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Cosmic Variance

Thursday, January 26, 2006

The ICE-CUBE experiment on the Southern Pole

Lubos on his blog meantioned this ICE CUBE experiment.

Sounds an interesting experiment. But what does it has to do with string theory? You have not shown us you can predict exactly how many down-going or up-going high energy neutrinos you can expect to detect, based on string theory calculation. String theory can't say anything about interaction cross-sections or reaction rates so it's out of the equation.

I am highly skeptical that they can obtain significant event counts to produce statistically meaningful result. If you read the 4 page paper carefully, you find that the author is trying desperately to STRETCH THE NUMBER to un-reasonable limit, in order to produce a reasonably looking event count.

According to the author, during a total of 15 years of experiment run (a very long time, isn't it?), he expects to detect mere 4 down going neutrino events and 20 up going events. Very small number and hardly enough to do any statistics, you would agree.

But even that (4,20) event count estimate is way too much optimistic. If you carefully exam his calculation, you find he stretched the numbers too much. A more realistic estimate would give you an event count 100 times lower. Rendering the experiment meaningless since your expectation of event count is less than ONE.

First big mistake the author made, is he used the effective aperture of individual detectors times the length of detector strings to estimate the number of target nucleons, thus attrived at NT = 6x10^38. That estimate is wrong because there is redundancy between detectors.

A more common sense estimate is actually calculate how many atoms are involves in the detection. This brochure says the total volume of ice in the IceCube is ONE CUBIC KILOMETER. One should be able to calculate how many nucleons is contained in one cubic kilometer of ice.

The density of ice is about 900 kilogram per cubic meter. So one cubic ice is 9x10^11 kilogram. The water molecule contains 3 nucleons, and has an atomic weight of 18. That means each 0.018 kilogram contains 3 times the Avogardro constant, 6x10^23 nucleons. Put those number together. The total number of target nucleons is 9x10^37.

The author used 6x10^38 nucleons, which is an over estimate of 7 times already.

The author also grossly over estimated the detection efficiency to be between 50% to 100%. No such efficiency exists. Think about it, one single muon is created a few hundred meters away, it does emit some number of photons, but for the photons to be almost 100% detectable by a detector a few hundred meters away, that is really a stretch. It takes many many many photos to trigger an event. During dark nights there are still billions of bilions of photons entering our eyes per second but we hardly see anything. I do not know how to calculate the quantum efficiency but it must be way below 100%.

Now the technical difficulties how you can run such an experiment for 15 years in the frigid cold in the southern pole? These detectors and instruments must run on continuous electricity. How do you supply stable electricity for 15 years? Using solar panels? Well half of the year on the southern pole will be permanent darkness without sun shine. So no solar energy.

You may think of batteries. But the temperature is so cold that the fluid of the batteries will freeze into solid, disabling the battery. If you read recent news about the cold snip in Russian, you know many people had to take their car batteries into their home to keep it warm over night and put it back on the car the next morning. Any one not bringing their battery home will not have a working car the next day. So battery option is out for the souther pole experiment due to the temperature.

Or some device burning gasoline to generate electric power? That would be subject to supply issues and human maintenence. And it is impossible to maintain it year around.

Anyway you look at it, the experiment simply can not be run continuously year around. You may be able to run some months during each year, but not all the time.

The author used a full 15 years to estimate the event count. Again that is a gross over estimate. The realistic number should probably be divided by 3 or 4.

After you factor in all these realistic consideration, I am sure the experiment simply will not produce enough event count to draw any statistically meaningful result of any kind.


At 2:31 PM, Anonymous Anonymous said...

This is the most boring experiment of them all.

I don't care what they detect.

I thought it was bad when they filled an underground tank with dry cleaning fluid to detect neutrinos when they react with chlorine.

It's all about expensive experiments, and its all rubbish. Remember the time they put up the Hubble telescope with a lens that was perfectly made to the WRONG SHAPE?

then they had to send up astronauts to put glasses on the Hubble space telescope so it could see clearly.

They are basically big-mouthed, taxpayer money wasting ignorant crackpots, who passed their exams by taking drugs or whatever to help them remember equations. They have no shame, no scientific competence, but are petty dictators who censor out all criticism.

At 6:45 PM, Anonymous Nick said...

The water molecule actually has 18 nucleons. You have to count every proton and neutron. Two for the two hydrogen and 16 in the oxygen nucleus. This puts your estimate at 18/3=6 times too small.


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