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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

The OPERA Anomaly - a Quick Summarywith Comments

Physics 841, Fall 2011

Prof. Brian Meadows

Brian Meadows, U. Cincinnati.

opera experiment gran sasso italy
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

time of flight measurement
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

baseline measurement l
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

opera s result
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

a few comments
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

sn1987a race between and
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

some observations
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

a few comments on gps
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

slide10
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

two solutions
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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