發(fā)布時(shí)間：2018-04-11 21:00

  本文選題：液氙探測(cè)器 + 暗物質(zhì)��； 參考：《上海交通大學(xué)》2014年碩士論文

【摘要】：大質(zhì)量弱相互作用粒子(weakly interacting massive particles WIMPs)是目前暗物質(zhì)粒子的最具吸引力的候選之一。近二十年來,無數(shù)暗物質(zhì)探測(cè)實(shí)驗(yàn)被開發(fā)用于WIMPs粒子的直接探測(cè)。其中,液氙探測(cè)器是所有直接探測(cè)試驗(yàn)中最有希望的一種。液氙探測(cè)器用來探測(cè)暗物質(zhì)粒子(WIMPs)與探測(cè)器中原子發(fā)生彈性散射作用所引起的核反沖,從而達(dá)到對(duì)暗物質(zhì)粒子的直接探測(cè)的目的。當(dāng)液氙探測(cè)器中的某個(gè)氙原子與暗物質(zhì)粒子發(fā)生彈性散射,該原子會(huì)獲得大約幾到幾十千電子伏特(keV)的動(dòng)能成為一個(gè)反沖原子。反沖原子在探測(cè)器介質(zhì)中運(yùn)動(dòng)并減速,在此期間會(huì)激發(fā)或者電離探測(cè)器中其他原子,產(chǎn)生實(shí)驗(yàn)中容易探測(cè)到的瞬時(shí)發(fā)光信號(hào)(以下簡(jiǎn)稱為發(fā)光信號(hào))S1或者電離正比發(fā)光信號(hào)(以下簡(jiǎn)稱為電離信號(hào))S2。其中發(fā)光信號(hào)是由激發(fā)電子退激發(fā),或者被電離電子與負(fù)離子重新結(jié)合并退激發(fā)而產(chǎn)生,而電離信號(hào)則是由于被電離的電子在外加電場(chǎng)作用下,漂移到氣態(tài)探測(cè)器室中而產(chǎn)生。在液氙探測(cè)器中,有兩個(gè)重要的參數(shù),即相對(duì)發(fā)光效率(relative scintillation e?ciency Leff)和電離效率(ionization yield Qy)。這兩個(gè)參數(shù)有效地的將實(shí)驗(yàn)易探測(cè)到發(fā)光信號(hào)S1或者電離信號(hào)S2與暗物質(zhì)粒子(WIMPs)在探測(cè)器中原子反沖的初始能量聯(lián)系起來。如果Leff或者Qy能夠精確的計(jì)算出來,那么結(jié)合實(shí)驗(yàn)對(duì)原子反沖所產(chǎn)生的發(fā)光信號(hào)S1或者電離信號(hào)S2測(cè)量,實(shí)驗(yàn)學(xué)家可以重構(gòu)原子反沖的能量,從而對(duì)暗物質(zhì)粒子的相關(guān)性質(zhì)進(jìn)行進(jìn)一步分析。原則上講,Leff和Qy可以通過實(shí)驗(yàn)進(jìn)行測(cè)量。然而這項(xiàng)任務(wù)在低能原子反沖區(qū)卻很有挑戰(zhàn)性。大多數(shù)實(shí)驗(yàn)通過中子源來產(chǎn)生核反沖,從而模擬暗物質(zhì)粒子產(chǎn)生的原子反沖信號(hào)來測(cè)量Leff和Qy,但是實(shí)驗(yàn)的性質(zhì)決定了核反沖的能量越低(keV能量區(qū)域附近),該實(shí)驗(yàn)的系統(tǒng)誤差就會(huì)越大。同時(shí),由于輕暗物質(zhì)粒子(WIMPs)的質(zhì)量多數(shù)在幾個(gè)吉電子伏特(GeV)左右,其產(chǎn)生的原子反沖能量多數(shù)在數(shù)個(gè)千電子伏特(keV)。針對(duì)這種情況,本文對(duì)液氙探測(cè)器在低能區(qū)的發(fā)光和電離過程進(jìn)行了詳盡的研究和理論分析,并且對(duì)Leff和Qy在低能區(qū)的行為做出了相應(yīng)的理論預(yù)測(cè)�；贚indhard的基本積分方程以及二體碰撞模型,我們開發(fā)了一個(gè)計(jì)算機(jī)程序來模擬原子反沖在液氙探測(cè)器中的減速過程。利用該程序,我們可以計(jì)算出原子反沖在減速過程中的電子能損的具體數(shù)值。通常來說,這個(gè)數(shù)值與原始原子反沖能量的比值被稱為Lindhard系數(shù)(Nuclear Quenching Factor qnc)。從而可以進(jìn)一步來計(jì)算發(fā)光信號(hào)和電離信號(hào)的數(shù)量。為了得到qnc在低能區(qū)的精確值,我們對(duì)低能區(qū)的氙原子在液氙介質(zhì)中的電子能損的過程,現(xiàn)存的理論模型,以及實(shí)驗(yàn)數(shù)據(jù)進(jìn)行了分析,對(duì)傳輸截面法(Transport Cross Section)求電子能損Se的方法做了修正,從而重新計(jì)算了Se。我們的理論結(jié)果與中等能量區(qū)域(40到100千電子伏特)的實(shí)驗(yàn)結(jié)果符合得很好。為了進(jìn)一步計(jì)算光信號(hào)和電離信號(hào)的數(shù)值,我們對(duì)電子與負(fù)離子的結(jié)合過程進(jìn)行了分析,修正并推廣了現(xiàn)有的Thomas-Imel模型。通過該修正,我們預(yù)測(cè)了電子與負(fù)離子在外場(chǎng)下的結(jié)合效率,從而能夠精確計(jì)算出發(fā)光信號(hào)和電離信號(hào)的數(shù)值。將我們所做的研究結(jié)合起來,我們得到Leff和Qy在低能區(qū)的理論預(yù)測(cè)值。我們對(duì)Leff和Qy的理論預(yù)測(cè)與中子散射實(shí)驗(yàn)的測(cè)量結(jié)果符合的很好。在無實(shí)驗(yàn)數(shù)據(jù)區(qū)域(低于3千電子伏特的區(qū)域),我們所預(yù)測(cè)的Leff迅速降低。該現(xiàn)象與之前文獻(xiàn)中所做的假設(shè)相矛盾。我們所預(yù)測(cè)的Qy隨著原子反沖能量的降低而升高,在2到3千電子伏特的區(qū)域達(dá)到最大值。這個(gè)預(yù)測(cè)結(jié)果可以將探測(cè)器的探測(cè)極限進(jìn)一步降低到大約1千電子伏特左右。由于電離信號(hào)相對(duì)易于探測(cè),該預(yù)測(cè)有可能被實(shí)驗(yàn)進(jìn)一步證實(shí)或者證偽。
[Abstract]:Wimps (weakly interacting massive particles WIMPs) is currently the dark matter particles. One of the most attractive candidates for the past twenty years, numerous dark matter detection experiment was developed for the direct detection of WIMPs particles. The liquid xenon detector is a direct test of the most promising. The liquid xenon detector is used to detect dark matter particles (WIMPs) and nuclear recoil detector in atomic elastic scattering effects, so as to achieve the direct detection of dark matter particles. The elastic scattering occurs when the particle liquid xenon detector in a xenon atom and dark matter, the atom will be about a few to tens of electron V (keV) kinetic energy become a recoil atom. The recoil atom movement in the detector medium and slow, can stimulate or in other atomic ionization detector during the test Instantaneous easily detected light signal (hereinafter referred to as the luminescence signal) or light signal is proportional to the ionization S1 (hereinafter referred to as the S2. ionization signal) the luminescence signal is excited by electron de excitation, or ionizing electron and negative ion recombination and de excitation generated, and ionization signal is due to the ionized electrons under electric field, drift to the room in which gaseous detector in liquid xenon detector, there are two important parameters, namely the relative luminous efficiency (relative scintillation e ciency? Leff) and ionization efficiency (ionization yield Qy). These two parameters effectively will be easy to detect the luminescence signal S1 experiment or ionization signal S2 and dark matter particles (WIMPs) in the probe atom recoil initial energy together. If Leff or Qy can be calculated accurately, then combined with the experiment of atomic recoil The luminescence signal S1 or S2 ionization signal measurement, experimental scientists can reconstruct atomic recoil energy, further analysis and related properties of dark matter particles. In principle, Leff and Qy can be measured by experiments. However, this task in the low-energy atomic recoil region is very challenging. Most of the experiments by neutron source to produce nuclear recoil, thereby simulating atomic recoil particles of dark matter signal generated by measurement of Leff and Qy, but the nature of the nuclear recoil energy is low (near the keV energy region), the system error of the experiment will be bigger and bigger. At the same time, because the light dark matter particles (WIMPs) in the majority of quality a few GeV (GeV), the atomic recoil energy most in a number of thousands of electron volts (keV). In this case, the liquid xenon detector in the low energy region of the light and electricity from the detailed process As the research and theoretical analysis, and the Leff and Qy in the low energy region acts made the corresponding theoretical predictions. The basic integral equations of Lindhard and two body collision model based on deceleration process we developed a computer program to simulate the recoil atoms in liquid xenon detector. By using this program, we can calculate the the specific value of atomic recoil electron energy loss during deceleration. Generally, the ratio of this value with the original atomic recoil energy is called Lindhard (Nuclear Quenching Factor coefficient QNC). The number of which can further calculate the light signal and the ionization signal. In order to get the exact value of QNC in the low energy region, we the low energy region of xenon atoms in liquid xenon electronic medium energy loss, the existing theoretical model, and the experimental data were analyzed on the transmission cross section method (Transport Cross Section) for Electronic energy loss Se method modification is made to re calculate the theoretical results of Se. and medium energy region (40 to 100 thousand EV). The experimental results are in good agreement. In order to further numerical calculation of optical signal and ionization signal, we on the electron and negative ion binding process was analyzed and the correction and extend the existing Thomas-Imel model. Through the correction, we predicted the binding efficiency of electrons and negative ions in the presence of magnetic field, which can accurately calculate the numerical luminescence signal and ionization signal. The research we have done together, we get Leff and Qy predictive value in the low energy region of the measurement result of our theory. The Leff and Qy theoretical prediction and neutron scattering experiments are in good agreement with experimental data. In the area (less than 3 thousand EV, area) we have predicted Leff decreased rapidly. The phenomenon of literature In the assumption made in contradiction. We predicted Qy increased with decreasing atomic recoil energy, 3 thousand EV in 2 areas reaches the maximum value. The prediction results can further reduce the detection limit of detector to about 1 thousand ev. The ionization signal is relatively easy to detect, the prediction of possible the experiment was further confirmed or falsified.

【學(xué)位授予單位】：上海交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：P145.9;O572.2

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