Upsilon meson

Key takeaways

Upsilon meson belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Upsilon meson to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Upsilon meson from memory before moving on to harder problems.

Reference excerpt

The Upsilon meson (ϒ) is a quarkonium state (i.e. flavourless meson) formed from a bottom quark and its antiparticle. It was discovered by the E288 experiment team, headed by Leon Lederman, at Fermilab in 1977. It has a lifetime of 1.21×10−20 s and a mass about 9.46 GeV/c2 in the ground state.

Overview

There are many species of bottomonium known, but the ones generated by e−e+ colliding beams (or proton–nucleus collisions decaying to μ+μ− + X) are the ones generally referred to as upsilon mesons. Thus, among the bound bb bottomonium species, the S-state triplet resonances are identified as upsilons, and are assigned the shorthand notations ϒ(S1), ϒ(S2), ϒ(S3), etc., where the numbers 1, 2, 3 represent the principal quantum number n. Alternatively, the notation parenthesizing the measured mass in MeV/c2 is used, e.g. ϒ(10860). In the narrow sense, "Upsilon particle" refers strictly to the ϒ(1S). As clear from its quark structure, the Upsilon meson carries no charge or flavor, and has 0 isospin. The zero spin state should have a lighter mass by about 0.1% to 1% according to quantum chromodynamics.

Discovery Lederman's E288 experiment team at Fermilab had made a preliminary finding of a resonance at 9.5 GeV/c2 in November 1976, but was more reticent in announcing it because earlier they had prematurely announced a 6 GeV/c2 resonance event (which they were planning to name upsilon; cf. Oops-Leon) with their equipment in dielectron (e+e−) mode; this find did not pan out and ultimately could not be confirmed. However, with their equipment converted to dimuon (μ−μ+) mode with increased sensitivity upped 100 times, they began measurement in May 1977 and clearly confirmed resonance peaks at 9.4/9.5. 10. 10.4 GeV/c2 (cf. § Resonance states under S1, S2, S3) These peaks were verified by the German team using DESY's DORIS storage ring. The upsilon was the first particle containing a bottom quark to be discovered because it is the lightest that can be produced without additional massive particles.

Resonant states

ϒ(1S) Mass measured at 9460.30±0.26 MeV/c2 (Lawrence Berkeley National Laboratory, Particle Data Group, 2008) Lifeime of about > 10−20 calculated from measured energy width to 1.21×10−20 s. The types of decay modes are diverse, with electron pair, muon pair, tauon pair decays (all three lepton decays) each occurring at 2.5% frequency. The short lifetime (τ) is calculable from the usual formula τ ΔE = ħ, so in the subsequent sections, the listing of the lifetimes will be eschewed.

ϒ(2S) Mass measured at 10.02326±0.00031 GeV/c2. Here again, decay modes are diverse, decaying into ϒ(1S) and charged pion pair, approx. 20% of the time, into ϒ(1S) and neutral π pair, approx. 10%, and into lepton (e, μ, τ) pairs, about 2% each. A B-factory at SLAC's PEP-II accelerator postponed the termination of operation by 2 months to conduct experiments starting February 2008 to generate ϒ(2S) and ϒ(3S) (cf. below). While the data remained to be fully analyzed, the team announced in the fall of 2008 that they discovered the spin 0 ground state bottomonium corresponding to the spin 1 ϒ(1S) state. The published mass difference with ϒ(1S) was 71.4+2.3−3.1 ± 2.7 MeV/c2.

ϒ(3S) Mass measured at 10.3552±0.0005 GeV/c2 Again, diversely decaying into Υ(2S) + X (such as pion pairs), approx. 10% Υ(1S) + X (such as pion pairs), also lepton (μ, τ) pairs, about 2% apiece, but e+e^ decay is quite rare.

ϒ(4S) Also called ϒ(10580) 10.5794±0.0012 GeV/c2。 Nearly completely decays (> 96%) into B meson pairs, almost fifty–fifty between charged pairs and uncharged pairs. Thus for B meson research, this ϒ(4S) mode of resonance is of great importance, and its research has been undertaken by various B-factories (up to c. 1999).。

ϒ(10860) Also called Y(5S). Measured mass of 10.865±0.008 GeV/c2 Main decay mode into B meson pairs only or with 1 or 2 pions, about 60% of the time, and into charm B meson pairs, about 20% of the time. In this 2008 data report, the strange B meson (Bs) decay is also tentatively reported. The energy threshold was also met by Japan's KEKB accelerator whose Belle B factory experiment also contemplated the strange B meson decay. The successes of Y(4S) research has led to the advent of studying Y(5S) at the higher luminosities From around 2008.

ϒ(11020) Mass measured at 11.019±0.008 GeV/c2. The decay modes are unclear except a small percentage of electron pair decays, as of 2008.。

See also Oops-Leon, an erroneously-claimed discovery of a similar particle at a lower mass in 1976. The ϕ particle is the analogous state made from strange quarks. The J/ψ particle is the analogous state made from charm quarks. List of mesons

Explanatory notes

References

Citations

Bibliography Hom, D.C.; et al. (1977). "Observation of a Dimuon Resonance at 9.5 Gev in 400-GeV Proton-Nucleus Collisions" (PDF). Physical Review Letters. 39 (5): 252–255. Bibcode:1977PhRvL..39..252H. doi:10.1103/PhysRevLett.39.252. OSTI 1155396. Lederman, Leon M.; Teresi, Dick (2006) [1993]. The God Particle: If the Universe is the Answer, what is the Question?. Boston: Houghton Mifflin Harcourt. ISBN 9780618711680. Yoh, John (1998). "The Discovery of the b Quark at Fermilab in 1977: The Experiment Coordinator's Story" (PDF). AIP Conference Proceedings. 424: 29–42. Bibcode:1998AIPC..424...29Y. doi:10.1063/1.55114. OSTI 645407.

Illustrations

Worked examples

Example 1 — a first encounter with Upsilon meson

Start with the simplest possible case. Write down what Upsilon meson claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Upsilon meson before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Upsilon meson ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Upsilon meson

In research: Upsilon meson appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Upsilon meson in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Upsilon meson is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mesons, Onia, Subatomic particles with spin 1, so understanding it makes those chapters shorter.
In everyday life: Look for Upsilon meson outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Upsilon meson in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Upsilon meson means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Upsilon meson out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Upsilon meson in simple terms?

The Upsilon meson (ϒ) is a quarkonium state (i.e. flavourless meson) formed from a bottom quark and its antiparticle. It was discovered by the E288 experiment team, headed by Leon Lederman, at Fermilab in 1977.

Why does Upsilon meson matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Upsilon meson?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Upsilon meson.