>> Long Baseline Neutrino Experiments: >> 长基线中微子实验:
Initial studies of neutrino oscillations from atmospheric and solar neutrinos 来自大气和太阳中微子的中微子振荡初步研究
Emphasis of neutrino research now on neutrino beam experiments 目前中微子研究的重点是中微子束实验
Allows the physicist to take control - design experiment with specific goals 让物理学家掌握控制权--设计具有特定目标的实验
In the last few years, long baseline neutrino oscillation experiments have started taking data: K2K, MINOS, CNGS, T2K 最近几年,长基线中微子振荡实验开始采集数据:K2K、MINOS、CNGS、T2K >> Basic Idea: >> 基本构思:
Intense neutrino beam 强中微子束
Two detectors: one close to beam the other hundreds of km away 两个探测器:一个靠近光束,另一个在数百公里之外
Measure ratio of the neutrino energy spectrum in far detector (oscillated) to that in the near detector (unoscillated) 测量远探测器(振荡)与近探测器(非振荡)中微子能谱的比率
Partial cancellation of systematic biases 部分消除系统偏差
Long Baseline Neutrino Experiments: 长基线中微子实验:
MINOS 米诺斯
> 120GeV>120 \mathrm{GeV} protons extracted from the MAIN INJECTOR at Fermilab > 120GeV>120 \mathrm{GeV} 从费米实验室主注入器提取的质子 > 2.5 xx10^(13)>2.5 \times 10^{13} protons per pulse hit target =>\Rightarrow very intense beam -0.3 MW on target > 2.5 xx10^(13)>2.5 \times 10^{13} 每个脉冲的质子击中目标 =>\Rightarrow 非常强烈的光束 -0.3 兆瓦击中目标
Two detectors: 两个探测器
Long Baseline Neutrino Experiments: 长基线中微子实验:
>> Neutrino detection via CC interactions on nucleon: >> 通过核子上的CC相互作用探测中微子:
>> The main feature of the MINOS detector is the very good neutrino energy resolution >> MINOS探测器的主要特点是中微子能量分辨率非常高
E_(v)=E_(mu)+E_(X)E_{v}=E_{\mu}+E_{X}
Muon energy from range/curvature in B-field 来自 B 场范围/曲率的μ介子能量
Hadronic energy from amount of light observed 从观测到的光量看强子能量 >> For the MINOS experiment L is fixed and observe oscillations as function of E_(v)E_{v} >> 对于 MINOS 实验,L 是固定的,观察振荡与 E_(v)E_{v} 的函数关系。 >> For |Deltam_(32)^(2)|∼2.5 xx10^(-3)eV^(2)\left|\Delta m_{32}^{2}\right| \sim 2.5 \times 10^{-3} \mathrm{eV}^{2} first oscillation minimum at E_(v)=1.5GeVE_{v}=1.5 \mathrm{GeV} >> 对于 |Deltam_(32)^(2)|∼2.5 xx10^(-3)eV^(2)\left|\Delta m_{32}^{2}\right| \sim 2.5 \times 10^{-3} \mathrm{eV}^{2} 第一次振荡最小值,位于 E_(v)=1.5GeVE_{v}=1.5 \mathrm{GeV} 处 >> To a very good approximation can use two flavor formula as oscillations corresponding to |Deltam_(21)^(2)|∼8xx10^(-5)eV^(2)\left|\Delta m_{21}^{2}\right| \sim 8 \times 10^{-5} \mathrm{eV}^{2} occur at E_(v)=50MeVE_{v}=50 \mathrm{MeV} beam contains very few neutrinos at this energy + well below detection threshold >> 非常近似地可以使用双味公式,因为与 |Deltam_(21)^(2)|∼8xx10^(-5)eV^(2)\left|\Delta m_{21}^{2}\right| \sim 8 \times 10^{-5} \mathrm{eV}^{2} 相对应的振荡发生在 E_(v)=50MeVE_{v}=50 \mathrm{MeV} 波束中,该能量下的中微子数量极少+远低于探测阈值
Several different nuclear reactions in the sun =>\Rightarrow complex neutrino energy spectrum 太阳中的几种不同核反应 =>\Rightarrow 复杂的中微子能谱
All experiments saw a deficit of electron neutrinos compared to experimental prediction - the SOLAR NEUTRINO PROBLEM 与实验预测相比,所有实验都发现电子中微子不足--太阳中微子问题
e.g. Super Kamiokande 例如:超级卡莫坎德
Solar Neutrinos I: Super Kamiokande 太阳中微子 I:超级 Kamiokande
50000 ton water Čerenkov detector 50000 吨水Čerenkov 探测器
Water viewed by 11146 Photo-multiplier tubes 11146 光电倍增管观察到的水
Deep underground to filter out cosmic rays otherwise difficult to detect rare neutrino interactions 深入地下过滤宇宙射线,否则难以探测到罕见的中微子相互作用
>> Detect neutrinos by observing Čerenkov radiation from charged particles which travel faster than speed of light in water c//nc / n >> 通过观察带电粒子在水中以超过光速的速度传播时产生的采伦科夫辐射来探测中微子 c//nc / n .
>> Can distinguish electrons from muons from pattern of light - muons produce clean rings whereas electrons produce more diffuse “fuzzy” rings >> 可以从光的模式区分电子和μ介子--μ介子产生干净的光环,而电子产生的光环则更分散、更 "模糊"。 >> Sensitive to solar neutrinos with E_(V) > 5MeVE_{V}>5 \mathrm{MeV} >> 通过 E_(V) > 5MeVE_{V}>5 \mathrm{MeV} 对太阳中微子敏感 >> For lower energies too much background from natural radioactivity ( beta\beta-decays) >> 对于较低能量,天然放射性( beta\beta -衰变)产生的背景太强。 >> Hence detect mostly neutrinos from ^(8)B rarr^(8)Be^(**)+e^(+)+v_(e){ }^{8} B \rightarrow{ }^{8} B e^{*}+e^{+}+v_{e} >> 因此主要探测到来自 ^(8)B rarr^(8)Be^(**)+e^(+)+v_(e){ }^{8} B \rightarrow{ }^{8} B e^{*}+e^{+}+v_{e} 的中微子。
Solar Neutrino Experiments 太阳中微子实验
>> Detect electron Čerenkov rings from >> 探测电子的切伦科夫环
Measure of electron neutrino flux + total flux! 测量电子中微子通量 + 总通量!
Solar Neutrino Experiments 太阳中微子实验
Using known cross sections can convert observed numbers of events into fluxes 利用已知的横截面可以将观测到的事件数转换为通量
The different processes impose different constraints 不同的过程有不同的限制
Where constraints meet gives separate measurements of v_(e)v_{e} and v_(mu)+v_(tau)v_{\mu}+v_{\tau} fluxes 在约束条件相遇时,可分别测量 v_(e)v_{e} 和 v_(mu)+v_(tau)v_{\mu}+v_{\tau} 通量
>> The interpretation of the solar neutrino data is complicated by MATTER EFFECTS >> 太阳中微子数据的解释因物质效应而变得复杂
The quantitative treatment is non-trivial and is not given here 定量处理并非易事,在此不再赘述。
Basic idea is that as a neutrino leaves the sun it crosses a region of high electron density 基本原理是,当中微子离开太阳时,它会穿过一个电子密度较高的区域
The coherent forward scattering process (v_(e)rarrv_(e):}\left(v_{e} \rightarrow v_{e}\right. for an electron neutrino) 电子中微子的相干前向散射过程 (v_(e)rarrv_(e):}\left(v_{e} \rightarrow v_{e}\right. )
is different to that for a muon or tau neutrino 与μ介子或头中微子不同
It can enhance oscillations - “MSW effect” 它能增强振荡--"MSW 效应" >> A combined analysis of all solar neutrino data gives: >> 对所有太阳中微子数据进行综合分析后得出:
>> Observe a lower ratio with deficit of v_(mu)//v_(mu)v_{\mu} / v_{\mu} coming from below the horizon, i.e. large >> 观察到来自地平线以下的 v_(mu)//v_(mu)v_{\mu} / v_{\mu} 赤字的比率较低,即较大。
distance from production point on other side of the Earth 与地球另一端生产点的距离
Atmospheric Neutrino experiment 大气中微子实验
Super Kamiokande Atmospheric Results 超级 Kamiokande 大气成果
>> Typical energy: E_(v)∼1GeV\mathrm{E}_{v} \sim 1 \mathrm{GeV} (much greater than solar neutrinos - no confusion) >> 典型能量: E_(v)∼1GeV\mathrm{E}_{v} \sim 1 \mathrm{GeV} (比太阳中微子大得多--不要混淆) >> Identify v_(e)v_{e} and v_(mu)v_{\mu} interactions from nature of Čerenkov rings >> 从采伦科夫环的性质确定 v_(e)v_{e} 和 v_(mu)v_{\mu} 相互作用 >> Measure rate as a function of angle with respect to local vertical >> 测量速率与当地垂直角度的函数关系 >> Neutrinos coming from above travel 20 km >> 来自上方的中微子飞行 20 千米 >> Neutrinos coming from below (i.e. other side of the Earth) travel 12800 km >> 来自下方(即地球的另一侧)的中微子飞行 12800 千米
Prediction for v_(e)v_{e} rate agrees with data 对 v_(e)v_{e} 速率的预测与数据一致
Strong evidence for disappearance of v_(mu)v_{\mu} for large distances v_(mu)v_{\mu} 在远距离消失的有力证据