Publications

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Tau reconstruction at CMS with a focus on high $ p_{T} $ taus

Soham Bhattacharya on behalf of The CMS Collaboration

SciPost Phys. Proc. 1, 050 (2019) · published 22 February 2019 | · pdf

We present the algorithm and performance of tau reconstruction at the CMS experiment, while highlighting a dedicated reconstruction algorithm that uses calorimeter hits instead of tracks to reconstruct taus with high transverse momentum. Describing the standard Hadrons-Plus-Strips (HPS) algorithm and its dependence on track reconstruction and shower modelling, we present the calorimetric tau (calo-tau) reconstruction that uses minimal track information for high $ p_{T} $ taus. The pros and cons of these algorithms are discussed along with their performance and potential uses. It is found that the calo-tau algorithm outperforms the HPS algorithm in the high efficiency region. This study is work in progress, and is an attempt to tune the reconstruction for high $ p_{T} $ taus. The calo-tau algorithm is not yet an official tau reconstruction algorithm for CMS.
Search for lepton-flavour-violating decays of the $Z$ boson into a $\tau$-lepton and a light lepton with the ATLAS detector

Wing Sheung Chan on behalf of the ATLAS collaboration

SciPost Phys. Proc. 1, 048 (2019) · published 22 February 2019 | · pdf

Lepton flavour violation in the charged lepton sector is an unambiguous signal of physics beyond the Standard Model. Searches for lepton flavour violation in decays of the $Z$ boson with the ATLAS detector is reported, focusing on decays into an electron or muon and a hadronically decaying $\tau$-lepton, using $pp$ collisions data with a centre-of-mass energy of 13 TeV. Upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95\% confidence level: $\mathcal{B}(Z\to e\tau) < 5.8\times10^{-5}$ and $\mathcal{B}(Z\to \mu\tau) < 2.4\times10^{-5}$. When combined with a previous ATLAS result based on $pp$ collisions data with a centre-of-mass energy of 8 TeV, an upper limit of $\mathcal{B}(Z\to \mu\tau) < 1.3\times10^{-5}$ is obtained.
Measurement of the spectral function for the $τ^-\to K^-K_Sν_τ$ decay in BABAR experiment

Sergey I. Serednyakov on behalf of the BABAR collaboration

SciPost Phys. Proc. 1, 046 (2019) · published 22 February 2019 | · pdf

The decay $\tau^{-}\to K^{-}K_S\nu_{\tau}$ has been studied using $430\times10^6$ $e^+e^-\to \tau^+\tau^-$ events produced at a center-of-mass energy around 10.6 GeV at the PEP-II collider and studied with the BABAR detector. The mass spectrum of the $K^{-}K_S$ system has been measured and the spectral function has been obtained. The measured branching fraction ${\cal B}(\tau^{-}\to K^{-}K_S\nu_{\tau}) = (0.739\pm 0.011(\rm stat.)\pm 0.020(\rm syst.))\times 10^{-3}$ is found to be in agreement with earlier measurements.
Status of DUNE

Alessandra Tonazzo on behalf of the DUNE Collaboration

SciPost Phys. Proc. 1, 043 (2019) · published 21 February 2019 | · pdf

The Deep Underground Neutrino Experiment (DUNE) is a next-generation underground observatory, to be located in the USA, aiming at precise measurements of long-baseline neutrino oscillations over a 1300 km baseline, detection of supernova neutrinos and search for nucleon decay and other physics beyond the Standard Model. The far detector, a very large liquid argon time projection chamber, requires a dedicated prototyping effort (ProtoDUNE), currently ongoing at CERN.

1 citation
Tau-lepton Physics at the FCC-ee circular e$^+$e$^-$ Collider

Mogens Dam

SciPost Phys. Proc. 1, 041 (2019) · published 21 February 2019 | · pdf

The future FCC-ee collider is designed to deliver $\mathrm{e^+e^-}$ collisions to study with ultimate precision the Z, W, and Higgs bosons, and the top quark. In a high-statistics scan around the Z pole, $1.3\times 10^{11}$ events $\mathrm{Z}\to\tau\tau$ will be produced, the largest sample of $\tau\tau$ events foreseen at any lepton collider. With their large boost, $\tau$ leptons from Z decays are particularly well suited for precision measurements. The focus of this report is on tests of lepton universality from precision measurement of $\boldsymbol{\tau}$ properties and on tests of charged lepton flavour violation in Z decays and in $\tau$ decays. In both of these areas, FCC-ee promises sensitivities well beyond present experimental limits.

25 citations
MEG final results and progress towards MEG II

Toshiyuki Iwamoto on behalf of the MEG II collaboration

SciPost Phys. Proc. 1, 040 (2019) · published 21 February 2019 | · pdf

The MEG experiment, which is to search for lepton flavor violating muon decay, had been successfully finished in 2013. The final sensitivity of the experiment was 5.3 × 10−13, and since the experiment did not find any signal, the upper limit of the branching ratio of the μ+ → e+γ was set to be 4.2 × 10−13 at 90% CL. The MEG II experiment will improve the sensitivity by an order of magnitude with three years data taking, and the target sensitivity is 6×10−14. In 2018 after the detector integration, the muon beam data taking will be planned with limited number of readout channels. In 2019, the engineering run and the physics run will be started.
$μ$-$e$ conversion experiments at J-PARC

Natsuki Teshima

SciPost Phys. Proc. 1, 039 (2019) · published 21 February 2019 | · pdf

There are two plans of experiments to search for muon to electron ($\mu$-$e$) conversion at J-PARC, which are called DeeMe and COMET. The $\mu$-$e$ conversion is one of the charged lepton flavor violation processes. The processes are forbidden in the Standard Model, but some theories beyond the Standard Model predict relatively large branching ratios at orders of $10^{-12}$ to $10^{-17}$. DeeMe will be conducted with a sensitivity of $1\times10^{-13}$ using a carbon target for 1 year, and COMET will be done with that of $3\times10^{-15}$ in Phase-I. In this article, the current status of these two experiments will be presented.

1 citation
Searching for muon to electron conversion: The Mu2e experiment at Fermilab

Richard Bonventre on behalf of the Mu2e Collaboration

SciPost Phys. Proc. 1, 038 (2019) · published 21 February 2019 | · pdf

The Mu2e experiment will measure the charged-lepton flavor violating (CLFV) neutrino-less conversion of a negative muon into an electron in the field of a nucleus. Mu2e will improve the previous measurement by four orders of magnitude, reaching a 90% C.L. limit of $8\times10^{-17}$ on the conversion rate. The experiment will reach mass scales of nearly $10^4$ TeV, far beyond the direct reach of colliders. The experiment is sensitive to a wide range of new physics, complementing and extending other CLFV searches. Mu2e is under design and construction at the Muon Campus of Fermilab; we expect to start taking physics data in 2022 with 3 years of running to achieve our target sensitivity.

4 citations
The Mu3e experiment at PSI

Alessandro Bravar on behalf of the Mu3e Collaboration

SciPost Phys. Proc. 1, 037 (2019) · published 21 February 2019 | · pdf

Mu3e will search for charged Lepton Flavor Violation in the neutrinoless muon decay $\mu^+ \rightarrow e^+ e^- e^+$ with a sensitivity down to $10^{-16}$ (90\% C.L.) using the world most intense continuous muon beam at PSI. This search requires a large acceptance detector capable of coping with rates of up to $2 \times 10^9$ stopped muons per second with excellent momentum, spatial, and time resolution. The Mu3e detector is based on thin monolithic active silicon pixel sensors for tracking in conjunction with scintillating fibers and tiles for timing measurements. The Mu3e apparatus is under constructions and first data is expected in 2020.
Tau-decay determination of the strong coupling

Antonio Pich

SciPost Phys. Proc. 1, 036 (2019) · published 21 February 2019 | · pdf

We review the current status of the determination of the strong coupling from tau decay. Using the most recent release of the ALEPH data, a very comprehensive phenomenological analysis has been performed, exploring all strategies previously considered in the literature and several complementary approaches. Once their actual uncertainties are properly assessed, the results from all adopted methodologies are in excellent agreement, leading to a very robust and reliable value of the strong coupling, $\alpha_s^{(n_f=3)}(m_\tau^2) = 0.328\pm 0.013$, which implies $\alpha_s^{(n_f=5)}(M_Z^2) = 0.1197\pm 0.0015$.

3 citations

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