scholarly journals The $$\uptau $$ challenges at FCC-ee

2021 ◽  
Vol 136 (9) ◽  
Author(s):  
Mogens Dam
Keyword(s):  
Branching Fraction ◽  
Neutral Current ◽  
Branching Fractions ◽  
Lifetime Measurement ◽  
Flight Distance ◽  
Vertex Detector ◽  
Lepton Universality ◽  
The Cross ◽  
Experimental Challenge ◽  
Polarisation Measurements

AbstractAt FCC-ee, about $$1.7 \times 10^{11}\,\hbox {Z} \rightarrow \uptau ^+\uptau ^-$$ 1.7 × 10 11 Z → τ + τ - events will be produced. This high statistics in the clean $$\hbox {e}^+\hbox {e}^-$$ e + e - environment opens the possibility of much improved determinations of $$\uptau $$ τ -lepton properties and, via the measurement of the $$\uptau $$ τ polarisation, of the neutral-current couplings of electrons and $$\tau $$ τ s. Improved measurements of $$\uptau $$ τ -lepton properties—lifetime, leptonic branching fractions, and mass—allow important tests of lepton universality. The experimental challenge is to match as far as possible statistical uncertainties generally at the $$10^{-5}$$ 10 - 5 level. This applies in particular to the lifetime measurement, which is derived from the 2.2-mm $$\uptau $$ τ average flight distance, and for the branching fraction and polarisation measurements, where the cross-channel contamination is of particular concern. These issues raise strict detector requirements, in particular, on the accuracy of the construction and alignment of the vertex detector and of the precise calorimetric separation and measurement of photons and $$\uppi ^0$$ π 0 s in the collimated $$\uptau $$ τ decay topologies.

scholarly journals Probing lepton universality with (semi)-leptonic B decays

2019 ◽  
Author(s):  
Giovanni Banelli ◽  
Robert Fleischer ◽  
Ruben Jaarsma ◽  
Gilberto Tetlalmatzi-Xolocotzi
Keyword(s):  
Standard Model ◽  
Branching Fraction ◽  
Branching Fractions ◽  
Belle Collaboration ◽  
New Physics ◽  
Recent Measurement ◽  
Beyond The Standard Model ◽  
Lepton Universality ◽  
Highly Sensitive ◽  
The Standard Model

The most recent measurements of the observables R_{D^{(*)}}RD(*) are in tension with the Standard Model offering hints of New Physics in b\rightarrow c \ell \bar{\nu}_{\ell}b→cℓν‾ℓ transitions. Motivated by these results, in this work we present an analysis on their b\rightarrow u \ell \bar{\nu}_{\ell}b→uℓν‾ℓ counterparts (for \ell=e, ~\mu, ~\tauℓ=e,μ,τ). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic BB decays (B^-\rightarrow \ell^- \bar{\nu}_{\ell}B−→ℓ−ν‾ℓ, \bar{B}\rightarrow \pi \ell \bar{\nu}_{\ell}B‾→πℓν‾ℓ and \bar{B}\rightarrow \rho \ell \bar{\nu}_{\ell}B‾→ρℓν‾ℓ). Here a key role is played by the leptonic BB processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel B^-\rightarrow \mu^-\bar{\nu}_{\mu}B−→μ−ν‾μ by the Belle collaboration. Secondly, we extract the CKM matrix element |V_{ub}||Vub| while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic BB decays.

MEASUREMENT OF THE $D \bar{D}$ CROSS SECTIONS AND D HADRONIC BRANCHING FRACTIONS

2005 ◽  
Vol 20 (16) ◽  
pp. 3701-3703
Author(s):  
Guang-Pei Chen
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Branching Fractions ◽  
Hadronic Decay ◽  
Decay Modes ◽  
The Cross

Using 57.2 pb-1 of data collected with the CLEO-c detector at the ψ(3770) resonance, we measure absolute branching fractions for three D0 and two D+ Cabibbo-allowed hadronic decay modes, and the cross section for [Formula: see text] at [Formula: see text].

Initial charm program on direct measurements of weak decay constant fDs and branching fraction B(Ds → μνμ) and prospect with high-precision

2020 ◽  
Vol 35 (35) ◽  
pp. 2030018
Author(s):  
C. C. Zhang
Keyword(s):  
High Precision ◽  
Decay Constant ◽  
Branching Fraction ◽  
Branching Fractions ◽  
Weak Decay ◽  
Precision Measurements ◽  
Direct Measurements

First direct measurements of the weak decay constant [Formula: see text] and the [Formula: see text] branching fractions to [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] at the BES experiments in 1990s are reviewed. Referring to the BESIII results of [Formula: see text] and branching fraction [Formula: see text] with best precision1 to date, prospect for challenge on precision measurements of [Formula: see text] and [Formula: see text] at BESIII is presented.

scholarly journals Improved accuracy in the determination of the thermal cross section of ${}^{14}{\rm N}({\rm n},{\rm p}){}^{14}{\rm C}$ for neutron lifetime measurement

2019 ◽  
Vol 2019 (9) ◽  
Author(s):  
R Kitahara ◽  
K Hirota ◽  
S Ieki ◽  
T Ino ◽  
Y Iwashita ◽  
...  
Keyword(s):  
Cross Section ◽  
Lifetime Measurement ◽  
Reaction Cross ◽  
Proton Accelerator ◽  
Incident Neutron ◽  
Neutron Lifetime ◽  
The Cross ◽  
Thermal Cross Section ◽  
Improved Accuracy

Abstract In a neutron lifetime measurement at the Japan Proton Accelerator Complex, the neutron lifetime is calculated from the neutron decay rate and the incident neutron flux. The flux is obtained by counting the protons emitted from the neutron absorption reaction of ${}^{3}{\rm He}$ gas, which is diluted in a mixture of working gas in a detector. Hence, it is crucial to determine the amount of ${}^{3}{\rm He}$ in the mixture. In order to improve the accuracy of the number density of the ${}^{3}{\rm He}$ nuclei, we have suggested using the ${}^{14}{\rm N}({\rm n},{\rm p}){}^{14}{\rm C}$ reaction as a reference because this reaction involves similar kinetic energy to the $^3$He(n,p)$^3$H reaction and a smaller reaction cross section to introduce reasonable large partial pressure. The uncertainty of the recommended value of the cross section, however, is not satisfied with our requirement. In this paper we report the most accurate experimental value of the cross section of the $^{14}$N(n,p)$^{14}$C reaction at a neutron velocity of 2200 m s$^{-1}$, measured relative to the $^3$He(n,p)$^3$H reaction. The result was 1.868 $\pm$ 0.003 (stat.) $\pm$ 0.006 (sys.) b. Additionally, the cross section of the $^{17}$O(n,$\alpha$)$^{14}$C reaction at the neutron velocity is also redetermined as 249 $\pm$ 6 mb.

The cross-section and branching fractions for dissociative recombination of the diacetylene cation C4D2+

2008 ◽  
Vol 273 (3) ◽  
pp. 111-116 ◽  
Author(s):  
M. Danielsson ◽  
M. Hamberg ◽  
V. Zhaunerchyk ◽  
A. Ehlerding ◽  
M. Kamińska ◽  
...  
Keyword(s):  
Cross Section ◽  
Branching Fractions ◽  
Dissociative Recombination ◽  
The Cross

SEARCH FOR THE DECAY Bs→μ+μ -ϕ IN $p\bar p$ COLLISIONS AT $\sqrt{s} =1.8\, {\rm TeV}$

2001 ◽  
Vol 16 (supp01a) ◽  
pp. 461-463
Author(s):  
◽  
THOMAS SPEER
Keyword(s):  
Confidence Level ◽  
Branching Fraction ◽  
Neutral Current ◽  
Current Decay ◽  
Flavor Changing ◽  
Upper Limit ◽  
Flavor Changing Neutral Current ◽  
Neutral Current Decay

We present a search for the flavor-changing neutral current decay Bs→ μ+μ-ϕ in [Formula: see text] collisions at [Formula: see text], using 91.4 pb-1 of data collected at the Collider Detector at Fermilab (CDF). We find two candicate events for this decay, which is consistent with the background estimate, and set a preliminary upper limit on the branching fraction of ℬ(Bs → μ+ μ-ϕ)<4.2 · 10-5 at a 90% confidence level.

τ LEPTON PHYSICS

1998 ◽  
Vol 13 (05) ◽  
pp. 695-739 ◽  
Author(s):  
GHITA RAHAL-CALLOT
Keyword(s):  
Neutral Current ◽  
Branching Fractions ◽  
New Physics ◽  
Precise Determination ◽  
Energy Scale ◽  
Hadronic Decay ◽  
Charged Current ◽  
Beyond The Standard Model ◽  
Decay Channels

General properties of the τ leptons are reviewed using the recent measurements of production and decay of τ leptons. The improvements in the knowledge of the τ mass and the limits on ντ mass are reported. New improved measurements of the τ polarization and asymmetries performed at LEP and SLC prove a measurement of the axial and vector part of the neutral current at the per mil level. For the leptonic charged current, no deviation from the V–A Lorentz structure of the current is observed. Improvements on the lifetime and leptonic branching fractions allow a check of the charged current universality at the 0.5% level. New hadronic decay channels have been measured, mainly those involving kaons and η mesons. A precise determination of αs at the τ mass energy scale is performed. Finally, tests of possible new physics beyond the Standard Model are discussed.

scholarly journals Rare Λb → nl+l− decays in the relativistic quark–diquark picture

2017 ◽  
Vol 32 (24) ◽  
pp. 1750125 ◽  
Author(s):  
R. N. Faustov ◽  
V. O. Galkin
Keyword(s):  
Momentum Transfer ◽  
Branching Fraction ◽  
Branching Fractions ◽  
Form Factors ◽  
Relativistic Effects

The form factors of the rare [Formula: see text] decays are calculated in the framework of the relativistic quark–diquark picture of baryons with the consistent account of the relativistic effects. Their momentum transfer squared dependence is determined explicitly in the whole accessible kinematical range. The decay branching fractions, forward–backward asymmetries and the fractions of longitudinally polarized dileptons are determined. The branching fraction of the rare [Formula: see text] decay are found to be [Formula: see text] and thus could be measured at the LHC. Prediction for the branching fraction of the rare radiative [Formula: see text] decay is also given.

scholarly journals Recent results from BABAR

2020 ◽  
Vol 235 ◽  
pp. 04001
Author(s):  
J. William Gary
Keyword(s):  
Data Collection ◽  
Direct Measurement ◽  
Decay Channel ◽  
Branching Fraction ◽  
Branching Fractions ◽  
Babar Collaboration ◽  
Lepton Number ◽  
Lepton Flavor ◽  
The Third

The BABAR Collaboration at SLAC continues to produce a wide variety of publications on interesting and unique topics despite having ceased data-collection operations more than 10 years ago. Presented here are the results of three recent studies. The first is on the direct measurement of the B± → K± X(3872) branching fraction, allowing the first determination of the branching fractions of the exotic X(3872) charmonium state. The second is a publication on the first observation of the D0 → K−π+e+e− branching fraction. The third is on searches for lepton flavor and lepton number violating decays in D0 meson decays, resulting in improvements over existing limits by factors that vary from 20 to almost 800 depending on the D0 decay channel.

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).

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