ATLAS collision animations
Posted on February 8, 2013 | by Serena | No Comments
At the Oskar Klein Center there are researchers working hard to figure out the content of the universe and the fundamental laws of physics. Erik Johansson, Professor emeritus at Stockholm University and Director emeritus of the Stockholm House of Science, has created some animations aimed at describing ATLAS collisions happening in Large Hadron Collider at CERN.
When two high energy protons collide, it is the constituents of the protons – the quarks and gluons – that interact. The dynamics of quark and gluon interactions are described in five animations, focusing on the main dynamic features. The animations describe the production of the Higgs boson, top quarks and particle jet production.
Jets of particles – gluon exchange
One very common interaction is the exchange of a gluon between a quark in one of the protons and a quark in the other proton, resulting in several jets of particles.
The Higgs particle – gluon fusion
The Higgs particle is expected to be produced in collisions when a gluon from each of the protons merges in a high energy collision – a gluon fusion.
Top quarks – gluon fusion
A pair of top quarks – a top quark and an antitop quark – is expected to be produced in collisions when a gluon from each of the protons merges in a high energy interaction.
The Z particle – quark antiquark annihilation
The massive Z particle is produced when a quark and an antiquark annihilate. Read more
Interview with Oscar Stål
Posted on January 29, 2013 | by Serena | No Comments
Oscar Stål is one of the OKC fellows working at the Cosmology, Particle astrophysics and String theory group (CoPS) since August 2012. He is doing his second postdoc and his filed of interest is particle physics phenomenology. He is Swedish and studied both as undergraduate and for his PhD at Uppsala University, before moving to Hamburg.
Can you tell us a bit of yourself? Where are you from?
I am 30 years old, and this is my second Postdoc. Before joining the OKC I spent two very nice years in the theory group at DESY, Hamburg. Originally I am from Enköping, which is a small town about 80 km west of Stockholm. I am married and we have a 2-year old son, Anton, who takes up most of my free time.
What is your field of research?
Broadly speaking, my area of research is particle physics phenomenology, that is theoretical work in close connection to experiment. The main experiment we consider at present (and probably for many years to come) is the LHC at CERN. To be somewhat more specific, my main interests lie in the phenomenology of physics beyond the standard model (SM), such as supersymmetry, with its interesting connections to electroweak symmetry breaking (the Higgs!) and also, of course, the dark matter. Read more
Discovery of a black hole in Andromeda
Posted on December 19, 2012 | by Serena | No Comments
The discovery of a black hole enjoying a feeding frenzy in our nearest neighbor galaxy, Andromeda, has provided new insights into a mysterious class of extreme astrophysical objects called “ultraluminous X-ray sources”.
It isn’t unusual for material falling into a black hole to generate copious X-ray emission, but ultraluminous X-ray sources are so bright that they sometimes outshine their entire host galaxy in the X-ray band. Astronomers have spent years debating the nature of these enigmatic objects and two main scenarios have emerged. Either ultraluminous X-ray sources are unusually massive black holes feeding steadily on gas from an orbiting companion star, or alternatively they may be black holes around ten or twenty times as massive as our Sun that are somehow being force-fed by the in-falling gas.
This image shows the Andromeda galaxy (also known as M31) as seen in X-rays with ESA's XMM-Newton space observatory (shown here in red, green, blue and white, according to the energy of the different sources). This X-ray view is combined with an image of Andromeda taken with ESA's Herschel space observatory at far-infrared wavelengths (shown here in grey). Amongst the hundreds of X-ray sources revealed by XMM-Newton in Andromeda are: novae – binary systems comprising a white dwarf accreting material from a companion star; X-ray binaries – binary systems hosting a neutron star or a black hole accreting material from a companion star; and supernova remnants. The sequence of images at the top depict the centre of Andromeda and were taken with XMM-Newton on four occasions during 2012. These images illustrate the discovery of a new source, XMMU J004243.6+412519 (highlighted with a circle). XMMU J004243.6+412519 was first detected on 15 January 2012 within an XMM-Newton survey of Andromeda, designed to study the X-ray source population of this galaxy with particular emphasis on novae. On 21 January 2012, XMM-Newton recorded a significant brightening of this source; with a luminosity in excess of 10^39 erg/s, it was classified as an ultra-luminous X-ray source, or ULX. This is only the second ULX known in the Andromeda galaxy. The source then became fainter, as shown in the last image of the sequence, taken on 8 August 2012. XMMU J004243.6+412519 is an X-ray binary system consisting of a stellar-mass black hole that is accreting matter from a low-mass companion star. The source's dramatic boost in X-rays indicates a transition to an accretion rate close to the black hole's Eddington limit, or even above it. Credit: ESA/XMM-Newton/MPE
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Happy ending for 2012!
Posted on December 19, 2012 | by Lars | No Comments
Hello all OKC-related people,
It is time to summarize the year 2012 for the Oskar Klein Centre. We will soon reach midterm (after 5 years, end of June 2013), and soon thereafter there will be an international review of all the Linneaus centres of 2008 conducted by Vetenskapsrådet. At this review, the scientific performance will be the top priority.
We received earlier today very good results for the bibliometry of OKC, as assembled by Stockholm University’s (SU’s) bibliometrist, Per Ahlgren. In fact, OKC is by quite a large margin top-ranked at SU in a field-normalized study. The Rektor, Kåre Bremer, sent personally his congratulations to this result.
Of course will still have to look forward, and there are a few interesting new scientific activities at the OKC emerging at the moment. The first is the Palomar Transient Factory (iPTF) and the Zwicky Transient Factory, which will open a whole new window for observations of supernovae and other transient events. At OKC, this collaboration with Caltech and a number of other outstanding institutions is led by Claes Fransson, Ariel Goobar and Jesper Sollerman.
Another interesting development concerns CTA, where Jan Conrad and myself have contacts with the US part of CTA, CTA-US, about collaborating on new mid-size mirrors that would roughly double the sensitivity of CTA for dark matter searches.
The IceCube collaboration have detected a couple of very interesting events with very high energy. They have started to investigate whether an even denser sub-array than their DeepCore, named PINGU, will be feasible. This could improve the dark matter search substantially.
Of course, there is great hope that all the 7 and 8 TeV data collected by ATLAS at LHC will show unexpected signals. For the time being, there has been discovery of a “Higgs-like” particle of mass around 125 GeV, but there remains a lot more data to search for exotic signals beyond the Standard Model of particle physics. This will surely be enough to keep our OKC-involved people searching for dark matter in the data busy over the next couple of years, when the machine will be stopped to begin the upgrade to roughly twice the energy.
Finally some assembled pieces of news of relevance to OKC during the last year: Read more
Interview with Emily Freeland
Posted on December 11, 2012 | by Serena | No Comments
Emily Freeland is one of the OKC fellows that joined the Oskar Klein Center after the summer. I asked her to tell us a bit about her research to get to know her better.
Hi Emily and welcome! Can you tell us a bit of yourself? Where are you from?
I am from the US. I grew up in Bloomington, Indiana, did my graduate work at the University of Wisconsin with Eric Wilcots, and my first postdoc with the newly formed astronomy group at Texas A&M University with Kim-Vy Tran.
What is your field of research?
The main theme that runs through the majority of my research is an exploration of the role that environment plays in galaxy evolution. The universe has a filamentary structure and these filaments are populated by individual galaxies and groups of galaxies. The group environment is the most common environment in the local universe so characterizing its influence is an important part of understanding the physical processes affecting the majority of galaxies.
Isolated galaxies tend to be disky, gas-rich, and currently forming stars. At the other extreme, galaxy clusters contain thousands of galaxies, many of which are red in color, ellipsoidal in shape, and not forming new stars. Galaxy groups span the range of properties intermediate between isolated galaxies and clusters. In our hierarchical universe, galaxy groups are the building blocks of galaxy clusters and as such we would like to understand to what extent galaxy morphologies and star formation rates are transformed in the group environment prior to their assembly into clusters.
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LOFAR starts Cycle 0 observing
Posted on December 5, 2012 | by Garrelt | No Comments
Last Saturday, December 1st, at 0:00 UT, LOFAR started its first official observing season, known as Cycle 0. The season will last 6 months and the observations that will be done are based on proposals that were sent in earlier this year. So as of last Saturday LOFAR can be said to be an operational telescope. I do not have detailed information on how the observing time in Cycle 0 will be distributed, but based on the decisions the Swedish LOFAR consortium made regarding the Swedish time, all different science drivers for the LOFAR telescope are likely to get time.
A 15 x 15 degree field around the North Celestial Pole as observed with the LOFAR High Band antennas. Several 10,000s of radio galaxies are detected. Image by Sarod Yatawatta for the Epoch of Reionization project.
LOFAR is a radio telescope observing at low frequencies. There are two frequency bands, the low band, 10 – 90 MHz and the high band, 110 – 250 MHz, which each come with their own set of antennas. LOFAR is a radio interferometer, consisting of different stations spread out over Europe, but with a large concentration of them in the north-east of the Netherlands.
With LOFAR a new wavelength regime in astronomy is opening up. Very few and limited observations have ever been performed at these low frequencies. However, several astrophysical objects are known to produce observable signals in this range. This includes for example the intracluster gas of clusters of galaxies, pulsars, the Sun, radio jets from active galactic nuclei, star forming galaxies in the nearby Universe, and cosmic rays entering the Earth’s atmosphere. LOFAR will also attempt to be the first telescope to detect the redshifted 21cm signal from the earliest epoch of galaxy formation (also known as the Epoch of Reionization). If this attempt is successful this will mean a major breakthrough in observational cosmology. This is the project where people at the Oskar Klein Centre are involved (Hannes Jensen, Kai Yan Lee, OKC fellow Kanan Datta, new postdoc Suman Majumdar and myself).
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Fermi observations of a GRB questions synchrotron emission based models
Posted on October 5, 2012 | by Serena | No Comments
photo by NASA och General Dynamics
Gamma-ray bursts are the biggest explosions observed in the Universe, and are among the most distant sources that can be seen. The emission we see is probably sent out when a black hole is born. In this catastrophic event matter is shot out almost at light speed in two narrow jets, and if the jet happens to point towards us we see a bright flash of radiation.
Interview with Katherine Freese
Posted on September 28, 2012 | by Serena | No Comments
Katherine Freese is in Stockholm these days since she will be receiving a prestigious Honorary doctorate at Stockholm University on Friday, the 28th September. I met with her in one of the offices at the Oskar Klein Centre in front of cup of coffee to talk a bit with this energetic and fascinating scientist, and try to grab her secrets.
What was you reaction when you heard you will receive this title?
Oh I was very happy, I think it is really an honor to get this. First when Lars told me I was a candidate, and then when I got it, I was very excited. It is going to be great tomorrow. Although I am jetlegget I am not nervous at all, I am excited!
So let’s see if we can get to know a bit about your career then. Lets start from the beginning: how did you get the idea of studying physics and how you turned into a cosmologist?
My parents are both scientists. My father has been student of Heisenberg before turning into biology, and of course the role model I had in my family pushed me for a career in academics. But how did I get into physics, well, that was probably just by chance. I went to a summer school in relativity when I was 15 years old, and I though that was very interesting. But really, I though physics was a kind of broad field that could open many possibilities, and then I was good at it. I think this is the way many people choose what to study, by exclusion, if you are good at something and not every one else is, you have to go for it. I did not have passion for astronomy as a kid, not at all. Isn’t this how most people choose their field of work? I tried a number of different styles of physics (experimental high energy, solid state, etc) then I found my inspiration with cosmology. I was living in Japan for a while after I graduated from Princeton. I was only 20 e I was teaching English, and then I was hospitalized. I was so bored that I took a book called Spacetime Physics, by Taylor and Wheeler, and that really made an impression on me and really turned me on and made me wanting to keep on studying cosmology. And I also felt it was a challenge!
Fresh Summer Harvest of ATLAS Results: Top quarks, Sleptons and Gauginos
Posted on August 15, 2012 | by Christophe | No Comments
Since monday the last of a string of summer High Energy Physics (HEP) conferences is unwinding in Beijing, SUSY-12 and before that in Melbourne ICHEP-2012. Some results with leading contributions from the Stockholm HEP group figure high in the topics of discussion. Finally ATLAS physicists can breathe a little bit, with most results out for now. The Higgs boson discovery got a lot of attention, and this is great because it is not every day that there is a discovery of that magnitude, but there is an other important reason: simply said, the existence of the Higgs boson is at the basis of much of the research being carried out at Stockholm University and in ATLAS.
One of the mysteries of the Standard Model is the top quark which has a mass (172 GeV) much much higher than the other quarks, this is also much heavier than expected initially and still remains unexplained. But thanks to the Higgs mechanism we know that the mass of a particle is set by how strongly it interacts with the Higgs field, so for some unknown reason the top quark very strongly couples with the Higgs. This is why we decided to study the top quark properties in details. It could be that some of the top quark properties deviate slightly from the standard model of particle physics, or that some of the top quarks are produced via new mechanisms inside the proton-proton collisions at LHC.
Normalised measured top differential cross section as function of the top quark pair invariant mass and theoretical predictions.
New heavy particles could decay into pairs of top quarks. The HEP group in Stockholm has lead the effort of a measurement of the so-called top quark pair differential cross section (see http://arxiv.org/abs/1207.5644 ), which would for instance be able to detect the presence of new particles decaying into top quarks pairs in the invariant mass distribution of the two top quarks. Similar measurements were performed at Tevatron, but thanks to the very high center of mass of the LHC, it is possible to probe new particles to much higher masses. No new particle turned up, and this measurement will have to be redone in 2015 when higher, 14TeV of energy LHC data will be available (and allow to probe even higher particle masses). For now this completely new measurement will allow theorists to tune and improve Monte Carlo simulation programs so that they agree with this new data in a previously unexplored region of phase space.
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Bad news for PoGOLite once again.
Posted on July 30, 2012 | by Mark | 1 Comment
PoGOLite during tests at Esrange in June
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What is dark energy? What and where is the dark matter? What physics lies behind the most energetic processes in the Universe such as supernovae, gamma-ray bursts and black holes?
