The NA62 experiment at
CERN for K    Giuseppe Ruggiero ­ Scuola Normale Superiore & INFN (Pisa)
KAON '09 ­ Tsukuba 12/06/2009
12/06/09

Giuseppe Ruggiero

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The K     decays: a clean theoreticalenvironment
FCNC loop processes: sd coupling and highest CKM suppression

Very clean theoretically: SD contributions dominate, hadronic matrix
element related to precisely measured quantities
SM predictions (main uncertainties from CKM matrix elements):

BR K       = 8.5 ± 0.7×10−11 [mc = 1286 ±13 MeV / c2 ]BR K L  0    = 2.76 ±0.40×10−11

Experimental results:−10BR  K       = 1.731.15
×10[ E787 , E959 ' 08]−1.05

BR  K L  0    ≤ 6.8 ×10−8 [ E391a ' 08]
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Giuseppe Ruggiero2

NP and The K     decays(courtesy by C. Smith)

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Giuseppe Ruggiero

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The NA62 Experiment

NA62

former NA48 exp hall

NA62 Collaboration: Bern ITP, Birmingham, Bristol, CERN, Dubna, Ferrara, Fairfax, Florence,Frascati, Glasgow, IHEP, INR, Liverpool, Louvain, Mainz, Merced, Naples, Perugia, Pisa,
Rome I, Rome II, San Luis Potosi, SLAC, Sofia, TRIUMF, Turin
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Experimental Principles of NA62
Goals: ŠO 100 K      events

BR(SM) ~ 8.510­11Acceptance: 10%~10% backgroundK decays: ~1013

Principles:”High” momentum K+ beam: easier rejection of the π0 induced background
Decay in­flight technique: beam­backgrounds suppressed wrt stoppingkaon experiments
Experimental techniques to exploit:(1) Kinematic rejection: against 2­body and 3­body backgrounds(2) Precise timing: matching of the outgoing π+ with the correct parent K+(3) Vetoes: rejection of events with γ and μ in final state(4) Particle Identification: K/π (in the primary beam), π/μ (final state)
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Giuseppe Ruggiero

5Detector Layout
SPS primary protons @ 400 GeV/c Unseparated secondary charged beam
75 GeV/c (∆P/P1%)
p//K (positron free, fraction of K ~6%)
Area @ beam tracker 16 cm2
Integrated average rate @ beam tracker 800 MHz
Kaon decays/year 4.81012



Sensitivity not limited by proton flux
Need ~same amount of protons as NA48

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Giuseppe Ruggiero61) Kinematic Rejection
Background constrainedby kinematic

Signal signature

Requirements
Minimization of multiple scattering
Low mass trackers for K and π
Tracking in vacuum for K and π~92 % of the total K decay BR
Two regions almost ”background”
free, separated by the K+ π+π012/06/09

Giuseppe RuggieroHigh resolution trackers
 ~100 m per coordinates

Detectors involved
Gigatracker: Kaon
Straw chambers: pion
72) Precise Timing
Needed for Kπ matching
Possible mismatches induce loss of kinematic
rejection power
Difficulty: recognize kaons in a ~GHz environment

Detectors involved:
CEDAR: (t) ~ 100 ps
Gigatracker: (t) ~ 200 ps / station
RICH: (t) < 100 ps
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Giuseppe Ruggiero

8Gigatracker
3 Si pixel stations before the decay
volumeGeometry matching the beam size

Requirements:
High space resolution: 300x300 μm pixels
Low X/X0: 200 μm sensor+100 μm chip
Si sensorpixelmatrixR­Ochipmechanical support
12/06/09(<0.5% X/X0 per station)
Excellent time resolution: sophysticatedRO chip bump bonded on the sensor (0.13μm technology)
Giuseppe Ruggiero

9Straw Chamber Spectrometer4 straw chambers in vacuum + 1
magnet (NA48 magnet, 256 MeV/c Pt

Magnetkick)4 views per chamber (XYUV)
4 staggered layers of tubes per view
9.6 mm mylar tubes
2.1 m long
Total X/X0 ~0.1% per view
6 cm ”radius” beam hole displaced in
the bending plane according to the75 GeV/c beam path
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10Straw Chamber Spectrometers R&D

Full length prototipe built in 2007

Placed in vacuum on the beam

RMS (cm)

Resolution from test beam (blue points)

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Giuseppe Ruggiero

RMS < 100 mRadius (cm)11

Kinematic rejection capabilities
Performance of the new tracking system(Geant4 MC):2­body rejection power

(PK)/PK ~0.2%, (dX,Y/dZ)~17 μrad

Sources of inefficiency:

(Pπ)/Pπ ~0.3%0.007% Pπ,

MS non guassian tails
Kπ mis­match

(dX,Y/dZ)~45 – 15 μrad

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104 (K+π+π0), 105(K++)Giuseppe Ruggiero

12m2miss GeV2/c43) Vetoes
Photon vetoes:
studied to reject K  π π in conjuction
with the kinematic rejection++0Requirements: O(10­8) π0 rejection
inefficiency
Detectors: electromagnetic calorimeters
LAV (10­50 mrad)
LKr [NA48] (1­10 mrad)

Key points:
Analysis request: P(π+)<35 GeV/c ⇒P(π0)> 40 GeV/c, it can hardly be
missed in calorimeters>1 GeV photons hit the liquid Kripton
calorimeter
10­5 inefficiency of the liquid Kripton
calorimeter for >10 GeV photons

SAC, IRC (<1 mrad)
Muon veto:studied to reject K+ μ+ν in conjuction with the kinematic rejection and particle ID

Requiremet: O(10­5) muon rejection inefficiency
Detector: hadronic calorimeter + fast pad­scintillator planes
Upgrade of the existing NA48 hadronic calorimeter
12/06/09
Giuseppe Ruggierosensitivity to the MIP and em/hadronic
shower separation capability

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NA48 Liquid Kripton em calorimetry inefficiency
Inefficiency measured on data
2006 bremmstrahlung photon beam (E>2.5 GeV)
2004 NA48 data @ 75 GeV (E>10 GeV)
K+ π+π0 selected using kinematic only

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Giuseppe Ruggiero

E (GeV)

Inefficiency

2.5 – 5.5

< 10­35.5 – 7.5< 10­47.5 – 10

< 5x10­5> 10< 8x10­614

Large Angle Veto (LAV)
OPAL lead glass:
12 rings along the detector line
(variable radius) in vacuum
5 staggered plane of modules
per ring
Array of blocks tested @ BTF(Frascati):
Inefficiency @ 471 MeV e+:~10­4 on the whole surface
Module prototype tested @ CERN in2008
Validation of the operation invacuum
Time resolution ~1 ns
First ring under construction: will betested @ CERN in autumn.
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Giuseppe Ruggiero

154) Particle Identification
Physical background notconstrained by kinematic~8% of the total K decay BR
Span across the signal region
Particle ID + Veto

Beam related background:hadronic interaction of the beam
particles with the gigatracker
stations
Interactions of the beam particles
with the residual gas in the decay
volume12/06/09

Requirements and Detectors
involved:~10­2 π/μ separation up to 35 GeV(mainly against K++(γ)): RICH
π/e separation: LKr and RICH
K identification: CEDARGiuseppe Ruggiero

16Purposes
π/μ separation with low
inefficiency and high purity
Time of the events:
excellent time performance

RICH

Radiator: Ne gas at 1 atm

2×1000 PMT(hex packing 18 mm side)

Mirror Mosaic(17 m Focal Length), 3 m dd

longVessel: 17 m

Main trigger for 1 track
eventsBeam Pipe

Test beam 2007

Results

ECN3 (NA48 cavern)@ CERN[NIM A 593, 2008]

200 GeV hadron
beam (pion/K)

Nhits ~ 17/event

Full length prototipe(0.5 m radius)Δθc ~ 50 μrad96 PMT Hamamtsu
R7400

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Δtevent ~ 70 ps

Giuseppe Ruggiero(biased by PMGeometry)

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Rich Test Beam '09

Full length prototype tested ona charged beam at CERN SPS~400 PMT installed~17 photon / positron detected
HPTDC and TELL1 boards forreadout (project developed within

the collaboration in the framework ofthe Trigger R&D)

35 GeV/c˝μ˝πe+PRELIMINARY
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Giuseppe Ruggiero

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radius (m)NA62 Sensitivity: signal acceptance

Simulation of the NA62 apparatus

interactions in the trackers simulatedusing GEANT4

Most important cut in the analysis:
15 < Pπ < 35 GeV/c

REGION IREGION II

For photon and muon rejection
RICH operational reasons

Acceptance: ~14.4%
3.5% ”region 1”, 10.9% ”region 2”
50% loss due to Pπ cut
Expected detector inefficiencies
considered
To be reduced because of losses due todead time, additional inefficiencies...
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The NA62 experiment matches
the goal of 10% acceptance

Giuseppe Ruggiero

19NA62 Sensitivity
Decay Mode

EventsSignal: K+→π +νν [ flux = 4.8×1012 decay/year]

55 evt/year

K+→π +π 0 [η π 0 = 2×10­8 (3.5×10­8) ]12/06/09

4.3% (7.5%)

K+→µ +ν

2.2%

K+→e+π +π − ν≤3%Other 3 – track decays≤1.5%

K+→π +π 0γ~2%

K+→µ +νγ~0.7%

K+→e+(µ +) π 0ν, others

negligible

Expected background≤13.5% (≤17%)

Giuseppe Ruggiero

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Conclusions
The physics case to study ultra rare kaon decays at CERN SPS in the LHC
era is very strong
With 2(+1) years of data taking NA62 will provide a 10% measurement of theBR of the K    
Key points: Excellent resolution, hermetic coverage, strong particle ID
x50 Kaon flux with respect to NA48 with ~same amount of protons from SPS

A rich physics NA62 program can be added to the ultra rare kaon decays
precision tests of lepton universality, study of strong interactions at low energy
searchs for (e.g.) Sgoldistinos, νMSM Neutral Leptons

The R&D is close to the end, the construction is already started
The construction schedule is mostly resource driven

The experiment was approved by the CERN Research Board (December 52008) ”subject to the definition of resource sharing within the Collaboration”
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Gigatracker R&D
Gigatracker R/O prototypes

CERN design:

INFN design: One TDC/pixel

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end­of­column TDC

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Photon ANTI counters

OPAL LEAD GLASS BEING PROCESSEDFOR USE IN NA62 in Building 904 at CERN

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Large Angle Veto (LAV) R&D
First ring at LNF (Frascati) for assemblyFirst layer assembled (may '09)

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Sub­detectors R/O andintegrated L0 trigger:
TELL1/TDC projectTrigger system

RICH, MUD, LAV, Straws
Gigatracker, LKr , CEDAR:
dedicated projects for R/Oand L0 trigger

L0 processor:
receives O(40 MB/s), takes
a decision delivered to all
the detectors.
L1 (subdetectors), L2(event) triggers: online
farm. Output O(kHz).
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TELL1/TDC R&D
LHCb TELL1 as underlying carrier board
High integration TDC daughter card with
HPTDCs developed (512ch/TELL1)
Linear fast preamp/discriminator gives PH
information with time­over­threshold
Local processing and power storage
TELL1/TDC based R/O system tested
successfully during the '09 RICH test
1 event
leading

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trailing

Giuseppe RuggieroTime 100xps27