Very early this morning we got the first lead-lead collisions at the LHC! I am all a twitter. This is a very exciting time. I just arrived at CERN today and I am very, very jet-lagged, so I’ll keep this short.
Pictures. What you all want to see is pictures.
Here are some event displays with the first Pb+Pb collisions seen by ALICE. This is an example:
These event displays only show information with the Inner Tracking System (ITS). Our main tracking detector, the Time Projection Chamber (TPC), was off for these collisions. The reason is that the beams were not perfectly stable for the first collisions and we did not want to damage our TPC.
And check out this video of an event display (the original video is here):
[video http://aliceinfo.cern.ch/static/Pictures/pictures_High_Resolution/wwwFirstPbPb/animation9968.avi]
And now that we have lead-lead data, we have a lot of work to do. Expect the first lead-lead paper soon. It will be a multiplicity paper like ALICE’s first few proton-proton papers. We will just measure the number of charged particles in an event. This information alone will tell us a lot about heavy ion collisions – the first estimates for how many particles we should see in an event varied by a factor of 4, from 2000-8000 tracks.
Tags: ALICE, first beam, first results, heavy ion physics
I am a noob m’ok ?
But could you answer some simple questions :
1 – Is there any difference of nature between, for example, an atom of “skin” and an atom of “chocolate” if the only difference is the number of proton, electron or else =
2 – does it mean that if we were able to “add” what “miss” at the atom of chocolate it could become an atom of skin ? =
3 – how appear the first atom of skin and chocolate ? =
4 – are they result of transformation of previous atoms ? =
5 – and if yes what was the constituants of the “original” main atom ? (was it possible that the “first” atom was lighter than it’s own transformation or was it heavier with more constituants) =
6 could atoms be an illusion (cause time and space are appear too from the moment when atoms “appears” so the nature of atom is impermanent also ? or a kind of illusion too cause space and time are dependant of atom, does atom is dependant of something else ?) ?
This is so exciting! I can’t wait to see what comes out of these collisions…
Can those of you who specialize in this field look at an event display like that and determine anything useful about the collision or do you need to use analysis tools for it to tell you something more than just that there was a collision? As a lay person I can look at a p-p event display labeled as a Z -> 2 muons event, for example, and see that there are 2 long lines emanating from a single point which must be the muons. With heavy-ion collisions, all I see is a mess of lines.
Hi James -
1. It is true the only differences between atoms in skin and atoms in chocolate are the number of protons, neutrons, and electrons and the molecules they form. But I think it’s safe to say these are really big differences.
2. With a lot of work, in principle we could change the atoms in skin to the same form as atoms in chocolate. That doesn’t mean it’s possible in practice or that it would be worth the trouble.
3. It kind of depends on what you mean by “skin” – does it have to be human skin? Both chocolate and skin are really complicated structures of molecules. But anyhow, this is more a biology question – these time frames are set more by evolution than physics.
4. Yes, skin and chocolate came from the transformation of atoms into their current form, but this was mostly through chemistry – molecules reacting with each other to form new molecules – than through changes in the nuclei.
5. The answer to this is really complicated, so let me point you to the wiki on nucleosynthesis http://en.wikipedia.org/wiki/Nucleosynthesis
6. No. There is tons of evidence atoms are real.
Andy – yes, there is some information we can get from this. In the control room we have a real time event display. In practice, this is often one of the first indications when something goes wrong with one of the detectors. For instance, when I was on STAR, there were several times when we immediately noticed a detector was missing on the event display so we knew to check that detector right away. In principle this information is all available in quality assurance plots available elsewhere, but sometimes we can see a problem faster with the event display. We can also see some geometry problems with the event display. The event display also gives us some indication of how central the events are – the more central, the more tracks. If all of the detectors go busy, we will stop getting data and there will be no event display. This is an immediate visual cue that something is wrong.
Ok thank you for your answers but it brought few more questions :
7 – the number of atoms existing in the universe is increasing or decreasing or remain the same ? because atoms are impermanent by nature so atoms appear from where or what if they are increasing ?
8 – about the question if atoms are illusions or not i didn’t mean that they are not existing but instead that their nature is not what we can perceive through experience (for example bouddhist say that in one atom there is as much particles that there is atoms in universe !) so i just meant : does the constituants of atoms have the same law of physics that we know for ourself (gravity etc…) or is this type of laws doesn’t apply to their constituants ?
Also about illusion i don’t know if you saw the movie “matrix” but it could be this type of illusion (we see a world but its not a world it’s an illusion create by a machine = we see an atom but it’s not an atom it’s an illusion created by our perception or something else) but whatever i guess only experiment will say us the truth !
I am not good in maths or physics by love the particles sciences and also the research, all of you must keep searching !
Thanks for your works.
I wonder if you could explain what is meant by the statement which one of the CERN scientists made recently on the BBC News: “strong force is responsible for most of the mass in the universe”. I think we were all taught in school that mass is simply a measure of the amount of matter in a given space. Is this an oversimplification? Why would the mass of individual protons & neutrons change in the absence of strong force? Does this mean that the sum of the masses of constituent subatomic particles does not equal the whole mass of their protons or neutrons?
Thanks,
A Very Excited Math Teacher in Illinois
Bill, I am not a scientist, but from what I know, the constituents (quarks) of proton are much lighter in total, than proton as a whole. Majority of the proton (an also neutron) mass lies somewhere else: in the strong force that keeps the quarks together.
This “mass of the strong force” is responsible also for the nuclear energy. When you put together 2 protons and 2 neutrons to form helium, the mass of helium is slightly less than the mass of the individual nucleons when they were separate. The mass of the quarks in the helium nucleus is the same as the mass of the quarks in the separate nucleons. What disappeared (and took some mass away) is part of the energy of the strong force.
Or at least this is my understanding. Feel free to correct me.
Hi James
7. I don’t know the answer to this question. Atoms are constantly being created and destroyed so it really matters which rate is faster. This is much more a question for an astrophysicist than a high energy physicist.
8. Our intuition doesn’t do very well even for things on scales we can see. For instance, if you poll an introductory physics class at the beginning of the semester, a large percentage will say that heavier objects fall faster. And this is just classical mechanics, which is conceptually much easier to understand than quantum mechanics. Atoms are at a scale where our intuition is just wrong. We have to use quantum mechanics to determine the behavior of objects on the size of atoms.
It’s not that the laws of physics are different for atoms – it’s that the scale is different. If you shoot an atom at a slit smaller than the atom, sometimes it will go through. If you try to drive your car through your front door (assuming your front door is a normal size), you will end up with a broken door. The heavier and larger an object is, the less likely it is to quantum mechanically tunnel through solid objects. So it is not that your car could never go through your door without damaging the door – it’s just that the probability is so low that it will only happen once in several billion lifetimes of the universe. Colloquially something that only happens once in several billion lifetimes of the universe is known as impossible. In principle you could calculate the trajectory of a car moving down the highway using quantum mechanics. It is just a much more difficult calculation than the calculation using only classical mechanics, and the key to being a good physicist is to not work any harder than you have to. If quantum mechanical effects are negligible, I don’t want to do the extra work.
Nature is a totalitarian dictator. Laws of nature cannot be broken. Our theories can be wrong and our calculations can be wrong, but all laws of nature apply all the time. Atoms must obey the laws of nature. Atoms are affected by gravity – this is why air pressure is lower at higher altitudes, for instance.
Hi Bill & Martin
I’m going to take advantage of the fact that someone else has already written a very good answer to this question and point you to his explanation:
http://cornellmath.wordpress.com/2007/07/25/the-origin-of-mass/
I have a really burning question that I can’t seem to find the answer to anywhere.
When you say Lead ions, I have read somewhere that (208Pb82+) are used. Does that mean you have stripped the lead ion of all its electrons? How do you go about doing this?
Thank you for your time!
Hi Kerri – excellent question. Electrons are removed from the lead in several stages. First a vapor of atoms is created and some electrons are stripped from the atoms using electrical current, creating lead ions. These ions are then accelerated in a linear accelerator (http://en.wikipedia.org/wiki/Linear_particle_accelerator). After this stage the ions are passed through a thin foil, which strips more electrons from them.
The protons are then injected into the Low Energy Ion Ring, where they are further accelerated. They then enter the Proton Synchrotron (http://en.wikipedia.org/wiki/Proton_Synchrotron) at which point they have a charge of +53 (in units of the electron charge.) Here they are accelerated more. When they exit the proton synchrotron, the remaining electrons are stripped off, leaving ions with a charge of +82. These ions are injected into the Super Proton Synchrotron (http://en.wikipedia.org/wiki/Super_Proton_Synchrotron), where they are accelerated up to the injection energy. Ions from the Super Proton Synchrotron are injected into the LHC and in the LHC they are accelerated up to full energy.
This article is directed at non-scientists
http://www.symmetrymagazine.org/breaking/2010/11/05/the-skinny-on-the-lhcs-heavy-ions/
And this is a relevant technical paper
http://iopscience.iop.org/1748-0221/3/08/S08001
The Everlasting Theory leads to the atom-like structure of baryons so also of the nucleons. The internal structure of neutrinos and new theory of their interactions show that it is very difficult to destroy the cores of baryons – they are the tori with mass in their centres and consist of the Einstein spacetime components i.e. of the binary systems of neutrinos. Inside our Universe, densities of energies and masses are too low to compress the cores of baryons. The liquid-like plasma consists of maximally packed cores of baryons. Theory of the liquid-like plasma leads to following formula for densities inside the liquid-like plasma:
Density=0.692•10^18 (2.07 + E) kg/m^3, where E is the number equal to energy per one proton-proton collision expressed in TeV. Closer observations should show the granulation inside the black holes in our Universe because they consists of the magnetars having masses a little greater than the neutron black holes – mass of the last cosmic objects is about 25 times the mass of the sun. We will not see the free quarks and gluons in the ion-ion collisions.
This is pretty interesting stuff. I’m sure after all these years of anticipation it is well worth the wait.
Cheers.
I was wondering if by using a set of Larry Fullerton Magnets especially the Correllated Programmable type if the atoms involved in the collision could be aligned more precisely during the collision. Basically it’s like racking the atoms and then hitting the atoms with the cue ball. Each energetic reaction being transfered through each ball where at each intersection of energetic event between each pool ball will create a forward momentum. After the rack has been broken the cue ball is then used to sink the balls into the pockets by using various angle techniques of the cue stick to place an surface area of the cue ball onto the surface area of the pool ball which the causes numerous results to occur which once the player has struck the cue ball the results of the actions of the interactions between the cue ball and pool ball are random. By using a Larry Fullerton Magnet the impact point of each and every collision could then be precisely controlled to achieve a better result of the impact of interaction between the atoms.