I have a more basic time-nut question. Why is it a problem at all? How can the time uncertainty between two known and fixed locations be that large? If they know they have a 70ns uncertainty in time, that would suggest that their time measurement is known to be varying at one or both places. Is this just from a spec or do they see a true variation in time between something, and if so compared to what? Is this time difference or variation between several difference timing devices at each end or is it variation when compared to time of flight of the supposedly same neutrinos? I can not say anything about the accuracy of my absolute time, but the difference and uncertainly comparing the phase difference between different external Osc Tbolts at the same location is way way under 70ns. Sure lots of BASIC things to do to make sure the two Tbolts are set the same so that their oscillator's phase do they agree, such as using the same type antenna and same cable and length, and getting the antenna's location correct, etc, etc, but basic stuff and seems like if using the same basic GPS system at two different locations, what would the additional problems be except to make sure both ends are syncing on the same 100ns 10MHz cycle. I was under the impression that getting down to ns uncertainly differences (and staying there) at theses distances is old stuff using common view GPS. So what are the problems that cause their large timing uncertainty? ws ***************** Good morning, Recently physicists using a neutrino beam from Geneva Switzerland to the Gran Sasso in Italy have reported a measurement of neutrino velocity that is faster than the speed of light. The effect over a 730 km path length is reported as 60 ns, which means that precise timing is required at both ends of the beam to have sensitivity to this effect. The reported result, if true, has major implications for the fundamental understanding of physics. Thus, it is important to carry out independent checks of this measurement. A similar beam exists between Fermi National Accelerator Lab in Batavia IL and the University of Minnesota's Underground Laboratory at Soudan in northeastern Minnesota. This U.S. beam has been used to make a similar measurement, but the GPS timing equipment that was used (Truetime XL-AK, Model 600-101-015) resulted in an estimated uncertainty of about 70 ns in the neutrino time-of-flight, too large to test the recently reported effect. I am one of a group of physicists working with the neutrino beam in the U.S. Although we are also talking with professionals at USNO and NIST, I am interested in possible suggestions from the "Time Nut" community with respect to the following: (a) the possibility of retrospectively improving the existing timing data recorded since 2005 using the Truetime XL-AK, and (b) a quick, low-cost improvement in the timing instrumentation that can be made right away, pending arrangements for techniques such as Two-Way Satellite synchronization. In addition, if there are any "Time Nuts" in the Minnesota area who would like to get more involved in this project, please feel free to contact me at marshak at umn.edu Thank you very much. Marvin Marshak

> I have a more basic time-nut question. Why is it a problem at all? > How can the time uncertainty between two known and fixed locations be that > large? In principal it's simple. But the logistics of equipment and cables and rooms and labs is quite complicated. Read a few documents at http://www.ohwr.org/projects/cngs-time-transfer/wiki and you'll get a sense. All the numbers should add up. But it didn't. The stakes are really high so everyone is double checking their piece of the pie more carefully than a moon landing. > If they know they have a 70ns uncertainty in time, that would suggest that > their time measurement is known to be varying at one or both places. > Is this just from a spec or do they see a true variation in time between > something, and if so compared to what? It's not varying. It was a 3 year experiment and there appears to be a fixed discrepancy of 60 ns in time or 18 meters in distance. Remember it's not certain that the error is in the timing at all; it could just as well be in the distance. Or in the start trigger, or the stop signal, etc. > Is this time difference or variation between several difference timing > devices at each end or is it variation when compared to time of flight of > the supposedly same neutrinos? The latter. > I can not say anything about the accuracy of my absolute time, but the > difference and uncertainly comparing the phase difference between different > external Osc Tbolts at the same location is way way under 70ns. Yeah, this is true for most GPS receivers, which is why it's hard to imagine the problem has anything to do with their GPS timing set up. Their error budget is a couple of ns, stable over years, which is why they use atomic clocks along with dual-frequency carrier-phase receivers in common view, and calibration visits by more than one national UTC lab, etc. It would appear they really did their homework. It's unfortunate that GPS even got brought into the whole neutrino situation because GPS brings with it all sort of UTC and physics and relativity baggage. The experiment could have done relative timing without using GPS at all. It's not about GPS; it's about having synchronized clocks at two locations. There are many ways to achieve that. And when the stakes are high, then one must do it in multiple independent ways. So that's why there's talk of direct fiber links, radio links, satellite links (non-GPS), traveling clocks, etc. > Sure lots of BASIC things to do to make sure the two Tbolts are set the same > so that their oscillator's phase do they agree, such as using the same type > antenna and same cable and length, and getting the antenna's location > correct, etc, etc, > but basic stuff and seems like if using the same basic GPS system at two > different locations, what would the additional problems be except to make > sure both ends are syncing on the same 100ns 10MHz cycle. > > I was under the impression that getting down to ns uncertainly differences > (and staying there) at theses distances is old stuff using common view GPS. > So what are the problems that cause their large timing uncertainty? Yes, it is very old hat to those in the timing community. It just takes time for the rest of the physics community to catch up. Many of us amateurs have better timing at home than most physics laboratories. /tvb

Hi! On 10/24/2011 10:02 PM, Tom Van Baak wrote: >> I have a more basic time-nut question. Why is it a problem at all? >> How can the time uncertainty between two known and fixed locations be >> that large? > > In principal it's simple. But the logistics of equipment and cables > and rooms and labs is quite complicated. Read a few documents > at http://www.ohwr.org/projects/cngs-time-transfer/wiki and you'll > get a sense. All the numbers should add up. But it didn't. > > The stakes are really high so everyone is double checking their > piece of the pie more carefully than a moon landing. I think I have essentially all the equipment needed for both sides. Double frequency receivers with antennas, counters, cesiums etc. Lacking 5071As but... What I don't have is the time to build two complete sets with software etc. Not that I am not trying, as being the time-nut that I am. I think a few other time-nuts such as Tom would also be able to provide the equipment. Again the time to build a pair of functional sets. >> If they know they have a 70ns uncertainty in time, that would suggest >> that their time measurement is known to be varying at one or both places. >> Is this just from a spec or do they see a true variation in time >> between something, and if so compared to what? > > It's not varying. It was a 3 year experiment and there appears to > be a fixed discrepancy of 60 ns in time or 18 meters in distance. > Remember it's not certain that the error is in the timing at all; it > could just as well be in the distance. Or in the start trigger, or the > stop signal, etc. Just re-validating the distance, time and time-distribution would be fun and time-consuming. >> Is this time difference or variation between several difference timing >> devices at each end or is it variation when compared to time of flight >> of the supposedly same neutrinos? > > The latter. > >> I can not say anything about the accuracy of my absolute time, but the >> difference and uncertainly comparing the phase difference between >> different external Osc Tbolts at the same location is way way under 70ns. > > Yeah, this is true for most GPS receivers, which is why it's hard > to imagine the problem has anything to do with their GPS timing > set up. Their error budget is a couple of ns, stable over years, > which is why they use atomic clocks along with dual-frequency > carrier-phase receivers in common view, and calibration visits by > more than one national UTC lab, etc. It would appear they really > did their homework. > > It's unfortunate that GPS even got brought into the whole neutrino > situation because GPS brings with it all sort of UTC and physics > and relativity baggage. The experiment could have done relative > timing without using GPS at all. It's not about GPS; it's about having > synchronized clocks at two locations. There are many ways to > achieve that. And when the stakes are high, then one must do it > in multiple independent ways. This is also why the preliminary PTB report is a bit unfortunate, as it leaves bits and pieces out which the professional should need, but also the larger picture of bias compensations intended for the non-professional on GPS based time-transfer systems. There are many enhancements to be done to be able to present to physics people. The necessary backlog of articles to read is quite high. > So that's why there's talk of direct fiber links, radio links, satellite > links (non-GPS), traveling clocks, etc. Indeed. PTB should have used a traveling clock alongside their GPS receiver system. >> Sure lots of BASIC things to do to make sure the two Tbolts are set >> the same so that their oscillator's phase do they agree, such as using >> the same type antenna and same cable and length, and getting the >> antenna's location correct, etc, etc, >> but basic stuff and seems like if using the same basic GPS system at >> two different locations, what would the additional problems be except >> to make sure both ends are syncing on the same 100ns 10MHz cycle. >> >> I was under the impression that getting down to ns uncertainly >> differences (and staying there) at theses distances is old stuff using >> common view GPS. >> So what are the problems that cause their large timing uncertainty? > > Yes, it is very old hat to those in the timing community. It just takes > time for the rest of the physics community to catch up. Many of us > amateurs have better timing at home than most physics laboratories. Indeed. It's strange that a few private time-nuts have the capability to do this, but it is fully possible. There is a few things like recording RINEX data, get it post-processed alongside some other measurement stuff. So, to come back to the original question, I agree with TvB that the way to go would be to get the assistance from NIST. I think we are a few time-nuts that would be "happy to assist" as a fun treat. :) However, I think that one should combine traveling clock (traveling both directions) with double frequency GPS receivers exercise. It would assist in providing consistency. Cheers, Magnus

On Mon, Oct 24, 2011 at 8:39 PM, WarrenS <warrensjmail-one@yahoo.com> wrote: > I have a more basic time-nut question.  Why is it a problem at all? > How can the time uncertainty between two known and fixed locations be that > large? Hi, sorry I am not checking my non-CERN account very often these days. I do not know the MINOS timing system at all. I can only speak for the CERN-LNGS system. I guess the 70 ns refers to short-term noise, which could be solved by a number of means people in this list know well. We chose a traditional common view arrangement. There is only one thing I'd like to point out in this list: the original goal of both the MINOS and OPERA experiments was *not* to measure the neutrino time of flight. That measurement just turned out to be possible with the available infrastructure and some extra effort in the CERN-LNGS case. These experiments were designed to study neutrino oscillations, i.e. the mechanism whereby a neutrino of one type (electron, muon or tau) turns into a neutrino of another type. In principle, for such experiments, one only needs timing to make sure the neutrinos detected on the far end have a very good chance of coming from your controlled source and not from the Sun or other sources. This can be done without much regard to high precision. Some 100 ns are OK. If neutrino time-of-flight had been the original goal of these experiments, quite a number of things would have been done differently from the start. I am very happy to see the MINOS people are contacting the right specialists. We are very eager to see results from an independent experiment! Cheers, Javier

Le 30/10/2011 20:21, Javier Serrano a écrit : > This can be done without > much regard to high precision. Some 100 ns are OK. If neutrino > time-of-flight had been the original goal of these experiments, quite > a number of things would have been done differently from the start. I read that the OPERA experiments are going to be repeated with more precision. http://www.bbc.co.uk/news/science-environment-15471118