You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
the anomalous magnetic moment ( anomaly ) of the @xmath6 , @xmath7 or @xmath8 lepton is defined by @xmath9 where @xmath10 is the magnetic dipole moment , and the factor @xmath11 is equal to @xmath12 in the dirac theory .
one of the important discoveries on the path to the development of qed , and then the standard model , was the measurement by kusch and foley  @xcite which showed definitively that @xmath13 .
almost simultaneously , schwinger showed that this difference could be explained by the ( one - loop in modern language ) radiative correction with the value @xmath14 , independent of the lepton mass .
the standard - model value of @xmath1 arises from loop contributions containing virtual photons , leptons , gauge bosons , and hadrons in vacuum polarization loops .
other talks at this meeting have discussed the standard - model contributions in some detail . for a general review
the reader is referred to the review article by miller , et al .
,  @xcite .
the muon anomaly has been measured in a series of experiments that began over fifty years ago@xcite , the most recent , e821 at the brookhaven ags , achieving a precision of of @xmath3 parts per million ( ppm )  @xcite : @xmath15 \times 10^{-11}\ , 0.54\,{\rm ppm}. \label{blr - eq : amue821}\ ] ] the result has been slightly adjusted from the value reported in ref .
@xcite because the value of the fundamental constant @xmath16 , the muon to proton magnetic moment ratio , ( see eq .
( [ blr - eq : lambda ] ) ) , has changed  @xcite . the statistical error in the anomaly is @xmath17  ppm and the systematic error is @xmath18  ppm .
the goal of the new fermilab experiment  @xcite is equal statistical and systematic errors of @xmath19  ppm , for a combined error of 0.14  ppm .
interestingly enough , the measured muon anomaly seems to be slightly larger than the standard - model value of  @xcite @xmath20 = 116\ , 591\ , 834 ( 49 ) ] \times 10^{-11 } \label{blr - eq : amusm}\ ] ] which uses @xmath21 annihilation into hadrons to determine the hadronic contribution , and the value of prades et al .
,  @xcite for the hadronic light - by - light contribution .
there is a difference of @xmath22 between the two .
if hadronic @xmath8 decays are used to determine the lowest - order hadronic contribution ( a determination that relies on significant isospin corrections ) , the difference drops to @xmath23  @xcite .
non - standard - model contributions could come from muon substructure , supersymmetry or extra dimensions , to name a few possibilities .
excellent reviews on this topic have been written by stckinger  @xcite , and czarnecki and marciano  @xcite .
the susy contribution depends on @xmath24 and the sign of the @xmath7 parameter  @xcite : @xmath25    both @xmath24 and the @xmath7 parameter will be difficult to determine at lhc .
the sign of the deviation of @xmath1 from the standard model gives the sign of @xmath7 , and the plot below illustrates the sensitivity of lhc and @xmath1 to @xmath24 .
it assumes that the sps1a scenario is realized at lhc  @xcite .
the difference between the standard model and the result from e821 is assumed to be @xmath26 .
the band labeled `` fermilab '' assumes the same @xmath27 but with an error of @xmath28 the improved error comes from the projected 0.14 ppm experimental error , and improved knowledge of the hadronic contribution to @xmath1 . see ref .
@xcite for more details .
the measurement of @xmath1 uses the spin precession resulting from the torque experienced by the magnetic moment when placed in a magnetic field .
an ensemble of polarized muons is introduced into a magnetic field , where they are stored for the measurement period .
assuming that the muon velocity is transverse to the magnetic field ( @xmath29 ) , the rate at which the spin turns relative to the momentum vector is given by the difference frequency between the spin precession and cyclotron frequencies . with an electric field
present as well as a magnetic one , the difference frequency becomes @xmath30\ , , \label{eq : blr - omegaa}\end{aligned}\ ] ] where @xmath31 .
( the reason for introducing an electric field will become apparent in the next section . )
the experimentally measured numbers are the muon spin frequency @xmath32 and the magnetic field , which is measured with proton nmr , calibrated to the larmor precession frequency , @xmath33 , of a _
free _ proton .
the anomaly is related to these two frequencies by @xmath34 @xmath35 , and @xmath36 .
the tilde over @xmath32 means it has been corrected for the electric - field and pitch ( @xmath37 ) corrections  @xcite .
the ratio @xmath38 is determined experimentally from the hyperfine structure of muonium , the @xmath39 atom  @xcite . as mentioned above ,
the recommended value of @xmath38 has changed slightly since the final results of e821 were published  @xcite , increasing the value of @xmath40 by @xmath41 , which is reflected in eq .
( [ blr - eq : amue821 ] ) .      in the 2001 data set ,
the systematic errors on the magnetic field were reduced to @xmath43  ppm .
a number of contributions went into this small error , but one which we wish to emphasize here is the average magnetic field experienced by the muon ensemble .
the magnetic field in eq .
( [ eq : blr - omegaa ] ) is an average that can be expressed as an integral of the product of the muon distribution times the magnetic field distribution over the storage region .
since the moments of the muon distribution couple to the respective multipoles of the magnetic field , either one needs an exceedingly uniform magnetic field , or exceptionally good information on the muon orbits in the storage ring , to determine @xmath44 to sub - ppm precision . thus traditional magnetic focusing used in storage rings , which involves magnetic quadrupole and higher multipoles , will cause large uncertainties in the knowledge of @xmath44 .
this problem was mitigated in the third cern experiment@xcite , and in e821 , by using electrostatic quadrupoles to provide the vertical focusing , freeing the magnetic - field design to be as close to a uniform dipole field as possible .
examination of eq .
( [ eq : blr - omegaa ] ) shows that for @xmath45 , called `` the magic @xmath42 , '' an electric field will not contribute to @xmath32 .
the electric - field effect vanishes for particles with the central momentum equal to @xmath46  gev / c , and is a small ( sub - ppm ) correction for other stored muons  @xcite .
the cern experiment used a rectangular aperture , which at their 7.3  ppm level of precision did not cause problems in determining the average field .
however , the large moments of a rectangular beam were not acceptable for the bnl experiment , which aimed at a factor - of - twenty improvement .
thus a circular beam aperture was chosen for e821 , which resulted in a systematic error on @xmath44 of 0.03  ppm , certainly adequate for the experiment now proposed at fermilab .
the experiment consists of repeated fills of the storage ring , each time introducing an ensemble of muons into a magnetic storage ring , and then measuring the two frequencies @xmath32 and @xmath33 .
the muon lifetime is given by @xmath47s , and the data collection period is typically @xmath48 muon lifetimes in the ring .
the @xmath0 precession period is 4.37  @xmath7s , and the cyclotron period is 149  ns . as the @xmath49 ( or @xmath50 ) decay , @xmath51 ( @xmath52 ) are emitted in the decay @xmath53 .
the high - energy decay electrons ( positrons ) carry information on the muon spin direction at the decay .
thus as the spin turns relative to the momentum , the number of high - energy decay electrons is modulated by the frequency @xmath32 , as shown in fig .
[ fg : blr - wiggle ] .
the e821 storage ring was constructed as a `` super - ferric '' magnet  @xcite , meaning that the iron determined the shape of the magnetic field .
thus @xmath54 needed to be well below saturation and was chosen to be 1.45  t. the resulting ring had a central orbit radius of 7.112  m , and 12 detector stations were placed symmetrically around the inner radius of the storage ring .
the detector geometry and number were optimized to detect the high - energy decay electrons , which carry the largest asymmetry , and thus information on the muon spin direction at the time of decay . in this design ,
many of the lower - energy electrons miss the detectors , reducing background and pileup .
the electrostatic quadrupoles  @xcite cover 43% of the ring , leaving significant gaps for the fast muon kicker@xcite and other objects in the ring .
while alternate schemes for measuring @xmath1 have been proposed , the magic @xmath42 technique has a number of things in its favor .
one of the most important is that since e821 , it is quite well understood and offers a straightforward path to a 0.1  ppm measurement , or perhaps somewhat beyond .
its features are :    * high muon polarization and decay asymmetry ; * large storage ring with ample room for detectors , field mapping , kickers , etc . ;
* muon injection , which has been shown to work ; * rates in the detectors that are easily handled with conventional technology ;
* data are fit over many @xmath0 cycles , which is a powerful tool to unmask systematic errors that depend on time ; * precision magnetic field techniques which are well understood ; * well understood systematic errors .
the fermilab proposal  @xcite uses the magic @xmath42 in the precision storage ring developed for e821 , with new detectors , electronics , along with improved magnetic field measurement and control .
central to the new proposal is the use of features unique to fermilab that will provide copious proton bunches of @xmath55 protons at 10 to 20  ms intervals .
this compares with @xmath56 protons per bunch at bnl , with a maximum of 12 bunches per machine cycle time of 2.7  s. the effective fill rate at bnl was 4.4  hz , compared with a projected rate of 18  hz at fermilab .    at bnl , pions 1.7% above the magic momentum decayed in an 80  m long fodo line ,
producing a beam that contained an equal number of pions , muons and electrons .
a large hadronic `` flash '' accompanied the injection into the ring causing a significant baseline shift in the detectors near the injection point .    at fermilab ,
the recycler ring will be used to re - bunch each proton batch from the booster into four bunches with @xmath55 protons each .
these will be extracted one at a time to a production target at the location of the present antiproton target .
the antiproton debuncher ring will be used as a 900  m long pion decay line .
the resulting pion flash will be decreased by a factor of 20 from the bnl level , and the muon flux will be significantly increased because of the ability to take zero - degree muons . the stored muon - per - proton ratio will be increased by a factor of 5 to 10 over bnl .
segmented detectors  @xcite and new electronics should easily be able to handle the increased data rates per fill of the ring .
the plan is to move the e821 muon storage ring to fermilab , and install it in a new building near the existing ap0 hall .
the proposal was well received by the fermilab program advisory committee , but funding has not yet been secured .
an optimistic schedule has the ring moved , re - assembled and shimmed by 2014 .
we estimate that in two years of running on @xmath50 , we could achieve the goal of the @xmath57  ppm error .
most of this running would be simultaneous with nova , using the extra booster batches that can not be used by the main injector program .
if the main injector program is down , then @xmath0 can use the full booster beam . with further running
we might be able to approach the 0.1  ppm level . during the project x era
, we could achieve a a comparable error for @xmath49 .
the muon anomalous magnetic moment has played an important role in the development of the standard model , and in constraining theories of physics beyond the standard model .
e821 at the brookhaven lab ags achieved a factor of 13.5 in precision over the famous cern experiments of the 1970s , and reached a relative precision of @xmath3  ppm .
the new muon @xmath0 collaboration has proposed to improve the error by a factor of four at fermilab . given the sensitivity of @xmath1 to a number of proposed extensions to the standard model , a more precise measurement , especially when combined with improvements in the knowledge of the hadronic contribution that are on the horizon , will provide valuable information for the interpretation of new phenomena that might be discovered at lhc .
90                      j. prades , e. de rafael and a. vainshtein , in _ lepton dipole moments _ , advanced series on directions in high energy physics -vol.20 , ed .
b. lee roberts and william j. marciano , world scientific , p. 303 , ( 2010 ) ; and arxiv:0901.0306 , jan .
2009 .
dominik stckinger , in _ lepton dipole moments _ , advanced series on directions in high energy physics -vol.20 , ed .
b. lee roberts and william j. marciano , world scientific , p. 393 , ( 2010 ) ; and j. phys . * g 34 * , r45 ( 2007 ) .    andrzej czarnecki and william j. marciano , in _ lepton dipole moments _ , advanced series on directions in high energy physics -vol.20 , ed .
b. lee roberts and william j. marciano , world scientific , p. 11 , ( 2010 ) ; and phys . rev . *
d 64 * , 013014 ( 2001 ) .
the new muon @xmath0 collaboration at fermilab has proposed to measure the anomalous magnetic moment of the muon , @xmath1 , a factor of four better than was done in e821 at the brookhaven ags , which obtained @xmath2 \times 10^{-11}$ ] @xmath3  ppm . 
 the last digit of @xmath4 is changed from the published value owing to a new value of the ratio of the muon - to - proton magnetic moment that has become available . at present 
 there appears to be a difference between the standard - model value and the measured value , at the @xmath5 standard deviation level when electron - positron annihilation data are used to determine the lowest - order hadronic piece of the standard model contribution . 
 the improved experiment , along with further advances in the determination of the hadronic contribution , should clarify this difference . because of its ability to constrain the interpretation of discoveries made at the lhc , the improved measurement will be of significant value , whatever discoveries may come from the lhc .    
 measurement , muon anomalous magnetic moment    13.40.em , 12.15.lk , 14.60.ef    2