Inclusive Pp Research Articles

NNLO QCD predictions of electron charge asymmetry for inclusive pp → W + X production in forward region at 13 and 14 TeV

This paper presents perturbative QCD predictions of the electron charge asymmetry for inclusive production in proton-proton (pp) collisions. Perturbative QCD calculations are performed at next-to-next-to-leading order (NNLO) accuracy using different parton distribution function (PDF) models at 8, 13, and 14 TeV center-of-mass energies of CERN LHC pp collisions. NNLO calculations are performed for electrons with transverse momenta above 20 GeV in the forward electron pseudorapidity region . NNLO predictions are first compared at 8 TeV with the measurements of the LHCb experiment at the LHC for the / cross section ratio and charge asymmetry distributions. The 8 TeV predictions using NNPDF3.1, CT14, and MMHT2014 PDF sets are reported to be in good agreement with the LHCb data for the entire region, justifying the extension of the calculations to 13 and 14 TeV energies. The charge asymmetry predictions at NNLO accuracy are reported in the forward bins at 13 and 14 TeV and compared among NNPDF3.1, CT14, and MMHT2014 PDF sets. Overall, the predicted differential cross-section and charge asymmetry distributions based on different PDF sets are found to be consistent with each other for the entire region. The charge asymmetry distributions are shown to be more sensitive to discriminate among different PDF models in terms of the 14 TeV predictions.

Measurement of long-range two-particle azimuthal correlations in Z-boson tagged pp collisions at sqrt{s}=8 and 13\xa0TeV

Results are presented from the measurement by ATLAS of long-range (|Delta eta |>2) dihadron angular correlations in sqrt{s}=8 and 13 TeV pp collisions containing a Z boson. The analysis is performed using 19.4 mathrm {fb}^{-1} of sqrt{s}=8 TeV data recorded during Run 1 of the LHC and 36.1 mathrm {fb}^{-1} of sqrt{s}=13 TeV data recorded during Run 2. Two-particle correlation functions are measured as a function of relative azimuthal angle over the relative pseudorapidity range 2<|Delta eta |<5 for different intervals of charged-particle multiplicity and transverse momentum. The measurements are corrected for the presence of background charged particles generated by collisions that occur during one passage of two colliding proton bunches in the LHC. Contributions to the two-particle correlation functions from hard processes are removed using a template-fitting procedure. Sinusoidal modulation in the correlation functions is observed and quantified by the second Fourier coefficient of the correlation function, v_{2,2}, which in turn is used to obtain the single-particle anisotropy coefficient v_{2}. The v_{2} values in the Z-tagged events, integrated over 0.5<p_{mathrm {T}}<5 GeV, are found to be independent of multiplicity and sqrt{s}, and consistent within uncertainties with previous measurements in inclusive pp collisions. As a function of charged-particle p_{mathrm {T}}, the Z-tagged and inclusive v_{2} values are consistent within uncertainties for p_{mathrm {T}}<3 GeV.

Measurement of the muon charge asymmetry in inclusive pp → W + X production at [formula omitted] at CMS and an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp→WX production at s=7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 fb-1 recorded with the CMS detector at the LHC. With a sample of more than twenty million W→μν events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10-3 to 10-1. These measurements are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis.

Measurement of diffractive dissociation cross sections inppcollisions ats=7 TeV

Measurements of diffractive dissociation cross sections in pp collisions at sqrt(s) = 7 TeV are presented in kinematic regions defined by the masses M[X] and M[Y] of the two final-state hadronic systems separated by the largest rapidity gap in the event. Differential cross sections are measured as a function of xi[X]= M[X]^2/s in the region -5.5 < log[10]xi[X] < -2.5, for log[10]M[Y] < 0.5, dominated by single dissociation (SD), and 0.5 < log[10]M[Y] < 1.1, dominated by double dissociation (DD), where M[X] and M[Y] are given in GeV. The inclusive pp cross section is also measured as a function of the width of the central pseudorapidity gap Delta eta for Delta eta > 3, log[10]M[X] > 1.1, and log[10]M[Y] > 1.1, a region dominated by DD. The cross sections integrated over these regions are found to be, respectively, 2.99 +/- 0.02 (stat) +0.32 -0.29 (syst) mb, 1.18 +/- 0.02 (stat) +/- 0.13 (syst) mb, and 0.58 +/- 0.01 (stat) +0.13 -0.11 (syst) mb, and are used to extract total SD and DD cross sections. In addition, the inclusive differential cross section, d sigma /d Delta eta[F], for events with a pseudorapidity gap adjacent to the edge of the detector, is measured over Delta eta[F] = 8.4 units of pseudorapidity. The results are compared to those of other experiments and to theoretical predictions, and found compatible with slowly-rising diffractive cross sections as a function of center-of-mass energy.

Measurement of the muon charge asymmetry in inclusivepp→W+Xproduction ats=7 TeVand an improved determination of light parton distribution functions

Measurements of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 inverse femtobarns recorded with the CMS detector at the LHC. With a sample of more than twenty million W to mu nu events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from 10E-3 to 10E-1. These measurements and the recent CMS measurement of associated W + charm production are used together with the cross sections for inclusive deep inelastic ep scattering at HERA in a next-to-leading-order QCD analysis. The determination of the valence quark distributions is improved, and the strange-quark distribution is probed directly through the leading-order process g + s to W + c in proton-proton collisions at the LHC.

Measurement of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV

Measurement of the muon charge asymmetry in inclusive pp to WX production at sqrt(s) = 7 TeV

Measurement of the Electron Charge Asymmetry in InclusiveWProduction inppCollisions ats=7 TeV

A measurement of the electron charge asymmetry in inclusive pp→W+X→eν+X production at s=7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 840 pb−1. The electron charge asymmetry reflects the unequal production of W+ and W− bosons in pp collisions. The electron charge asymmetry is measured in bins of the absolute value of electron pseudorapidity in the range of |η|<2.4. The asymmetry rises from about 0.1 to 0.2 as a function of the pseudorapidity and is measured with a relative precision better than 7%. This measurement provides new stringent constraints for parton distribution functions.Received 12 June 2012DOI:https://doi.org/10.1103/PhysRevLett.109.111806This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

The top quark and Higgs boson masses and the stability of the electroweak vacuum

The ATLAS and CMS experiments observed a particle at the LHC with a mass ≈126 GeV, which is compatible with the Higgs boson of the Standard Model. A crucial question is, if for such a Higgs mass value, one could extrapolate the model up to high scales while keeping the minimum of the scalar potential that breaks the electroweak symmetry stable. Vacuum stability requires indeed the Higgs boson mass to be MH≳129±1 GeV, but the precise value depends critically on the input top quark pole mass which is usually taken to be the one measured at the Tevatron, mtexp=173.2±0.9 GeV. However, for an unambiguous and theoretically well-defined determination of the top quark mass one should rather use the total cross section for top quark pair production at hadron colliders. Confronting the latest predictions of the inclusive pp¯→tt¯+X cross section up to next-to-next-to-leading order in QCD to the experimental measurement at the Tevatron, we determine the running mass in the MS¯-scheme to be mtMS¯(mt)=163.3±2.7 GeV which gives a top quark pole mass of mtpole=173.3±2.8 GeV. This leads to the vacuum stability constraint MH⩾129.4±5.6 GeV to which a ≈126 GeV Higgs boson complies as the uncertainty is large. A very precise assessment of the stability of the electroweak vacuum can only be made at a future high-energy electron–positron collider, where the top quark pole mass could be determined with a few hundred MeV accuracy.

Measurement of the lepton charge asymmetry in inclusive W production in pp collisions at $ \sqrt {s} = 7\;{\text{TeV}} $

A measurement of the lepton charge asymmetry in inclusive pp to WX production at sqrt(s)= 7 TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 inverse picobarns. This high precision measurement of the lepton charge asymmetry, performed in both the W to e nu and W to mu nu channels, provides new insights into parton distribution functions.

Λ0 POLARIZATION IN EXCLUSIVE AND INCLUSIVE p-NUCLEUS REACTIONS

Both Λ0 polarization from inclusive and exclusive p-Nucleus reactions follow the same trend as function of xF and [Formula: see text]. It is valid for -1.0&lt;xF&lt;+1.0 and 0.0&lt;PT&lt;2.0 GeV/c and for Nucleus=p, Be, Cu, W and Pb. The value of a depends on the target nature: it is -(0.443 ± 0.037), in exclusive pp reactions; -(0.376 ± 0.024), in inclusive pp reactions; -(0.232 ± 0.012), in inclusive p Be reactions; -(0.124 ± 0.015), in inclusive p Cu reactions; -(0.274 ± 0.023), in inclusive p W reactions; -(0.147 ± 0.023), in inclusive p Pb reactions. It is independent of the beam energy. And this equation is the most simple bilinear form that describes Λ0 polarization in -1.0&lt;xF&lt;+1.0 and 0.0&lt;PT&lt;2.0 GeV/c .

K − meson production in the proton–proton reaction at 3.67 GeV/ c

The total cross section of the reaction pp→ ppK + K − has been determined for proton–proton reactions with p beam =3.67 GeV/c . This represents the first cross section measurement of the pp→ ppK − K + channel near threshold, and is equivalent to the inclusive pp→ ppK − X cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive pp→ ppK + X meson production at the same CM energy above the corresponding threshold. This large difference in the K + and K − meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.

Bose-stimulated pion production in relativistic nuclear collisions.

We demonstrate the importance of the Bose-statistical effects for pion production in relativistic heavy-ion collisions. The evolution of the pion phase-space density in central collisions of ultrarelativistic nuclei is studied in a simple kinetic model taking into account the effect of Bose-stimulated pion production by the NN collisions in a dense cloud of mesons. It is assumed that pions are produced within a finite formation time at the stage of the projectile-target interpenetration. The mutual slowing down of nuclei is described schematically by introducing an effective deceleration length. The role of the quasideuteron and \ensuremath{\Delta}-isobar mechanisms of pion absorption is investigated. The model predicts the enhancement of the soft pion yield as compared to inclusive pp data. The effect is sensitive to the pion formation time and is more pronounced at midrapidity and for heavy nuclei. The results are compared with pion spectra observed in central 10.7A GeV Au+Au and 200A GeV S+S collisions. We suggest new experiments sensitive to the Bose enhancement phenomena.

Measurements of cross sections and analyzing powers for the inclusive pp-->pn pi

Single arm spectrometer measurements of the differential cross sections and analyzing powers of the pp pn reaction have been performed at 400 and 450 MeV incident proton energy. The measurements covering an angular range from 46 to 90 (lab) spanned pion energies corresponding to production of the np system with relative energies between 0 and 30 MeV, a region where the influence of the np final state interaction is particularly important. The trend of the measured analyzing power is very similar to that of the pp d reaction, and is well explained by calculations that use this latter data as input. Dominance of the triplet pn final state is implied by these results.

Evidence for Λ c+ in inclusive pp → ( Λ0π+π+π−) + X and pp → (K −π+p) + X at √ s = 53 and 62 GeV

A search for the charmed baryon, Λ c +, has been carried out in inclusively, measured Λ 0 π ± π + π − and K − π ± p final states with longitudinal x > 0.75 in an experiment at the CERN intersecting storage rings. An effect with invariant mass near 2.3 GeV is observed in Λ 0π +π +π − with cross section times branching ratio Bσ = (2.8±1.0) μb; similar effect is observed in K −π +p with Bσ = (2.3 ± 0.3) μb. The effect is seen only in the positive charge state, in agreement with an interpretation as Λ c +. However, it is pointed out that in the same experiment, the non-charmed hyperon state Σ(1385) + also has a cross section much larger than its corresponding negative charge state Σ(1385) −.

Diffraction Dissociation of High-Energy Protons on Hydrogen and Deuterium Targets

We report results from a measurement of the inclusive processes pp ..-->.. Xp and pd ..-->.. Xd in the range 5 < M/sub x//sup ts2//s < 0.1, 0.01 9 or approx. = 0.1 (GeV/c)/sup 2/, and incident proton momenta of 65, 154, and 372 GeV/c. Both pp and pd data show an exponential t dependence and a dominant 1/M/sub x//sup ts2/ behavior for M/sub x//sup ts2//s 9 or approx. = 0.05. By comparing pp and pd data we test factorization and, using the Glauber model, we measure the XN total cross section, sigma/sub X N/ = 43 +- 10 mb.

Absorptive corrections to the inclusive spectrum and the bare triple-pomeron coupling

Using the AKG cutting rules we compute the absorptive corrections to the inclusive pp → pX spectrum in the triple-Regge region. The absorption corrections are very large (much larger than in the elastic amplitude) and are quite sensitive to the t dependence of the triple-pomeron coupling on its “third leg”. Since this t dependence cannot be measured it is impossible to extract from inclusive data the exact value of the triple-pomeron coupling. The phenomenological consequences both for the rise with s of σ T pp and for the tests of pomeron factorization are carefully studied.

Triple Regge and finite mass sum rule analysis of the inclusive reaction pp → pX

We present the results of a comprehensive analysis of inclusive pp → pX data in terms of the triple Regge formalism. We use all available data and in the theory include PPP, PPR, RRP, RRR, ππP, and ππR terms. Further we examine the importance of interference terms (e.g. PRP) and present solutions with the triple pomeron either vanishing or non-vanishing at t = 0. Predictions are made for both pp → pX and pn → pX at NAL and ISR energies. In addition, finite mass sum rules (FMSR), constructed from low-mass diffractive dissociation data, are shown to be in good agreement with the high-energy, high-mass fits. The energy, momentum transfer and moment dependence of the FMSR are discussed in detail.

Correlations between the leading proton and pions in high-energy proton-proton collisions

The study of inclusive rapidity spectra pp → pX and pp → pπX at high energies provides a test of the assumptions of the diffractive excitation model. The magnitude and shape of correlations between the leading proton and produced pions favours a modified model, in which the diffractive cluster decays longitudinally, rather than isotropically.

Phenomenological failure of sum rules for inclusive distributions based on PCAC

PCAC is applied to the inclusive processes pp yields piplus or minusX, K⁺p Y pi⁻ X, pi ⁻p yields pi plus or minusX; the results are found to be negative in the sense that the sum rules predicted by PCAC are not phenomenologically satisfied. An explanation for the discrepancy of the sum rules is offered; it is concluded that discrepancies in the sum rules should appear for increasing-multiplicity final states and, as a consequence, for the inclusive distributions. (LBS)

Observation of vector meson production in inclusive pp reactions

We have measured cross sections, rapidity and transverse momentum distributions, and vector meson polarization for the reactions pp→ ϱ o +anything, pp→ ω+charged particles, and pp→ K ∗±+ anything at incident laboratory momenta of 12 and 24 GeV/ c. We discuss various consequences of our results as well as possible connections with lepton pair production.