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| {{redirect|NEDM|the Sussex experiment|Sussex/RAL/ILL neutron EDM experiment|}}
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| The '''[[neutron]] [[electric dipole moment]] (nEDM)''' is a measure for the distribution of positive and negative charge inside the neutron. A finite electric dipole moment can only exist if the centers of the negative and positive charge distribution inside the particle do not coincide. So far, no neutron EDM has been found. The current best upper limit amounts to {{nowrap|{{!}}''d<sub>n</sub>''{{!}} < {{val|2.9|e=-26}}[[Elementary charge|''e'']]·cm}}.<ref>{{cite journal
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| | last = Baker | first = C. A. | coauthors = et al.
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| | year = 2006
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| | title = Improved Experimental Limit on the Electric Dipole Moment of the Neutron
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| | journal = [[Physical Review Letters]]
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| | volume = 97 | pages = 131801
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| | doi = 10.1103/PhysRevLett.97.131801
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| | pmid=17026025
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| | bibcode=2006PhRvL..97m1801B
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| | issue = 13
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| |arxiv = hep-ex/0602020 }}</ref>
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| == Theory ==
| | Bonus: WP Twin and WP Twin Auto Backup: (link to ) While not a theme, I think this software is essential if you are maintaining your Wordpress blog or regularly create new blog sites. You can either install Word - Press yourself or use free services offered on the web today. The effect is to promote older posts by moving them back onto the front page and into the rss feed. s and intelligently including a substantial amount of key words in the title tags, image links, etc. If you are happy with your new look then click "Activate 'New Theme'" in the top right corner. <br><br>Thus, it is imperative that you must Hire Word - Press Developers who have the expertise and proficiency in delivering theme integration and customization services. While direct advertising is limited to few spots in your site and tied to fixed monthly payment by the advertisers, affiliate marketing can give you unlimited income as long as you can convert your traffic to sales. A Wordpress plugin is a software that you can install into your Wordpress site. You can add new functionalities and edit the existing ones to suit your changing business needs. The biggest advantage of using a coupon or deal plugin is that it gives your readers the coupons and deals within minutes of them becoming available. <br><br>ve labored so hard to publish and put up on their website. The following piece of content is meant to make your choice easier and reassure you that the decision to go ahead with this conversion is requited with rich benefits:. After age 35, 18% of pregnancies will end in miscarriage. Storing write-ups in advance would have to be neccessary with the auto blogs. Websites using this content based strategy are always given top scores by Google. <br><br>If all else fails, please leave a comment on this post with the issue(s) you're having and help will be on the way. The SEOPressor Word - Press SEO Plugin works by analysing each page and post against your chosen keyword (or keyword phrase) and giving a score, with instructions on how to improve it. The templates are designed to be stand alone pages that have a different look and feel from the rest of your website. Word - Press is the most popular open source content management system (CMS) in the world today. Wordpress template is loaded with lots of prototype that unite graphic features and content area. <br><br>Website security has become a major concern among individuals all over the world. Automated deal feed integration option to populate your blog with relevant deals. It's not a secret that a lion share of activity on the internet is takes place on the Facebook. If you loved this article and you also would like to obtain more info about [http://deurl.de/backup_plugin_597075 wordpress dropbox backup] kindly visit the page. Thus, Word - Press is a good alternative if you are looking for free blogging software. I have never seen a plugin with such a massive array of features, this does everything that platinum SEO and All In One SEO, also throws in the functionality found within SEO Smart Links and a number of other plugins it is essentially the swiss army knife of Word - Press plugins. |
| [[Image:NEDM P&T violation.png|thumb|right|Parity (P) and time reversal (T) violation due to an electric dipole moment]]
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| A permanent electric dipole moment of a fundamental particle violates both [[Parity (physics)|parity]] (P) and [[T-symmetry|time reversal symmetry]] (T). This can be understood by examining the neutron with its [[Magnetic moment|magnetic dipole moment]] and hypothetical electric dipole moment. Under time reversal, the magnetic dipole moment changes its direction, whereas the electric dipole moment stays unchanged. Under parity, the electric dipole moment changes its direction but not the magnetic dipole moment. As the resulting system under P and T is not symmetric with respect to the initial system, these symmetries are violated in the case of the existence of an EDM. Having also [[CPT symmetry]], the combined symmetry [[CP-violation|CP]] is violated as well.
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| === Standard Model prediction ===
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| As seen above, in order to generate a finite nEDM one needs processes that [[CP violation|violate]] [[CP symmetry]]. CP violation has been observed in [[weak interaction]]s and is included in the [[Standard Model|Standard Model of particle physics]] via the CP-violating phase in the [[Cabibbo–Kobayashi–Maskawa matrix|CKM]] matrix. However, the amount of CP violation is very small and therefore also the contribution to the nEDM: {{nowrap|{{!}}''d<sub>n</sub>''{{!}} ~ 10<sup>–32</sup>''e''·cm}}.<ref>
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| {{cite arxiv
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| | last = Dar | first = S.
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| | year = 2000
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| | title = The Neutron EDM in the SM : A Review
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| | class = hep-ph | eprint = hep-ph/0008248
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| }}</ref>
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| === Matter–antimatter asymmetry ===
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| {{main|Baryogenesis}}
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| From the asymmetry between matter and antimatter in the universe, one suspects that there must be a sizeable amount of [[CP-violation]]. Measuring a neutron electric dipole moment at a much higher level than predicted by the Standard Model would therefore directly confirm this suspicion and improve our understanding of CP-violating processes.
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| === Strong CP problem ===
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| {{main|CP-violation}}
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| As the neutron is built up of [[quark]]s, it is also susceptible to CP violation stemming from [[strong interaction]]s. [[Quantum chromodynamics]] – the theoretical description of the strong force - naturally includes a term which breaks CP-symmetry. The strength of this term is characterized by the angle ''θ''. The current limit on the nEDM constrains this angle to be less than 10<sup>−10</sup> rad. This [[fine-tuning]] of the ''θ''-angle, which is naturally expected to be of order 1, is the strong CP problem.
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| === SUSY CP problem ===
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| [[Supersymmetry|Supersymmetric]] extensions to the Standard Model, such as the [[Minimal Supersymmetric Standard Model]], generally lead to a large [[CP-violation]]. Typical predictions for the neutron EDM arising from the theory range between {{nowrap|10<sup>–25</sup>''e''·cm}} and {{nowrap|10<sup>–28</sup>''e''·cm}}.<ref>{{cite journal
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| | last = Abel | first = S. | last2 = Khalil
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| | last3 = Lebedev
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| | year = 2001
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| | title = EDM constraints in supersymmetric theories
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| | journal = [[Nuclear Physics B]]
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| | volume = 606 | pages = 151–182
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| | doi = 10.1016/S0550-3213(01)00233-4 | first2 = S. | first3 = O.
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| |arxiv = hep-ph/0103320 |bibcode = 2001NuPhB.606..151A }}</ref><ref>
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| {{cite journal
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| | last = Pospelov | first = M. | last2 = Ritz
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| | year = 2005
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| | title = Electric dipole moments as probes of new physics
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| | journal = [[Annals of Physics]]
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| | volume = 318 | pages = 119–169
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| | doi = 10.1016/j.aop.2005.04.002 | first2 = A.
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| |arxiv = hep-ph/0504231 |bibcode = 2005AnPhy.318..119P }}
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| </ref> As in the case of the [[strong interaction]], the limit on the neutron EDM is already constraining the CP violating phases. The [[fine-tuning]] is, however, not as severe yet.
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| == Experimental technique ==
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| In order to extract the neutron EDM, one measures the [[Larmor precession]] of the neutron [[Spin (physics)|spin]] in the presence of parallel and antiparallel magnetic and electric fields. The precession frequency for each of the two cases is given by
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| :<math> h\nu = 2\mu_n B \pm 2d_n E </math>,
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| the addition or subtraction of the frequencies stemming from the precession of the [[magnetic moment]] around the [[magnetic field]] and the precession of the electric dipole moment around the [[electric field]]. From the difference of those two frequencies one readily obtains a measure of the neutron EDM:
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| :<math> d_n = \frac{h\,\Delta\nu}{4E} </math>
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| The biggest challenge of the experiment (and at the same time the source of the biggest systematic false effects) is to ensure that the [[magnetic field]] does not change during these two measurements. | |
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| == History ==
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| [[Image:NEDM limit history.png|300px|thumb|right|Measured upper limits of the neutron EDM. Given are also the predictions stemming from Supersymmetry and the Standard Model]]
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| The first experiments searching for the electric dipole moment of the neutron used beams of [[Neutron temperature|thermal]] (and later [[Neutron temperature|cold]]) neutrons to conduct the measurement. It started with the experiment by Smith, [[Edward Mills Purcell|Purcell]] and [[Norman Foster Ramsey, Jr.|Ramsey]] in 1951 (and published in 1957) obtaining a limit of {{nowrap|{{!}}''d<sub>n</sub>''{{!}} < {{val|5|e=-20}}''e''·cm}}.<ref>{{cite journal
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| | last = Smith | first = J. H. | last2 = Purcell | first2 = E. M.
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| | last3 = Ramsey | first3 = N. F.
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| | year = 1957
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| | title = Experimental Limit to the Electric Dipole Moment of the Neutron
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| | journal = [[Physical Review]]
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| | volume = 108 | pages = 120–122
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| | doi = 10.1103/PhysRev.108.120
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| |bibcode = 1957PhRv..108..120S }}</ref> Beams of neutrons were used until 1977 for nEDM experiments. At this point, systematic effects related to the high velocities of the neutrons in the beam became insurmountable. The final limit obtained with a neutron beam amounts to {{nowrap|{{!}}''d<sub>n</sub>''{{!}} < {{val|3|e=-24}}''e''·cm}}.<ref>
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| {{cite journal
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| | last = Dress | first = W. B. | coauthors = et al.
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| | year = 1977
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| | title = Search for an electric dipole moment of the neutron
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| | journal = [[Physical Review D]]
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| | volume = 15 | pages = 9–21
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| | doi = 10.1103/PhysRevD.15.9
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| |bibcode = 1977PhRvD..15....9D }}</ref>
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| After that, experiments with [[ultracold neutrons]] took over. It started in 1980 with an experiment at the [[Leningrad Nuclear Physics Institute]] obtaining a limit of {{nowrap|{{!}}''d<sub>n</sub>''{{!}} < {{val|1.6|e=-24}}''e''·cm}}.<ref>
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| {{cite journal
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| | last = Altarev | first = I. S. | coauthors = et al.
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| | year = 1980
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| | title = A search for the electric dipole moment of the neutron using ultracold neutrons
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| | journal = [[Nuclear Physics A]] | |
| | volume = 341 | pages = 269–283
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| | doi = 10.1016/0375-9474(80)90313-9
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| | issue = 2
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| |bibcode = 1980NuPhA.341..269A }}</ref> This experiment and especially the experiment starting in 1984 at the [[Institut Laue-Langevin]] pushed the limit down by another two [[Order of magnitude|orders of magnitude]] yielding the above quoted best upper limit in 2006.
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| During these 50 years of experiments, six [[Order of magnitude|orders of magnitude]] have been covered thereby putting stringent constraints on theoretical models.<ref>
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| {{cite journal
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| | last = Ramsey | first = N. F.
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| | year = 1982
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| | title = Electric-Dipole Moments of Particles
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| | journal = [[Ann. Rev. Nucl. Part. Sci.]]
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| | volume = 32 | pages = 211–233
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| | doi = 10.1146/annurev.ns.32.120182.001235
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| |bibcode = 1982ARNPS..32..211R }}</ref>
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| == Current experiments ==
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| Currently, there are at least five experiments aiming at improving the current limit (or measuring for the first time) on the neutron EDM with a sensitivity down to {{nowrap|10<sup>–28</sup>''e''·cm}} over the next 10 years, thereby covering the range of prediction coming from [[Supersymmetry|Supersymmetric]] extensions to the Standard Model.
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| * [[Cryogenic neutron EDM experiment]] being set up at the [[Institut Laue-Langevin]]<ref>[http://hepwww.rl.ac.uk/EDM/index_files/CryoEDM.htm hepwww.rl.ac.uk Cryogenic EDM]</ref>
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| * nEDM experiment under construction at the new UCN source at the [[Paul Scherrer Institute]]<ref>[http://nedm.web.psi.ch/ nedm.web.psi.ch]</ref>
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| * nEDM experiment being envisaged at the [[Spallation Neutron Source]]<ref>[http://p25ext.lanl.gov/edm/edm.html p25ext.lanl.gov on EDM]</ref>
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| * nEDM experiment being built at the [[Institut Laue-Langevin]]<ref>[http://nrd.pnpi.spb.ru/LabSereb/neutronedm.htm nrd.pnpi.spb.ru Neutron EDM page]</ref>
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| * nEDM experiment being built at the [[Forschungsreaktor München II]]<ref>[http://nedm.ph.tum.de/index.html nEDM experiment FRM-II]</ref>
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| == References ==
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| <div class="references-1column">
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| <references/>
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| </div>
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| {{DEFAULTSORT:Neutron Electric Dipole Moment}}
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| [[Category:Electromagnetism]]
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| [[Category:Particle physics]]
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ve labored so hard to publish and put up on their website. The following piece of content is meant to make your choice easier and reassure you that the decision to go ahead with this conversion is requited with rich benefits:. After age 35, 18% of pregnancies will end in miscarriage. Storing write-ups in advance would have to be neccessary with the auto blogs. Websites using this content based strategy are always given top scores by Google.
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