CMS Detector at the LHC: Calorimetry (EM, Had, Forward)

CMS Detector at the LHC: Calorimetry (EM, Had, Forward) CMS structure: Solenoid: Most particles are stopped by the detector except for few, such as muons, neutrino. Main difference between ATLAS and CMS is that CMS has solenoid on the outer layer, so it bends the trajectory of the muons again in an opposite direction (opposite pointing magnetic field). Depending on how much the trajectory is bent, we can deduce the momentum of the particle. Tracking system and both EM and Hadronic calorimeters fit inside the superconducting CMS solenoid, which generated Magnetic Field of 3.8 Tesla (100 000 that of the Earth). Tracking detector (measures momentum, charge, decay) – silicon detector is the inner most layer. The CMS tracker records the paths taken by charged (not neutral) particles by registering their positions at various key points. The tracker can detect the paths of high energy muons, electrons and hadrons, as well as tracks coming from decays of very short lived particles such as b quark used to study the differences between matter and antimatter. (WEB: http://cms.web.cern.ch/news/tracker-detector). The tracker is very lightweight and precise, so it has minimal effect on the paths the particles take. Each position measurement is accurate to 10 micrometers. The tracker material is selected to withstand high levels of radiation, since it is the inner most layer and so receives the highest volume of particles. CMS uses silicon strip sensors (detectors) in shape of rods, covering area of 206 sq.m. (wiki), adding up to 25000 silicon sensors. Also used silicon pixel detectors, which are in principle very similar to silicon strip sensors, but have a segmentation of pixel diodes instead of strip diodes. The 65 million pixels (each generating ~50 microwatts) are mounted on the cooling tubes form the 3 inner most layers. Silicon microstrip detectors then stretch out in a 130 cm combined radius barrel with inner and outer endcaps to close off the tracker. Calorimeter (an apparatus to measure energy of the particle AND particle identification) – scintillating crystal (EM calorimeter made of lead tungsten, a very dense material that produces light when hit), and then sampling calorimeter for hadrons. The ECAL is sandwiched inside the solenoid after the tracking system and before the HCAL. EM calorimeter is used to measure energies of electrons and photons, because they are likely to be produced in reactions for Higgs and other new physics. LHC collides bunches of high energy protons every 25 ns, so the calorimeter material is required to have very specific properties. PbWO4 – lead tungstate is the crystal of choice for the following reasons: 1. the material is high density and has heavy nuclei (explain why is this good); 2. the oxide crystal is transparent and scintillates, emits a small flash of light(well-defined photon bursts), when electron or photon pass through it. This means the calorimeter system is very precise an d very compact; 3.lead tungstate is relatively easy to manufacture from readily available raw materials. Each crystal is equipped with a photodetector (specially designed to work in a high radiation levels and strong magnetic field) that registers the scintillation light which is converted into an electric signal, amplified, and sent for analysis. The ECAL made in a barrel shape (to fit inside the solenoid, of course) with two flat endcaps (one closing off each side of the barrel). The barrel part consists of 36 supermodules, each containing 1700 crystals, adding up to 61,200 crystals in total. The endcaps are made up of almost 15000 crystals. There are 75,848 crystals in ECAL. Each crystal (volume 2.22.223 cm in the barrel; 3x3x22 cm in the endcaps) weights 1.5 kg, each crystal took 2 days to grow, in total it took 10 years to grow all crystals. The crystals were manufactured in Russia and China, where appropriate facilities already existed. Issues: The yield of light in the crystal depends strongly on temperature, so a sophisticated cooling system is required to keep the crystals at constant temperature. Also, the light signal needs to be converted into an electrical signal (via photodetectors) to be recorded, and since the initial signal is relatively weak, amplification is required. Photodetectors: Avalanche photodiodes (APD) for the barrel and vacuum phototriodes (VPT) for endcaps (because the radiation is too high to use silicon photodiodes), as these can operate in strong magnetic field and high radiation. Lead tungstate crystals (though fairly radiation resistant) suffer limited radiation damage – the crystal structure is disturbed, hence the optical transmission decreases. This effect is accounted for during the operation of the detector and appropriate corrections are included in the data analysis. The crystals are probed by light monitoring system to register the optical transmission. The radiation damag e can be reversed (anneal) when CMS is not operating. In room temperature the atoms within the crystal return to orderly positions. Each crystal is identified with a unique barcode, registered in a database, and measured (light transmission and scintillating properties in ACCOS machine). Cut to micrometer precision. Getting the material right was only one of the challenges for the ECAL team; each crystal had to be cut, machined, polished, tested and given a photodetector. Groups of crystals were then assembled side-by-side in glass-fibre or carbon-fibre â€Å"pockets† to form larger structures known as â€Å"supercrystals†, â€Å"modules† and â€Å"supermodules†. The crystals arent pure, but doped to improve their properties. Each crystal is cut and polished to a precise size, so that all pass the light the same way. There are 34 categories of crystal, 22 slightly different varieties of capsules with an attached photodetector. For barrel the crystals are first grouped into sub-modules: 10 crystals per lightweight glass fibre box. 40-50 sub-modules then make up a module, and 4 modules m ake up one of the 36 supermodules. Endcaps are constructed from 25 (55) crystal blocks, or supercrystals. Monitoring and cooling systems as well as final electronics are added to the supermodules before they are placed inside the experimental cavity. To ensure stable and equal operation of the crystals, the cooling system keeps all crystals within 0.1 oC of the optimum temperature. What is scintillation? Scintillation detectors are one of the most often used particle detection devices (Leo 157). Scintillators are made of specific materials that emit a flash of light when struck by a particle or radiation. The emitted light signal is amplified by photomultipliers and converted into an electrical signal which is then analysed. In ECAL electron or photon collides with the heavy nuclei of PbWO4, generating a shower of electrons, positrons and photons. These shower particles penetrate the scintillator further, colliding with more nuclei and producing more shower particles. Atomic electrons take fraction of energy from the passing particles and enter excited states. When they de-excite back into a ground state, the atomic electrons emit a photon of blue light, i.e. a scintillation. The blue light is picked up by photodetectors. The lead tungstate crystals produce a relatively low yield for each incoming particle, so the signal needs to be amplified. (transmitted to t he photomultiplier, converted into a weak current of photoelectrons, and further amplified by an electron multiplier system LEO 158). The total generated light signal is linearly proportional to the energy of the incident particle. Photodetectors? All photodetectors are glued to the crystals. Avalanche Photodiodes (APDs) are made of silicon with a strong electric field applied to them. Scintilation photons knock an electron out of an atom, and the electron accelerates in the E field, striking more electrons from silicon atoms. The latter also accelerate and knock out more electrons (the number increases exponentially), hence creating an avalanche. This method allows producing a high current in a short period of time. The amplified and digitized signal is transported away by fibre optics cables away from the radiation area for analysis. A different kind of photodetectors is used in the endcaps due to much higher radiation levels than in the barrel. Vacuum Phototrides (VPTs) contain three electrodes within a vacuum (hence the name). When the scintillating photon strikes atoms in the first electrode, released electrons accelerate towards the second electrode (positive anode) and knock out more electrons. The latter accelerate towards the third electrode (dynode with a higher electric potential than the anode) and again knock out more electrons. This method also produces a strong current form a weak light signal, which is carried away from the high radiation zone via optic fibre cables (what kind of optic fibre cables). http://cms.web.cern.ch/news/crystal-calorimeter The region in the endcaps must was designed to distinguish between closely spaced particle pairs (such as for example in case of a short lived neutral pion decaying into two closely spaced low energy photons that might be mistaken for one high energy photon from Higgs decay). A special ECAL preshower is located in the endcaps before the EM calorimeter crystals. It is the made of two lead panels followed by silicon sensors (6.3cm x 6.3cm x 0.3mm). Each silicon sensor is divided into 32 strips each 2mm wide. Compared to 3cm wide scintillator crystals the preshower sensor resolution is better (5% precise energy measurement Ph.Bolch). The photon passing through lead sheet produces a shower containing e e+ pairs which are measured by the silicon detector strips. The silicon detectors are kept at temperatures between -10 oC and -15 oC for optimal and long-term performance. The outside of the preshower is heated to temperatures of the ECAL, since the crystals performance Muon chamber, muon detectors which are inside the return yoke of the magnet (Track, muons identification). To identify muons and measure their momenta CMS uses three types of detectors: Drift tubes DT (in barrel position measurement), cathode strip chambers CSC (in endcaps position measurement), and resistive plate chambers RPC (in barrel and endcaps trigger). Energy measurement: calorimetry- by creation and total absorption of showers, either EM (light ammount) or hadronic (penetration depth). Social Work Provisions for the Elderly: History and Politics Social Work Provisions for the Elderly: History and Politics In this paper, I aim to discuss the historical and political context of social work provision for the elderly. By using and reviewing the views expressed in previous work on the elderly in our society, I hope to demonstrate the context in which social work and social care operate. One of the concerns of this essay is the impacts of discrimination and oppression on the elderly. I will discuss how listening to the views of service users is crucial to developing effective methods of providing social care. In the last two to three decades, a fairly wide body of academic work has become available, approaching the issues of ageing and of care for the elderly, within the discipline of Social Policy. Social Policy is an interdisciplinary field born from, and derived upon, other social sciences economics, politics, sociology etc. (Tinker:1992:3) Within this field, the specific discipline of gerontology the study of ageing has developed in recent decades because the elderly population has increased so sizeably in the last 50 years. Cherry Rowlings wrote in 1977 that while in 1951, just 13% of the British population was of retirement age, by 1977 this had increased to 17.3%. (Rowlings:1981:27) Since the 1970s we have seen this trend continue. This change can be attributed both to comparatively low birth rates, and the increased life expectancy. Businesses, the professions and the media are finding now that pensioners form one of their biggest markets. (Tinker: 1992: 3) Rather than using medical and biological models, social gerontology focuses on the ways in which social and cultural factors influence peoples experiences of growing older. Tinker writes that the elderly are unusual in that they have been labelled a special group in our society, and yet the only think that marks them out is their age unlike groups seen as deviant they are normal people and we all expect to join this group in time. (Tinker:1992:4) However, although not labelled deviant, the elderly have nonetheless been constructed as a problem, as Jacki Pritchard writes: An elderly person is thought to be of no use once they reach retirement age, probably because they are not seen to be producing anything for the society in which they live. They are considered to have had their life.' She notes that this differs from other cultures, in which capitalism is less advanced. (Pritchard:1992:16) And Nicholas Bosanquet has noted that the rate at which the elderly population is growing causes great anxiety in society. He cites Professor Sir Ferguson Anderson as saying in 1976, Britain faces social disaster because of the rate at which the proportion of elderly people is rising. (Bosanquet:1978:7) He goes on, The emphasis has come to be more and more on the elderly as a burden even as a threat to the standards of service or opportunity enjoyed by the rest of the population. (Bosanquet:1978:79) Changes in medicine have made illness and disability a problem particular to the elderly. Diseases that effected the young in previous centuries, have been controlled or wiped out in this country, and now children and young adults can expect to be in good health. Similarly, disability from birth is relatively rare; and blindness, deafness and mobility problems are impairments by far most commonly experienced by the elderly. (Bosanquet:1978:21) The medical model of disability has traditionally seen disability as naturally and inevitably arising out of a physical or mental impairment. The more contemporary social model, however, has argued against this, in saying that whilst a person may have a natural impairment, it is societys failure to accommodate people with this difference to the norm, which disables them. For example, though a person may be unable to walk and require the use of a wheelchair, this does not inevitably make their life so very different from the life of an able-bodied person. Rather, it is a lack of easy access to public buildings and transport, poor adaptations in housing and so on, which turn this impairment into a striking disability. In the case of elderly people, because ill health and disability is now so much restricted to the oldest generations, it is seen as natural and inevitable that older people will lead very different lives from younger adults, and that the quality of their lives will decrease. However, this can be seen as only a construction, as many of the problems faced by older people could be altered by changes in public provisions and social care. Bosanquet notes that mental health, most significantly depression, are as great a problem as physical health for the elderly. He writes that this is because the most important factors people attribute to their happiness at all stages of life, are ones which elderly people are least able to take for granted. These include: oHealth oFamily life/friends. The elderly will almost inevitably face bereavement, but also having decreased transport/mobility, and fewer places to go where they can meet and make friends, both increases their sense of isolation and decreases their independence. oFinancial/ home stability. The elderly live on pensions. The decrease in their health can lead to them losing their home. (Bosanquet: 1978:10) The elderly are increasingly separated from the rest of the population. They suffer great isolation. But policy has been seen only as pension policy. Nicholas Bosanquet argues that the Government needs to intervene not only when the elderly person has no relatives, but even in addition or instead of care from family. He stresses that policy must increase choice and opportunity, as the elderly find themselves unable to decide and control their own futures. (Bosanquet:1978:75-77) One of the most fundamental issues facing the elderly is the problem of housing. Bosanquet reports that since the 1970s, governments have been concerned with designing special flats for the elderly. These solve some housing problems and give people the opportunity to form small communities with others in their own age bracket. (Bosanquet:1978:92) He writes that this is not a new idea; in the Majority Report of the Royal Commission on the Poor Law I 1909, there is mention of special housing for the elderly. However, the views of what elderly people require from housing has been deeply flawed, due to a failure of policy makers to listen to the ideas of the elderly, about what they need in day to day life. After the Second World War, there was great interest in building small housing for the elderly. However, reports of the time did not view it as necessary to provide many special features or fittings for the elderly. The post-war Rowntree Report stated that bungalows were the preferable type of housing; two-story houses provided problems for pensioners with impaired mobility, and the elderly often did not like living in flats, as they were not considered private or independent enough. The report stated that houses for the elderly people must be built with easy access to local shops, close to the persons family and friends, and near housing for younger generations so that the elderly did not feel cut off from the rest of society. The report did state that flooring and any stairs in the property must be designed for safety and ease of manueverability. This would mean using non-slip materials on flooring, and ensuring that stairs were neither too steep or built around awkward angles. However, these precautions aside, there were no provisions made for wardens or for providing a safe environment for those with health problems. (Bosanquet:1978:95) Subsequently, between 1945 and the early 70s, a good number of small flats were built, but these were not reserved exclusively for pensioners and many housed younger adults. Very few were built with any special design features which would have made them safer and more convenient for the elderly. More recently the idea of sheltered accommodation has grown up, though many people see this simply as a compromise before the nursing home. (Bosanquet:1978:97) Bosanquet concludes that the elderly need schemes which help them find a new lifestyle and to decrease their sense of isolation. Luncheon clubs, good neighbour schemes, day centres and holiday schemes are essential provisions in his view. He believes that these services are more important than simply focusing on income support; however policy makers have tended to see this is a luxury, rather than one of the essentials of government spending plans.(Bosanquet:1978:97) He argues that services should increase their focus on the over 75s. Younger retired people are more likely to still be living with spouses and in their own homes. More years after retirement, however, and any savings the person may have had will likely have run out, and pensions become increasingly inadequate whilst the cost of living actually increases, as for example the elderly person needs to spend more on maintaining their health, in heating bills and medicine/doctors fees. (Bosanquet:1978:124) While this and many other books on the subject of elderly people outline the historical, political and economic factors in pensioners lives, they do not all cite the opinions of elderly service users themselves. Very often social policy and research is based on accounts given by social workers, or by representatives of a vulnerable group for example the families of children or in this case elderly people. To address this, Jacki Pritchards book The Abuse of Elderly People includes a great deal of anecdotal evidence and transcriptions of interviews with elderly people. By focusing on cases of actual abuse, the book may appear to be dealing with an extreme aspect of poor care for the elderly it may not be expected that abuse is a concern of the majority of older people. However, the principles of the book are useful as it outlines some of the ways in which older people are discriminated against, and how many of their needs and interests are oppressed. Pritchard is keen to stress the d ifferent areas in which elderly people may be abused 1. Physical, which includes medical maltreatment and neglect. 2. Psychological abuse, including threats of abuse, humiliation, harassment, emotional neglect and threats of any kind of abuse. 3. Legal abuse, including material and personal exploitation. (Pritchard:1992:21) Elderly people are not always given othe right to choose othe right to privacy othe right to independence. Pritchard considers it vital that if a person is mentally sound, and chooses to stay with their family even when the professional considers the family to be abusive, then the social carer must do no more than offer the elderly person support and inform them of their options. However, of course, there are different standards over what is mentally sound, and even what to do if someone is not. She is also keen to point out the difference in practices between the various professions involved in an elderly persons life. Very often, the policies of the doctors, care home nurses, and social workers arein direct conflict, and the normal policies of one may seem unacceptable to another. Subsequently, what is important returns to ensuring the rights listed above are honoured, and judgement of whether or not this is done can be made only by the elderly persons own experience. (Pritchard:1992:25) Pritchard reports that carers are more likely to become abusive, when they themselves are denied adequate support. The carers sense of isolation, their resentment towards the tasks they undertake, and their lack of external support, leads to an increase in abusive behaviour towards the elderly person being cared for. As a common sense measure, therefore, policy must be adapted to provide support and respite for carers, in the interests of all parties involved. (Pritchard:1992:33) In conclusion, it has been seen that many of the problems that elderly people face could be significantly diminished by improvements in social care. Rather than being natural effects of ageing, these problems are more frequently caused by discrimination in society against older people. As society has placed most significance on the needs of younger adults, there have not been adequate provisions made for the elderly for housing, health care and social integration. In response to these needs, social work needs to take steps to reduce the oppression of older people. This will involve maximising elderly peoples ability to make independent choices in their lives, and to enjoy the same standard of life as younger adults. Above all, social workers and researchers should listen to service users as they explain what services they need. Bosanquet, Nicholas (1978) A Future for Old Age: Towards a New Society. Temple Smith: London. Pritchard, Jacki (1992) The Abuse of Elderly People: A Handbook for Professionals. Jessica Kingsley Publishing: London. Rowlings, Cherry (1981) Social Work with Elderly People. Harper Collins: London. Tinker, Anthea (1992) Elderly People In Modern Society, Third Edition. Longman: London and New York.