New Limits on Heavy Neutrino from NA62 Michal Koval (CERN) michal.koval@cern.ch on behalf of the NA62 collaboration EPS HEP 2017 Venice, Italy, 5 12 July 2017
Kaon Decay Experiments at CERN Earlier: NA31 1997: ε /ε: K L +K S 1998: K L +K S Switzerland Jura mountains SPS NA48/NA62: centre of the LHC LHC France NA48 discovery of direct CPV NA48/1 1999: K L +K S K S HI 2000: K L only K S HI 2001: K L +K S K S HI 2002: K S /hyperons 2003: K + /K NA48/2 2004: K + /K Geneva airport N NA62 R K phase 2007: K ± e2/k ± µ2 2008: K ± e2/k ± µ2 2014: pilot run tests tests This talk Kaon decay in flight experiments. NA62: 200 participants, 30 institutes NA62 2015: commissioning run 2016 : K + π + νν run 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 1
Heavy Neutrino: Motivation Observation of neutrino oscillations massive neutrinos need to be accommodated in SM Example of a SM extension: Neutrino Minimal SM (νmsm) [Asaka et al., PLB 620 (2005) 17] 3 right-handed neutrinos added to SM, masses:, : dark matter candidate : extra CPV-phases to account for Baryon Asymmetry, produce SM masses via see-saw mech. 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 2
Heavy Neutrino: Motivation Observation of neutrino oscillations massive neutrinos need to be accommodated in SM Example of a SM extension: Neutrino Minimal SM (νmsm) [Asaka et al., PLB 620 (2005) 17] 3 right-handed neutrinos added to SM, masses:, : dark matter candidate : extra CPV-phases to account for Baryon Asymmetry, produce SM masses via see-saw mech. If, heavy neutrinos observable via production in: R. Shrock PLB96 (1980) 159 This talk: search for peaks in NA62 2007 data sample: NA62 2015 data sample: Other searches look for decays of heavy neutrinos (HN), e.g. Kinematic enhancement factor 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 3
NA62 Experiment in 2007 Main measurement: Phys. Lett. B 719 (2013) 326 Beam momentum: (74 ± 2) GeV/c Triggers: 1-track, 1-track (scaled down) Subdetectors: Magnetic spectrometer (4 DCHs) Scintillator hodoscope (HOD) Liquid Krypton EM calorimeter (LKr) Muon veto system (MUV) 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 4
Data Sample in 2007 Kaon decays in fiducial volume: Heavy neutrino (HN) MC simulation Acceptance vs. HN mass: Missing mass resolution vs. HN mass: Missing mass: Signal region: 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 5
Heavy Neutrino Search in 2007 Data Rolke-Lopez method used to find upper limits on number of signal events Heavy neutrino mass step: Search window size defined by HN mass resolution No HN signal observed with >3σ significance 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 6
NA62 Experiment in 2015 Main goal, 10% precision measurement of: NA62 collaboration, JINST 12 (2017) P05025 Beam momentum: 75 GeV/c (±1%) Subdetectors: Tracking: kaon (GTK), π/μ/e (Straw) Hermetic veto detectors: Photons (LAV, LKr, SAC, IRC) Muons (MUV) Particle identification Kaon in the beam (KTAG) π/μ/e (RICH, LKr, MUV) Data taking conditions in 2015: Minimum bias at 1% of design beam intensity Beam tracker not available; kaon momentum estimated as beam average 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 7
Data Sample in 2015 Kaon decays in fiducial volume: Heavy neutrino (HN) MC simulation Acceptance vs. HN mass: Missing mass resolution vs. HN mass: Squared missing mass: Signal region: 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 8
Heavy Neutrino Search in 2015 Data Rolke-Lopez method used to find upper limits on number of signal events Heavy neutrino mass step: Search window size for each mass hypothesis: Expected background Observed events No HN signal observed with >3σ significance 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 9
Upper Limits on U l4 2 Limits from heavy neutrino production searches NA62 2007 data analysis: Extends the mass range for upper limits on Most stringent limit in NEW NEW NA62 2015 data analysis: Reaches on limits in the range 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 10
Summary and Outlook NA62 searches for heavy neutrino production in charged kaon decays were presented No heavy neutrino signal observed Analysis of NA62 2007 data (arxiv:1705.07510): About 60 million K + decays in the fiducial volume Improves limits on for Limits from heavy neutrino production searches Analysis of NA62 2015 data: About 300 million K + decays in the fiducial volume New limits on reaching for Future prospects: Major analysis improvements with NA62 2016 high intensity data set, e.g. fully working beam tracker 7. 7. 2017 EPS HEP 2017, michal.koval@cern.ch 11