POLENKEVICH IRINA (JINR, DUBNA)ON BEHALF OF THE NA62 COLLABORATION
XXI INTERNATIONAL WORKSHOP ON HIGH ENERGY PHYSICS AND QUANTUM FIELD THEORY
(QFTHEP'2013)
23 – 30 JUNE, 2013
Prospects for K → observation at CERN
Outline
MotivationPrinciples of NA62Sensitivity StudiesResults from the 2012 Technical RunConclusions
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Irina Polenkevich QFTHEP'2013 , June 25 2013
K → : a theoretical clean environment
FCNC processes described with penguin and box diagrams
Very clean theoretically: SD contributions dominate BR proportional to |Vts*Vtd |2 → theoretical clean Vtd dependence SM predictions [Brod, Gorbahn, Stamou, Phys. Rev. D 83, 034030
(2011)] : BR(KL → 0 ) = (2.43 ±0.39 ±0.06) ×10-11
Pure theoretical error, mostly LD corrections
BR (K → ) = (7.81 ± 0.75 ± 0.29)×10-11
Parametric error dominated by Vcb, Present experimental results:
BR(K → ) = (17.3 −10.5 +11.5)×10−11[E787, E959]
BR(KL → ) < 2.6×10−8[E391a]
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Irina Polenkevich QFTHEP'2013 , June 25 2013
QFTHEP'2013 , June 25 2013Irina Polenkevich
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Experimental Measurements and Techniques
Stopped Work in kaon
frame High kaon purity Compact detectors
In-Flight Decays in vacuum Separated or not
separated beams Extended decay
regions
Upcoming experiments:
• NA62 @ CERN• KOTO @ JPARC• ORKA @ Fermilab
The NA62 detector for K →
Goal: 10% precision branching ratio measurement of K → O(100) SM K → events (2 years of data)
Requirements Statistics: BR(SM) 8 x 10-11
K decays (2 years): 1013
Acceptance: 10%
Systematics: >1012 background rejection (<20% background) <10% precision background measurement
Technique “High” momentum K+ beam
Kaon intensity
Signal efficiency
Signal purity
Detector redundancy
Decay in flight
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Irina Polenkevich QFTHEP'2013 , June 25 2013
SPS proton beam @ 400 GeV/c Proton on target: 1.1 x 1012/ s P secondary charged beam 75 GeV/c Momentum bite 1% Angular spread in X and Y < 100
mrad
Size @ beam tracker: 5.5 x 2.2 cm2
Rate @ beam tracker: 750 MHz 6% K+(others: +, proton) Rate downstream 10 MHz
(K+decay mainly) K decay rates / year: 4.5 x1012
(60 m decay volume)
Beam line
Irina Polenkevich QFTHEP'2013 , June 25 2013
Detectors7
The CEDAR – differential Cerenkov counter K+ components in the beam
GTK – Gigatracker 3 Si micro-pixel station Time, direction and momentum of the beam
particle The STRAW Tracker 4 Chambers inside the high
vacuum (10-6) tank Coordinate and momentum of secondary
charged particles from decay volume The RICH detector 17m long radiator filled with
neon Gas at 1 atm, THE MUV – Muon-Veto Detectors 2-part hadron calorimeter, iron and a transversally-segmented hodoscope Separate pions and muons between 15 and 35
Gev/c
System of Photon-Veto detectors: The LKR – high resolution Liquid
Krypton electro-magnetic calorimeter
IRC and SAC– Intermediate Ring and Small-Angle Calorimeters
12 annular photon-veto LAV detectors Hermetic coverage 0-50 mrad
angles from the decay region Counters CHANTI and charge-
particle hodoscope CHOD Acceptance
High-performance trigger and Data-acquisition (TDAQ) system
Irina Polenkevich QFTHEP'2013 , June 25 2013
Scheme for Selection
One reconstructed track in the Straw (+track)
Signal in RICH compatible with only 1 +
hypothesis Signal in Calorimeters (CHOD, LKr,
MUV1,2,3) compatible with only 1 +
hypothesis No clusters in LKr compatible with
hypothesis No signals in LAVs, IRC, SAC compatible
with hypotesis
At least one track in Gigatracker matched in space and time with the + track (K+
track) and compatible with the beam parameters (75 GeV/c)
No extra activity in CHANTI compatible with a MIP signal
Signal in KTAG compatible with a K hypothesis
Z vertex in the first 60 m of the decay volume15 < P + < 35 GeV/c
Irina Polenkevich QFTHEP'2013 , June 25 2013
Signal and Background
Signal Kinematic variable:
Background1) K+ decay modes 2) Accidental single track matched with a K-like track
Signal signature: Incoming high momentum(75 GeV/c) K+
Outcoming low momentum(<35 GeV/c) + in time with the incoming K+
2222 11 KKK
KKmiss PP
P
Pm
P
Pmm
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Irina Polenkevich QFTHEP'2013 , June 25 2013
2K
2miss )P-(Pm
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Background Rejection
Decay BR
K+→+(K2) 0.64
K+→+0(K2) 0.21
K+→++K+→+00 0.07
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Irina Polenkevich QFTHEP'2013 , June 25 2013
~92% of kaon decays separated by kinematical cut
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Particle Identification
K+ positive identification (CEDAR) / separation (RICH) /e separation (E/p)
Decay BR
K+→e+(Ke3) 0.051
K+→0+(K3) 0.034
K+→+(K2) 6.210-3
K+→+-e+(Ke4) 4.110-5
K+→+-+(K4) 1.4 10-5
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Irina Polenkevich QFTHEP'2013 , June 25 2013
Physics Sensitivity
Decay event/year
K+ → π+ν ν [SM] (flux 4.5x1015) 45
K+ → π+π0 5
K+ → μ+ν 1
K+ → π+π-π+ < 1
K+ → π+π-e+ ν + other 3-track decays < 1
K+ → π+π0 γ (IB) 1.5
K+ → μ+ν γ (IB) 0.5
K+ → π0e+(μ+) ν , other decays negligible
Total background < 10
Cut & count analysis without any optimization e.g. Use of the 𝑚𝑚𝑖𝑠𝑠
2 shape to add further signal/background discrimination
The background must be measured with at least 10% precision Background evaluation to be done on data
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Irina Polenkevich QFTHEP'2013 , June 25 2013
Results from the 2012 Technical Run
Goals: Analysis of the time and spatial correlation between the subdetectors Estimation of the time resolution and efficiency of the subdetectors
Partial set –up: KTAG (50% PMs), 1 straw plane, CHOD, LKr (30% readout), MUV2, MUV3
Analysis Method: selection of K++0events Selection based on the Liquid Kripton Calorimeter Photon tagging from the shape of the reconstructed clusters 0 reconstruction:
Z vertex from 2 on the LKr assuming m0
X and Y vertex from the assumed K direction K momentum (PK) and divergence well defined by
the beam line P+ = (PK--P0) P2
+= m2+ for K++0
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Irina Polenkevich QFTHEP'2013 , June 25 2013
The Final K++0 Sample
Exploit the timing and spatial correlations between the subdetectors to define a Kaon candidate, pion candidate and a muon candidate.
Signal region: 0 < m2
miss < 0.04 GeV2/c4
Background @ % level mmiss
2=(0.0199±0.0005) GeV2/c4
(mmiss2) =3.8 10-3 GeV2/c4
m2(+)=0.0195 GeV2/c4
Time resolution: KTAG 150 ps, LKr 350 ps, CHOD 400 ps, MUV3 450 ps
KTAG efficiency about 87% (corresponding to 95% for a fully instrumented detector)
6% of events with a muon in-time (upper limit to the punch-through)
This analysis will be used in the final analysis to monitor the tails of the mmiss
2 reconstructed with the tracking system.
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Irina Polenkevich QFTHEP'2013 , June 25 2013
Conclusions
The Na62 will allow us: 10% precision BR(K → ) measurement in two years of data taking observe and study of other rare decays
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to fulfill a strong test for the SM or to indicate a new physics
We look forward to the 2014 data
Irina Polenkevich QFTHEP'2013 , June 25 2013
Thank you