POLENKEVICH IRINA (JINR, DUBNA) ON BEHALF OF THE NA62 COLLABORATION XXI INTERNATIONAL WORKSHOP ON...

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

POLENKEVICH IRINA (JINR, DUBNA) ON BEHALF OF THE NA62 COLLABORATION XXI INTERNATIONAL WORKSHOP ON...

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