Measuring K+ → π

+νν with NA48/3

Rainer Wanke

Institut fur Physik, Universitat Mainz

on behalf of

CERN, Dubna, Ferrara, Florence, Frascati, Mainz, Merced, Moscow, Naples,

Perugia, Pisa, Protvino, Rome, Saclay, Sofia, Torino

K-RARE Meeting

Frascati, May 26, 2005

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.1/25

Outline

Introduction

K+ Beam

Detector Design

Time Schedule

Summary and Conclusion

Nota bene:

Exp. historically dubbed NA48/3, but not direct successor of NA48/2!Mainly new detectors, and will get new name when approved.

Correct name at the moment: P326 (Proposal no. 326)

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.2/25

The Opportunity

Expected SPS Performance for Fixed-Target: (R. Garoby, Villars 2004)

=⇒ ≥ 3 × 105 proton spills per year for fixed-target.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.3/25

High Intensity K+ Beam

Parameters of the high intensity K+ beam:

K12 in 2004 HI-K+ ≥ 2007(NA48/2) (NA48/3)

Eff. run time/year (pulses) 3 × 105 3 × 105

SPS protons/pulse 1 × 1012 3 × 1012

K+ momentum 60.0 ± 2.5 GeV/c 75.0 ± 0.8 GeV/c

Acceptance solid angle 0.4 µsterad 16 µsterad

Total beam flux/pulse 5.5 × 107 250 × 107

kaons/pulse 0.3 × 107 15 × 107

K+ decays/year 1.0 × 1011 4.8 × 1012

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.4/25

K+ → π

+νν at the CERN SPS

NA48/3:

4.8 × 1012 K+ decays/year

Br(K+ → π+νν) ∼ 10−10

Acceptance ∼ 10%

Dead time ∼ 20%

=⇒ About 80 K+ → π+νν

events in 2009/10.

Background:

K+ → π+π0 (Br ≈ 0.2),K+ → µ+ν (Br ≈ 0.6)

=⇒ Photon/muon vetos,exact momentum meas.

Signal/Background ≈ 10.

θπKPK

Pπ

Pν

Pν

Pπ (GeV/c)

θπK PK = 75 GeV/c

Kµ2

K+ π+νν−

K+ ππ0

K+ π+π0π0

K+ π+π+π−

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

0 10 20 30 40 50 60 70

Region 1

Region 2

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.5/25

Acceptance

Two regions for measuring K+ → π+νν:

Region 1: 0 < m2miss < 0.01 GeV2/c4 =⇒ Acc ≈ 4.5 %

Region 2: 0.026 < m2miss < 0.068 GeV2/c4 =⇒ Acc ≈ 14.5 %

(Both with 15 < pπ < 35 GeV/c, no analysis cuts, no dead time yet)

-0.15 -0.1 -0.05 0 0.05 0.1 0.154/c2 GeVmiss

2m

Arb

itra

ry U

nit

s

0π+π→+K

ν+µ

→+K

-π+π+π→+K

νν+π→+K

Reg

ion

I

Region II

m2miss = (pK − pπ)2 = m2

K + m2π − 2 EK Eπ + 2 ~pK ~pπ cos θKπ

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.6/25

In 2010?

(Standard model)100 events

100 events(E949 value)

(3 events)Now:

?

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.7/25

Backgrounds for K+ → π

+νν

Decay B.R. [%] Type of rejection

K+ → µ+ν (Kµ2) 63 µ particle ID, kinematicsK+ → µ+νγ (Kµ2γ ) 0.55 µ particle ID, photon vetoK+ → π+π0

21 photon veto, kinematicsK+ → π+π+π−

6 charged veto, kinematicsK+ → π0π0π+

2 photon veto, kinematicsK+ → π0µ+ν (Kµ3) 3 photon veto, µ particle IDK+ → π0e+ν (Ke3) 5 photon veto, E/p

-0.15 -0.1 -0.05 0 0.05 0.1 0.154/c2 GeVmiss

2m

Arb

itra

ry U

nit

s

0π+π→+K

ν+µ

→+K

-π+π+π→+K

νν+π→+K

Reg

ion

I

Region II

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.8/25

Detector Design

Detector design follows from need for maximum background rejection:

Precise knowledge of K+ momentum for m2miss determination.

=⇒ Gigatracker — K+ beam spectrometer

Photon rejection.

=⇒ Photon-Vetos — LAV, Lkr, SAC

Precise π+ momentum measurement to reject two-body decays

=⇒ Straw Tracker — double magnetic spectrometer

Optimal π+/µ+ separation for K+ → µ+ν rejection

=⇒ Muon Detector, RICH

K+–π+ matching

=⇒ CEDAR in K+ beam, Hodoscope for charged particles

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.9/25

Detector Layout

VACUUM

CEDAR

LKr

ANTIANTI

ANTI

IRC

1,2

SAC

Target

200 240

Z (m)

0 100

1 m

Ne

1 atm

C1 C2TAX

CHOD

M1 M2

Final Coll.

MAMUDRICH

FTPC

Achromat 1

SPIBES1,2C3

Achromat 2

Straw Tubes

10 MHzKaon decays

800 MHzK, pi, mu

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.10/25

CEDAR — K+ Identification

Requirement: K+/π+ separation in charged particle beam.

=⇒ CEDAR Differential Cerenkov Counter

CEDAR counters have been in use in SPS beams.(Two versions: He-filled “North-CEDAR”, N2-filled “West-CEDAR”.)

West-CEDAR, filled with hydrogen, perfect for NA48/3 application.

Beam

Mirror

Light path

CorrectorRing ImagePMs

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.11/25

Gigatracker — K+ Momentum

Requirements:K+ momentum resolution ∼ 0.3%.

Angular resolution ∼ 10 µrad.

Time resolution ∼ 150 ps per station.

Material budget ≤ 0.5 X0 per station.

Survive 1 GHz hadron beam (60 MHz/cm2).

Design: Hybrid detector

SPIBES (Fast Si micro-pixels)

Momentum and time measurement.2 stations of hybrid silicon pixel detectors.

FTPC

Angular measurement (track direction).Micromegas TPC’s as in NA48/2 (but with FADC read-out).

=⇒ See presentation by M. Scarpa tomorrow!Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.12/25

Photon Vetos

Requirement:

Suppression of K+ → π+π0, K+µ3, K+ → π+γγ, . . .

=⇒ Inefficiency ≤ 10−4 for Eγ > 100 MeV (and ≤ 10−5 for Eγ > 1 GeV).

Components:

Large Angle Vetos (ANTI)

Lead-scintillator sandwich calorimeter around decay region.

Liquid-Krypton Calorimeter (LKr)

Use existing NA48 calorimeter.

Small Angle Vetos (IRC, SAC)

Covering of the beam pipe, lead-scintillator sandwich.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.13/25

Large Angle Photon Vetos (ANTI)

Coverage: > 8.5 mrad (LKr calorimeter)

< 50 mrad (kinematical limit for γ’s from K+ → π+π0)

=⇒ 13 veto counters around decay region.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.14/25

Large Angle Photon Vetos (ANTI)

Design of each veto counter:

80 layers lead-scintillator sandwich, each 16 X0 deep.

Arrangement in segmented rings inside vacuum tank.

Read-out by WLS fibers.

=⇒ ∼ 20 photo electrons/minimum ionizing particle.

Alternative design:

Lead with embeddedscintillator(“spaghetti calorimeter”).

Better time, energyresolution.

Currently investigated.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.15/25

Liquid-Krypton Calorimeter

Main detector element forNA48/0/1/2.

13212 cells of 2 × 2 cm2 alongbeam axis in ∼ 10 m3 liquidkrypton.

Very good energy resolution(3.2%/

√

E [GeV])

Noise about 90 MeV.

Veto capabilities to be verified.

Few upgrades necessary(Read-out, kryogenic system).

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.16/25

Small Angle Photon Vetos

Detectors:

IRC: Coverage of beam pipe inside calorimeters.

SAC: Coverage down to θ = 0.

SAC

beam

LKr

IRC

RICH

CHOD

MAMUD

Design: Two possibilities considered:

Shashlik technique.Layers of Pb + scintillator (total ≈ 17 X0)

PbWO4 crystals.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.17/25

Magnetic Spectrometer

Requirements:

Suppress K+ → µ+ν by 10−8 =⇒ Exact momentum measurement

Minimum material =⇒ Minimum of multiple scattering.

Redundancy =⇒ Suppression of non-gaussian errors.

=⇒ Design: Double spectrometer, operation in vacuum.

Z

MNP33(1)

10 m 7 m 7 m

2.3 m

5 m 5 m

from the target

205 m

MNP33(2)

VUX YX Y U VVUYXX Y VUX Y U V X Y U V

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.18/25

Magnetic Spectrometer

Chamber design: Straw chambersLayer 2

Layer 1

Pion track

Operation in vacuum possible.

Well-known technology (ATLAS TRT, COMPASS).

Experience available (JINR, Dubna).

18 cm

X(Y)

X(Y)

X(Y)

U(V)

U(V)

U

U

Y

X

U(V

)

230 cm

Compass

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.19/25

MAMUD — Magnetized Muonand hadron Detector

Requirements:

π/µ separation for Kµ2 suppression

Beam sweeping for SAC operation.

Design:

Magnetised iron =⇒ 0.9 T field in beam region.

Instrumented by scintillators =⇒ muon rejection ∼ 105.

sum(Emax)/sum(E)

K+ → πνν

K+ → µν (x4)

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.20/25

Charged Hodoscope, RICH

Charged Hodoscope (CHOD)

Excellent time resolution < 100 ps.

Rejection of high-multiplicity events (K+ → π+π+π−, . . . ).

Trigger (together with photon vetos and CEDAR).

Design: Multigap glass RPC, similar to ALICE TOF.

RICH

Needed for additional Kµ2, Kµ2γ rejection.(π/µ seperation at 2 sigma level is sufficent.)

Design currently under investigation (e.g. KPLUS design).

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.21/25

Expected Background

Decay B.R. [%] Bkg. Estim.

K+ → µ+ν (Kµ2) 63.4 ∼ 1.6

K+ → µ+νγ (Kµ2γ) 0.6 ∼ 0.4

K+ → π+π0 21.1 ∼ 4.4

K+ → π+π0γ 0.03 < 0.1

K+ → π0e+ν (Ke3) 4.9 ∼ 1.6

K+ → π0µ+ν (Kµ3) 3.3 < 0.1

K+ → π+π+π− 5.6 in progress

Total: ∼ 8 (+ 3-track)

=⇒ See presentation by G. Ruggiero this afternoon!

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.22/25

Timeline

2005:

Proposal to the SPSC — being submitted.(CERN-SPSC-2005-013)

Design and Development of main detector components.(Beam spectrometer, magnet spectrometer, photon vetos,muon detector, RICH)

2006 – 2008:

Building, tests and installation of detector components.( =⇒ SPS test-beam in 2006.)

2009/2010:

Beam time at the CERN SPS.

Til 2011/2012: Data analysis.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.23/25

CERN Recommendation for NA48/3

From the Villars report (CERN-SPSC-2005-010, Feb 28, 2005):

=⇒ Formally invited by the SPSC to submit a proposal.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.24/25

Summary and Conclusion

NA48/3: Impressive opportunity to measure

≥ 80 K+ → π+νν events in 2009/2010 at the CERN SPS.

Backgrounds are challenging, but under control!

Expect: Signal/background ≈ 10.(Even better when using RICH detector!)

NA48/3 detector currently developped.

Main components: Beam spectrometer, photon vetos,straw tracker, muon rejection.

Rely if possible on well-known technology.Reuse of few components (Lkr) from old NA48.

Proposal written, signed by about 80 physicists.

We are still open to new collaborators.

Rainer Wanke, K-RARE Meeting, Frascati, May 26, 2005 – p.25/25