Search results for "Standard Model"
showing 10 items of 1206 documents
Reduced hadronic uncertainty in the determination of $V_{ud}$
2018
We analyze the universal radiative correction $\Delta_R^V$ to neutron and superallowed nuclear $\beta$ decay by expressing the hadronic $\gamma W$-box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the $\gamma W$ interference structure function $F_3^{(0)}$. By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of $\Delta_R^V = 0.02467(22)$, wherein the hadronic uncertainty is reduced. Assuming other Standard Model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of $|V_{ud}| = 0.97366(15)$, raising tension with …
New physics constraints from atomic parity violation in Cs133
2021
Our improved calculation of the nuclear spin-independent parity violating electric dipole transition amplitude ($E{1}_{\mathrm{PV}}$) for $6s{^{2}S}_{1/2}\ensuremath{-}7s{^{2}S}_{1/2}$ in $^{133}\mathrm{Cs}$ in combination with the most accurate (0.3%) measurement of this quantity yields a new value for the nuclear weak charge ${Q}_{W}=\ensuremath{-}73.71(26{)}_{ex}(23{)}_{th}$ against the Standard Model (SM) prediction ${Q}_{W}^{\mathrm{SM}}=\ensuremath{-}73.23(1)$. The advances in our calculation of $E{1}_{\mathrm{PV}}$ have been achieved by using a variant of the perturbed relativistic coupled-cluster theory, which treats the contributions of the core, valence, and excited states to $E{1…
Dark Matter in Leptoquark Portal
2021
A beyond the standard model portal scenario for Majorana fermion dark matter (DM) particle with leptoquark being the mediator field is of the main focus of this study. We explore the parameter space of the only unknown coupling in the model which is sensitive to all three main features of a DM model, namely, relic density, direct detection as well as indirect detection, while being consistent with the collider searches. The AMS-02 data for antiproton flux imposes stringent bound till date which excludes the DM mass up to \(400\,\)GeV at 95% C.L. The LUX 2016 data for DM-neutron scattering cross section allows the region compatible with relic density; however, the future sensitivity of LZ ex…
Determination of the θ23 octant in long baseline neutrino experiments within and beyond the standard model
2018
The recent data indicate that the neutrino mixing angle $\theta_{23}$ deviates from the maximal-mixing value of 45$^\circ$, showing two nearly degenerate solutions, one in the lower octant (LO) ($\theta_{23}45^\circ$). We investigate, using numerical simulations, the prospects for determining the octant of $\theta_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($\theta_{23}-45^\circ$, $\delta$)--plane, where $\delta$ is the $CP$ phase, showing the true values of $\theta_{23}$ for which the octant can be experimentally determined at 3$\,\sigma$, 2$\,\sigma$ and 1$\,\sigma$ confidence level. In particular, we study the impact of the p…
Supersymmetric electroweak baryogenesis
1999
We calculate the baryon asymmetry generated at the electroweak phase transition in the minimal supersymmetric standard model, using a new method to compute the CP-violating asymmetry in the Higgsino flux reflected into the unbroken phase. The method is based on a Higgs insertion expansion. We find that the CP asymmetry at leading order is proportional to the change in $\tan \beta$ in the bubble wall, which is at most of order $10^{-2}$, while at next-to-leading order this suppression factor disappears. This result may enhance the final baryon asymmetry generated during the electroweak phase transition for small $\Delta \beta (< 10^{-3}$).
Detecting the Diffuse Supernova Neutrino Background in the future Water-based Liquid Scintillator Detector Theia
2021
A large-scale neutrino observatory based on water-based liquid scintillator (WbLS) will be excellently suited for a measurement of the diffuse supernova neutrino background (DSNB). The WbLS technique offers high signal efficiency and effective suppression of the otherwise overwhelming background from neutral-current interactions of atmospheric neutrinos. To illustrate this, we investigate the DSNB sensitivity for two configurations of the future Theia detector by developing the expected signal and background rejection efficiencies along a full analysis chain. Based on a statistical analysis of the remaining signal and background rates, we find that a rather moderate exposure of $190\text{ }…
Search for new phenomena in the WW→lνl′ν′ final state in pp collisions at s=7TeV with the ATLAS detector
2013
This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at root s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb(-1). WW -> lvl'v' (l,l' = e or mu) final states are considered and the distribution of the transverse mass of the W W candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively.
Search for ResonantWWandWZProduction inpp¯Collisions ats=1.96 TeV
2011
We search for resonant WW or WZ production using up to 5.4 fb-1 of integrated luminosity collected by the D0 experiment in Run II of the Fermilab Tevatron Collider. The data are consistent with the standard model background expectation, and we set limits on a resonance mass using the sequential standard model (SSM) W' boson and the Randall-Sundrum model graviton G as benchmarks. We exclude an SSM W' boson in the mass range 180 - 690 GeV and a Randall-Sundrum graviton in the range 300 - 754 GeV at 95% CL.
Strong Enhancement ofɛ′/ɛthrough Final State Interactions
2000
We quantify the important effect of strong final state interactions in the weak $K\ensuremath{\rightarrow}2\ensuremath{\pi}$ amplitudes, using the measured $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ phase shifts with $J\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ and $I\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0,2$. The final rescattering of the two pions provides a strong enhancement of the $\ensuremath{\Delta}I\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ amplitude, which so far has been neglected in the theoretical predictions of ${\ensuremath{\varepsilon}}^{\ensuremath{'}}/\ensuremath{\varepsilon}$. This correction increases the standard model predictio…
Pseudoscalar decays into lepton pairs from rational approximants
2016
The pseudoscalar decays into lepton pairs P! ‘‘ are analyzed with the machinery of Canterbury approximants, an extension of Pade approximants to bivariate functions. This framework provides an ideal model-independent approach to implement all our knowledge of the pseudoscalar transition form factors driving these decays, can be used for data analysis, and allows to include experimental data and theoretical constraints in an easy way, and determine a systematic error. We find that previous theoretical estimates for these branching ratios have underestimated their theoretical uncertainties. From our updated results, the existing experimental discrepancies for p 0 ! e + e and h! m + m channels…