A Calculation of a Form Factor at large ##q^2##

In summary, on page 180, the authors discuss the form factors for heavy hadrons and how they are normalized by the constraint that the Coulomb contribution equals the total hadronic charge at zero momentum transfer. They also mention that the form factor should agree with standard non-relativistic calculations at small momentum transfer, and this is satisfied by the form F^M_{(0,0)}(q^2). At large momentum transfer, the form factor can be written as F^M_{(0,0)}=e_1 \frac{16\pi\alpha_s f_M^2}{9q^2}(\frac{M_H^2}{m_2^2})+(1\leftrightarrow 2).
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A question on a calculation in the book of Mueller, Perturbative QCD, from page 180.
On page 180 they write the following passage:
The form factors for the heavy hadrons are normalized by the constraint that the Coulomb contribution to the form factor equals the total hadronic charge at ##q^2=0##. Further, by the correspondence principle, the form factor should agree with the standard non-relativistic calculation at small momentum transfer. All of these constraints are satisfied by the form:
[tex]F^M_{(0,0)}(q^2)=e_1\frac{16\gamma^4}{(q^2+\gamma^2)^2}(\frac{M_H^2}{m_2^2})^2 \bigg( 1-\frac{q^2}{4M_H^2}\frac{2m_2}{m_1}\bigg)+1\leftrightarrow 2 .[/tex]
At large ##q^2## the form factor can also be written as:
[tex]F^M_{(0,0)}=e_1 \frac{16\pi\alpha_s f_M^2}{9q^2}(\frac{M_H^2}{m_2^2})+(1\leftrightarrow 2), f_M/(2\sqrt{3})=\int_0^1dx \phi(x,Q)[/tex]
where ##f_M=(6\gamma^3/\pi M_H)^{1/2}## is the meson decay constant.

My question is how do I get ##F^M_{(0,0)}## from ##F^M_{(0,0)}(q^2)## for large ##q^2##.
I tried using Mathematica's free input to get the series ##1/(1+x^2)^2=1-2x^2+3x^4+O(x^6)##, in our case ##x=\gamma/q##.
But it doesn't seem to fit the result from the book, perhaps there's something I am missing, any help?
A remark, ##\gamma## is Lorentz factor.

Thanks!
 
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FAQ: A Calculation of a Form Factor at large ##q^2##

What is a form factor in physics?

A form factor in physics is a mathematical function used to describe the internal structure of a particle. It is used to calculate the probability of finding a particle at a certain momentum transfer (q) during a scattering experiment.

How is the form factor calculated?

The form factor is calculated using a theoretical model of the particle's internal structure, such as the Standard Model of particle physics. This model is then used to calculate the scattering amplitude, which is related to the form factor by a mathematical equation.

What is the significance of calculating a form factor at large q^2?

Calculating the form factor at large q^2 allows scientists to study the particle's internal structure at high momentum transfers. This can provide insights into the strong nuclear force and the behavior of quarks and gluons within the particle.

What are the units of a form factor?

The units of a form factor depend on the specific form factor being calculated. For example, the electric form factor of a particle has units of charge, while the magnetic form factor has units of magnetic moment.

How is the form factor experimentally measured?

The form factor can be experimentally measured through scattering experiments, where particles are accelerated and scattered off of a target. By measuring the angle and energy of the scattered particles, the form factor can be calculated and compared to theoretical predictions.

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