The K + + experiment at CERN Monica Pepe INFN Perugia Europhysics Conference on High Energy Physics Manchester, England - July 19 - 25 2007.

The K+ + experiment at CERNMonica Pepe

INFN Perugia

Europhysics Conference on High Energy Physics

Manchester, England - July 19 - 25 2007

HEP 2007 2 Monica Pepe – INFN Perugia

CP

Standard Model predictions

BR(K++) (1.6×10-5)|Vcb|4[2+(c-)2] (8.0 ± 1.1)×10-11

BR(KL0) (7.6×10-5)|Vcb|42 ± 0.6×10-11

Golden modes

FCNC loop processes

Short distance dynamics dominated

One semileptonic operator, hadronic matrix element related to measured quantities

K+→: decisive test of SM sensitive to new

physics

Present measurement (E787/949): BR(K+) = 1.47 × 1010 (3 events)+1.30

-0.89

HEP 2007 3 Monica Pepe – INFN Perugia

CERN-SPSC-2005-013 SPSC-P-326

September 2005: presented at CERN SPSCDecember 2005: R&D endorsed by CERN Research BoardStart of test beams at CERN in 20062007: prototypes construction and test beams at CERN and Frascati2008 – 2010: Technical design and constructionStart of data taking 2011

Schedule

Located in the same hall as NA48

CERN, Dubna, Ferrara, Firenze, Frascati, Mainz, Merced,

Moscow, Napoli, Perugia, Pisa, Protvino, Roma,

Saclay, San Luis Potosi, Sofia, Torino, Triumf

P326 a 10% new measurement (100 events)

Proposal to Measure the Rare Decay K at the CERN SPS

HEP 2007 4 Monica Pepe – INFN Perugia

O(100) K++events ~ 10% background

Kaon decay in flight techniqueIntense proton beam from SPSHigh energy K (PK = 75 GeV/c) Kaon ID (CEDAR)

Kinematical rejection

Kaon 3-momentum: beam trackerPion 3-momentum: spectrometer

KK+

m2miss=(PKP)2

P326 guidance principles

Veto and particle ID/ detection: calorimetersCharged veto: spectrometer//e separation: RICH

BR(SM) = 8×10-11

Acceptance 10%~ 1013 K+ decays in 2 years

HEP 2007 5 Monica Pepe – INFN Perugia

92% of total background

Allows us to define a signal region K+ +0 forces us to split it into

two parts (Region I and Region II)

Span across the signal region Rejection must rely on vetoes

Kinematically constrained Not kinematically constrained

8% of total background

Kinematics and Backgrounds

HEP 2007 6 Monica Pepe – INFN Perugia

Background Rejection

K+→ (K)

Largest BR: 63.4% Need ~10-12 rejection factor• Kinematics: 10-5

• Muon Veto: 10-5 MAMUD• Particle ID: 5×10-

3RICH

K+→ (K)

2nd Largest BR: 20.9% Need ~10-12 rejection factor• Kinematics: 5×10-3

• Photon Veto: 10-5 per photon

Large angle: 13 ANTIs (10 < acceptance < 50 mrad)

Medium angle: NA48 LKr (1 < acceptance < 10 mrad)

Small angle: IRC1,2 SAC (acceptance < 1 mrad)

Assuming the above veto inefficiencies and an acceptance of 10%, a S/B > 10 is obtained if

(mmiss)2 ~ 8×10-3GeV2/c4

Resolution requirements:

P< 1 %

PK 0.3 % K 50-60 μrad

HEP 2007 7 Monica Pepe – INFN Perugia

• P Kaon = 75 GeV/c (P/P ~ 1.1%)• Fraction of K+ ~ 6.6%• Negligible amount of e+

• Beam acceptance = 12 str (×25 NA48/2)• Area @ beam tracker = 58×24 mm2

• Integrated average rate = 760 MHz• K+ decays / year = 4.8 × 1012

• P proton = 400 GeV/c• Proton/pulse 3.3×1012 (×3.3 NA48/2)• Duty cycle 4.8/16.8 s

Primary beam Secondary beam

The BeamVertic

al

viewDECAYDECAY

VOLUME VOLUME (~100 m)(~100 m)

K+ decay rate: ~11 MHz

p

Achromat 1

Quadrupoles

Radiator

Achromat 2Cedar

Scraper

Gigatracker

20 mm

5 m

Target

HEP 2007 8 Monica Pepe – INFN Perugia

The P326 layout

+

VACUUM10-6 mbar

50 MHz

800 MHz 11 MHz

K+ ~ 75 GeV

Technical Design Report in preparation

HEP 2007 9 Monica Pepe – INFN Perugia

6 chambers with 4 double layers of straw tubes each ( 9.6 mm)

The Gigatracker (i.e. the beam spectrometer)

The Double Spectrometer (i.e. the downstream tracker)

3 Si pixel stations across the 2nd achromat: (60 × 27 mm2)

The tracking system

Rate: ~ 45 KHz per tube (max 0.8 MHz beam halo)

Low X/X0 0.1% X0 per view in vacuum

Good hit space resolution 130 m per view

Redundant p measurement 2 magnets (270 and 360 MeV/c pt kick)

Veto for charged particles 5cm radius beam hole displaced in the bending plane according to beam path

m2miss resolution ~1.1×103 GeV2/c4

main contribution from θK measurement

θK

p

pK

θK

θ

m2miss

resolution

8.8

m

7.2

m2.1

m

Time resolution (ps)

Sig

nal

/Bac

kgr

oun

d

(PK)/PK ~ 0.22%(K) ~ 16 rad(

(

Rate 760 MHz (charged particles) ~ 60 MHz / cm2

300×300 m2 pixels

200 Si m sensor + 100 Si m chip Low X/X0

Readout chip bump-bonded on the sensor (0.13 m technology)

Excellent time resolution needed for K+/+ association (t)~200 ps / station

HEP 2007 10 Monica Pepe – INFN Perugia

CEDAR: existing Cerenkov counter at CERN

18 m long tube ( 2.5 m ), 17 focal lentgh mirrors

The CEDAR (i.e. the kaon ID)

The RICH (i.e. the pion ID)

Adapted to P326 need:

Vary gas pressure and diaphragm aperture to select Kaons

• H2 instead of Nitrogen

• New PMs and electronics

Ne @ 1 atm (thr = 13 GeV/c)

>3 / separation up to 35 GeV/c

High granularity (2000 PMTs)

Small pixel size (18 mm PMT)

Disentangle pileup in Gigatracker (t)~100 ps

PMTs tested in 2006

Prototype Test Beam in 2007

Beam Composition

00,10,20,30,40,50,60,70,8

1650 1700 1750 1800 1850 1900 1950 2000 2050

Pressure

%

p

K

Beam composition 2006 Test

The particle ID system

HEP 2007 11 Monica Pepe – INFN Perugia

Large angle (10-50 mrad): 13 ANTISTwo options under test: Lead-scintillator tiles orLead-scintillator fibers (KLOE-like)

Photon vetoes

Muon veto MAMUD

The Veto system

• Rings calorimeters (in vacuum)

• Rate: ~4.5 MHz () + ~0.5 MHz () (OR 12)

• 10-3 inefficiency for 0.05 < E< 1 GeV

• 10-4 inefficiency for E> 1 GeV Medium angle (1-10 mrad): NA48 LKr Calorimeter

New Readout• Rate: ~8.7 MHz () + ~4 MHz () + ~4 MHz ()

• 10-4 inefficiency for 1 < E< 5 GeV

• 10-5 inefficiency for E> 1 GeV

Inefficiency for E> 10 GeV tested on NA48/2 data (K+→)

Small angle (< 1 mrad): Shashlik technology

• Rate: ~0.5 MHz ()

• 10-5 inefficiency for high energy (>10GeV) photons

Sampling calorimeter + Magnet for beam deflection

• Rate: ~7 MHz () + ~3 MHz ()

• 10-5 inefficiency for detection

• Sensitivity to the MIP• em/hadronic cluster separation• 5Tm B field in a 30×20cm2 beam hole: deviate the beam out from the SAC

The NA48 LKr calorimeter

ANTI ring

Shashlik calorimeter

HEP 2007 12 Monica Pepe – INFN Perugia

A possible scheme:

TRIGGER

Level L0 “hardware” L1-L2 “software”

Input ~10 MHz 1 MHz

Output 1 MHz O(KHz)

Implementation Dedicated hardware TDAQ farm

Actions RICH 1Track, μ veto, LKr () veto

L1 = single sub-detectors

L2 = whole event

Software trigger reduction ~ 40

HEP 2007 13 Monica Pepe – INFN Perugia

Acceptance (60 m fiducial volume):

Region I: 4% Region II: 13% Total: 17%

could be reduced after analysis cuts(losses due dead time, reconstruction inefficiencies…)

Simulation of the P-326 apparatus

Acceptance ~ 10% is achievable

Preliminary sensitivity studies

Region I and II Momentum range: 15 < P < 35

GeV/c Against muons RICH operational reasons Plenty of energy in photon vetoes

Remind:

K m2miss = 0.0182 GeV2/c4

K m2miss

< 0

0<m2miss<0.01 0.026<m2

miss<0.068 GeV2/c4

HEP 2007 14 Monica Pepe – INFN Perugia

Events/year Total Region I Region II

Signal (acc=17%) 65 16 49

K++0 2.7 1.7 1.0

K++ 1.2 1.1 <0.1

K+e++ ~2 negligible ~2Other 3 – track decays

~1 negligible ~1

K++0 1.3 negligible 1.3

K++ 0.5 0.2 0.2

K+e+(+)0, others

negligible

Total bckg. 9 3.0 6 S/B ~ 8 (Region I ~5, Region II ~9)

Signal and Backgrounds

HEP 2007 15 Monica Pepe – INFN Perugia

Conclusions

P326 experiment: Search for new physics using rare Kaon decays

A new experiment (~10-12 sensitivity per event) at an existing machine and employing the infrastructures of an existing experiment

General design mostly defined. Overall simulation and performance under review

R&D program: construction of detector prototypes and test in progress. Important results by end of 2007

P-326 proposed for K++ but Kaon Flux ~100 times wrt NA48/2

many other physics opportunities can be addressed