THE DISTANCE FROM CERN TO LNGS

D. Missiaen

M. JONES, D. MISSIAEN, CERN, SWITZERLAND

MATTIA CRESPI, G. COLOSIMO, A. MAZZONI, UNIVERSITY LA

SAPIENZA, ROMA, ITALY

STEPHANE DURAND, ESGT, LE MANS, FRANCE

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Introduction

First determination of the parameters

Redetermination of these parameters

Possible additional controls that can be added and

have been realised

Conclusion

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Outlook

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CNGS is project which aims at sending neutrinos from CERN to the Gran Sasso National Laboratory(LNGS)

The goal was the study of the neutrino oscillation

conversion of a given neutrino type into another during their travel from the source to the detector (for example, muon-type to tau-type neutrino oscillation).

Several experiments are hosted in the underground lab (OPERA, ICARUS and Borexino)

The distance between CERN and LNGS is about 730km

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Introduction

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The project was approved at the beginning of the 2000’s

The production of the neutrinos at CERN started in 2006

On May 31st, 2010, the first tau-neutrino “appearing” out of several billion of billions muon neutrinos sent from CERN !

September 2011 : The Experiment Opera announced that «The neutrinos are circulating faster than the speed of light»

The CERN SUrvey team was of course involved in these announcement as it participates since beginning of 2011 in the determination of the distance in collaboration with the University of Roma appointed by Opera for this calculation

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Status and Results

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Geographical situation

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GNSS measurements between benchmarks in CERN

and Gran Sasso to get co-ordinates in a global co-

ordinates system

A network of measurements to link the benchmarks on

the surface at CERN to the SPS/CNGS tunnel points

including a vertical descent

A network of measurements to link the benchmarks on

the surface at Gran Sasso to the LNGS lab

including a traverse of 11 km from the extremities of the

motorway tunnel to the lab

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Ingredients to calculate the distance

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Initial calculation was done in the late 90’s

The angular precision requested at that time in both H

and V was ~15 arc seconds at 3s (~50m at 730km)

The orientation of CERN site was vital NOT the

distance between both sites

GPS measurements done on both sites

CERN network was known at +-5mm

2 new points were determined in LNGS

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Initial determination of the parameters

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No link between surface benchmarks and tunnel at

CERN

the previous link was done in the 80’s for the LEP

The uncertainty was considered to be less than 20-30

mm

A redetermination of the transformation between the

Cern Co-ordinate system (CCS) and ITRF97 (ep

1998.5) was realised with the collaboration of OFT

(Federal Office of Topography))

A new geoid was defined as the levelling

measurements are linked to it

Co-ordinates of the CERN target known in CCS

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Initial determination of the parameters

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Link between surface benchmarks and Experiments at LNGS

As the access to the lab from Surface is a road tunnel of 11 km and it was difficult and expensive to close the motorway

The original survey data and design plans were used to determine co-ordinates of some reference points

The LNGS points were then transformed in the ROMA40 reference frame, then in ITRF97 and then in the CERN Co-ordinate System (CCS)

We got two angles and a distance 730520.3m

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Initial determination of the parameters

D

A

C

B E

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Redetermination of the distance

The OPERA team observes some anomaly of 60 ns in the speed of neutrinos (equivalent to 15-20 m)

Interest for the distance CERN-OPERA

Main uncertainty was link in LNGS

July 2010 a traverse was done to link 4 benchmarks and the OPERA experiment using a total station TS30 (no gyrotheodotite measurements)

Local system taking into account the geoid undulation

The OPERA reference point accuracy estimated to be with 200mm

September 2010, GNSS measurements done of the 4 benchmarks and on 3 permanent antennas of EPN

Data processing in ETRF2000

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Redetermination of the distance

On the CERN site, co-ordinates were transformed to

ITRF97 and then to ETRF2000

The estimated accuracy was still 20-30 mm

New distance calculated 730534.61m

~ +14 m difference coming from the difference of

point measured in LNGS

All computations were done by the University of Roma

Global accuracy 200mm

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Possible additional controls

Meeting at CERN in February 2011

Independant treatment of GPS and traverse

measurements

Simultaneous GNSS measurements on both sides

Add gyrotheodolite in the traverse in LNGS

Link between surface benchmarks and tunnel at CERN

These possibilities were considered taking into

account difficulty and cost w.r.t the decrease of the

uncertainty

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Additional distance controls

GNSS measurements done in Spring 2011

No major changes in the accuracy estimate

Recalculation of the 2010 and 2011 GNSS

measurements

Done by CERN in June 2012 with the collaboration of

ESGT using Bernese (ITRF2008 >ETRS89)

transformation into CCS with a Helmert transformation

All coordinates in CCS gives a new estimated distance

of 730534.545 (difference of 75 mm)

GPS Measurements

Permanent

GPS Station

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Link between benchmarks and tunnel

On the CERN site the link was done between points at

the surface and some points on the CNGS line

GPS benchmarks

Others stations

BCT : origin of the

timing measurements

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Vertical descent

Shaft of 50-60 m deep

The plumb bobs technique

Forced centring systems

Station Station Station

BCT in

CNGS/TT40

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Vertical descent

Shaft of 50-60 m deep

The zenith optical plummet

Forced centring systems

Station Station Station

BCT in

CNGS/TT40

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IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Vertical descent

Results

Difference between points at surface and plumb bobs points underground are in the range of 0.1 mm

Differences with zenith optical plummet and the value was worse 0.8 mm

As a whole surface pillars and CNGS beam components relative position has been found to be within

an accuracy of 16 mm

But with an rotation of 14 mgon

This was nonetheless a confirmation of our estimate of 20-30 mm

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The distance has been redetermined with several

types of measurements

The estimated accuracy of the distance between CERN

and LNGS is within 200mm

A number of different controls have been carried to

minimise the risk of measurements and/or

computations

The error could be reduced by adding gyrotheodolite

measurements on the LNGS side

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Conclusions

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Finally it appered that a connection fault in the timing

system was at the origin of the 60ns anomaly

EINSTEIN is still right : particles are

NOT going faster than c

IWAA2012, 10-14 Sep. 2012, FNAL, Batavia D. Missiaen

Conclusions (cont’d)