• fast neutrinos and bad connections

    From RichD@21:1/5 to All on Tue Jul 7 19:35:15 2020
    Recall a few years back, a physics lab in Italy reported
    faster than light neutrino observations. After some ado,
    they finally diagnosed a dodgy optical interconnect.

    How does that result occur? An intermittent interface
    would produce a broken signal, or reduced RMS power, or
    perhaps data bit errors, if used for communication.

    But how does a faulty connection result in a spuriously
    high velocity measurement?

    --
    Rich

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  • From Joe Gwinn@21:1/5 to r_delaney2001@yahoo.com on Wed Jul 8 10:29:57 2020
    On Tue, 7 Jul 2020 19:35:15 -0700 (PDT), RichD
    <r_delaney2001@yahoo.com> wrote:

    Recall a few years back, a physics lab in Italy reported
    faster than light neutrino observations. After some ado,
    they finally diagnosed a dodgy optical interconnect.

    The facility was in Italy, but the work was done by CERN.


    How does that result occur? An intermittent interface
    would produce a broken signal, or reduced RMS power, or
    perhaps data bit errors, if used for communication.

    But how does a faulty connection result in a spuriously
    high velocity measurement?

    It was explained to me by an engineer from CERN a few years ago, but I
    cannot find the reference right now. The delay (in the nanoseconds)
    was because an impedance bump due to the bad connection acted as an
    low pass filter, slowing the critical edge just enough. As I recall,
    the offset was something like 60 ns.

    Joe Gwinn

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  • From torty5737@gmail.com@21:1/5 to Joe Gwinn on Fri Jul 10 05:59:36 2020
    On Wednesday, 8 July 2020 15:30:04 UTC+1, Joe Gwinn wrote:
    On Tue, 7 Jul 2020 19:35:15 -0700 (PDT), RichD
    <r_delaney2001@yahoo.com> wrote:

    Recall a few years back, a physics lab in Italy reported
    faster than light neutrino observations. After some ado,
    they finally diagnosed a dodgy optical interconnect.
    ...
    It was explained to me by an engineer from CERN a few years ago, but I
    cannot find the reference right now. The delay (in the nanoseconds)
    was because an impedance bump due to the bad connection acted as an
    low pass filter, slowing the critical edge just enough. As I recall,
    the offset was something like 60 ns.

    The implication being that the fibre is carrying discrete pulses to provide a time reference for the detected particles, rather than e.g. a network link.

    Hence, changing the arrival time of the optical pulse alters the measured speed of the detected neutrinos.

    Is that correct?

    Thanks

    Henry

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  • From Joe Gwinn@21:1/5 to torty5737@gmail.com on Fri Jul 10 14:21:46 2020
    On Fri, 10 Jul 2020 05:59:36 -0700 (PDT), torty5737@gmail.com wrote:

    On Wednesday, 8 July 2020 15:30:04 UTC+1, Joe Gwinn wrote:
    On Tue, 7 Jul 2020 19:35:15 -0700 (PDT), RichD
    <r_delaney2001@yahoo.com> wrote:

    Recall a few years back, a physics lab in Italy reported
    faster than light neutrino observations. After some ado,
    they finally diagnosed a dodgy optical interconnect.
    ...
    It was explained to me by an engineer from CERN a few years ago, but I
    cannot find the reference right now. The delay (in the nanoseconds)
    was because an impedance bump due to the bad connection acted as an
    low pass filter, slowing the critical edge just enough. As I recall,
    the offset was something like 60 ns.

    The implication being that the fibre is carrying discrete pulses to provide a time reference for the detected particles, rather than e.g. a network link.

    As you surmise, these are not data network links. Pulses in optical
    fiber travel at almost exactly 2/3 the speed of light.


    Hence, changing the arrival time of the optical pulse alters the measured speed of the detected neutrinos.

    Is that correct?

    Yes. The time reference pulses were delayed, making the data pulses
    seem to arrive earlier than expected.


    Joe Gwinn

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