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Topic 1: "Fundamental Particles and Forces"

Physics at the Large Hadron Collider

The LHC is the particle accelerator operating at the energy frontier and has tremendous potential for the discovery of New Physics and for the study of its properties as the accelerator and experiments are only at the beginning of their operating life. In 2015, after the first long shutdown (LS1), the machine and detectors will be prepared for the design centre-of-mass energy of 14 TeV and an order of magnitude more luminosity will be accumulated during the running period. With this extension the LHC is the gateway to further understanding of the fundamental laws of nature.

 

 

DESY at the LHC

The engagement in the LHC programme is a fundamental part of DESY's mission to perform particle physics research at the forefront of knowledge. It ensures a rich research programme and is instrumental in attracting some of the world's best and most innovative researchers and students.

 

As a national laboratory, DESY supports the German universities in their contributions to the LHC in a variety of ways: DESY's computing facilities, specifically the National Analysis Facility and the Tier-2 centre, are essential to respond to the community's computing needs for data analysis; DESY's test-beam is widely used for detector design studies and development; and the Helmholtz Alliance "Physics at the Terascale" hosted at DESY is a key engine for scientific exchange, training and education of scientists at all career levels. Furthermore, DESY provides an exceptional technical infrastructure that has been key to many successes over the history of the laboratory. It will have to be expanded to allow the construction of large detector components such as those foreseen for future upgrades of the LHC.

 

DESY's impact in the LHC experiments is substantial and results from its long-standing expertise: DESY scientists have shaped crucial aspects of detector operation, data preparation and data analysis at the LHC. They have also in fluenced the detector upgrade projects and are entrusted with the responsibility for several central coordination roles in both ATLAS and CMS. In addition DESY scientists assumed highly visible management roles from the start. A prominent example is Kerstin Borras, who has been appointed as CMS Deputy Spokesperson for the period 2014–15. Other important positions held by DESY physicists are Publication Committee chair, Authorship Board chair, Conference Committee chair, Speakers Committee Advisory Board deputy chair, deputies of the Collaboration Board chair and of the Technical Coordinator. DESY physicists are involved in shaping the future of the LHC physics programme.

 

These achievements on the national and international level are not the least due to the engagement in both major experiments, ATLAS and CMS. The emerging synergy effects are being exploited in common R&D and construction projects, e.g. for the detector upgrades, and have fostered a profound scientific exchange between ATLAS and CMS and the strong theory and phenomenology group at DESY. With all these activities, DESY has a unique advantage and is highly attractive as an LHC institute.

 

The highest priority in particle physics today is to fully exploit the LHC physics potential. The upgrade schedule for the collider has been laid down. The foreseen energy increase to 13 and later 14 TeV will boost the discovery potential in 2015. The physics studies concentrate on searches for New Physics and on precision measurements of the newly discovered Higgs boson. Indirect searches compare precision measurements with SM predictions, where deviations would signal New Physics.

 

The challenges in the coming funding periods are closely related to the upgrade schedule of the LHC machine and its consequences for the experiments. The first priority in 2015 will be the successful operation of the detectors at higher energies with significantly increased luminosity. The increased event rate requires higher selectivity of the trigger algorithms, a task that is further aggravated by the larger number of collisions in the same bunch-crossing (pile-up). Compared to previous data taking, triggering, selection and reconstruction of the collision events will be much more demanding. The high pile-up level is a perturbation and a background also for Standard Model precision measurements (e.g. in the electroweak or top-quark sectors) that constitute an important part of the physics programme. With such high data rates and an overwhelming SM contribution the search for rare processes will demand ingenuity.

 

Achieving sensitivity down to extremely small rates of potentially New Physics is the main rationale of the high-luminosity upgrade plans for the LHC (HL-LHC), the next step in the LHC programme. The current LHC planning foresees the collection of a data set of 3000 fb-1 until 2030. Such a huge data sample will, for example, allow even rare processes like the decay of the Higgs boson into muons to be measured. It will also substantially increase the sensitivity for investigating longitudinal vector-boson scattering. The detector challenge here is to design new radiation-hard detector elements with fine granularity and a fast readout that can deal with these high luminosities. For the upgrades DESY is focusing on tracking detectors, for which promising R&D is carried out in the laboratory. In the course of the upgrade programme these components will have to be integrated into fully developed detector systems to demonstrate their viability. Such a plan requires large infrastructures and in-house expertise to be successful.