scholarly journals Branching fraction for Z decays to four leptons and constraints on new physics

2019 ◽  
Vol 99 (1) ◽  
Author(s):  
J. Lovelace Rainbolt ◽  
Michael Schmitt
Keyword(s):  
Branching Fraction ◽  
New Physics ◽  
Z Decays ◽  
Four Leptons

scholarly journals HEAVY QUARK LIFETIMES, MIXING AND CP VIOLATION

2000 ◽  
Vol 15 (10) ◽  
pp. 1393-1414
Author(s):  
GUY BLAYLOCK
Keyword(s):  
Cp Violation ◽  
Heavy Quark ◽  
Heavy Quark Physics ◽  
Branching Fraction ◽  
New Physics ◽  
Unitarity Triangle ◽  
Lifetime Measurements ◽  
Physics First ◽  
Charm Decay ◽  
Charm Mixing

This paper emphasizes four topics that represent some of the year's highlights in heavy quark physics. First of all, a review is given of charm lifetime measurements and how they lead to better understanding of the mechanisms of charm decay. Secondly, the CLEO collaboration's new search for charm mixing is reported, which significantly extends the search for new physics in that sector. Thirdly, important updates in Bs mixing are summarized, which result in a new limit on ΔMs, and which further constrain the unitarity triangle. Finally, the first efforts to measure CP violation in the B system are discussed. Results are shown for the CDF and ALEPH measurements of sin 2β, as well as the CLEO branching fraction measurements of B→Kπ, ππ, which have implications for future measurements of α.

scholarly journals Search for single production of vectorlike top partners through th channel at the HE-LHC and FCC-hh

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Xi-Yan Tian ◽  
Liu-Feng Du ◽  
Yao-Bei Liu
Keyword(s):  
Standard Model ◽  
Production Cross ◽  
Branching Fraction ◽  
Hadron Collider ◽  
High Energy ◽  
New Physics ◽  
Beyond The Standard Model ◽  
The Standard Model ◽  
Single Production ◽  
Integrated Luminosity

AbstractThe vectorlike top partners are potential signature of some new physics beyond the Standard Model at the TeV scale. In this paper, we propose to search for the vectorlike T quark with charge 2/3 in the framework of a simplified model where the top partners only couples with the third generation of Standard Model quarks. We investigate the observability for electroweak production of a vectorlike T quark in association with a standard model bottom quark through the process $$pp \rightarrow T\bar{b}j$$ p p → T b ¯ j with the subsequent decay mode of $$T\rightarrow t(\rightarrow b W^+\rightarrow b \ell ^{+} \nu _{\ell })h( \rightarrow \gamma \gamma )$$ T → t ( → b W + → b ℓ + ν ℓ ) h ( → γ γ ) , at the proposed High Energy Large Hadron Collider (HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh) including the realistic detector effects. The 95% confidence level excluded regions and the $$5\sigma $$ 5 σ discovery reach in the parameter plane of $$\kappa _{T}-m_T$$ κ T - m T , are respectively obtained at the HE-LHC with the integrated luminosity of 15 ab$$^{-1}$$ - 1 and the FCC-hh with the integrated luminosity of 30 ab$$^{-1}$$ - 1 . We also analyze the projected sensitivity in terms of the production cross section times branching fraction at the HE-LHC and FCC-hh.

scholarly journals Probing new physics in semileptonic $$\Xi _{b}\rightarrow \Lambda (\Xi _{c})\tau ^{-}\bar{\nu }_{\tau }$$ decays

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Jiao Zhang ◽  
Xiuyun An ◽  
Ruirui Sun ◽  
Jianfeng Su
Keyword(s):  
Standard Model ◽  
B Meson ◽  
Branching Fraction ◽  
Branching Fractions ◽  
New Physics ◽  
Effective Theory ◽  
Tau Decays ◽  
Lepton Flavor ◽  
Measurement Results ◽  
Quark Level

Abstract Recently, several observed anomalies in semileptonic B meson decays have implied hints of lepton flavor universal violation. Motivated by these inspiring results, we study the baryon decays $$\Xi _{b}\rightarrow \Lambda (\Xi _{c})\tau ^{-}\bar{\nu }_{\tau }$$Ξb→Λ(Ξc)τ-ν¯τ which are mediated by $$b\rightarrow u(c)\tau ^{-}\bar{\nu }_{\tau }$$b→u(c)τ-ν¯τ transitions at quark level in the Standard Model and different New Physics scenarios. In the framework of the extended Standard Model on assuming a general effective theory, we constrain the Wilson coefficients of the NP operators using the experimental measurement results for the $$Br(B_{c}^+\rightarrow \tau ^+ \nu _{\tau })$$Br(Bc+→τ+ντ), $$R^{l}_{\pi }$$Rπl, $$R_{D^{(*)}}$$RD(∗), $$R_{J/\psi }$$RJ/ψ and $$F_{L}^{D^{*}}$$FLD∗ anomalies and investigate their New Physics effects on several observables relative to the $$\Xi _{b}\rightarrow \Lambda (\Xi _{c})\tau ^{-}\bar{\nu }_{\tau }$$Ξb→Λ(Ξc)τ-ν¯τ decays. We mention the differential branching fraction $${\text {d}}Br/{\text {d}}q^2$$dBr/dq2, the ratio of branching fractions $$R(q^2)$$R(q2), the lepton-side forward–backward asymmetry $$A_{FB}(q^2)$$AFB(q2), the longitudinal polarization $$P_{L}^{\Lambda (\Xi _{c})}(q^2)$$PLΛ(Ξc)(q2) of the daughter baryons $$\Lambda (\Xi _{c})$$Λ(Ξc) and $$P_{L}^{\tau }(q^2)$$PLτ(q2) of the $$\tau $$τ lepton, and the convexity parameter $$C_{F}(q^2)$$CF(q2).

scholarly journals Gauge Model of Quark–Lepton Nonuniversality

2003 ◽  
Vol 18 (20) ◽  
pp. 1367-1375 ◽  
Author(s):  
Xiao-Yuan Li ◽  
Ernest Ma
Keyword(s):  
New Physics ◽  
Low Energy ◽  
Gauge Model ◽  
Small Deviations ◽  
Lepton Universality ◽  
Quark Mixing ◽  
Z Decays ◽  
Mixing Matrix ◽  
Accidental Symmetry

We consider a gauge model where quark–lepton universality is an accidental symmetry which is only approximate, in analogy to the well-accepted notion that strong isospin is accidental and approximate. This is a natural framework for explaining possible small deviations of quark–lepton universality which is applicable to the recently reported apparent nonunitarity of the quark mixing matrix. As a result, small departures from quark–lepton universality are expected in Z decays as well as in the recent neutrino data of the NuTeV collaboration and in future low-energy experiments. New physics is predicted at the TeV scale.

scholarly journals Study of electroweak penguin B decays at Belle II experiment

2021 ◽  
Vol 2145 (1) ◽  
pp. 012018
Author(s):  
J Ineead ◽  
S Nishida ◽  
B Asavapibhop ◽  
N Suwonjandee
Keyword(s):  
Branching Fraction ◽  
Neutral Current ◽  
New Physics ◽  
Lepton Flavor ◽  
Flavor Changing ◽  
Penguin Diagram ◽  
The Status ◽  
Flavor Changing Neutral Current ◽  
Belle Ii ◽  
Exclusive Decay

Abstract The electroweak b → sll (l = e, µ) transition is a flavor-changing neutral current process that mediates through a one-loop penguin diagram. The decay is considered to be a good probe for the New Physics as particles predicted in the beyond Standard Model theories can enter into the loop. The exclusive decay B → K (*) l + l − was first observed by the Belle experiment and it provides many observables such as the branching fraction, CP asymmetry, forward-backward asymmetry, and other angular observables. Recently, the LHCb experiment has reported some clue of a lepton flavor universality violation from the branching fraction ratio of the B → Kµ + µ − and B → Ke + e − decays. In this presentation, we report the status of the B → Kl + l − decay analysis at the Belle II experiment which started the data taking in 2019. We also, present an activity at the Belle II Chulalongkorn University group where we study the B → KJ/ψ decay which has the same topology as the B → Kl + l − .

Study of B̄s → ϕμ+μ− decays in the G(211) model and vector leptoquark model

2017 ◽  
Vol 32 (25) ◽  
pp. 1750155 ◽  
Author(s):  
Shuai-Wei Wang
Keyword(s):  
Standard Model ◽  
Large Deviation ◽  
Branching Fraction ◽  
New Physics ◽  
Decay Process ◽  
Angular Distributions ◽  
The Standard Model ◽  
Lepton Polarization ◽  
Text Model

We study [Formula: see text] decay in the [Formula: see text] model and vector leptoquark model, respectively. We consider the effects of these two new physics (NP) models on some measured physical observables of this decay process, such as the differential branching fraction and the angular distributions. We find that the large deviation of the differential branching fraction between the measurement and the Standard Model (SM) prediction can be explained in these two NP models. However, we found that not all observables of the double-lepton polarization asymmetries are sensitive to the contributions of these NP models.

scholarly journals Probing the Effects of New Physics in B¯⁎→Plν¯l Decays

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Qin Chang ◽  
Jie Zhu ◽  
Na Wang ◽  
Ru-Min Wang
Keyword(s):  
Spin Asymmetry ◽  
Branching Fraction ◽  
New Physics ◽  
Heavy Flavor ◽  
Independent Vector ◽  
Vector Type ◽  
Scalar Type ◽  
The Future ◽  
Significant Divergence ◽  
Model Independent

The significant divergence between the SM predictions and experimental measurements for the ratios, RD(⁎)≡B(B¯→D(⁎)τ-ν¯τ)/B(B¯→D(⁎)l′-ν¯l′) with (l′=e,μ), implies possible hint of new physics in the flavor sector. In this paper, motivated by the “RD(⁎) puzzle” and abundant B⁎ data samples at high-luminosity heavy-flavor experiments in the future, we try to probe possible effects of new physics in the semileptonic B¯u,d,s⁎→Pl-ν¯l  (P=D,Ds,π,K) decays induced by b→(u,c)l-ν¯l transitions in the model-independent vector and scalar scenarios. Using the spaces of NP parameters obtained by fitting to the data of RD and RD⁎, the NP effects on the observables including branching fraction, ratio RP⁎, lepton spin asymmetry, and lepton forward-backward asymmetry are studied in detail. We find that the vector type couplings have large effects on the branching fraction and ratio RP⁎. Meanwhile, the scalar type couplings provide significant contributions to all of the observables. The future measurements of these observables in the B¯⁎→Pl-ν¯l decays at the LHCb and Belle-II could provide a way to crosscheck the various NP solutions to the “RD(⁎) puzzle”.

scholarly journals PHYSICS OF W BOSONS AT LEP2

1999 ◽  
Vol 14 (21) ◽  
pp. 3277-3312 ◽  
Author(s):  
MARIO CAMPANELLI
Keyword(s):  
Cross Section ◽  
Production Cross ◽  
Branching Fraction ◽  
Vector Boson ◽  
Center Of Mass ◽  
W Bosons ◽  
New Physics ◽  
Threshold Region ◽  
Indirect Determination ◽  
The Matrix

After the first observations of W bosons in leptonic interactions, about 4000 WW candidate events per experiment have been collected at LEP2. This data allows the measurement of the WW production cross section at different center-of-mass energies, as well as W decay branching fractions. The W hadronic branching fraction can be converted into a test of the unitarity of the CKM matrix, or into an indirect determination of the matrix element |V cs |. A more direct measurement coming from charm tagging is also performed. The W mass has been measured via the cross section (in the threshold region) and the direct reconstruction of the W decay products, using different techniques to account for the distortions due to experimental effects. The main systematic error to the mass reconstruction in the fully hadronic channel comes from QCD effects like Color reconnections and Bose–Einstein correlations, extensively studied in WW events. In e+e- collisions W pairs can be produced in s-channel via a three-vector boson vertex, so a direct study of the trilinear gauge boson couplings is possible. Modification of WW cross section and distributions of W production and decay angles would be an indication of nonstandard couplings, thus a first hint for the presence of new physics.

scholarly journals B-meson decays into final states with a τ lepton

2014 ◽  
Vol 29 (07) ◽  
pp. 1430007 ◽  
Author(s):  
Abner Soffer
Keyword(s):  
B Mesons ◽  
B Meson ◽  
Branching Fraction ◽  
Large Data ◽  
New Physics ◽  
Final States ◽  
Initial State ◽  
Lepton Flavor ◽  
Event Reconstruction ◽  
The Standard Model

Decays of B mesons into final states containing a τ lepton are sensitive to new charged current interactions that break lepton-flavor universality. These decays have been studied only at e+e- colliders, where the low-background environment and well-known initial state make it possible to observe small signals with undetectable neutrinos. In particular, the large data samples of the B factories and recent advances in techniques for full-event reconstruction have led to evidence for the decay B+→τ+ ντ and unambiguous observation of the decays [Formula: see text]. These results exclude large regions of the parameter space for a variety of new physics models. Furthermore, the branching fraction for [Formula: see text] has been measured to be higher than the Standard Model expectation by more than three standard deviations, making this an interesting topic for further research. This paper reviews the theoretical and experimental status of this topic, summarizing the results at this time and outlining the path for further improvements.

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