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Measuring The Weak Charge Of The Proton At Jefferson Lab
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Book Synopsis Measuring the Weak Charge of the Proton at Jefferson Lab by :
Download or read book Measuring the Weak Charge of the Proton at Jefferson Lab written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The JLab Q weak Collaboration is designing and constructing an experiment to measure the protonâ s weak charge, Q W p, by measuring the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer. The standard model predicts Q W p = 1 - 4 sin2 theta w from the running of the weak mixing angle sin2 theta w, corresponding to a 10sigma effect in the experiment. The experiment will determine Q W p with 4% combined statistical and systematic uncertainties, which leads to 0.3% uncertainty in sin2 theta w . Installation of the experiment will begin in September 2009.
Download or read book Q Weak written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment, which took data at Jefferson Lab in the period 2010 - 2012, will precisely determine the weak charge of the proton by measuring the parity-violating asymmetry in elastic e-p scattering at 1.1 GeV using a longitudinally polarized electron beam and a liquid hydrogen target at a low momentum transfer of Q2 = 0.025 (GeV/c)2. The weak charge of the proton is predicted by the Standard Model and any significant deviation would indicate physics beyond the Standard Model. The technical challenges and experimental apparatus for measuring the weak charge of the proton will be discussed, as well as the method of extracting the weak charge of the proton. Finally, the results from a small subset of the data, that has been published, will also be presented. Furthermore an update will be given of the current status of the data analysis.
Book Synopsis Measuring the Weak Charge of the Proton Via Elastic Electron-Proton Scattering by :
Download or read book Measuring the Weak Charge of the Proton Via Elastic Electron-Proton Scattering written by and published by . This book was released on 2015 with total page 251 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment which ran in Hall C at Jefferson Lab in Newport News, VA, and completed data taking in May 2012, measured the weak charge of the proton QpW via elastic electron-proton scattering. Longitudinally polarized electrons were scattered from an unpolarized liquid hydrogen target. The helicity of the electron beam was flipped at approximately 1 kHz between left and right spin states. The Standard Model predicts a small parity-violating asymmetry of scattering rates between right and left helicity states due to the weak interaction. An initial result using 4% of the data was published in October 2013 [1] with a measured parity-violating asymmetry of -279 ± 35(stat) ± 31 (syst) ppb. This asymmetry, along with other data from parity-violating electron scattering experiments, provided the world's first determination of the weak charge of the proton. The weak charge of the proton was found to be pW = 0.064 ± 0.012, in good agreement with the Standard Model prediction of pW(SM) = 0.0708 ± 0.0003[2].
Download or read book Qweak written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the parity-violating asymmetry in elastic scattering at very low Q[sup 2] of a longitudinally polarized electron beam on a proton target. The experiment will measure the weak charge of the proton, and thus the weak mixing angle at low energy scale, providing a precision test of the Standard Model. Since the value of the weak mixing angle is approximately 1/4, the weak charge of the proton Q[sub w][sup p] = 1-4 sin[sup 2] [theta][sub w] is suppressed in the Standard Model, making it especially sensitive to the value of the mixing angle and also to possible new physics. The experiment is approved to run at JLab, and the construction plan calls for the hardware to be ready to install in Hall C in 2007. The theoretical context of the experiment and the status of its design are discussed.
Download or read book QWEAK written by R. D. Carlini and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Q_weak experiment at Jefferson Lab will measure the parity-violating asymmetry in e-p elastic scattering at low Q^2 using a polarized electron beam and a LH_2 target. The experiment will provide the first measurement of the weak charge of the proton to an accuracy of 4%. Q^P_W is related to the weak mixing angle, and thus provides the means for a precision test of the SM. Since the value of sin^2 theta_w is approximately 1/4, the weak charge of the proton Q^p_w = 1 - 4sin^2 theta_w is suppressed in the SM, making it sensitive to the value of the mixing angle and to possible new physics. At the kinematics selected, the systematic uncertainties from hadronic processes are strongly suppressed.
Book Synopsis Measurement of the Proton's Weak Charge at the Qweak Experiment by :
Download or read book Measurement of the Proton's Weak Charge at the Qweak Experiment written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment at Jefferson Laboratory measures the parity violating asymmetry of polarized electrons scattering from a proton target at very low momentum transfer. In the Standard Model, this asymmetry reveals the proton's coupling to the neutral vector current, the weak charge. This value, measured directly for the first time, will provide a precision test of the Standard Model and will constrain the possibility of relevant physics beyond the Standard Model. The planned precision will probe certain classes of new physics at the 2̃ TeV scale. In order to challenge the precise predictions, the asymmetry will be measured with a 2.5 percent accuracy. To achieve such a precision, great care has to be taken on many aspects of the experiment. The very low momentum transfer reduces the hadronic effects to the asymmetry and must be determined to half of a percent accuracy. Beam stability is controlled and monitored constantly and background events are carefully studied.
Download or read book The Qweak Experiment written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The $Q_{weak}$ Collaboration has completed a challenging measurement of the parity-violating asymmetry in elastic electron-proton ($\vec{e}$p) scattering at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). The initial result reported here is extracted from the commissioning part of the experiment, constituting about 4% of the full data set. The parity-violating asymmetry at a low momentum transfer $Q^2$=0.025 GeV$^2$ is $A_{ep}$ = -279 $\pm$ 35 (stat) $\pm$ 31 (syst) ppb, which is the smallest and most precise asymmetry ever measured in $\vec{e}$p scattering. This result allowed the first determination of the weak charge of the proton $Q_W^p$ from a global fit of parity-violating elastic scattering (PVES) results from nuclear targets, where earlier data at higher $Q^2$ constrain uncertainties of hadronic structure. The value extracted from the global fit is $Q_W^p$ (PVES) = 0.064 $\pm$ 0.012, in agreement with the standard model prediction $Q_W^p$ (SM) = 0.0710 $\pm$ 0.0007. The neutral weak charges of up and down quarks are extracted from a combined fit of the PVES results with a previous atomic parity violation (APV) measurement on $^$Cs. The analysis of the full $Q_{weak}$ data is ongoing and expected to yield a value for the asymmetry within 10 ppb of precision. Because of the suppression of $Q_W^p$, such a high precision measurement will place significant constraints to models of physics beyond the standard model.
Book Synopsis The Qweak^p Experiment at Jefferson Laboratory by :
Download or read book The Qweak^p Experiment at Jefferson Laboratory written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A major new experiment is being prepared at Jefferson Laboratory to measure the proton's weak charge via the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer. The Standard Model makes a firm prediction of the protonâ s weak charge, Q_w^p = 1 - 4 sin2thetaW, based on the running of the weak mixing angle sin2thetaW from the Z^0 pole down to low energies, corresponding to a 10sigma effect in our experiment. Our ultimate goal is to determine the protonâ s weak charge with 4% combined statistical and systematic errors, which in turn leads to a 0.3% measurement of sin2 thetaW. The experiment is currently under construction; installation in Hall C at Jefferson Lab followed by data taking is planned for 2009.
Book Synopsis The Weak Charge of the Proton. A Search For Physics Beyond the Standard Model by :
Download or read book The Weak Charge of the Proton. A Search For Physics Beyond the Standard Model written by and published by . This book was released on 2015 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment, which completed running in May of 2012 at Jefferson Laboratory, has measured the parity-violating asymmetry in elastic electron-proton scattering at four-momentum transfer Q2 =0.025 (GeV/c)2 in order to provide the first direct measurement of the proton's weak charge, QWp. The Standard Model makes firm predictions for the weak charge; deviations from the predicted value would provide strong evidence of new physics beyond the Standard Model. Using an 89% polarized electron beam at 145 microA scattering from a 34.4 cm long liquid hydrogen target, scattered electrons were detected using an array of eight fused-silica detectors placed symmetric about the beam axis. The parity-violating asymmetry was then measured by reversing the helicity of the incoming electrons and measuring the normalized difference in rate seen in the detectors. The low Q2 enables a theoretically clean measurement; the higher-order hadronic corrections are constrained using previous parity-violating electron scattering world data. The experimental method will be discussed, with recent results constituting 4% of our total data and projections of our proposed uncertainties on the full data set.
Download or read book Weak Charge of the Proton written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: I review the role of two-boson exchange corrections to parity-violating elastic electron-proton scattering. Direct calculations of contributions from nucleon and Delta intermediate states show generally small, [script O](1-2%), effects over the range of kinematics relevant for proton strangeness form factor measurements. For the forward angle Qweak experiment at Jefferson Lab, which aims to measure the weak charge of the proton, corrections from the gammaZ box diagram are computed within a dispersive approach and found to be sizable at the E~1 GeV energy scale of the experiment.
Book Synopsis A Measurement of the Weak Charge of the Proton Through Parity Violating Electron Scattering Using the Qweak Apparatus by :
Download or read book A Measurement of the Weak Charge of the Proton Through Parity Violating Electron Scattering Using the Qweak Apparatus written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: After a decade of preparations, the Qweak experiment at Jefferson Lab is making the first direct measurement of the weak charge of the proton, Q^p_W. This quantity is suppressed in the Standard Model making a good candidate for search for new physics beyond the SM at the TeV scale. Operationally, we measure a small (about -0.200 ppm) parity-violating asymmetry in elastic electron-proton scattering in integrating mode while flipping the helicity of the electrons 1000 times per second. Commissioning took place Fall 2010, and we finished taking data in early summer 2012. This dissertation is based on the data taken on an initial two weeks period (Wien0). It will provide an overview of the Qweak apparatus, description of the data acquisition and analysis software systems, and final analysis and results from the Wien0 data set. The result is a 16% measurement of the parity violating electron-proton scattering asymmetry, A = -0.2788 +/- 0.0348 (stat.) +/- 0.0290 (syst.) ppm at Q^2 = 0.0250 +/- 0.0006 (GeV)^2. From this a 21% measurement of the weak charge of the proton, Q_w^p(msr)= +0.0952 +/- 0.0155 (stat.) +/- 0.0131 (syst.) +/- 0.0015 (theory) is extracted. From this a 2% measurement of the weak mixing angle, sin^2theta_W(msr)= +0.2328 +/- 0.0039 (stat.) +/- 0.0033 (syst.) +/- 0.0004 (theory) and improved constraints on isoscalar/isovector effective coupling constants of the weak neutral hadronic currents are extracted. These results deviate from the Standard Model by one standard deviation. The Wien0 results are a proof of principle of the Qweak data analysis and a highlight of the road ahead for obtaining full results.
Book Synopsis First Determination of the Weak Charge of the Proton by : Fang Guo (Ph. D.)
Download or read book First Determination of the Weak Charge of the Proton written by Fang Guo (Ph. D.) and published by . This book was released on 2016 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment measures the parity violating asymmetry in elastic e[upper script right arrow]p scattering at Q2 = 0.02455 (GeV/c)2 with a 180 [mu]A and 88.7% longitudinally polarized electron beam of 1.165 GeV and a 34.4 cm liquid hydrogen target in experimental Hall C at Jefferson Lab. As the Q2 at the Qweak experiment is much lower than all previous experiments, the Qweak measurement can be considered as the first direct determination of the weak charge of the proton, Qp/w, which is related to the weak mixing angle, sin2 [theta]w, an important Standard Model parameter. The preliminary and blinded asymmetry of the Run 2 data set, which constitutes approximately 60% of all the data collected in the experiment, is Aep/PV = -232.7 +/- 8.7 (stat) +/- 6.4 (syst) ppb. The value of Qp/w obtained by fitting this blinded asymmetry and earlier parity violating electron scattering (PVES) data at higher Q2 is Qp/w (PVES) = 0.0705 +/- 0.0051. When combining this result with the 133Cs atomic parity violation (APV) measurement, further constraints can be placed on the neutral weak quark coupling constants C1u and C1d. The combined PVES and APV analysis yields the blinded neutron's weak charge to be Qn/w (PVES+APV) = -0.9798 +/- 0.0065. The Qweak experiment also measures the parity violating asymmetry in nonresonance inelastic e[upper script right arrow]p scattering at Q2 ~/= 0.09 (GeV/c)2 with 3.35 GeV electron beams to provide inputs for the [gamma]Z box calculation. The preliminary measured inelastic asymmetry is Aep/inelastic-PV = 2.91 +/- 0.35 ppm.
Book Synopsis The JLab Qweak Proposal - A Search for New Physics at the TeV Scale Via a Measurement of the Proton's Weak Charge by :
Download or read book The JLab Qweak Proposal - A Search for New Physics at the TeV Scale Via a Measurement of the Proton's Weak Charge written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: From a distance, the proton's weak charge is seen through the distorting effects of clouds of virtual particles. The effective weak charge can be calculated by starting with the measured weak coupling at the Z-pole and "running" the coupling to lower energy or, equivalently, longer distances. Because the "electroweak radiative corrections" or "loop diagrams" which give rise to the running depend not only on known particles, but on particles which have not yet been discovered, a difference between the calculated and measured weak charges may signal new physics. A measurement of Qweak to 4% will be sensitive to new physics at the few TeV scale. The Qweak experiment is based on the fact that the parity-violating longitudinal analyzing power, Az, in electron-proton scattering at low momentum transfer and small scattering angle, is proportional to the proton's weak charge. The experiment plans to measure the predicted Az of -0.3 ppm with a combined statistica.
Book Synopsis First Determination of the Weak Charge of the Proton by :
Download or read book First Determination of the Weak Charge of the Proton written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment has measured the parity-violating asymmetry in polarized e-p elastic scattering at Q2 = 0.025(GeV/c)2, employing 145 microamps of 89% longitudinally polarized electrons on a 34.4cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run are reported here, constituting approximately 4% of the data collected in the experiment. From these initial results the measured asymmetry is Aep = -279 +- 35 (statistics) +- 31 (systematics) ppb, which is the smallest and most precise asymmetry ever measured in polarized e-p scattering. The small Q2 of this experiment has made possible the first determination of the weak charge of the proton, QpW, by incorporating earlier parity-violating electron scattering (PVES) data at higher Q2 to constrain hadronic corrections. The value of QpW obtained in this way is QnW(PVES) = 0.064 +- 0.012, in good agreement with the Standard Model prediction of QpW(SM) = 0.0710 +- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be QnW(PVES+APV) = -0.975 +- 0.010.
Book Synopsis Determination of the Proton's Weak Charge Via Parity Violating Electron Scattering by :
Download or read book Determination of the Proton's Weak Charge Via Parity Violating Electron Scattering written by and published by . This book was released on 2015 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment, which completed running in May of 2012 at Jefferson Laboratory, has measured the parity-violating asymmetry in elastic electron-proton scattering at four-momentum transfer Q2=0.025 (GeV/c)2 in order to provide the first direct measurement of the proton's weak charge, Qpw. The Standard Model makes firm predictions for the weak charge; deviations from the predicted value would provide strong evidence of new physics beyond the Standard Model. Using an 89% polarized electron beam at 145 microA scattering from a 34.4 cm long liquid hydrogen target, scattered electrons were detected using an array of eight fused-silica detectors placed symmetric about the beam axis. The parity-violating asymmetry was then measured by reversing the helicity of the incoming electrons and measuring the normalized difference in rate seen in the detectors. The low Q2 enables a theoretically clean measurement; the higher order hadronic corrections are constrained using previous parity-violating electron scattering world data. The experimental method will be discussed, with recent results constituting 4% of our total data and projections of our proposed uncertainties on the full data set.
Book Synopsis The Weak Charge of the Proton by : Scott James MacEwan
Download or read book The Weak Charge of the Proton written by Scott James MacEwan and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak experiment will provide the most precise determination of the proton's weak charge Q^p_W by measuring the parity-violating asymmetry in elastic electron-proton scattering at low momentum transfer Q^2 = 0.0250 (GeV/c)^2. Qpw is related to the weak mixing angle sin^2\theta_W, a fundamental parameter of the standard model. A final measurement of the weak charge at the proposed 4% relative uncertainty is sensitive to certain types of new parity-violating physics beyond the standard model at the TeV mass-scale. Data were taken over a two year period beginning in 2010, using a custom apparatus installed in Hall-C at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. A 180 microamp beam of longitudinally polarized electrons was accelerated to 1.165 GeV and then scattered from unpolarized protons in a liquid hydrogen target. The scattered electrons were then collimated and steered using a magnetic spectrometer onto a set of azimuthally symmetric quartz bar Cherenkov detectors. The performance of this main detector subsystem will be described in detail in this dissertation. A blinded analysis of Run-II, roughly 2/3 of the entire Qweak data set, resulted in an elastic ep asymmetry of -235.6 +/- 8.7 (Stat) +/- 9.3 (Syst.) +/- 39.3 (Blind) ppb. Using this value, the proton's weak charge was calculated to be QpW = 0.0714 +/- 0.0093. This constitutes a 17% relative measurement, that will reduce to
Book Synopsis The Qweak Experiment at Jefferson Lab--A Search for New Physics at the TeV Scale by :
Download or read book The Qweak Experiment at Jefferson Lab--A Search for New Physics at the TeV Scale written by and published by . This book was released on 2009 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Qweak collaboration will make the first precision determination of the proton's weak charge, QWP = 1-4 sin2 thetaw, from a measurement of the parity-violating asymmetry in elastic electron-proton scattering at very low momentum transfer. The results will determine the proton's weak charge with a 4% total error. The Standard Model makes a firm prediction of QWP, based on the running of the weak mixing angle, sin2 thetaw, from the Z0 pole down to low energies, corresponding to a 10sigma effect in this experiment. Any significant deviation of sin2 thetaw from the Standard Model prediction at low Q2 would be a signal of new physics, wheras agreement would place new and significant constraints on possible Standard Model extensions at the TeV mass scale.
