D0 Experiment Research Articles

Impact of dissolved lignin in oxygen delignification and chlorine dioxide stages

While carryover of dissolved lignin between stages in the pulp mill fiber line is a well-known problem, it is still typically seen only as a minor disturbance factor or bias in the control of oxygen (O2) delignification and bleaching stages. The present study, however, reveals that it plays a larger role than anticipated, and that it should be properly analyzed in order to correctly control the process stages. This is especially important for the O2 and D0 stages as the lignin content is still high in these positions. The results of the study show that dissolved lignin carried over between stages may have a significant impact on the bleaching chemical consumption and, indirectly, on the pulp quality. Mill investigations have shown very large variations in the dissolved lignin content in the pulp before the oxygen delignification stage and before the D0 stage that have significantly influenced the bleaching chemical demand and, subsequently, the degree of delignification. In order to develop a better understanding of the mechanisms of the dissolved lignin’s reactions, laboratory O2 and D0 experiments with controlled levels of dissolved lignin were conducted. It was anticipated that a better feedforward control could be achieved using an online dissolved lignin measurement, and results from mill trials are presented. Chlorine dioxide laboratory experiments using different levels of carryover (i.e., different dissolved lignin contents) were conducted. It was concluded that the filtrate kappa number provides a relevant measure of the bleach demand due to the dissolved lignin and that, subsequently, the combined fiber and filtrate kappa number provides an appropriate measure for optimum feedforward control of the stages. Mill results support these findings, which show that the chemical consumption is reduced significantly using the total kappa number. The post-D or post-DE kappa number feedback control can most probably be eliminated by using this technology.

Measurements of the top quark mass with the D0 detector

The mass of the top quark is a fundamental parameter of the standard model (SM) and has to be determined experimentally. In this talk, I present the most recent measurements of the top quark mass in pp‾ collisions at s=1.96 TeV recorded by the D0 experiment at the Fermilab Tevatron Collider. The measurements are performed in final states containing two leptons, using 5.4 fb-1 of integrated luminosity, and one lepton, using 9.7 fb-1 of integrated luminosity. The latter constitutes the most precise single measurement of the mass of the top quark, corresponding to a relative precision of 0.43%. I conclude with a combination of our results with the results by the CDF collaboration, attaining a relative precision of 0.37%.

Evidence for Simultaneous Production of J/ψ and ϒ Mesons.

We report evidence for the simultaneous production of J/ψ and ϒ mesons in 8.1 fb^{-1} of data collected at sqrt[s]=1.96 TeV by the D0 experiment at the Fermilab pp[over ¯] Tevatron Collider. Events with these characteristics are expected to be produced predominantly by gluon-gluon interactions. In this analysis, we extract the effective cross section characterizing the initial parton spatial distribution, σ_{eff}=2.2±0.7(stat)±0.9(syst) mb.

Predictions for the top-quark forward-backward asymmetry at high invariant pair mass using the principle of maximum conformality

The D0 collaboration at FermiLab has recently measured the top-quark pair forward-backward asymmetry in $\bar p p \to t \bar{t} X$ reactions as a function of the $t\bar{t} $ invariant mass $M_{t\bar{t}}$. The D0 result for $A_{\rm FB}(M_{t\bar{t}}>650\, {\rm GeV})$ is smaller than $A_{\rm FB}(M_{t\bar{t}})$ obtained for small values of $M_{t\bar{t}}$, which may indicate an "increasing-decreasing" behavior for $A_{\rm FB}(M_{t\bar{t}}>M_{\rm cut})$. This behavior is not explained using conventional renormalization scale-setting, even by a next-to-next-to-leading order (N$^2$LO) QCD calculation -- one predicts a monotonically increasing behavior. In the conventional scale-setting method, one simply guesses a single renormalization scale $\mu_r$ for the argument of the QCD running coupling and then varies it over an arbitrary range. However, the conventional method has inherent difficulties. ...... In contrast, if one fixes the scale using the Principle of Maximum Conformality (PMC), the resulting pQCD predictions are renormalization-scheme independent since all of the scheme-dependent $\{\beta_i\}$-terms in the QCD perturbative series are resummed into the QCD running couplings at each order. ...... In this paper we show that if one applies the PMC to determine the top versus anti-top quark forward-backward asymmetry by properly using the pQCD predictions up to N$^2$LO level, one obtains the predictions without renormalization scheme or scale ambiguities. ...... In addition, the PMC prediction for $A_{\rm FB}(M_{t\bar{t}}> M_{\rm cut})$ shows an "increasing-decreasing" behavior for increasing values of $M_{\rm cut}$ which is not observed in the NLO and N$^2$LO predictions for $A_{\rm FB}(M_{t\bar{t}}> M_{\rm cut})$ with conventional scale-setting. This behavior could be tested by the future more precise measurements at the LHC.

Condensate-enclosed chiral-bag model of the proton and pp elastic scattering at LHC 13 TeV

Our investigation of high energy [Formula: see text] and [Formula: see text] elastic scattering over the last ten years has led us to consider that the proton has three regions: (i) an outer region consisting of a quark–antiquark [Formula: see text] condensate ground state (also described as quark–antiquark outer cloud), (ii) an inner shell of topological (geometrical) baryonic charge of size [Formula: see text] 0.44 fm, and (iii) a core of size [Formula: see text] 0.2 fm, where the three valence quarks of a proton with baryonic charges are confined. The proton structure that has emerged leads to four main elastic scattering processes in [Formula: see text] scattering. The first process (which gives rise to diffraction scattering) is described by a profile function. The second process involves multiple [Formula: see text]-exchanges. The third process in [Formula: see text] scattering is quark–quark scattering via gluon–gluon interaction. The fourth process — which appears for the first time in our investigation of [Formula: see text] scattering — is a glancing collision at the boundary of a proton with that of the other proton. To describe quantitatively the four processes, their parameters have to be determined. For this purpose, we investigate: (i) [Formula: see text] 7 TeV [Formula: see text] measured by the TOTEM Collaboration and (ii) [Formula: see text] 1.96 TeV [Formula: see text] measured by the D0 Collaboration. Once the parameters are satisfactorily obtained, we calculate [Formula: see text] [Formula: see text] at 7 TeV and compare with the TOTEM data. We also calculate [Formula: see text] [Formula: see text] at 1.96 TeV and compare with the D0 data. We then predict [Formula: see text] elastic [Formula: see text] at 13 TeV which will soon be measured at LHC by the TOTEM Collaboration. This measurement will establish how well we have predicted the 13 TeV [Formula: see text] and determined the structure of the proton.

Inclusive Production of the X(4140) State in pp[over ¯] Collisions at D0.

We present a study of the inclusive production of the X(4140) state with the decay to the J/ψϕ final state in hadronic collisions. Based on 10.4 fb^{-1} of pp[over ¯] collision data collected by the D0 experiment at the Fermilab Tevatron collider, we report the first evidence for the prompt production of an X(4140) state and find the fraction of X(4140) events originating from b hadrons to be f_{b}=0.39±0.07(stat)±0.10(syst). The ratio of the nonprompt X(4140) production rate to the B_{s}^{0} yield in the same channel is R=0.19±0.05(stat)±0.07(syst). The values of the mass M=4152.5±1.7(stat)_{-5.4}^{+6.2}(syst) MeV and width Γ=16.3±5.6(stat)±11.4(syst) MeV are consistent with previous measurements.

Top quark pair production at NNLO in the quark-antiquark channel

We present the derivation of the NNLO two-parton final state contributions to top pair production in the quark-antiquark channel proportionnal to the leading colour factor $N_c^2$. Together with the three and four-parton NNLO contributions presented in a previous publication, this enables us to complete the phenomenologically most important NNLO corrections to top pair hadro-production in this channel. We derive this two-parton contribution using the massive extension of the NNLO antenna subtraction formalism and implement those corrections in a parton-level event generator providing full kinematical information on all final state particles. In addition, we also derive the heavy quark contributions proportional to $N_h$. Combining the new leading-colour and heavy quark contributions together with the light quark contributions derived previously, we present NNLO differential distributions for LHC and Tevatron. We also compute the differential top quark forward-backward asymmetry at Tevatron and find that our results are in good agreement with the measurements by the D0 collaboration.

Heavy flavor at the Tevatron

The CDF and D0 experiments at the Tevatron proton-antiproton collider have pioneered and established the role of hadron collisions in exploring flavor physics through a broad program that continues to offer competitive results. I report on latest results in the flavor sector obtained using the whole CDF and D0 data sets corresponding to ∼ 10 fb−1 of integrated luminosity; including B-mesons spectroscopy and production asymmetries, flavor specific decay bottom-strange mesons lifetime. I also present measurements of direct and indirect CP violation in bottom and charm meson decays.

QCD analysis of W- and Z-boson production at Tevatron

Recent measurements of the $W$-boson charge asymmetry and of the $Z$-boson production cross sections, performed at the Tevatron collider in Run II by the D0 and CDF collaborations, are studied using the HERAFitter framework to assess their impact on the proton parton distribution functions (PDFs). The Tevatron measurements, together with deep-inelastic scattering data from HERA, are included in a QCD analysis performed at next-to-leading order, and compared to the predictions obtained using other PDF sets from different groups. Good agreement between measurements and theoretical predictions is observed. The Tevatron data provide significant constraints on the $d$-valence quark distribution.

Resolving the Tevatron Top Quark Forward-Backward Asymmetry Puzzle: Fully Differential Next-to-Next-to-Leading-Order Calculation.

We determine the dominant missing standard model (SM) contribution to the top quark pair forward-backward asymmetry at the Tevatron. Contrary to past expectations, we find a large, around 27%, shift relative to the well-known value of the inclusive asymmetry in next-to-leading order QCD. Combining all known standard model corrections, we find that A(FB)(SM)=0.095±0.007. This value is in agreement with the latest DØ measurement [V. M. Abazov et al. (D0 Collaboration), Phys. Rev. D 90, 072011 (2014)] A(FB)(D∅)=0.106±0.03 and about 1.5σ below that of CDF [T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 87, 092002 (2013)] A(FB)(CDF)=0.164±0.047. Our result is derived from a fully differential calculation of the next-to-next-to leading order (NNLO) QCD corrections to inclusive top pair production at hadron colliders and includes-without any approximation-all partonic channels contributing to this process. This is the first complete fully differential calculation in NNLO QCD of a two-to-two scattering process with all colored partons.

Tevatron constraints on models of the Higgs boson with exotic spin and parity using decays to bottom-antibottom quark pairs.

Combined constraints from the CDF and D0 Collaborations on models of the Higgs boson with exotic spin J and parity P are presented and compared with results obtained assuming the standard model value JP=0+. Both collaborations analyzed approximately 10 fb(-) of proton-antiproton collisions with a center-of-mass energy of 1.96 TeV collected at the Fermilab Tevatron. Two models predicting exotic Higgs bosons with JP=0- and JP=2+ are tested. The kinematic properties of exotic Higgs boson production in association with a vector boson differ from those predicted for the standard model Higgs boson. Upper limits at the 95% credibility level on the production rates of the exotic Higgs bosons, expressed as fractions of the standard model Higgs boson production rate, are set at 0.36 for both the JP=0- hypothesis and the JP=2+ hypothesis. If the production rate times the branching ratio to a bottom-antibottom pair is the same as that predicted for the standard model Higgs boson, then the exotic bosons are excluded with significances of 5.0 standard deviations and 4.9 standard deviations for the JP=0- and JP=2+ hypotheses, respectively.

D0 diffractive summary

We present a summary of results from studies of diffraction at the Fermilab Tevatron collider by the D0 experiment. These include the elastic scattering measurement and studies of dijet exclusive production using Run II data. A brief description of Run I results is also given.

Review of Tevatron results: Top quark physics

We present results on top quark physics from the CDF and D0 collaborations at the Fermilab Tevatron [Formula: see text] collider. These include legacy results from Run II that were published or submitted for publication before mid-2014, as well as a summary of Run I results. The historical perspective of the discovery of the top quark in Run I is also described.

Review of physics results from the Tevatron

We present a comprehensive review of the physics results obtained by the CDF and D0 collaborations up to summer 2014, with emphasis on those achieved in the Run II of the Tevatron collider which delivered a total integrated luminosity of ~10 fb-1 at [Formula: see text]. The results are presented in six main physics topics: QCD, Heavy Flavor, Electroweak, Top quark, Higgs boson and searches for New Particles and Interactions. The characteristics of the accelerator, detectors, and the techniques used to achieve these results are also briefly summarized.

Review of physics results from the Tevatron: QCD physics

We present a summary of results from studies of quantum chromodynamics at the Fermilab Tevatron collider by the CDF and the D0 experiments. These include Run II results for the time period up to the end of Summer 2014. A brief description of Run I results is also given. This review covers a wide spectrum of topics, and includes measurements with jet and vector boson final states in the hard (perturbative) energy regime, as well as studies of soft physics such as diffractive and elastic scatterings, underlying and minimum bias events, hadron fragmentation, and multiple parton interactions.

Review of physics results from the Tevatron: Searches for new particles and interactions

We present a summary of results for searches for new particles and interactions at the Fermilab Tevatron collider by the CDF and the D0 experiments. These include results from Run I as well as Run II for the time period up to July 2014. We focus on searches for supersymmetry, as well as other models of new physics such as new fermions and bosons, various models of excited fermions, leptoquarks, technicolor, hidden-valley model particles, long-lived particles, extra dimensions, dark matter particles and signature-based searches.

Mixing asymmetries inBmeson systems, the D0 like-sign dimuon asymmetry, and generic new physics

The measurement of a large like-sign dimuon asymmetry $A^b_{SL}$ by the D0 experiment at the Tevatron departs noticeably from Standard Model expectations and it may be interpreted as a hint of physics beyond the Standard Model contributing to $\Delta B\neq 0$ transitions. In this work we analyse how the natural suppression of $A^b_{SL}$ in the SM can be circumvented by New Physics. We consider generic Standard Model extensions where the charged current mixing matrix is enlarged with respect to the usual $3\times 3$ unitary Cabibbo-Kobayashi-Maskawa matrix, and show how, within this framework, a significant enhancement over Standard Model expectations for $A^b_{SL}$ is easily reachable through enhancements of the semileptonic asymmetries $A^d_{SL}$ and $A^s_{SL}$ of both $B^0_d$ - $\bar B^0_d$ and $B^0_s$ - $\bar B^0_s$ systems. Despite being insufficient to reproduce the D0 measurement, such deviations from SM expectations may be probed by the LHCb experiment.

Measurement of the forward-backward asymmetry in the production of B(±) mesons in pp̄ collisions at √s=1.96 TeV.

We present a measurement of the forward-backward asymmetry in the production of B(±) mesons, A(FB)(B(±)), using B(±)→J/ψK(±) decays in 10.4 fb(-1) of pp̄ collisions at sqrt[s]=1.96 TeV collected by the D0 experiment during Run II of the Tevatron collider. A nonzero asymmetry would indicate a preference for a particular flavor, i.e., b quark or ̄b antiquark, to be produced in the direction of the proton beam. We extract A(FB)(B(±)) from a maximum likelihood fit to the difference between the numbers of forward- and backward-produced B(±) mesons. We measure an asymmetry consistent with zero: A(FB)(B(±))=[-0.24±0.41 (stat)±0.19 (syst)]%.

High Energy Resummation: BFKL vs Sudakov

In this talk, we review recent theoretical developments on QCD resummation in high energy scattering processes in pp and pA collisions. In particular, we will show that the transverse momentum resummation (Sudakov) can be performed consistently in the small-x factorization formalism (BFKL) at the leading double logarithmic approximation. We further discuss the physics beyond the above approximation, and show that the TMD resummation at next-to-leading logarithmic order can describe the dijet production experimental data from D0 collaboration. Finally, we comment on the TMD resummation effects in the so-called Mueller-Navelet jet production in hadronic collisions.

Top Quark Mass from the Tevatron and LHC Colliders

The discovery of the top quark in 1995 has been one of the great successes of the CDF and D0 experiments at the Fermilab Tevatron collider. Since then, many measurements of the top quark properties have been performed in different channels and using many methods. The importance of measuring its mass lies in the possibility of verifying the predictions and the consistency of the Standard Model as well as in setting constraints on possible, still unobserved, physics. In 2010, the new CERN experiments, ATLAS and CMS, started to measure the top quark properties exploiting the large amount of data collected at the Large Hadron Collider. In March 2014, the very first combination of measurements from all the four experiments has been performed yielding Mtop = 173.34 ± 0.76 GeV, with a precision below 0.5%. In these proceedings a selected review of the most recent or relevant results obtained by the Tevatron and LHC Collaborations is presented.