A48 NNA62 s d ν ν
+ + K → π νν – NA62 First Result
Bob Velghe* , on behalf of the NA62 collaboration
CIPANP 2018 Palm Springs, CA, May 29, 2018
*TRIUMF, Vancouver, BC Outline of the Talk
10−4 Camerini Experimental upper limit
10−5
Klems 10−6 Cable ) ¯ ν −7 Asano ν 10
+ E787 π
+ + → → π νν + − Decay K 8 K ( 10 B
−9 NA62 Experiment 10 E949
10−10
10−11 1970 1980 1990 2000 2010 2020 Publication year
In blue: Dahl 1969, Gaillard 1974, Ellis 1988, Buchalla 1996, Mescia 2007, Brod 2011 and Buras 2015 + + K → π νν – In the Standard Model
s d W u, c, t s d ds u, c, t u, c, t u, c, t WW 0 W W Z0 Z l ν ν νν ν ν Flavour Changing Neutral Current: GIM suppression, involved CKM matrix elements are small (|Vts| ≈ 0.039, |Vtd| ≈ 0.008) + 0 + Hadronic matrix element related to K → π e νe decay F. Mescia and C. Smith [arXiv:0705.2025]
In terms of the CKM parameters:
. 2 8 h i0.74 + + −11 |Vcb| γ B K → π νν = (8.39 ± 0.30) × 10 40.7 × 10−3 73.2° − = (8.4 ± 1.0) × 10 11
A. J. Buras et al [arXiv:1503.02693]
+ + +1.15 −10 B( → π νν¯) = (1.73 ) × 10 E787/949 Collaboration [arXiv:0808.2459] K −1.05 1 / 22 + + K → π νν – Beyond the Standard Model + + K → π νν¯ has been studied in many BSM scenarios. To name a few: 0 I Z models, A. Buras et al [arXiv:1211.1896],[arXiv:1507.08672] I Randall and Sandrum models, M. Blanke et al [arXiv:0812.3803] I Littlest Higgs models, M. Blanke et al [arXiv:1507.06316] I Supersymmetry, M. Tanimoto, K. Yamamoto [arXiv:1603.07960], T. Blažek, P. Maták [arXiv:1410.0055] I Lepton Flavour Violation models. M. Bordone et al [arXiv:1705.10729]
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A. J. Buras et al [arXiv:1507.08672] M. Bordone et al [arXiv:1705.10729] 2 / 22 Setup & Measurement Principle NA62 / CERN SPS
NA62 is a kaon decay in flight experiment. The main objective is to + + measure B(K → π νν¯) with a relative uncertainty around 10 %.
(Also, heavy neutrinos, lepton flavour universality, exotic physics, etc.) CMS
I 2005 Proposal, North Area ALICE LHC LHC-b I 2009 Approved, TI8 SPS TT10 TI2 ATLAS AWAKE I 2010 Technical design, West Area AD TT60
I 2012 Technical run, TT2 BOOSTER ISOLDE East Area I 2014–15 Pilot runs, LINAC 2 PS n-TOF CTF3 I 2016–18 Physics runs. LINAC 3
14 countries, 31 institutes, 214 authors.
3 / 22 + + K → π νν – Measurement Principle
2 2 The missing mass squared, mmiss = (pk − pπ) , gives an handle on 92 % of the background channels → Core aspect of the experiment.
1
Γ 2 miss +→π+π0 γ d K ( ) dm
tot -1 1 10 Γ (γ) + + ν µ K →π+ µ νν × 10 + → ( 10 ) 10-2 K K+→π+π+π- +→π+π0 π0 10-3 K + +π0ν K → e e
-4 + π0 ν µ 10 + →µ K
10-5
+ ν -6 - e e 10 π+ π + → K
10-7 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12 2 2 4 mmiss [GeV /c ]
I Identification of K and π, I Measurements of K and π momentum, I Vetoes for γ and µ, ps I O (100 ) timing capabilities for K - π matching.
+ + + + 0 Main kaon backgrounds: K → µ νµ (γ), K → π π (γ), + + + − + + − + K → π π π , K → π π e νe. 4 / 22 Kaon Collected
This talk: 2016 data, 4 weeks of data taking, 35 − 40% of the nominal intensity. 2017 data, about 23 weeks of data taking, 60 − 65% of the nominal intensity, higher data quality → about 10× more data.
11 + ≈ 1 × 10 good decays. 12 + K > 3 × 10 good K decays.
5 / 22 NA62 / CERN SPS – Layout
Beam: 75 GeV/c ± 1%, K, π and p (6:70:23), 750 MHz.
L = 53 m L = 24 m L = 38 m Ø = 1.92 m Ø = 2.4 m Ø = 2.8 m RICH CHOD LKr
Bend. KTAG GTK Magnet SAC
CHANTI
LAV 1-11 MNP33 IRC MUVs Magnet STRAWs LAV 12
T + 70 m T + 265 m
NA62 Collaboration [arXiv:1703.08501]
Kaon & pion tracking, PID, calorimeters, hermetic photon vetos, muon veto, hodoscope and inelastic interactions veto → redundancy.
Minimize beam – gas interactions: vacuum 10−6 mbar.
Signal selection sketch: K - π association, 15 < Pπ < 35 GeV/c, decay vertex in fiducial volume, no photon / muon / upstream activity.
6 / 22 Signal Selection Kaon Identification & Tracking
Average beam intensity: 2016 → 35 − 40%, 2017–2018 → 60 − 65%.
KTag – Diff. Cherenkov counter,
I N2 (H2) gas radiator, I Kaon time resolution ≈ 70 ps, I > 98% K ID efficiency.
GigaTracker – Silicon pixel tracker, I Sensor surface is 60 by 27 mm – Match beam size,
I Thickness ≤ 0.5 % X/X0 – Minimize beam induced background, + + I Temporal resolution < 150 ps – K – π matching.
+ KTag and GTK : 75% K reconstruction and identification efficiency.
7 / 22 Pion Tracking
Pion spectrometer – STRAW
Four STRAW chambers, I 4 views / chamber, 448 straws / view, I 1.3 m long dipole (0.9 Tm), I straws are 2.1 m long, 9.8 mm in diam., 36 µm walls,
I X/X0 < 1.8%,
I 70% Ar, 30% CO2.
> 95% reconstruction efficiency.
8 / 22 Particle Identification
Pion / muon separation – RICH & Calorimeters
Ring-imaging Cherenkov detector, I Ne gas radiator, I Ring time resolution ≈ 80 ps, 2 I µ/π separation > 10 (15 < P < 35 GeV/c).
Likelihood PID discriminant. Efficiency 2.5 × 10−3 / 0.75 for µ+/π+.
Calorimeters, I Electromagnetic calo. (LKr), I Hadronic calo. (MUV1,2), I Scintillator pads behind 80 cm Fe wall (MUV3).
MUV3 and BDT classifier. Efficiency 0.6 × 10−5 / 0.77 for µ+/π+. 9 / 22 Photon VETOs
Main cuts: I No in-time signals in LAVs and SAV, + I No in-time signals in hodoscope and LKr (if not associated with π ), I Segment rejection in Straw.
Typical timing coincidence: ±3/ ± 5 ns, energy dependent for LKr.
+ + − Fraction of K → π π0 passing the cuts: 2.5 × 10 8.
10 / 22 Signal Selection – Result
Signal and control regions blinded, selection developed on about 10% of the data set.
11 / 22 Single Event Sensitivity Single Event Sensitivity (SES) + + K → π π0 (from control data) used as normalization channel.
+ + − K → π νν acceptance (MC) (4.0 ± 0.1) × 10 2 Random veto efficiency 0.76 ± 0.04 Trigger efficiency 0.87 ± 0.2
−10 SES = (3.15 ± 0.01stat. ± 0.24syst.) × 10