Study of tau neutrino production in NA65
experiment at CERN SPS
Yury Gornushkin (JINR, Dubna)
For DsTau Collaboration

Outline• Motivation• Technique description• Analysis status• Summary and Prospects

Yu.Gornushkin, Lomonosov Conference 2021

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Tau neutrino interaction cross-section
Tau neutrino is the least studied particle at the moment
Only a few measurements:
Direct detection in beam-dump: DONuT (DIS) – 9 events
Oscillated : OPERA (DIS), Super-K (QE), IceCube(DIS)
Cross section by DONuT: statistical error 33%
systematic error >50%
due to uncertainty in ντ flux
1-σ statistical errors

constnµn=6.1 based onPYTHIA

Using PYTHIA-derived value of n=6.1

Yu.Gornushkin, Lomonosov Conference 2021

More accurate measurementof ντ cross-section would
provide a complementary testof LU in neutrino scattering2

Hints of Lepton Universality Violation• Semi-leptonic decays of B meson prefers to decay into τ and ντ• Experimental results and SM prediction disagree by 4 σ• ΒC à J/Ψ + τ + ντ also has similar tendency (2 s)• Flavour Anomaly?
3The NA65/DsTau experiment at the CERN SPS• Study of ντ production for future tau neutrino experiments.
• 𝑫𝒔 double differential production cross section measurement as 95% of ντ are produced in𝑫𝒔 → 𝝉 → 𝑿 decays

To reduce 𝜈# flux
uncertainty from>50% to 10%

Fundamental input forfuture ντ experiment: SHiP,and indirectly FASER,
SND@LHC𝜈 oscillation experiments

DONuT-2008

Ds TauRe-evaluation of 𝜈! cross-section(2020)SND@LHC
𝜈! flux estimation202x?

𝜈! flux
coproduc nstraint throution
gh the studyof charm.
Yu.Gornushkin, Lomonosov Conference 2021

Precise 𝝂𝝉 cross section
New physics searches inneutrino scattering2022-Astrophysical 𝜈!
observations

4Principle of the experiment

Detection of double-kink + another Primary
protondecay topology within a few mm
with emulsion detector

Kink angle of Ds → τ
7 mradντDsD+Xτντ

X'~5 mm

Yu.Gornushkin, Lomonosov Conference 2021

5DsTau Collaboration§ Letter of Intent submitted to the CERN-SPSC in 2016
§ Test Beam Studies in November 2016 and May 2017
§ Technical Proposal in 2017
§ Pilot run 2018
‾ 1/10 of the full-scale experiment with tungsten target‾ 30 % uncertainty on 𝜈𝜏 flux
‾ Revise the DONUT result‾ Charm physics§ Approved as NA65 in 2019
§ DsTau paper: JHEP 01(2020)033§ Physics run 2021-2022– Full scale experiment with tungsten and molybdenum targets

DsTau web site: https://na65.web.cern.ch/Yu.Gornushkin, Lomonosov Conference 2021

Japan:
Aichi
Chiba
Kobe
KyushuNagoyaSwitzerland:
Bern

Romania:
Bucharest

Russia:Dubna
Turkey:METU
6Expected performance
Run

Beamtime

EmulsionsurfaceSystematic uncertainty forthe cross section
measurement

2018
pilot run

1 week48 m2(30 modules)

30% à Re-evaluationof the DONUT result

2021
physics run

2 weeks

545 m2(338 modules)

10% à Input for future
measurement2022
physics run

2 weeks

2018 run

2021-2022 run

DsTau goal

Systematic uncertainties

DONUT

With
DsTau

Ds differential cross section(xF dependence)

~0.5

0.1

Charm production cross section

0.17

Decay branching ratio

0.23

Target atomic mass effects(A dependence)

0.14

0.057

Nuclear Emulsion detectors have highest spatial resolution
Emulsion film

Nucl.Instrum.Meth.A 556 (2006) 80-86

Single emulsion film ishigh angular resolution tracker
Cross-sectional view
200 nmσx = 50 nm
θσθ = 0.35 mrad(0.02°)
Plastic base (200 μm)

Emulsion layers (70 μm)

Yu.Gornushkin, Lomonosov Conference 2021

• 1014 AgBr crystals per film
• Volume occupancy 30%• Detection efficiency
per crystal
16%
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Principle of DsTau experiment
A target instrumented
with high resolution
detectors uniformly
exposed to the proton
beam at SPS

400 GeV P

W: 0.05λ~105 p/cm2 !

Dsτ

X

D+

X’

In 2021-2022: 300 modules will be exposed to 4.9x109
protons to accumulate ~2.3x108 interactions with ~105
charmed particles pairs and ~1000 Ds → τ+X events
Yu.Gornushkin, Lomonosov Conference 2021

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Progress in automatic emulsion readout technique~4000 tracks in 2 x 2 mm2, 15 films

36 CPU72 GPU

13GB/s1000 μm

arxiv:1704.06814

0.5 m2 /hour
HTS - fastest emulsion data readout system wide field lens, multi-sensors, GPU.
20 GB/s or 2 PB/day with capability to process1000 m2 of emulsion per year

Data stored after scanning –3D coordinates and direction of track 10segments

Yu.Gornushkin, Lomonosov Conference 2021

Pilot run data processing
Scanning -> tracksegments (vectors) ineach plate

Tracking -> segments
combined to tracks

Precise alignment of
the emulsion plateswith reconstructed
tracksTracking withimproved geometry of
the setup after thealignment

TRUBA Computing Center
resources
CPU, GPU, 128 GB RAM
Storage capacity: 100+ TB

2 servers
CPU, GPU, 128/256 GB RAM
Storage : ~100 TB

1 processing server
CPU, GPU, 256 GB RAM
Storage: ~40 TB

Decay searchTurkey (METU):

Japan (Nagoya/Kyushu):

Russia (JINR):

Search for thevertexes

CERN
EOS
100 TB (data)
20 TB (MC)Romania (ISS):
1 processing server
CPU, GPU, 128 GB RAM
Storage: ~40 TB• 16 / 30 modules reconstructed, 2-4 months to process the rest.
Yu.Gornushkin, Lomonosov Conference 2021

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Pilot run data reconstruction performance:
Track registration efficiency >95%

Track density according to simulation

Alignment with proton
beam tracks,
100 tracks/mm2
Residual of track
segments to fitted line(RMS) ≃ 0.4 μm

Vertex density 500/cm2Reconstructed vertex position in the detector

Tracks emerging from tungsten
targetObserved tracks and vertexes density,
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secondary tracks multiplicity andangular distribution are consistent withFLUKA and Geant4 simulation

Yu.Gornushkin, Lomonosov Conference 2021

Efficiency of Ds → τ → X detection
Selection

Total
efficiency (%)(1) Flight length of Ds ≥ 2 emulsion layers

77(2) Flight length of t ≥ 2 layers & Δθ(Ds®t) ≥ 2
mrad

43

(3) Flight length of Ds < 5 mm & flight length of t 31
< 5 mm(4) Δθ(t) ≥ 15mrad

28(5) Pair charm: 0.1 mm < flight length < 5 mm(charged decays with Δθ > 15 mrad or neutraldecays)
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Yu.Gornushkin, Lomonosov Conference 2021

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Background estimation• Signal:• Main background: Hadron

Ds→τ decay: small kink
~7 mradinteractions of secondary hadrons ofproton interactions
No nuclear fragment detectedτ

Ds

X
D+X

τ

Ds

Charged hadrons
mimic kinks

XD0X

Neutral hadrons mimic
neutral charm decays

Signal probability 2.2x10-7/proton

Yu.Gornushkin, Lomonosov Conference 2021

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Ds momentum reconstruction

by Artificial Neural Network using topological variables

ProtontDs

FLtFLDsqtqXX

FL: Flight Length• Difficult to measure Ds momentum directly due toshort lifetime
à Ds momentum reconstruction by topologicalvariables• A Neural Network with 4 variables was trained withMC events• Momentum resolution for τ→1 prong decays
Δp/p = 18%
Yu.Gornushkin, Lomonosov Conference 2021

Δp/p = 18%

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True PDs (GeV)Double-decay topology events search• Kink• IP of daughter 291.6 μm• FL 2536.6 μm• kink angle 118 mrad
• Vee
• IP of daughters 20.9,
109.7 μm
• FL 554.5 μm• opening angle 242 mrad

About 23% of the data sample
processed with vertex searchand decay search programs.

•Work now is focused on
the software
optimization andupgrade to make it
faster and more efficient.

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100 μmYu.Gornushkin, Lomonosov Conference 2021

New algorithm of small kink search

Yu.Gornushkin, Lomonosov Conference 2021

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Preparation for 2021 physics run• Beam time is schedule in Sep-Oct 2021
• 20% of full statistics (30% including the pilotrun)• Scaled down due to COVID - 100 modules

Yu.Gornushkin, Lomonosov Conference 2021

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Preparation for the main physics runs
New gel production facility
electron microscopic view

Larger film size
10x12.5 à 25 cm x 20 cm

Film production facility – 15 m2 per day

Yu.Gornushkin, Lomonosov Conference 2021

HTS (0.5 m2/h) à HTS II (2.5 m2/h)

19Summary and outlook• Progress in nuclear emulsion readout made possible new generation of theexperiments• DsTau aims to measure double differential cross section of 𝑫𝒔 → 𝝉 production inproton-nuclei interactions to reduce uncertainty of tau neutrino flux in future
experiments down to 10% .
• The analysis of the pilot run data is ongoing, very high track density requires
upgrading software instruments and increasing computing resources.
• The physics run in September of 2021 is under preparation. Both hardware andsoftware have been revised to meet very challenging experimental conditions.
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DsTau paper: JHEP 01(2020)033
DsTau web site: https://na65.web.cern.ch/
Yu.Gornushkin, Lomonosov Conference 2021

Thank you!

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Yu.Gornushkin, Lomonosov Conference 2021

Backup

22Emulsion = a detector with high detection channel density

ATLAS-IBL pixel sensor
FE-14
1 pixel =250 µm x 50 µm x 200 µm

150 µm x 120 µm x50 µm

231.2x108 channels (crystals) in thisvolume.
1014 channels in a film (12.5 cm x 10cm).
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Sum of all channels in ATLAS =~108

High density of detection channels, O(10 ) channels/cc, makes emulsion attractive
for many purposes.

Analysis scheme of double-kink search
Step 2

Step 1••Proton
beam

Full area scanning by the fast scanning system
Select decays with Δθ > 20 mrad

ντDsX

τ

•

Precise measurement to detect
Ds -> τ decay (a few mrad)Dsτντ

D+X'Hyper Track Selector (HTS)Scanning speed 0.5 m2/h/layer
Angular resolution ~2 mrad

Dedicated high-precision systems (Bern, Dubna)

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Angular resolution ~0.3 mrad

25

Neutrino beam line in DONuT
Target(Tungsten 1m, 10λint)

nt detector

Sweeping magnets(pT kick 6GeV/c, 3GeV/c)

Passive shielding(Iron, lead, concrete)

Emulsion + SFT
hybrid detector

800 GeVprotonsMuID

40mnt Beam sourceνμνe

Calculated energy
spectra of neutrinos
interacting in theemulsion targetντντ

Main source
neD0 , D± , Ds , ΛcnμD0 , D± , Ds , Λc , π, K

nt

Ds26

Results from DONuTντ CC cross section

nt CC cross section was calculated as a function of one parameter.
The energy-independent part was parameterized aswhere n is the parameter controlling the longitudinal part ofthe Ds differential cross section
Phenomenological formulaxF is Feynman x (xF =2pCMz/√s) andpT is transverse momentum

longitudinal
dependencetransverse
dependence27