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 Johannes.Bernhard@cern.ch
Dark Sectors • Dark sectors naturally present in many theoretical models (e.g. SUGRA, DarkSUSY, U D (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: U D (1) vector portal with “dark photon” A’ A’ decays: M. Battaglieri et al., arXiv:1707.04591 • If m A’ < 2 m c : visible decays into SM particles (e + e – , µ + µ – , hadrons) • If m A’ > 2 m c : invisible decays A’ à cc Johannes.Bernhard@cern.ch Status and Plans for NA64 2
The NA64 Experiment • 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 Johannes.Bernhard@cern.ch Status and Plans for NA64 3
The NA64 Experiment • 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 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/c 2 X-boson from the 8 Be excess • Search for dark photon decays into visible e + e – pairs • • 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 Johannes.Bernhard@cern.ch Status and Plans for NA64 4
NA64e Set-up for Invisible Mode • 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 10 5 – 10 7 electrons per 4.8s SPS extraction • Hermetic 4π detector with electromagnetic (pre-shower/PS and ECAL, 40 X 0 in total) and hadronic (HCAL1 – HCAL4, 4 x 7 l ) 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) Johannes.Bernhard@cern.ch Status and Plans for NA64 5
NA64e Set-up for Invisible Mode • 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 Johannes.Bernhard@cern.ch Status and Plans for NA64 6
Invisible Mode Searches • Process: A’ production in electron scattering, e – Z à e’ – Z A’, A’ à cc • 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 of 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) Johannes.Bernhard@cern.ch Status and Plans for NA64 7
Invisible Mode Searches • Statistics 2016 - 2018: 2.84 x 10 11 electrons on target (EOT) SM events • Crosscheck with dimuon production (Region I) • Rare QED reference process, only happening once per 10 5 EOT • Used for MC benchmarking due to similar q 2 as for A’ production • Cross-check of A’ yield, systematic errors, overall efficiency • Background prediction from data • No events observed in signal region (expected background 0.5 events) Johannes.Bernhard@cern.ch Status and Plans for NA64 8
Invisible Mode Searches 90% C.L. exclusion regions 90% C.L. exclusion regions • 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 a D now surpassing previous beam dump results and and start probing the parameter space for the elastic/inelastic scalar relic DM. Johannes.Bernhard@cern.ch Status and Plans for NA64 9
Visible Mode Searches • ATOMKI experiment: observed excess in e + e – pair production for p + 7 Li à 8 Be* à 8 Be + 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 π 0 à Xγ decay • Motivation to start measurement campaign for visible mode searches in NA64 Johannes.Bernhard@cern.ch Status and Plans for NA64 10
NA64e Set-up for Visible Mode • 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 (E WCAL + E WCAL = E beam ) • No signal in Veto and HCAL Johannes.Bernhard@cern.ch Status and Plans for NA64 11
Visible Mode Searches • Statistics: 8 x 10 10 EOT (2017+2018) 2017 data • Observed 3 events in 2017, identified Signal region as photons (no associated tracks) • No events observed in 2018 data 90% C.L. exclusion regions 2018 data Signal region Johannes.Bernhard@cern.ch Status and Plans for NA64 12
NA64 with Muon Beams A’ à e + e – • 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 [arXiv:1903.08767] • NA64µ proposal in context of “Physics beyond Colliders” initiative at CERN to CERN Courier, April 2017 clarify with high energy muon beams available at the M2 beamline [CERN-SPSC-P359] • Additional benefit: Improvement of NA64e sensitivity towards higher mass ranges A’ à invisible Johannes.Bernhard@cern.ch Status and Plans for NA64 13
NA64 with Muon Beams • 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 10 8 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 Johannes.Bernhard@cern.ch Status and Plans for NA64 14
NA64 with Muon Beams • Signature • Incoming tagged single 160 GeV/c µ • Outgoing less than 80 GeV/c µ • No energy in ECAL, VETO, HCAL • Sensitivity proportional to g µ2 • Backgrounds π, K à µ n decays • = Beam Momentum Station (spectrometer) • 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) 200 Y (mm) Y (mm) Mean x Mean x 0.1125 0.1125 3000 150 Mean y Mean y 13.99 13.99 − − Std Dev x 24.8 Std Dev x 24.8 Beam size ! x ~ ! y ~ 20 mm • 2000 100 Std Dev y 36.3 Std Dev y 36.3 1000 50 Divergence ! x’ ~ ! y’ ~ 0.2 mrad • 0 0 − 50 − 1000 • Large halo component − 100 − 2000 − 150 [CERN-PBC-REPORT-2018-002] NB: Change of scale (scattered muons) − 3000 − 200 − 200 − 150 − 100 − 50 0 50 100 150 200 − 3000 − 2000 − 1000 0 1000 2000 3000 X (mm) X (mm) Johannes.Bernhard@cern.ch Status and Plans for NA64 15
Expected Sensitivities µ Z à µ Z + (S,Z’), (S,Z’) à invisible • Possible to cover (g-2) µ favoured S. Gninenko et al., arXiv:1412.1400 parameter space with 10 10 MOT Assuming 160 GeV/c beams / no background (running time only a few days) • Running time for 10 12 MOT only a few months µ Z à µ Z + A’, A’ à invisible Johannes.Bernhard@cern.ch Status and Plans for NA64 16
Expected Sensitivities [S. N. Gninenko et al., Phys. Let. B 796 (2019) 117-122] Johannes.Bernhard@cern.ch Status and Plans for NA64 17
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