCb experiment on parton distribution functions at low x

The impact of recent measurements of heavy-flavour production in deep inelastic $ep$ scattering and in $pp$ collisions on parton distribution functions is studied in a QCD analysis in the fixed-flavour number scheme at next-to-leading order. Differential cross sections of charm- and beauty-hadron production measured by LHCb are used together with inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA. The heavy-flavour data of the LHCb experiment impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions $x$ of the proton momentum, down to $x \sim 5 \times 10^{-6}$. This kinematic range is currently not covered by other experimental data in perturbative QCD fits.

The inclusive jet production in the BFKL–Bartels approach with a running coupling introduced via bootstrap

The inclusive cross section for production of a jet with a given transverse momentum off a heavy nucleus is derived in the BFKL framework with a running coupling on the basis of the bootstrap relation. The cross section depends on the same three different coupling constants as the total cross section unlike the cross section for gluon production derived in the dipole approach.

Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in thelepton+jetsfinal state with ATLAS

A measurement is presented of the $t\bar{t}$ inclusive production cross-section in $pp$ collisions at a center-of-mass energy of $\sqrt{s}=8$ TeV using data collected by the ATLAS detector at the CERN Large Hadron Collider. The measurement was performed in the lepton+jets final state using a data set corresponding to an integrated luminosity of 20.3 fb$^{-1}$. The cross-section was obtained using a likelihood discriminant fit and $b$-jet identification was used to improve the signal-to-background ratio. The inclusive $t\bar{t}$ production cross-section was measured to be $260\pm 1{\textrm{(stat.)}} ^{+22}_{-23} {\textrm{(syst.)}}\pm 8{\textrm{(lumi.)}}\pm 4{\mathrm{(beam)}}$ pb assuming a top-quark mass of 172.5 GeV, in good agreement with the theoretical prediction of $253^{+13}_{-15}$ pb. The $t\bar{t}\to (e,\mu)+{\mathrm{jets}}$ production cross-section in the fiducial region determined by the detector acceptance is also reported.

Pinning down top dipole moments with ultraboosted tops

We investigate existing and future hadron-collider constraints on the top dipole chromomagnetic and chromoelectric moments, two quantities that are expected to be modified in the presence of new physics. We focus first on recent measurements of the inclusive top pair production cross section at the Tevatron and at the Large Hadron Collider. We then analyse the role of top-antitop events produced at very large invariant masses, in the context of the forthcoming 13-14 TeV runs of the LHC, and at a future 100 TeV proton-proton collider. In this latter case, the selection of semileptonic decays to hard muons allows to tag top quarks boosted to the multi-TeV regime, strongly reducing the QCD backgrounds and leading to a significant improvement in the sensitivity to anomalous top couplings.