Status and Plans for NA64 16 th International Conference on Topics in - - PowerPoint PPT Presentation

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Status and Plans for NA64 16 th International Conference on Topics in - - PowerPoint PPT Presentation

Jun 15, 2023 169 likes •367 views

Status and Plans for NA64 16 th International Conference on Topics in Astroparticle and Underground Physics, Toyama 2019 Johannes Bernhard (CERN) on behalf of the NA64 collaboration and the PBC Conventional Beams Working Group

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SLIDE 1

Status and Plans for NA64

16th International Conference on Topics in Astroparticle and Underground Physics, Toyama 2019

Johannes Bernhard (CERN) on behalf of the NA64 collaboration and the PBC Conventional Beams Working Group

Johannes.Bernhard@cern.ch

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SLIDE 2

Dark Sectors

Johannes.Bernhard@cern.ch Status and Plans for NA64 2

  • Dark sectors naturally present in many theoretical models (e.g. SUGRA,

DarkSUSY, UD(1), 2HDM, …)

  • In the Standard Model, only via weak coupling via gravitation (SM singlets)
  • In BSM models: additional portals via e.g. gauge kinetic mixing
  • One example: UD(1) vector portal with “dark photon” A’
  • M. Battaglieri et al., arXiv:1707.04591

A’ decays:

  • If mA’ < 2 mc: visible decays

into SM particles (e+e–, µ+µ–, hadrons)

  • If mA’ > 2 mc: invisible

decays A’ àcc

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SLIDE 3

The NA64 Experiment

Johannes.Bernhard@cern.ch Status and Plans for NA64 3

  • Active beam-dump experiment at CERN SPS North Area
  • Search for dark sector physics in the sub-GeV range with missing energy

events

  • International collaboration of 50+ researchers from 14 institutes
  • History
  • 12/2013

Proposal to SPSC (P348)

  • 04/2014

Recommended for tests

  • 10/2015

Two-week test run

  • 02/2016

Proposal approved as SPS experiment NA64

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SLIDE 4

The NA64 Experiment

Johannes.Bernhard@cern.ch Status and Plans for NA64 4

2016 – 2018 data taking

  • Search for vector mediator A’ of light thermal dark matter

production via invisible decay channel

  • Search for a possible 17 MeV/c2 X-boson from the 8Be excess
  • Search for dark photon decays into visible e+e– pairs
  • Active beam-dump experiment at CERN SPS North Area
  • Search for dark sector physics in the sub-GeV range with missing energy

events

  • International collaboration of 50+ researchers from 14 institutes
  • History
  • 12/2013

Proposal to SPSC (P348)

  • 04/2014

Recommended for tests

  • 10/2015

Two-week test run

  • 02/2016

Proposal approved as SPS experiment NA64

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SLIDE 5

NA64e Set-up for Invisible Mode

Johannes.Bernhard@cern.ch Status and Plans for NA64 5

  • Tertiary electron beam at 100 GeV/c in H4 beam line with low

impurities (1% π and low momentum e–, less than 0.2% µ and K)

  • Intensity 105 – 107 electrons per 4.8s SPS extraction
  • Hermetic 4π detector with electromagnetic (pre-shower/PS and ECAL,

40 X0 in total) and hadronic (HCAL1 – HCAL4, 4 x 7l) calorimetry

  • Electron tagging by synchrotron radiation detector (SRD) and

Micromega and GEM trackers (T1 – T4) around magnetic spectrometer (Magnet 1+2), 1% momentum resolution

  • Coincidence Trigger with scintillators (S1 – S3),

Veto system (V1 – V2), PS and ECAL

  • Muon ID (MU1 – MU4)
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SLIDE 6

NA64e Set-up for Invisible Mode

Johannes.Bernhard@cern.ch Status and Plans for NA64 6

  • Improvements for 2018
  • Re-arrangement of HCALs for suppression of the neutral upstream

background

  • New Straw trackers with larger area for suppression of the charged

upstream background

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SLIDE 7

Invisible Mode Searches

Johannes.Bernhard@cern.ch Status and Plans for NA64 7

  • Process: A’ production in electron scattering, e– Z à e’– Z A’, A’ àcc
  • Signal: Tagged incoming 100 GeV/c electron

beam, energy deposition from the recoil e’– in the ECAL of less than 50 GeV, no energy in the Veto and HCAL

  • Backgrounds
  • Upstream interactions of beam

with material

  • µ, π, K decays in flight
  • Beam tails below momentum
  • f 50 GeV/c
  • Energy leak from ECAL or HCAL
  • Additional check: Lateral and longitudinal shower shape consistent

with that expected from a electromagnetic shower

  • Detection efficiency: 50% – 60% (depending on A’ mass)
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SLIDE 8

Invisible Mode Searches

Johannes.Bernhard@cern.ch Status and Plans for NA64 8

  • Statistics 2016 - 2018: 2.84 x 1011 electrons
  • n target (EOT)
  • Crosscheck with dimuon production (Region I)
  • Rare QED reference process, only

happening once per 105 EOT

  • Used for MC benchmarking due to similar q2

as for A’ production

  • Cross-check of A’ yield, systematic errors,
  • verall efficiency
  • Background prediction from data
  • No events observed in signal region

(expected background 0.5 events)

SM events

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SLIDE 9

Invisible Mode Searches

Johannes.Bernhard@cern.ch Status and Plans for NA64 9

  • Recently accepted in PRL, to be published as PRL Editor’s suggestion.

Published also in EPJ Web Conf. 212 (2019) 06005.

  • Resulting constraints on models depending on aD now surpassing previous

beam dump results and and start probing the parameter space for the elastic/inelastic scalar relic DM.

90% C.L. exclusion regions 90% C.L. exclusion regions

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SLIDE 10

Visible Mode Searches

Johannes.Bernhard@cern.ch Status and Plans for NA64 10

  • ATOMKI experiment: observed excess in e+e– pair production for

p + 7Li à 8Be* à 8Be + e+ + e–

[A. J. Krasznahorkay et al. Phys. Rev. Lett.116, 042501 (2015)]

  • Possible explanation via new ‘protophobic’ gauge boson X with mass

around 17 MeV [J. L. Feng et al. Phys. Rev. D95, 035017 (2017)]

  • Boson X excluded to be A’ due to constraints from π0 àXγ decay
  • Motivation to start measurement campaign for visible mode searches

in NA64

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SLIDE 11

NA64e Set-up for Visible Mode

Johannes.Bernhard@cern.ch Status and Plans for NA64 11

  • Process: Short-lived X-boson would be produced in e– Z à e– Z + X followed

by a prompt X à e+e– decay

  • Set-up changes:
  • Addition of tungsten calorimeter as active beam dump
  • Re-arrangement of ECAL and trackers for e+e– detection (2017)
  • Increase of beam energy to 150 GeV/c and re-arrangement of HCAL and

addition of Straw tracker for vetoing upstream background (2018)

  • Signature
  • 100 / 150 GeV/c incoming e– track
  • Single shower in WCAL and single shower in ECAL
  • Energy conservation between WCAL and ECAL

(EWCAL + EWCAL = Ebeam)

  • No signal in Veto and HCAL
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SLIDE 12

Visible Mode Searches

Johannes.Bernhard@cern.ch Status and Plans for NA64 12

  • Statistics: 8 x 1010 EOT (2017+2018)
  • Observed 3 events in 2017, identified

as photons (no associated tracks)

  • No events observed in 2018 data

Signal region 2018 data 2017 data Signal region

90% C.L. exclusion regions

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SLIDE 13

NA64 with Muon Beams

Johannes.Bernhard@cern.ch Status and Plans for NA64 13

  • Explanation of (g-2)µ anomaly ruled out

in both visible e+e– and invisible channels

  • Still possible in case of

new scalar or vector state coupling pre- dominantly to µ and t

  • NA64µ proposal in context of “Physics

beyond Colliders” initiative at CERN to clarify with high energy muon beams available at the M2 beamline [CERN-SPSC-P359]

  • Additional benefit: Improvement of

NA64e sensitivity towards higher mass ranges

[arXiv:1903.08767] CERN Courier, April 2017

A’ à e+e– A’ à invisible

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SLIDE 14

NA64 with Muon Beams

Johannes.Bernhard@cern.ch Status and Plans for NA64 14

  • Production reaction µ Z à µ Z + (S,Z’), (S,Z’) à invisible
  • Proposed set-up
  • 160 GeV µ beam from M2 beamline impinging on target (e.g. Pb or W)
  • High intensity beam with larger than 108 µ / 4.8s SPS extraction
  • Tagging of incoming µ: BMS + MS1 spectrometers (Magnets + Trackers)
  • Tagging of outgoing µ: MS2 spectrometer (Magnets + Trackers)
  • 4π fully hermetic detector ECAL + HCAL + Veto
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SLIDE 15

X (mm)

200 − 150 − 100 − 50 − 50 100 150 200

Y (mm)

200 − 150 − 100 − 50 − 50 100 150 200

Mean x 0.1125 Mean y 13.99 − Std Dev x 24.8 Std Dev y 36.3 Mean x 0.1125 Mean y 13.99 − Std Dev x 24.8 Std Dev y 36.3

NA64 with Muon Beams

Johannes.Bernhard@cern.ch Status and Plans for NA64 15

  • Signature
  • Incoming tagged single 160 GeV/c µ
  • Outgoing less than 80 GeV/c µ
  • No energy in ECAL, VETO, HCAL
  • Sensitivity proportional to gµ2
  • Backgrounds
  • π, K à µn decays
  • Energy leaks / Non-hermetic detectors
  • Low energy incoming muons (from tails below 75 GeV/c)
  • Physical background (trident, EW processes, …)
  • Beam studies within PBC Conventional Beams Working Group

(Dipanwita Banerjee, JB)

  • Beam size !x ~ !y ~ 20 mm
  • Divergence !x’ ~ !y’ ~ 0.2 mrad
  • Large halo component

(scattered muons)

3000 − 2000 − 1000 − 1000 2000 3000

X (mm)

3000 − 2000 − 1000 − 1000 2000 3000

Y (mm)

= Beam Momentum Station (spectrometer) NB: Change of scale [CERN-PBC-REPORT-2018-002]

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SLIDE 16

Expected Sensitivities

Johannes.Bernhard@cern.ch Status and Plans for NA64 16

  • Possible to cover (g-2)µ favoured

parameter space with 1010 MOT (running time only a few days)

  • Running time for 1012 MOT only

a few months

  • S. Gninenko et al., arXiv:1412.1400

Assuming 160 GeV/c beams / no background

µ Z à µ Z + (S,Z’), (S,Z’) à invisible µ Z à µ Z + A’, A’ à invisible

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SLIDE 17

Expected Sensitivities

Johannes.Bernhard@cern.ch Status and Plans for NA64 17

[S. N. Gninenko et al., Phys. Let. B 796 (2019) 117-122]

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SLIDE 18

Summary and Outlook

Johannes.Bernhard@cern.ch Status and Plans for NA64 18

  • Active beam dump searches for light dark matter have been proven by

the NA64 experiment to be very powerful via both invisible and visible modes.

  • The combined search with both electron and muon beams has a great

potential to probe a large area of the light dark matter parameter space.

  • NA64e is approved to continue data taking in 2021 with an improved

set-up after CERN’s currently ongoing accelerator consolidation and upgrade period (LS2).

  • The NA64µ proposal is currently under discussion by SPSC and

detailed studies have been provided by the PBC Conventional Beams Working Group, report available [CERN-PBC-REPORT-2018-002].

  • A pilot run for tests in the M2 beamline is currently being prepared.
  • Further searches for invisible decays of hadrons and for milli-charged

particles are being investigated.

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SLIDE 19

Thank you!

Acknowledgements: The NA64 collaboration and the PBC Conventional Beams Working Group. These slides contain valuable input from discussions with and presentations from

  • D. Banerjee, S. Gninenko, P. Crivelli, L. Molina Bueno and E. Depero.