Cross Section For Pp Research Articles

Next-to-leading order QCD corrections to [formula omitted] production at 14 TeV LHC

Since the precise study of Higgs gauge couplings is important to test the Standard Model (SM), we calculate the complete next-to-leading order QCD (NLO QCD) correction to the pp→HZW± production in the SM at 14 TeV LHC. Our results show that the NLO QCD correction can enhance the leading-order cross section of pp→HZW± by 45%, when mH=125.3 GeV. We also study the dependence of the LO and NLO corrected cross sections on the renormalization and factorization scale μ. Besides, due to the unbalance of parton distribution functions, we investigate the charge asymmetry of W± in the production of pp→HZW±, which can reach 32.94% for μ=(mH+mZ+mW)/2 at 14 TeV LHC.

Modeling hadronic collisions using genetic programming approach

New technique, Genetic Programming, is presented for modeling total cross section of both pp and ¯ pp collisions from low to high energy regions. Recent total cross section data are taken from Particle Data Group and LHC collaboration. The model seems to fit the experimental data well.

Study of the NN$\eta '$ Production with COSY-11

We describe a new high precision measurement of the production cross-section for the eta' meson in proton-proton collisions for five beam momenta at low access energy region Q conducted at the COSY-11 detection system together with an updated results of all other previous measurements of cross-section for (pp-->pp eta') at COSY-11.

The HERA Proton

The almost 1 fb −1 of ep data collected by the H1 and ZEUS collider exper- iments at HERA allows for a precise determination of the proton's parton distribution functions (PDFs). Measurements used to constrain the PDFs — inclusive and jet cross sections, charm contribution to the F2 proton structure function, F c¯ c 2 — are presented herein. The measurement process itself includes cataloguing the sensitivity of the cross sections to the various sources of correlated systematic uncertainties. In the jet measure- ment, correlations of a statistical nature are also quantified and catalogued. These corre- lations provide a basis to combine measurements of the same physical observable across different time periods, experiments and measurement methodology. The subsequent PDF fitting procedure also takes into account such correlations. The resulting HERAPDF1.5 set based on inclusive data as well as PDF sets derived from inclusive plus charm data are presented togeteher with their predictions for pp cross sections at the LHC.

Relativistic Meson-Proton and Proton-Proton Cross- Sections and Quantum Molecular Dynamics Model

Above 104 GeV/c projectile momenta, the total cross-sections for pp and( p) ̅ p collisions as a function of laboratory beam momentum and center of mass energy, are independent. In the range, 0.1 up to 104 GeV/c the total cross-section depends on the nature of the interacting particles and on the geometrical interpretations in terms of the impact parameter. This could explain in terms of the Quantum Molecular Dynamic QMD model and its ultra relativistic approach UrQMD, in terms of the isospin of the colliding particles, their flavor, and center of mass energies. The model can give also a qualitative success for such dependencies for π^+ p and k^+ p interactions.

Diffractive dissociation of gluons into heavy quark–antiquark pairs in proton–proton collisions

We discuss diffractive dissociation of gluons into heavy quark pairs. The particular mechanism is similar to the diffractive dissociation of virtual photons into quarks, which drives diffractive deep inelastic production of charm in the low-mass diffraction, or large β-region. There, it can be understood, with some reservations, in terms of a valence heavy quark content of the Pomeron. The amplitude for the gp→QQ¯p is derived in the impact parameter and momentum space. The cross section for single diffractive pp→QQ¯pX is calculated as a convolution of the elementary cross section and gluon distribution in the proton. Integrated cross section and the differential distributions in e.g. transverse momentum and rapidity of the charm and bottom quark and antiquark, as well as the quark–antiquark invariant mass are calculated for the nominal LHC energy for different unintegrated gluon distributions from the literature. The ratio of the bottom-to-charm cross sections are shown and discussed as a function of several kinematical variables.

Effect of anomalous couplings on the associated production of a single top quark and a Higgs boson at the LHC

Abstract We consider the production of a single top quark in association with a Higgs boson at the LHC. In particular, we compute the cross sections for the processes pp → thj, thb, thW , thjj, thjb, thW j, thW b in the presence of the anomalous W tb, W W h and tth couplings. We find that the anomalous W tb and tth couplings can enhance the cross sections significantly. We also analyze a few signatures and show that, if these couplings are indeed anomalous, then with enough data, one should be able to observe the production of the Higgs boson in association with single top quark.

Electroweak bosons in heavy-ion collisions with the CMS detector at =2.76 TeV

Electroweak gauge bosons W and Z, do not interact strongly, and thus constitute clean probes of the initial state of nucleus-nucleus collisions. The comparison of their production cross-sections in pp and in nuclear collisions provides an estimate of the nuclear parton distribution functions. Despite the low production cross section of weak bosons compared to other nuclear processes, the relatively clean signal of their leptonic decay channel allows their detection. This paper reports measurements of Z and W bosons, produced in PbPb and pp collisions both at nucleon-nucleon center of mass energy =2.76 TeV with the CMS detector. The Z boson yield and the nuclear modification factor (RAA) corresponding to the integrated luminosity of 150 μb−1 for PbPb collisions are presented. The search for W bosons has been performed in the muon plus neutrino channel, using the data sample with integrated luminosity of 7.2 μb−1 for PbPb collisions. Event centrality an muon pseudorapidity dependencies are studied for the complete W candidate sample as well as samples separated by charge (W+ and W−).

Measurement of the cross-section for Z → e+e- production in pp collisions at $\sqrt{s}=7$ TeV

Abstract A measurement of the cross-section for pp → Z → e+e− is presented using data at $\sqrt{s}=7$ TeV corresponding to an integrated luminosity of 0.94 fb−1. The process is measured within the kinematic acceptance p T > 20 GeV/c and 2 < η < 4.5 for the daughter electrons and dielectron invariant mass in the range 60–120 GeV/c 2. The cross-section is determined to be $\sigma \left( {\mathrm{pp}\to \mathrm{Z}\to {{\mathrm{e}}^{+}}{{\mathrm{e}}^{-}}} \right)=76.0\pm 0.8\pm 2.0\pm 2.6\;\mathrm{pb}$ where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD.

Measurement of the ratio of three-jet to two-jet cross sections in [formula omitted] collisions at [formula omitted

We present a measurement of the ratio of multijet cross sections in pp¯ collisions at s=1.96 TeV at the Fermilab Tevatron Collider. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb−1 collected with the D0 detector. The ratio of the inclusive three-jet to two-jet cross sections, R3/2, has been measured as a function of the jet transverse momenta. The data are compared to QCD predictions in different approximations. Popular tunes of the pythia event generator do not agree with the data, while sherpa provides a reasonable description of the data. A perturbative QCD prediction in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects, gives a good description of the data.

New Results from the CMS experiment

We'll present recent results from the CMS experiment on measureme nts, such as the total inelastic pp cross section, diffractive phenomena, leading particle spectra and energy flow in the forward region, measurements relevant for tuning o f Monte Carlo programs used for cosmic rays studies. We'll also give a brief overv iew of the searches for new physics and the recent results on the discovery of a higgs-like p article with a mass of 125 GeV.

Diffraction studies with ALICE

The measurement of Single and Double Diffraction cross-sections in pp collisions by the ALICE Collaboration at √ s = 0.9, 2.76 and 7 TeV will be presented. The relevance of diffraction to the understanding of inelastic pp interactions will be discussed and the measurement of the inelastic pp cross-section will be presented. A brief status of ALICE’s studies of centrally produced systems, selected with a two-pseudorapidity gap topology, will also be given.

Results from TOTEM

The TOTEM experiment at the CERN LHC is focussed on the measurement of the elastic proton-proton scattering, the total pp cross-section, and all kinds of di ffractive phenomena. Detectors housed in Roman Pots which can be moved close to the out- going proton beams allow to trigger on elastic and diffractive protons and to determine their parameters like the momentum loss and the transverse momentum transfer. In ad- dition, charged particle detectors in the forward regions detect almost all inelastic events. Together with the CMS detector, a large solid angle is covered enabling precise studies of Min. Bias as well as Single Diffractive and Double Pomeron Interactions. The results will considerably help the interpretation of the Cosmic Ray Showers at highest energies and will give insight into the proton structure and the QCD theory of strong interactions. TOTEM measured the elastic pp- scattering over a large range of t (the squared momen- tum transfer) from 10 −3 - 4 GeV 2 . None of the considered models could yield a satisfac- tory fit over the complete range. However, the exponential slope at low |t|-values and the position of the diffractive minimum are well within the extrapolation from lower energies. The total pp cross-section has been determined in different ways from the extrapolation of the elastic scattering to t=0 (optical point) and the inelastic rate: (i) From the elastic scattering using the optical theorem and the CMS, (ii) luminosity independently, using the inelastic rate, elastic scattering and the optical theorem, (iii) � independently, by using elastic scattering, inelastic rate and the CMS luminosity. The results for the total cross- section obtained from the different methods are in excellent agreement with each other. First studies of the data on diffractive phenomena have been performed by correlating the momentum loss of the forward protons with the topology of the particle flux. The data look very promising and further studies will follow. Since the conference, data have also been taken with specialized optics to reach even lower |t|-values. A determination of the � value is now in reach. The TOTEM results and the ways how they have been obtained are described in the publications (1-8) listed below.

Measurement of proton-proton elastic scattering and total cross-section at

At the LHC energy of , under various beam and background conditions, luminosities, and Roman Pot positions, TOTEM has measured the differential cross-section for proton-proton elastic scattering as a function of the four-momentum transfer squared t. The results of the different analyses are in excellent agreement demonstrating no sizeable dependence on the beam conditions. Due to the very close approach of the Roman Pot detectors to the beam center (≈5σbeam) in a dedicated run with β* = 90 m, |t|-values down to 5·10−3 GeV2 were reached. The exponential slope of the differential elastic cross-section in this newly explored |t|-region remained unchanged and thus an exponential fit with only one constant B = (19.9 ± 0.3) GeV−2 over the large |t|-range from 0.005 to 0.2 GeV2 describes the differential distribution well. The high precision of the measurement and the large fit range lead to an error on the slope parameter B which is remarkably small compared to previous experiments. It allows a precise extrapolation over the non-visible cross-section (only 9%) to t = 0. With the luminosity from CMS, the elastic cross-section was determined to be (25.4 ± 1.1) mb, and using in addition the optical theorem, the total pp cross-section was derived to be (98.6 ± 2.2) mb. For model comparisons the t-distributions are tabulated including the large |t|-range of the previous measurement (TOTEM Collaboration (Antchev G. et al), EPL, 95 (2011) 41001).

Summary of Physics Results from the TOTEM Experiment

The TOTEM experiment has performed several measurements related to its physics program in dedicated (high β*, low ℒ) LHC fills at √s = 7 TeV. Under various beam and background conditions, the differential elastic (as a function of |t|), elastic, inelastic and total pp cross-sections have been measured. A measurement of the forward charged particle η density has also been performed. A summary of these measurements is here reported, as well as the first results from runs at the LHC energy of √s = 8 TeV.

Comment on the CMS search for charge-asymmetric production of [formula omitted] boson in [formula omitted] events

A reanalysis is presented on the CMS result on a search for a W′ boson that couples to the top and down quarks. The model is motivated by the Tevatron results on the forward–backward asymmetry of tt¯ pair production. In the evaluation of the theoretical cross section of pp→tt¯j, the interference effect between the SM and W′ amplitudes is shown to be important, though it is ignored in the CMS analysis. The lower mass bound on the W′ boson is relaxed from 840 GeV to 740 GeV at the 95% C.L. due to the interference effect at the leading order calculation of the cross section. The bound is also compared to the top forward–backward asymmetry.

Commentary on “Total Hadronic Cross-Section Data and the Froissart–Martin Bound,” by Fagundes, Menon, and Silva

This commentary on the paper “Total Hadronic Cross-Section Data and the Froissart–Martin Bound,” by Fagundes, Menon, and Silva (Braz. J. Phys. doi: 10.1007/s13538-012-0099-5 , 2012) was invited by the editors of the Brazilian Journal of Physics to appear directly after the above authors’ printed version, in the same journal issue. We here challenge the paper’s conclusions that the Froissart bound was violated. We will show that this conclusion follows from a statistical methodology that we question and will present compelling supplementary evidence that the latest ultrahigh-energy experimental pp cross-section data are consistent with a ln 2 s behavior that satisfies the Froissart bound.

Search for exclusive or semi-exclusive γγ production and observation of exclusive and semi-exclusive e+e− production in pp collisions at $ \sqrt{s}=7 $ TeV

Abstract A search for exclusive or semi-exclusive γγ production, pp → p(*) + γγ + p(*) (where p* stands for a diffractively-dissociated proton), and the observation of exclusive and semi-exclusive e+e− production, pp → p(*) + e+e− + p(*), in proton-proton collisions at $ \sqrt{s}=7 $ TeV, are presented. The analysis is based on a data sample corresponding to an integrated luminosity of 36 pb−1 recorded by the CMS experiment at the LHC at low instantaneous luminosities. Candidate γγ or e+e− events are selected by requiring the presence of two photons or a positron and an electron, each with transverse energy E T > 5.5 GeV and pseudorapidity |η| < 2.5, and no other particles in the region |η| < 5.2. No exclusive or semi-exclusive diphoton candidates are found in the data. An upper limit on the cross section for the reaction pp → p(*) + γγ + p(*), within the above kinematic selections, is set at 1.18 pb at 95% confidence level. Seventeen exclusive or semi-exclusive dielectron candidates are observed, with an estimated background of 0.85 ± 0.28 (stat.) events, in agreement with the QED-based prediction of 16.3 ± 1.3 (syst.) events.

Checks of asymptotia in pp elastic scattering at LHC

We parametrize TOTEM data for the elastic differential pp cross section at s=7 TeV in terms of two exponentials with a relative phase. We employ two previously derived sum rules for pp elastic scattering amplitude in impact parameter space to check whether asymptotia has been reached at the LHC. A detailed study of the TOTEM data for the elastic differential cross section at s=7 TeV is made and it is shown that, within errors, the asymptotic sum rules are satisfied at LHC. We propose to use this parametrization to study forthcoming higher energy data.

Measurement of the cross section for production of $ b\overline b X $ decaying to muons in pp collisions at $ \sqrt {s} = 7 $ TeV

Abstract A measurement of the inclusive cross section for the process pp → $ {\text{b}}\overline {\text{b}} {\text{X}} $ → μμX′ at $ \sqrt {s} = 7 $ TeV is presented, based on a data sample corresponding to an integrated luminosity of 27.9 pb−1 collected by the CMS experiment at the LHC. By selecting pairs of muons each with pseudorapidity |η| < 2.1, the value σ(pp → $ {\text{b}}\overline {\text{b}} {\text{X}} $ → μμX′) = 26.4 ± 0.1 (stat.) ±2.4 (syst.) ±1.1 (lumi.) nb is obtained for muons with transverse momentum p T > 4 GeV, and 5.12 ± 0.03 (stat.) ± 0.48 (syst.) ± 0.20 (lumi.) nb for p T > 6 GeV. These results are compared to QCD predictions at leading and next-to-leading orders.