Go for it! Tohoku Big Bang
Video: Tohoku Conference for the promotion of the ILC

Sefuri ILC High school
Video: Saga Prefecture, Fukuoka Prefecture

Steinar Stapnes (at that time leading the European Strategy process) announced the launch of the process to update the European strategy for particle physics during an ECFA-EPS special session in Grenoble, France, on 23 July, 2011.
Image: LPSC/Tomas Jezo

The European Strategy for Particle Physics has been submitted to the CERN Council. The goal is final approval in the coming weeks. The significance of the Strategy document is high. It has been drafted by a combination of a scientific preparation group and various appointed representatives of the CERN member states, including also representatives from other countries and/or regions. One important feature of the European process is that from draft to final approval in the Council takes only months, and the Council members/decision represent the governments directly. Secondly – as “global projects” have large cross-regional consequences and this process pre-dates other on-going processes in the US, Japan and other places – it has wide impact also beyond Europe, as a minimum serving as a possible example.

The LHC including its luminosity upgrade is a clear and rather obvious priority for the future, but the physics potential of future Linear Colliders is also well recognised in the Strategy statements. The relevant phrases were already quoted by Lyn Evans in his Director Corner in March:

For CLIC and higher energy hadron machine than LHC as options for post-LHC projects at CERN, “CERN should undertake design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines. These design studies should be coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, in collaboration with national institutes, laboratories and universities worldwide.”

For the ILC, “There is a strong scientific case for an electron-positron collider, complementary to the LHC, that can study the properties of the Higgs boson and other particles with unprecedented precision and whose energy can be upgraded. The Technical Design Report of the International Linear Collider (ILC) has been completed with large European participation. The initiative of the Japanese particle physics community to host the ILC in Japan is most welcome, and European groups are eager to participate. Europe looks forward to a proposal from Japan to discuss a possible participation”.

Other statements mention the importance of accelerator R&D, detector R&D and discuss CERNs role in the implementation of projects outside the CERN laboratory as well as its continued work with the European Commission (EC) to implement these strategies. Also these statements are relevant for the LC community.

What can and should we expect to happen in practice as a result? There are at least three main areas that are affected by this strategy: the CERN budget planning itself, the European Commission (EC) support for projects and activities, and various national funding programmes.

The CERN budget planning for 2014 and beyond is underway and it will be important to see these statements reflected in realities. Some key recommendations, in particular turning the LHC luminosity upgrade into a real-construction project over the next decade require significant resources, so the balance is non-trivial and delicate. Equally important, over the coming years, Horizon 2020 projects representing the EC implementation tools will unfold and the R&D efforts mentioned are expected to become priorities – discussed as part the implementation of the European Strategy for Particle Physics as stipulated in the Memorandum of Understanding between the European Commission and CERN. Finally the national priorities determine in many cases how the community can participate in the these projects and we all need to work hard to turn there priorities into realities also at this level. For the ILC there is an additional clear wish; a proposal from Japan to participate in such a project is seen as the next natural step to achieve a change of gear towards realisation.

Being optimistic, we can hope that other regional and national processes will not diverge in a significant way from the result of the European process. If this is the case, we will have reached – largely thanks to a bottom up process – an important consensus that should help the transition from strategies to realities in the coming years. New LHC results in 2015-16 might and will hopefully provide additional guidance but for the time being the directions are relatively clear.

We will also be very much helped if the linear collider community can plan and use resources across CLIC and ILC as efficiently as possible, to make the best possible use of our resources. In all areas related to luminosity performance of the machines, detector and physics studies, project planning and implementation studies, there are huge potentials for common efforts. Another feature of the real world and realities is that resources will remain a limitation and determine the speed of our progress.

Image: Matt Beardsley, SLAC

ATF-2 beamline – view looking downstream.

A key feature of the ILC is that it is a single-pass machine. In contrast to a circular accelerator, where the beam goes around many times, the ILC beams pass through each accelerator element only once, including the interaction point. For the accelerator, this means that for each accelerating module, the machine must be very efficient at transferring wall power into the machine beam, with the added requirement that the final beam must emerge with very low emittance so that it can be focused to the very tiny beam spot required to achieve high luminosity. The ATF-2 at KEK is a special test beam line that has been built to demonstrate the ability to achieve ILC-like namometre beam spots and stabilise them. Recent tests have demonstrated beam spots that are within a factor of two of the ILC design and promise to improve in the future.

The Accelerator Test Facility (ATF) at KEK is a prototype storage ring that is being used for ILC R&D aimed at creating and demonstrating that a low emittance beam can be focused to namometre sizes, which is required to obtain ILC luminosities. Earlier final focus studies were carried out at SLAC using different beam optics.

A vertical beam size of 167.9 nanometres had been achieved at the time of the Project Advisory Committee review in December 2012

The compact ATF-2 optics represent an improved scheme based on local chromaticity corrections that should be capable of achieving a vertical beam size of about 37 nanometres at the interaction point (IP). Once achieved, the R&D programme will shift the focus to maintaining the small spot size, controlling beam jitter and stabilising the beam at the IP at the nanometer level.

The ATF programme is being carried out by an international team

It should be emphasised that ATF-2 is an international R&D effort, being carried out with equipment contributions from all around the world. It has an international governance and a strong international presence in carrying out the R&D programme. In some ways, this collaborative programme is a successful mini-version of the type of collaboration we formed to carry out the global ILC R&D and accelerator design programmes and that will continue to implement the project.

Unfortunately, the ATF/ATF-2 programme was set-back by about one year due to the Japanese earthquake, and as a result our goals had not been achieved at the time the ILC Technical Design Report was submitted last autumn. As a result, the Project Advisory Committee (PAC) expressed concern in their technical review report and commented as follows:

“The lack of progress towards the 37 nm ATF2 IP goal is a concern. Several issues have already been resolved, and the currently scheduled modifications should lead to significant progress towards the goal.”

ATF-2 achieved a 72.8-nanometre vertical beam spot soon after the PAC review and improved further to 65 nanometres by March 2013.

As I indicated above, our progress had been slowed by the earthquake in Japan, however there was significant progress almost immediately following the technical review (see figure). Nevertheless, because of the importance of demonstrating the final focus of the ILC, we decided to follow up by initiating a technical review of the ATF-2 goals, progress and plans. We held the review on 3 and 4 April 2013 with the goal of assessing the present technical status and plans, as well as give guidance regarding future programme needs for the ILC. The GDE ATF-2 review report will be available soon. I summarise some key findings below.

Nick Walker, chairing the GDE ATF-2 review in April

The GDE review was led very capably by Nick Walker, GDE project manager. The presentations were excellent, enabling us to make conclusions that were very positive and constructive. Some key findings of the review were the following:

1.  the 65 nm vertical beam spot size achieved at low bunch charge is an important and encouraging accomplishment. This already demonstrates the optics and ability to control aberrations;
2. although improving the focus to the 37-nanometre goal will require a systematic stepwise programme, the committee is confident that can be achieved and uncovered no fundamental obstacles;
3. understanding emittance preservation at higher bunch charge is a new goal that has emerged from the studies to date.

The ATF/ATF-2 R&D programme is one of the central ILC R&D tasks needed to establish feasibility and to develop technologies for a linear collider (ILC and CLIC). The tests have been very successful, despite the earthquake setbacks, however not all of its ILC goals have been achieved yet. The next stages of the programme are crucial for the ILC and for establishing the even more ambitious goals for CLIC. The demanding final focus optics can only be studied at this unique facility. It was pointed out to us that the ATF programme at KEK is under severe financial stress. We hope the resources will be found to successfully continue the programme and carry out the next stages of this important and successful R&D.

In September 2012, hundreds of amateur and professional photographers had the rare opportunity to explore and photograph accelerators and detectors at particle physics laboratories around the world.

The photograph of Nino Bruno, a building contractor in L’Aquila, picturing a tunnel connecting the underground halls of INFN’s Gran Sasso National Laboratory garnered the most online votes and a panel of international judges awarded the top prize to Joseph Paul Boccio’s detailed photograph of the KLOE detector at INFN’s Frascati National.

Read the press release

View top thirty-nine photographs from the Photowalk

From left: Hitoshi Murayama, LCC Deputy Director, Masatoshi Koshiba, 2002 Nobel laureate in Physics, Lyn Evans, Shinzo Abe, and Takeo Kawamura, Chair of the Diet members association for ILC. Images: Prime Minister of Japan and His Cabinet

Our recent meeting with Prime Minister Shinzo Abe was a very special moment for me. He said a linear collider was a dream for humankind.

The moment happened when LCC Director Lyn Evans visited Japan for three days at the end of March to meet many dignitaries. He had come to invite Japan to host the International Linear Collider. I had the privilege to join him in some of the meetings, basically as Lyn’s Japanese voice, but also representing the US community of particle physicists.

Lyn thanked Mr. Abe that Japanese contribution to the Large Hadron Collider (editor’s note: Lyn Evans used to be Project Manager of CERN’s LHC) was the first one announced outside the CERN member states, which helped his negotiation with other partners. He also pointed out that at the same time Japanese industry was critical in making the LHC happen at all. Eventually, Japanese industry benefited from this contribution in gaining international stature and experience working on the cutting-edge research project that involves about ten thousand people from around the world. Some of the products developed for this purpose turned out profits to some companies too.

Then Lyn moved to the next point, stating that hosting a linear collider would give Japan the opportunity to receive wide international recognition as a leader in fundamental science as well as involvement of scientists and industry from all over the world. It would also bring many non-Japanese scientists and their families to Japan, in the same way it happens at CERN. This kind of recognition and attention is what Japan has been eager to receive.

Finally Lyn pointed out that Europe could not host this attractive project at this point because it is tied up in the LHC for the foreseeable future. The draft of the European Strategy update document, the final version of which will be adopted by CERN Council in May, says “The initiative from the Japanese particle physics community to host the ILC in Japan is most welcome, and European groups are eager to participate. Europe looks forward to a proposal from Japan to discuss a possible participation.”  I added that the US was also under tremendous pressure to reduce the budget deficit and was not likely to host ILC either. The recent report from the High Energy Physics Advisory Panel of US Departement of Energy on future facilities evaluated the ILC to be “absolutely central” to the field, and added “The initiative from the Japanese particle physics community to host the ILC in Japan is very welcome, and the US particle physics community looks forward to a proposal from Japan to discuss possible participation.”

Masatoshi Koshiba, who received the Nobel Prize in Physics in 2002 for the pioneering work on neutrino astronomy, remarked that hosting the ILC would be a great opportunity for Japan when neither Europe nor US can do so. It would bring thousands of people from abroad, creating an international science city in Japan.

The Prime Minister promised to “monitor the development carefully,” and to evaluate “what role Japan can play.” We were all tremendously encouraged by these remarks.

In addition to the Prime Minister, we met Hakubun Shimomura, Minister of Ministry of Education, Culture, Sports, Science and Technology, Itta Yamamoto, Minister of State for Special Missions in charge of science and technology policy, and many other politicians. The level of attention ILC receives in Japan is quite amazing.

Particle tracks inside a detector. Image: John Marshall

When particles collide, they often produce sprays of new particles called jets. Given the complexity of these particles’ interactions, measuring the energy of jets with high precision is a formidable challenge. New detector designs, such as those being developed for the ILC and CLIC, are based on a paradigm called particle flow which will allow physicists to identify and measure each particle within a jet using the subdetector which provides the best measurement.

To understand how particle flow works, you need to think about the way particles move through a detector’s subcomponents. A given jet may include about twenty particles, many of which will carry a charge. The detector’s tracker will capture the momentum of the charged particles and the calorimeters will measure the energy of both charged and neutral particles.  The energy of a jet is then reconstructed by adding the momenta of the charged particles, as measured by the tracker, and the energies of the neutral particles, as measured with the calorimeter. This provides the best energy resolution.

Particle flow requires that scientists correctly identify the energy deposits in the calorimeter as originating from either charged or neutral particles. To do this, they must match the charged particles observed in the tracker to energy deposits in the calorimeter. Energy deposits without a match come from neutral particles.

The concept may sound simple but in practice it requires pushing calorimeters further than ever before. The calorimeters must be finely segmented in order to provide more resolution, resulting in tens of millions of channels and an image-like level of detail. “This is a really novel endeavor,” says Argonne scientist José Repond. “Only recent developments in electronics have made this possible.” Repond and colleagues recently created a one cubic meter prototype of a hadron calorimeter, compatible in design with the detectors planned for the ILC or CLIC, that had 500 thousand channels, more than the total number of channels on all four calorimeters at the Large Hadron Collider combined.

Read more about particle flow.

Complete setup of the SiW-ecal test in the test beam. The small silver box makes sure that the power pulsing works.

Particle detectors are expected to detect a lot of signal and very little background noise so that scientists can see what went on in their detector without being distracted by irrelevant signals. The technological prototype of the silicon-tungsten (SiW) electromagnetic calorimeter passed its first test in summer 2012 with flying colours with a signal to noise ratio that was between 14 and 20 to one (way better than the required ten to one). But that was then. Now, the task was to test the same prototype, but under different conditions: in a different powering mode, in a magnet, with beam.

The new powering scheme saves both space (no major cooling mechanisms are needed because very little heat is generated by the electronics) and power (thus money) by powering the components down between beam cycles. “Right now it’s more of an engineering challenge than a physics challenge,” says Roman Poeschl fom LAL in France. “Indeed it’s a completely new technique,” says engineer Remi Cornat of the French Laboratoire Leprince-Ringuet (LLR). “By trying it out in the DESY test beam we wanted to find out how feasible the system is.” They did two separate tests: running the prototype with power pulsing in a 2-Tesla magnet, and in the test beam from the DESY accelerator, but without a magnetic field. First results of the tests were presented at the CALICE Meeting at the University of Hamburg in March 2013.

Close-up of the technological protoype that was successfully tested with power pulsing in a magnetic field as well as with beam.

In the test, physics signals were well distinguished from detector noise in particular in power-pulsed detector layers. The exact signal-over-noise ratio needs to be evaluated, but the team is very happy with the first results of operation in power-pulse mode. “There seems to be no extra signal from the power supply, which means that the signal is just as clean as in continuous mode,” says Cornat. However, the team also learned more about the limits of their system. There was some cross-talk, issues with grounding and other prototype-stage flaws that help improve the system in the next step. “We know the limitations of our front-end electronics much better,” reports the engineer, and Pöschl concludes: “We have proof of the principle for our detector technology.”

The next step is a refined version of the detector, with more channels, more chips, more front-end boards that will grow to more than three times as many layers as it is now and a total length of two metres. Then there’s more testing to check the reliability and predictability of the new system. The final calorimeter would have about 100 000 front-end boards, 10 000 detector layers and consist of 1000 modules – a scale that can only be produced by industry. The team has already started discussions with the Japanese company Hamamatsu to see how labs and industry could produce the final detector.

VIDEO:
A short video showing the effect of the magnetic field on the cable that feeds the detector cards when a pulse of current passes. (Needless to say that the cards do not move)