results from na62 and koto · results from na62 and koto 10th international workshop on the ckm...

Results from NA62 and KOTO

10th International Workshop on the CKM Unitarity TriangleHeidelberg, Germany, 17 – 21 September 2018

Michal Koval (CERN)[email protected]

on behalf of the NA62 collaboration

Outline

Review of the present experimental status of the 𝐾 → 𝜋𝜈 ҧ𝜈 decays

• 𝐾+ → 𝜋+𝜈 ҧ𝜈: first result from NA62 experiment at CERN SPS

• 𝐾𝐿 → 𝜋0𝜈 ҧ𝜈: KOTO experiment at JPARC

19. 9. 2018 CKM2018, NA62 and KOTO [email protected] 1

Motivations for 𝐾 → 𝜋𝜈 ҧ𝜈


Box and penguin diagrams:• FCNC process forbidden at tree level

• Highly CKM suppressed (BR ~ |Vts*Vtd|2)

• Extraction of Vtd with minimal (few %)

non-parametric uncertainty

Theoretically very clean:

• dominant short-distance contribution

• hadronic matrix element extracted from precisely measured BR(K+ → π0e+ν)

BR(𝐾+ → 𝜋+𝜈 ҧ𝜈) = (8.4 ± 1.0) × 10−11 BR(𝐾𝐿 → 𝜋0𝜈 ҧ𝜈) = (3.4 ± 0.6) × 10−11

SM Predictions, error CKM parametric [Buras et al., JHEP 1511 (2015) 033]:

𝐾 → 𝜋𝜈 ҧ𝜈: New Physics Sensitivity


Z'(5 TeV) in Constrained MFV Randall Sundrum

• Simplified Z, Z’ models [Buras, Buttazzo,Knegjens, JHEP 1511 (2015) 166]

• Littlest Higgs with T-parity [Blanke, Buras, Recksiegel, EPJ C76 (2016) no.4 182]

• Custodial Randall-Sundrum [Blanke, Buras, Duling, Gemmler, Gori, JHEP 0903 (2009) 108]

• MSSM analyses [Tanimoto, Yamamoto, PTEP 2016 (2016) no.12, 123B02; Blazek, Matak, IntlJModPhys.A29 (2014), 1450162; Isidori et al. JHEP 0608 (2006) 064]

• LFU violation models [Isidori et. al., Eur. Phys. J. C (2017) 77]

LFU violation

Measurement of charged (K+ → 𝜋+𝜈 ҧ𝜈) and neutral (𝐾𝐿 → 𝜋0𝜈 ҧ𝜈) modes can discriminate among different new physics scenarios

New physics searches complementary/alternative to LHC

𝐾 → 𝜋𝜈 ҧ𝜈: Experimental Status


Publication Date

1970 1980 1990 2000 2010 2020

)n

n+

p®

+B

r(K

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10 Camerini

Klems

Ljung

Cable

Asano

E787

E787

E787

E787

E787

E787+E949

E787+E949

Measurementnn+p®+

History of K

11-10´1.0)±) = (8.4nn+p®+

SM : Br(K

90% CL

Measurement

𝐾+ → 𝜋+𝜈 ҧ𝜈 in E787/E949


E787/E949:• Kaon decay at rest technique• 𝐾+ decays: ∼ 3.5 × 1012

• Single Event Sensitivity: ∼ 0.8 × 10−10

• BR(K+ → 𝜋+𝜈 ҧ𝜈) = (17.3−10.5+11.5) × 10−11

[Phys. Rev. D 77, 052003 (2008)] [Phys. Rev. D 79, 092004 (2009)]

NA62 Experiment at CERN – SPS


~200 participants from: Birmingham, Bratislava, Bristol, Bucharest, CERN, Dubna (JINR), Fairfax (GMU), Ferrara, Florence, Frascati, Glasgow, Lancaster, Liverpool, Louvain-la-Neuve, Mainz, Moscow (INR), Naples, Perugia, Pisa, Prague, Protvino (IHEP) , Rome I, Rome II, San Luis Potosi, Sofia, TRIUMF, Turin, Vancouver (UBC)

SPSNA62:centre of the LHC

Jura mountains

Geneva airport

LHC

N

Primary goal: • Measurement of BR(K+ → 𝜋+𝜈 ҧ𝜈)

Technique:• Kaon decay-in-flight• Kaon momentum: 75GeV/c

Requirements:• 1013 𝐾 decays• Signal acceptance 𝒪(10%)• 𝒪(1012) background rejection

NA62 Experiment at CERN – SPS


~200 participants from: Birmingham, Bratislava, Bristol, Bucharest, CERN, Dubna (JINR), Fairfax (GMU), Ferrara, Florence, Frascati, Glasgow, Lancaster, Liverpool, Louvain-la-Neuve, Mainz, Moscow (INR), Naples, Perugia, Pisa, Prague, Protvino (IHEP) , Rome I, Rome II, San Luis Potosi, Sofia, TRIUMF, Turin, Vancouver (UBC)

LHC

N

Data taking runs:

• 2014 Pilot run• 2015 Commissioning run• 2016 Commissioning + Physics run• 2017 Physics run• 2018 Ongoing Physics run

Measurement Strategy


Keystones of the analysis:• Timing between sub-detectors ∼ O(100 ps)• Kinematic suppression ∼ O(104)• Muon suppression > 107

• 𝜋0 suppression (from) > 107

𝑚𝑚𝑖𝑠𝑠2 = 𝑃𝐾 − 𝑃𝜋+

2

+Background suppression:• 15 < 𝑃𝜋+ < 35 GeV/c• Particle ID(Cherenkov detectors)• Particle ID(Calorimeters)• Photon veto

Kaon decays:• 𝐾+ → 𝜋+𝜋0 𝛾 ; BR = 0.2067• 𝐾+ → 𝜇+𝜈 (𝛾); BR = 0.6356• 𝐾+ → 𝜋+𝜋+𝜋−; BR = 0.0558

Decay kinematics:

Reg

ion

I

Region II

NA62 Beam & Detector


Cherenkovkaon tagger t=70ps

Spectrometerstraw chambers

Z [m]

~5 MHz K+ Decays

[NA62 Detector Paper, 2017 JINST 12 P05025]

X [m]

t=70ps

[NA62 Detector Paper, 2017 JINST 12 P05025]

SPS Beam:• 400 GeV/c• 2⋅1012 protons / spill• 3.5s spill• Target: Beryllium

Secondary Positive Beam:• Unseparated hadrons:

K+(6%)/ +(70%)/p(24%) • Momentum: 75GeV/c (±1%)• Divergence < 100rad• Transverse size: (60 x 30) mm2

• 750MHz beam rate @ GTK

Decay Region:• 60m long fiducial region• ∼5MHz K+ decay rate• Vacuum ∼ 10-6 mbar

Event Selection


Selection criteria:

• Single track topology

• 𝜋+ identification

• Photon rejection

• Multi-track rejection

Performances:

• 𝜀𝜇+ = 1 ⋅ 10−8

• 64% 𝜋+ efficiency

• 𝜀𝜋0 = 3 ⋅ 10−8

• 𝜎 𝑚𝑚𝑖𝑠𝑠2 = 1 ⋅ 10−3 GeV2/c4

• 𝜎𝑇 ∼ O(100ps)

R1

R2

𝐾+ → 𝜋+𝜋+𝜋−

𝐾+ → 𝜋+𝜋0

𝐾+ → 𝜇+𝜈

NA62 Control dataPreliminary

𝐾+decay events in the fiducial decay region

Signal and background control regions are kept blind throughout the analysis

Single Event Sensitivity


Signal Acceptance: 4%

• Control trigger 𝐾+ → 𝜋+𝜋0 used for normalization

• Normalization acceptance: 10%

• Number of kaon decays (NK) in fiducial volume NK = 1.21(2) × 1011

Single Event Sensitivity: SES = (3.15 ± 0.01stat ± 0.24syst) ×10-10

R1

R2 3%

1%

Background Summary


Results


Results


One event observed in R2

NA62 𝐾+ → 𝜋+𝜈 ҧ𝜈: Result


• One event observed in signal region R2

• Full exploitation of the CLs method in progress

• The results are compatible with the SM

RICH ring for the event

For comparison:

NA62 𝐾+ → 𝜋+𝜈 ҧ𝜈: Prospects

• Analysis of data collected in 2017 started

• Data sample x 20 larger than presented statistics

• Expect improvements on signal acceptance, efficiency and S/B ratio

• Data taking is ongoing (April-November 2018)

• Expect ∼20 SM events before LS2

• Data taking after 2018 to be approved

• Conditions for ultimate sensitivity under evaluation


The KOTO Experiment


Primary 30 GeV/c protons on gold target

Secondary neutral beam (KL , neutrons, photons)

• P = 1.4 GeV/c peak

• Transverse size: 80 x 80 mm2

• Fiducial decay region ∼ 2 m

CsI Calorimeter from KTeV + Hermetic Veto Systems To suppress 𝐾𝐿 → 𝜋0𝜋0background

Arizona, Chicago, Chonbuk, Hanyang, Jeju, JINR, KEK, Kyoto, Michigan, NDA, NTU, Okayama, Osaka, Pusan, Saga & Yamagata

Study of 𝐾𝐿 → 𝜋0𝜈 ҧ𝜈 @ JPARC 30GeV Main Ring

Goal is to search for New Physics at 𝐵𝑅 ∼ 10−11

𝐾𝐿 → 𝜋0𝜈 ҧ𝜈 Signal at KOTO


Signal 𝐾𝐿 → 𝜋0𝜈 ҧ𝜈 in KOTO detector

Assuming 2g from 0, calculate Z vertex (Zvtx).

Signal region defined by 0 Zvtx and transverse momentum (PT)

KOTO 2013 Run 49 Result


Data from ∼ 100 hours in 2013 run

• N(KL) ∼ 2.4 x 1011 (SES 1.3x10-8)

Set upper limit on BR(𝐾𝐿 → 𝜋0𝜈 ҧ𝜈)

• < 5.1 x 10-8 (90% C.L.)

Background in signal region dominated by neutrons

[PTEP 2017, 021C01]

KOTO Improvement after 2013


• Thinner vacuum window (125μm → 12.5μm) to

reduce neutron interaction

• Beam Profile Monitor for better beam alignment

• Beam Pipe Charged Veto (BPCV) added

• 1/10 reduction of 𝐾𝐿 → 𝜋+𝜋−𝜋0 background

• Special run with Al target to collect neutron

enriched events

• Better photon – neutron ID in CsI calorimeter

Halo Neutrons

hitting the NCC

𝐾𝐿 → 𝜋+𝜋−𝜋0

Halo Neutrons

hitting the Calo

KOTO Data Taking


New results from 2015 data:

• N(KL) ∼ x 20 of 2013 run

• Better control samples to study neutron BG

• Detector upgrades

• Several detectors installed to reduce kaon-decay BG

[Koji SHIOMI @ ICHEP, 2018] [Kota Nakagiri @ FPCP, 2018]

KOTO 2015 Results


[Koji SHIOMI @ ICHEP, 2018]

KOTO 2015 Results



Improved by one order of magnitude

* Systematic uncertainty is not taken into account

KOTO Prospects• 2016-2018 data analysis is ongoing, additional × 1.5 physics data

• With 2015-2018 data, expected SES: 5 × 10−10

• Expect O(10−11) SES with runs after 2018


Detector upgrades and improvements:• Gradual beam power

increase: 50→90kW • CSI upgrade to reduce the

neutron BG during 2018 summer shutdown


𝐾 → 𝜋𝜈 ҧ𝜈: Prospects


O(20) events ≥ 2018

Summary


• The novel NA62 decay-in-flight technique works

• SM sensitivity for 𝐾+ → 𝜋+𝜈 ҧ𝜈 reached with the completion of 2016 data analysis

• One event observed in 2016 data (0.3 SM expected in R1+R2)

𝐵𝑅(𝐾+ → 𝜋+𝜈 ҧ𝜈) < 14.0 × 10−10 @ 95% 𝐶𝐿

• 𝐾𝐿 → 𝜋0𝜈 ҧ𝜈: KOTO

• New result (2015 data): 𝐵𝑅(𝐾𝐿 → 𝜋0𝜈 ҧ𝜈) < 3.0 × 10−9 @ 90% 𝐶𝐿

• O(10−11) sensitivity expected with with runs after 2018

• Both experiments are running and data analyses are ongoing

KOTO• 𝐾+ → 𝜋+𝜈 ҧ𝜈: NA62

• BR measurement

expected in the next

few years

NA62

SPARES Results from NA62 and KOTO

10th International Workshop on the CKM Unitarity TriangleHeidelberg, Germany, 17 – 21 September 2018

Michal Koval (CERN)[email protected]

on behalf of the NA62 collaboration

Connection with Flavor Physics – CKM Triangle


(littlest Higgswith T parity)

CKM unitarity triangle with kaons

Kaons alone can fully constrain the

CKM triangle

Comparison with B physics can provide hints on NP dynamics

NA62 “Luminosity”


G. Ruggiero, CERN seminar (2018), https://cds.cern.ch/record/2310580

Signal Regions and Kinematic Suppression


Kinematic suppression• Measured using data• 𝐾+ → 𝜋+𝜋0 and 𝐾+ → 𝜇+𝜈 samples• Selected using calorimeters

Fraction of events in signal regions• 𝐾+ → 𝜋+𝜋0 ∼ 1 ⋅ 10−3 (resolution tails)• 𝐾+ → 𝜇+𝜈 ∼ 3 ⋅ 10−4

Three ways to compute the 𝑚𝑚𝑖𝑠𝑠2 :

• 𝑚𝑚𝑖𝑠𝑠2 𝑆𝑇𝑅𝐴𝑊,𝐺𝑇𝐾

• 𝑚𝑚𝑖𝑠𝑠2 𝑅𝐼𝐶𝐻, 𝐺𝑇𝐾

• 𝑚𝑚𝑖𝑠𝑠2 𝑆𝑇𝑅𝐴𝑊,𝐵𝑒𝑎𝑚

• Protects against mis-reconstruction

K+ → π+π0 γ Background


R. Marchevski, Moriond EW2018G. Ruggiero, CERN seminar (2018), https://cds.cern.ch/record/2310580

K+ → 𝜇+𝜈 γ Background



K+ → 𝜋+𝜋−e+𝜈𝑒 Background



Upstream Background



results from na62 and koto · results from na62 and koto 10th international workshop on the ckm...

Documents