Prospects for K + → p + nn observation at CERN

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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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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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


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


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


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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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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~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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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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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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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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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


Thank you

Documents

Prospects for K + → p + nn observation at CERN