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Stephen Brooks 2002-06-20 16:52:32 | I was back at the laboratory this week (and will be for most of the next). Two URLs may be of interest. http://stephenbrooks.org/ral/report/ Displays work-in-progress of a report I'm writing on all this. http://stephenbrooks.org/ral?muon1 Displays the files on a web-based backup I keep of my work HDD. While writing the report I was thinking about the irritating random behavior (see section 2.2.3) caused by the pion decay and I'm considering various options for changing the simulation to reduce this. I also noticed than an equation I was using to calculate the motion of the particles simplified algebraically, getting rid of a pesky sqrt() evaluation. But I tested the speed of that and it is only negligably faster. There might be a version 4.12 once I've made up my mind what I'm going to change. "As every 11-year-old kid knows, if you concentrate enough Van-der-Graff generators and expensive special effects in one place, you create a spiral space-time whirly thing, AND an interesting plotline" [This message was edited by Stephen Brooks on 2002-Jun-21 at 16:05.] [This message was edited by Stephen Brooks on 2002-Jun-21 at 16:06.] |
gogomaus 2002-06-21 13:50:37 | Stephen, that´s really great ! Having a look over your shoulder to see actual work/report in progress. Thanks a lot for your open mind. I hardly dare to indicate two "mistakes". One refers to decay time of pions+ to muons+. To my knowledge 26 ns is the value of _mean_ life time = the decay to 1/e and not to 1/2. The other issue concerns the 3 "clones" of user scottsaxman within your result overview table... ![]() |
Stephen Brooks 2002-06-21 16:04:03 | Err you've got me worried temporarily about that 1/e vs. 1/2 thing. I think all timescales quoted are half-lifes to 1/2 rather than "characteristic" lifetimes to 1/e but I'll re-check with the place I got the data from. Aha nope - from the very facility where I work comes this page... http://www.isis.rl.ac.uk/muons/index.htm?content_area=/muons/muonsIntro/isisMuons/isisMuons.htm&side_nav=/muons/muonsSideNav.htm& ...which states the half-life to be 26.0 ns. Scottsaxman. I'll look into it. "As every 11-year-old kid knows, if you concentrate enough Van-der-Graff generators and expensive special effects in one place, you create a spiral space-time whirly thing, AND an interesting plotline" |
Stephen Brooks 2002-06-25 15:13:08 | Ok that's fixed [bumps this thread to the top again] "As every 11-year-old kid knows, if you concentrate enough Van-der-Graff generators and expensive special effects in one place, you create a spiral space-time whirly thing, AND an interesting plotline" |
Helix_Von_Smelix 2002-06-28 07:09:40 | small point i know, but,,,,,,, you may want to ask someone about the information that you have given people access to, with regard to the data protection act. You could be in deep do do!!!!! ![]() ![]() Best of luck ![]() If you make instant coffee in to a microwave do you go back in time?? |
gogomaus 2002-07-02 09:28:19 | quote: Hello again, meanwhile I had a look on above cited sites. They are pretty nice PR-educational pages, but I´m still concerned about data quality. F.e. muons are reported with a life time of 2.2 µs; that´s in fact their correct mean life time, and not a half-life !!! (Your report also uses 1.5x µs for half-life of muons !). I got my info from the particle physics booklet (Rev. of Part.Physics; D.E.Groom et al., The European Physics Journal C15 (2000)). Data are available under http://pdg.lbl.gov -> particle listings 2001 -> mesons -> pi+ions = ( pdg.lbl.gov/2001/s008.pdf ). Find at bottom of page 2 value for _mean_ life time = 26.033 +/-0.005 ns . The meaning of _mean_ life time is defined as the time for reducing initial amount of particles to 1/e ; while half-life is used for decay down to 1/2. Many people tend to mix up both meanings/values. I found a noteworthy example on a website not to far away from you, the Durham/RAL database, which is linked under pdg.lbl.gov -> Part.Physics Info+databases. Look for SLAC/VVC under the HEPDATA screen; then use theory and search for "life-time and half-life" ( http://cpt19.dur.ac.uk/vcc/theory/halflife.html ). You will find a graph and the well-known equation for statistically determinated decay. A mean life time T is defined and also a half-life t1/2; simple mathematical operations lead to the final conclusion : t1/2 = ln(2)*T. That´s fine and absolutely correct. Unfortunately the graph N(t) shows No/2 for time = T on x-axis. (Thus would be a prove that ln(2) = 1; hahaha...). Maybe, you now understand my scepticism about correct data on public web-sites. It´s really a mess using decay time values with so much laissez-faire. Please, try to use a real reliable data source, otherwise all your simulations have to be revised (the later the worse). Hope, you will accept the inconvenience caused by me ; but isn´t it better to do it now instead of creating a lot of work for a cucumber castle ? ![]() |
Stephen Brooks 2002-07-07 05:28:14 | I think the error here has appeared from a mis-naming of a variable in my simulation. Let me explain - I found the original paper where I got the lifetime data from (it was not a PR site - I just used a random other site to do a quick check that my figure was correct, and apparently that site also made exactly the same error, which is confusing), and it does indeed say "mean life" rather than half-life. Then in my source-code I had #define Thalf_pi 2.6033e-8 ...so it looked for a while as if the simulations were wrong. Then I checked where I worked out the actual decay times, and my disribution was calculated from pn->t_decay=-log(frnd(1))*Thalf_pi; ...which is the correct formula if Thalf_pi was the MEAN lifetime, which by mistake it was. So the only correction to my code I had to make was renaming Thalf_pi to T_pi and adding a comment about this being the mean-life not the half-life. I honestly don't know whether this resulted from two consecutive mistakes that cancelled, or whether I really did know what I was doing all along but used a non-intuitive constant name in my code! However the value in my report _is_ incorrect, so I shall now change that. "As every 11-year-old kid knows, if you concentrate enough Van-der-Graff generators and expensive special effects in one place, you create a spiral space-time whirly thing, AND an interesting plotline" |
Stephen Brooks 2002-07-07 06:27:44 | quote: Don't worry - my site already violates the data protection act, so putting that up is no big change. Besides, there's not actaully _that_ much sensitive information in there (if any). "As every 11-year-old kid knows, if you concentrate enough Van-der-Graff generators and expensive special effects in one place, you create a spiral space-time whirly thing, AND an interesting plotline" |