12 th flavor physics & cp violation may 26 th -30 th , 2014

The NA62 experiment at CERN: status and perspectives

R. Fantechi

CERN and INFN – Sezione di Pisaon behalf of the NA62 Collaboration

Birmingham, Boston, Bratislava, Bristol, Bucharest, CERN, Dubna, Fairfax, Ferrara, Florence, Frascati, Glasgow, IHEP, INR, Liverpool, Louvain, Mainz,

Merced, Naples, Perugia, Pisa, Prague, Rome I, Rome II, San Luis Potosi, SLAC, Sofia, Turin

12th Flavor Physics & CP Violation May 26th-30th, 2014

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Outline• K+ ® p+ nn theory (short reminder)

• NA62 detector layout

• Strategy for the measurement

• Perspectives for 2014 and beyond

• Conclusions

R. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

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K+ ® p+ nn: clean theoretical environment


FCNC loop processes:s->d couplingHighest CKM suppression

SD contribution dominates

• top quark contribution computed at NLO QCD and 2-loop EW corrections• c quark loop contribution computed at NNLO QCD and NLO EW corrections• correction for LD contributions• Hadronic matrix element related to the precisely measured BR (K+ ® p0e+n)

Branching ratio proportional to |Vts *Vtd|2

SM predictions [Brod, Gorbahn, Stamou, Phys. Rev D83,034030 (2011)]BR(K0) = (2.43 ± 0.39 ± 0.06)*10-11

BR(K+) = (7.81 ± 0.75 ± 0.29)*10-11 First error CKM parametric, dominated by VcbSecond error theoretical, mostly LD corrections

K ® pnn are the most sensitive probes to NP models among B and K decays

The combined measurement of K+ and KL modes could shed light on the flavour structure of NP (DS=2 / DS=1 correlation)

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K ® pnn NP sensitivity


General model with new flavour structure: Z’ gauge boson mediating FCNC at tree level [A. Buras, F. De Fazio, J. Girrbach, JHEP 1302 (2013) 116]

K sensitive to mass scales beyond those explored from LHC (MZ’ > 5 TeV/c2)

More specific NP models Littlest Higgs with T-parity,Acta Phys. Polonica B41(2010)657 Custodial Randall-SundrumJHEP 0903 (2009) 108 Started to be probed at LHC, small effects in B

physics.Best probe of MSSM non-MFV [JHEP 0608 (2006) 064]• E.g. non-MFV in up-squarks trilinear terms• Still not excluded by the recent LHCb data.

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Today status of K ® pnn


E787/E949 @Brookhaven: 7 candidates K+ ® p+nn2 experiments, stopped kaon technique

Separated K+beam(710 MeV/c, 1.6MHz)PID: range (entire π+→μ+→e+decay chain)Hermetic photon veto system

Probability of all events to be background ~ 10-3

Expected background: 2.6 events 1015.1

05.1 10)73.1()( +

++ ® nnpKBR

E391a @ KEK:80 106.2)( ® nnpLKBR

Future experiments: KOTO@JPARC (KL® p0nn), ORKA@FNAL (K+ ® p+nn)

Phys. Rev. D81,072004 (2010)

Phys. Rev. D77,052003 (2008), Phys. Rev. D79,092004 (2009)

cancelledFirst results during summer

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NA62 goals– Collection of O(100) K+ ® p+ nn events in two years of

running• 10 % measurement of the branching ratio• This requires at least 1013 Kaon decays• 75 GeV beam helps in background rejection

– Event selection with Pp<35 GeV/c– i.e. Kp2 decays have around 40 GeV of electromagnetic energy

– O(1012) rejection factor of common K decays• Main contribution from Km2 (63%) and Kp2 (21%)• Kinematics resolution• Efficient veto detectors• Particle ID• Precise timing

– Expected acceptance O (10%)R. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

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SPS primary proton beam @ 400 GeV/cProtons on target: 3 x 1012 / pulseDuty cycle ~ 0.3Simultaneous delivery to LHCSecondary charged beam 75 GeV/c

To optimize kaon productionMomentum bite 1%Angular spread in X and Y < 100 mrad

Size @ beam tracker: 5.5 x 2.2 cm2

Rate @ beam tracker: 750 MHz6% K+ (others: 70% p+, 24%proton)Rate downstream 10 MHz (mainly K+ decay)K decay rates: 4.5 x 1012 /year

In a 60 m decay volume

KTAG

NA62 high-intensity kaon beam


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KTAG

The NA62 detector


8LAV

CHOD

SACIRC

KTAG

SPECTROMETER

Target

GTK

RICH

LKr MUV

CHANTI

Beam Pipe

Differential Cherenkov for K+ ID in beam

Beam trackerSi pixels, 3 stations

Large angle photon vetoesOPAL lead glass11 stations in vacuum, 1 in air

Charged veto

Dipole magnet4 straw-tracker stations

p/m ID17m, 1 atm Ne

Muon vetoFe/Scint

g veto

g veto

Forward g vetoNA48 LKr calorimeter

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The measurement• Signature: one incident kaon, 1 charged output track• Missing mass distributions: m2

miss = (PK-P track(hyp p+))2

• Define two regions to accept candidate events

• Backgrounds• K+ decay modes• Accidental signal track matched with a K-like one

Photon and muon vetoes + particle ID to fight the background


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Guiding principles for the detectors– Good tracking devices

• Accurate measurement of the kaon momentum• Accurate measurement of the pion momentum• Missing mass cut: O(105) rejection factor on Km2, O(104) on

Kp2

– Veto detectors• For photons to reduce the background by a factor 108

• For muons add a rejection factor of O(105)– Particle identification

• Identify kaons in the beam • Identify positrons • Additional p/m rejection [O(102)]

– Precise timing• To associate in time the kaon with the decay products


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Reconstruction of the beam kaon• Time : Gigatracker, KTAG• Track reconstruction: Gigatracker

• Gigatracker:– 3 Si pixel station (300*300 mm2 pixels)

with readout chips bonded– X/X0 < 0.5%/station– Capability to handle 750 MHz beam rate– Installed inside an achromat

• From test beam and simulation– s(t) ~ 200 ps/station– s(PK)/PK = 0.2%– s(dX,Y/dZ)K = 15 mrad


Chip under test at CERNCommissioning on the beam line in September 2014

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Reconstruction of the charged pion• Time : RICH • Track reconstruction: Straw

spectrometer

• RICH time resolution < 100 ps• Spectrometer

– 4 straw chambers in vacuum– 9.6 mm radius mylar tubes, 2.1 m

long– 4 planes of staggered tubes per

view, 4 views in a chamber– X/X0 0.1% per view ®2% total– Dipole magnet with 265 MeV/c PT

kick• Resolution

– s(P)/P = 0.32% Å 0.008 P [GeV/c]– s(dX,Y/dZ) = 20-50 mrad


Construction almost finishedCommissioning in September 2014

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Kaon-pion matching• Very different rate

– Beam@Gigatracker: 750 MHz– decays@downstream detectors: 10

MHz• Wrong kaon-pion assignment will

spoil the kinematical reconstruction• Match in time and in space

– Gigatracker resolution: 200 ps/station– KTAG resolution: < 100 ps– RICH resolution: < 100 ps

– Find a vertex in Gigatracker (CDA cut)

• Mis-matching probability < 1%, could go down with analysis optimizationR. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

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Kinematics


Signal/background rejection by kinematicsK+ ® p+ p0 : ~5 *103

K+ ® m+ n : ~1.5 *104

Inefficiencies due to:

Non gaussian tails from multiple scatteringPileup in the Gigatracker

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Photon rejection• IRC, SAC, LKr, LAV• Hermetic coverage up to 50 mrad• O(108) p0 rejection from K+ ® p+p0

– Thanks to the cut Pp <35 Gev ® Ep0 >40 Gev– If one photon is lost above 50 mrad, the other is going in the LKr– For Eg >10 GeV, LKr inefficiency measured from data is <10-5

– 10-4 inefficiency down to 100 MeV in LAV


Lead glass blocks from OPAL12 stations (11 in vacuum)Ready

NA48 em calorimeterNew readout electronics being commissioned

Calorimeters at low angle (<1 mrad)Shashlik technologyIRC being built, SAC in place

LAV

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Particle ID: calorimeters• p/m/e separation

– NA48 LKr calorimeter• Em/hadronic/mip cluster id• Very good mip signal

– MUV1&2: Fe-scintillator• Hadronic/mip cluster id• Usable also in the trigger

(pion energy)– MUV3: scintillator tiles seen

by two PMs• Fast muon counter, ineff. <

%• Used in the L0 trigger

• Global p/m separation (from simulation + test beam): 105

• MUV2 and MUV3 ready, MUV1 to be installed during the summerR. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

From technical run 2012

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Particle ID: Rich• p-m separation: RICH

– 17 m long filled with Ne at 1 Atm– Array of 20 mirrors, 17m focal

length– 2x 1000 PMs in the focal plane– 9 cm radius internal beam pipe– 14 GeV threshold for pions– Full length prototype tested in

2009– Full detector under installation

• p-m separation > 102 up to 35 GeV

• Time resolution 80 ps• To be used also in the L0 triggerR. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

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Particle ID in the beam• K-p separation in the beam:

KTAG– Differential Cherenkov counter

(CEDAR, from SPS)– Filled with N2 or H2– New external optics, PMs and readout– 50 MHz particle rate– Installed and partly commissioned in

2012

• Kaon tagging with <100 ps time resolution

• Sub-percent pion mis-tagging for K efficiency > 95%

• K-p time matching• Suppression of background for

accidental tracks by interactions of the beam with the Gigatracker stationsR. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

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Trigger and DAQ• Strong requirement: handle 10

MHz kaon decay rate and reduce it to 10 KHz bandwidth to tape

• Multilevel trigger system– L0 based on digital primitives from

fast detectors– FPGA based, latency ~ 1ms– A smart L0 trigger processor gathers

all primitives and issue a L0 decision– Reduction factor: 10 MHz -> 1 MHz– L1 PC based– Uses data from all the detectors

except LKr– Whole event analysed by a single PC– Max latency 1s– Reduction factor: 1 MHz -> 100 KHz– L2 PC based, uses all data– Performed by the same PC as L1– Latency: spill length– Reduction factor: 100 KHz -> 10 KHz


Trigger primitives construction

Use fast detectors (RICH, MUV), energy in the LKr and at least in a fraction of the LAV system

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Decay event/year

K+®p+nn [SM] (flux 4.5×1012) 45K+®p+p0 5K+®m+n 1K+®p+p+p < 1K+®p+pe+n + other 3 tracks decays < 1K+®p+p0g (IB) 1.5K+®m+ng (IB) 0.5K+®p0e+(m+)n, others negligibleTotal background < 10

NA62 Sensitivity & backgrounds


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Additional NA62 K Physics Program


Decay Physics Present limit NA62p+m+e- LFV 1.3*10-11 0.7*10-12

p+m-e+ LFV 5.2*10-10 0.7*10-12

pm+e+ LNV 5.0*10-10 0.7*10-12

p-e+e+ LNV 6.4*10-10 2.0*10-12

p-m+m+ LNV 1.1*10-9 0.4*10-12

m-ne+e+ LFV/LNV 2*10-8 4.0*10-12

e-nm+m+ LNV No data 1.0*10-12

p+c0 New particle 5.9*10-11 Mc0 = 0 1.0*10-12

p+cc New particle No data 1.0*10-12

p+p+e-n DS ¹ DQ 1.2*10-8 1.0*10-11

p+p+m-n DS ¹ DQ 3.0*10-6 1.0*10-11

p+g Angular momentum 2.3*10-9 1.0*10-11

m+nh, nh®ng Heavy neutrino Limits up to Mnh = 350 MeV/c2 1.0*10-12

RK LU (2.488 ± 0.010)*10-5 >*2 betterp+gg cPT < 500 events 105 events

p0p0e+n cPT 66000 events O(106) eventsp0p0m+n cPT O(105) events

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Status of the installation


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NA62 data taking plans• Complete the installation of the detector

– Before the SPS restart in Autumn after LS1

• 2 months run at the end of 2014– Complete the commissioning with particles– Lower intensity– Likely reach SM sensitivity

• Nominal beam intensity in 2015, 2016, 2017– To collect ≥100 events – Complete data taking before LS2


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Conclusions• NA62 detector construction is almost

complete

• The first run with beam will start on October 2014– Commissioning with particles– Almost SM sensitivity

• Data taking will continue at least up to LS2

• Beside K+ ® p+ nn , plans for studies of many rare decay channelsR. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

25Thank you!

Artist’s view of the installation activity…


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Spares


27R. Fantechi - 12th Flavor Physics & CP Violation - May, 30th, 2014

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Overview of TREK

0.25% precision

|U|<2 10-8 for M<200 MeV

SM extensions with massive gauge boson A’Sensitivity: mixing parameter ~10-6 for 10<M(A’)<100 MeV

12 th flavor physics & cp violation may 26 th -30 th , 2014

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