1. Anomalies in Kaon Physics: the NA62 program
Francesca Bucci (INFN, Sezione di Firenze)
on behalf of NA62 Collaboration
XIIth Meeting on B Physics.
Tensions in Flavour measurements: a path toward Physics beyond the SM
22-24 May 2017
Centro Congressi, Università di Napoli Federico II

2. Kaon Physics: a Building Block of the SM
Discovery of strange particles: first observation of a quark-flavour not present in the ordinary matter [Nature (1947) 855]
Postulation of neutral meson oscillation [Phys. Rev 97 (1955) 1387]
 -  puzzle: first hint of P violation [Phys. Rev. 104 (1956) 254]
Discovery of CP violation in the K0 mixing [Phys. Rev. Lett. 13 (1964) 138]
3-quark-model to describe the observed meson/baryon spectra [Phys. Lett. 8 (1964) 214]
Prediction of the c-quark to explain the unexpectly low observed branching ratio of decay the KL  +- [Phys. Rev. D 2 (1970) 1285]
First evidence of direct CP violation in the K0 [Phys. Lett. B 206 (1988) 169]
F.Bucci

3. Kaon Physics: Toward the Present Era
Kaon Experiments [ ]
NA48 (CERN), KTeV (FNAL), KLOE (LNF), CPLEAR (CERN), E865 (BNL), ISTRA+ (Protvino)
Measurement of direct CP violation in the K0 [Phys. Lett. B 544 (2002) 97, Phys. Rev. D 83 (2010) ]
Test of CPT symmetry invariance [K.A. Olive et al. (Particle Data Group, Chin. Phys. C, 38, (2014)]
Precision test of the CKM unitarity [Eur. Phys. J. C 69 (2010)]
Test of lepton universality [Phys. Lett. B 719 (2013) 326]
F.Bucci

4. Anomalies in Kaon Physics: /
’ one of the important actors of 1990s particle physics
Strong interplay of QCD and EW penguin contributions
New results on hadronic matrix elements of QCD and EW penguin operators leads to a prediction in the SM significantly below experimental data.
F.Bucci
Buras, Gorbahn, Jager, Jamin ArXiV
World average from NA48 and KTeV
 3  discrepancy
Impact on various NP models: in particular models where there is a strong correlation between / and the branching ratio for K++ and KL0
Z’ general (Buras, Buttazzo, Knegjens, ), Littlest Higgs Model (Blanke, Buras, Recksiegel, ), 331 Models (Buras, De Fazio, , )

5. K in the SM …
Flavour Changing Neutral Current process forbidden at tree level in the SM
Highest CKM suppression  very sensitive to New Physics
Theoretical uncertainties at the level of 2% in BR but significant parametric uncertainties due to |Vub|, |Vcb| and 
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[Buras et al. arXiv: ], [Brod et al. Phys. Rev. D 83, (2011)]

6. … and beyond the SM
Pattern of correlation between BR(K++) and BR(KL0) discriminates among models
Z model
[A. J. Buras, F. De Fazio and J. Girrbach JHEP 1302 (2013) 116]
Randall-Sundrum
[JHEP 0903 (2009) 108]
Littlest Higgs
[Acta Phys. Polon. B41 (2010) 657]
F.Bucci

7. The long K march
First search: 1969 (10-4) Observation: 1997 (10-10)
K++
KL0
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KOTO
KOTO
NA62 
[Phys. Rev. D77, (2008), Phys. Rev. D79, (2009)]

8. The NA62 Experiment for K++
SPS proton
400 GeV
1012p/s
3.5 s spill
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Secondary Beam
Momentum GeV/c, p/p 1%
Divergence (RMS) 100 rad
Composition K(6%), (70%), p(23%)
Nominal rate 1011 (750 MHz at GTK3)
Transverse size 30 mm2
Decay region
Fiducial region 60 m length
K+ decay rate  5 MHz
Vacuum O(10-6) mbar

9. The NA62 Status
2014 Pilot run 2015 Commissioning run 2016 Commissioning + Physics run
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2016 Run
07/05-22/07 Detector commissioning
23/07-13/09 Final Commissioning /L1 trigger, GTK)
Physics (exotics, rare/forbidden decays)
16/09-03/11 Physics (, exotics, rare/forbidden decays)

10.  Analysis NA62 goal : K++ BR measurement with O(10%) precision
O(10%) Signal acceptance
O(5/1) Signal/Background
On disk ( period, 60m fiducial volume)
131011ppp on T10 (40% of nominal)
Intensity and DAQ capability depend on spill quality
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2016 Analysis goal : assess the sensitivity at the level of 10%
In the next slides a preliminary exploratory analysis shown ( 5% of 2016 data)

11.  Analysis Strategy Signal signature: Background: Incoming K+
Outgoing p+ in time with the K+
Nothing else
Background:
K++
K++
K++- 
Analysis tools:
Precise kinematic reconstruction
PID: K upstream, e// downstream
Hermetic  detection
Sub-ns timing
F.Bucci

12.  Selection
NA62 Keystone O (100 ps) Timing between sub-detectors O(104) Background suppression from kinematics > 107 Muon suppression > 107 0 (from K++0 ) suppression
K+ Decay Event
Fiducial Decay Region
Particle ID
Photon Rejection
Multiple charged particle rejection
Kinematic selection of the signal regions
F.Bucci

13. Kaon Decay Selection Single + topology Kaon ID in KTAG
K -  matching
+ timing:
(TCHOD)250 ps, (TRICH)100 ps
K+ timing:
(TKTAG)80 ps, (TGTK)100 ps
Closest distance of approach between GTK and Straw track
TGTK-TKTAG
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NA62 Preliminary
NA62 Preliminary
(CDA)1.5mm
Mis-tagging probability:  1.7% [40% nominal intensity, 75% efficiency]

14. Fiducial Decay Region Origin of Kaon Decays Events
K+ decays downstream GTK3
K+ interactions in GTK3
K+ decays upstream GTK3
early decays
Fiducial Decay Region
110/115 < Zvertex < 165 m
lower limit against early decays
CHANTI against interactions in GTK3
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15. Kinematics
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16. Signal and Background Regions
To control non gaussian tails from mis-match and mis-measurements
m2miss resolution
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compute the missing mass also
with RICH indipendently from STRAW
with nominal K momentum
design value reached : 10-3 GeV4/c2

17. Particle ID
Samples of  and  from K++0 and K++ selected kinematically
Combined efficiency
PID with calorimeters
 ID efficiency  80%
 mis-ID probability  10-5
NA62 Preliminary
PID with RICH
 ID efficiency  80%
 mis-ID probability  10-2
Efficiency of  ring
reconstruction  90% [depends on p ]
F.Bucci
NA62 Preliminary
RICH, calorimeter independent
Performances improvement expectd

18. Photon Rejection
To measure  rejection, consider events left in the K++0 region after the  selection
Before -rejection
minimum bias, D=400
After -rejection
PNN trigger
NA62 Preliminary
NA62 Preliminary
 accidental losses measured on K++
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events passing signal selection with photon veto
= (1.20.2)10-7
Events in control trigger passing the signal selection but the photon veto
downscale factor of control trigger

19. Expected Signal and Background
in 5% of 2016 statistics
85% (preliminary) measured on data
Normalization: K++0 cfrom control trigger data passing the signal selection but the photon rejection
Acceptance: ratio between signal and normalization: 0.60/0.86
N (K decays)  2.3  1010 [5% of 2016 statistics]   acceptance 0.033
F.Bucci
Process Expected Events Branching ratio
K++
K++
K++- 
Early decays < 0.005
K++- + suppression very preliminary

20. K++ Result No events in signal region
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Event in box has m2miss (no GTK) outside the signal region

21. NA62 Physics besides K++
The high-intensity and high-performance setup make NA62 suited for other NP searches
Exotic searches
Dark Photons (A’), Heavy Neutral Leptons (HNL), Axion-like particles (ALP)
Rare/Forbidden Decays
K++l+l- [O(10-7)] , 0e+e- [BR=6.4610-8]
K++l1+l2-, K+l1-l1+l2- (l1,2= e,), K++e, 0 e
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22. Invisible Vector from 0 decay
K++0, 0A’, A’ invisible
N(K decays) 1.5  1010 ( 4% 2016 statistics) 
mA’ (GeV)
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23. Conclusions Kaons ? New Physics could be already there: ’ ?
NA62 fully working
Good 2016 run
51011 kaon decays taken in the last 40 days
goal: test sensitivity down to 10-10
First preliminary results on K++ (5% data) are promising
analysis of the full 2016 data set in progress
optimization/improvement of the analysis in progress
Excellent prospects for a broader physics program
F.Bucci

24. Spare Slides

25. RK Final Result RK= (2.488 ± 0.010) 10-5
Fully exploit kinematics and strong particle ID Main background from K2
10 improvement, consistent with SM
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NP potential still open
NA62 prospects: expected uncertainty 0.2%
(more statistic, more hermetic vetoing, better resolution and PID)
TREK stopped K proposal: expected uncertainty 0.25%
KLOE (2009) 14K events, 16% bkg
NA62 (2013) 146K events, 11% bkg

26. KL0→p0nn
The charm contribution can be fully neglected since it proceeds in the
SM almost entirely through direct CP violation → determination of h
Exp
Machine
Meas. or UL 90% CL
Notes
KTeV
Tevatron
<5.710-7(p0→eeg)
E391a
KEK-PS
<2.610-8
KOTO
J-PARC
Aim at 2.7 SM evts/3y
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Need a huge number of KL decays
NA48 KL flux corresponding to 31010/year
NA62 possible KL flux 5-10 times NA48 one
After SPS upgrade 100 times more

27. Anomalies in Kaon Physics: K  Ms,d Tension
New results from Fermilab Lattice and MILC collaboration
Construct the UUT (CMFV) by using only
and derive
Strategy 1: Ms determines Vcb  |Vcb| = (39.51.3)10-3
Strategy 2: K determines Vcb  |Vcb| = (39.51.3)10-3
F.Bucci
Blanke, Buras
Tension between Ms and K
Impact on the branching ratio of K++ and KL0