Post on 11-Mar-2020
New Result on ๐+ โ ๐+๐เดค๐from the NA62 Experiment
Giuseppe Ruggiero (Lancaster University)
KAON 2019
Perugia, 10/09/2019
On behalf of the NA62 Collaboration
Outline
K+ โ ฯ+ฮฝเดคฮฝ @ NA62 (2017 Data)
โข Physics case
โข The NA62 experiment
โข Data selection
โข ๐0 rejection and the ๐0 โ invisible decay
โข Determination of the single event sensitivity
โข Background studies
โข Result
210/09/2019 Giuseppe Ruggiero - Kaon 2019
๐ โ ๐๐เดค๐ decays: a theoretically clean environment
โข FCNC loop processes: sd coupling and highest CKM suppression
โข Very clean theoretically: Short distance contribution. No hadronic uncertainties.
โข SM predictions [Buras et al. JHEP 11 (2015) 33]
BR ๐พ+ โ ๐+๐ าง๐ = 8.39 ยฑ 0.30 โ 10โ11๐๐๐
0.0407
2.8๐พ
73.2ยฐ
0.74
= 0.84 ยฑ 0.10 โ 10โ10
BR ๐พ๐ฟ โ ๐0๐ าง๐ = 3.36 ยฑ 0.05 โ 10โ11๐๐ข๐
0.00388
2๐๐๐
0.0407
2sin ๐พ
sin 73.2ยฐ
2
= 0.34 ยฑ 0.06 โ 10โ10
310/09/2019 Giuseppe Ruggiero - Kaon 2019
๐ โ ๐๐เดค๐ NP Sensitivity
โข Simplified Z, Zโ models [Buras, Buttazzo,Knegjens, JHEP 1511 (2015) 166]
โข Littlest Higgs with T-parity [Blanke, Buras, Recksiegel, EPJ C76 (2016) no.4 182]
โข Custodial Randall-Sundrum [Blanke, Buras, Duling, Gemmler, Gori, JHEP 0903 (2009) 108]
โข MSSM non-MFV [Tanimoto, Yamamoto, PTEP 2016 (2016) no.12, 123B02; Blazek, Matak, IntlJModPhys.A
29 (2014), 1450162; Isidori et al. JHEP 0608 (2006) 064]
โข LFU violation models [Isidori et. al., Eur. Phys. J. C (2017) 77]
โข Leptoquarks [S.Fajfer, et al. arXiv:1802.00786]
โข Constraints from existing measurements (correlations model dependent)
Randall - SundrumZโ (5 TeV) in constrained MFV LFU violation
410/09/2019 Giuseppe Ruggiero - Kaon 2019
๐+ โ ๐+๐เดค๐ Experimental State of the Art
๐พ+ decay in flight technique NA62๐พ+ decay at rest technique E787/E949
Data 2016
NA62
๐ต๐ ๐พ+ โ ๐+๐ าง๐ = 1.73โ1.05+1.15 ร 10โ10
Phys. Rev. D 77, 052003 (2008)
Phys. Rev. D 79, 092004 (2009)
Phys. Lett. B 791, 156 (2019)
510/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 @ CERN - SPS
LHC
NA62
SPS
Primary goal:
Measurement of BR(K+ โ ฯ+ฮฝเดคฮฝ)
Technique:
K Decay โ in โ flight
Broader Physics program
~200 participants: Birmingham, Bratislava, Bristol, Bucharest, CERN, Dubna (JINR), Fairfax (GMU), Ferrara,Firenze, Frascati, Glasgow, Lancaster, Liverpool, Louvain-la-Neuve, Mainz, Moscow (INR), Naples, Perugia,Pisa, Prague, Protvino (IHEP) , Rome I, Rome II, San Luis Potosi, Torino, TRIUMF, Vancouver (UBC)
610/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Layout
Secondary positive beamDecay region and Detectors
Momentum 75 GeV/c, 1% rms
Divergence (RMS) 100 ฮผrad
Transverse Size 60 ร 30mm2
Composition ฮคK+ 6% ฮคฯ+ 70% p 24%
2017 typical Intensity 19 ร 1011 ppp (450 MHz @ GTK3)
Fiducial region 60 m
K+ decay rate ~ 3 MHz
Vacuum ๐ช 10โ6 mbar
Si pixel beam tracker + Straw tracker
LKr Calorimeter from NA48
Cerenkov counters for K id, RICH for p/m id
[NA62 Detector Paper, 2017 JINST 12 P05025]
MNP33400 GeV/c
SPS protons
710/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Runs
810/09/2019 Giuseppe Ruggiero - Kaon 2019* Including periods of beam off
๐๐ซ๐จ๐ญ๐จ๐ง๐ฌ๐จ๐ง๐ญ๐๐ซ๐ ๐๐ญ
2014-15 (16) Pilot run, Commissioning runs
2016 Physics run (45 days*)
2017 Physics run (160 days*)
2018 Physics run (217 days*)
๐๐๐ญ๐
NA62 Runs: Data Analyzed
910/09/2019 Giuseppe Ruggiero - Kaon 2019
~19 ร 1011 protons per spill (3 s)
~2 ร 1012 K+ decays
This talk
2014-15 (16) Pilot run, Commissioning runs
2016 Physics run (45 days*)
2017 Physics run (160 days*)
2018 Physics run (217 days*)
* Including periods of beam off
๐๐ซ๐จ๐ญ๐จ๐ง๐ฌ๐จ๐ง๐ญ๐๐ซ๐ ๐๐ญ
๐๐๐ญ๐
๐+ โ ๐+๐เดค๐ Decay-in-flight
mmiss2 = PK+ โ Pฯ+
2 Process Branching ratio
K+ โ ฯ+ฯ0 ฮณ 0.2067
K+ โ ฮผ+๐ ฮณ 0.6356
K+ โ ฯ+ฯ+ฯโ 0.0558
K+ โ ฯ+ฯโe+ฮฝ 4.25 โ 10โ5
1010/09/2019 Giuseppe Ruggiero - Kaon 2019
๐+ โ ๐+๐เดค๐ Decay-in-flight
mmiss2 = PK+ โ Pฯ+
2 Process Branching ratio
K+ โ ฯ+ฯ0 ฮณ 0.2067
K+ โ ฮผ+๐ ฮณ 0.6356
K+ โ ฯ+ฯ+ฯโ 0.0558
K+ โ ฯ+ฯโe+ฮฝ 4.25 โ 10โ5
Kinematic signal identificationR
eg
ion
1
Region 2
1110/09/2019 Giuseppe Ruggiero - Kaon 2019
๐+ โ ๐+๐เดค๐ Decay-in-flight
mmiss2 = PK+ โ Pฯ+
2
๐๐ < ๐๐+ < ๐๐ GeV/c
Particle ID (Cherenkov detectors)
Particle ID (Calorimeters, ๐ - veto)
Photon veto
Process Branching ratio
K+ โ ฯ+ฯ0 ฮณ 0.2067
K+ โ ฮผ+๐ ฮณ 0.6356
K+ โ ฯ+ฯ+ฯโ 0.0558
K+ โ ฯ+ฯโe+ฮฝ 4.25 โ 10โ5
Kinematic signal identificationR
eg
ion
1
Region 2
1210/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Cornerstones
๐ช 100 ps Timing between sub-detectors
๐ช 103 รท 104 Background suppression from kinematics
> 107 Muon suppression
> 107 ฯ0 (from K+ โ ฯ+ฯ0) suppression
1310/09/2019 Giuseppe Ruggiero - Kaon 2019
๐+ โ ๐+๐เดค๐ Analysis
โข Trigger streams (hardware L0 + software L1): โข ยซPNNยป: kaon and charged particle identification, photon and muon veto
โข ยซControlยป: minimum bias
โข Offline Analysis:
โข Data samples: PNN; Control: K+ โ ฯ+ฯ0, K+ โ ฮผ+ฮฝ, K+ โ ฯ+ฯ+ฯโ
โข Blind analysis procedure: signal /control regions masked during the analysis
1) Selection
2) Determination of the single event sensitivity
3) Estimation and validation of the background
4) Opening of signal regions and results
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๐+ โ ๐+๐เดค๐ Selection
Selection
โข K+- ฯ+ matching
โข K+ decays in the decay volume
โข ฯ+ identification (PID)
โข photon rejection
โข Multi-track rejection
1510/09/2019 Giuseppe Ruggiero - Kaon 2019
Measured performance
GTK-KTAG-RICH timing: ๐ช 100 ps
ฯ mmiss2 ~ 10โ3 ฮคGeV2 c4
ฯ+ ID: ฮตฮผ~10โ8, ฮตฯ+~64%
๐0 rej: ๐๐0~1.4 โ 10โ8, ๐๐+๐ 15,35 GeV/c
๐๐๐๐ ๐ 2 : ฯ+/K+ 3-momentum from Straw/Gigatracker, ๐+ mass hypothesis
Control data
ฯ+ฯ+ฯโ Region
ฯ+ฯ0 Region
ฮผ+ฮฝ
Region
Signal Region 2
Signal
Region 1
๐พ+decays selected before PID
and ๐พ/multi-track rejection
๐ + ๐ฆ๐จ๐ฆ๐๐ง๐ญ๐ฎ๐ฆ [๐๐๐/๐]
๐๐๐๐๐
๐ฮค
๐ฎ๐๐ฝ๐๐๐
๐๐ rejection and search for ๐๐ โ invisibleA-priori evaluation of ฯ0 rejection in ๐พ+ โ ๐+๐0 (0.015 < ๐๐๐๐ ๐
2 < 0.021 ฮคGeV2 c4)
โข Same selection, and trigger stream as ๐พ+ โ ๐+๐ าง๐, about ฮค1 3 of the data used for ๐๐๐
โข Single-๐พ detection efficiency from data minimum-bias ๐พ+ โ ๐+๐0 (Tag & Probe)
โข ฯ0 rejection evaluated from convolution with MC ๐พ+ โ ๐+๐0 ๐พ
โข Validation: side-bands with expected rejection ๐ช 10โ7 where ๐0 โ invisible excluded
โข ฯ0 rejection expected: 2.8โ2.1+5.0 ร 10โ9 (๐+ momentum 25-40 GeV/c)
1610/09/2019 Giuseppe Ruggiero - Kaon 2019
[E949, PRD72 (2005)]
Resultโข BR(ฯ0 โ invisible) normalized to ๐0 โ ๐พ๐พ
โข Background expected: 10โ8+22 (๐พ+ โ ๐+๐0)
โข Events observed: 12
BR ฯ0 โ invisible < 4.4 ร 10โ9 @ 90% CLUL 60 times stronger than past measurement
๐ ๐๐: Data After Selection
Region 2
Region 1
ฯ+ฯ0
Control Regions
Upstream background control region
ฮผ+ฮฝControl Region
High - P
control region
Control and signal regions MASKED
1710/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
ฯ+ฯ+ฯโ
Control Region
๐ ๐๐ Single Event Sensitivity (S.E.S.)
S. E. S. =Br ฯฮฝฮฝ
Nฯฮฝฮฝ๐๐ฅ๐
โข Ratio of ฯฮฝฮฝ and ฯ+ฯ0 acceptances allows cancellation of systematic effects
โข Computation in bins of ฯ+ momentum and instantaneous beam intensity
Nฯฮฝฮฝ๐๐ฅ๐
โ Nฯฯ ฮตRV ฮตtriggerAฯฮฝฮฝAฯฯ
Br ฯฮฝฮฝ
Br ฯฯ
Nฯฮฝฮฝ๐๐ฅ๐
Expected number of ฯฮฝฮฝ events
Br ฯฮฝฮฝ SM ฯฮฝฮฝ branching ratio
Nฯฯ K+ โ ฯ+ฯ0 from control ฯฮฝฮฝ-like selected without ฮณ/multiplicity rejection
ฮตRV ฯฮฝฮฝ loss due to ฮณ/multi-track rejection because of random activity
ฮตtrigger PNN trigger efficiency
Aฯฮฝฮฝ,ฯฯ Monte Carlo acceptances for ฯฮฝฮฝ (~3.0%*) and ฯ+ฯ0 (~8.5%)
Br ฯฯ PDG K+ โ ฯ+ฯ0 branching ratio
1810/09/2019 Giuseppe Ruggiero - Kaon 2019* Vector form factors
๐ ๐๐ Single Event Sensitivity
๐๐๐ measured on K+ โ ฮผ+ฮฝ data ๐๐๐๐๐๐๐๐ measured on data
1910/09/2019 Giuseppe Ruggiero - Kaon 2019
โข Intensity measured event-by-event using Gigatracker time sidebands
NA62 Preliminary๐๐ ๐ 2017 = 0.638 ยฑ 0.014
๐ ๐๐ S.E.S: Results
โข Integrated over beam intensity and ๐+ momentum
โข Error budget (S.E.S.)
โข External error on ๐๐๐๐๐๐ฅ๐
from ๐ต๐(๐๐๐) = 0.84 ยฑ 0.10 ร 10โ10
2010/09/2019 Giuseppe Ruggiero - Kaon 2019
๐. ๐ธ. ๐. = 0.389 ยฑ 0.021 ร 10โ10 ๐๐๐๐๐๐ฅ๐
= 2.16 ยฑ 0.12 ยฑ 0.26๐๐ฅ๐ก
๐ ๐๐: Data After Selection
ฯ+ฯ0
Control Regions
Upstream background control region
ฮผ+ฮฝControl Region
High - P
control region
Control and signal regions MASKED
2110/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
ฯ+ฯ+ฯโ
Control Region
Region 2
Region 1
๐+ โ ๐+๐๐ Backgrounds
Fraction of ฯ+ฯ0
in signal region measured on control data
Data in ฯ+ฯ0 regionafter ฯฮฝฮฝ selection:ฮณ โrejection applied
Minimum bias K+ โ ฯ+ฯ0 data used
to study the tails of the mmiss2
Expected K+ โ ฯ+ฯ0
in signal regions afterฯฮฝฮฝ selection
2210/09/2019 Giuseppe Ruggiero - Kaon 2019
Background Validation
K+ โ ฯ+ฯ0 background expectedand observed in control regions(CR1+CR2) after ฯฮฝฮฝ selection
K+ โ ฮผ+ฮฝ background expected andobserved in control region (CR) afterฯฮฝฮฝ selection
2310/09/2019 Giuseppe Ruggiero - Kaon 2019
Expected Background from ๐ฒ+
decays
2410/09/2019 Giuseppe Ruggiero - Kaon 2019
Normal ๐+Decay
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay region
๐+(๐๐ ๐๐๐)
๐ธ, ๐
๐ธ, ๐
Decay vertex
Gigatracker
z
y
2510/09/2019 Giuseppe Ruggiero - Kaon 2019
Normal ๐+Decay
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay region
๐+(๐๐ ๐๐๐)
๐ธ, ๐
๐ธ, ๐
Decay vertex
z
y
๐พ+ โ ๐+๐ าง๐ projected at collimator (MC)
2610/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
Upstream Decay / Interaction
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay region
๐ธ๐ธ
โข K+ decays/interacts in the achromat
โข Secondary ๐+ downstream
โข Beam elements block additional particles
2710/09/2019 Giuseppe Ruggiero - Kaon 2019
z
y
Upstream Background
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay regionIn-time pileupbeam particle
๐ธ๐ธ
โข K+ decays/interacts in the achromat
โข Secondary ๐+ downstream
โข Beam elements block additional particles
โข Pileup beam particle tagged as K+
Fake decay vertex
2810/09/2019 Giuseppe Ruggiero - Kaon 2019
z
y
Upstream Background
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay regionIn-time pileupbeam particle
๐ธ๐ธ
Fake decay vertex
โข K+ decays/interacts in the achromat
โข Secondary ๐+ downstream
โข Beam elements block additional particles
โข ๐+ scattering in straw chamber 1
โข Pileup beam particle tagged as K+
2910/09/2019 Giuseppe Ruggiero - Kaon 2019
z
y
NA62 Preliminary
Upstream Background
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay regionIn-time pileupbeam particle
๐ธ๐ธ
Fake decay vertex
โข K+ decays/interacts in the achromat
โข Secondary ๐+ downstream
โข Beam elements block additional particles
โข ๐+ scattering in straw chamber 1
โข Pileup beam particle tagged as K+
3010/09/2019 Giuseppe Ruggiero - Kaon 2019
z
y
NA62 PreliminaryRegion removed offline
Upstream Background
Achromat
๐+(๐๐ ๐๐๐)
Collimator
1st Straw Chamber
Decay regionIn-time pileupbeam particle
๐ธ๐ธ
โข K+ decays/interacts in the achromat
โข Secondary ๐+ downstream
โข Beam elements block additional particles
โข ๐+ scattering in straw chamber 1
โข Pileup beam particle tagged as K+
Count events on data withinverted ๐พ โ ๐ matching
Estimate the probability tooccur from data/simulation
3110/09/2019 Giuseppe Ruggiero - Kaon 2019
z
y
Fake decay vertex
Total Expected Background
3210/09/2019 Giuseppe Ruggiero - Kaon 2019
Final Background ValidationSignal and background evaluated in the 35-40 GeV/c signal-like regions
๐๐๐๐ค๐ ๐ซ๐จ๐ฎ๐ง๐ = ๐. ๐๐ ยฑ ๐. ๐๐
๐ฌ๐ข๐ ๐ง๐๐ฅ = ๐. ๐๐ ยฑ ๐. ๐๐
3310/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
Final Background Validation1 event observed in 35-40 GeV/c region
3410/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
Opening the Box
3510/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
3610/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
Box Opened
3710/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
Box Opened2 events observed in signal region
2017 Resultโข Counting experiment
๐ต๐ ๐พ+ โ ๐+๐ าง๐ = 0.20โ0.20+0.69 ร 10โ10โข Two-sided 68% band:
โข Upper limits (CLs method)
3810/09/2019 Giuseppe Ruggiero - Kaon 2019
Observed Expected (background only) CL
๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.76 ร 10โ10 ๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.41 ร 10โ10 90%
๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 2.11 ร 10โ10 ๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.76 ร 10โ10 95%
Events observed 2
Single event sensitivity 0.389 ยฑ 0.021 ร 10โ10
Expected background 1.50 ยฑ 0.30
๐๐๐๐๐๐ Signal and Background 2017
3910/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
2016+2017 Result
๐ต๐ ๐พ+ โ ๐+๐ าง๐ = 0.47โ0.47+0.72 ร 10โ10โข Two-sided 68% band:
โข Upper limits (CLs method)
4010/09/2019 Giuseppe Ruggiero - Kaon 2019
Observed Expected (background only) CL
๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.85 ร 10โ10 ๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.32 ร 10โ10 90%
๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 2.44 ร 10โ10 ๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.62 ร 10โ10 95%
Events observed 3
Single event sensitivity 0.346 ยฑ 0.017 ร 10โ10
Expected background 1.65 ยฑ 0.31
โข 2016 and 2017 data uncorrelated
๐+ โ ๐+๐เดค๐ Experimental Status
4110/09/2019 Giuseppe Ruggiero - Kaon 2019
PRD 10 (1974) 897
NPB 304 (1988) 205
PRD 54 (1996) 6782
PRD 76 (2007) 034017
PRD 83 (2011) 034030
JHEP 11 (2015) 33
NA62 Preliminary
๐+ โ ๐+๐เดค๐ Experimental Status
4210/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
๐ฒ+ โ ๐ +๐เดค๐ and ๐ฒ๐ณ โ ๐ ๐๐เดค๐
4310/09/2019 Giuseppe Ruggiero - Kaon 2019
โข New Grossman โ Nir limit: ๐ต๐ ๐พ๐ฟ โ ๐0๐๐ < 8.14 ร 10โ10 @ 90% ๐ถ๐ฟ
Conclusions
โข Two events in signal region observed in 2017 dataโข S. E. S. = 0.389 ยฑ 0.021 ร 10โ10
โข Expected background: 1.50 ยฑ 0.30 events
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โข Constraints on the largest enhancements allowed by NP models
โข ๐พ+ โ ๐+๐, ๐ โinvisible at the ๐0 mass:
โข 2016+2017 NA62 result:
๐ต๐ ๐พ+ โ ๐+๐ าง๐ < 1.85 ร 10โ10 @ 90% ๐ถ๐ฟ
๐ต๐ ๐พ+ โ ๐+๐ าง๐ = 0.47โ0.47+0.72 ร 10โ10
๐ต๐ ฯ0 โ invisible < 4.4 ร 10โ9 @ 90% ๐ถ๐ฟ
Plans
โข 2018 data analysis in progressโข 2 ร 2017 data sample
โข On-going studies to increase signal efficiency
โข On-going studies to reduce the random veto
โข Shape analysis
4510/09/2019 Giuseppe Ruggiero - Kaon 2019
โข >2021 data taking: โข Plans to strongly suppress the upstream background
โข Run at higher beam intensity foreseen
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SPARES
Particle Identification
Calorimeters RICH
4710/09/2019 Giuseppe Ruggiero - Kaon 2019
NA62 Preliminary
Upstream Background Estimate
โข Probability to tag a pileup beam particle as a K+ depends onโข Closest distance of approach (CDA) between kaon and pion track
โข Timing between KTAG โ Gigatracker โ RICH
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โข Probability estimation (ยซmis-tag probabilityยป)โข CDA shape of upstream events from simulation validated with data
โข Computed as a function of KTAG โ Gigatracker and KTAG โ RICH time difference
โข Background estimationโข Number of upstream events from data selected with inverted K+/ฯ+ matching
โข Upstream events weigthed with the mis-tag probability as a function of the KTAG โ Gigatracker and KTAG โ RICH time difference
โข Estimation validated on data inverting cuts against upstream events
Upstream Background Validation
4910/09/2019 Giuseppe Ruggiero - Kaon 2019
โข Sample: upstream-enriched data sets selected
in mmiss2 signal regions
โข Expectation: result of the upstream estimation applied to a given sample
NA62 Preliminary
๐+ โ ๐+๐โ๐+๐ (๐ฒ๐๐) Background:
Validation
5010/09/2019 Giuseppe Ruggiero - Kaon 2019
โข Sample: Ke4-enriched data
sets selected in mmiss2 signal
regions
โข Expectation: MC normalized to ๐พ+ โ ๐+๐0 like ๐๐๐
NA62 Preliminary