Chamonix conference considers LHC running parameters

January 25, 2011

As the Large Hadron Collider once again cools down ready for its 2011 startup in February, the collider directorate are at Chamonix to discuss how they will operate in 2011 and beyond. The presentation slides for the 5 day meeting that started yesterday are being put online as the week progresses. Most of these are technical discussions of limited interest to an outsider but a couple at least are worth looking at.

The opening talk was about how the teams from the detector side saw the progress during 2010. The message is mixed with obvious pleasure that the main luminosity goal was exceeded at the end of the years run, but also some frustration at just how slow the build-up process was. For example they ask why 100/pb could not have been collected rather than 45/pb. In fact 100/pb could easily have been collected either by pushing the build-up of luminosity faster, or simply by doing more physics runs after the target luminosity was met. However, the beam directorate decided to use the time to try out bunch trains with shorter gaps between. This gave them valuable information about limitation factors that are essential to making the decisions about how to run the machine this year. However, the main message from the detectors seems to be that they would like things to move much quicker this year.

The most significant decisions that need to be made before the collider starts up are what energy to run at, and what bunch separation to use. The currently favoured energy for 2011 is 8TeV compared with 7TeV last year. This may not look like a big difference but in fact it provides a significant increase in production rates for heavy particles. For example, it will mean 40% more Top quarks produced. That will be very important because some of the most promising signals for new physics seen at the Tevatron require top production. The improvements in sensitivity for heavier SUSY particles is even better. A talk this evening on the LHC potential will give all the detailed analysis. That will be followed by other talks that consider the operational consequences and risks of running with energies of 8Tev, 9TeV or even 10 TeV, but the conclusion is likely to be that anything above 8 TeV is too risky.

How much luminosity will they collect next year? 1/fb is still the official target and 1/fb-3/fb is the official estimate, but some people are thinking optimistically about up to 5/fb . It depends on factors such as the bunch separation they will use. This is likely to be 75ns comapred to last year’s 150ns. 50ns was tried last year but found to produce too many side effects.

The next decision will be whether or not to continue the 2011 run into 2012. That would provide much more data, probably enough to get first postive observations of the Higgs sector. But the longer run would delay the upgrade to the full 14TeV. It would also make components more radioactive which is bad news for the engineers who have to carry out the upgrade. The directorate announced earlier that it was in favour of the longer run but the technicalities may get in the way. It’s a tough call.

Update 28-Jan-2011: With the Chamonix conference drawing to a close the proposal is that the LHC will run at 3.5TeV during 2011, not 4 TeV as hoped. However, the physics runs will continue into 2012 and it is hoped that after the normal end-of-year break they will be able to increase the energy for 2012 to “Hopefully higher than 4TeV”.

The 4TeV energy was seen as too much of a risk in exchange for the extra physics it will produce for 2011. Thermal amplifier development during 2011 could make the higher energies possible during 2012. The target integrated luminosity remains at 1/fb per experiment, but estimates put the actual figure at about 3/fb. This depends very much on how quickly they can recommission the beam and how efficiently they can run during the rest of the year.

 


BBC Horizon: What is Reality? (and will the holometer see it?)

January 21, 2011

Last time I commented on a BBC Horizon program it was quite popular so perhaps people will be interested in the latest one entitled “What is Reality?” which aired in the UK this week.

I thought the title did not sound promising but it turned out to be a whistle stop tour through a number of interesting current ideas in theoretical and experimental physics. It started with Jacobo Konisberg talking about the discovery of the Top quark at Fermilab. Frank Wilceck then featured to explain some particle physics theory at his country shack using bits of fruit. Anton Zeilinger showed us the double slit experiment and then Seth Lloyd showed us the worlds most powerful quantum computer, which is not very powerful. Lloyd has some interesting ideas about the universe being like a quantum computer which I encorporated into my FQXi essay, but somehow I dosed off at that point in the program so I will need to watch it again :)

Lenny Susskind then made an appearance to tell us about how he had discovered the holographic principle after passing an interesting hologram in the corridor. The holgraphic principle was illustated by projecting an image of Lenny onto himself. Max Tegmark then drew some of his favourite equations onto a window and told us that reality is maths before he himself dissolved into equations.

The most interesting part of the program was a feature about an experiment to construct a holometer at Fermilab described by one of the project leaders Craig Hogan. The holometer is a laser inteferometer inspired by the noise produced at the gravitational wave detectors such as LIGO. It is hoped that if the holographic principle is correct this experiment will detect its effects. Some sceptisicm might be fair dues, but it has to be worth trying. There is info about the holometer here.

I can find the program on Youtube but I wont link because I don’t know if it is an official version that will stay, or whether it is available everywhere or just limited to the UK.


First Earth-Like Planet Discovered!

January 15, 2011

So How often do we think we are going to see the headline announcing the discovery of the “First Earth-Like Planet” ? The latest example (CoRoT-7 b) came just as the New Year arrived. It turned out to be a firey world with temperatures ranging between -210 to 2000 degrees centigrade because it is tidally locked with its star. That’s not what most of us would consider Earth-Like. It earned its dubious title by being a rocky planet not very different in size than Earth.

Even as the news broke the sense of deja-vu was overwhelmingly strong. The previous “First Earth-like planet” (Gliese 581g) had been discovered just four months previously. This one is in the Goldilocks zone of its star meaning that it is at the right distance for liquid water to form on the planet. However, water would only actually form if it was rotating to give the surface an even temperature, but this one is probably tidal locked too.

Looking back through the news archives it is no surprise to find that news of the first Earth-like planets first appeared as far back as 1998 when just a handful of exoplanets were known. since then there have been a number of candidates, hopefully with each one being a little bit more Earth-like than its predecessor, although it is also the case that some of these discoveries later turn out to be errors.

At viXra log we confidently predict that the next collection of such headlines will hit us when the next major update from the Keplar mission is released on February the first, if not before. The pre-release of info about CoRoT-7 b may however signal that nothing much better has been found. In any case we can be sure that planets described as more and more Earth-like will be appearing for many years to come.

So what do we really think should be counted as an Earth-like planet? The data we get from Keplar and other observations should tell us about the planet’s size, mass, and distance from its star. From this information we can infer its average temperature, whether it is likely to be tidally locked, the strength of its surface gravity. Then from this we can make a guess about whether it could support liquid oceans of water, and an atmosphere of the right density as well as whether it has a molten iron-rich core. the latter is important because it could give the planet a magnetic field that protects it from radiation.

If “Earth-like” means a planet could support an ecosystem like ours it will need to be in the Goldilocks zone of a star that is not too dim so that it does not tidally lock and liquid water can exist. It will also need to have a size and density reasonably close to Earth’s. That will ensure that it can retain its atmosphere without it becoming too dense. It also means that large land based animals will not be hindered by excess gravity and the molten core will not solidify to remove the magnetic field as it did on Mars.

It follows form these considerations that the star around which the planet orbits must also be like our Sol. If it were less bright the planet would need to get nearer and would be tidally locked. Bigger stars tend not to last long enough to provide a stable environment in which life can evolve. Other types of star may be too variable in brightness, or may have regular deadly flares that could strip any nearby planet of its atmosphere, even with the protection of a magnetic field.

Taking these things into consideration, the parameters that we can currently measure of exoplanets and the stars they orbit need to be very close to those of Earth and our Sun.

Apart from these considerations, an important feature of our planet is its large moon. Without it there would be no tides and these have surely been very important in promoting the evolution of live. The Moon is also said to keep our planet’s rotation axis stable. If it were otherwise we might suffer catastrophic changes in climate that would ruin the atmosphere of our planet. There may be an outside chance that Kepler could see the presence of such a moon as the system transits in front of its star.

Even if a star meets these requirements it really just makes it potentially Earth-like. The planet also needs to have the right chemical mix of elements in the right quantities to make oceans and an atmosphere that would support rather than poison life. Will we ever be able to detect their presence?

After Keplar has made a long (hopefully) list of potentially Earth-like exoplanets the next step will be to examine them more closely using other observatories. The best hope of being able to do this in the foreseeable future lies with the James Webb Space Telescope that is due for launch in 2014. The JWST will have spectrometers sensitive enough to see the slight differences in a systems spectra when planets pass behind their stars. It will even have a special camera with a spot that can block out the light from a star so that some planets can be seen away from the glare. This should certainly be good enough to work for the gas giants but it may require the next generation of space telescope to be able to do the same for smaller (potentially) Earth-like planets.

In the long term the prospects for finding truly Earth-like planets can only get better. Just how fast depends on technological and economic developments that are hard to predict. Ultimately there is no reason why we should not be able to determine the chemical composition of the atmospheres of Earth-sized exoplanets and if they have the right proportions of oxygen and nitrogen we will know that Earth-like plant and animal life must be present. Perhaps we will even be able to see the tale-tale signature of chlorophyl or other molecules that can only be produced in quantity by vegetation. That’s  if such planets even exist nearby.

In any case one thing is for sure:  Headlines telling us of the “First Earth-like Planets” are going to be around for some time.


Tevatron will not have extended run

January 10, 2011

In September we reported that the Tevatron would continue running until 2014 in order to discover the Higgs Boson. Some of us thought this was not a great idea because the LHC will soon overtake the Tevatron and continuing to run the Tevatron would detract from other important physics projects at Fermilab. In fact the main question mark over the continuation was the lack of funds. Now it has been confirmed that there is indeed insufficient funds to cover the extra expense and the Tevatron will end its search for the Higgs and other new physics at the end of 2011 as planned.

Meanwhile physicists at the LHC are trying to make up their minds whether or not it would be a good idea to extend next years run into 2012 to delay the long shutdown. This would give the LHC a better chance of finding the Higgs earlier. Without the extended life of the Tevatron some of the will to do this may have faded, but there is still good reason to do it if the LHC can produce significantly more luminosity in 2011 than previously anticipated. In the end it may come down to technicalities such as the problem of extra radiation that would make repairs during the long shutdown more dangerous if the LHC runs for longer. These are issued due to be discussed soon in Chamonix this month.

 

 


Follow

Get every new post delivered to your Inbox.

Join 281 other followers