n-nbar at ILL Dirk Dubbers U. Heidelberg n-nbar at ILL Fermilab - - PowerPoint PPT Presentation

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n-nbar at ILL Dirk Dubbers U. Heidelberg n-nbar at ILL Fermilab - - PowerPoint PPT Presentation

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n-nbar at ILL Dirk Dubbers U. Heidelberg n-nbar at ILL Fermilab 18.06.2012 1 1. Introduction Institut Laue-Langevin, Grenoble ESRF n-nbar ILL Highway Grenoble - Lyon n-nbar at ILL Fermilab 18.06.2012 2 ILL Instruments To n-nbar

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Fermilab 18.06.2012 1 n-nbar at ILL

n-nbar at ILL

Dirk Dubbers

  • U. Heidelberg
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Fermilab 18.06.2012 2 n-nbar at ILL

  • 1. Introduction

Institut Laue-Langevin, Grenoble

ESRF ILL n-nbar Highway Grenoble

  • Lyon
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Fermilab 18.06.2012 3 n-nbar at ILL

ILL Instruments

To n-nbar Now EDM2 EDM1 n-lifetime PERKEO

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Fermilab 18.06.2012 4 n-nbar at ILL

ILL reactor n-source

Cold n-guides, to n-nbar Core  LD2 cold sources D2O Cold n-guides, to PERKEO Thermal n-guides Very cold n-guide, to EDM H2O

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Fermilab 18.06.2012 5 n-nbar at ILL

Early History of n-nbar

Lab., reactor Neutron intensity I  Neutron number N = IT Effect. runtime  T n-temp., n-velocity υ  n-TOF

t =

(L/υ)21/2 Eff. length  L Residual B-field Limit (90%) n-nbar Reference ILL HFR 109/s 1016 1.5 year Very cold 160 m/s 25 ms 4 m 0.1 μT 106 s PL B 156, 122 (1985)

  • U. Pavia

TRIGA 31010/s 1016 1 year Thermal 2200 m/s 10 ms 20 m ~ 1 μT ½106 s ZPh C 43, 175 (1989) ILL HFR 1011/s 1017 1 week Cold 600 m/s 100ms 70 m < 10 nT 107 s PL B 236, 95 (1990) Cont’d. 31018  = 0.52 1 year ~ 108 s ZPh C 63, 409 (1994)

2

( / ) :

nn

N N t   

4 parameters for improvement: n-intensity I, running time T, n-velocity υ, free-flight length L

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Fermilab 18.06.2012 6 n-nbar at ILL

Cold neutrons 

  • 2. ILL n-nbar beam line

Beam stop Annihilation detector

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Fermilab 18.06.2012 7 n-nbar at ILL

Inside the n-nbar beam line (U. Heidelberg)

2.5% beam losses 2.7% beam losses

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Fermilab 18.06.2012 8 n-nbar at ILL

θ(λ) at horn entrance: θ(λ) at horn exit: n-wavelength λ/Å

Divergent n-guide cuts beam divergence θ(λ)

  • T. Bitter et al.,

NIM A 321, 284 (1992)

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Fermilab 18.06.2012 9 n-nbar at ILL

Neutron horn tolerances

Neutron losses Waviness A 2δ = 6 mrad

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Fermilab 18.06.2012 10 n-nbar at ILL

n-nbar beam line

Sun shield Vacuum vessel Mumetal 1mm Movable magnetometer Current lead for radial demagnetization Stationary magnetometer n-Horn Personell transport Rolls for thermal expansion 1 m

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Fermilab 18.06.2012 11 n-nbar at ILL

  • 3. Magnetic field suppression

Philosophy: Long mumetal tube has very good transverse shielding factor S = 2000, but has negligible longitudinal shielding. No transverse field components means: longitudinal field is very uniform. A uniform field can be suppressed by active field compensation. Mumetal tube dimensions given by largest 1000C vacuum furnace available.

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Fermilab 18.06.2012 12 n-nbar at ILL

Transverse active field-compensation

Current leads for radial field compensation Residual field

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Fermilab 18.06.2012 13 n-nbar at ILL

Axial active field-compensation

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Fermilab 18.06.2012 14 n-nbar at ILL

B(t) under active field-compensation

 B(t) from Observatoire Magnetique in Orleans (400 km distance)  B(t) at ILL site  Servo signal  B(t) inside mumetal stable on the nT level

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Fermilab 18.06.2012 15 n-nbar at ILL

Joints of mumetal tubes

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Fermilab 18.06.2012 16 n-nbar at ILL

B(z) with mumetal

10 μT

Mechanical  connection welding connections

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Fermilab 18.06.2012 17 n-nbar at ILL

B(z) with mumetal + active compensation

1 μT

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Fermilab 18.06.2012 18 n-nbar at ILL

B(z) with mumetal + active compensation + demagnetization

  • T. Bitter et al.,

NIM A 309, 521 (1991)

  • U. Kinkel,
  • Z. Ph. C 54, 573 (1992)

μeff = 2106 50 Hz axial plus 1 Hz radial Measured twice daily

10 nT

0.9840.003 quasifree efficiency

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Fermilab 18.06.2012 19 n-nbar at ILL

Can n-nbar be restored in a dressed-neutron arrangement?

Answer: yes, partially, but … DD, NIM A 284, 22 (1989) n-spin rotation vanishes  when dressing with rf-quanta of arbitrary frequency

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Fermilab 18.06.2012 20 n-nbar at ILL

Measurement of B(t) with neutron itself

  • U. Schmidt et al.,

NIM A 320, 569 (1992): With spin-echo method: Spin rotation angle  = Bt = (21)  Quasifree efficiency = 99.8%

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Fermilab 18.06.2012 21 n-nbar at ILL

  • 4. Radiation background

Along beam line:

Lost neutrons, Without baffles: with baffles:

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Fermilab 18.06.2012 22 n-nbar at ILL

Background: Annihilation foil

6LiF shield

C Target Target: exfoliated graphite 1.1 m  0.13 mm thick Shield: 900 tiles 20 m2 2 mm thick

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Fermilab 18.06.2012 23 n-nbar at ILL

Target region

1.4 m 9 cm below n-beam axis

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Fermilab 18.06.2012 24 n-nbar at ILL

Measured background from target

  • F. Eisert et al.,

NIM A 313, 477 (1992) Neutrons incident on target 1.31011 s-1 Neutrons scattered on C 7108 s-1

  • n 5% H

5108 s-1 n's transmitted by LiF shield 3106 s-1 (10-5 neutron suppression!) and mostly transformed to gammas. Gammas emitted from C 3106 s-1 from H 5106 s-1 Total gammas in annihilation detector ~ 107 s-1.

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Fermilab 18.06.2012 25 n-nbar at ILL

Typical crew size during data taking

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Fermilab 18.06.2012 26 n-nbar at ILL

Annihilation detector (INFN Padova and Pavia)

  • 1. Inner Vertex Detector: 10 layers of Limited Streamer Tubes (LST), 0.3 g/cm3, Vertex 4 cm
  • 2. Outer Calorimeter: 12 layers of LST interleaved with Pb/Al planes
  • 3. Timing: Inner and outer planes of Plastic Scintillators (PSc), 700 ps,
  • 4. Cosmic ray rejection with 95 m2 outmost layer of PSc, separated by 10 cm Pb.

60 000 electronic channels Overall nbar detection efficiency 522%. Explosion-proof gas mixture

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Fermilab 18.06.2012 27 n-nbar at ILL

Trigger and data analysis

Cuts to reduce background without losing true events:

  • 1. Cosmic ray veto, 99.5% veto eff.

1.3 MHz, 7% dead time

  • 2. Hardware filter (trigger):

(mostly from scattered neutrons) 2 timing signals in one quadrant 2000 Hz 1 track in vertex detector of same quadrant 800 Hz 1 further timing signal 6 Hz 120 LST channels respond 4 Hz, on tape

  • 3. Software filter on-line

70 Million triggers total deposited energy between 1 and 2 GeV total momentum  0 timing inside-out vertex on target |z| < 15 cm 12 000 events left, mostly cosmics

  • 4. Visual inspection by trained scanners

403 events left

  • 5. Vertex reconstruction by physicists

0 events left

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Fermilab 18.06.2012 28 n-nbar at ILL

Vertex distribution

Target Vacuum tube 15 cm ↕

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Fermilab 18.06.2012 29 n-nbar at ILL

Hardware rejected: Cosmic ray muon

 TOF/ns

OU IU OL IL IR OR ID OD OL IL IR OR

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Fermilab 18.06.2012 30 n-nbar at ILL

Software rejected: Cosmic ray secondary event in the beam tube

 TOF/ns

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Fermilab 18.06.2012 31 n-nbar at ILL

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Fermilab 18.06.2012 32 n-nbar at ILL

Rejected by scanner inspection

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Fermilab 18.06.2012 33 n-nbar at ILL

Rejected after vertex reconstruction

 TOF

 Position information

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Fermilab 18.06.2012 34 n-nbar at ILL

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Fermilab 18.06.2012 35 n-nbar at ILL

Last remaining event nearest to nbar signal

Barycenter too low, rejected

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Fermilab 18.06.2012 36 n-nbar at ILL

Summary

In upscaled n-nbar experiment:

  • 1. Magnetic shielding on 1 nT scale is feasible with state-of-the-art techniques.
  • 2. Radiation background, beam related, should be improved by using

thinner and cleaner target and tighter 6LiF shield.

  • 3. Annihilation detector with higher track resolution is desirable.