44294435
Bounding the Higgs boson width through interferometry.
We study the change in the diphoton-invariant-mass distribution for Higgs boson decays to two photons, due to interference between the Higgs resonance in gluon fusion and the continuum background amplitude for gg→γγ. Previously, the apparent Higgs mass was found to shift by around 100 MeV in the standard model in the leading-order approximation, which may potentially be experimentally observable. We compute the next-to-leading-order QCD corrections to the apparent mass shift, which reduce it by about 40%. The apparent mass shift may provide a way to measure, or at least bound, the Higgs boson width at the Large Hadron Collider through "interferometry." We investigate how the shift depends on the Higgs width, in a model that maintains constant Higgs boson signal yields. At Higgs widths above 30 MeV, the mass shift is over 200 MeV and increases with the square root of the width. The apparent mass shift could be measured by comparing with the ZZ* channel, where the shift is much smaller. It might be possible to measure the shift more accurately by exploiting its strong dependence on the Higgs transverse momentum.
58938119
Exclusive soft function for Drell-Yan at next-to-next-to-leading order
We present next-to-next-to-leading-order (NNLO) results for an exclusive soft function that appears in a recently developed factorization theorem for transverse momentum distributions. The factorization theorem, derived using the Soft Collinear Effective Theory, involves both a soft function and unintegrated nucleon distribution functions fully differential in momentum coordinates. The soft function is given by the vacuum matrix element of soft Wilson lines and is also fully differential in all components. We give results and relevant technical details for the NNLO calculation of the soft function, including finite parts, and derive the corresponding anomalous dimension. These results are necessary for achieving low transverse momentum resummation at next-to-next-to-leading-logarithmic accuracy in this effective field theory approach with unintegrated distribution functions.
118708445
Jet vetoes for Higgs boson production at future hadron colliders
We study Higgs boson production in exclusive jet bins at possible future 33 and 100 TeV proton-proton colliders. We compare the cross sections obtained using fixed-order perturbation theory with those obtained by also resuming large logarithms induced by the jet-binning in the gluon-fusion and associated production channels. The central values obtained by the best-available fixed-order predictions differ by $10-20\%$ from those obtained after including resummation over the majority of phase-space regions considered. Additionally, including the resummation dramatically reduces the residual scale variation in these regions, often by a factor of two or more. We further show that in several new kinematic regimes that can be explored at these high-energy machines, the inclusion of resummation improvement is mandatory.
116807042
Disentangling radiative corrections using the high-mass Drell-Yan process at the LHC
We present a detailed numerical study of lepton-pair production via the Drell-Yan process above the Z-peak at the LHC. Our results consistently combine next-to-next-to-leading order QCD corrections and next-to-leading order electroweak effects, and include the leading photon-initiated processes using a recent extraction of the photon distribution function. We focus on the effects of electroweak corrections and of photon-photon scattering contributions, and demonstrate which kinematic distributions exhibit sensitivity to these corrections. We show that a combination of measurements allows them to be disentangled and separately determined.
118502239
Electroweak Corrections at High Energies
We present a survey of the most abundant processes at the LHC for sensitivity to electroweak corrections at \sqrt{s} = 8, 14, 33, and 100 TeV proton-proton collision energies. The processes studied are pp -> dijet, inclusive W and Z, W/Z+jets, and WW. In each case we compare the experimental uncertainty in the highest kinematic regions of interest with the relative magnitude of electroweak corrections and fixed-order \alpha_S calculations.
3842086
Higgs-boson production through gluon fusion at NNLO QCD with parton showers
We discuss how the UN2LOPS scheme for matching next-to-next-to-leading order (NNLO) calculations to parton showers can be applied to processes with large higher-order perturbative QCD corrections. We focus on Higgs-boson production through gluon fusion as an example. We also present an NNLO fixed-order event generator for this reaction.
118638462
Branching Fractions and CP Asymmetries of B --> K_0*(1430) rho and B --> K_0^*(1430) phi Decays in the Family Nonuniversal Z' Model
In this work, within the QCD factorization approach, we investigate the branching fractions and CP asymmetries of decays $B \to K_0^*(1430)\rho$ and $B \to K_0^*(1430)\phi$ under two different scenarios both in the standard model and the family nonuniversal $Z^\prime$ model. We find that the annihilation terms play crucial roles in these decays and lead to the main uncertainties. For decays $B^- \to \bar K_0^{*-} (1430)\rho^0 (\omega)$, the new $Z^\prime$ boson could change branching fractions remarkably. However, for other decays, its contribution might be clouded by large uncertainties from annihilations. Unfortunately, neither the standard model nor $Z^\prime$ model can reproduce all experimental data under one certain scenario. We also noted that the CP asymmetries of $B^-\to \bar K_0^{*-}(1430) \rho^0 (\omega)$ could be used to identify the$K_0^*(1430)$ meson and search for the new physics contribution.
123079556
Reply to "Comment on 'Noncoplanarity effects in proton-proton bremsstrahlung' "
We respond to the Comment by Huisman and Kalantar-Nayestanaki [Phys. Rev. C 64, 029801 (2001)]. In particular, we point out that the proposal to present noncoplanar proton-proton bremsstrahlung data as squared matrix elements involves unresolved theoretical problems.
73528276
Temporal characteristics of a SASE FEL
We have performed a single-shot, time-resolved measurement of the output field of a SASE FEL using the frequency-resolved optical gating (FROG) technique. The measurement reveals the phase and the amplitude of the SASE output as functions of time and frequency, hence enables us to perform a full characterization of the SASE FEL output. We examined both the single-shot field evolution as well as the statistics over multiple shots on the phase and intensity evolution.
118518380
Investigating the Effect of Family Non-universal $Z^\prime$ Boson in $B \to \phi\phi$ Decay
Within the perturbative QCD approach, we re-calculate the branching ratio and polarization fractions of the pure annihilation decay $B \to \phi \phi$ in both the standard model (SM) and the family non-universal $Z^\prime$ model. We find that this decay is dominated by the longitudinal part, while the transverse parts are negligibly due to the absence of the $(S-P)(S+P)$-type operator. In SM, the branching ratio is predicted as $(4.4^{+0.8+0.3}_{-0.6-0.5}) \times 10^{-8}$, which is larger than the previous predictions. With an additional $Z^\prime$ boson, the branching ratio can be enhanced by a factor of 2, or reduced one half in the allowed parameters space. These results will be tested by the ongoing LHCb experiment and forthcoming Super-B experiments. Moreover, if the $Z^\prime$ boson could be directly detected at hadron collider, this decay can be used to constrain its mass and the couplings in turn.
121496385
Meson exchange currents in neutron-proton bremsstrahlung
Background: The meson exchange current (MEC) contribution is important in the neutron-proton bremsstrahlung process (np gamma) when the two nucleon-scattering angles are small. However, our understanding of such effects is limited, and the reason why meson exchange current effects dominate the np gamma cross section has not been thoroughly investigated. Purpose: The primary focus of this investigation is to understand the origin of the MEC contribution, to identify the leading MEC amplitudes, and to comprehend why these MEC amplitudes dominate the np gamma cross sections. Method: We used a new method that combines the one-boson-exchange (OBE) approach with the soft-photon approach to define 10 different np gamma amplitudes. These amplitudes are used to calculate np gamma cross sections at 225 MeV for nucleon laboratory scattering angles lying between 12(degrees) and 43(degrees). The results of these calculations are then compared to investigate the meson exchange current effect in np gamma. Results: (i) The OBE amplitude M(np gamma,mu)(PS) and the two-u-two-t special (TuTts) soft-photon amplitude M(np gamma,mu)(TuTts) predict quantitatively similar np gamma cross sections. (ii) The MEC effect is found to be significant when the two nucleon-scattering angles are far from the elastic limit (45(degrees)), but the effect is insignificant when the nucleon angles approach the elastic limit. (iii) The origin of the MEC effect and the leading MEC amplitudes have been identified in this investigation. Furthermore, the reason is now clear why the leading MEC amplitudes dominate the np gamma cross section when the nucleon-scattering angles are small. (iv) The contribution from the anomalous magnetic moments of the proton and the neutron is confirmed to be negligibly small. (v) In general, the theoretical cross sections using the amplitude M(np gamma,mu)(PS), or the amplitude M(np gamma,mu)(TuTts), are consistent with the triple differential cross sections recently measured at the Los Alamos National Laboratory. However, there exists an unexplained discrepancy between theory and experiment in some cases. Conclusions: The findings of this investigation have enhanced our understanding of the meson exchange current effect in np gamma. The comparative amplitude method introduced can be used for other bremsstrahlung investigations.