WARP: WIMP Dark Matter search with Liquid Argon

最近，威尔金森微波各向异性探测器（WMAP）的测量为暗物质的存在提供了非常有说服力的证据。 只有4%的宇宙总能量是由重子组成的，我们和恒星都是由重子组成的。 更大的一部分（22%）是一种不同的物质，它不会坍缩成恒星，也不会发光-因此称为暗物质。 然而，暗物质在宇宙的演化中扮演着非常重要的角色。 它受到引力的影响，它的存在确实允许了银河系的形成。 到目前为止，我们还不清楚暗物质与普通物质的相互作用是仅仅通过引力还是其他力。 然而，粒子物理学提供了一个有吸引力的解决方案，即大爆炸后不久产生的残余中性粒子，遍布宇宙空间，并与普通物质发生微弱的相互作用。 这类暗物质的候选者被称为弱相互作用大质量粒子（WIMP）。WARP（WIMP氩计划）的构想是为了寻找WIMP暗物质。 WARP能够观测到WIMP与普通核碰撞产生的极低能量信号，同时，最大限度地减少宇宙射线和自然放射性背景的信号，这些信号通常限制了WIMP暗物质的观测。 WARP的两相漂移室使用氩气作为靶。 它有一个独特的能力，大大提高了它的灵敏度：它使用两个完全独立的技术来区分最小电离事件从核反冲。 这些依赖于两种不同类型的事件在WARP中观察到的信号中产生的细微差异。（3.8公斤），但非常敏感的原型探测器在LNGS，位于意大利中部格兰萨索山峰下的天体粒子物理实验室（距离罗马1小时车程），深度3,800英尺。 WARP合作将于2006年在LNGS安装一个更大（140公斤）的探测器，这将使WIMP搜索的灵敏度提高约两个数量级。 WARP计划的PI是Gran Sasso-Princeton Summer School的创始人之一。 现在，在其第二年，学校带来了20个有前途的高中学生从格兰萨索地区到普林斯顿大学校园的密集的物理学4周的计划。 该学院在格兰萨索取得了立竿见影的成功，2005年有300多名申请者，并有望成为意大利青年男女科学和文化丰富的持久平台。 该学院帮助美国与世界上最好的地下物理实验室之一建立了密切的联系，该实验室拥有许多美国研究人员和美国资助的工作。WARP项目还将在未来几年为一些美国学生提供机会，直接参与普林斯顿和LNGS的项目。 研究机会将包括部分实验装置的建造和测试，以及实验数据的分析。 这种实践经验将为学生提供一个难得的窗口，让他们了解实验过程的性质，这些实验过程产生和测试他们在教科书中找到的知识。 该项目的研究经验将建立学生的信心，扩大他们的知识和文化视野，并希望，激励一些追求学位，甚至在科学或工程职业生涯，并作为其他年轻学生的榜样。

The recent measurements of the Wilkinson Microwave Anisotropy Probe (WMAP) made the evidence for the existence of dark matter very compelling. Only 4% of the total energy of the Universe is made of baryons, the ordinary matter of which we, and stars, are made. A much larger fraction (22%) is a different kind of matter, which does not collapse into stars and does not shine - hence the term Dark Matter. Dark Matter, though, plays a very important role in the evolution of the Universe. It is subject to the gravitational force, and its presence has indeed allowed the formation of Galaxies. It is what ultimately keeps Galaxies and Clusters of Galaxies together.To date, it is not clear if Dark Matter interacts with the ordinary matter only through the gravitational force or also through other forces. However, particle physics offers an attractive solution in the form of relic neutral particles produced shortly after the Big Bang, pervading the cosmic space, and interacting weakly with ordinary matter. This class of Dark Matter candidates go under the name of Weakly Interacting Massive Particles (WIMPs).The WARP (Wimp ARgon Program) was conceived to search for WIMP Dark Matter. WARP is capable of observing the extremely low energy signals produced by WIMP collisions with ordinary nuclei and, simultaneously, minimizing the signals from cosmic ray and natural radioactivity backgrounds that often limit observation of WIMP dark matter. WARP's two-phase drift chamber uses argon as a target. It has a unique capability that greatly enhances its sensitivity: it uses two fully independent techniques for discriminating minimum ionizing events from nuclear recoils. These rely on the subtle differences produced in the signals observed in WARP by the two different types of events.The viability of the WARP experiment was well established with the successful operation of a small (3.8-kg) yet extremely sensitive prototype detector at the LNGS, the laboratory for astroparticle physics located underneath the peak of the Gran Sasso mountain in central Italy (1 hour by car from Rome) at a depth of 3,800 feet. The WARP collaboration will install in 2006 a much larger (140-kg) detector at LNGS which should improve the sensitivity by about two orders of magnitude for WIMP searches.Education and Outreach are integral to the WARP effort. The PIs of the WARP Program are among the founders of the Gran Sasso-Princeton Summer School. Now in its second year, the School brings 20 promising high-school students from the Gran Sasso region to the Princeton University campus for an intensive 4-week program in physics. The School has become an instant success in Gran Sasso, with more than 300 applicants in 2005, and promises to become a lasting platform for the scientific and cultural enrichment of young Italian men and women. The school helps in establishing a strong link between the US and one of the prime laboratories for underground physics in the world, which hosts a number of US researchers and US funded efforts.The WARP program will also offer in the forthcoming years an opportunity for a number of US students to get directly involved with the project both at Princeton and at LNGS. Research opportunities will include construction and testing of part of the experimental apparatus, and analysis of the data from the experiment. This hands-on experience will give the students a rare window into the nature of the experimental process that produces and tests the very knowledge that they find in their textbooks. The research experience on the project will build the student's confidence, expand their intellectual and cultural horizons, and, hopefully, inspire some to pursue degrees and even careers in science or engineering and to serve as role models for other young students.