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The OPERA Anomaly - a Quick Summary with Comments

The OPERA Anomaly - a Quick Summary with Comments. Physics 841, Fall 2011 Prof. Brian Meadows. OPERA Experiment (Gran Sasso, Italy). Purpose: Look for “appearance” of ¿ leptons from a º ¹ “beam” from CERN (SPS) 730 km away. At CERN ¼ ( K ) mesons decay ¼ § ( K § )  ¹ § º ¹

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The OPERA Anomaly - a Quick Summary with Comments

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  1. The OPERA Anomaly - a Quick Summarywith Comments Physics 841, Fall 2011 Prof. Brian Meadows Brian Meadows, U. Cincinnati.

  2. OPERA Experiment (Gran Sasso, Italy) • Purpose: • Look for “appearance” of ¿ leptons from a º¹ “beam” from CERN (SPS) 730 km away. • At CERN ¼(K) mesons decay ¼§(K§) ¹§º¹ • The º¹ travel to OPERA Possibly º¹º¿ • At OPERA some º(very few) interact to make either ¹§’s or ¿’s that can be observed. Brian Meadows, U. Cincinnati

  3. Time of Flight Measurement • Individual º’s are not timed by “start” and “stop” signals • There is a profile of positions over some 10’s of meters from which the º’s originate (where the ¼ or K decays can occur) • There is also a profile of positions over several meters where the arriving º’s are observed • A convolution of individual flight times ¢ti can therefore be made to arrive at the most likely value for the mean time of flight T PDF for Interaction of º’s PDF for Birth of º’s Individual ¢t’s Brian Meadows, U. Cincinnati

  4. Baseline Measurement L • By this we mean average distance between the two PDF’s • Briefly, use was made of GPS locators at each end • Some difficulty with this since both ends were under several meters of rock I believe • Local site surveys were also required • Note that GPS devices are reasonably accurate (~ 1m) • They only achieve this precision by making corrections for refraction (a delay) in the ionosphere and for general relativistic effects upon the satellite orbits • The discrepancy reported (60 ns) corresponds to about 20m Brian Meadows, U. Cincinnati

  5. OPERA’s Result • The OPERA team make a “no frills” comparison of T with the baseline length L T – L/c = - 60.7 ± 6.9 (stat.) ± 7.4 (sys.) ns • NOTE this is negative by ~ 6 standard deviations Brian Meadows, U. Cincinnati

  6. A few Comments • º’s are known to experience the MSW effect on passage through material (effectively a refractive index effect). • This makes the discrepancy even worse • Photons also have a (different) refractive index • Gravitational red shift makes the distance from end to end longer than simple geometric length • Again, makes the discrepancy worse – same for photons • A direct “race” between a  and a º would be the best test !! Physics 841, U. Cincinnati, Fall, 2011 Brian Meadows, U. Cincinnati

  7. SN1987a - Race Between º and ° • A supernova occurred in the Large Magellanic Cloud (LMC) approximately 150 Klyr away • This produced much light and nuclear fusion in the implosion produces a huge ºe (and ºe) flux • Both light and º pulses were short and simultaneous • In 1987, about 150,000 years later, this was observed visually on Earth • Within an hour, some large º detectors observed ~2-5 º interactions • Usually only see ~1 or 2 in a 24 hr period • These were AFTER the light pulse, so º’s are SLOWER than light! • If º’s from LMC and CERN are the same, the ones from LMC should have arrived 4 years earlier ! Brian Meadows, U. Cincinnati

  8. Some Observations • The OPERA result is reported as a “discrepancy” • The authors call for other º experiments to check the finding • They also ask for constructive comments on their methodology • One could also ask that any tapes from a few years before SN1987a be checked to see if there were any º “bursts” about 3-4 years earlier • Let’s hope for another nearby supernova soon • Maybe not too near though! • Suppose we have just observed tachyons for the first time !! • It would be a surprise, • It would not help to understand “dark matter” since this seems to hover around galaxies and cannot be made of tachyons A bit like finding the ¹ when we were looking for the Yukawa particle ? Brian Meadows, U. Cincinnati

  9. A few Comments on GPS D Earth • GPS technology has complexities that may shake our blind belief that we can really measure distances of 730 km as accurately as claimed? • Basic principal • 4 satellites in each of 6 orbits equally oriented wrt the equator • Measure distance D and use triangulation to find position on Earth Physics 841, U. Cincinnati, Fall, 2011 Brian Meadows, U. Cincinnati

  10. GPD … • Two effects it has to deal with are • The ionosphere slows down the signal by an amount \propto the electron density that varies with Sun activity, etc. • Satellites are not stationary(!) and their orbits precess in the solar wind and due to GR. • A target on Earth like a car also moves (though CERN and Opera tend to stay where they are!) • So corrections of several 10’s of feet are required. [We DO assume that the signals do not travel with speed >c, though!] Physics 841, U. Cincinnati, Fall, 2011 Brian Meadows, U. Cincinnati

  11. Two solutions D2 D1 Earth • Differential GPS • The position can be found using signals from a nearby, fixed station with known position and for which the ionosphere effect is similar. • Only works for distances up to ~ 30 km. • Use of two frequencies • Two frequencies calibrate the ionosphere effect • Works for larger distances but uncertainty is larger. Physics 841, U. Cincinnati, Fall, 2011 Brian Meadows, U. Cincinnati

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