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L’esperimento MEG

A. Baldini

17 settembre 2002

http://meg.pi.infn.it

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Layout della presentazione

• Introduzione fisica

• Descrizione dei rivelatori

• Sensibilita’ dell’esperimento

• Necessita’ finanziarie

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Motivazioni• SUSY SU(5) predictions

Lepton Flavour Violation (LFV) induced by finite slepton mixing through radiative corrections

The mixing could be large due to the top-quark mass

in SU(5) (larger by ~30 order of magnitudes than SM predictions)1315 1010 )eγμ( BR

• SO(10) predicts even larger BR

J.Hisano et al.,Phys. Lett. B391 (1997) 341

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

)eγμ( 100)eγμ( )eγμ( )5()5(

2

μ

τ)10(

SUSUSO m

m

clear evidence for physics beyond the SM

Our goal

Analisi combinate degli esperimenti a LEP favoriscono 10tan

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Limiti combinati degli esperimenti LEP per SUGRA MSSM

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SO10

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Connection with neutrino oscillations

J.Hisano et al.,Phys. Lett. B437 (1998) 351

• -oscillations

Contribution to slepton mixing from (mixing responsible for solar -deficit) 21V

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•muon (g-2)

Results from BNL experiment

Sizeable deviations ( tan) are expected

e) enhanced

-101016)34( SMmeas aa

6.26.1 measa

More recently: hep-ex/0208001 v2(2002)

dal valore “predetto”

g-2

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- dal decadimento di a riposo sulla superficie del bersaglio (surface muons)

- misure nel 1999: contaminazione circa 10%18 107.1 sR stop

e

Il fascio

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Studi di fascio

-Studio della versione “U” per migliorare la separazione dai positroni

- Misure estive e a fine anno

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Detector overview

• Liquid Xe e.m. calorimeter

• Magnetic spectrometer

• Timing counter

),/,( γγγγ tEpE

ep

),/( eee tEp

%9π4

ps 150

mrad 5.2017

%4

%9.070

eγ

eγ

γ

e

t

E

.E

FWHM resolutions

“espulsione” dei positroni

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Montecarlo

Simulazione di tutte le parti del rivelatore

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COBRA spectrometer

Gradient field

Gradient field

Uniform field

Uniform field

COnstant Bending RAdius (COBRA) spectrometer

• Constant bending radius independent of emission angles

• Low energy positrons quickly swept out

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Il magnete

• 3 raggi diversi di avvolgimento

•Cavo superconduttore gia’ prodotto

•Test su prototipi per verificare che gli stress meccanici possono essere sostenuti

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Campo magnetico lungo l’asse e nella zona dei fototubi del calorimetro e.m.

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Camere a drift

Catodi sagomati per una buona risuoluzione longitudinale

Miscela He/C2H6

(50%/50%)

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m

m

long

R

7425

1093

(no magnetic field)

R&D delle camere a drift

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Miglioramento della lettura e prestazioni dello spettrometro

mmx

mrad

PP

orig

e

ee

5.21.2

129

%9.07.0/

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Dipendenza del limite (90% C.L.) dalla risoluzione longitudinale

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Timing counter

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TC prototype results

(although depend on the number of photoelectrons)

ps 60~..aw

2,1

from rms of (T3-T4)/2 distribution

almost independent of muon passage along the counter

• (T1 - T2)/2

independent of reference

gives similar results

•Weighted average222refTi i

ps 562 ref

We obtain

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Timing MC studies•Timing efficiency

60 ps for E 2 MeV

mainly dominated by photoelectron statistics

E > 5 MeV energy deposit on adjacent

-cells to achieve 100 ps FWHM resolution

•Trigger efficiency

Use of hit z-cells and -cells to determine initial positron direction

correlation with max. charge PMT in LiXe calorimeter (providing direction)

Yet to be studied: use of Q1/Q2 (instead of z-cells layer) to determine the z-position

e+

2

2

.. /1

/

i

iiaw

TT

use of more than 2 PMT’s

need to know T(E,x,z)

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EfficienciesTiming efficiency evaluated for different configurations:

• 1cm thick inner layer, 2 cm thick outer layer

(E>5 MeV) = 85 %

(mainly due to e+ interaction in the inner layer)

(trigger) = 96.8 %

• 0.5 cm thick inner layer, same thickness for outer

(E>5 MeV) = 93.6 %

(trigger) = 97.4 %

• reversed layers

(E>5 MeV) = 97.5 %

(trigger) = 75.4 %

( many events with no hit on z-sliced layer)

unavailable provided one uses Q1/Q2 to determine z

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Configurazione dei rivelatori dello spettrometro

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Il calorimetro a xenon liquido

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Large calorimeter prototype•264 PMTs, 100 l LiXe•Use of inverse-Compton scattered -beam provided at TERAS, AIST, Tsukuba, Japan• -energy spread < 1% at Compton edge• E = 40 MeV• Test with alphas and cosmic rays (movabletelescope)•INFN participation

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ico)(pessimist cm 80abs

.

1.00.3.

3.06.2/

aletMiyajima

meas

GXeLXe

metroabs 1

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Risoluzione in energia

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Detector resolutions

pstmmz

mmx

EE

85 14

.)(exp 5.109

%4/

Posizione

Nuove misure sul Large Prototype

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TriggerUse of “on-line” reconstruction of energy, direction for both positron and photon

•Photon

PMT charge sum energy deposit

Use of 100 MHz FADC

max. charge PMT direction

•Positron

DCs provide information about positron momentum (constant bending radius) and direction (correlation of chamber plane index with )

but slower device (~200 ns drift) information available only at high-level trigger

Timing Counters instead:

• provide fast (~10 ns) information about timing and direction

(correlation of scintillator slices with positron direction)• work as a filter (e.g. no hit on TC) for Michel positrons with p<40 MeV/c

or out of the acceptance angular range ( )

-13γ s 102~ 97.3%, MeV/45 RcE

99.5%)5.3( 1.2 oo

-16TC s 105~ R

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1st level triggerCoincidence of an event in Xe with a TC hit within ΔT = 10 nsSince

-13s102R -16 s105TCR

then-1

1 s 2002 TRRR TC

2nd level triggerBased on an association of γ direction with TC-rods hit by the positron

2f5f

(hard to improve due to target size)

-112 s 20 ffRR

3rd level triggerUse of outer hit DC wires to determine the radius of the turning point By requiring cm 24DCR

-123 s 102 RfRf RR

Trigger levelsTrigger levels

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Trigger implementation

• Use of 100 MHz, 10-bit resolution Flash-ADC for PMT charge sampling

• Data processed by FPGA so as to:

• subtract the pedestals

• equalize the PMT gain

• compute the Q-sum

• find the PMT with max charge

• compute the min. arrival time

• store waveforms in FIFO

Two types of VME board

1-Analog-to-Digital 6U2-Digital 9U

arranged in a

layer tree structure

1 board

2 VME 6U

1 VME 9U

Type2

Type2

LXe inner face(312 PMT)

. . . 20 boards

20 x 48

Type1Type1

Type1

16

3

Type2

2 boards

. . . 10 boards

10 x 48

Type1Type1

Type1

16

3

LXe lateral faces

(488 PMT: 4 to 1 fan-

in)Type2

1 board

. . .

12 boards

12 x 48

Type1Type1

Type1

16

3

Timing counters

(160 PMT)Type2

Type2

2 boards2 x 48

4 x 48

2 x 48

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Readout: digitizzazione a 2 - 2.5 GHz

Primo prototipo pronto a fine anno

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selesig RTBRN

4)

4/(1 seleRTSES

Segnale:

Sensibilita’

sRsTsele / 103.0 106.2 7.0~)9.0( 6.0~ 0.9~ 873

)peggiori irisoluzion e102.0per menterispettiva 106.1 e 106.5(

101 di C.L. 90% al limiteun a entecorrispond 108.381314

1314

R

SES

Il rate e’ abbassato per avere ~ 0.5 eventi di fondo e 1 evento di segnale

Scoperta: 4 eventi misurati (P )3102~ 13102.24.1~ BR

In tal caso il rate di muoni verra’ aumentato per migliorare

la comprensione del fondo e capire meglio il segnale

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Fondi

Fondo Accidentale: un positrone di Michel ed un fotone dal decadimento radiativo o dall’annichilazione di un positrone

Fondo prompt: dal decadimento radiativo (calcolabile)

sig

back

sig

eff

N

N

BR

BR SESNBR backeff

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m

Ey

2

Photon yield

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KL0 e

K e

A eA

eee

e

Previous searches

After Y. Kuno and Y. Okada

Limits improved by ~ 2 orders of

magnitude in the last 25 years

Since 1948 E.P.Hincks and B.Pontecorvo, PR 73 (1948) 257

010

210

410

610

810

1010

1210

1940 1950 1960 1970 1980 1990 2000

BR

year

15103~ promptBR

1422 105.32.2~ eeeacc tEERBR

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INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, D. Nicolo’, R. Pazzi, F. Sergiampietri, G. Signorelli

ICEPP, University of Tokyo T. Mashimo, S. Mihara, T. Mitsuhashi, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamashita

KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura

Osaka University Y. Kuno

Waseda University T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamashita, T. Yoshimura

Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

PSI, Villigen J. Egger, P. Kettle, S. Ritt

The MEG collaboration

INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet

INFN & Genova University F. Gatti

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Stima dei costi

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Preventivo globale

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Pisa 2003

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Finanziamenti/anticipi 2003

Pisa

M.E. 2 m.u. PSI + 0.5 Giappone

M.I. 5 k€

Inv + Consumo 25 k€ PMT (10) + 75 k€ LXe facility

Pavia

M.E. 1 m.u. PSI

M.I. 2 k€

Inv. + Consumo 50 k€ test PMT in c.m.

Rimborsi dotazioni (no)

Genova

M.E. 0.5 m.u. PSI

M.I. 1 k €

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LXe Facility

1) Gruppo di pompaggio con:

pompa vuoto primario scroll (2 stadi, a secco, senza olio)

pompa secondario turbomolecolare (a secco)

10 kEuro

2) Misuratori di vuoto 2 kEuro

3) Cercafughe (scroll+turbo+cella analisi) 20 kEuro

4) Dewars, flange CF, tuberie, valvole 23 kEuro

5) Criostato per Xenon liquido,

con scambiatore di calore a LN2,

finestre, passanti alta e

bassa tensione,

componentistica vuoto varia. 20 kEuro

Totale 75 kEuro