We present searches for the leptonic decays B+ -> l+ nu and the lepton flavor violating decays B0 -> l+ tau-, where l=e,mu, with data collected by the BaBar experiment at SLAC. This search demonstrates a novel technique in which we fully reconstruct the accompanying Bbar in Upsilon(4S)->BBbar events, and look for a monoenergetic lepton from the signal B decay. The signal yield is extracted from a fit to the signal lepton candidate momentum distribution in the signal B rest frame. Using a data sample of approximately 378 million BBbar pairs (342fb-1), we find no evidence of signal in any of the decay modes. Branching fraction upper limits of B(B+ -> e+ nu)<5.2x10^-6, B(B+ -> mu+ nu)<5.6x10^-6, B(B0 -> e+ tau-)<2.8x10^-5 and B(B0 -> mu+ tau-)<2.2x10^-5, are obtained at 90% confidence level.
We present a new measurement of the decay B- -> tau- nu_tau-bar with a semileptonic B tagging method, using a data sample containing 657*10^6 BB-bar pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. A sample of BB pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_tau-bar candidate in the recoil. We obtain a signal with a signicance of 3.8 standard deviations including systematics, and measure the branching fraction to be B(B- -> tau- nu_tau-bar)=(1.65+0.38-0.37(stat)+0.35-0.37(syst))*10^4. Thi…
The tau identification and reconstruction algorithms developed for the LHC experiments Atlas and CMS are presented. Reconstruction methods suitable for use at High Level Trigger and off-line are described in detail
The presence of tau leptons in the final state is an important signature in many Higgs boson and SUSY searches. With the ATLAS detector, hadronically decaying tau leptons can be reconstructed in a wide range of transverse energies. The reconstruction algorithm for hadronically decaying tau leptons is explained and the performance of tau lepton identification is shown. Particularly important is the discrimination of hadronically decaying tau leptons against overwhelming backgrounds from QCD jets.
We present a measurement of the decay B- -> tau- nu_bar using a data sample containing 657 million BB_bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. A sample of BB_bar pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_bar candidate in the recoil. We obtain a signal with a significance of 3.6 standard deviations including systematic uncertainties, and measure the branching fraction to be Br(B- -> tau- nu_bar) = [1.54+0.38-0.37(stat)+0.29-0.31(syst)]*10^-4. This result confi…
Hadronically decaying tau leptons are of prime importance in numerous physics analyses in ATLAS. The spectrum of the possible applications of hadronically decaying tau leptons reaches from Standard Model measurements, including Higgs searches, to searches for physics beyond the Standard Model. The basic principles behind the sophisticated tau reconstruction and identification techniques, which are specifically designed to identify hadronically decaying taus and reject various background processes, are delineated here along with current data-driven estimates of their respective performance.
We present measurements of B -> D^* tau nu and B -> D tau nu decays using 604.5 fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We obtain Br(B^+ -> D^0-bar tau^+ nu) = (1.51 +0.41/-0.39 +0.24/-0.19 +/- 0.15)%, Br(B^+ -> D^*0-bar tau^+ nu) = (3.04 +0.69/-0.66 +0.40/-0.47 +/- 0.22)%, Br(B^0 -> D^- tau^+ nu) = (1.01 +0.46/-0.41 +0.13/-0.11 +/- 0.10)%, Br(B^0 -> D^*- tau^+ nu) = (2.56 +0.75/-0.66 +0.31/-0.22 +/- 0.10)%, where the first error i…
We present a search for the decay B^+ --> tau^+ nu using $383 \times 10^{6}}$ BBbar pairs collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II B Factory. We select a sample of events with one completely reconstructed tag B in a hadronic decay mode ($B^- \to D^{(*)0} X^-$), and examine the rest of the event to search for a B^+ --> tau^+ nu decay. We identify the tau lepton in the following modes: tau^+ --> e^+ nu nu,tau^+ --> mu^+ nu nu, tau^+ --> pi^+ nu and tau^+ --> pi^+ pi^0 nu. We find a 2.2 sigma excess in data and measure a branching fraction of B(B+ --> tau^…
We present a search for the decay B+ --> tau+ nu_tau using 467.8 x 10^6 B B-bar pairs collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II B-Factory. We select a sample of events with one completely reconstructed B- in an hadronic decay mode (B- --> D{(*)0}X- and B- --> J/psi X-). We examine the rest of the event to search for a B+ --> tau+ nu_tau decay. We identify the tau+ lepton in the following modes: tau+ --> e+ nu nu, tau+ --> mu+ nu nu, tau+ --> pi+ nu and tau+ --> rho nu. We find an excess of events with respect to expected background, which excludes the nu…
A recent publication based on ALEPH $\mathrm{e}^+\mathrm{e}^-$ data taken near the Z resonance reports an excess, near 30 GeV, in the di-muon mass spectrum for events containing b quarks. In this paper we measure the di-muon mass spectrum for L3 data with a bottom tag, recorded in the years 1994 and 1995 at the LEP collider at CERN, and compare it to Monte Carlo predictions.
Selected results on hadronic decays of the tau lepton from the TAU98 Workshop are reviewed. A comprehensive picture emerges for strange particle branching fractions, and exploration of resonant substructure of both strange and non-strange decays is seen to have matured substantially.
The identification of hadronic tau lepton decays is an important requirement for the LHC physics program, both in terms of standard model measurements and the search for beyond-the-standard-model physics. The ATLAS and CMS algorithms for identification and energy calibration of hadronic tau lepton decays are conceptually different. They are described together with measurements of relevant performance figures.
We present a search for the decay B+ -->tau+ nu using 467.8 x 10^6 B B pairs collected at the Y(4S) resonance with the BaBar detector at the SLAC PEP-II B-Factory. We select a sample of events with one completely reconstructed B- in the hadronic decay modes (B- --> D(*)0 X- and B- --> J/ψX-). We examine the rest of the event to search for a B+ --> tau+ nu decay. We identify the tau+ lepton in the following modes: tau+ --> e+ nu nu, tau+ --> mu+ nu nu, tau+ --> pi+ nu, and tau+ --> rho+ nu. We find an excess of events with respect to the expected background, which excludes the null signal hypot…
I outline recent results using CLEO3 data involving the decay of the tau to three charged hadrons and a neutrino, as well as an investigation of the structure of the decay tau to KKpinu and the Wess-Zumino term in this decay.
Using the ARGUS detector at the $e^+ e^-$ storage ring DORIS II, we have measured the Michel parameters $ρ$, $ξ$, and $ξδ$ for $τ^{\pm}\to l^{\pm} ν\barν$ decays in $τ$-pair events produced at center of mass energies in the region of the $Υ$ resonances. Using $τ^\mp \to ρ^\mp ν$ as spin analyzing tags, we find $ρ_{e}=0.68\pm 0.04 \pm 0.08$, $ξ_{e}= 1.12 \pm 0.20 \pm 0.09$, $ξδ_{e}= 0.57 \pm 0.14 \pm 0.07$, $ρ_μ= 0.69 \pm 0.06 \pm 0.08$, $ξ_μ= 1.25 \pm 0.27 \pm 0.14$ and $ξδ_μ= 0.72 \pm 0.18 \pm 0.10$. In addition, we report the combined ARGUS results on $ρ$, $ξ$, and $ξδ$ using this work und p…
B^0-anti-B^0 flavor oscillations are studied in e^+e^- annihilation data collected with the BABAR detector at center-of-mass energies near the Y(4S) resonance. One B is reconstructed in a hadronic or semileptonic decay mode, and the flavor of the other B in the event is determined with a tagging algorithm that exploits the relation between the flavor of the heavy quark and the charges of its decay products. Tagging performance is characterized by an efficiency e_i and a probability for mis-identification, w_i, for each tagging category. We report a determination of the wrong-tag probabilities,…
New physics beyond the Standard Model could well preferentially show up at the LHC in final states with taus. The development of efficient and accurate reconstruction and identification of taus is therefore an important item in the CMS physics programme. The potentially superior performance of a particle-flow approach can help to achieve this goal with the CMS detector. Preliminary strategies are presented in this summary for the hadronic decays of the taus.
Tau leptons play an important role in the physics program in ATLAS. They can be used not only in searches for new phenomena like the Higgs boson or Supersymmetry, or for electroweak measurements but also in detector related studies like the determination of the missing transverse energy scale. Identifying hadronically decaying tau leptons requires good understanding of the detector performance, combining information from calorimeter and tracking detectors. The current status of the tau reconstruction and identification with the ATLAS detector is presented. The identification efficiencies are m…
Results from the nu_tau appearance search in a neutrino beam using the full NOMAD data sample are reported. A new analysis unifies all the hadronic tau decays, significantly improving the overall sensitivity of the experiment to oscillations. The "blind analysis" of all topologies yields no evidence for an oscillation signal. In the two-family oscillation scenario, this sets a 90% C.L. allowed region in the sin^2(2theta)-Delta m^2 plane which includes sin^2(2theta)<3.3 x 10^{-4} at large Delta m^2 and Delta m^2 < 0.7 eV^2/c^4 at sin^2(2theta)=1. The corresponding contour in the nu_e->nu_tau os…
A model-dependent analysis of the hadronic substructure in tau- -> pi- pi- pi+ neutrino decay is reported. The decay is dominated by the process tau- -> a1(1260)- + neutrino, in which a1(1260)- -> rho0 pi- in an S-wave decay. Amplitudes involving a1(1260) decays into isoscalars, especially a_1(1260)- -> f0(600)pi-, are large. tau- -> pi- pi- pi+ neutrino decays via the pseudoscalar pi(1300)- are small. These results support the resonant substructure reported in the previously reported analysis of tau- -> pi0 pi0 pi- neutrino decay mode from the same CLEO II data sample.
This Letter describes a direct search for charged Higgs boson production in proton-antiproton collisions at sqrt(s)=1.8 TeV recorded by the Collider Detector at Fermilab. Two-Higgs-doublet extensions to the standard model predict the existence of charged Higgs bosons. In such models, the branching fraction for top quarks B(t --> H b --> tau nu b) can be large. This search uses the hadronic decays of the tau lepton in this channel to significantly extend previous limits on charged Higgs production.
This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from $pp$ collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy $\sqrt{\mathrm{s}} = 8$ TeV. The performance of these algorithms is measured in most cases with $Z$ decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb$^{-1}$. An uncertainty on the offline reconstructed tau energy scale of $2-4$%, depending on transverse energy and pseudorapidity, is…
Tau lepton decays with open strangeness in the final state are measured with the OPAL detector at LEP to determine the strange hadronic spectral function of the tau lepton. The decays T- ->(Kpi)-nu tau, (Kpipi)-nu tau and (Kpipipi) -nu tau with final states consisting of neutral and charged kaons and pions have been studied. The invariant mass distributions of 93.4% of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining 6.6% and for the strange final states including eta mesons. The reconstructed strange final states, corrected for r…
The article describes the identification of hadronically decaying tau leptons in ppbar collisions at 1.96 TeV collected by the DZero detector at the Fermilab Tevatron. After a brief description of the motivations and the challenges of considering tau leptons in high energy hadronic collisions, details of the tau reconstruction and identification will be discussed. The challenges associated for tau energy measurements in an hadronic environment will be presented including approaches to deal with such measurements.
We report on measurements of branching fractions for several hadronic tau decays to final states with kaons, which can be used to determine the strange quark mass and the element |V_us| of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix. The results are obtained from data collected with the BaBar and Belle detectors at the PEP-II and KEKB asymmetric-energy e+e- colliders at SLAC and KEK, respectively, both operating at center-of-mass energies near the Y(4S) resonance.
We present a study of hadronic tau decays, especially decay into three-hadron final states with kaon(s), using more than 500fb^-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We measure the branching ratios both inclusively and exclusively while considering the intermediated states of K(892)^*0. The following results are obtained: B(tau- -> K- pi+ pi- nu)=(3.25 +- 0.02 +0.16-0.15)x10^-3, B(tau- -> K- K+ pi- nu)=(1.53 +- 0.01 +- 0.06)x10^-3, B(tau- -> K- K+ K- nu)=(2.60 +- 0.23 +- 0.10)x10^-5 and B(tau- -> K^*(892)^0 K-nu)=(1.56 +- 0.02 +- 0.09)x10^-3. …
We present the first exclusive observation of the ttbar to hadronic tau + jets decay channel. Using these events from 1.96 TeV ppbar collisions at CDF, we measure the ttbar cross section as well as the top quark mass. Events require a single hadronic tau, large missing transverse energy, and exactly 4 jets of which at least one must be tagged as a b jet. The cross section measurement is extracted from a Poisson likelihood function based on the observed number of events and the predicted number of signal and background events for a given ttbar cross section. The mass is extracted from a likelih…
We have studied hadronic tau decay modes involving an eta meson using 490 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The following branching fractions have been measured: B(tau- -> K- eta nu)=(1.58 +- 0.05 +- 0.09)x 10^{-4}, B(tau- -> K- pi0 eta nu)=(4.6 +- 1.1 +- 0.4)x 10^{-5}, B(tau- -> pi- pi0 eta nu)=(1.35 +- 0.03 +- 0.07)x 10^{-3}, B(tau- -> pi- KS eta nu)=(4.4 +- 0.7 +- 0.2)x 10^{-5}, and B(tau- -> K^{*-} eta nu)=(1.34 +- 0.12 +- 0.09)x 10^{-4}. These results are substantially more precise than previous measurements. The new measurement…
We present the result of a search for charged Higgs decays of the top quark, produced in $p\bar{p}$ collisions at $\surd s =$ 1.8 TeV. When the charged Higgs is heavy and decays to a tau lepton, which subsequently decays hadronically, the resulting events have a unique signature: large missing transverse energy and the low-charged-multiplicity tau. Data collected in the period 1992-1993 at the Collider Detector at Fermilab, corresponding to 18.7$\pm$0.7~pb$^{-1}$, exclude new regions of combined top quark and charged Higgs mass, in extensions to the standard model with two Higgs doublets.
The ATLAS experiment at the Large Hadron Collider (LHC) has been able to collect 5.25 fb-1 of data in 2011. For many physics analyses both in context of the Standard Model (SM) and Beyond the Standard Model (BSM) theories such as Higgs boson searches, tau leptons play an important role. Thus, triggering on hadronic tau decays is an essential ingredient for the success of those measurements. This contribution will summarize the developed efforts to meet this challenge. Efficiency measurements using data taken in 2011 at a center-of-mass energy of 7 TeV are described and results are presented. A…
We present a new measurement of the purely leptonic decay B- -> tau- nu_tau-bar with a semileptonic B tagging method, using a data sample containing 657*10^6 BB-bar pairs collected with the Belle detector at the KEKB asymmetric e+e- collider. A sample of BB-bar pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_tau-bar candidate in the recoil. We obtain a signal with a significance of 3.8 standard deviations including systematics, and measure the branching fraction to be B(B- -> tau- nu_tau-bar) = 1.65+0.38-0.37(stat)+0.35-0.37(syst))*10^-4. T…
Hadronic decays of the $τ$ lepton provide a clean environment to study hadron dynamics in an energy regime dominated by resonances, with the interesting information captured in the spectral functions. Recent results from ALEPH on exclusive channels are presented, with some emphasis on the $π\piz$ final state which plays a crucial role for the determination of the hadronic contribution to the muon anomalous magnetic moment. Inclusive spectral functions are the basis for QCD analyses, delivering an accurate determination of the strong coupling constant, quantitative information on nonperturbativ…
The spectral functions of the vector current and the axial-vector current have been measured in hadronic tau decays using the OPAL detector at LEP. Within the framework of the Operator Product Expansion a simultaneous determination of the strong coupling constant alpha_s, the non-perturbative operators of dimension 6 and 8 and of the gluon condensate has been performed. Different perturbative descriptions have been compared to the data. The Contour Improved Fixed Order Perturbation Theory gives alpha_s(mtau**2) = 0.348 +- 0.009 +- 0.019 at the tau-mass scale and alpha_s(mz**2) = 0.1219 +- 0.00…
A search for supersymmetric partners of quarks is performed in the topology of multijet events accompanied by at least one tau lepton decaying hadronically and large missing transverse energy. Approximately 1 fb-1 of ppbar collision data from the Fermilab Tevatron Collider at a center of mass energy of 1.96 TeV recorded by the D0 detector is analyzed. Results are combined with the previously published D0 inclusive search for squarks and gluinos. No evidence of physics beyond the standard model is found and lower limits on the squark mass up to 410 GeV are derived in the framework of minimal su…
The lifetimes of the B0bar and B- mesons are extracted from 29.1/fb of data collected with the Belle detector at the KEK B-factory. A fit to the decay length differences of neutral and charged B meson pairs, measured in events where one of the B mesons is fully reconstructed in several hadronic modes, yields tau_B0bar = 1.554 +/- 0.030(stat) +/- 0.019(syst) ps, tau_B- = 1.695 +/- 0.026(stat) +/- 0.015(syst) ps, and tau_B-/tau_B0bar = 1.091 +/- 0.023(stat) +/- 0.014(syst).
The distribution of particles inside hadronic jets produced in the decay of boosted $W$ and $Z$ bosons can be used to discriminate such jets from the continuum background. Given that a jet has been identified as likely resulting from the hadronic decay of a boosted $W$ or $Z$ boson, this paper presents a technique for further differentiating $Z$ bosons from $W$ bosons. The variables used are jet mass, jet charge, and a b-tagging discriminant. A likelihood tagger is constructed from these variables and tested in the simulation of $W'\rightarrow WZ$ for bosons in the transverse momentum range 20…
This paper presents a new method of reconstructing the individual charged and neutral hadrons in tau decays with the ATLAS detector. The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the existing tau reconstruction. The performance of the reconstruction algorithm is optimised and evaluated using simulation and validated using samples of $Z\toττ$ and $Z(\toμμ)$+jets events selected from proton-proton collisions at a centre-of-mass ener…
This contribution reviews several new or updated results on substructure in semi-hadronic tau decays, recently published by the CLEO Collaboration. These results are all based on data collected with the CLEO detector at Cornell's CESR collider, in the reaction $e^+e^-\to τ^+τ^-$ at $\sqrt{s} \simeq 10.6$ GeV. Most of these results are based on $\approx 4.3\times 10^6$ $τ^+τ^-$ pairs collected with the CLEO II detector between 1990 --- 1995. Some (where noted) also use $\approx 8.0\times 10^6$ $τ^+τ^-$ pairs collected with the CLEO II.V detector (which includes a silicon vertex detector and bet…
A search for new particles has been conducted using events with two high transverse momentum (pt) tau leptons that decay hadronically, at least two high-pt jets, and missing transverse energy from the tau lepton decays. The analysis is performed using data from proton-proton collisions, collected by the CMS experiment in 2015 at sqrt(s) = 13 TeV, corresponding to an integrated luminosity of 2.1 inverse femtobarns. The results are interpreted in two physics models. The first model involves heavy right-handed neutrinos, N[l] (l = e, mu, tau), and right-handed charged bosons, W[R], arising in a l…
The B0 and B+ meson lifetimes have been measured in e+e- annihilation data collected in 1999 and 2000 with the BABAR detector at center-of-mass energies near the Upsilon(4S) resonance. Events are selected in which one B meson is fully reconstructed in a hadronic final state while the second B meson is reconstructed inclusively. A combined fit to the B0 and the B+ decay time difference distributions yields tau_{B0} = 1.546 +/- 0.032 (stat) +/- 0.022(syst) ps, tau_{B+} = 1.673 +/- 0.032 (stat) +/- 0.023 (syst) ps and tau_{B+} / tau_{B0} = 1.082 +/- 0.026 (stat) +/- 0.012 (syst).
Results on semi-hadronic decays of the $τ$ lepton are presented, from studies of $e^+e^-$ annihilation data obtained at the Cornell Electron Storage Ring with the CLEO-II detector. Branching fractions have been measured for decays to two, three and four hadrons, namely $τ^-\!\!\rightarrow\! ν_τh^-π^0$, $τ^-\!\!\rightarrow\! ν_τh^-h^+h^-$, and $τ^-\!\!\rightarrow\! ν_τh^-h^+h^-π^0$, where $h^\pm$ represents a charged pion or kaon. CLEO-II has also observed decays with charged and/or neutral kaons; preliminary results for branching ratios and structure arising from the decay dynamics are given. …
We report on a search for the rare decay modes $B^+\to e^+ ν_e$ and $B^+\to μ^+ ν_μ$ with data collected from the BaBar detector at the PEP-II $e^+e^-$ storage ring. This search utilizes a new technique in which we fully reconstruct the accompanying $B^-$ in $Υ(4S)\righarrow B^+ B^-$ events, and look for a mono-energetic lepton in the $B^+$ rest frame. No signal candidates are observed in either of the channels, consistent with the expected background, in a data sample of approximately 229 million $B\bar{B}$ pairs. The branching-fraction upper limits are set at $\mathcal{B}(B^+\to e^+ν_{e})<7.…
Triggering on hadronic tau decays is essential for a wide variety of analyses of interesting physics processes at ATLAS. The ATLAS tau trigger combines information from the tracking detectors and calorimeters to identify the signature of hadronically decaying tau leptons. In Run 2 operation expected to start in 2015, the trigger strategies will become more important than ever before. In this paper, the tau trigger performance during Run 1 is summarized and also an overview of the developments of Run 2 tau trigger strategy is presented.
A measurement of the cross section of top quark pair production in proton-proton collisions recorded with the ATLAS detector at the LHC at a centre-of-mass energy of 7 TeV is reported. The data sample used corresponds to an integrated luminosity of 2.05 fb^-1. Events with an isolated electron or muon and a tau lepton decaying hadronically are used. In addition, a large missing transverse momentum and two or more energetic jets are required. At least one of the jets must be identified as originating from a b quark. The measured cross section, sigma_ttbar = 186+/- 13 (stat) +/- 20 (syst) +/- 7 (…
A search for production of supersymmetric particles in final states containing jets, missing transverse momentum, and at least one hadronically decaying tau lepton is presented. The data were recorded by the ATLAS experiment in sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 2.05 fb-1 of data. The results are interpreted in the context of gauge mediated supersymmetry breaking models with Mmess = 250 TeV, N5 = 3, mu > 0, and Cgrav = 1. The production of supersymmetric particles is excluded at 95% C.…
The presence of tau leptons in the final state is an important signature in searches for physics beyond the Standard Model. Hadronically decaying tau leptons can be reconstructed over a wide kinematic range at ATLAS. The reconstruction algorithm for hadronically decaying tau leptons and the performance of tau lepton identification is described. A review of physics processes with tau lepton final states is given, ranging from Standard Model processes in early data, such as W and Z boson production, to searches for new phenomena beyond the Standard Model.
ParticleTransformer is all you need for reconstructing hadronic tau leptons
National Institute Of Chemical Physics And Biophysics (NICPB)（国立化学物理与生物物理学研究所）；Tallinn University of Technology (TalTech)（塔林理工大学）；Institute for Experimental Physics, Universität Hamburg（汉堡大学实验物理研究所）
针对 FCC-ee 的 TeraZ 计划，提出首个全机器学习强子 tau 重建方法，通过多任务模型实现识别、衰变模式分类、电荷重建和四动量回归，性能优于传统方法。
The branching ratios of the τ^- -> h^- ν_τ, τ^- -> h^- π^0 ν_τ, τ^- -> h^- >=2 π^0 ν_τdecays have been measured using the 1991-1995 data recorded with the OPAL detector at LEP. These branching ratios are measured simultaneously using three selection criteria and are found to be BR(τ^- -> h^- ν_τ) = (11.98 +/- 0.13 +/- 0.16)% BR(τ^- -> h^- π^0 ν_τ) = (25.89 +/- 0.17 +/- 0.29)% BR(τ^- -> h^- >=2 π^0 ν_τ) = ( 9.91 +/- 0.31 +/- 0.27)% where the first error is statistical and the second is systematic.
Many theoretical models, like the Standard Model or SUSY at large tan(beta), predict Higgs bosons or new particles which decay more abundantly to final states including tau leptons than to other leptons. At the energy scale of the LHC, the identification of tau leptons, in particular in the hadronic decay mode, will be a challenging task due to an overwhelming QCD background which gives rise to jets of particles that can be hard to distinguish from hadronic tau decays. Equipped with excellent tracking and calorimetry, the ATLAS experiment has developed tau identification tools capable of worki…
In the framework of precision experiments, the search for electric dipole moments and the precise determination of magnetic dipole moments (g-2) have since long been of prime interest. Hadronic decays offer the best accuracy, since only the kinematic information carried by a single neutrino per decay is lost. Thus, they reveal more easily precious information on the helicity of the initial tau lepton. However, in contrast to one- or two-body hadronic final states, the description of hadronic multi-body final states depends on the model for the hadronic current. In this work, we determine how t…
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$--$τ$ conversion in nuclei, with $\ell = e,μ$. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments.
Exclusive hadronic decays of the tau lepton provide an excellent framework to study the hadronization of QCD currents in a non-perturbative energy region populated by many resonances. I give a short review both on the main theoretical tools employed to analyse experimental data and on how Theory compares with Experiment.
The structure of the form factors stemmed from the hadronization of QCD currents in the energy region of the resonances can be explored through the analyses of exclusive hadronic decays of the tau lepton. I give a short review on the later theoretical progress achieved in the description of experimental data.
We discuss the quantitative impact of duality violations on the determination of the strong coupling constant from hadronic tau decays, based on a preliminary analysis of OPAL data.
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and $\ell$-$τ$ conversion in nuclei ($\ell=e,μ$). Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. The related information from Belle II and foreseen future experiments can be easily incorporated into the resulting framework.
This PhD thesis studies some hadronic and radiative decays of the tau lepton using a Chiral Lagrangian including resonance fields. After a theoretical introduction, the decays to the $(πππ)^-$, $(KKπ)^-$ and $η^{(\prime)} π^- π^0$ hadronic states and $τ\to (π/K)^- γν_tau$ are analysed. Some material, which was not included in the corresponding references, is also discussed: The structure functions analysis for the 3 pion modes, the differential decay width as a function of the two-particle invariant masses in the considered three-meson modes and a simplified study of the $τ\to$η^{(\prime)} π^-…
We perform a global analysis of exclusive hadronic tau decays into one and two mesons using the low-energy limit of the Standard Model Effective Field Theory up to dimension six, assuming left-handed neutrinos. A controlled theoretical input on the Standard Model hadronic form factors, based on chiral symmetry, dispersion relations, data and asymptotic QCD properties, has allowed us to set bounds on the New Physics effective couplings using the present experimental data. Our results highlight the importance of semileptonic $τ$ decays in complementing the traditional low-energy probes, such nuc…
