THE CERN Experiment P326 for Rare Kaon Decays Massimo Lenti INFN Sezione di Firenze
Jan 15, 2016
THE CERN Experiment P326for Rare Kaon Decays
Massimo Lenti
INFN Sezione di Firenze
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Outline of the presentation
• Physics motivations for K+→• The beam• The main background channels• The apparatus• The signal acceptance and S/B• Time schedule and Conclusions
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Physics motivations for K+→
CP
Standard Model predictions
BR(KBR(K++++) ) (1.6×10 (1.6×10-5-5)|V)|Vcbcb||44[[22+(+(cc--))22] ] (8.0 ± 1.1)×10 (8.0 ± 1.1)×10-11-11
BR(KBR(KLL00) ) (7.6×10 (7.6×10-5-5)|V)|Vcbcb||442 2 ± 0.6± 0.6×10×10-11-11
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Physics motivations, II• Theoretically very clean• Sensitive to Vtd
• Very sensitive to New Physics
Present (E787/949): BR(K+) = 1.47 ×1010
with 3 events
+1.30-0.89
Need a 10% measurement (100 events): P326
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How many K decays?• BR(K+→) ~ 8×10
• Look for ~100 signal events• Signal acceptance ~ 10%
~1013 K+ decays
NA48/P326
Use the existing CERN accelerators
Use the existing NA48 experimental hall
]
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The Beam
Primary Beam:• 400 GeV/c protons• 3×1012 protons/pulse (3×NA48/2)• 4.8/16.8 s duty cycle Secondary Beam:
• 75 GeV/c momentum (p/p~1%)• Beam acc.: 15 str (30×NA48/2)• Total rate: 800 MHz• K+ ~ 6%• 4.8×1012 K+decays/y
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The Beam purity
Keep vacuum at 106 mbar: use existing NA48 decay tank(already directly measured)
Tag the K+ in the beam: use a CEDAR
Only 6% K+ but:• protons and electrons don’t decay...• pions and muons decays cannot mimic K+ decays• but beam-gas interactions !!
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The CEDAR
The CEDAR is a Cherenkov counterUsed at CERN since long timeVary gas pressure and diaphragm aperture to select K+
November 2006: test beam with a CEDAR100 GeV/c beamFilled with Nitrogen
Adapt to P326 needs:Fill with HydrogenChange Phototubes and electronics
Beam Composition
00,10,20,30,40,50,60,70,8
1650 1700 1750 1800 1850 1900 1950 2000 2050
Pressure
%
PionsPions
KaonsKaonsProtonsProtons
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KinematicsK
K+
m2miss=(PKP)2
92% K+ decays 8% K+ decays
PK : beam spectrometerP : straw chambers spectrometer
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Beam Spectrometer (I)
CEDAR
Gigatracker
Achromat
Achromat
p
• 3 Silicon Pixels stations across the 2nd Achromat: 36(X) × 48(Y) mm per station• Beam rate: 800 MHz (“Gigatracker”), 50 MHz/cm2
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Beam Spectrometer (II)• 300×300 m pixels
• 200 m Si sensor + 100 m chip
• 0.13 m CMOS technology
(PK)/PK ~ 0.4%(K) ~ 16 rad
Low X/X0
(t) ~ 200 ps/station
Important for beam pile-up
Strong R&D ongoning...
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Straw Chambers Spectrometer
• 6 chambers with 4 double layers• Ø 9.6 mm straw tubes in vacuum• 0.1% X0 per view• 130 m hit resolution per view• 2 magnets (270 and 360 MeV/c pt kick)• holes follow beam path
8.8 m186.3 mfrom T0
5.4 m 5.4 m
7.2 m 7.2 m 3 coordinates
4 coordinates2 coordinates
1 coordinate
10 cm
Gas CF4-CO2-isoC4H10
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Kinematics Reco.
P
K
PK
K
Double spectrometer:almost independent momentummeasurement
Missing mass measurement: dominated by angle between Kaon and pion
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Background 1: K+→ (K)
Largest BR: 63.4%
Need ~ rejection factor• Kinematics: 10
• Muon Veto: 10• Particle ID: 5×10
MAMUD
RICH
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Muon Veto: MAMUD
MAgnetized MUon Detector
Sampling calorimeter + Magnet for beam deflection
Em/hadronic clusters separation
Sensitivity to MIP
10 detection inefficiency
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RICH
3 separation up to 35 GeV/c
• 18 m long• Neon at 1 atm ( thr.: 12 GeV/c)• 2000 PMT• 18 mm granularity• 100 ps resolution (to disentanglepileup in the Gigatracker)
PMTs tested in 2006 CEDAR testPrototype test beam in 2007
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Background 2: K+→ (K)2nd Largest BR: 20.9%
Large angle: 13 ANTIs (10 < acceptance < 50 mrad) Medium angle: NA48 LKr (1 < acceptance < 10 mrad) Small angle: IRC1,2 SAC (acceptance < 1 mrad)
Need ~ rejection factor• Kinematics: 5×10
• Photon Veto: 10per photon
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Large Angle Veto
Two options under test:• lead-scint. tiles read by WLS fibers• lead+scint.fibers (KLOE like)
• 13 ring em calorimeters in vacuum• 10ineff. 0.05<E<1 GeV• 10 ineff. E>1 GeV
Prototypes under constructionsTests at Frascati tagged photon beam
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Small Angle Veto
Tested in October 2006In the NA48 tagged photon beam(see later)
• shaslyk calorimeter on the beam axis• 10 ineff. High energy
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Liquid Kripton Calorimeter
Ineff. for E>10 GeV tested on data collected by NA48/2 (K+→)
Use the existing NA48 LKr calorimeter• 10 ineff. E>5 GeV• 10 ineff. 1<E<5 GeV
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Liquid Kripton Calorimeter (II)
October 2006 test:Tagged photon beamUsing the existing NA48 setup
vacuum
Electron beam
(25 GeV/c)Bremsstrahlung
Kevlarwindow
Driftchambers
MagnetCalorimeter
e-
X LKr cm
Energy deposition in LKr
electronelectron
En
erg
y G
eV
• 2×108 electrons collected• 10 ineff.sensitivity below 10 GeV
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The P326 Layout800 MHz
50 MHz
11 MHz
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Signal AcceptanceRegion I:0<mmiss
2<0.01 GeV2/c4
Region II:0.026<mmiss
2<0.068 GeV2/c4
Remind:K mmiss
2 < 0K mmiss
2 = 0.0182 GeV2/c4
Momentum range: 15 <p< 35 GeV/cFiducial decay region: 60 m
Acceptance: 4% (Region I), 13% (Region II): 17% (I+II)10% goal feasible (after analysis cuts, etc.)
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Signal/BackgroundEvents/year Total Region I Region
II
Signal (acc=17%) 65 16 49
K++0 2.7 1.7 1.0
K++ 1.2 1.1 <0.1
K+e++ ~2 negligible
~2
Other 3 – track decays
~1 negligible
~1
K++0 1.3 negligible
1.3
K++ 0.5 0.2 0.2
K+e+
(+)0,othersnegligibl
e
Total bckg. 9 3.0 6
S/B ~ 8 (Region I ~5, Region II ~9)
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Trigger Levels
• 11 MHz L0 trigger input
• 1track × × → 1 MHz L1 trigger input → PC farm
• Software trigger reduction ~ 40
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Conclusions
• 2006-2007: R&D, test beam• 2008-2010: Construction• 2011: start data-taking
• Full approval and funding expected end of 2007• Still need to strengthen the collaboration
• Clear Physics case• many other physics channels