The DsTau experiment (NA65) : Study of tau neutrino production at the CERN-SPS

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Recent news

2019/11/12 DsTau paper accepted for publication in JHEP

A paper describing DsTau's physics goals, design and results from beam tests has been accepted by JHEP for publication.

2019/06/12 DsTau approved by the CERN Research Board

A great news arrived. DsTau was approved by CERN as a CERN experiment! An experiment number NA65, which means 65th experiment at the North Area, is given to DsTau. Congratulations to everybody. The real endevor will start from here!

2019/06/11 DsTau paper has appeared on arXiv

A paper descrbing our motivation, detector setup and analysis scheme was submitted. The preprint is available here .

2019/04/04 CERN SPSC recommended approving DsTau

In the 133rd meeting of the SPSC, the SPSC recommended approving DsTau. Now we wait for the decision of the CERN Research Board, which will be held in the middle of June.

2019/04/02 Open presentation at the SPSC

It is time for the annual review. The status report of DsTau was submitted. And, an open presentation was given by A. Ariga in the 133rd meeting of the SPSC. The increased statistics of double charm candidates has allowed us to analyze them in a statistical way.

2018/10/10 Japanese grant has been approved

A JSPS grant (KAKENHI): Fund for the Promotion of Joint International Research (Fostering Joint International Research (B)) was approved, which would cover the major cost of the 2021 run.

2018/8/29 DsTau pilot run successfully finished

The pilot run before the long shut down of the CERN accelerator complex (LS2) was performed at the CERN SPS H2 beamline from 22nd to 29th August. It is a 1/10 scale experiment with respect to the full physics program. Ten collaborators from the DsTau collaboration joined this campaign. All the planned programs were completed thanks to the excellent performance of the accelerators. Now we are developing and analysing data. We are aiming to revise the past tau neutrino cross-section result with this data, by reducing its systematic uncertainty.

2018/6/16 DsTau on the CERN EP news letter

An article concerning the DsTau project was published in the newsletter of the CERN EP department (, or the direct link to the article). This article was written by A. Ariga (LHEP) and T. Ariga (LHEP and Kyushu University), and explains an overview of the project. DsTau is getting the communityfs notice.

2018/6/4 Film production has started

The film production in Nagoya (about 25 m^2, 50% of the total to be produced) has been started. Colleagues from Russia, Romania, Trukey as well as Japan are working hard.

2018/2/3 Turkish funding has been approved

The Turkish group is actively participating for the construction and data analysis of DsTau. The funding for next 3 years has just been approved.

2018/1/25 SPSC fixed the 2018 run schedule and recommended the 2021 run

T. Ariga gave a presentation concerning the DsTau proposal at the open session of the SPSC held on 22nd January 2018 ( The first double charm candidate from the beam test was also reported. As the outcome of the SPSC, our beam schedule for the 2018 run was fixed at the end of August for 1 week. Furthermore, the beamtime request for 2021 (Physics run) was recommended by the SPSC.

2017/10/19 SPSC recommended the 2018 run (pilot run)

The beamtime request for 2018 (Pilot run) has been approved by the CERN SPSC (SPS PS Scientific Committee) on 17th October 2017. The 2018 run will be used to establish analysis scheme for the physics run beyond the long shutdown of the CERN accelerator complex (LS2).

2017/9/1 Japanese funding for the 2018 run has been granted

The Japan Society for the Promotion of Science funded the pilot run in 2018 in the framework of Grant-in-Aid for Research Activity start-up.

2017/8/29 Proposal of the DsTau project has been submitted

The proposal of DsTau , titled "Study of tau-neutrino production at the CERN SPS" (SPSC-P-354) was submitted to SPSC.

Tau neutrino :

The least known standard model particle

Key to explore new physics

quarksu c t
d s b
leptonse μ τ
νe νμ

Direct observation of tau neutrino production

Measurement of Ds→τ→X decays

Detection of double kink topology.

Nano-resolution trackers

50 nm spatial resolution with emulsion detectors

International collaboration:

Young, experienced and talented

And we need you!

The DsTau project

The DsTau project has been proposed at the CERN SPS to study tau-neutrino production aiming at providing important information for future ντ measurements where high ντ statistics is expected. The results of DsTau are a prerequisite for measuring the ντ charged-current cross section, which has never been adequately measured (only the DONUT measurement was reported so far). Precise measurement of the cross section would enable a search for new physics effects in ντ-nucleon CC interactions. It also has practical implications for neutrino oscillation experiments and high-energy astrophysical ντ observations. The dominant source of ντ is the sequential decay of Ds mesons, Ds+ → τ+ ντ → X ντ ντ and Ds- → τ- ντ → X ντ ντ produced by high-energy proton interactions. Directly measuring Ds→ τ decays will provide an inclusive measurement of the Ds production rate and the decay branching ratio to τ. The Ds momentum will be reconstructed by combining the topological variables measured in the emulsion detector.

The project aims at detecting 103 Ds → τ decays to measure the Ds differential production cross section and to reduce systematic uncertainty in the tau-neutrino cross section measurement from about 50% to 10%. For this purpose, emulsion detectors with a nanometer precision readout will be used. An emulsion detector with a crystal size of 200 nm has a position resolution of 50 nm, allowing for kink detection with a threshold of 2 mrad at the 4σ confidence level. The global analysis will be based on fast scanning of the full area by the HTS system. After the τ decay trigger, the events will be analysed by dedicated high-precision systems using a piezo-based high-precision z-axis, allowing the emulsion hits to be measured with a nanometric resolution. Each detector unit consists of a 500-µm-thick tungsten target, followed by 10 emulsion films interleaved with 200-µm-thick plastic sheets acting as decay volumes for short-lived particles as well as high-precision particle trackers. Ten such units are used to construct a module, which is followed by an ECC to measure the momenta of the daughter particles. With this module, 4.6 × 109 protons on target are needed to accumulate 2.3 × 108 proton interactions in the tungsten plates.

The data generated by this project will enable the ντ cross section measured by DONUT to be re-evaluated, which should significantly reduce the total systematic uncertainty. Once ντ production is established, the next stage will be to increase the number of ντ detected events. This could be achieved within the framework of the SHiP project at CERN because its beamline is well suited for this task. The DsTau project aims to look for new physics effects in ντ-nucleon CC interactions with a total uncertainty of 10%. In addition to the main aim of measuring Ds, analysing 2.3 × 108 proton interactions, combined with the high yield of 105 charmed decays produced as by-products, will enable the extraction of additional physical quantities. Based on the results of beam tests in 2016 and 2017, a pilot run is scheduled for 2018 and physics runs are planned from 2021 after the upcoming long shutdown of the accelerator complex at CERN.

Movie of the target mover

The first double charm candidate (associate charm production)

The first double charm candidate, which is a benchmark for the short lived particle detection, was found in the analysis of about 1800 proton interactions. The observed feature is shown in figure, conssistent with a D0, D± pair production and a D0→Kπ decay since the D0 and the vee plane made by the vee's daughters is coplanar (i.e. two body decay). The flight lengths of the kink and vee parents are 2536 µm and 554 µm, respectively. (The unit of the red scale bar is µm.)

Interactive display of the first double charm event found in the test beam data (detail).

Try mouse click to rotate.

Zoom   Highlight double charm   Animation

Red scale bar = 500 micron. Mouse drag to rotate. Wheel or slide bar to zoom. Open with new tab (recommended).

Movie of the event display

More reading

Our DsTau proposal can be found at the following links.
Proposal (SPSC-P-354) 2017/8/29:

Presentation at the 128th Meeting of the SPSC (open session, 2018/1/23):


  Aichi University of Education
  Kobe University
  Kyushu University
  Nagoya University

  Institute of Space Science

  JINR-Joint Institute for Nuclear Research

  University of Bern

  METU-Middle East Technical University


Spokesperson: A. Ariga (, University of Bern, Switzerland
Deputy Spokesperson: T. Ariga (, Kyusyu University, Japan

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