September 27, 2005P-326@SPSC731 Proposal to Measure the Rare Decay K at the CERN SPS CERN,...

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

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|

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

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

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

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

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

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

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

September 27, 2005 P-326@SPSC73 10

P-326 Detector Layout

800 MHz beam/K/p

K+

+

~11 MHz

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

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

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

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

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

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

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

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

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

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

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]

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:

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+

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

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

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

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

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

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

September 27, 2005 P-326@SPSC73 30

RICH Layout

September 27, 2005 P-326@SPSC73 31

RICH as velocity spectrometer….

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

September 27, 2005 P-326@SPSC73 32

…and RICH for - separation

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

September 27, 2005 P-326@SPSC73 34

Photon Vetoes

September 27, 2005 P-326@SPSC73 35

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

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

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

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

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

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

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

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

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

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

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

September 27, 2005 P-326@SPSC73 47

Spares

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

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

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

September 27, 2005 P-326@SPSC73 51

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

September 27, 2005 P-326@SPSC73 53

Possible Photon detector

September 27, 2005 P-326@SPSC73 54

Sigma = ~ 80 ps

~750000 e-

Simulation of average channel response

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!