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
2
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)
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