september 27, 2005p-326@spsc731 proposal to measure the rare decay k at the cern sps cern,...
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September 27, 2005 P-326@SPSC73 1
Proposal to Measure the Rare Decay K at the CERN SPS
CERN, Dubna, Ferrara, Florence, Frascati, Mainz, Merced, Moscow, Naples,
Perugia, Protvino, Pisa, Rome, Saclay, San Luis Potosi, Sofia, Turin
CERN-SPSC-2005-013 SPSC-P-326
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September 27, 2005 P-326@SPSC73 2
Physics Introduction:CKM matrix and CP-Violation
'
'
'
ub
cb
td
ud us
cd cs
ts tb
V
V
V V
d d
s s
b b
V
V
V
V V
Ng=2 Nphase=0 No CP-Violation
Ng=3 Nphase=1 CP-Violation Possible
Quark mixing is described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix
e.g., Im t= Im Vts*Vtd ≠ 0 CP
KM mechanism:
=Vus
Im t = A2 5 Re t = A2 5
The unitarity of the CKM matrix can be expressed by triangles in a complex plane.
K+→+ is sensitive to |Vtd|
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September 27, 2005 P-326@SPSC73 3
Physics Motivation
• The Kobayashi-Maskawa mechanism appears to be the main (only?) source of CP-violation
• Now look for inconsistencies in SM using independent observables affected by small theoretical uncertainties and different sensitivity to new physics
• The rare process K belongs to the theoretically cleanest decays in the field of
K- and B-mesons • It allows one to determine |Vtd| independently from
B0-B0 mixing, thus providing a decisive test of the Standard Model
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September 27, 2005 P-326@SPSC73 4
K→ : Theory in Standard Model
2 2
5 5
20 0L L 5
Im Re Re( ) ( ) ( ) ( )
Im( ) ( )
t t ct t c
tt
B K X x X x P X
B K X x
charm
contribution
topcontributions
2 08
2 4
3 ( )
2 sinKW
Br K er
The Hadronic Matrix Element is measured and isospin rotated (~10% correction)
*
*
us
c cs cd
t ts td
VV VV V
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September 27, 2005 P-326@SPSC73 5
Predictions in SM
11( ) (8.0 1.1) 10 BR K
( ) 0.367 0.033( ) 0.012( ) 0.009( )c c c sP X m
This used to be the largest theoretical error(+/- 0.037). It was reduced by a NNLO calculation (Buras et al. hep-ph/0508165)
0 0 11(Buras et al. 04)L( ) (3.0 0.6) 10 BR K
The errors are due to the uncertaintyof the CKM parameters and not to the hadronic uncertainties
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September 27, 2005 P-326@SPSC73 6
Setting the bar for the next generation of K+→+ experiments
100 eventsMean=SM
100 eventsMean=E787/949
Current constraint on plane
?
E787/E949: BR(K+ → + ) = 1.47+1.30-0.89 × 10-10
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September 27, 2005 P-326@SPSC73 7
Some BSM Predictions
SM 8.0 ± 1.1 3.0 ± 0.6
MFVhep-ph/0310208
19.1 9.9
EEWPNP B697 133
7.5 ± 2.1 31 ± 10
EDSQhep-ph/0407021
15 10
MSSMhep-ph/0408142
40 50
0 0 11L( ) 10BR K 11( ) 10BR K
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September 27, 2005 P-326@SPSC73 8
Other Physics Opportunities
• The situation is similar to NA48, which was designed to measured “only” ’/ but produced many more measurements
• Accumulating ~100 times the flux of NA48/2 will allow us to address, for instance:
1. Cusp like effects ( scattering)– K e
2. Lepton Flavour Violation K e , K e+, (Ke2/K2)
3. Search for new low mass particles – K X – K P (pseudoscalar sGoldstino)
4. Study rare decays 5. Improve greatly on rare radiative kaon decays6. Compare K+ and K- (alternating beam polarity)
– K (CPV interference)– T-odd Correlations in Kl4
7. And possibly, given the quality of the detector, topics in hadron spectroscopy
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September 27, 2005 P-326@SPSC73 9
Principle of the measurement
• Collect ~ 5 1012 Kaon decays/year from a secondary SPS hadron beam (K12)
high energy kaons: 1. high acceptance
2. good resolution
3. good photon detection efficiency
4. redundancy
pions and protons cannot be separated: 1. large rate in the beam tracker
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September 27, 2005 P-326@SPSC73 10
P-326 Detector Layout
800 MHz beam/K/p
K+
+
~11 MHz
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September 27, 2005 P-326@SPSC73 11
Background rejection
Guidance: Guidance: S/B = 10S/B = 10 ~~1010-12 -12 rejectionrejection
1) Kinematical rejection based on the missing mass:
2) Veto and Particle ID, , charged particles
– e separation
2222 ||||||
||1
||
||1 KK
K
KKmiss PP
P
Pm
P
Pmm
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September 27, 2005 P-326@SPSC73 12
Backgrounds kinematically constrained
Decay BR
K+K2
)0.634
K++0 0.211
K+++- K+00
0.070
92% of K+ decaysAllows us to define the signal region
K+0 forces us to split it into two parts
Region I: 0 < m2miss < 0.01 GeV2/c4
Region II: 0.026 < m2miss < 0.068 GeV2/c4
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September 27, 2005 P-326@SPSC73 13
Backgrounds not kinematically constrained
Decay BRK+0e+
(K(Ke3e3))
0.049
KK33 0.033
KK22 5.5×10-3
K+++00
1.5×1
0-3
KKe4e4 4×10-5
KK44 1×10-58% of K+ decays
They span accross the signal regionsMust rely on Particle ID and veto
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September 27, 2005 P-326@SPSC73 14
Signal Acceptance
Acceptance (5 m < Zvertex < 65 m)
REGION I: 4%
REGION II: 13%
Total: 17%
For safety, a 10% acceptance is quoted in the proposal
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September 27, 2005 P-326@SPSC73 15
Signal & backgrounds from K decays / year
Total Region I Region II
Signal 65 16 49
K++0 2.7±0.2 1.7±0.2 1.0±0.1
K2 1.2±0.3 1.1±0.3 <0.1
Ke4 2±2 negligible 2±2K++ and other 3-tracks
bckg.
1±1 negligible 1±1
2 1.3±0.4 negligible 1.3±0.4
K2 0.4±0.1 0.2±0.1 0.2±0.1Ke3,
K3 ,othersnegligible
Total bkg 9±3 3.0±0.2 6±3
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September 27, 2005 P-326@SPSC73 16
Summary
Signal events expected per year@BR=8 10-11
65 (16 Region I, 49 Region II)
Background events~9 (3 Region I, ~6 Region II)
Signal/Background ~ 8S/B (Region I) ~5
S/B (Region II) ~ 9
Backgrounds from beam scattering and interactions not included
For Comparison: In the written proposal we quoted 40 events/year@BR=10-10 to account for some reconstruction and deadtime losses
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September 27, 2005 P-326@SPSC73 17
Choice of K+ momentum:
(for 400 GeV/c proton momentum)
40 50 60 70 80 90 100 110 120 130 140 1500
1
2
3
4
5
6
7
8
9
10
11
12
13
Acceptance
K+ flux/ 3 1012 inc.p)
/ Total beam
K+ decays in 50 m/ Total beam
Acc. K+ to
K+ / Total beam
K+ / +
/ 3 1012 inc. p
K+ decays in 50 m
x 10-1
x 108
x 10-14
x 10-3
x 10-2
x 10-2
x106
K+ momentum [GeV/c]
At 75 GeV/c from 400 GeV/c protons
•K+/K- per proton ~ 2.1•(K+/+)/(K-/-) ~ 1.2•(K+/Total +ve)/(K-/Total –ve) ~ 1.0
4
3
2
7 = 5 x 6
5
1
6(reg. 1, no p cut)
Choice of positive beam
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September 27, 2005 P-326@SPSC73 18
Beam:
Present K12
(NA48/2)
New HI K+
> 2006
Factor
wrt 2004
SPS protons per pulse on T10 1 x 1012 3 x 1012 3.0
Duty cycle (s./s.) 4.8 / 16.8 1.0
Solid angle (sterad) 0.40 16 40
Av. K+momentum <pK> (GeV/c) 60 75 K+ ~ 1.5
Mom. band RMS: (p/p in %) 4 1 ~0.25
Area at Gigatracker (cm2) 7.0 14 2.0
Total beam per pulse (x 107)
per Effective spill length MHz
MHz/cm2 (gigatracker)
5.5
18
2.5
250
800
60
~45 (~27)
~45 (~27)
~24(~15)
Eff. running time / yr (pulses)
3 x 105 3 * 105 1.0
K+ decays per year 1.0x1011 4.8x1012 48
New high-intensity K+ beam for P-326 AlreadyAvailable
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September 27, 2005 P-326@SPSC73 19
Required vacuum in the decay tank
• A FLUKA simulation led us to conclude that the vacuum should be better than 6 10-8 mbar to keep the background to less than one event per year
• This figure can be relaxed by an order of magnitude by positively tagging the kaons
• The best vacuum achieved in the current tank is about 10-5 mbar, compatible with the outgassing of painted steel
• To reach the specified vacuum either a stainless steel tank or a new pumping system is required
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September 27, 2005 P-326@SPSC73 20
CEDAR
• Positive identification of Kaons is important to avoid mistaking a beam pion interaction in the residual gas as signal
• Upgraded version of an existing West type CEDAR• Use H2 (3 bars) to reduce multiple scattering• Excellent time resolution (< 100 ps) is required• Use, for example, 8 Hamamatsu Linear Array H7260 (32
pixel/unit) as photon detectors to stand the high rate (50 MHz)
6 m
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September 27, 2005 P-326@SPSC73 21
0 1 2 3 4 50
20
40
60
80
100
Cedar N(He) versus W(H2) Comparison
Cedar-N, He
Cedar-W, H2
+, 7-fold
K+, 7-foldCedar-N, He
Cedar-W, H2
Efficien
cy [%]
Diaphragm aperture [mm]
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September 27, 2005 P-326@SPSC73 22
Gigatracker
22
X/X0 << 1%
Pixel size ~ 300 x 300 m(p)/p ~ 0.4% (t)
GT ~100ps on the track: time
coincidence to select the right kaon track
Provide precise measurements on all beam tracks (out of which only ~6% are K+)Provide very good time resolution Do not spoil beam and downstream measurementsSustain high, non-uniform rate ( 800 MHz total)
P
PK
Instrument the 2nd beam achromat for redundant momentum and angular measurement:•Two Silicon micro-pixel detectors (SPIBES)
•Timing•Pattern Recognition
•One FTPC (Improved KABES)•To minimise scattering in the last station
SPIBES:
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September 27, 2005 P-326@SPSC73 23
Required Gigatracker time resolutionP(>1hit in t) =1-exp(-t*rate)
t ( ±2) @0.8GHZ @1GHZ400 27% 33%500 33% 39%600 38% 45%
Dependence of the signal to background (from K+ )as a function of the gigatracker time resolution
K+
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September 27, 2005 P-326@SPSC73 24
Gigatracker: SPIBES Front-End
p-sub
p+
n-sub
n+
p+ p+
n+ n+
h e-
he-
➊
➋
Simulation of signal collection: Alice pixel size (425 * 50 m)
➊
➋
MeV
Signal simulation:G4 v6.2 75 GeV/c KSi sensor 200 m thick(e.g. ALICE SPD)
at least 11000 e-/holes
Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/EDGroups with the ALICE SPD
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September 27, 2005 P-326@SPSC73 25
SPIBES Read out Chip
20-21 mm
N chips
To achieve the time resolution a very complex
read-out chip bump-bonded on the sensor is needed
(technology choice required: 0.25 vs. 0.13 m CMOS)
Photolithographic process max 20-21mm wide chip
Beam spot adjusted to fit maximum chip size
GT area per pixel station: 36mm(X) x 48mm(Y)
- 2 half detectors to cover the area w/o overalp
•beam rate: high and not uniform
2-3mm I/O
Maximum rate in the hottest regions:
(Normalized to total rate of 1GHz)~1.5MHz/mm2 in sation1, ~1.6MHz/mm2 in station2, ~1.9MHz/mm2 in station3
y
x2mm/bin
2mm
/bin
Station 1(pixels) 2(pixels) 3(FTPC)
25
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September 27, 2005 P-326@SPSC73 26
FTPC (KABES)
driftE
driftETdrift
1
Tdrift2
Micromegas
Gap 25 μm
Micromegas
Gap 25 μm
KABES principle: TPC + micromegas Pioneered in NA48/2
Tested in 2004 at highintensity (see Villars)
Latest Developments:
Signal occupancy with Gas Compass 50µm strip + V1 = 30 ns 50µm strip + FAMMAS = 22 ns 25µm strip + V1 = 22 ns 25µm strip + FAMMAS = 10 ns
New electronic + 25µm mesh strip signal occupancy divided by 3
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September 27, 2005 P-326@SPSC73 27
Advantages:
• can (in principle) operate in vacuum decay volume• can be designed without internal frames and
flanges• can work in high rate of hits• good space resolution (~130 m/hit for 9.6 straw)
• small amount of material (~0.1% X0 per view)
but
no previous straw system has been operated in high vacuum
Straw Tracker
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September 27, 2005 P-326@SPSC73 28
Glue – 5m12.5 m0.2 m Al
9.6 mm
25 m
Gold plated Tungsten wire 30 m
Straw Elements and Design
8.8 m186.3 mfrom T0
5.4 m 5.4 m
7.2 m 7.2 mk12hika+ (Niels)
About 2000 * 6 -> 12000 straws in total
3 coordinates
4 coordinates2 coordinates
1 coordinate
10 cm
2300 mm
To fit easily into decay volume an octagonal shape is proposed
Two double layers form a view
Gas mixture: 20%Ar+80%CO2
12 ns rise time100 ns total width
Polycarbonate spacer, 25 mg
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September 27, 2005 P-326@SPSC73 29
Layout of the Straw Tracker
P() = 60 GeV/c
P(K+) = 75 GeV/c
Holes in Straw-Chambers 5 cm radius Chambers 3, 4, 5 and 6 are off-axis Magnets: pt kick 270 and 360 MeV/c
The off-axis layout in the bending plane is essential to reject K edecays in which the e is lost and the carries most of the kaon momentum
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September 27, 2005 P-326@SPSC73 30
RICH Layout
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September 27, 2005 P-326@SPSC73 31
RICH as velocity spectrometer….
Resolution of a 17m P-326 RICH(CKMGEANT)
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September 27, 2005 P-326@SPSC73 32
…and RICH for - separation
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September 27, 2005 P-326@SPSC73 33
MAMUD
Pole gap is 2 x 11 cm V x 30 cm H
Coils cross section 10 cm x 20cm
•To provide pion/muon separation and beam sweeping.
–Iron is subdivided in 150 2 cm thick plates (260 260 cm2 )
•Two coils magnetise the iron plates to provide a 5 Tm field integral in the beam region •Active detector:
–Strips of extruded polystyrene scintillator (as in Opera)
–Light is collected by WLS fibres with 1.2 mm diameter
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September 27, 2005 P-326@SPSC73 34
Photon Vetoes
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September 27, 2005 P-326@SPSC73 35
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September 27, 2005 P-326@SPSC73 36
Photon Vetoes
E range Inefficiency
ANTI< 50 MeV 1
(0.5, 1) GeV 104
> 1 GeV 105
LKR
< 1 GeV 1
(1,3) GeV 104
(3,5) GeV 104 105
> 5 GeV 105
IRCs,
SAC
All 106
P-326 Simulation: Allowed inefficiency/photon
From: Ajimura et al., NIMA, in press
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September 27, 2005 P-326@SPSC73 37
NA48 LKr as Photon VetoEnergy of photonsfrom K hitting LKr: > 1 GeV
GeVUrgent consolidation of thesafety/control system is needed
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September 27, 2005 P-326@SPSC73 38
Large Angle Vetoes (ANTI)
• Two designs under test:– spaghetti (KLOE)– lead/scintillator
sandwich (CKM)
• Extensive simulation under way
• A tagged photon beam is available in Frascati to test existing prototypes
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September 27, 2005 P-326@SPSC73 39
Fast Hodoscope (MGG-RPCs)
• To make tight time coincidence with gigatracker
• Propose to use the Multi-gap Glass RPC (ALICE-TOF technology)
• High rate test are mandatory to validate performance up to 5 kHz/cm2
• A prototype PCB suitable for P-326 application is under fabrication
ALICE-TOF
ALICE-TOF
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September 27, 2005 P-326@SPSC73 40
Trigger & DAQ
• Total input to L0: 11 MHz • L0 (example):
– > 1 hit hodoscope 73%– muon veto 24%– Photon Veto 18%– <2 EM quadrants & E<50 GeV
2%
• L0 output:– 2% x 11 MHz = 220 KHz
Keep: L0 + Control + Calibration + Spin-offs < 1 MHz
• L1 in PC farm (à la LHCb) to keep as much flexibility as possible
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September 27, 2005 P-326@SPSC73 41
Cost Estimation (Materials)Element Cost (MCHF) Comments
BEAM LINE 0.4 Modified K12 line
CEDAR 0.5
GIGATRACKER 2.7 1.4 MCHF if 0.25 m CMOS can be used
VACUUM 1.0 Upgrade of vacuum system
ANTI 4.2
STRAW 2.4
MNP33/2 2.5 1.2 MCHF + He extension
CHOD 0.9 MGG-RPC
RICH 4.0 Indication
LKR 2.0 New supervion system and R/O
MAMUD 1.5
SAC & IRC 0.4
TRIGGER & DAQ 1.5
TOTAL 24.0
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September 27, 2005 P-326@SPSC73 42
Strengthening P-326
• The demise of the US kaon programme has triggered negotiations with members of KOPIO/CKM to join P-326
• The following groups have signed up since the proposal submission:– San Luis Potosi (Mexico, J. Engelfried)– Moscow, INR
• Interest to join has been expressed by the following groups:– Fermilab (P. Cooper) – BNL (L. Littenberg, S. Kettell)– British Columbia (D. Bryman)– George Mason (P. Rubin)
• It is our understanding that a possible participation of US groups is subject to: – DOE support towards a strong contribution to the construction of
the detector (notably the RICH counter)– The involvement of US University in addition to National Labs
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September 27, 2005 P-326@SPSC73 43
Status of R&D
• A talk in itself, but in a nutshell:– Gigatracker (CERN/INFN TO/FE)
• Study of sensors for fast signal collection• Study of chip architecture
– Straw Tracker (Mainz/Dubna)• Study of prototype in vacuum
– Photon vetoes (INFN, CERN, Protvino, Sofia)• Tests of existing prototypes with photon sources (Frascati) • Construction of prototypes for IRC/SAC• Use of LKr as photon detector (more data needed in 2006)
– Fast Hodoscope (INFN FI/PG)• Investigation of MGG-RPC operated at high rate (≤5 KHz/cm2)
– CEDAR (CERN)• Fast photon detectors
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September 27, 2005 P-326@SPSC73 44
SPS Availability
• There are two approved competitors for beam: LHC and CNGS
• P-326 requires ~5 105 SPS pulses/year with 4.8 s flat top
• For comparison, the Fixed Target request quoted in the Villars Report (SPSC-M-730) is 7.2 105 pulses/year
• P-326 is completely compatible with the simultaneous running of COMPASS in the M2 beam line and with experiments and tests in the H2, H4, H6 and H8 beams
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September 27, 2005 P-326@SPSC73 45
Beam Request 2006
• We request 30 days of K12 beam in 2006 to operate the NA48/2 hardware as P-326 test facility in order to:– Measure beam induced backgrounds– Measure LKr inefficiency collecting K
– Test prototype elements of the new detectors
• In addition we request that a standard (nitrogen gas-filled) CEDAR-W counter is made available in a beam to test the device with new, high rate, photon detectors
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September 27, 2005 P-326@SPSC73 46
Timeline
• 2006– Tests in the present K12 beam
• 2007-2008– Construction, installation and tests of the
new beam (2007) and new detectors (2007-2008)
• 2009-2010– Data Taking
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September 27, 2005 P-326@SPSC73 47
Spares
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September 27, 2005 P-326@SPSC73 48
Possibly the Cleanest SM test
• In The phase derives from Z0 diagrams (S=1) whereas in A(J/ KS) originates in the box diagram (B=2)
• Any non-minimal contribution to Z0 diagrams would be signalled by a violation of the relation:
• A deviation from the predicted rates of SM would be a clear indication of new physics
• Complementary programme to the high energy frontier:– When new physics will appear at the LHC, the rare decays may
help to understand the nature of it
K
S/(sin 2 ) (sin 2 )K B J K
0 0d dB B
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September 27, 2005 P-326@SPSC73 49
Kaon Rare Decays and the SM
Kaons provide quantitative tests of SM independentfrom B mesons…
…and a large windowof opportunity exists!
|Vtd|
G. Isidori
Im t = A2 5 Re t = A2 5
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September 27, 2005 P-326@SPSC73 50
K+→+ : State of the art
BR(K+ → + ) = 1.47+1.30-0.89 × 10-10
•Compatible with SM within errors
hep-ex/0403036 PRL93 (2004)
Stopped K~0.1 % acceptance
AGS
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September 27, 2005 P-326@SPSC73 51
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September 27, 2005 P-326@SPSC73 52
98 99 100 101 102 103 1040
20000
40000
60000
80000
100000Cedar-West (H
2-filled)
+K+
Freq
uenc
y
Radius at diaphragm [mm]
100.0
±0.4
8 m
m
102.3
±0.4
5 m
m
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September 27, 2005 P-326@SPSC73 53
Possible Photon detector
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September 27, 2005 P-326@SPSC73 54
Sigma = ~ 80 ps
~750000 e-
Simulation of average channel response
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September 27, 2005 P-326@SPSC73 55
The simulations by Lau G. shows that the average rate per channel is ~ 3 MHz. This gives an average current/ch = 0.4 uA or 13 uA in total. But if the pulsed operation of the beam is taken into account. The averaged current over 30 sec is 1/3 of these values!
Safety factor of 24 is OK!