Transcript Perspective on P326

A proposal to Study Rare Kaon Decays
at the CERN SPS
Augusto Ceccucci/CERN
• Physics Introduction
– Rare Kaon Decays in the SM….
– …and Beyond
• Flavour as a probe of New Physics
complementary to the high energy frontier
• Experimental state-of-the-art
– Recent Results and world-wide perspectives
• Description of the CERN proposal P-326
– Technique
– Status
February 27, 2006
Lausanne
1
Quark Mixing and CP-Violation
Cabibbo-Kobayashi-Maskawa (CKM) matrix:
 d '   Vud Vus Vub  d 
  
 
 s '    Vcd Vcs Vcb  s 
 b '   V V V  b 
ts
tb  
   td
•Non-diagonal (e.g. Vus ≠0)
 Flavour Violation
•3 or more quark generations
 CP-Violation in SM (KM)
Ng=2
Nphase=0  No CP-Violation
Ng=3
Nphase=1  CP-Violation Possible
e.g., Im lt= Im Vts*Vtd ≠ 0  CPV
February 27, 2006
GIM mechanism
 No FCNC at tree level
Violation at one loop depending on
quark masses and CKM couplings
Lausanne
2
CKM Unitarity and Rare Kaon Decays
The unitarity of the CKM matrix can be expressed by triangles
in a complex plane.
There are six triangles but one is more “triangular”:
VudVub*+VcdVcb*+VtdVtb*=0
It is customary to employ the Wolfenstein parameterization:
Vus ~ l
Vcb ~ l2 A
Vub ~ l3 A(r- ih)
Vtd ~ l3 A(1-r- ih)
Sensitive to |Vtd|
Im lt = A2 l5 h
Re lt = A2 l5 r
February 27, 2006
Lausanne
3
Status of Unitarity Triangle
•
95% confidence regions
extracted using| Vub|/| Vcb|, εK,
ΔmBd, ΔmBs and sin2β
ρ = 0.214 ± 0.047
η = 0.343 ± 0.028
•
Constraints from | Vub|/| Vcb|,
ΔmBd and ΔmBs compared with
constraints from CP violating
quantities in the kaon (εK) and in
the B (sin2β) sectors
ρ = 0.181 ± 0.060
η = 0.404 ± 0.035
Rare kaon decays are loop-dominated. Assuming SM they provide
strong independent constraints to the UT
February 27, 2006
Lausanne
4
The four golden modes of Kaon
Physics
Short-distance
contrib (Gsd /G)
Irreducible
Total SM BR
theory err. on
amplitude
K0Lp0 n n
>99%
1%
3  10-11
K+p+ n n
88%
3%
8  10-11
K0Lp0 e+e-
38%
15%
3.5  10-11
K0Lp0 m+m-
28%
30%
1.5  10-11
•Short distance dynamics:
– W-top quark loops constitute the
dominant contribution:
•The EW short-distance amplitude is common in the SM…
•…but potentially different beyond SM
•Important to address all these decays
Adapted from G. Isidori @ Flavour in the LHC era, 5-7 Nov 05, CERN
February 27, 2006
Lausanne
5
K→p nn : Theory in Standard
Model
2
2
 Im lt
Re lc
  Re lt
 
B ( K  p nn )   +   5 X ( xt )  +  5 X ( xt ) +
Pc ( X )  
l
  l
 
 l
+
B ( K L0
+
 Im l

 p nn )   L   5 t X ( xt ) 
 l

l  Vus
lc  Vcs*Vcd
lt  Vts*Vtd
3 2 Br ( K +  p 0e+n ) 8
 +  rK + 
l
2
4
2p sin W
February 27, 2006
2
0
charm
contribution
top
contributions
The Hadronic Matrix Element is
measured and isospin rotated
Lausanne
6
Predictions in SM
Pc ( X )  0.367  0.033(mc )  0.012( mc )  0.009( s )
This used to be the largest theoretical error
(+/- 0.037). It was reduced by a NNLO calculation
A. Buras, M. Gorbahn, U. Haisch, U. Nierste hep-ph/0508165)
Standard Model predictions
BR(K+p+nn)  (1.6×10-5)|Vcb|4[sh2+(rc-r)2]  (8.0 ± 1.1)×10-11
BR(KLp0nn)  (7.6×10-5)|Vcb|4h2  (3.0 ± 0.6)×10-11
The errors are mostly due to the uncertainty of the CKM parameters
and not to the hadronic uncertainties
February 27, 2006
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7
Theory vs. Experiment
SM Observable
Theoretical error Experimental error
B(K0Lp0 n n)
~3%
??
B(K+p+ n n)
~6%
~75%
AFB(B  Xsl+l-)
~8%
??
B(B  Xsg)
~10%
~9%
B(B  Xsl+l-)
~13%
~20%
AFB(B  K(*)l+l-)
~15%
~30%
B(B  (K(*),r,w)g)
~25%
~40%
B(Bs  m+m-)
~30%
??
B(B  K*l+l-)
~35%
~13%
Adapted from U. Haisch @ Flavour in the LHC era, 6-8 Feb 06, CERN
February 27, 2006
Lausanne
8
Intrinsic theory error
Combining information from BR(K+→p+ nn ) and
BR(K0→p0 nn ) one obtains:
(Buras et al. hep-ph/0508165)
s | Vtd |
s ( Pc )
 0.41
Vtd
Pc
(
)
s ( sin 2  )
s ( Pc )
 0.34
sin 2 
Pc
So for a 10% uncertainty on Pc,
one can extract, in priciple,
a 3.4%exp. determination of
sin2 from kaon decays.
It is currently 4.6% from B decays
s (g )
s ( Pc )
 0.83
g
Pc
February 27, 2006
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9
Beyond Standard Model
• Compare two scenarios:
– Minimal Flavour Violation
• All mixing governed by universal CKM matrix
– No Extra Complex Phases
• Same operators as in SM
• Different coefficients
• Stringent correlation with B rare decays
– New sources of Flavour Symmetry Breaking ~ TeV scale
• Extra phases can lead to large deviations from SM
predictions, especially for the CP-Violating modes
February 27, 2006
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10
MFV: Sensitivity to Z0 Penguin
from Bobeth et a. (2005)
February 27, 2006
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11
New Sources of Flavour Symmetry
Breaking
Generic MSSM
February 27, 2006
Enhanced EW Penguins
Lausanne
12
Experimental State-of-the-art
February 27, 2006
Lausanne
13
K+→p+ nn
hep-ex/0403036 PRL93 (2004)
AGS
Stopped K+
~0.1 % acceptance
BR(K+ → p+ nn ) = 1.47+1.30-0.89 × 10-10
•Compatible with SM within errors
February 27, 2006
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14
Setting the bar for the next generation
of K+→p+nn experiments
E787/E949: BR(K+ → p+ nn ) = 1.47+1.30-0.89 × 10-10
Current
constraint on
r,h plane
?
100 events
Mean=SM
100 events
Mean=E787/949
February 27, 2006
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15
K0L  p0nn : E391a Upper Limit
10% of RUN I
•Pencil beam
•Expected background
from K0L decays: 0.02
•Acceptance: 0.73%
BR(K0L  p0nn )<2.8610-7 90%CL
Preliminary (Ken Sakashita@KAON2005)
6 improvement over KTeV one day special run
2 improvement over published limit (KTeV Dalitz technique)
•For the future: JPARC LOI-05
•Recently, J-PARC made a call for proposals
February 27, 2006
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16
K0S,L →p0 e+e- and K0S,L →p0 m+mBR(KS→p0ee)  10-9 = 5.8 +2.8-2.3(stat) ± 0.8(syst)
BR(KS→p0mm)  10-9 = 2.9 +1.4-1.2(stat) ± 0.2(syst)
PLB 576 (2003)
PLB 599 (2004)
KS →p0 mm
NA48/1
NA48/1
6 events, expected back. 0.22
7 events, expected back. 0.15
BR(KL → p0 ee ) < 2.8 × 10-10 @90%CL
BR(KL → p0 mm ) < 3.8 × 10-10 @90%CL
February 27, 2006
Lausanne
KTeV PRL93, 021805 (2004)
KTeV PRL86, 5425 (2001)
17
K0L→p0ee (mm) in SM
With the KS measurements, the KL BR can be predicted
* Interference between short- and long-distance physics*
(Isidori, Unterdorfer, Smith,
EPJC36 (2004))
Br (KL  p0m+m- )
( 10-12 )
Constructive
-11
BK 0 p0e+e-  3.7+-1.1
0.9 10
L
-11
BK 0 p0m+m-  1.5+-0.3
0.3 10
L
now favored by two
independent analyses*
Destructive
-11
BK 0 p0e+e-  1.7+-0.7
0.6 10
L
-11
BK 0 p0m+m-  1.0+-0.2
0.2 10
L
*G. Buchalla, G. D’Ambrosio, G. Isidori,
Nucl.Phys.B672,387 (2003)
*S. Friot, D. Greynat, E. de Rafael,
hep-ph/0404136, PL B 595
*
February 27, 2006
Lausanne
Br ( L  p0e+e- )
( 10-12 )
18
Summary
•
•
•
K+ p+nn
–
–
–
–
–
–
Already 3 clean events are published (E787/E949)
Experiment in agreement with SM within errors
Next round of exp. need to collect O(100) events to be useful
Move from stopped to in flight technique (FNAL Proposal turned down by P5)
Proposal for in-flight decays: CERN P-326
Letter of Intent at J-PARC to continue the study with decays at rest
–
–
–
–
–
Large window of opportunity exists.
Upper limit is 4 order of magnitude from the SM prediction
First results E391a (proposed SES~3 10-10)
LOI to continue at J-PARC
KOPIO TERMINATED
–
–
–
–
–
Long distance contributions under good control
Measurement of KS modes has allowed SM prediction
KS rates to be better measured
Background limited (study time dep. Interference?)
100-fold increase in kaon flux to be envisaged
K0L  p0nn
K0L  p0ee(mm)
February 27, 2006
Lausanne
19
CERN-SPSC-2005-013
SPSC-P-326
Proposal to Measure the Rare
Decay K+p+ n n at the CERN SPS
CERN, Dubna, Ferrara, Florence, Frascati,
Mainz, Merced, Moscow, Naples,
Perugia, Protvino, Pisa, Rome, Saclay,
San Luis Potosi, Sofia, Turin
February 27, 2006
Lausanne
20
NA48@CERN
Direct CP-Violation established
1996
NA48: ’/
1997
’/
1998
’/
1999
no spectrometer
KL
’/
NA48/1 KS
Re ’/ = 14.7 ± 2.2 10-4
2000
Ave: Re ’/ = 16.7 ± 2.3 10-4
2001
+ KL Rare Decays
NA48/1: KS
2002
First observation of
NA48/2: K
2003
NA48/2: K
2004
lower inst. intensity
February 27, 2006
K0S →p0 e+e- and K0S →p0 m+m•Search for Direct CP-Violation
in charged kaon decays
• pp scattering: PLB 633 (2006)
(a0-a2)m+= 0.268 +/- 0.017
Lausanne
21
Status of P-326 (a.k.a. NA48/3)
•
•
•
•
•
•
Presented at the CERN SPSC in September
2005
R&D Endorsed by CERN Research Board on
December 2005 (subject to funding)
Beam Test foreseen in August 2006
Still seeking groups to fund the RICH
counter
Seeking full approval by end of 2006….
…to be able to start data taking some time
in 2009-2010
February 27, 2006
Lausanne
22
Background rejection
Guidance: S/B = 10
1) Kinematical Rejection
~10-12 rejection
 | P |
 |P |
2
mmiss
 mK2 1 - p  + mp2 1 - K - | PK || Pp | p2K
 | PK | 
 | Pp | 
2) Photon vetoes and PID (p-m)
Basic idea to reject K+ p+p0
P(K+) = 75 GeV/c
Require P(p+) < 35 GeV/c
P(p0) > 40 GeV/c
It cannot be missed in
the calorimeter/photon veto
February 27, 2006
Lausanne
23
Backgrounds kinematically constrained
Decay
BR
K+m+n (Km2)
0.634
K+ p+p0
0.211
K+ p+p+pK+ p+p0p0
0.070
Allows us to define the signal region
92% of K+ decays
K+p+p0 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
February 27, 2006
Lausanne
24
Backgrounds not kinematically constrained
Decay
K+p0e+n
(Ke3)
BR
0.049
Km3
0.033
Km2g
5.5×10-3
K+p+p0g 1.5×10-3
Ke4
Km4
4×10-5
1×10-5
They span accross the signal regions
Must rely on Particle ID and veto
8% of K+ decays
February 27, 2006
Lausanne
25
P-326 Detector Layout
K+p+ n n
Gigatracker
p+
K+
~11 MHz
75 GeV/c
800 MHz beam
p/K/p
February 27, 2006
n
n
(KABES)
Lausanne
26
P-326 Detector Layout
K+p+p0
Gigatracker
g
p+
K+
~11 MHz
75 GeV/c
800 MHz beam
p/K/p
February 27, 2006
g
(KABES)
Lausanne
27
Signal & backgrounds from K decays / year
Total
Region I
Region II
Signal
65
16
49
K+p+p0
2.7±0.2
1.7±0.2
1.0±0.1
Km2
1.2±0.3
1.1±0.3
<0.1
Ke4
2±2
negligible
2±2
K+p+p+p- and
other 3-tracks bckg.
1±1
negligible
1±1
p2g
1.3±0.4
negligible
1.3±0.4
Km2g
0.4±0.1
0.2±0.1
0.2±0.1
Ke3, Km3 ,others
negligible
-
-
Total bkg
9±3
3.0±0.2
6±3
February 27, 2006
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28
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 ~ 8
S/B (Region I) ~5
S/B (Region II) ~ 9
For Comparison: In the written proposal we
quoted 40 events/year@BR=10-10 to account for
some reconstruction and deadtime losses
February 27, 2006
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29
New high-intensity K+ beam for P-326
Beam:
SPS protons per pulse on T10
Duty cycle (s./s.)
Already
Available
Present K12
(NA48/2)
New HI K+
> 2006
Factor
wrt 2004
1 x 1012
3 x 1012
3.0
1.0
4.8 / 16.8
 0.40
 16
40
Av. K+momentum <pK> (GeV/c)
60
75
K+ ~ 1.5
Mom. band RMS: (Dp/p in %)
4
1
~0.25
 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 x 105
1.0
1.0x1011
4.8x1012
 48
Solid angle (msterad)
Area at Gigatracker (cm2)
K+ decays per year
February 27, 2006
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30
Decay Tank
•
Specification: 10-6 mbar
– Study performed with Monte
Carlo using Fluka and Gheisha
to simulate the hadronic
interactions with the residual gas.
•
Measurements:
– Vacuum test performed on the
existing tube of NA48.
– A 10-5 mbar level reached
with only 1 pump.
– With a few 50000 l/s diffusion or
cryogenics pumps the requested
vacuum level can be achieved
•
Conclusions:
– The existing decay tank can be used
February 27, 2006
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31
Gigatracker
Provide precise measurements on all beam tracks (out of which only ~6% are K+)
Provide very good time resolution
Minimise mass (multiple scattering and beam interactions)
Sustain high, non-uniform rate ( 800 MHz total)
•Two Silicon micro-pixel detectors (SPIBES)
•Timing
•Pattern Recognition
•FTPC (Improved KABES)
•To minimise scattering in the last station
SPIBES:
p
PK
 Pp
X/X0 << 1%
Pixel size ~ 300 x 300 mm
s(p)/p ~ 0.4%
excellent time resolution
to select the right kaon track
Dependence of the signal to
background (from K+ p+p0 ) ratio
as a function of the gigatracker
time resolution
February 27, 2006
Lausanne
32
32
SPIBES (Hybrid Pixel)
G. Anelli, M. Scarpa, S. Tiuraniemi
•
•
•
•
200 mm Silicon sensor (>11 000 e/h mip)
– Following Alice SPD
– Bump-bonding
Read-out chip
– Pixel 300 mm x 300 mm
– Thinned down to ~100 mm (Alice
SPD 150 mm)
Beam surface ~ 14 cm2
– Adapted to the size of the SPIBES
r-o chips
~125 mm Cfibre for cooling & support
y
Front End and R/O
considerations based on
the experience of the
CERN-PH/MIC and PH/ED
Groups with the
ALICE SPD
2mm/bin
x
Station 1(pixels)
February 27, 2006
2(pixels)
3(FTPC)
Lausanne
MeV
33
FTPC (KABES)
KABES principle: TPC + micromegas
Edrift
Tdrift2
Pioneered in NA48/2
Tested in 2004 at high
intensity with 1 GHz FADC
Micromegas
Gap 25 μm
Micromegas
Gap 25 μm
Tdrif
t1
In NA48/2 KABES has achieved:
•Position resolution ~ 70 micron
•Time resolution ~ 0.6 ns
•Rate per micro-strip ~ 2 MHz
E drift
New electronic + 25µm mesh
strip signal occupancy divided by 3
February 27, 2006
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34
Straw Tracker
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 mm/hit for 9.6 straw)
• small amount of material (~0.1% X0 per view)
but
no previous large straw system has been
operated in high vacuum
February 27, 2006
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35
Straw Elements and Design
12 ns rise time
100 ns total width
12.5 mm
0.2 mm Al
Glue – 5mm
Polycarbonate
spacer, 25 mg
9.6 mm
25 mm
Gold plated Tungsten wire 30 mm
Two double layers form a view
Gas mixture: 20%Ar+80%CO2
2300 mm
To fit easily into decay volume
an octagonal shape is proposed
3 coordinates
4 coordinates
2 coordinates
1 coordinate
5.4 m
10 cm
k12hika+ (Niels) 
February 27, 2006
186.3 m
from T0
8.8 m
5.4 m
7.2 m
7.2 m
About 2000 * 6 -> 12000 straws in total
Lausanne
36
RICH Layout
February 27, 2006
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37
RICH as velocity spectrometer….
Resolution of a 17m P-326 RICH
(CKMGEANT)
February 27, 2006
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38
…and RICH for p-m separation
February 27, 2006
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39
NA48 LKr as Photon Veto
Energy of photons
from K+ p+p0
hitting LKr: > 1 GeV
Consolidation of the
safety/control system and
read-out under way
February 27, 2006
GeV
Lausanne
40
LKr efficiency measured with data
K+  p+ p0 collected by NA48 in 2004
Events are kinematically selected.
p+ track and lower energy g are use to
predict the position of the other g
Photon
E=11 GeV
Pion
P=42 GeV/c
+p+p0p0
Cluster not
reconstructed
Eg = 22 GeV
Expected
position
February 27, 2006
Lausanne
41
Example: “hadronic” cluster of a photon
Expected energy: ~29 GeV
Deposited energy: ~9 GeV
Maximum energy ~300 MeV
Expected g position
Measured LKr inefficiency per photon (Eg > 10 GeV):
h = (2.8 ± 1.1stat ± 2.3syst) × 10-5
February 27, 2006
(preliminary)
Lausanne
42
Beam test 2006
• Idea for measuring inefficiency in the range 2 GeV < Eg< 10 GeV
– Use of the NA48 set-up.
Beam test foreseen during
– Photons produced by bremsstrahlung.
the 2006 SPS run
– SPS can provide a suitable electron beam.
Kevlar
window
Magnet
Calorimeter
vacuum
eg
Electron beam
(25 GeV/c)
Bremsstrahlung
Drift
chambers
Calorimeter inefficiency below Eg < 5 GeV is not critical
February 27, 2006
Lausanne
43
ANTI-Photon Rings
From: Ajimura et al., NIMA 552 (2005)
•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
February 27, 2006
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44
MAMUD
•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)
Pole gap is 2 x 11 cm V x 30 cm H
–Light is collected by WLS
fibres with 1.2 mm diameter
Coils cross section 10 cm x 20cm
February 27, 2006
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45
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
 3%
L0 output:
– 3% x 11 MHz = 330 KHz
Keep: L0 + Control + Calibration +
Spin-offs < 1 MHz
• L1 in PC farm (à la LHCb) to
keep as much flexibility as
possible
• Software trigger reduction ~40
February 27, 2006
Important synergies with LHC
to be exploited: for instance, the LHCb
TELL1 board
Lausanne
46
Other Physics Opportunities
•
•
The situation is similar to NA48, which was designed to measure
“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 (p-p scattering)
–
K+  p0 p0 e+ n
2.
Lepton Flavour Violation
3.
Search for new low mass particles
4.
5.
6.
7.
K+  p+ m+ e- , K+p- m+ e+, (Ke2/Km2)
–
–
K+  p+ X
K+  p+ p0 P (pseudoscalar sGoldstino)
–
–
K+/-  p+/-p0g (CPV interference)
T-odd Correlations in Kl4
Study rare p+ & p0 decays
Improve greatly on rare radiative kaon decays
Compare K+ and K- (alternating beam polarity)
And possibly, given the quality of the detector, topics in hadron
spectroscopy
February 27, 2006
Lausanne
47
Summary
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Clear physics case
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The discovery of New Physics will dramatically increase the
motivation for searches of new flavour phenomena
Healthy competition worldwide:
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Exploit synergies and existing infrastructures
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NA48
NA48/1
NA48/2
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P-326
’/
KS rare decays
Dg/g in K  3p
+  p+nn
SPS
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J-PARC   SPS
SPS used as LHC injector (so it will run in the future)
No flagrant time overlap with CNGS
P-326 fully compatible with the rest of CERN fixed target
because P-326 needs only ~1/20 of the SPS protons
Join us!
February 27, 2006
Lausanne
48