Physics Introduction Rare Kaon Decays in the SM…. …and Beyond

February 27, 2006 Lausanne 1

• 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

A proposal to Study Rare Kaon Decaysat the CERN SPS

Augusto Ceccucci/CERN


Quark Mixing 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

Cabibbo-Kobayashi-Maskawa (CKM) matrix:

•Non-diagonal (e.g. Vus ≠0) Flavour Violation•3 or more quark generations CP-Violation in SM (KM)

e.g., Im t= Im Vts*Vtd ≠ 0 CPV

GIM mechanism No FCNC at tree levelViolation at one loop depending on quark masses and CKM couplings


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 ~ Vcb ~ Vub ~ iVtd ~ i

Sensitive to |Vtd|

Im t = 2 5 Re t = 2 5


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


The four golden modes of Kaon Physics

Short-distance contrib (sd /)

Irreducible

theory err. on

amplitude

Total SM BR

KL >99% 1% 3 10-11

K 88% 3% 8 10-11

KLee 38% 15% 3.5 10-11

KL 28% 30% 1.5 10-11

Adapted from G. Isidori @ Flavour in the LHC era, 5-7 Nov 05, CERN

•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


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

*

*

us

c cs cd

t ts td

VV VV V


Predictions in SM ( ) 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 A. Buras, M. Gorbahn, U. Haisch, U. Nierste hep-ph/0508165)

The errors are mostly due to the uncertainty of the CKM parameters and not to the hadronic uncertainties

Standard Model predictions

BR(KBR(K++++) ) (1.6×10 (1.6×10-5-5)|V)|Vcbcb||44[[22+(+(cc--))22] ] (8.0 ± (8.0 ± 1.1)×101.1)×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


Theory vs. Experiment

SM Observable Theoretical error Experimental error

B(KL ~3% ??

B(K ~6% ~75%

AFB(B Xsll) ~8% ??

B(B Xs) ~10% ~9%

B(B Xsll) ~13% ~20%

AFB(B K(*)ll) ~15% ~30%

B(B (K(*))) ~25% ~40%

B(Bs ) ~30% ??

B(B K*ll) ~35% ~13%

Adapted from U. Haisch @ Flavour in the LHC era, 6-8 Feb 06, CERN


Intrinsic theory error

Combining information from BR(K→ ) and BR(K→ ) one obtains: (Buras et al. hep-ph/0508165)

| |0.41

sin 20.34

sin 2

0.83

td c

ctd

c

c

c

c

V P

V P

P

P

P

P

So for a 10% uncertainty on Pc,

one can extract, in priciple,a 3.4%exp. determination ofsin2 from kaon decays.It is currently 4.6% from B decays


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


MFV: Sensitivity to Z0 Penguinfrom Bobeth et a. (2005)


New Sources of Flavour Symmetry Breaking

Generic MSSM Enhanced EW Penguins


Experimental State-of-the-art


K+→+

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


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


K0L E391a Upper Limit

BR(K0L )<2.8610-7 90%CL

Preliminary (Ken Sakashita@KAON2005)6 improvement over KTeV one day special run2 improvement over published limit (KTeV Dalitz technique)

•For the future: JPARC LOI-05

•Recently, J-PARC made a call for proposals

10% of RUN I

•Pencil beam •Expected background from K0

L decays: 0.02

•Acceptance: 0.73%


K0S,L →0 ee and K0

S,L →0

KS →0

BR(KS→0ee) 10-9 = 5.8 +2.8-2.3(stat) ± 0.8(syst)

PLB 576 (2003)

7 events, expected back. 0.15

BR(KS→0) 10-9 = 2.9 +1.4-1.2(stat) ± 0.2(syst)

PLB 599 (2004)

6 events, expected back. 0.22

NA48/1 NA48/1

BR(KL → 0 ee ) < 2.8 × 10-10 @90%CL KTeV PRL93, 021805 (2004)

BR(KL → 0 ) < 3.8 × 10-10 @90%CL KTeV PRL86, 5425 (2001)


0 12L(K ) 10Br

0 12L( ) 10Br e e

Constructive

now favored by two independent analyses*

(Isidori, Unterdorfer, Smith,

EPJC36 (2004))

0 0L

0 0L

1.1 110.9

0.3 110.3

3.7 10

1.5 10

K e e

K

B

B

Destructive

0 0L

0 0L

0.7 110.6

0.2 110.2

1.7 10

1.0 10

K e e

K

B

B

*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*

K0L→0ee () in SM

With the KS measurements, the KL BR can be predicted* Interference between short- and long-distance physics*


Summary• K+

– 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

• K0L

– 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

• K0L ee()

– 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


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


NA48@CERN

1997

1998

1999

2000

2001

2002

2003

NA48: ’/

’/

’/

’/ lower inst. intensity

NA48/1 KS

NA48/1: KS

KL

no spectrometer

NA48/2: K

1996

2004NA48/2: K

Re ’/= 14.7 ± 2.2 10-4

First observation ofK0

S →0 ee and K0S →0

Ave: Re ’/= 16.7 ± 2.3 10-4

+ KL Rare Decays

•Search for Direct CP-Violation in charged kaon decays• scattering: PLB 633 (2006) (a0-a2)m+= 0.268 +/- 0.017

Direct CP-Violation established


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


Background rejection

Guidance: Guidance: S/B = 10S/B = 10 ~~1010-12 -12 rejectionrejection

1) Kinematical Rejection

2) Photon vetoes and PID ()

Basic idea to reject K++0P(K) = 75 GeV/c

Require P() < 35 GeV/c

P() > 40GeV/c It cannot be missed in

the calorimeter/photon veto

2222 ||||||

||1

||

||1 KK

K

KKmiss PP

P

Pm

P

Pmm


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


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


P-326 Detector Layout

75 GeV/c800 MHz beam/K/p

K+

+

~11 MHz

Gigatracker

(KABES)

K


P-326 Detector Layout

75 GeV/c800 MHz beam/K/p

K+

+

~11 MHz

Gigatracker

(KABES)

K


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


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

For Comparison: In the written proposal we quoted 40 events/year@BR=10-10 to account for some reconstruction and deadtime losses


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 x 105 1.0

K+ decays per year 1.0x1011 4.8x1012 48

New high-intensity K+ beam for P-326 AlreadyAvailable


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


Gigatracker

32

X/X0 << 1%

Pixel size ~ 300 x 300 mm(p)/p ~ 0.4% excellent time resolution

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 Minimise mass (multiple scattering and beam interactions)Sustain high, non-uniform rate ( 800 MHz total)

P

PK

•Two Silicon micro-pixel detectors (SPIBES)

•Timing•Pattern Recognition

•FTPC (Improved KABES)•To minimise scattering in the last station

SPIBES:

Dependence of the signal to background (from K+ ) ratioas a function of the gigatracker time resolution


SPIBES (Hybrid Pixel)

• 200 m Silicon sensor (>11 000 e/h mip)

– Following Alice SPD

– Bump-bonding

• Read-out chip

– Pixel 300 m x 300 m

– Thinned down to ~100 m (Alice SPD 150 m)

• Beam surface ~ 14 cm2

– Adapted to the size of the SPIBES

r-o chips

• ~125 m Cfibre for cooling & support y

x2mm/bin

2mm

/bin

Station 1(pixels) 2(pixels) 3(FTPC)

G. Anelli, M. Scarpa, S. Tiuraniemi

Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/ED Groups with the ALICE SPD

MeV


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 with 1 GHz FADC

In NA48/2 KABES has achieved: •Position resolution ~ 70 micron•Time resolution ~ 0.6 ns•Rate per micro-strip ~ 2 MHz

New electronic + 25µm mesh strip signal occupancy divided by 3


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 large straw system has been operated in high vacuum

Straw Tracker


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


RICH Layout


RICH as velocity spectrometer….

Resolution of a 17m P-326 RICH(CKMGEANT)


…and RICH for - separation


NA48 LKr as Photon VetoEnergy of photonsfrom K hitting LKr: > 1 GeV

GeVConsolidation of thesafety/control system and read-out under way


LKr efficiency measured with data

Cluster not reconstruct

edE = 22

GeV

Pion P=42 GeV/c

Photon E=11 GeV

Expected

position

K+ collected by NA48 in 2004Events are kinematically selected. track and lower energy are use topredict the position of the other

+00


Example: “hadronic” cluster of a photon

Expected position

Maximum energy ~300 MeVExpected energy: ~29 GeVDeposited energy: ~9 GeV

Measured LKr inefficiency per photon (Eg > 10 GeV): = (2.8 ± 1.1= (2.8 ± 1.1statstat ± 2.3 ± 2.3systsyst) × 10) × 10-5 -5 (preliminary)(preliminary)


Beam test 2006• Idea for measuring inefficiency in the range 2 GeV < E< 10 GeV

– Use of the NA48 set-up.– Photons produced by bremsstrahlung.

– SPS can provide a suitable electron beam.

vacuum

Electron beam

(25 GeV/c)Bremsstrahlung

Kevlarwindow

Driftchambers

MagnetCalorimeter

e-

Calorimeter inefficiency below E < 5 GeV is not critical

Beam test foreseen duringthe 2006 SPS run


ANTI-Photon RingsFrom: 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


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


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 ~40Important synergies with LHCto be exploited: for instance, the LHCbTELL1 board


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 ( 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


Summary

• Clear physics case – The discovery of New Physics will dramatically increase the

motivation for searches of new flavour phenomena • Healthy competition worldwide:

– J-PARC SPS • Exploit synergies and existing infrastructures

NA48 ’/ NA48/1 KS rare decays NA48/2 g/g in K 3

P-326 • 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!

Documents

Physics Introduction Rare Kaon Decays in the SM…. …and Beyond