Edit: We're signing off now, but some of us may still be around to respond to questions later on. Stay tuned for physics at 13 TeV planned for early June.

Hi reddit!

Last week, the Large Hadron Collider had its first-ever collisions at a centre-of-mass energy of 13 teraelectronvolts (TeV), breaking the world record for the highest energy attained in a particle accelerator. We're very excited to be back after our previous AMAs [1, 2], to discuss what lies ahead. We are:

  • Reyes Alemany Fernandez (raf), LHC operations
  • Andreas Weiler (aw), DESY and CERN Theory division
  • Federico Ronchetti (fr), INFN Frascati and ALICE Experiment
  • Beate Heinemann (bh), Lawrence Berkeley National Lab and ATLAS Experiment
  • Luca Malgeri (lm), CERN and CMS Experiment
  • Adam Morris (am), University of Edinburgh and LHCb Experiment

We'll sign our responses with our initials so you know who said what. Just to be clear, we are speaking with you in our personal capacities and CERN does not necessarily support the views expressed during the AMA. Joining us are a few of our friends from CERN:

We'll answer your questions from 16:00 until 17:30 CEST (UTC+02).

EDIT: A picture of us during the AMA. Clockwise from bottom left — Beate, Luca, Bartosz, Andreas, Adam, Reyes, Andres, Steve, Claire, André, Kate, Federico. Achintya's behind the camera.

About CERN and the LHC

CERN is the European Laboratory for Particle Physics, located in Geneva, Switzerland. Its flagship accelerator is the Large Hadron Collider (LHC), which has four main particle detectors: ALICE, ATLAS, CMS and LHCb. Nearly three years ago, CMS and ATLAS announced the discovery of a new particle that we now know is a Higgs boson. Scientists here are now looking forward to physics research at unprecedented energies.

Get social!

For updates, news and more, head over to our unofficial home on reddit: /r/CERN!

Comments: 3124 • Responses: 47  • Date: 

FantastiqueDutchie2304 karma

Explain to me like I am five: why are you doing this and what makes it important? What could we/you do with this data in the future?

askCERN3230 karma

i can give you an example. in 1800 the study of electricity and magnetism were considered an highly theoretical study with no practical uses. at most was used for circus shows. once understood by means of theory and experiments it shaped the modern world. try to think how could you live without electricity. the research we are carrying out at cern may seem far from everyday life today however will bring forward our knowledge of the natural phenomena and it has already practical spin offs. for instance accelerator technology is used for inoperable cancer surgery and as you may know the software protocol that powers the web was invented at cern (fr)

askCERN172 karma

We are just curious. Just as you (5-year old) are curious. For instance if you see a hole you want to find out if there is anything in that hole, and what it is. We see the Universe and particle physicists want to understand what it is made of and how it came to be. Whether this is useful or not we don't know as we don't know what we will find.


shafable1184 karma

I run LHC@Home, does my i5 actually help you guys in any sort of meaningful way?

askCERN1502 karma

of course you do. you are basically using the same geographically distributed computing protocol we run among our computing centers. so your CPU cycles are also crunching some bits of a potential new discovery! be sure of that! (fr)

askCERN538 karma

You can also run ATLAS@home. With that you actually help the ATLAS experiment simulate collision data. We have detailed simulations we run and these are critical for us to fully use the LHC data we record. And, we are always short of computing power (even though we have a lot). Thanks very much in advance!!!


askCERN456 karma

...and if you encourage also your friends to do so it will help us even more! (lm)

AlasPoorOstrava561 karma

Does anyone at the lab ever call it the Large Hardon Collider and giggle?

askCERN787 karma

I made that typo in an email response once. It's infrequent enough to still be funny.

A quick search on the CERN Document Server brings up 24 results. (am)

VeryLittle370 karma

I know from that song that "LHCb sees where the antimatter's gone."

Will collisions at 13 TeV give you new data to understand the baryon asymmetry in a way that lower energy collisions couldn't? How?

askCERN274 karma

During the next few years ("Run 2"), LHCb expects to more than double the amount of proton-proton collisions collected in 2011 and 2012 (technical talk: we hope to add 5 fb−1 of collisions to our existing 3 fb−1). In addition, the production rates for B hadrons are expected to roughly double with the increase in energy.

The size of the uncertainties on a lot of key measurements relating to matter-antimatter asymmetry are expected to decrease significantly.

See slide 19 in this presentation, and compare the columns highlighted in brown and blue. (am)

VeryLittle72 karma

Are there any specific theories/models you'll be able to confirm or rule out?

The size of the uncertainties on a lot of key measurements relating to matter-antimatter asymmetry are expected to decrease significantly.

I'm going to guess there's some CP violating processes you're trying to investigate?

askCERN111 karma

Are there any specific theories/models you'll be able to confirm or rule out?

In general: not directly. Our detector can make very precise measurements that give sensitivity to possible new heavy particles at energy scales far below their masses. If we measure something that disagrees with its Standard Model prediction, then that suggests there is something new, but it's difficult to conclusively say which model might be responsible.

I'm going to guess there's some CP violating processes you're trying to investigate?

Yep. We have already made several measurements of processes that are known to violate charge-parity symmetry. More B particles with Run II will give us access to rarer and rarer decays.


Uhfolks341 karma

Is there a certain energy "goal" you are aiming for? Or simply trying to increase it as much as you can?

notanotherclairebear425 karma

Well, in an ideal world we'd want as much energy as we can get! :) But there are many limitations. The LHC as it is currently designed is for 14 TeV centre-of-mass collisions. The magnets have now been trained for 6.5 TeV per beam, making 13 TeV centre-of-mass collisions, but if all goes well in the next year or so we'll try to get up to the design energy of 7 TeV per beam.

Of course, the experiments themselves were built specifically as per the energy designs, and we have already started working on the upgrades to our detectors for when we do the higher luminosity running.

And then, in the far future, people are already working on the design and physics scope for future colliders, even up to a 100km-circumference Future Circular Collider

thenoblepenguin208 karma

If the LHC is designed for 14 TeV center-of-mass collisions, why is it necessary to start at lower energies? What are the barriers to "get[ting] up to the design energy?"

askCERN392 karma

Hello! This is RAF from LHC Operations. Thanks for your question!! The commissioning process of the machine starts always with beams with very low intensity and at the injection energy of LHC (450 GeV). Those beam can be safely lost in our magnets without compromising the integrity of the LHC. Those beams help the operations crew to set up all the basic parameters of the accelerator to make sure that "when more energetic beams" are present, i.e. when we accelerate them, they will be "behaving correctly" i.e. the beam dynamics will be under control and the beams will not be lost anywhere in the magnets. Another point is that, before we accelerate the beams, we qualify all the machine protection systems, and this has to be done with beams that cannot damage the machine. Once the machine protection systems are qualify, more energetic beams, if fail, they will safely dumped in our beam dump systems. Another point: during season 1 (from 2009 to 2013) you might remember we ramp our beams to no more than 4 TeV per beam. The reason was a problem in the super conduction magnets interconnections. After very careful calculations by the experts, 4 TeV was found to be a safe energy to run LHC until we took the time, between 2013 and 2014 to fix the interconnections. This intervention allows us, today, to ramp our beams to, for the moment 6.5 TeV.

Please ask me again if the answer was confusing.

askCERN117 karma

Hello! This is RAF from LHC Operations. Thanks for your question!! The energy goal is 7 TeV per beam. This number is fixed by the magnetic field our magnets can achieved "by design" and by the circumference of LHC. So these are design limits, it is not possible to overcome them. To overcome the limits we would need magnets able to stand more than 12000 amps of current or an LHC-like with bigger circumference than LHC, i.e. more than 27 km. In fact the next proton-proton accelerator design is based on a 100 km circumference to get 50 TeV per beam (but this is a project under study). Some more details can be found here: http://home.web.cern.ch/about/engineering/restarting-lhc-why-13-tev

If I was not clear, let me know!

Kimbobbins207 karma

Is there any possibility at all of you guys creating a black hole in the middle of Switzerland and wiping out the human race..?

askCERN292 karma

In very simple terms, there is absolutely no risk of creating macroscopic black holes that are of any danger. For more details you can check a dedicated webpage where all details are given with also explanation about what we call hypothetical micro blackholes. (lm)

AsAChemicalEngineer154 karma

We're looking for all kinds of crazy things at the LHC. As experimentalists, which predictions by theorists does everybody like best?

Are you hoping for SuperSymmetry?

Extra dimensions?

Dark matter candidate?

Which triggers do you have your eye on?

askCERN193 karma

Indeed we are looking for a very broad range of things at the LHC, and Supersymmetry, Dark matter and extra dimensions are among them. As an experimental physicist I don't actually care myself which of them (if ANY) is right as I just want to find out about what Nature is. We conduct typically 100 searches for particles at any moment in time, and have also several hundred triggers which decide which data we record. Dark matter is indeed a particularly well motivated thing to look for as we know for sure it exists! We just don't know what it is and indeed we search for events with a large imbalance in momentum to find dark matter.


rossislegend136 karma

Hey, I visited CERN last November with my school, glad to see an AMA.

What is the biggest thing limiting your research with the LHC?

askCERN157 karma

Glad that you enjoyed your visit! Currently the LHC is the most powerful machine in the world for this kind of research and it is ready to produce physics results at least for the next 20 years. In collider physics there are usually two limiting factors: 1) the total available energy (we are now at 13 TeV) and 2) the rate of collisions we produce. More energy opens up the possibility to produce more massive particles while the collisions rate increase the possibility of producing very rare processes. We are already addressing the collision rate with upgrades foreseen in the next few years that will push it up by two orders of magnitude. For a substantial increase in energy we have started studies for a new potential accelerator that might push it up by a factor of 10 but this will take several decades to be realized. We are sure that the LHC will show us the way to go before building the next machine! (lm)

insertacoolname103 karma

As far as I understand dark matter doesn't interact in any other way than gravity. Considering that any dark matter created in collisions will be much to small for the gravity to be detected. How will you study it? Will you just be looking at energy calculations and saying that some of the energy disappeared so it must be dark matter?

askCERN146 karma

Good question! Although we have very good evidence for dark matter interacting gravitationally, we don’t know if dark matter interacts with known matter. In order to produce dark matter at the LHC we need to assume that there is such a (possibly weak) interaction. In the most interesting models of physics beyond the Standard Model, dark matter does indeed interact with known matter: we can hope for man-made dark matter to be produced during the next run! Once produced we could then detect it using missing energy signatures. (Dark matter is also searched for in important underground and in satellite experiments.)


dudettte101 karma

what is the biggest enigma in particle physics that you guys want to find answers in your lifetime?

askCERN162 karma

These are my top three questions:

  • What is dark matter is made of ? We know it's there but have never been able to produce or detect it on earth.

  • Why the Higgs is so much lighter than the Planck mass? This is the so-called hierarchy problem (http://arxiv.org/pdf/0801.2562v2.pdf). Supersymmetry or a composite Higgs would explain this but we haven't seen any evidence for either theory.

  • Why are there 3 copies of quarks and leptons? They have the same properties (e.g. charges and spins) but they have very different masses, e.g. the up quark is ~100,000x lighter than the top quark. We have no idea why that is.

Edit: fixed typo, thanks roarphony. Found a better link.


BartJoJo86 karma

Hi, so now that Higgs is around 125GeV are the theories of Multiverse hold any merit?

askCERN156 karma

Well… Before the discovery, we had two main contenders for physics beyond the standard model both predicting a range of Higgs masses (supersymmetry and the Higgs as a composite particle, like the e.g. the proton). Supersymmetry prefers a slightly lighter Higgs and composite Higgs models generically predict heavier Higgs particles. Both theories are still alive since the predicted Higgs ranges overlap with what has been discovered, but the allowed parameter spaces have been reduced and the kind of cancellations required to make it work have increased a bit.

Multiverse theories do not provide clear predictions for the Higgs mass, but they offer an explanation for the absence of any visible beyond the Standard Model physics (like new particles). Maybe one could say: as long as we keep not finding any evidence for physics beyond the Standard Model, theories of the multiverse will increase in attractivness for some physicists.


dudettte83 karma

any chance of finding graviton?

askCERN127 karma

Yes! There are theoretical ideas that there could be additional spatial dimensions in the world, and if those are large or warped it may be possibly that we see signs of gravitons at the LHC. You can find more about it here.


LBJSmellsNice81 karma

If the LHC was transparent, what would we see when the collisions occur?

askCERN147 karma

no you cannot see collisions with naked eyes. we need detectors to record the product of the elementary interactions and powerful computer to reconstruct the traces that these particles leave into them such as tracks of energy depositions (fr)

anondude4760 karma

Can't believe I caught an AMA as its happening.

Hey guys, I have a few questions:

1) Pop science keeps claiming you're trying to recreate conditions at the Big Bang. Are you actually doing that? If yes, are you trying to recreate inflationary epoch as well? If yes, can you ELI5 as to how?

2) There was a brilliant article on Aeon magazine (link) about theoretical physicists taking mathematics way too literally. As in, just because the mathematics of string theory is beautiful, many physicists think that multi-universe is real. Do you think this is in any way hindering the progress of science at the moment? Or does this sort of public debate happen on the sidelines and not affect actual theoretical physics work?

3) Why do you guys even use Google+?

edit: linked article

askCERN74 karma

1) we are creating conditions shortly after the big bang, about 10-10 seconds, so 1 tenth of a billionth of a second.

2) This is an interesting question. Indeed beauty has been a powerful guide to theorists in the past and so it is used as a guide for the future. There is a nice article by Eugene Wigner on the Unreasonable Effectiveness of Mathematics in the Natural Sciences


andykazam59 karma

What was the party like after you discovered Higgs Boson?

askCERN49 karma

About a year after the discovery we also got a prize from the European Physics Society and we used that award to throw a big party on the lawn at CERN for all of ATLAS and CMS.


jrohlfing40 karma

You are all doing fantastic and extremely important work. What are you looking forward to discovering this season?

PS Are you looking for any amazing IT/IS people? I would love to move to Switzerland and work on this amazing project.

askCERN45 karma

Thanks! It's a quite an exciting time for us. After the Higgs discovery we are now looking for new physics that we know must be there. One of the many searches is to detail what the dark matter might be and if it is composed by " standard" particles. We know about the existence of dark matter by its gravitational effects but we don't have really a clue of what it is. LHC might help in finding it. CERN as a quite active IT division. Please refer to the cern jobs page and good luck for your application. (lm)

ross_bohr28 karma

Isn't the LHC designed for 14 TeV? If yes, when are you reaching it?

askCERN55 karma

Yes, indeed the LHC is designed for 14 TeV. The reason we are running at slightly lower energy this year is that it takes time to condition the magnets to be able to hold the current necessary to run at higher energy. This conditioning of the magnets to go to 14 TeV will be done in the future but when exactly is not yet clear. For now we are already very excited to have 13 TeV collisions as this is already a big increase compared to the previous 8 TeV.


amansuraj12326 karma

It's believed that there was equal antimatter and matter at the beginning. Also, I saw a video which said that LHC season 2 aims 2 find out what happened to the antimatter. Are there any theories about this that physicists think might answer the question?

Thanks Aman

askCERN50 karma

Yes! There are plenty of models that try to explain why we live in a universe with much more matter than antimatter. They can be grouped under the categories of 'Baryogenesis' and 'Leptogenesis', but we generally talk about the former.

There are three conditions that Baryogenesis must satisfy (as posited by Andrei Sakharov):

  1. There must exist processes that produce more matter than antimatter. (Baryon number violation)

  2. There must be an asymmetry between these processes and their inverse counterparts. (Charge-parity violation)

  3. The imbalance must have occurred away from thermal equilibrium. This one is difficult to explain.

The first condition has never been observed, but LHCb and other experiments are searching for it.

Measuring the second condition is the key focus of LHCb: we have known for more than 60 years that the Weak force treats matter and antimatter slightly differently, and decays of heavy particles are a good way to measure this asymmetry and improve the precision of the numbers used in theory.


RealBillWatterson24 karma

What language do you speak at CERN?

askCERN56 karma

the official languages at CERN are (broken :) english and french. however many other languages are spoken. many physicists from all over the world work and communicate at CERN (fr)

celerym23 karma

Any plans for facilities to supersede the current experiments?

askCERN27 karma

Yes! We are already thinking about this. You have to start early: the first discussions about the LHC took place in 1984. More information on future projects is e.g. here (https://fcc.web.cern.ch/Pages/default.aspx). One of the ideas is to dig a larger ring to reach energies of the order of a 100 TeV.

CERN actually also has a range of smaller experiments running (http://cast.web.cern.ch/CAST/cast_pub.php) or planned which are not related to the big ring, e.g. (http://ship.web.cern.ch/ship/) or (http://iaxo.web.cern.ch).


askCERN4 karma

yes! studies are ongoing already to design a 100-km accelerator ring https://fcc.web.cern.ch/Pages/default.aspx (fr)

jabbaciv22 karma

What are some of the long term practical applications you can envision for this research? Feel free to go wild.

askCERN60 karma

you may have heard about project for reaching mars or even for deep space travel. one showstopper there is propulsion. we won't get very far with chemical thrusters. fully understanding the nature of fundamental forces may pave the way for a new kind of engine that can power deep space exploration. however developing space technologies is not a current research topic at CERN (fr)

chelsea_avb21 karma

When will the next update meeting be about the newer particles that you found this time around with the higher energy collisions? Do you expect to see newer particles this time around?

askCERN30 karma

The short answer is that we don't know since we just don't know what particles exist in Nature. We are exploring higher mass particles in the new run and if there are any we might find them in a few months, or it could take years or even decades. It depends a lot on what exactly the new particles are, what their mass is etc.


AshFair18 karma

Could you send round an orange in one direction and a melon round the other and just see what would happen when they collide?

askCERN48 karma

Hmmmm... there are a few problems with that. Oranges and melons don't have an electric charge (unlike protons) and so we cannot make them go in a circle. We could not use neutrons either. To accelerate an orange to the energy of a proton would need a collider much much more powerful. An orange is more than 1025 times heavier than a proton and so it would take that much more energy. Unless we can achieve such spectacularly high energies we will just get an orange-melon smoothie.


venustrapsflies31 karma

we will just get an orange-melon smoothie

you say that like it's a bad thing.

askCERN24 karma

fair enough, it would probably be quite tasty!

FlooDragon9914 karma

As an undergrad physics student really hoping to get into this field, what can I do in my own time that might aid me on the experimental side? Get good at coding? EE work?

Also, I'm curious to hear about how you guys ended up at CERN, I know most people don't always know where their life is taking them, any cool stories?

Thanks for the AMA, big fan of your work!!

askCERN21 karma

Indeed getting good at coding is a great skill to have, and extremely useful for particle physicists. And, try to find an opportunity to do research during a summer with a professor. There is also the CERN summer student program you can apply for.


NathaSupertramp13 karma

How long will it take for your results to become statistically significant?

(Or how many runs does it take?)

askCERN19 karma

This depends a lot on what "it" is. For instance there are some particles called "excited quarks" for which only a few weeks of data could already reveal a statistically significant signal. However, for other theories it can take years. Since we don't know what our next discovery is we really don't know how long it takes. We are doing many analyses all simultaneously to make sure we cast a wide net and find whatever there is.


thehawkpower12 karma

Hi, I always wondered if what you guy's are doing could be done on a much smaller scale?

askCERN12 karma

It depends on what you mean by scale. If it is with "reduced energy", this is, I'm afraid, not really possible. Energy gives us the way to explore new territories. The usual analogy is the microscope. The more energy we manage to put in the collisions, the more is the magnifying factor we can reach. If size is intended to be physical dimensions of the accelerator there are promising R&D studies on new technologies that would allow to reach the same energy in much smaller space and building up the equivalent of the LHC in a "room". For more details you can have a look at this webpage (lm)

askCERN10 karma

think of the LHC and its detectors as a lenses. the smaller the details you want to study the larger have to be the lenses. so the answer is no. the discovery potential of the LHC and its detectors cannot be achieved with smaller scales (fr)

askCERN5 karma

Some of the questions we are trying to answer are also addressed in a complementary way on a smaller scale. For instance dark matter is being looked for in experiments deep underground which are much smaller than the LHC, see LUX for instance. But to get collisions at this high energy we need currently sucha large accelerator. However, there is very interesting research ongoing indeed to invent technology to make much more powerful accelerators that would then be able to create such high-energy beams with smaller facilities, see this wikipedia article about plasma accelerators.


tahlyn10 karma

What sort of particles are you looking for? Everyone knew about the Higgs Boson, but what sort of things do you anticipate uncovering with your current experiments? Or is it just verification of the Higgs?

El Psy Congroo

askCERN7 karma

The discovery of the Higgs has basically completed all missing pieces of the theory governing the interaction among particles (and as such governing the worls as we know it, apart for gravity:-)). This is what we call Standard Model. We know that this theory breaks up at very high energy and some kind of new physics must enter in the game. It is expected that this "new physics" materializes with new particles as well as new interactions among them. They might be linked to dark matter (see other posts here) or even more exotic kind of matter. The new energy opens up a new window on these hypothetical particles and we are ready to catch them (if they are there). (lm)

iLoVeSpOnGeBoB6 karma

Is there any kind of blog one of you run, a live feed of sorts when you are conducting these collisions? If not, is there any possibility of that happening in the future?

askCERN8 karma

I don't run these, but there are a few neat web tools

Live voice announcer: http://announcer.web.cern.ch/announcer/

Lots of graphs and charts about the LHC and more: https://op-webtools.web.cern.ch/op-webtools/vistar/vistars.php?usr=LHC1

A twitter feed with live comments from the people operating the LHC: https://twitter.com/lhcstatus/

SlashStar5 karma

As someone who has no knowledge of physics what should I be most excited about?

askCERN13 karma

I would say that it is exciting to explore Nature. We are sort of detectives trying to understand how the Universe works. This is a long process and we are making steps towards that. The LHC has for instance found out that the vacuum is permeated by a Higgs field, a field with no direction or orientation. This is interesting!? As a scientist it just seems like Nature is this big puzzle out there and we should tried to understand it. It is actually fascinating to me how much mankind has already understood (particularly in the last century). The LHC is really at the forefront and exploring Nature very deeply.


enken903 karma

What kind of previously unobserved high-energy phenomena does the standard model predict will happen at 13 TeV? What kind of observations at 13 TeV could refute the standard model?

askCERN4 karma

What kind of previously unobserved high-energy phenomena does the standard model predict will happen at 13 TeV?

The particles of the standard model are all lighter than the top quark (175 GeV). We have naturally produced all of them at the LHC at 8 TeV. What we can hope for at the next run are either very energetic processes with known particles (and use those to test if they behave like in the SM) or look for very rare standard model processes. Rare processes are extremely useful tests of the standard model.

One of the most interesting targets for the LHC at 13 TeV is to simultaneously produce a pair of Higgs bosons. This would allow us to learn more about nature: we can test the shape of the Higgs potential (the famous Mexican hat) and measure how strongly the Higgs boson interacts with itself.

What kind of observations at 13 TeV could refute the standard model?

There are many possibilities, e.g. discovering a new particle, finding anomalies in the behaviour of the Higgs boson, or measuring a process that is forbidden in the standard model (or predicted to be unobservable small).


Jeremy1026-1 karma

I read an article that linked the Nepal earthquakes to the LHC. Do you think there is any merit to the dumps of energy into the ground follow LHC runs could have contributed to the disaster?

askCERN7 karma

the energy released by the LHC beams when they are dumped is practically negligible with respect to any noticeable geological activity. for instance geyser in Iceland may release much more energy than a beam dump and for sure cannot trigger a quake on the other side of the world and not even locally (fr)