Production In Pp Collisions Research Articles

Measurement of double-differential cross sections for top quark pair production in pp collisions at sqrt{s} = 8,text {TeV} and impact on parton distribution functions

Normalized double-differential cross sections for top quark pair (mathrm{t}overline{mathrm{t}}) production are measured in pp collisions at a centre-of-mass energy of 8,text {TeV} with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7,text {fb}^{-1}. The measurement is performed in the dilepton mathrm {e}^{pm }mu ^{mp } final state. The mathrm{t}overline{mathrm{t}} cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and mathrm{t}overline{mathrm{t}} system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured mathrm{t}overline{mathrm{t}} cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.

Identified hadron production in pp collisions measured with ALICE.

The production of identified hadrons in proton-proton collisions is frequently studied as a reference for the investigation of the strongly-interacting medium created in heavy-ion collisions. In addition, at LHC energies measurements in pp and p–Pb collisions as a function of the event multiplicity have shown some features reminiscent of those related to collective effects in Pb–Pb collisions. Thanks to its excellent PID capabilities and p Τ coverage, the ALICE detector offers a unique opportunity for the measurement of p Τ spectra, integrated yields (dN/dy) and mean transverse momenta (〈p Τ〉) of identified light-flavour hadrons at midrapidity over a wide p Τ range.In this contribution, results on π, K, p, , Λ, Ξ, Ω and K*0 as a function of multiplicity in pp collisions at are presented. The results are compared with those measured in p–Pb and Pb–Pb collisions. A similar evolution of the spectral shape, the p Τ-differential particle ratios and the integrated yield ratios with the charged particle multiplicity in both small and large systems is observed. The production rates of strange hadrons in pp collisions increase more than those of non-strange particles, showing an enhancement pattern with multiplicity which is remarkably similar to the one measured in p–Pb collisions.In addition, results on the production of light flavour hadrons in pp collisions at , the highest centre-of-mass energy reached so far in the laboratory, are also presented and the behaviour observed as a function of are discussed.

Constraints on the trilinear Higgs coupling from vector boson fusion and associated Higgs production at the LHC

We examine the constraints on the trilinear Higgs coupling λ that originate from associated (V h) and vector boson fusion (VBF) Higgs production in pp collisions in the context of the Standard Model effective field theory. The 1-loop contributions to pp → Vh and pp → jjh that stem from insertions of the dimension-6 operator O6 = −λ (H†H)3 are calculated and combined with the mathcal{O}left(lambda right) corrections to the partial decay widths of the Higgs boson. Employing next-to-next-to-leading order QCD predictions, we analyse the sensitivity of current and forthcoming measurements of the signal strengths in Vh and VBF Higgs production to changes in λ. We show that future LHC runs may be able to probe modifications of λ with a sensitivity similar to the one that is expected to arise from determinations of double-Higgs production. The sensitivity of differential Vh and VBF Higgs distributions to a modified h3 coupling is also studied.

The landscape of W± and Z bosons produced in pp collisions up to LHC energies

We consider a selection of recent experimental results on electroweak W±,Z gauge boson production in pp collisions at BNL RHIC and CERN LHC energies in comparison to prediction of perturbative QCD calculations based on different sets of NLO parton distribution functions including the statistical PDF model known from fits to the DIS data. We show that the current statistical PDF parametrization (fitted to the DIS data only) underestimates the LHC data on W±,Z gauge boson production cross sections at the NLO by about 20%. This suggests that there is a need to refit the parameters of the statistical PDF including the latest LHC data.

Energy dependence of forward-rapidity mathrm {J}/psi and psi mathrm {(2S)} production in pp collisions at the LHC

We present results on transverse momentum (p_{mathrm {textsc {t}}}) and rapidity (y) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive mathrm {J}/psi and psi mathrm {(2S)} at forward rapidity (2.5<y<4) as well as psi mathrm {(2S)}-to-mathrm {J}/psi cross section ratios. These quantities are measured in pp collisions at center of mass energies sqrt{s},=5.02 and 13 TeV with the ALICE detector. Both charmonium states are reconstructed in the dimuon decay channel, using the muon spectrometer. A comprehensive comparison to inclusive charmonium cross sections measured at sqrt{s},=2.76, 7 and 8 TeV is performed. A comparison to non-relativistic quantum chromodynamics and fixed-order next-to-leading logarithm calculations, which describe prompt and non-prompt charmonium production respectively, is also presented. A good description of the data is obtained over the full p_{mathrm {textsc {t}}} range, provided that both contributions are summed. In particular, it is found that for p_{mathrm {textsc {t}}}>15 GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield.

Measurement of the cross section for inclusive isolated-photon production in pp collisions at [formula omitted] using the ATLAS detector

Inclusive isolated-photon production in pp collisions at a centre-of-mass energy of 13 TeV is studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 3.2 fb−1. The cross section is measured as a function of the photon transverse energy above 125 GeV in different regions of photon pseudorapidity. Next-to-leading-order perturbative QCD and Monte Carlo event-generator predictions are compared to the cross-section measurements and provide an adequate description of the data.

Measurement of the inclusive cross-sections of single top-quark and top-antiquark t-channel production in pp collisions at sqrt{s}=13 TeV with the ATLAS detector

A measurement of the t-channel single-top-quark and single-top-antiquark production cross-sections in the lepton+jets channel is presented, using 3.2 fb−1 of proton-proton collision data at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC in 2015. Events are selected by requiring one charged lepton (electron or muon), missing transverse momentum, and two jets with high transverse momentum, exactly one of which is required to be b-tagged. Using a binned maximum-likelihood fit to the discriminant distribution of a neural network, the cross-sections are determined to be σ(tq) = 156 ± 5 (stat.) ± 27 (syst.) ± 3 (lumi.) pb for single top-quark production and sigma left(overline{t}qright)=91pm 4 (stat.) ± 18 (syst.) ± 2 (lumi.) pb for single top-antiquark production, assuming a top-quark mass of 172.5 GeV. The cross-section ratio is measured to be {R}_t=sigma (tq)/sigma left(overline{t}qright)=1.72pm 0.09 (stat.) ± 0.18 (syst.). All results are in agreement with Standard Model predictions.

Triple Parton Scatterings in High-Energy Proton-Proton Collisions.

A generic expression to compute triple parton scattering cross sections in high-energy proton-proton (pp) collisions is presented as a function of the corresponding single parton cross sections and the transverse parton profile of the proton encoded in an effective parameter σ_{eff,TPS}. The value of σ_{eff,TPS} is closely related to the similar effective cross section that characterizes double parton scatterings, and amounts to σ_{eff,TPS}=12.5±4.5 mb. Estimates for triple charm (cc[over ¯]) and bottom (bb[over ¯]) production in pp collisions at LHC and FCC energies are presented based on next-to-next-to-leading-order perturbative calculations for single cc[over ¯], bb[over ¯] cross sections. At sqrt[s]≈100 TeV, about 15% of the pp collisions produce three cc[over ¯] pairs from three different parton-parton scatterings.

High-ET isolated-photon plus jets production in pp collisions at [formula omitted] with the ATLAS detector

The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb−1. Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.

Measurement of J/ψ production in pp collisions at LHC energies with ALICE

An overview of ALICE results on the measurement of J/ψ production in pp collisions at collected during the LHC Run-1 period is presented, as well as first results at forward rapidity from pp collisions at collected during the LHC Run-2 period. In particular, the measurement of J/ψ production as a function of transverse momentum and charged-particle multiplicity are discussed and compared to theoretical model calculations.

Experimental overview on heavy-flavor production

Hadrons containing heavy-flavors are unique probes of the properties of the hot and dense QCD medium produced in heavy-ion collisions. Due to their large masses, heavy quarks are produced at the initial stage of the collision, almost exclusively via hard partonic scattering processes. Therefore, they are expected to experience the full collision history propagating through and interacting with the QCD medium. The parton energy loss, which is sensitive to the transport coefficients of the produced medium, can be studied experimentally by measuring the nuclear modification factor which accounts for the modification of the heavy–flavored hadron yield in Pb–Pb collisions with respect to pp collisions. In semi-central Pb–Pb collisions, the degree of thermalization of charm quarks in the QCD medium can be accessed via the measurement of the heavy flavor elliptic flow v2 at low pT. Furthermore, the measurement of heavy-flavors production in pp collisions allows testing the perturbative QCD calculations. The PHENIX and STAR Collaborations at the Relativistic Heavy-Ion Collider and ALICE, CMS and ATLAS Collaborations at the Large Hadron Collider have measured the production of charmonium and bottonium states as well as open heavy flavor hadrons via their hadronic and semi-leptonic decays at mid-rapidity and in the semi-muonic decay channel at forward rapidity in pp, p-A and A–A collisions in an energy domain that ranges from = 0.2 TeV to = 13 TeV in pp collisions and from = 0.2 TeV to = 5.02 TeV in A–A collisions. In this contribution the latest experimental results will be reviewed.

Measurement of the transverse momentum spectrum of the Higgs boson produced in pp collisions at sqrt{s}=8 TeV using H \u2192 WW decays

The cross section for Higgs boson production in pp collisions is studied using the H → W+W− decay mode, followed by leptonic decays of the W bosons to an oppositely charged electron-muon pair in the final state. The measurements are performed using data collected by the CMS experiment at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.4 fb−1. The Higgs boson transverse momentum (pT) is reconstructed using the lepton pair pT and missing pT. The differential cross section times branching fraction is measured as a function of the Higgs boson pT in a fiducial phase space defined to match the experimental acceptance in terms of the lepton kinematics and event topology. The production cross section times branching fraction in the fiducial phase space is measured to be 39 ± 8 (stat) ± 9 (syst) fb. The measurements are found to agree, within experimental uncertainties, with theoretical calculations based on the standard model.

Light flavour hadron production in pp collisions at = 13 TeV with ALICE

The ALICE detector has excellent Particle IDentification (PID) capabilities in the central barrel (|η| < 0.9). This allows identified hadron production to be measured over a wide transverse momentum (pT) range, using different sub-detectors and techniques: their specific energy loss (dE/dx), the velocity determination via time-of-flight measurement, the Cherenkov angle or their characteristic weak decay topology. Results on identified light flavour hadron production at mid-rapidity measured by ALICE in proton-proton collisions at = 13 TeV are presented and compared with previous measurements performed at lower energies. The results cover a wide range of particle species including long-lived hadrons, resonances and multi-strange baryons over the pT range from 150 MeV/c up to 20 GeV/c, depending on the particle species.

New indication on scaling properties of strangeness production in pp collisions at RHIC

Experimental data on transverse momentum spectra of strange particles [Formula: see text] produced in [Formula: see text] collisions at [Formula: see text] obtained by the STAR and PHENIX collaborations at RHIC are analyzed in the framework of [Formula: see text]-scaling approach. The concept of the [Formula: see text]-scaling is based on fundamental principles of self-similarity, locality, and fractality of hadron interactions at high energies. General properties of the data [Formula: see text]-presentation are studied. Self-similarity of fractal structure of protons and fragmentation processes with strange particles is discussed. A microscopic scenario of constituent interactions developed within the [Formula: see text]-scaling scheme is used to study the dependence of momentum fractions and recoil mass on the collision energy, transverse momentum and mass of produced inclusive particle, and to estimate the constituent energy loss. We consider that obtained results can be useful in study of strangeness origin, in searching for new physics with strange probes, and can serve for better understanding of fractality of hadron interactions at small scales.

Search for anomalous Wtb couplings and flavour-changing neutral currents in t-channel single top quark production in pp collisions at sqrt{s}=7 and 8 TeV

Single top quark events produced in the t channel are used to set limits on anomalous Wtb couplings and to search for top quark flavour-changing neutral current (FCNC) interactions. The data taken with the CMS detector at the LHC in proton-proton collisions at sqrt{s}=7 and 8 TeV correspond to integrated luminosities of 5.0 and 19.7 fb−1, respectively. The analysis is performed using events with one muon and two or three jets. A Bayesian neural network technique is used to discriminate between the signal and backgrounds, which are observed to be consistent with the standard model prediction. The 95% confidence level (CL) exclusion limits on anomalous right-handed vector, and left- and right-handed tensor Wtb couplings are measured to be |fVR| < 0.16, |fTL| < 0.057, and − 0.049 < fTR < 0.048, respectively. For the FCNC couplings κtug and κtcg, the 95% CL upper limits on coupling strengths are |κtug|/Λ < 4.1 × 10− 3 TeV−1 and |κtcg|/Λ < 1.8 × 10− 2 TeV−1, where Λ is the scale for new physics, and correspond to upper limits on the branching fractions of 2.0 × 10−5 and 4.1 × 10−4 for the decays t → ug and t → cg, respectively.

Measurement of forward tt‾, W+bb¯ and W+cc¯ production in pp collisions at s=8 TeV

The production of $t\overline{t}$, $W+b\overline{b}$ and $W+c\overline{c}$ is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 $\mbox{fb}^{-1}$. The $W$ bosons are reconstructed in the decays $W\rightarrow\ell\nu$, where $\ell$ denotes muon or electron, while the $b$ and $c$ quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.

Charmonium production in pp collisions with ALICE at the LHC

We report on forward-rapidity charmonium production in pp collisions at a center-of-mass energy , as measured by ALICE at the LHC. Differential cross sections for both J/ψ and ψ(2S) are presented as a function of the charmonium transverse momentum and rapidity. Results are compared to similar measurements performed by LHCb, to measurements at lower energies and to state-of-the-art model calculations.

Identified particle production in pp collisions at = 7 and 13 TeV measured with ALICE

Proton-proton (pp) collisions have been used extensively as a reference for the study of interactions of larger colliding systems at the LHC. Recent measurements performed in high-multiplicity pp and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. In this context, the study of identified particle spectra and yields as a function of multiplicity is a key tool for the understanding of similarities and differences between small and large systems. We report on the production of pions, kaons, protons, , Λ, Ξ, Ω and K*0 as a function of multiplicity in pp collisions at = 7 TeV measured with the ALICE experiment. The work presented here represents the most comprehensive set of results on identified particle production in pp collisions at the LHC. Spectral shapes, studied both for individual particles and via particle ratios as a function of pT, exhibit an evolution with charged particle multiplicity that is similar to the one observed in larger systems. In addition, results on the production of light flavour hadrons in pp collisions at = 13 TeV, the highest centre-of-mass energy ever reached in the laboratory, are also presented and compared with previous, lower energy results.

Heavy-flavour production in pp collisions and correlations in pp and p-Pb collisions measured with ALICE at the LHC

Thanks to its excellent tracking and particle identification performance, the ALICE detector is capable of measuring D mesons at mid-rapidity via their hadronic decay channels down to very low transverse momentum. We show an extension of the prompt D0 pT-differential cross section measurement down to zero transverse momentum, which allows us to determine the pT-integrated charm production cross section at mid-rapidity in pp collisions at . We also present measurements of azimuthal correlations of prompt D0, D+ and D*+ mesons with charged hadrons in pp collisions at and p-Pb collisions at and compare the results with expectations from models.

Measurements of \u03c8(2S) and X(3872) \u2192 J/\u03c8\u03c0+\u03c0\u2212 production in pp collisions at sqrt{s}=8 TeV with the ATLAS detector

Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and ψ(2S), in the decay mode J/ψπ+π−, measured using 11.4 fb−1 of pp collisions at sqrt{s}=8 TeV by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/ψ(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and ψ(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and ψ(2S) production gives {R}_B=frac{mathrm{mathcal{B}}left(Bto X(3872)+mathrm{any}right)mathrm{mathcal{B}}left(X(3872)to J/psi {pi}^{+}{pi}^{-}right)}{mathrm{mathcal{B}}left(Bto psi (2S)+mathrm{any}right)mathrm{mathcal{B}}left(psi (2S)to J/psi {pi}^{+}{pi}^{-}right)}=left(3.95pm 0.32left(mathrm{s}mathrm{tat}right)pm 0.08left(mathrm{s}mathrm{y}mathrm{s}right)right)times {10}^{-2} separating short- and long-lived contributions, assuming that the short-lived component is due to Bc decays, gives RB = (3.57 ± 0.33(stat) ± 0.11(sys)) × 10−2, with the fraction of non-prompt X(3872) produced via Bc decays for pT(X(3872)) > 10 GeV being (25 ± 13(stat) ± 2(sys) ± 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and ψ(2S) decays are also measured and compared to theoretical predictions.