Seminar at LNGS  May 17, 2012

Yuri Kamyshkov/ ITEP-Moscow and University of Tennessee

email: yurikamyshkov@gmail.com

Status Review and New Searches of n n with Cold Neutrons

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Observation of violation of Baryon number is one of the pillars of modern Cosmology and Particle Physics

- it is required for explanation of Matter-Antimatter asymmetry BAU (Sakharov)- it follows from the inflation (Dolgov, Zeldovich)- it is motivated by GUT models

Proton decay with B = 1 so far has failed to demonstrate existence of BV

(B L) must be violated idea of Leptogenesis with L = 2.Majorana nature of ’s should experimentally demonstrate L = 2,however experimental prove of Leptogenesis will be hardly possible.

Alternative search is transformation with B = 2 and (B L)V

New developments in NNbar search in US within the “Project X”

n n

Is Neutron a Majorana Particle? Is Neutron a Majorana Particle? In the famous E. Majorana 1937 paper “Teoria simmetrica dell’elettrone e del positrone”,Il Nuovo Cimento, v.14, 1937, pp. 171-184:

“ ... this method ... allows not only to cast the electron-positron theory into a symmetric form, but also to construct an essentially new theory for particles not endowed with an electric charge (neutrons and the hypothetical neutrinos).”

(translated by L. Maiani)

This mixing fraction must be small (otherwise it would be already observed) unless there are some suppression conditions or mechanisms present. 3

However, the presence of some small fraction of the antineutron component in the neutron wave function can not be excluded, and the question whether neutron is Majorana particle should remain.  

But antineutron discovered in 1956  by B. Cork et al. @ LBL was turned out  to be a particle different from neutron. 

Such mixing occurs when some symmetry is broken

• Gauge symmetry mixing of U(1) x SU(2) in SM Z0 and

• Strangeness, beauty in

• Flavor number in neutrino flavor oscillation

• Lepton number in Majorana neutrinos

• Baryon number

0 0 0 0, K K B B

emn n

e en n

n n

4

B and L are “accidental symmetries” might be violated: B, L 1

e.g. conserves B and L: B=0 and L=0e

n p e n- + +

B and L are connected via conservation of angular momentum.L = B . (BL) = 0 or (BL) = 2. Is (BL) conserved ?

Naively (BL) is strongly violated in regular matter: #n + #p #e ≠ 0

However, on the scale of the universe it might be compensated bythe unknown number of relic neutrinos and antineutrinos …

Standard Model conserves (BL) but violates B, L and (B+L) at tiny level at present temperature [G. ‘t Hooft, 1976];

at electroweak scale fast (B+L) violation would wipe out BAU if the latter is due to (BL) conservation processes at GUT scale

[V. Kuzmin, A. Rubakov, M. Shaposhnikov, 1985].

5

Starting point for Leptogenesis [Fukugita, Yanagida, 1986]

66

LBNE Physics Working Group Report arXiv:1110.6249v1 [hep-ex]

J. L. Raaf @ IF-2011

“Proton decay is not a prediction of baryogenesis.” [Yanagida, 2002]

are motivated by (B‐L) conserving models

Several experiments are currently searching for Majorana neutrino in “neutrinoless double beta decay”. Majorana neutrinos means and L = 2, thus violating (BL) by 2.

n n«

If (BL) is violated by 2 that also means that B=2 should exist and thus is possible

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n n«

Some history of ideasn n«

There are no laws of nature that would forbid the N Nbartransitions except the conservation of "baryon charge (number)"

M. Gell-Mann and A. Pais, Phys. Rev. 97 (1955) 1387L. Okun, Weak Interaction of Elementary Particles, Moscow, 1963

N Nbar -like process was suggested as a possible mechanism for explanation of Baryon Asymmetry of Universe V. Kuzmin, 1970

Recent models explaining neutrino masses, low-scale baryogenesis, connecting with dark matter, involving gravity, extra-Ds, predicting new particles at LHC…

K. Babu, R. Mohapatra et al; Z. Berezhiani et al;A. Dolgov et al; G. Dvali and G. Gabadadze, …

N Nbar works within GUT + SUSY ideas. First considered and developed within the framework of L/R symmetric Unification models

R. Mohapatra and R. Marshak, 1979 …

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1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012

LHC nn

Low QGmodels

GeVDvali & Gabadadze (1999)

( )Scales of n n B L V -

32 WKLB

1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020

nn nn

5 LB

GeVLB

Supersymmetric Seesaw for m

BL , LR

Mohapatra & Marshak (1980)

Dutta-Mimura-Mohapatra (2005)

Non-SUSYmodel

Left-Rightsymmetric

GUTSUSYGUTPDK

Plankscale

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Experimental motivation!large increase of sensitivity:factor of 1,000 is possible

Baryogenesis at TeV scaleBerezhiani et al (2005)Babu et al (2006)Dolgov et al (2006)

Goity, Sher (1994)

BerezhianiBento (2005)

nnbar transition probability

, 0

mixed n-nbar QM state

H

;

part different for and

n

n

n n n n n n

n n

n

n

E

E

E m U E m U

U U V n n

aa

æ ö÷ç ÷çY = ÷ç ÷÷çè ø

æ ö÷ç ÷ç= ÷ç ÷÷çè ø

= + = +

= ¬

-mixing amplitude

All beyond SMphysics is here

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where is a potential symmetrically different for and (e.g. due to non-compensated Earth mag. field, or nuclear potential); is observat

2 222

2 2 sin

V n

t

n

n nV tP t

Vaa

a

æ ö÷çæ ö ÷ç÷ ÷ç ç÷ ÷⋅ç ç÷ ÷ç ç÷ ÷çè ø ÷ç ÷çè ø+ ⋅=

+

ion time in an experiment.

In ideal situation of no suppression i.e.

"vacuum oscillations" : 0

and experimentally ~ 0.1 s to 1 s 0t

V =

22

n nnn

tP t

at

æ öæ ö ÷÷ çç ÷= ´ ÷ = çç ÷÷ çç ÷ ÷çè ø è ø

24 is characteristic "oscillation" time [ , as presently 2 wn10 kno ]nn eVa

at -< ⋅=

25 26 observable Predictions of t effect around heoret ~ 1ical models: 0 10 eVa - --

2 Sensitivity (or figure of merit) is nN t ´

11

2t

P Nt

æ ö÷ç ÷µ ⋅ç ÷ç ÷çè øLet’s try to configure such an experiment

• Slowest possible neutrons with maximum observation time

• Need many neutrons: reactor or spallation source Produced as ~ 2 MeV

Even moderated to 300K vn ~ 2,200 m/swith broad Maxwell-Boltzmann spectrum

• Earth magnetic field shielding: 2 1 10 B B nTt

m < < -

• Vacuum < 105 Pa

• Concept: after time t some of the neutrons might be spontaneously converted to antineutrons and will annihilate with target producing a star of pions.

• Distance ? L

22

22

det

n

AN I I

LL

tv

= ⋅DW = ⋅

=

Adet

• Gravity effect on horizontal beam

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Doesn’t matter here

HFR @ ILL 57 MW

Cold n-source25 D2

fast n, background

Bended n-guide Ni coated, L ~ 63m, 6 x 12 cm 2

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H53 n-beam~1.7 10 n/s. 11

(not to scale)

Magnetically shielded

95 m vacuum tube

Annihilation target 1.1mE~1.8 GeV

Detector:Tracking&

Calorimetry

Focusing reflector 33.6 m

Schematic layout ofHeidelberg - ILL - Padova - Pavia nn search experiment

at Grenoble 89-91

Beam dump

~1.25 10 n/s11

Flight path 76 m< TOF> ~ 0.109 s

Discovery potential :N tn 2 91 5 10. sec

Measured limit : nn 8 6 107. sec

At ILL/Grenoble reactor in 89‐91 by Heidelberg‐ILL‐Padova‐Pavia Collaboration M. Baldo-Ceolin et al., Z. Phys., C63 (1994) 409

Previous n‐nbar search experiment with free neutrons

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2 9 2

8

No candidates observed.

Measured limit for a year of running:

with L ~ 76 m and 0.109 sec

measured 1.606 10

sensitivity:

No GeV ba

1.5 1

c

0 s

kgroun

s

d!

"ILL sensitivity unit"

0.86 10

nn

nnt

P

N t

st

-

=

< ´

⋅ = ´

> ´

~ 700 m/sn

v

13

Top view of horizontal experiment

n nbar for bound n inside nuclei is strongly suppressed

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2

Neutrons inside nuclei are "free" for the time: ~ ~ ~ 2.2 1030

each oscillating with "free" probability

1and "experiencing free condition" times per second

well

nn

t sE MeV

t

Nt

t

-D ´

æ öD ÷ç ÷= ç ÷ç ÷çè ø

=D

2

V.Kuzmin)(

.

1 1Transformation probability per second: A

A nn

tP

tt t

æ ö æ öD ÷ ÷ç ç÷= = ´ ÷ç ç÷ ÷ç ç ÷÷ç Dè øè ø

22 1

22

AIntranuclear (exponential) lifetime:

1where ~ ~ 4.5 10 is "nuclear suppression factor"

nnnn

R st

Rt

tt t

-´D

= = ´D

(Friedman and Gal, 2008)22 1(Oxygen) 5 10 s ( 15%)R -» ´ 14

16 2 56 40

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Actual nuclear theory suppression calculations for , , , by C. Dover

et al; W.Alberico et al; B.Kopeliovich and J. Hufner, and most recently by

Friedman and Gal (2008) for with correcti

O D Fe Ar

O on of factor of 2 to the previous´

Bound neutron N-Nbar search experiments Bound neutron N-Nbar search experiments

* Not yet published

Observed improvement is weaker than SQRT due to irreducible background of atmospheric ’s.

Still possible to improve a limit(though slowly) but impossible to claim a discovery.

Experiment Year A nyear  (1032) Det. eff. Candid. Bkgr. nucl , yr (90% CL)

Kamiokande 1986 O 3.0 33% 0 0.9/yr >0.431032

Frejus 1990 Fe 5.0 30% 0 4 >0.651032

Soudan‐2 2002 Fe 21.9 18% 5 4.5 >0.721032

Super‐K 2007 O 245.4 10.4% 20 21.3 >1.81032

Super‐K  2009 O 254.5 12% 23 24 >1.971032

SNO * 2010 D 0.54 41% 2 4.75 >0.3011032

Super‐K 2011 O 245 12.1% 24 24.1 >1.891032

Vacuum N-Nbar transformation from bound neutrons:

Best result so far from Super-K in Oxygen-16

16

321.89 10 (90% CL)O

yrt > ´

16

22 1if 5 10 from Friedman and Gal (2008) O

R s-= ⋅

16 times higher than sensitivity of ILL expt.´

24 observed candidates;

24.1 exp. background

ìïï¬ íïïî

16

8 24(from bound) 3.5 10 or 2 10s eVt a - > ´ < ´

2 freenucl nnRt t= ´

8ILL limit (1994) for free neutrons: 0.86 10nn st > ´

Free Neutron and Intranuclear NNbar Limits Comparison

Large improvement with free-neutron experiments is possible

2nucl nnRt t= ´

intranuclear search experiments:Super-K,Soudan-2Frejus

Free neutronsearch limit (ILL)

Goal of new NNbar searchwith free neutrons

Factor of 1,000 sensitivity increase

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udd

udd

Existing intranuclear NNbar limits need to be re-evaluated

Theoretical nuclear NNbarsuppression model is incomplete

n

n

'sp

q

q4q

All these processes include the same amplitude and result in the same indistinguishable final state (of ~ 5 s)

Suggested by S. Raby (2011)

J. Basecq and L. Wolfenstein (1983)

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Usualapproach

Nt2

• Use many neutrons (spallation source or reactor)

• Use slow neutrons: cold, VCN, UCN

• Neutron manipulation by mirror reflections

• Neutron manipulation by gravity

How the major improvement in sensitivity can be made?

20

22

Staged constructionTo start ~ 2015

H. S

him

izu,

KE

K/J

apan

3/2011 statusR=50%at m=10

Progress in neutron super-mirrors

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Neutron reflection was first explained by E. Fermi

Can reflect neutrons withvT 70 m/s

Neutron reflection

1000 kWp, 1-3 GeV

Pb: OD=20 cm, L=60 cm D2O : OD=40 cm, L=70 cm

Liquid D2 : OD=60 cm, L=80 cm

Should try to use neutrons produced within 4rather than few % of 4 for most n-beam lines

Spallation neutrons produced with kinetic energy ~ 2 MeVshould be moderated down to thermal T~300K velocities ~ 2 km/sand then to the cryogenic velocities ~ 600 m/s. Some fraction of Maxwellian spectrum will have velocities 100 m/s

```

Heavy Metal Target: Pb, Bi, W, Ta

Heavy Water

Liquid Deuterium

UCN Converter

High-m Super Mirror

Carbon Reflector

Dedicated spallation target with VCN-UCN converter

(view along the beam)

SolidDeuterium

Scheme being optimized by simulations 25Cold Neutrons

Ultra-Cold Neutrons (UCN): 6 m/sVery-Cold Neutrons (VCN): 100 m/s

vv<<

E.g. using existing MINOS vertical shaft for housing the experiment.

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Vacuum Tube andMag. ShieldL ~ 100 mDia ~ 5 m

FocusingSuper-m ReflectorL ~ 20m

L~100 mdia ~ 4 m

o New concept of large focusing neutron reflector using super-mirror.Sensitivity increases as ~ L2

o Proton beam from MI or Project X; with power > 200 kW

o Dedicated spallation target optimized for cold neutron production

o “Background free” detector:one event = discovery !

o Expected sensitivity > 2,000 ILL units

27

The conceptual scheme of antineutron detectorfor NNbarX experimentplanned at Fermilab

5n C p+

The idea of backgroundlessdetector was demonstrated by ILL experiment 28

29

http://arxiv.org/abs/1203.1035Eur. Phys. J. C (2012) 72:1974

PNPI Experiment to search for nn disappearance at ILL/Grenoble reactor, A. Serebrov et al (2009)

NIM A611 (2009) 137-140

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det ( ) ( )( )

( ) ( )B B

BB B

N t N tA t

N t N t-

-

-=

+

Measured asymmetry ~ (71.4)104 (~5)n n oscillation time ~ 2-5 sec;resonance mag. field ~ 0.1 G

Measurements of UCN life-time asymmetryunder alternation of vertical magnetic field

B

10 m/s neutron falls 175 m for ~ 5 s.

Pulsed target operation would explores different velocities

Controlled variation of lab field B and its direction should detect resonance in the disappearance

If one absorbs all neutrons in the max of disappearance it will be possible to observe the regeneration effect (appearance on neutrons)

B

Let’s assume that ~ 175 m long verticalshaft can be used

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NNbar Summary 

If  NOT discovered:

• within the reach of improved experimental sensitivity will set a new limit on the stability of matter exceeding the sensitivity of XL nucleon decay experiments.Will test/constraint  models of low scale baryogenesis. 

New physics beyond the SM can be discovered by new NNbar search experimentNew direction within US Intensity Frontier initiative Requires R&D on design of dedicated optimized spallation UCN‐VCN sourceExpected improvement in N‐Nbar search sensitivity is a big factor of >1,000 that is within the predicted range of several models  Without  a background one event can be a discovery !     Effect can be uniquely checked/controlled by weak magnetic field             

If  discovered:

• NNbar will establish a new force of nature and a new phenomenon of (BL)V leading  to the exploration of the new physics beyond the SM at the energy scale  above  TeV. Can be also an interesting CPT laboratory measuring  n nm -D

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