If the measured value of \sin^2{\theta_{W}} deviates from the predicted value (given in the above figure) in a statistically significant way, then this way indicate important new physics beyond the Standard Model.

Q^P_weak is one of a number of experiments that map out the so called running of the weak mixing angle (the term running referring to the variation of \kappa(Q)sin^2{\theta_{W}} with energy). Each experiment measures this quantity in a different system or interaction (such as the proton in this case) with a different dependence on the underlying physics. In this way the full dependence of the Standard Model on the weak mixing angle is determined.

Q^P_weak is one of a number of experiments that map out the so called running of the weak mixing angle (the term running referring to the change of \kappa(Q)sin^2{\theta_{W}} with energy). Each experiment measures this quantity in a different system or interaction (such as the proton in this case) with a different dependence on the underlying physics. In this way the full dependence of the Standard Model on the weak mixing angle is determined.

If the measured value of {$\sin^2{\theta_{W}}$ deviates from the predicted value (given in the above figure) in a statistically significant way, then this way indicate important new physics beyond the Standard Model.

Q^P_weak constitutes the first measurement of the weak charge of the proton.

the weak mixing angle becomes energy dependent (\kappa(Q)sin^2{\theta_{W}}) as a result of corrections to the basic interaction (referred to as radiative corrections).

In reality, especially at higher energies, the value of the weak mixing angle becomes energy dependent (\kappa(Q^2)sin^2{\theta_{W}}) as a result of corrections to the basic interaction (referred to as radiative corrections).

Q^P_weak uses its eight main detectors to measure the difference in the number of electrons scattered from protons in a liquid hydrogen target, as a function of the electron polarization. The electrons are accelerated to near the speed of light, before they collide with the protons. The electrons must be this fast (among other reasons) in order to resolve ("see") the individual protons (rather than the hydrogen molecule as a whole). The normalized difference in the number of scattered electrons is referred to as an asymmetry (or sometimes as the analyzing power of the target):

handed electron helicity (polarization), which is produced with circularly polarized laser light at the electron source (cathode) before the electrons are accelerated. A right-handed electron has its magnetic moment (think of a compass needle) aligned with its direction of motion, while a left-handed electron has its magnetic moment anti-aligned with its direction of motion.

The so called weak mixing angle \theta_{W} is a fundamental parameter of the Standard Model, which means that it does not depend on other parameters and that it must have a single specific value for all interactions that are described by the Standard Model. The quantity given by sin^2{\theta_{W}} is therefore also fixed in the Standard Model, but this is only true under very simple assumptions.

The so called weak mixing angle \theta_{W} is a fundamental parameter of the Standard Model, which means that it does not depend on other parameters and that it must have a single specific value for all interactions that are described by the Standard Model. The quantity given by sin^2{\theta_{W} is therefore also fixed in the Standard Model, but this is only true under very simple assumptions.

takes on an energy dependence

The so called weak mixing angle \theta_{W} is a fundamental parameter of the Standard Model, which means that it does not depend on other parameters and that it must have a single specific value for all interactions that are described by the Standard Model.

The so called weak mixing angle \theta_{W} is a fundamental parameter of the Standard Model, which means that it does not describe a quantity that depends on other parameters. It must have a single specific value for all interactions that are described by the Standard Model.

physical context. In other words, we want to use experimental results to test our scientific theories. In order to do so consistently, we must have a mathematical expression (i.e. a model) and equate it with the measured asymmetry above. For subatomic physics, the currently accepted model is referred to as the "Standard Model" of the electro-weak and strong interactions, combining three of the four currently known forces of nature. Within this model (leaving out all of the real computational detail, but see, for example: AIP 1 and references within) the asymmetry can be expressed as a combination of two main parts:

The first part arises as a result of the so called weak charge of the proton (like the electromagnetic charge sets the strength of the electromagnetic interaction, the weak charge of a particle sets the strength with which it interacts via the weak interaction with other particles):

physical context. In other words, we want to use experimental results to test our scientific theories. In order to do so consistently, we must have a mathematical expression (i.e. a model) and equate it with the measured asymmetry above. For subatomic physics, the currently accepted model is referred to as the "Standard Model" of the electro-weak and strong interactions, combining three of the four currently known forces of nature. Within this model (leaving out all of the real computational detail, but see, for example: AIP 1 and references within.)

physical context. In other words, we want to use experimental results to test our scientific theories. In order to do so consistently, we must have a mathematical expression (i.e. a model) and equate it with the measured asymmetry above. For subatomic physics, the currently accepted model is referred to as the "Standard Model" of the electro-weak and strong interactions, combining three of the four currently known forces of nature. Within this model (leaving out all of the real computational detail, but see, for example: )

The above expression for the asymmetry is entirely experimental (e.g. Y_{L,R} are measured quantities), but the ultimate goal (as in any scientific endeavor) is to compare the measured results to a theoretical model that claims to, or is proven to have predictive power in some physical context. In other words, we want to use experimental results to test our scientific theories. In order to do so consistently, we must have a mathematical expression (i.e. a model) and equate it with the measured asymmetry above. For subatomic physics, the currently accepted model is referred to as the "Standard Model" of the electro-weak and strong interactions, combining three of the known four forces of nature.

handed electron helicity (polarization), which is produced with circularly polarized laser light at the electron source (cathode) before the electrons are accelerated.

The measured signal yield depends on many things, including physical parameters, such as scattering angle (w.r.t the incoming electron direction) and electron energy, as well as experimental effects, such as detector gain and efficiency, spectrometer performance and target performance.

A high precision measurement of this asymmetry is a challenging undertaking and requires years of careful design and development of the experimental components.

The above expression for the asymmetry is entirely experimental (e.g. Y_{L,R} are measured quantities), but the ultimate goal (as in any scientific endeavor) is to compare the measured results to a theoretical model that claims to or is proven to have predictive power in some physical context.

Q^P_weak uses its eight main detectors to measure the difference in the number of electrons scattered from protons in a liquid hydrogen target, as a function of the electron polarization. The electrons are accelerated to near the speed of light, before they are scattered off the target. The electrons must be this fast (among other reasons) in order to resolve ("see") the individual protons (rather than the hydrogen molecule as a whole). The normalized difference in the number of scattered electrons is referred to as an asymmetry (or sometimes as the analyzing power of the target):

handed helicity (polarization), which is produced with circularly polarized laser light at the electron source (cathode) before they are accelerated. The measured signal yield depends on many things, including physical parameters, such as scattering angle (w.r.t the incoming electron direction) and electron energy and experimental effects, such as detector gain and efficiency, spectrometer performance and target performance.

Q^P_weak uses its eight main detectors to measure the difference in the number of electrons scattered from protons in a liquid hydrogen target, as a function of the electron polarization. The electrons are accelerated to near the speed of light, before they scattered off the target. The electrons must be this fast (among other reasons) in order to resolve ("see") the individual protons (rather than the hydrogen molecule as a whole). The normalized difference in the number of scattered electrons is referred to as an asymmetry (or sometimes as the analyzing power of the target):

handed helicity (polarization), which is produced with circularly polarized laser light at the electron source (cathode) before they are accelerated.

Q^P_weak uses its eight main detectors to measure the difference in the number of electrons scattered from protons in a liquid hydrogen target, as a function of the electron polarization. The electrons are accelerated to near the speed of light, before they scattered off the target. The electrons must be this fast (among other reasons) in order to resolve ("see") the individual protons (rather than the hydrogen molecule as a whole). The normalized difference is referred to as an asymmetry (or sometimes as the analyzing power of the target):

handed helicity (polarization), which is adjusted at the electron source before .

Where Y_{L,R} are the experimentally measured signal yields in the main detectors, for left (L) and right (R) handed helicity (polarization).

the analyzing power of the target):

the analyzing power of the target) $\vec{e}$"

the analyzing power of the target) \vec{e}"

Q^P_weak uses its eight main detectors to measure the difference in the number of electrons scattered from protons in a liquid hydrogen target, as a function of the electron polarization. The normalized difference is referred to as an asymmetry (or sometimes as the analyzing power of the target)"

Q^P_weak uses its eight main detectors

Q^P_weak uses its eight main quartz detectors

Q^P_weak will measure the parity violating asymmetry in the number of ~1 GeV polarized electrons, scattered at forward angles from protons in a high power liquid hydrogen target:

$$f(x,y) = x^2 + y^2$$

Attach:qweak_running.jpg Δ

The Q^P_weak Experiment Physics:

Q^P_weak will measure the parity violating asymmetry in the number of ~1 GeV polarized electrons, scattered at forward angles from protons in a high power liquid hydrogen target. The goal is to measure this asymmetry with an error of 2.5%. At that accuracy, the measurement will determine the so called weak charge of the proton (Q^P_weak) with an error of 4.1% (see theory), making this a sensitive test of new physics beyond the Standard Model. Q^P_weak is currently being installed in Hall C at Jefferson Laboratory. ||Attach:qweak_running.jpg Δ

Physics