Why is impact parameter not directly measurable?

Click For Summary

Discussion Overview

The discussion revolves around the challenges of measuring the impact parameter in collision processes, particularly in the context of high-energy physics and particle collisions. Participants explore the implications of precision measurements and the nature of the particles involved.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that the impact parameter is calculated from the scattered angle of the projectile, questioning if this is correct.
  • Another participant raises the distinction between measuring impact parameters for elementary particles versus larger objects like billiard balls, emphasizing the difficulty in achieving the necessary precision for particles.
  • A later reply highlights the extreme precision required in high-energy physics, suggesting a measurement accuracy of 10^-16 meters over several meters.
  • One participant expresses confusion regarding the suggested precision and questions its relation to the concept of point-likeness.
  • Another participant notes that to measure the impact parameter to within 10%, one must control the collision geometry to a fraction of a proton's radius, which is approximately 10^-16 meters.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of measuring the impact parameter directly, with some emphasizing the challenges involved and others questioning the assumptions behind the proposed measurements. The discussion remains unresolved regarding the practicality of such measurements.

Contextual Notes

Limitations include the dependence on the definitions of impact parameter and precision, as well as the unresolved nature of how to achieve the necessary measurement accuracy in practice.

says
Messages
585
Reaction score
12
I'm trying to understand a few things about the kinematics of collision processes.

I guess it's because we calculate the scattered angle of the projectile and then back calculate to get a value for the impact parameter. Is this right?
 
Physics news on Phys.org
Are you talking about elementary particles or billiard balls?

If the former, a direct measurement of impact parameter would require a trajectory that is good to 10^-16 meters or so over several meters. How do you propose to do that?
 
  • Like
Likes   Reactions: phoenix95
Can you simplify you answer...
 
Cab you answer my questions?
 
For high-energy physics: Try to measure the position of a particle "somewhere in the accelerator" with a precision of 0.000000000000001 meters.
 
  • Like
Likes   Reactions: phoenix95 and says
to be honest I don't get how you suggested that number (E-16 meters). Does it have anything to do with point-likeness?
 
A proton is 10^-15 meters across. If you want to measure the impact parameter to 10%, you need to control the collision geometry to 10% of a proton radius, or about 10^-16 meters.
 
  • Like
Likes   Reactions: says

Similar threads

  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 42 ·
2
Replies
42
Views
7K
Replies
4
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K