ترغب بنشر مسار تعليمي؟ اضغط هنا

NLO QCD corrections to W-b-bbar and Z-b-bbar production

154   0   0.0 ( 0 )
 نشر من قبل Laura Reina
 تاريخ النشر 2008
  مجال البحث
والبحث باللغة English




اسأل ChatGPT حول البحث

We present NLO QCD results for W/Z gauge boson production with bottom quark pairs at the Tevatron including full bottom-quark mass effects. We study the impact of QCD corrections on both total cross-section and invariant mass distribution of the bottom-quark pair. Including NLO QCD corrections greatly reduces the dependence of the tree-level cross-section on the renormalization and factorization scales. We also compare our calculation to a calculation that considers massless bottom quarks and find that the bottom-quark mass effects amount to about 8-10% of the total NLO QCD cross-section and can impact the shape of the bottom-quark pair invariant mass distribution, in particular in the low invariant mass region.



قيم البحث

اقرأ أيضاً

88 - Julien Baglio 2016
The study of the Higgs boson properties is one of the most important tasks to be accomplished in the next years, at the Large Hadron Collider (LHC) and at future colliders such as the Future Circular Collider in hadron-hadron mode (FCC-hh), the poten tial 100 TeV follow-up of the LHC machine. In this view the precise study of the Higgs couplings to weak gauge bosons is crucial and requires as much information as possible. After the recent calculation of the next-to-leading order QCD corrections to the production cross sections and differential distributions of a Standard Model Higgs boson in association with a pair of weak bosons, matched with parton shower in the POWHEG-BOX framework, we present the gluon fusion correction $g gto H W^+_{} W^-_{} ( H Z Z)$ to the process $p p to H W^+_{} W^-_{} (H Z Z)$. This correction can be sizeable and amounts to $+3,%$ ($+10,%$) in the $H W^+_{} W^-_{}$ process and $+5,%$ ($+18,%$) in the $H Z Z$ process at the LHC (FCC-hh). We also present the first study of the impact of the bottom--quark initiated channels $bbar{b}to H W^+_{} W^-_{} / H Z Z$ and find that they induce a significant $+18,%$ correction in the $H W^+_{} W^-_{}$ channel at the FCC-hh. We present results on total cross sections and distributions at the LHC and at the FCC-hh.
The forward-backward (FB) asymmetry of $b$ quarks in $e^+e^-$ collisions at the Z pole measured at LEP, $A_{FB}^{0,b} = 0.0992pm0.0016$, remains today the electroweak precision observable with the largest disagreement (2.4$sigma$) with respect to the Standard Model prediction, $(A_{FB}^{0,b})_{_{rm th}} = 0.1030 pm 0.0002$. Beyond the dominant statistical uncertainties, QCD effects, such as $b$-quark showering and hadronization, are the leading sources of $A_{FB}^{0,b}$ systematic uncertainty, and have not been revised in the last twenty years. We reassess the QCD uncertainties of the eight original $A_{FB}^{0,b}$ LEP measurements, using modern parton shower PYTHIA-8 and PYTHIA-8 + VINCIA simulations with nine different implementations of soft and collinear radiation as well as of parton fragmentation. Our analysis, combined with NNLO massive $b$-quark corrections independently computed recently, indicates total propagated QCD uncertainties of $sim$0.7% and $sim$0.3% for the lepton-charge and jet-charge analyses, respectively, that are about a factor of two smaller than those of the original LEP results. Accounting for such updated QCD effects leads to a new $A_{FB}^{0,b} = 0.0996pm0.0016$ average, with a data-theory tension slightly reduced from 2.4$sigma$ to 2.1$sigma$. Confirmation or resolution of this long-term discrepancy requires a new high-luminosity $e^+e^-$ collider collecting orders-of-magnitude more data at the Z pole to significantly reduce the $A_{FB}^{0,b}$ statistical uncertainties.
In this note we compute the flavor-dependent chiral-logarithmic corrections to the decay Z to b bbar in the three site Higgsless model. We compute these corrections diagrammatically in the gaugeless limit in which the electroweak couplings vanish. We also compute the chiral-logarithmic corrections to the decay Z to b bbar using an RGE analysis in effective field theory, and show that the results agree. In the process of this computation, we compute the form of the chiral current in the gaugeless limit of the three-site model, and consider the generalization to the N-site case. We elucidate the Ward-Takahashi identities which underlie the gaugeless limit calculation in the three-site model, and describe how the result for the Z to b bbar amplitude is obtained in unitary gauge in the full theory. We find that the phenomenological constraints on the three-site Higgsless model arising from measurements of Z to b bbar are relatively mild, requiring only that the heavy Dirac fermion be heavier than 1 TeV or so, and are satisfied automatically in the range of parameters allowed by other precision electroweak data.
155 - Jiri.Chyla 2003
Understanding the data on the total cross section $sigma_{tot}($e$^+$e$^-to$e$^+$e$^-bbar{b})$ measured at LEP2 represents a serious challenge for perturbative QCD. In order to unravel the origins of the discrepancy between data and theory, we invest igate the dependence of four contributions to this cross section on $gammagamma$ collision energy. As the reliability of the existing calculations of $sigma_{tot}($e$^+$e$^-to$e$^+$e$^-bbar{b})$ depends, among other things, on the stability of calculations of the cross section $sigma_{tot}(gammagammato bbar{b})$ with respect to variations of the renormalization and factorization scales, we investigate this aspect in detail. We show that in most of the region relevant for the LEP2 data the existing QCD calculations of $sigma_{tot}(gammagammato bbar{b})$ do not exhibit a region of local stability and should thus be taken with caution. The source of this instability is suggested and its phenomenological implications for LEP2 data are discussed.
In this paper we calculate the technicolor correction to the production of a charged top pion in association with a W boson via bbar{b} annihilation at the CERN Large Hadron Collider in the context of the topcolor assisted technicolor model. We find that the cross section of pp rightarrow bbar{b} -> W^{pm}pi_t^{mp} at the tree level can reach a few hundred femtobarns for reasonable ranges of the parameters, roughly corresponding to the result of the process pp -> bbar{b} -> W^{pm}H^{mp} in the minimal supersymmetric standard model; the relative corrections arising from the one-loop diagrams are about a few percent to two dozen percent, and they will increase the cross section at the tree level. As a comparison, we also discuss the size of the hadron cross section via the other subprocess gg -> W^{pm}pi_t^{mp}.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا