Accelerator searches Accelerator searches

for for oscillations oscillations

Accelerator searches Accelerator searches

for for oscillations oscillations

Ioannina, 20-23 April Ioannina, 20-23 April 20002000

Roumen TzenovCERN and University of Sofia

Legend

• Introduction to neutrino oscillations• Short baseline accelerator

searches for – CHORUS– NOMAD

• Future long baseline accelerator searches

Associate neutrino flavour with the charged lepton flavour as seen in charged-current interactions:

For massive neutrinos: flavour eigenstate need not be a mass eigenstate but can be a coherent superposition:Mixing matrix U is unitary

The propagation of different mass eigenstates leads to flavour oscillation in vacuum:

Simplification for 2 mixing flavours with mixing angle (phase ):

Interactions are now nondiagonal with the mass eigenstates!

A U e Um

iM L

Em

m

m

2

2 *

A B

l m mm

U

Ue

e

i

i

cos sin

sin cos

Neutrino mixing

The probability that a neutrino oscillates (changes flavour):

With definition:

To have a large effect:

Maximum at 1/4 oscillation length

P M eVL km

E GeV

sin sin .2 2 2 22 127

M M M222

12

M eVL km

E GeV2 2

1

L

EM

1

22127

.

Neutrino oscillations

Two parametric oscillation plot

10 -1210 -1110 -1010 -910 -810 -710 -610 -510 -410 -310 -210 -1110100

m2

(

eV

2)

LSND

Cosmologically relevantSolar + seesaw + DM ?

Atmospheric

Solar (MSW)

Solar (vacuum oscillation)

KamiokandeSuperKamiokande

10 -5 10 -4 10 -3 10 -2 10 -1 1.sin2 2

e

e

e

CHORUS and NOMAD

The The CollaborationCollaboration

Belgium (Brussels, Louvain-la-Neuve), CERN, Germany (Berlin, Münster), Israel (Haifa), Italy (Bari, Cagliari, Ferrara, Naples, Rome, Salerno),Japan (Toho, Kinki, Aichi, Kobe, Nagoya,Osaka, Utsunomiya) ,Korea (Gyeongsang),The Netherlands (Amsterdam), Russia (Moscow), Turkey (Adana, Ankara,Istanbul)

• appearance in the SPS WBB beam via oscillation

• P() down to 1•10-4 for m2 ~10 eV2

• direct detection in 770 kg nuclear emulsion target

Tag: visible 1- and 3- prongs

decay of primary -lepton

(decay path ~1.5 mm)

CHORUS Main objectiveCHORUS Main objective

-

h-ne- e+--n

R

“Kink”

CHORUS NOMAD

124 m 290 m 408 m

450 GeVSPS

protonsBeryllium

target horn reflector vacuum tunnelearth/ironshielding

CERN West Area Neutrino CERN West Area Neutrino FacilityFacility

<L> ~0.6 km; L(rms)/L~0.2

• WBB, <E > = 26.6 GeV

•~5•10 protons on target•~840K CC in CHORUS

• CC / CC ~ 3. 10

19

-6

(~0.1 background event)(~0.1 background event)(~0.1 background event)(~0.1 background event)

WANFWANF West Area West Area Neutrino Facility Neutrino FacilityWANFWANF West Area West Area Neutrino Facility Neutrino Facility

The “horn”

SPS and WANF SPS and WANF (() neutrino beam) neutrino beamSPS and WANF SPS and WANF (() neutrino beam) neutrino beamProtons on neutrino from 1994 to 1998

0.0E+00

2.0E+18

4.0E+18

6.0E+18

8.0E+18

1.0E+19

1.2E+19

1.4E+19

1.6E+19

1.8E+19

2.0E+19

1 21 41 61 81 101 121 141 161 181 201 221

19941995199619971998

protons

number of days of operation

1994

1998

1997

1995

1996

CHORUSCHORUS detectordetectorCHORUSCHORUS detectordetector

770 kg emulsion target

and scintillating fibre tracker

Calorimeter

Air core spectrometer andemulsion tracker

Air core spectrometer andemulsion tracker Veto plane

Muon spectrometerMuon spectrometer

- -

h-h-

T=5°T=5°Nucl. Instr. Meth A 401 (1997) 7

Scintillating fibreScintillating fibretrackerstrackersScintillating fibreScintillating fibretrackerstrackersNucl. Instr. Meth A 412 (1998) 19

~ 2 mrad, xy~150 m

External electronicExternal electronicdetectors:detectors:External electronicExternal electronicdetectors:detectors:

P(h±)<20 GeV/cp/p ~25%

P(h±)<20 GeV/cp/p ~25%

E/E ~35%/E(GeV) E/E ~35%/E(GeV)

• sign and momentum of pions

• Hadronic and e-m shower energy and direction

• Muon momentum and idEvent pre-selection and

post-scanning analysis 3<P(±),GeV/c<100

p/p = 11-20% 3<P(±),GeV/c<100

p/p = 11-20%

Neutrino data-taking collection efficiency 1994-1997

N.B. Longest/Largest emulsion exposure ever done

Predictions and Scanback

tan

1947, first nuclear emulsions. Lattes et al., Brown et al.:

Discovery of Discovery of ee

Nuclear emulsion yesterdayNuclear emulsion yesterday

Target = 4 stacks (1.4Target = 4 stacks (1.41.4 m1.4 m22))

1 stack = 36 1 stack = 36 platesplates

MIP : 30 MIP : 30 40 grains / 100 40 grains / 100 mm

– Grain size ~ 0.3 mm

– Angular resolution 1.5 mrad 80 80 mm

100

1

00

mm emulsion 350 mkm

base 90 mkm

1/4 plate1/4 plate

CHORUS emulsion plateCHORUS emulsion plate

CCD and XYZ stage

CCD and XYZ stage

New Track SelectorNew Track Selector

Host CPUHost CPU

Network Network data data

storagestorage

CHORUS automatic microscopesCHORUS automatic microscopes

Megapixel CCD and XYZ stageMegapixel CCD and XYZ stage

High Performance optics

High Performance optics

DSPsDSPs

Processing ClusterProcessing Cluster

CHORUS automatic microscopesCHORUS automatic microscopes

1 m

Inside a “vertex plate”Inside a “vertex plate”

-54 m-54 m

-36 m-36 m

-21 m-21 m

0 m0 m

View size: 120x150 View size: 120x150 mm22

Focal depth : ~3 Focal depth : ~3 mm

Red frame: ~30x40 Red frame: ~30x40 mm22

beam

Decay searchDecay searchDecay searchDecay search

Offline selectionOffline selection small impact parameter between parent and daughter kink point is in the vertex plate

- kink detection (parent search)

or h

PrinciplePrinciple:Parent track () can be detected bywider view and general angle scanningat the vertex plate

Impact parameter

scan-back track

general scanning area

Off-line video-image analysisOff-line video-image analysisCHORUS Emulsion Display

sD

*s NDN

Phys. Lett. B 435(1998) 458-464.

Manual scanning on special Manual scanning on special events:events:Diffractive D*s production, double leptonic decay

* 0 decay search not finished yet (1996-1997), not

included in current results

Status of Phase I scanningStatus of Phase I scanningStatus of Phase I scanningStatus of Phase I scanning

kink

11CC

CC

)(BrNA

AS

Det efficiency:

Ratio of Acceptances

Located Vertexes

S=N if P=1A=detector acceptanceN=normalization=Kink finding efficiency

In the same way, it is applied to the 0 sample

• 1 sample (--)– charm production from antineutrino CC (with primary

lepton (e+ or +) unidentified

contamination of the beam

• 0 sample (-h-)

– charm production from antineutrino CC

– 1-prong nuclear interaction without visible recoil or

nuclear break-up (White kinks)

BackgroundBackgroundBackgroundBackground

~10-6 / N~10-6 / N

~10-7 / N~10-7 / N

~2•10-6 / N~2•10-6 / N

~2•10-5 / N~2•10-5 / N

Includes also 17% systematic error (NIM A320 (1993) 331)

Includes also 17% systematic error (NIM A320 (1993) 331)

CHORUS current limit

sin2 2 < 8 •10-4• No candidates found

• n CC (expected) = P•S,

•S = 6003 ± 17% (syst)

•P < 2.38 / 6003 =

4•10-4 (@ 90% C.L.)

• No candidates found

• n CC (expected) = P•S,

•S = 6003 ± 17% (syst)

•P < 2.38 / 6003 =

4•10-4 (@ 90% C.L.)

sin2 2 sin2 2

m2/e

V2

m2/e

V2

Current ResultCurrent ResultCurrent ResultCurrent Result

OutlookOutlook::OutlookOutlook::• Phase I scanning: Going to finish this year

Expected gain in sensitivity:

• ~1.2 from 1 (short decays, statistics)

• ~1.2 from 0 (3prongs, 0 96+97)

• Phase II scanning and analysis: years 2000-2001• New generation of automatic systems• Upgraded predictions• 3prongs dedicated search e ? (electron id by MS in emulsion)• Full vertex analysis

(NETSCAN, General tracking) charm physics:|Vcd|2,cc,D+/D0

PP < 1.0•10 < 1.0•10 -4 -4 (in absence of (in absence of -candidates)-candidates)

What to dofurther with accelerator beams?

Long baseline experiments

Long base line beams compared to WANF

MINOS detector

ICANOE detector

OPERA detector

200 ton iron/emulsion sandwiches + muon identificator

OPERA module

Long baseline experiments’ claims ...

Conclusion

Current short baseline accelerator searches for oscillations have almost done their job;

No oscillations seen (so far) for large m2 and small mixing angles;

Atmospheric neutrino data suggest, on the opposite, small mass difference and large mixing angle;

Several long baseline accelerator experiments are on the start scratch to clarify the issue...