Heavy Flavor Jets Research Articles

μxboosted-bottom-jet tagging andZ′boson searches

We present a new technique for tagging heavy-flavor jets with p_T > 500 GeV called "mu_x tagging." Current track-based methods of b-jet tagging lose efficiency and experience a large rise in fake rate in the boosted regime. Using muons from B hadron decay, we combine angular information and jet substructure to tag b jets, c jets, light jets, and "light-heavy" jets (those containing B hadrons from gluon splitting). We find tagging efficiencies of epsilon_b = 14%, epsilon_c = 6.5%, epsilon_{light-light} = 0.14%, and epsilon_{light-heavy} = 0.5%, respectively, that are nearly independent of transverse momentum at high energy. We demonstrate the usefulness of this new scheme by examining the discovery potential for multi-TeV leptophobic Z-prime bosons in the boosted-b-tagged dijet channel at the Large Hadron Collider.

Precision measurements of Standard Model parameters and Review of Drell-Yan and vector boson plus jets measurements with the ATLAS detector

The inclusive productions of the W and the on- or off-shell Z/γ * bosons are standard candles at hadron colliders, while the productions of light and heavy-flavour jets in association with a W or a Z boson are important processes to study quantum-chromodynamics (QCD) in multi-scale environments. The measurements of their production cross-sections integrated and differential in several variables have been measured at 7 and 8 TeV centre-of-mass energies and are compared to high-order QCD calculations and Monte Carlo simulations. These measurements have an impact on our knowledge of the parton densities of the proton, and test soft resummation effects and hard emissions for small and large momentum transfers and in multi-scale processes. Precision measurements of fundamental Standard Model parameters in Drell-Yan final states are also performed to describe the angular distributions of the decay lepton.Run-1 studies carried out by the ATLAS Collaboration are re-viewed and first LHC Run-2 results are included.

Flavor tagging TeV jets for physics beyond the Standard Model

We present a new scheme for tagging boosted heavy flavor jets called “µ x tagging.” At the LHC, the primary method to tag b -jets relies on tracking their charged constituents. However, when highly boosted, track-based b -tags lose efficiency, and the probability to mistag light jets rises dramatically. Using muons from B hadron decay and defining a particular combination “x ” of angular information and boost estimation, we find fairly flat efficiencies to tag b -jets, c -jets, light-quark jets, and light-heavy jets (containing B hadrons from gluon splitting) of ϵ b = 14%, ϵ c = 6:5%, ϵ light–light = 0:1%, and ϵ light-heavy = 0:5%, respectively. We demonstrate the usefulness of this new scheme by showing the reach for discovery of a leptophobic Z′ → bb in the dijet channel.

Search for intrinsic charm in vector boson production accompanied by heavy-flavor jets

Up to now, the existence of intrinsic (or valence-like) heavy quark component of the proton distribution functions has not yet been confirmed or rejected. The LHC with pp-collisions at $\sqrt{s}$ = 7-13 TeV can supply us with extra unique information concerning this hypothesis. On the basis of our theoretical studies, it is demonstrated that investigations of the intrinsic heavy quark contributions look very promising in processes like $pp \rightarrow Z/W + c(b) + X$. A ratio of $Z+$ heavy jets over $W+$ heavy jets differential cross section as a function of the leading jet transverse momentum is proposed to maximize the sensitivity to the intrinsic charm component of the proton.

Gluon Radiation off Heavy flavour Jets

It is known that gluon bremsstrahlung emission off heavy flavor jet is suppressed in the forward direction compared to that of light quark due to the mass effect ( ‘ dead cone effect’). Most of the models that address jet quenching generally assume that a jet always travels in straight eikonal path. However, once the eikonal approximation of propagation is called off and jet is allowed to bend, additional gluons pop- up within the so called ‘depopulated’ region deluging the dead cone. This color synchrotron by color charge, once wound in an ambiance of color field, seems to be more physical for better understanding of jet quenching in hot and dense deconfined quark-gluon medium.

Recent results on associated vector boson production with the ATLAS and CMS experiments

Several aspects of the associated vector boson production in pp collisions at √s = 7 TeV and √s = 8 TeV at the LHC have been recently investigated by the ATLAS and CMS collaborations. The production cross sections of the W and Z bosons in association with jets, as well as their ratio and the double differential cross section in the Z + jets final state are presented. Measurements of the cross sections of a vector boson (W or Z) in association with heavy flavour jets (b, c) and a top quark pair are also described. The measured cross sections are compared to expectations based on next-to-leading order QCD calculations as well as on Monte Carlo simulations.

Review of single vector boson production in pp collisions at $$\sqrt{s} = 7$$ s = 7 TeV

This review summarises the main results on the production of single vector bosons in the Standard Model, both inclusively and in association with light and heavy flavour jets, at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of 7 TeV. The general purpose detectors at this collider, ATLAS and CMS, each recorded an integrated luminosity of $\approx 40\,{\rm pb^{-1}}$ and $5\,{\rm fb^{-1}}$ in the years 2010 and 2011, respectively. The corresponding data offer the unique possibility to precisely study the properties of the production of heavy vector bosons in a new energy regime. The accurate understanding of the Standard Model is not only crucial for searches of unknown particles and phenomena but also to test predictions of perturbative Quantum-Chromo-Dynamics calculations and for precision measurements of observables in the electroweak sector. Results from a variety of measurements in which single W or Z bosons are identified are reviewed. Special emphasis in this review is given to interpretations of the experimental results in the context of state-of-the-art predictions.

Study of heavy-flavor quarks produced in association with top-quark pairs ats=7 TeVusing the ATLAS detector

Using a sample of dilepton top-quark pair (ttbar) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, ttbar+b+X or ttbar+c+X, collectively referred to as ttbar+HF. The dataset used corresponds to an integrated luminosity of 4.7 fb-1 of proton--proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF quarks in the ttbar sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b-quarks from the ttbar decays and the third to additional HF production. The dominant background to ttbar+HF in this sample is ttbar+jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. To determine the heavy- and light-flavor content of the additional b-tagged jets, a fit to the vertex mass distribution of b-tagged jets in the sample is performed. The result of the fit shows that 79 +/- 14 (stat.) +/- 22 (syst.) of the 105 selected extra b-tagged jets originate from HF quarks, three standard deviations away from the hypothesis of zero ttbar+HF production. The result for extra HF production is quoted as a ratio (R_HF) of the cross section for ttbar+HF production to the cross section for ttbar production with at least one additional jet. Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. R_HF is measured to be [6.2 +/- 1.1 (stat.) +/- 1.8 (syst.)]% for jets with pT>25 GeV and |eta|<2.5, in agreement with the expectations from Monte Carlo generators.

Searches for light- and heavy-flavour three-jet resonances in pp collisions at [formula omitted

A search for three-jet hadronic resonance production in pp collisions at a centre-of-mass energy of 8 TeV has been conducted by the CMS Collaboration at the LHC with a data sample corresponding to an integrated luminosity of 19.4 fb−1. The search method is model independent, and events are selected that have high jet multiplicity and large values of jet transverse momenta. The signal models explored assume R-parity-violating supersymmetric gluino pair production and have final states with either only light-flavour jets or both light- and heavy-flavour jets. No significant deviation is found between the selected events and the expected standard model multijet and tt¯ background. For a gluino decaying into light-flavour jets, a lower limit of 650 GeV on the gluino mass is set at a 95% confidence level, and for a gluino decaying into one heavy- and two light-flavour jets, gluino masses between 200 and 835 GeV are, for the first time, likewise excluded.

Vector boson+jets as background to top-quark physics at Tevatron and LHC

I review here the latest measurements related to vector boson production in association with light or heavy flavor jets at the Tevatron and at the LHC. The methods to estimate the W+jets and Z+jets background in top-quark analyses are also presented.

Wand Z production in association with light and heavy-flavour jets at the LHC and the Tevatron

Recent results on W and Z production in association with light and heavy-flavour jets at the Tevatron and the LHC are reviewed. The integrated luminosity which is used for physics analysis by each of the two Tevatron experiments (CDF and D0) corresponds to a maximum of≈10 fb −1 , at an energy in the centre of mass of 1.96 TeV. The LHC analyses of ATLAS and CMS use the data sample collected in 2011 which corresponds to an integrated luminosity of≈5 fb −1 , at an energy in the centre of mass of 7 TeV. Events with W and Z bosons accompanied by jets represent one of the main background samples in the analyses of rare Standard Model processes and in searches for New Physics. Furthermore these measurements provide a test of perturbative QCD calculations and probe the strange and heavy flavour cont ent of the proton.

W and Z production in association with light and heavy-flavour jets at the LHC and the Tevatron

Measurements of W and Z production in association with jets provide a stringent test of perturbative QCD calculations. In addition, these measurements are of great relevance to searches for new particles and new interactions as these Standard-Model processes often represent a significant background. In these proceedings, recent results on the W and Z production for light and heavy-flavour jets at the Tevatron and the LHC are presented.

Prompt Photon Production at the Tevatron and LHC

Prompt photon production has been studied by the CDF and DØ experiments at the Fermilab Tevatron collider in pp̅ collisions at the centre of mass energy of √s = 1.96 TeV and by the ATLAS experiment at LHC in pp collisions at √s = 7 TeV.Measurements of the inclusive photon, inclusive photon plus jet, photon plus heavy flavor jet, and diphoton production cross sections are discussed. The results are compared to the perturbative QCD calculations and predictions from Monte Carlo generators.

Measurements of the production cross-section of top quark pairs using the ATLAS detector at the LHC

An overview of several ATLAS measurements of top quark pair production in proton-proton collisions at the LHC at center-of-mass energies of 7 and 8 TeV is presented. Inclusive cross-section measurements of top quark pair production in various decay channels, analyses of differential cross-sections, studies of additional jet activity in top quark pair production, as well as an analysis of top quark pair production with associated heavy flavor jets are presented. All of the measurements shown are in good agreement with the latest Standard Model predictions.

Heavy Flavour Production at HERA

Measurements of heavy-quark production at HERA constrain the structure of the proton, and have provided valuable indications of perturbative QCD. In this publication measurements of heavy-flavour jet cross sections in photoproduction and deep inelastic scattering (DIS), performed by the H1 and ZEUS collaborations, are presented using inclusive techniques for the signal extraction. The results are compared to next-to-leading order QCD calculations and found to be in reasonable agreement with theory predictions.

Search for supersymmetry inppcollisions ats=7 TeVin final states with missing transverse momentum andb-jets with the ATLAS detector

The results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to 2.05 fb−1 of pp collisions at s=7 TeV recorded with the ATLAS detector at the Large Hadron Collider are reported. No significant excess is observed with respect to the prediction for standard model processes. Results are interpreted in a variety of R-parity conserving models in which scalar bottoms and tops are the only scalar quarks to appear in the gluino decay cascade, and in an SO(10) model framework. Gluino masses up to 600–900 GeV are excluded, depending on the model considered.4 MoreReceived 28 March 2012DOI:https://doi.org/10.1103/PhysRevD.85.112006This 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.© 2012 CERN, for the ATLAS Collaboration

Searches for diboson production at the Tevatron in final states containing heavy-flavor jets

Recent searches performed by the CDF and D0 collaborations at the Tevatron for diboson production in final states containing heavy-flavor jets are reported. The searches for WZ and ZZ can be regarded as the ultimate benchmark for the corresponding searches for a low-mass Higgs boson in the WH and ZH final states. Using the exact same techniques as for those Higgs boson searches, the D0 collaboration measured a cross section for WZ/ZZ production of 1.13 +/- 0.36 times its expectation in the standard model, with a diboson signal significance of 3.3 standard deviations (2.9 expected).

Measurement of thett¯production cross section inpp¯collisions ats=1.96 TeVusing events with large missing transverse energy and jets

In this paper we report a measurement of the ttbar production cross section in ppbar collisions at sqrt(s)=1.96 TeV using data corresponding to an integrated luminosity of 2.2fb-1 collected with the CDF II detector at the Tevatron accelerator. We select events with significant missing transverse energy and high jet multiplicity. This measurement vetoes the presence of explicitly identified electrons and muons, thus enhancing the tau contribution of ttbar decays. Signal events are discriminated from the background using a neural network, and heavy flavor jets are identified by a secondary-vertex tagging algorithm. We measure a ttbar production cross section of 7.99 +/- 0.55(stat) +/- 0.76(syst) +/- 0.46(lumi) pb, assuming a top mass m_top = 172.5 GeV/c^2, in agreement with previous measurements and standard model predictions.

Measuring the top Yukawa coupling at the ILC ats=500 GeV

We report on the feasibility of the direct measurement of the top Yukawa coupling g_t at the International Linear Collider (ILC) during its first phase of operation with a center-of-mass energy of 500 GeV. The signal and background models incorporate the non-relativistic QCD corrections which enhance the production cross section near the t-tbar threshold. The e+e- -> t tbar H signal is reconstructed in the 6-jet + lepton and the 8-jet modes. The results from the two channels are combined. The background processes considered are e+e- -> t bbar W- / tbar b W+ (which includes e+e- -> t tbar), e+e- -> t tbar Z, and e+e- -> t tbar g* -> t tbar b bar. We use a realistic fast Monte-Carlo detector simulation. Signal events are selected using event shape variables, through jet clustering, and by identifying heavy flavor jets. Assuming a Higgs mass of 120 GeV, polarized electron and positron beams with (Pe-,Pe+) = (-0.8,+0.3), and an integrated luminosity of 1 ab-1, we estimate that the e+e- -> t tbar H events can be seen with a statistical significance of 5.2 sigma, corresponding to the relative top Yukawa coupling measurement accuracy of |Delta g_t / g_t| = 10%.

Measurement of the top quark pair production cross section in thelepton+jetschannel in proton-antiproton collisions ats=1.96 TeV

We present a measurement of the inclusive top quark pair production cross section in \ppbar collisions at (\sqrt{s}=1.96) TeV utilizing data corresponding to an integrated luminosity of \lumi\ collected with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing one high-$p_{T}$ isolated electron or muon and at least two jets, and we perform three analyses: one exploiting specific kinematic features of \ttbar events, the second using $b$-jet identification, and the third using both techniques to separate \ttbar\ signal from background. In the third case, we determine simultaneously the $t\bar{t}$ cross section and the ratio of the production rates of $W$+heavy flavor jets and $W$+light flavor jets, which reduces the impact of the systematic uncertainties related to the background estimation. Assuming a top quark mass of 172.5 GeV, we obtain $\sigma_{t\bar{t}} = 7.78^{+0.77}_{-0.64} $ pb. This result agrees with predictions of the standard model.