Loomio
Fri 13 Jan 2017 5:26AM

HYPATIA Exercise 1 - In which view is the momentum conserved?

BG Ben Garrard Public Seen by 21

Looking at "EXERCISE I : Looking at events" on the HYPATIA analysis tool, I'm stumped by the very first question.

In which view do you think that the momentum is conserved?

I've looked at a lot of events and am none the wiser...

BG

Poll Created Fri 13 Jan 2017 5:30AM

test - Exercise 1 Proposal - transverse view Closed Mon 16 Jan 2017 5:02AM

Outcome
by Ben Garrard Tue 25 Apr 2017 6:03AM

:thumbsup:

For reasons X, Y, Z I believe the transverse view is the one in which momentum is preserved...

Results

Results Option % of points Voters
Agree 100.0% 1 JW
Abstain 0.0% 0  
Disagree 0.0% 0  
Block 0.0% 0  
Undecided 0% 28 MF BG BG SV KM LD OG BK DU SV LC SG KT MS LS DG BM DW HF ZS

1 of 29 people have participated (3%)

JW

Janette Wilmott
Agree
Sun 15 Jan 2017 9:15PM

neither can I decide in which one momentum is conserved

BG

Poll Created Mon 16 Jan 2017 11:41PM

Q: Closed Tue 17 Jan 2017 6:36AM

A: appears here

Results

Results Option % of points Voters
Agree 0% 0  
Abstain 0% 0  
Disagree 0% 0  
Block 0% 0  
Undecided 0% 29 JW MF BG BG SV KM LD OG BK DU SV LC SG KT MS LS DG BM DW HF

0 of 29 people have participated (0%)

JW

Janette Wilmott Tue 17 Jan 2017 7:37AM

Momentum will be conserved. So if it doesn't seem to be, it's because particles got out of the ATLAS without being detected. Particles like the slippery neutrino that heads right through just about everything. I found info about 'Missing transverse momentum' at http://hypatia.iasa.gr/en/help.html#cuts. The missing momentum is indicated by the thick dashed red line in some of the view events. So maybe the answer is: those events where no red dashed line is shown?

JW

Janette Wilmott Tue 17 Jan 2017 8:07AM

There is other useful material for understanding the data analysis in the Help menu on HYPATIA.

SV

Stelios Vourakis Fri 20 Jan 2017 12:23AM

Momentum is always conserved. However in the side view of the detector (right view) we don't know the momentum of each proton constituent before the collision. So we can't use momentum conservation in that view.

However, In the XY (left) view we know that the momentum before the collision is 0. So it's easy to add the momenta of all resulting particles and see what's missing. In theory the total should be 0 but in practice due to experimental errors (errors in measurements, particles escaping through parts of ATLAS that have no detectors etc) it'll never be 0.

If the magnitude of the missing momentum is low (something like 10 GeV) it can be attributed to that. If however it's high, then we can guess that one or more neutrinos (which are impossible to detect) were created and are mostly responsible for the missing momentum.

The dashed red line, as you mentioned, indicates the direction of the missing momentum. You can make the line disappear for low ETMiss values. If you open the menu (button with downwards pointing arrow) and go to options you will see the ETMiss cut. You can adjust this so that the line is only shown if ETMiss is higher than that value.