Large Hadron Collider : Beaming success

Discussion in 'International Politics' started by ppgj, Jan 15, 2010.

  1. ppgj

    ppgj Senior Member Senior Member

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    Beaming success

    R.RAMACHANDRAN

    After a 14-month hiatus, the Large Hadron Collider is poised for good physics runs.

    PICTURES COURTESY CERN
    [​IMG]
    Compact Muon Solenoid detector. CMS is designed to see a wide range of particles and phenomena resulting from high-energy collisions at the LHC. Consisting of 100 million individual detecting elements, each looking for signatures of new particles and phenomena at 40 million times a second, it is one of the most complex scientific instruments ever constructed.

    IF the year 2008 ended on an extreme low for the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN), 2009 ended on a real high note. When the LHC was shut down for Christmas on December 16, 2009, it had ended its first full period of operation, as a CERN release put it, “in style”. The two counter-rotating beams of protons in the accelerator attained a record-breaking beam energy of 1.18 tera (trillion or 1012) electronvolt (TeV) each, which means a total collision energy of 2.36 (1.18 + 1.18) TeV. The highest energy reached hitherto was 0.98 TeV per beam at Tevatron, the linear hadron collider at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, in 2001. The particle detectors located at different points along the 27-kilometre circumference of the ring accelerator had already recorded interesting collision events at this energy, which is just one-sixth of the LHC’s designed peak value.

    Key questions

    In the LHC, the counter-rotating proton beams are brought to intersect at various points along the accelerator ring where particle detectors of the six different experiments (see box) will record the characteristics of the secondary particles that are produced in the collisions, such as their energies and momenta, and enable their identification. From these data, scientists expect to find answers to the following key questions. Is there any new physics beyond the Standard Model (SM) – which has been enormously successful in describing sub-nuclear physics at lower energies – lurking at the energy scales that the LHC is slated to attain? Are there any signs of new particles like those predicted by supersymmetric theories? And, most importantly, does the Higgs boson, the hypothetical particle in the SM that endows other particles with mass, exist at all and what determines the hierarchy of particle masses that is seen in nature?

    “So far,” said CERN Director General Rolf Heuer, “it is all systems go for the LHC. This first running period has served its purpose fully: testing all the LHC systems, providing calibration data for the experiments and showing what needs to be done to prepare the machine for a sustained period of running at higher energy. We could not have asked for a better way to bring 2009 to a close.”

    “It has been a truly remarkable 24 days,” said Steve Myers, CERN’s Accelerator and Technology Director, in his presentation to CERN’s audience on December 18 soon after its Christmas shutdown. “Things have moved so quickly that it has been hard to keep up with the progress. [There have been] Many firsts for the LHC and the detectors,” he added.

    Indeed, this time around there was no false start or any major hiccup in putting the machine back in operation after its 14-month hiatus. The accelerator was shut down in September 2008 for repairs and upgrade following the mishap caused by faulty soldering of the busbar joints between superconducting magnets that maintain the beams in their paths (Frontline, January 30, 2009). After the initial check runs that began in October 2009, as expected (Frontline, December 4, 2009), the LHC was fully back on stream on November 23, 2009, with proton beams sent around the full circle of the LHC simultaneously for the first time since the fateful day of September 19, 2008.

    Following the successful first run, the world’s most powerful accelerator is now poised to attain its chief objective of extracting physics out of the zillions of head-on collisions among these high-energy protons in the first quarter of 2010. The LHC has now been put on standby mode and will restart in February following a short technical stop to prepare the machine for its beam energy to be ramped up to the planned value of 3.5 TeV for real physics to begin (Frontline, December 4, 2009).

    Ramping up the machine to a higher collision energy of 7 (3.5 + 3.5) TeV – three times its present 2.36 TeV – requires higher currents in the LHC magnet circuits. A higher energy also implies more exacting demands on the new machine protection systems. The commissioning work for higher energy will be carried out in January, according to a CERN release. During this technical maintenance period, one of the experiments (CMS), in fact, plans to open up the detector in order to improve the reliability of the cooling system for the end caps.

    During the restart, things progressed more smoothly than the LHC scientists and engineers had expected and the record-breaking energy of 1.18 TeV per proton beam was reached just within a week of the restart. Notwithstanding the conservative approach warranted by the accident, which called for a careful injection of the beam and cautious modulation of its energy, there was no serious hold-up. (There was, however, a power cut in one section of the accelerator – across the site at Meyrin – caused by a failure in an 18,000-volt line on December 2 that shut down the main computer centre and caused an abrupt cessation of all operations. The most critical element, namely the cryogenics that keeps the machine at 1.9 Kelvin (-271oC), however, remained unaffected. Until this “minor teething problem” was fixed, the Meyrin site drew power from a diesel power back-up system.)

    After all the multitude of checks in the various parts of the machine, the entire machine was cooled down to its operating temperature on October 8, 2009. On October 23, the first particles were injected, but not circulated. A beam was steered around three octants of the machine on November 7 when the so-called “splash events” were recorded (see Frontline, December 4).

    [​IMG]
    CANDIDATE COLLISION EVENT. The collisions, though only for a short period as a trial, were good enough to test the synchronisation of the beams and gave the experiments their first chance to witness proton-proton collisions.

    And on November 20, circulating beams in both directions were established separately. After studying each beam carefully over the next couple of days, the beam lifetimes could be brought up to 10 hours from its earlier 10 minutes. And on November 23, the beams were ramped up to 450 giga (or billion) eV (GeV) each and the first collisions (at a total of 900 GeV) were recorded. The corresponding current in the dipoles is about 0.8 kilo ampere, as against the peak value of 12 kA at 7 TeV per beam.

    These collisions were, however, few because of the low intensity of the beams. Each beam had only one pilot bunch of particles (of over two billion protons) as against 2,808 bunches of more than one hundred billion protons each when the LHC becomes fully operational. Also, despite billions of protons in each beam, each bunch would be mostly empty space unless it is “squeezed” to increase the chances of collisions, and for this test phase the beams were not “squeezed”. Also, these collisions were only for a short period as a trial. But this was good enough to test the synchronisation of the beams and gave the experiments their first chance to witness proton-proton collisions. With just one bunch circulating in each direction, the beams could be made to cross at only two points in the ring. First, they were made to cross at ATLAS and CMS detectors, both of which were tuned to record collisions. Later the beams were made to cross at ALICE and LHCb experiments.

    Coming just three days after the restart, these developments indicated excellent performance of the beam control system. This prompted Myers to remark: “I was here 20 years ago when we switched on CERN’s last major particle accelerator, LEP [Large Electron Positron Collider]. I thought that was a great machine to operate, but this is something else. What took us days or weeks with LEP, we’re doing in hours with the LHC.”

    These first events were useful for the experiments to check if the detectors are ‘in time’; that is, when a collision occurs, every part of the detector sees it happening at exactly at the same time. Such precise timing is critical for the huge detectors, each of which has millions of detectors with some of them separated from each other by several metres. Each of these detector elements must be synchronised to within one billionth of a second.

    The smooth operations notwithstanding, the LHC operators were still being cautious and were expecting the LHC to reach the record-breaking energy of about 1.2 GeV per beam only by Christmas. However, this happened much sooner than expected. In the early hours of November 30, the LHC accelerated its twin beams to 1.18 TeV, demonstrating once again the smooth progress of the machine. At 21.48 hours on November 29, beam 1 was accelerated to 1.05 TeV and three hours later both the beams were successfully accelerated to the record value of 1.18 TeV, corresponding to a dipole current value of about 2 kA.

    After attaining the highest energy ever reached in a particle accelerator, the LHC went through a concentrated commissioning phase aimed at increasing the beam intensity, which would provide each of the experiments adequate numbers of collisions for more accurate calibrations of the detectors and for testing their millions of complex detector elements. This phase was intended to ensure that these higher intensities can be handled safely and that stable conditions during collisions can be guaranteed for the experiments. This phase took around a week and the first real period of collisions started on December 6, though initially at a ramped-down energy of 450 GeV but with improved intensity with four bunches in each beam and five billion protons in each bunch. On December 8, the beams were once again accelerated to 1.18 TeV. Already, with this marginal increase in intensity, on December 6 the CMS experiment recorded interesting candidate events with a muon in the forward direction and ‘dijet events’ with twin high-energy jets of particles in the transverse directions opposite to each other.

    On December 11, the beam intensity was increased to 70 billion protons per beam and in the early hours of December 14 the LHC operators achieved beams with much longer lifetimes. Having been able to maintain the beams extremely stable for long periods, the same night the number of proton bunches were increased to 16 per beam with the total intensity reaching 1,850 billion protons a beam. This greatly increased intensity, in fact, resulted in interesting multijet and dimuon events in the CMS experiment.

    Finally, in the early hours of December 16, the beams were also “squeezed”; that is, their transverse profiles were reduced by focussing with magnets to increase the collision rate. Now that the beams had not only achieved record energy and were more intense and stable but also were well focussed, the initial run of the LHC after a highly successful restart was officially brought to a close the same evening. The LHC is now all set for the first physics run with 3.5 TeV a beam, which would get under way in February.

    After a successful initial physics run, the energy is expected to be gradually increased to 5 TeV a beam (interview with Steve Myers, Frontline, December 4) in six months or so. Tejinder Virdee, the CMS spokesperson, remarked, “The events so far mark the start of the second half of this incredible voyage of discovery of the secrets of nature [at the LHC].”

    Beaming success
     
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  3. ppgj

    ppgj Senior Member Senior Member

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    Indian presence

    CERN
    [​IMG]
    THE PHOTON MULTIPLICITY Detector, an important component of the ALICE detector. Its fabrication was entirely India's responsibility.

    THE six experiments that will record events at the Large Hadron Collider (LHC) are: A Large Ion Collider Experiment (ALICE); ATLAS; the Compact Muon Solenoid (CMS); the LHC beauty (LHCb) experiment; the LHC forward (LHCf) experiment; and the TOTal Elastic and diffractive cross section Measurement (TOTEM) experiment. ALICE, ATLAS, CMS and LHCb are installed in four huge underground caverns built around the four collision points of the LHC beams. TOTEM will be installed close to the CMS interaction point and LHCf near ATLAS. There is significant Indian participation in ALICE and CMS.

    The participating institutions in ALICE are the Variable Energy Cyclotron Centre (VECC), Kolkata; the Saha Institute of Nuclear Physics (SINP), Kolkata; the Institute of Physics, Bhubaneswar; the Indian Institute of Technology Bombay; Aligarh Muslim University (AMU); Punjab University, Chandigarh; Jammu University; and Rajasthan University, Jaipur. Participating in CMS are Punjab University; University of Delhi; the Bhabha Atomic Research Centre (BARC), Mumbai; and the Tata Institute of Fundamental Research (TIFR), Mumbai. While participation in ALICE is led by Bikash Sinha, former Director of the VECC, that in CMS is led by Atul Gurtu of the TIFR.

    ALICE is a detector specially designed to analyse lead-ion collisions. When LHC delivers its peak energy of 7 TeV, a lead ion (with 82 protons in its nucleus) will have a total per beam energy of 574 TeV, which means a total energy of 1,150 TeV will be available for ion-ion collisions. At such extreme energies, lead-ion collisions are expected to recreate conditions of extreme temperature and density just after the Big Bang under laboratory conditions. Under these conditions it is believed that the bound constituents of protons and neutrons – quarks and gluons – will break free for a very short time, creating a soup of quarks and gluons. This state of matter is called Quark-Gluon Plasma (QGP). The data obtained will allow the study of QGP as it expands and cools and help understand how progressively particles that constitute the matter of our universe arise.

    For this purpose, ALICE will carry out a comprehensive study of the hadrons, electrons, muons and photons produced in the collision of heavy nuclei for which its detectors are appropriately designed and tuned. An important component of the ALICE detector is the Photon Multiplicity Detector (PMD), whose fabrication was entirely India’s responsibility. The PMD is a unique detector based on highly granular, honeycomb gas cell detectors consisting of 220,000 cells. India was also responsible for making some parts of the Muon Chamber Arm. The most significant element in the contribution to the muon arm is the design of a pre-amplifier ASIC chip (application-specific integrated circuit chip) called MANAS by the VECC, which was fabricated by Semiconductor Complex Ltd. (SCL), Chandigarh.

    Each chip reads data from 16 electronic channels. India has supplied 100,000 MANAS chips for the 1.6 million channels in the muon arm as well as 14,000 chips for all the PMD channels. MANAS being a generic ASIC for high-energy experiments, these chips are also being used in the ongoing STAR experiment at Brookhaven National Laboratory (BNL).

    Though ions will be introduced into the LHC only in a couple of years from now, until such time ALICE will not sit idle. While the primary objective of ALICE is to study strongly interacting matter at extreme energy densities where QGP is expected to form, it will also study proton-proton collisions both as a comparison with lead-lead collisions when they happen and in physics areas where ALICE is competitive with other LHC experiments. Interestingly, of the six experiments, ALICE has come out with the first physics paper using the limited data gathered from the first 284 collision events at 900 GeV that were observed over a period of one hour on November 23. (When the LHC is running at its peak energy and intensity, it will produce 600 million collisions per second.)

    ALICE scientists measured the multiplicity of charged particles produced in these proton-proton collisions. Since data of such (low) energy collisions were available from other earlier experiments, ALICE data served to confirm the same as well as validate the model calculations made for the experiment.

    CMS is an advanced detector comprising many layers. Consisting of 100 million individual detecting elements, each looking for signatures of new particles and phenomena at 40 million times a second, it is one of the most complex scientific instruments ever constructed. It derives its name from the fact that it is small and compact for its enormous weight of 12,500 tonnes. It is designed specially to detect and measure muon energies and it has a large 13 m x 7 m solenoid coil, the largest and the most powerful ever built, for its huge superconducting magnet around which the detector is built. The magnet has a field of 4 tesla, which is 100,000 times stronger than that of the earth. CMS is designed to see a wide range of particles and phenomena resulting from high-energy collisions at the LHC. The 21 m x 15 m x 15 m detector is like a giant filter, a cylindrical onion, each layer of which is designed to stop, track or measure different particles emerging from proton-proton collisions. Particles emerging from collisions first meet a tracker, made entirely of silicon, which traces their positions as they move through the detector, allowing a measurement of their momenta. While the silicon tracker interferes with the particles as little as possible, the calorimeters in the outer layers are specifically designed to stop the particles in their tracks and provide a measure of their energies.

    The next layer is the Electromagnetic Calorimeter (ECAL) – made of lead tungstate crystals, a very dense material that produces light when struck – which measures the energy of photons and hadrons. The Hadron Calorimeter (HCAL), which is the next layer, is designed mainly to detect particles made up of quarks. The size of the magnet allows the tracker and calorimeters to be placed inside its coil, thus resulting in an overall compact detector. For the measurement of muon energies, the outer part of the detector, which is the iron magnet “return yoke”, is utilised. It stops all particles except muons and other weakly interacting particles, such as neutrinos, from reaching the muon detectors.

    The Indian contribution to CMS includes the fabrication of 1,000 of the 4,300 pre-shower silicon strip detector modules that are attached to the end caps of ECAL and HCAL for discriminating against pions and photons before they deposit energy in the calorimeters. These detectors were developed by BARC and fabricated and tested by Bharat Electronics Ltd (BEL). Like MANAS, these strip detectors are generic devices for use in other high-energy experiments as well. Another important contribution is the complete fabrication, installation and commissioning of the Outer Hadron Calorimeter, a supplementary system outside the magnet (but just before the muon detector) to enable total containment of hadronic energy from particle showers in HCAL. It consists of 72 honeycomb panels of scintillation detectors (each 2.5 m x 2 m) with a data read-out system using wavelength shift fibre and hybrid photo diodes. K. Sudhakar of the TIFR was responsible for this part.

    A unique method was employed in the construction of the CMS detector. It was designed in 15 separate sections or “slices” that were built on the surface and lowered down ready-made into the cavern 100 m below. This enabled saving valuable time as excavating the cavern and building the detector could go on in parallel. Lowering CMS by means of heavy lifting was a decision that was taken right in the beginning, some 16 years ago, inspired by experiences with Large Electron Positron Collider (LEP). The first lowering took place in November 2006 and the last in January 2008. According to Alain Herve, CMS’s original technical coordinator, the concept of building large objects on the surface and transferring them underground as completed elements is the clear way to go in the future.

    CMS has the same physics goals as the other general purpose detector ATLAS, but the two have quite different technical solutions and designs. In a sense, the two are complementary. The chief difference between the two is that while CMS is built around a huge superconducting solenoid, ATLAS has a toroidal configuration. A toroidal configuration can either have an air core or an iron core, and ATLAS has chosen an air core. The tracker in CMS is all silicon whereas in ATLAS it is half silicon and half gaseous detectors. Similarly, while CMS has a solid lead-tungstate calorimeter, ATLAS has a liquid argon calorimeter. “The first thing one actually does in the design of the experiment,” points out Tejinder Virdee of CMS, “is actually to figure out the magnetic field configuration for the measurement of muons. That then determines the rest of the design. We start from the physics and then we have to build these complicated experiments that allow you to get to the physics. Physics determines the performance that you require.”

    The data thus gathered by CMS and ATLAS will be used to answer questions such as: What is the universe really made of and what forces act within it? And what gives everything substance or mass? CMS is tuned to measure the properties of previously discovered particles with unprecedented precision as well as discover new particles, such as the Higgs boson, supersymmetric particles and gravitons, and completely new phenomena. The experiments are also expected to throw light on what constitutes dark matter and whether there are more than three dimensions of space. Indeed, CMS and ATLAS will be the two key experiments that will be keenly followed by physicists for their results on the elusive Higgs boson.

    R. Ramachandran

    Indian presence
     
  4. ppgj

    ppgj Senior Member Senior Member

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    Discovery machine

    R. RAMACHANDRAN

    Interview with Dr. Jim Virdee, spokesperson, CMS experiment at the Large Hadron Collider.

    PICTURES COURTESY CERN
    [​IMG]
    PROFESSOR TEJINDER VIRDEE was involved in the development of the CMS detector concept from the earliest days and has been influential in many areas of the detector design.

    PROFESSOR Tejinder (Jim) Virdee of Imperial College, London, has played an extremely prominent role in the design and implementation of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). He was involved in the development of the CMS detector concept from the earliest days and has been influential in many areas of the detector design. The innovative concepts in CMS are likely to influence the next generation of high-energy physics experiments. He proposed the idea of discovering the elusive Higgs boson via its decay into two photons, which is central to the concept of the high resolution lead-tungstate crystal calorimeter, one of the major components of the CMS design. Having served for many years as CMS deputy spokesperson, he was elected CMS spokesperson in January 2007. He will thus be the scientific leader of the experiment during first LHC data gathering and analyses. Experts from an interview with him shortly before the restart of the LHC at CERN in Geneva:

    Are there any changes in your plans at CMS now that the machine is slated to begin its physics run only at 3.5 TeV per beam initially instead of the original 5 TeV?

    Well, it has taken us a long time to build the experiment and we have also been commissioning the experiment. The commissioning of such an experiment actually has several phases in it. Straight after finishing construction we were ready to take beam last year and we took some good data, but then the incident occurred. Nevertheless we continued. We ran the experiment for about six weeks round the clock for several reasons. One was to see whether this very complicated piece of scientific equipment actually can sustain long operation. We also have to figure out if it is working as expected. What do I mean by that? We have documents written down ten years ago, which run into a stack three-quarters of a metre thick, which explain what performance of these would be to get to the physics at the LHC. So we have to check whether the instrument is actually working as we had written down. For that we ran the detector for six weeks round the clock, recording cosmic rays.

    Cosmic rays actually manifest themselves at sea level as muons. And some of these muons have very high energy. They can penetrate 100 metres of earth and still have a lot of energy. These are the particles that go through the detector and we could actually check whether the detector was working: Does it have the expected efficiency – close to 95-99 per cent? Does it have the position resolution – in some cases 15 microns and in other cases 200 microns? And does it have the time resolution – order of nanoseconds? And does it work as a whole system? Does it have the [expected] performance in kinematics like momentum resolution, energy resolution and so on? And all in all we found that the amount of the detector that was working was very high – order of a per cent not functioning of this complex instrument that has 100 million electronic channels in all. So everything was very encouraging. There were a few issues that cropped up which were related actually to cooling. A few detectors had to be replaced. And some refurbishment in terms of the infrastructure, like the cooling system and so on. We had to install one detector and we did that.

    What are the special characteristics of the detector and what are the various steps involved in your checks?

    We have a design which is entirely based on a single magnet, a high field solenoid. The first thing one actually does in the design of the experiment is actually to figure out the magnetic field configuration for the measurement of muons. That then determines the rest of the design. The detector is built such that [see diagram] the first layer is within a tracker, which is all silicon. It has a volume of a cylinder of 6 m in length and 2.5 m in diameter. The next layer is the electromagnetic calorimeter, which uses lead-tungstate crystals (in green). Then the hadron calorimeter, which is a brass scintillator. The fourth layer is the muon system, which is dominated by the coil. It is the most powerful coil ever built. It is 13 metres long and 6 m in diameter and it has a very high magnetic field which supplies the field for this detector and when the field returns in the iron yoke (shown in red), we use it to analyse the momenta of the muons.

    We had also taken data when the beams were stopped at the collimator and that actually allowed us to check some of the timing characteristics. With this large number of channels they also have to sing in tune to hit the right note – to see the track. If they are out of time you see a jagged track. From there we can actually figure out if the detector is functioning well. After we finished the maintenance part, we started taking the data again about three or four weeks ago. The detector seems to work well and we are analysing that data so as to be as ready as we can when the beam comes. That’s the first part – commissioning of the experiment without beam.

    The next thing to do is to commission it with beam. When the beam comes, particles actually go outwards and time synchronisation is quite different. So we have to check that we actually reproduce or have performance that this set of data are indicating. This is independent of energy. The next step is what we call “Rediscover the Standard Model”. So this is known physics. We know how some of these standard model processes are: things like W and Z production, particles discovered in the early 1980s. These particles are used to check whether the experiment is working properly or not. By checking it means: are the rate of the W and Z production and the way they decay as we expect from the Standard Model? What it is at [Fermilab’s] Tevatron energies [2 TeV] we know. And the standard model’s predictions are precise to a few per cent. It will be a first challenge for us to make measurements at that precision. We know what the answer should be. And so that again is also, roughly speaking, independent of energy because W and Z production cross-sections are not changing very fast with energy. So sitting at 7 TeV for some period of the time, collecting these data will take a little bit longer than at higher energy but not that much longer. So that’s the next step, what I would call “Physics Commissioning” the detector.

    Won’t some new channels open up even at 7 TeV?

    At 7 TeV if you start picking up a lot of data then you would go beyond what Fermilab is doing currently. What we are talking about is something we do in orders of six months to one year at most, to compare with something that’s been going on since 1989. That’s the first thing. If we get confidence there and if we understand Ws and Zs production, the top-antitop quark production, things like J/psi and upsilon particles – these are what we call the standard candles – we will clearly be looking for new things. Then after a certain time at 7 TeV – when we understand the detector, when we get familiar with the machine and start playing with the beam – we will go up in energy and there the aim is to take sizable data sets. And it is clear that as we go above 7 TeV, closer to 10 TeV, each unit of data brings us beyond Fermilab all the more faster, go to new territory, make a significant step beyond Fermilab, in terms of new physics like supersymmetry, extra dimensions, heavy Ws and Zs. Higgs will take time.

    Why do you say Higgs will take time?

    [​IMG]

    Because, first, the amount of time that something takes depends on two or three different things. One clearly is the centre-of-mass energy. Second is how heavy it is, and how easily it is produced. So, for example, in supersymmetric particles, they have high cross-sections so they are easily produced, but their masses are high. When I say beyond the Fermilab territory, it is some number like 450 GeV and when I say go significantly beyond, it will be a few hundred GeV above that. The higher the mass, the rarer they are and the more the luminosity you need. Luminosity at higher energy is significantly more. The Higgs is a rare beast to be produced and at the LHC, depending on its mass, its signatures that are easily visible are rare as well. So we need to take a lot more collisions to see it. We have to accumulate a lot more proton-proton collisions, preferably at higher energies than at lower energies. That’s why it will take a bit of time.

    But as soon as you have a 3.5 TeV beam – that’s 7 TeV – are there are any particular things that you would be looking for?

    We would be looking for everything.

    That’s true. But are there any specific things because of their higher cross-sections and things like that?

    Supersymmetric particles…

    At 7 TeV itself?

    If we stay there for some period of time, because the idea is to go up in energy after a reasonable time but not too long a time either. Higher energy gives you more reach, but even at that energy if you stay there for significant length of time we would be exploring territories beyond what Fermilab is doing because, after all, it is 3.5 times that energy.

    As you continuously ramp up the energy beyond 7 TeV, would you progressively be setting lower limits on Higgs mass? When will you be able to say with confidence that there is no Higgs below such and such energy?

    Well, the LHC is a discovery machine. We are actually looking to make discoveries. So, I think that’s the name of the game. As the data come in, the emphasis will be on the high statistical significance of the statements that we make at the end of the programme – we are half way through the LHC programme today and so [there is] another 10-15 years to go. The name of the game is actually to retrieve all the physics that is at this special energy scale of the LHC. There is some magic, I think, about this energy scale. We expect things to happen because we know that the standard model doesn’t work at this energy. There are some parts of it which fail. And so there is something which nature has done to give mass and also to control some other things which give nonsensical answers as we extrapolate standard model to these energies. So what is it? That’s what we want to find out. When we find it out we need to know how nature has done this. What is the underlying theory and that will take time as well and that’s why the programme is longish. Discovering is one thing, getting into a deep understanding is another game.

    One of the great things about Higgs is that, when we started, its mass was not known. It is still not known. It can actually range from 115 GeV to 1 TeV although the measurements indicate that it is closer to 115 GeV. The good thing about Higgs is that depending on the mass it actually manifests itself inside the detector in completely different ways. And many different ways depending on the mass, and we have to cover all the different ways and, in fact, when you have done you find that detector can do anything that the nature has in store for us. Anything.

    So I think it will be very exciting time coming up.

    Discovery machine
     
  5. hbogyt

    hbogyt Regular Member

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    NNNuuuuuu! We are doomed! We are doomed! So how long do we have before blackholes suck us in?
     

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