The Detector for the Kaon Rare Decays Experiment NA62 at CERN

The Detector for the Kaon
Rare Decays Experiment
NA62 at CERN
Massimo Lenti
INFN Sezione di Firenze
Outline of the presentation
• 
• 
• 
• 
• 
• 
Physics motivations for K+→π+νν
The beam
The main background channels
The apparatus
The signal acceptance and S/B
Time schedule and Conclusions
IPRD10, 10.5.2010
M. Lenti
2
Physics motivations
•  Theoretically very clean
•  Sensitive to Vtd
•  Very sensitive to New Physics
Present (E787/949): BR(K+→π+νν) = 1.73
with 7 events
  Predicted:
" 
+1.15
-1.05
×10-10
Need a 10% measurement (100 events): NA62
IPRD10, 10.5.2010
M. Lenti
3
How many
+
K
decays?
•  BR(K+→π+νν) ~ 8×10-11
•  Look for ~100 signal events
•  Signal acceptance ~ 10%
]
~1013 K+ decays
NA48/NA62
Use the existing
CERN accelerators
Use the existing
NA48 experimental hall
IPRD10, 10.5.2010
M. Lenti
4
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
(Δp/
p~1%)
•  Beam acc.: 12.7 µstr
(32×NA48/2)
•  Total rate: 750 MHz
•  K+ ~ 6%
•  4.5×1012 K+decays/y (45×NA48/2)
IPRD10, 10.5.2010
M. Lenti
5
The Beam purity
Only 6% K+ but:
•  protons and positrons don’t decay...
•  pions and muons decays cannot mimic K+ decays
•  but beam-gas interactions !!
Keep vacuum at 10-6 mbar:
use existing NA48 decay tank
(already directly measured)
Tag the K+ in the beam:
use a CEDAR
IPRD10, 10.5.2010
M. Lenti
6
The CEDAR
The CEDAR is a Cherenkov counter
Used at CERN since long time
Vary gas pressure and diaphragm
aperture to select K+
November 2006:
test beam with a CEDAR
100 GeV/c beam
Filled with Nitrogen
Adapt to NA62 needs:
Fill with 4 bar Hydrogen
(<7⋅10-3 X0)
Change PMT and FE
IPRD10, 10.5.2010
M. Lenti
7
Background: K+ decays
Decay
BR
µ+ν
(Κµ2)
63.5%
π+π0
(Κπ2)
20.7%
π+π+π-
5.6%
π0e+ν (Κe3)
5.1%
π0µ+ν (Κµ3)
3.3%
π+π0π0
1.8%
µ+νγ
(Κµ2γ)
π+π0γ
2.7×10-4
π+π-e+ν (Ke4)
4.1×10-5
π0π0e+ν (Ke400)
2.2×10-5
e+ν
1.5×10-5
(Ke2)
π+π-µ+ν (Kµ4)
IPRD10, 10.5.2010
0.62%
1.4×10-5
M. Lenti
8
Kinematics
K+
ν
θKπ
ν
m2miss=(PK-Pπ)2
92% K+ decays
8% K+ decays
PK : beam spectrometer
Pπ : straw chambers spectrometer
IPRD10, 10.5.2010
M. Lenti
9
Beam Spectrometer (I)
•  3 Silicon Pixels stations across the 2nd Achromat:
60(X) × 27(Y) mm per station (18000 pixel/station)
•  Beam rate: 750 MHz (“Gigatracker”), 50 MHz/cm2
IPRD10, 10.5.2010
M. Lenti
10
Beam Spectrometer (II)
•  300×300 µm pixels p-in-n
(18000 pixel per station)
•  200 µm Si sensor + 100 µm chip
•  0.13 µm CMOS technology
Si sensor
Pixel matrix
IPRD10, 10.5.2010
R-O chip
σ(PK)/PK ~ 0.2%
σ(θK) ~ 15 µrad
<0.5% X0 /station
σ(t) ~ 200 ps/station
Sensor
prototype
M. Lenti
11
Beam
Spectrometer
(III)
Readout
See M. Noy’s talk
VESSEL’S SIDE CLAMPED DETECTOR’S EDGE CLAMPED The cooling System
IPRD10, 10.5.2010
DETECTOR’S EDGE SLIDING M. Lenti
VESSEL’S SIDE SLIDING 12
Straw Chambers
•  4 chambers with 4 layers/view
•  Ø 9.6 mm straw tubes in vacuum
•  2.1 m long straws
•  0.1% X0 per view (4 views)
•  130 µm hit resolution per view
•  NA48 magnet (256 MeV/c pt kick)
•  holes follow beam path
IPRD10, 10.5.2010
M. Lenti
13
Straws Prototype
In vacuum
2007 prototype
IPRD10, 10.5.2010
M. Lenti
14
Kinematics Reco.
Missing mass measurement: dominated by angle between
Kaon and pion
IPRD10, 10.5.2010
M. Lenti
15
Background 1: K+→µ+ν
Kµ2 :largest BR: 63.4%
Need ~10-12 rejection factor
•  Kinematics: 0.5×10-5
•  Muon Veto: 10-5
•  Particle ID: 10-2
MUV
RICH
IPRD10, 10.5.2010
M. Lenti
16
Muon Veto: MUV
•  Re-use of Front Module of
NA48 Hadron Calorimeter
 Build a new module
 Build a Fast Plane for trigger
10-5 µ detection inefficiency
New module: sandwich of iron plates
and scintillator strips
IPRD10, 10.5.2010
M. Lenti
17
The NA62 RICH
3σ π-µ separation (15-35 GeV/c)
•  Neon at 1 atm (π thresh.:12 GeV/c)
•  2000 PMT
•  18 mm pixel
•  100 ps
Mirrors
17 m
Beam Pipe
PMT: Hamamatsu R7400 U03
IPRD10, 10.5.2010
M. Lenti
18
RICH prototype:
2009 test beam
15 GeV/c
π
e
µ
p×mπ/mµ
Ring Radius (mm)
35 GeV/c
π
e
p×mπ/mµ
Muon suppression (15.35 GeV/c):
0.7%
(see E.Marinova’s talk)
IPRD10, 10.5.2010
Ring Radius (mm)
M. Lenti
19
Background 2:
K+→π+π0 (Kπ2)
2nd Largest BR: 20.9%
Need ~10-12 rejection factor
•  Kinematics: 5×10-5
•  Photon Veto: 10-5 per photon (10-8 per π0)
"   Large angle:
12 ANTIs (8.5 < acceptance < 50 mrad)
"   Medium angle: NA48 LKr (1 < acceptance < 8.5 mrad)
"   Small angle:
IRC, SAC (acceptance < 1 mrad)
IPRD10, 10.5.2010
M. Lenti
20
Large Angle Veto
•  12 ring em calorimeters in vacuum
•  5 staggered planes per ring
•  inefficiencies:
  <10-4 Eγ<1 GeV
  <10-5 Eγ>1 GeV
OPAL Lead Blocks
reused
IPRD10, 10.5.2010
M. Lenti
21
Large Angle Veto: 1° ring
First ring built in Frascati and installed at CERN.
Test beam in mid-october 2009
2° ring under test beam august 2010
IPRD10, 10.5.2010
M. Lenti
See Poster
by P. Valente
22
Small Angle Veto
•  shaslyk calorimeter on the beam axis
•  10-5 ineff. High energy γ
Tested in October 2006
In the NA48 tagged photon beam
(see later)
IPRD10, 10.5.2010
M. Lenti
23
Liquid Kripton Calorimeter
Use the existing NA48 LKr calorimeter
•  10-5 ineff. Eγ>5 GeV
•  10-4 ineff. 1<Eγ<5 GeV
Ineff. for Eγ>10 GeV tested on data
collected by NA48/2 (K+→π+π0)
IPRD10, 10.5.2010
M. Lenti
24
Liquid Kripton Calorimeter (II)
vacuum
Electron beam
(25 GeV/c)
Bremsstrahlung
Magnet
Calorimeter
eγ
Drift
chambers
Energy deposition in LKr
•  2×108 electrons collected
•  10-5 ineff.sensitivity below 10 GeV
IPRD10, 10.5.2010
October 2006 test:
Tagged photon beam
Using the existing
NA48 setup
M. Lenti
Energy GeV
Kevlar
window
25
X LKr cm
Multibody Background
Ex. K+→π+π-e+ν
Stagger Straws to
be hermetic for πup to 60 GeV/c
IPRD10, 10.5.2010
M. Lenti
26
CHANTI
•  Need to veto inelastic scattering
in Gigatracker and last collimator
•  Veto stray muons upstream
•  Need a CHarged ANTIcounter
1600 mm
33x17x150(max)mm
Six stations (x-y views)
Extruded scintillator
WLS fiber
GTK3
See G.Saracino’s talk on MU-RAY
IPRD10, 10.5.2010
M. Lenti
27
The NA62 Layout
10 MHz
45 MHz
IPRD10, 10.5.2010
750 MHz
M. Lenti
28
NA62 Event Display
IPRD10, 10.5.2010
M. Lenti
29
Trigger Levels
•  10 MHz L0 trigger input
•  1track × µ! × γ! → 1 MHz
L1 trigger input → PC farm
•  Software trigger reduction
~ 40
IPRD10, 10.5.2010
M. Lenti
30
Signal Acceptance
Region I:
0<mmiss2<0.01 GeV2/c4
Region II:
0.026<mmiss2<0.068 GeV2/c4
Remind:
Kµ2 mmiss2 < 0
Kπ2 mmiss2 = 0.0182 GeV2/c4
15 <pπ< 35 GeV/c
Fiducial decay region: 60 m
Acceptance: 3.5% (Region I), 10.9% (Region II): 14.4% (I+II)
IPRD10, 10.5.2010
M. Lenti
31
Signal/Background
IPRD10, 10.5.2010
M. Lenti
32
Conclusions
•  2006-2009: R&D, test beam
•  2010-2011: Construction
•  july 2012: technical run
•  november 2012: first physics run
•  NA62 approved by CERN Research Board: 5.12.2008
•  NA62 approved by INFN: 24.7.2009
•  Clear Physics case
•  many other physics channels
The NA62 Collaboration: ITP Bern, Birmingham, Bristol, CERN, Dubna,
INFN (Ferrara, Firenze, Frascati, Napoli, Perugia, Pisa, Rome I, Rome II, Torino),
Fairfax, Glasgow, IHEP, INR, Liverpool, Louvain, Mainz, Merced, San Louis
Potosi, SLAC, Sofia, TRIUMF
IPRD10, 10.5.2010
M. Lenti
33