First results from the meg re12 experiment at psi
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First results from the MEG/RE12 experiment at PSI. A.M. Baldini 29 sep 2009. Hep-ex:0908.2594v1 18 Aug 2009. Most recent m +  e + g Experiments. Two orders of magnitude improvement tough experimental challenge! But

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First results from the MEG/RE12 experiment at PSI

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First results from the meg re12 experiment at psi

First results from the MEG/RE12 experiment at PSI

A.M. Baldini 29 sep 2009

Hep-ex:0908.2594v1 18 Aug 2009


Most recent m e g experiments

Most recent m+  e+g Experiments

Two orders of magnitude improvement

tough experimental challenge! But

several SUSY GUT and SUSY see-saw models predict BRs at the reach of MEG


Susy gut sugra first contribution v ckm clfv

SUSY SU(5) predictions

BR (meg)  10-14  10-13

SUSY SO(10) predictions

BRSO(10) 100 BRSU(5)

Experimental limit

Our goal

SUSY-GUT (SUGRA) First contribution: VCKM cLFV

LFV induced by slepton mixing

R. Barbieri et al., Phys. Lett. B338(1994) 212

R. Barbieri et al.,Nucl. Phys. B445(1995) 215

combinedLEP results favour tanb>10


First results from the meg re12 experiment at psi

SO10


V pmns n oscillations clfv

Experimental limit

Our goal

VPMNS (n oscillations) cLFV

Independent contribution toslepton mixingfrom n masses (see-saw model): V less known

J. Hisano, N. Nomura, Phys. Rev. D59 (1999)

tan(b)=30

tan(b)=1

After SNO

After Kamland

in the Standard Model !!

If it is seen it is not SM!


Signal and background

e+ +g

e+ +g

n

n

n

n

e+ +

Signal and background

background

signal

eg

accidental

en n

egn n

ee  g g

eZ  eZ g

physical

egn n

qeg = 180°

Ee= Eg=52.8MeV

Te = Tg

g


The sensitivity is limited by the accidental background

The sensitivity is limited by theaccidental background

The n. of acc. backg events (nacc.b.) depends quadratically on the muon rateand on how well we measure the experimental quantities: e-g relative timing and angle, positron and photon energy

Effective BRback (nback/Rm T)

Integral on the detector resolutions of the Michel and radiative decay spectra


Required performances

Required Performances

BR (meg) 10-13 reachable

BRacc.b. 2 10-14 and BRphys.b.  0.1 BRacc.b.with the following resolutions

FWHM

Need of a DC muon beam


Experimental method

Experimental method

  • Detector outline

  • Stopped beam of 3 107 /sec in a 150 mm target

  • Solenoid spectrometer & drift chambers fore+ momentum

  • Scintillation counters for e+ timing

  • Liquid Xenon calorimeter for  detection (scintillation)

  • Method proposed in 1998: PSI-RR-99-05: 10-14 possibility

  • MEG proposal: september 2002: 10-13 goal: A. Baldini and T. Mori spokespersons: Italy, Japan, Switzerland, Russia


Detector construction

Detector Construction

Switzerland

Drift Chambers

Beam Line

DAQ

Russia

LXe Tests

Beam line

Italy

e+ counter

Trigger LXe Calorimeter

Japan

LXe Calorimeter,Spectrometer’s magnet

USA(UCI)

Calibrations/Target/DC pressure system


Next slides

Next slides...

  • The PSI pE5 beamline

  • The Positron spectrometer

  • The Liquid Xenon calorimeter

  • DAQ

  • The 2008 run

  • Future


1 the psi p e5 dc beam

Primary proton beam

1) The PSI pE5 DC beam

Particles intensity as a function of the selected momentum

m+

  • 1.8 mA of 590 MeV/c protons (most intense DC beam in the world)

  • 29 MeV/c muons from decay of  stop at rest: fully polarized


Beam studies

Beam studies

  • Optimization of the beam elements:

    • Wien filterform/e separation

    • Degrader to reduce the momentum stopping in a150mmCH2target

    • Solenoid to couplebeam with COBRA spectrometer

  • Results (4 cm target):

  • Z-version

  • Rm(total)1.3*108m+/s

  • Rm(after W.filter & Coll.)1.1*108m+/s

  • Rm(stop in target)6*107m+/s

  • Beam spot (target)s 10 mm

  • m/e separation (at collimator)7.5s(12 cm)

108m/s could be stopped in the target but only 3x107 are used because of accidental background


2 the positron spectrometer cobra spectrometer

Gradient field

Uniform field

Gradient field

Uniform field

2) The positron spectrometer: COBRA spectrometer

COnstantBendingRAdius(COBRA) spectrometer

  • High pT positrons quickly swept out

  • Constant bending radius independent of emission angles


The magnet

The magnet

  • Bc = 1.26T current = 359A

  • Five coils with three different diameters

  • Compensation coils to suppress the stray field around the LXe detector

  • High-strength aluminum stabilized superconductor

  • thin magnet (1.46 cm Aluminum, 0.2 X0)


Gradient field

Gradient field


The drift chambers

The drift chambers

  • 16 chamber sectors aligned radially with 10°intervals

  • Two staggered arrays of drift cells

  • Chamber gas: He-C2H6 mixture

  • Vernier pattern to measure z-position made of 15 mm kapton foils

goals

(X,Y) ~200 mm (drift time) (Z) ~ 300 mm

(charge division

vernier strips)


First results from the meg re12 experiment at psi

2 10-3 X0 along positrons trajectory


The timing counter

The Timing Counter

BC404

  • One (outer) layer of scintillator read by PMTs : timing

  • One inner layer of scintillating fibers read by APDs: trigger (the long. Position

  • is needed for a fast estimate of the positron direction)

  • Goal time~ 40 psec (100 ps FWHM)

5 x 5 mm2


Tc final design

APD Cooled Support

TC Final Design

APD F.E. Board

Fibers

• A PLASTIC SUPPORT STRUCTURE ARRANGES THE

SCINTILLATOR BARS AS REQUESTED

• THE BARS ARE GLUED ONTO

THE SUPPORT

• INTERFACE ELEMENTS ARE GLUED ONTO THE BARS AND SUPPORT THE

FIBRES

• FIBRES ARE GLUED AS WELL

• TEMPORARY ALUMINIUM BEAMS ARE USED TO HANDLE THE DETECTOR DURING INSTALLATION

• PTFE SLIDERS WILL ENSURE

A SMOOTH MOTION ALONG THE RAILS

APD

PM

Divider Board

Main Support

Scintillator Slab

Scintillator Housing

PM-Scintillator Coupler


3 the liquid xe calorimeter

800 l of Liquid Xe

848 PMT immersed in LXe

Only scintillation light

High luminosity

Unsegmented volume

H.V.

Refrigerator

Signals

Cooling pipe

Vacuum

for thermal insulation

Al Honeycomb

Liq. Xe

window

PMT

filler

Plastic

1.5m

3) The Liquid Xe calorimeter

Experimental

check

In a Large Prototype


First results from the meg re12 experiment at psi

The liquid xenon calorimeter


Pmt development

PMT development

OK!


First results from the meg re12 experiment at psi

Xenon purification

New (2009) liquid phase purification system completely made inside the collaboration (F. Sergiampietri)


First results from the meg re12 experiment at psi

m radiative decay

Laser

20 cm

3 cm

LED

Laser

Lower beam intensity < 107

Is necessary to reduce pile-ups

Better st, makes it possible to take data with higher beam intensity

A few days ~ 1 week to get enough statistics

g

e

m

(rough) relative timing calib.

< 2~3 nsec

n

n

PMT Gain

Higher V with light att.

Can be repeated frequently

p0 gg

p- + p  p0 + n

p0  gg (55MeV, 83MeV)

p- + p  g + n (129MeV)

10 days to scan all volume precisely

(faster scan possible with less points)

LH2 target

alpha

Xenon

Calibration

PMT QE & Att. L

Cold GXe

LXe

e+

g

e-

Nickel g Generator

Proton Acc

Li(p,)Be

LiF target at COBRA center

17.6MeV g

~daily calib.

Can be used also for initial setup

9 MeV Nickelγ-line

on

off

quelle

K

Bi

NaI

Illuminate Xe from the back

Source (Cf) transferred by comp air  on/off

Tl

Li(p, 1) at 14.6 MeV

F

Polyethylene

0.25 cm Nickel plate

Li(p, 0) at 17.6 MeV


Calorimeter energy resolution and uniformity at 55 mev by means of

Calorimeter energy Resolution and uniformity at 55 MeV by means of

Energy resolution on the calorimer

Entrance face

sR = 1.5%

FWHM = 4.6 %


Cw beam line

CW beam line


First results from the meg re12 experiment at psi

LiF target

LITHIUM  - spectrum +

FLUORINE  - spectrum

Automatic insertion/Extraction from the experiment center (target)


4 daq trigger

2 boards

LXe inner face

(312 PMT)

. . .

. . .

10 boards

20 boards

1 board

LXe lateral faces

(488 PMT: 4 to 1 fan-in)

1 board

2 x 48

Type1

Type1

Type1

Type1

Type1

Type1

Type1

Type1

Type1

12 boards

2 boards

3

16

16

3

16

3

. . .

Timing counters

(160 PMT)

Type2

Type2

Type2

Type2

Type2

Type2

2 VME 6U

1 VME 9U

2 x 48

4 x 48

20 x 48

12 x 48

10 x 48

4) DAQ: trigger

  • Uses easily quantities:

    •  energy

    • Positron-  coincidence in time and direction

  • Built on a FADC-FPGA architecture

  • More complex algorithms implementable

  • Beam rate108 s-1

  • Fast LXe energy sum > 45MeV2103 s-1

    g interaction point (PMT of max charge)

    e+ hit point in timing counter

  • time correlation g – e+200 s-1

  • angular correlation g – e+20 s-1

 5 Hz in 2008 data taking


On line e resolution

On-line Eγresolution

55 MeVγ-line from π0-decay

σ= 3.8%

45 MeV threshold

(@4s from signal)


Daq readout the domino principle

DAQ: readout The Domino Principle

0.2-2 ns

Inverter “Domino” ring chain

IN

Waveform

stored

Out

FADC

33 MHz

Clock

Shift Register

“Time stretcher” GHz  MHz

Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS)

Low cost One “oscilloscope” per channel


Liquid xenon waveforms 2 digitizers

Liquid xenon: waveforms: 2 digitizers

[email protected] MHz

DRS2 @ 500 MHz or 2 GHz


4 2008 run

4) 2008 run

  • - First 3 months physics data taking (september-december 2008)

  • DCHs instability on part of the chambers after some months of operation: reduction of efficiency to 30% (now 2009 corrected: new HV distribution system )

  • Xe LY increase (now 2009 at the nominal value)

CW Calibration each three days during 2008 run


First results from the meg re12 experiment at psi

2008

2009


In 2009 xenon scintillation waveforms have the right time decay constant longer for gammas

In 2009 xenon scintillation waveforms have the right time decay constant: longer for gammas

2008

2009


2008 run 10 14 muons stopped in target

RD

RD

RD

RD

RD

RD

2008 run : 1014 muons stopped in target

We also took RMD data once/week at reduced beam intensity

Programmed beam shutdowns

Air test in COBRA

Cooling system repair


Dch resolutions from 2008 data

DCH resolutions from 2008 data

Tracks with two turns in the spectrometer are used to detetrmine the

Angular resolutions

s(Df) =14 mrad

s(f)=10 mrad

The edge of Michel positrons used to

determine momentum resolution

score = 374 keV (60%)

stail1 = 1.06 MeV (33%)

stail2 = 2 MeV (7%)

s(Dq) = 25 mrad

s(q) = 18 mrad


Timing resolutions from 2008 data

Timing resolutions from 2008 data

Photon - positron timing resolution by using Radiative muon decay: physical background

Intrinsic timing resolution by using positrons hitting several bars

DT 80 ps

Problems with DRS2 : will improve with DRS4


Dedicated rmd runs at lower thresholds

Dedicated RMD runs at lower thresholds


Blind analysis e g vs d t g e window

Blind analysis: Eg vs Dtge window


Sidebands d te g 1 ns are used to measure accidental background distributions

Sidebands (|DTeg| > 1 ns ) are used to MEASURE accidental background distributions

g Energy

Radiative decay + In flight positron annihilation +

resolution + pileup: in agreement with MCs


Likelihood analysis accidentals radiative signal pdfs to fit data feldman cousins

Likelihood analysis: accidentals + radiative + signal PDFs to fit data + Feldman Cousins

Best fit in the signal region

Agreement of 3 different analyses


E g vs e e

Eg vs Ee+


Normalization measured michel events simultaneous with the normal meg trigger

Normalization: measured Michel eventssimultaneous with the normal MEG trigger

dove:

pre-scaling 107

  • Independent of instantaneous beam rate

  • Nearly insensitive to positron acceptance and efficiency factors associated with DCH and TC


90 cl limit

90% CL limit

  • 90 % C.L. NSig 14.6 corresponds to BR(m→eg)  3.0 x 10-11

  • Computed sensitivity1.3 x 10-11

  • Statistical fluctuation 5%

  • From side bands analysis we expected 0.9 (left) and 2.1 (right) x 10-11

  • Bad luck


Future prospects

Future prospects

  • Re-start of data taking in september, until december (as in 2008)

  • Instabilities eliminated: DRS2DRS4 (timing improvement + noise reduction)

  • Data taking and trigger efficiencies: 3-5 factor improvement

  • Corresponding improvement in sensitivity: 2-4 * 10-12 for 2009 run

  • Continue running in 2010 + 2011 for the final (10-13) goal

Proposal

now

LoI

Planning

R & D

Assembly

Data Taking

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011

http://meg.psi.ch

http://meg.pi.infn.it

http://meg.icepp.s.u-tokyo.ac.jp

More details at


First results from the meg re12 experiment at psi

Pm

(Y. Kuno et al., MEG TN1, 1997 and references)

Det. 1

Det. 2

  • For suitable geometry big  factors can be obtained

  • This is not the case for MEG (detailed calculations are necessary )

  • In some theories (minimal SU(5) model) the positron has a definite helicity  Pm is less effective


Drs charge vs trigger wfm charge tc

DRS charge vs Trigger WFM Charge (TC)


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