Study of the B- --> J/psi K- pi+ pi- Decay and Measurement of the B- --> X(3872) K- Branching Fraction

BABAR Collaboration; B.Aubert; et al

REVIEW

Study of the B- --> J/psi K- pi+ pi- Decay and Measurement of the B- --> X(3872) K- Branching Fraction

B.Aubert, et al, BaBar Collaboration

High Energy Physics - Experiment · Submitted 7 Jun 2004 · 16 references

Pith's verdict: A solid, citable BaBar confirmation of the X(3872) with a mass measured relative to the psi(2S); the product branching fraction's error bar is slightly tighter than the analysis actually earns.

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arXiv IDhep-ex/0406022 (version 1)

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CitationBABAR Collaboration, B.Aubert, et al. "Study of the B- --> J/psi K- pi+ pi- Decay and Measurement of the B- --> X(3872) K- Branching Fraction." arXiv:hep-ex/0406022 (2004). https://pith.science/paper/YEJO5IOJ

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Editor's note

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Bottom line: this is a competent, useful BaBar measurement. It confirms the X(3872) at 3.5 sigma in 117 million BBbar events, fixes its mass at 3873.4 +/- 1.4 MeV/c2, and improves the total B- -> J/psi K- pi+ pi- rate by roughly a factor of two over the then-world average. The numbers will get cited. The one caveat before you quote the product branching fraction is that its uncertainty is a bit optimistic relative to what was actually propagated. What is genuinely new: an independent confirmation of Belle's and CDF's state, a mass quoted as a difference from the psi(2S) so the absolute scale cancels, the product rate (1.28 +/- 0.41) x 10^-5, and two 90% limits. The analysis design is deliberately error-cancelling, and it works: the total rate is a ratio to B- -> psi(2S) K- with an MC efficiency ratio of 1.17 +/- 0.03, and the frequentist construction folds systematics into the interval rather than bolting them on afterwards. The B- -> J/psi D0 pi- limit is a real result, since it rules out the intrinsic-charm explanation of the low-momentum J/psi excess. Where it is soft: Eq. (3) randomizes N_bkg, N_psi(2S), and the two PDG branching fractions, but holds epsilon_w fixed and never includes the X-to-psi(2S) reconstruction efficiency ratio at all. The text justifies this with one clause, 'assuming the same efficiency.' They know how to do this properly, because they did it for the total rate. A 10% uncertainty on that ratio would widen the quoted +/- 0.41 by a visible amount. Second, N_peak = 10.5 +/- 3.2 comes from a linear extrapolation of the 15-45 MeV sideband; a 2 sigma shift there moves the signal by about 20%. Both points are acknowledged in prose and neither overturns the central value, which is internally consistent at 30.5 events. The 1.8 sigma electron-versus-muon split is reported but not explained; minor, but a sentence would help. The h_c limit inherits the same efficiency assumption, though at that precision it hardly matters. Who should read it: anyone quoting the X(3872) mass or production rate, and anyone working the charmonium-exotic question. It deserves a serious referee; the fixes are small and mostly about the error budget.

Referee report

Significance

The result is a genuine and useful contribution. The analysis is deliberately built so that systematic uncertainties cancel rather than being fought: the total rate is a ratio to a well-measured external normalization channel (Eq. 1), the X(3872) mass is measured as a difference from the ψ(2S) mass so the absolute momentum scale drops out, and the small-sample confidence interval folds the external branching-fraction uncertainties in directly rather than adding them afterwards. The internal cross-checks are explicit and quantitative: the counting estimate of 30.5 X(3872) events agrees with the 25.4 ± 8.7 from the two-dimensional fit, and the J/ψ→e+e− and J/ψ→μ+μ− subsamples are quoted separately. The hc and J/ψD0π− limits are falsifiable statements that constrain specific models. If the numbers hold, the X(3872) is confirmed in an independent sample and the three-body branching fraction is improved by roughly a factor of two over the then-current average.

Major objections (2)

[Eq. (3) and the paragraph defining εw] The product branching fraction for B−→X(3872)K− is obtained from Eq. (3), which contains only Nψ(2S) and εw and therefore implicitly sets the X(3872)-to-ψ(2S) reconstruction-efficiency ratio to unity. The text justifies this with the single clause 'assuming the same efficiency', and εw = (92 ± 1)% is held fixed in the confidence-level computation, so this assumption enters neither the central value's error nor the interval. The same assumption is applied to the hc search at 3526 MeV/c², where the mass difference from the ψ(2S) is larger still. This is inconsistent with the treatment of the J/ψD0π− limit later in the paper, where the analogous ratio is quoted as ε/εψ(2S) = 1.00 ± 0.07 and is used. Please quantify εX/εψ(2S) from Monte Carlo (the pion momenta differ substantially between the two states) and propagate it, or state explicitly why it is expected to be unity to better than the precision that matters. The shared resolution function does justify transferring the window fraction εw, so the concern is specifically the reconstruction efficiency, not the mass resolution.
[Summary paragraph, final sentence on B−→J/ψD0π−] The statement that the limit B(B−→J/ψD0π−) < 5.2 × 10−5 'rules out the explanation of the inclusive J/ψ momentum spectrum with intrinsic charm proposed in [8]' is stronger than the measurement supports. The limit constrains one specific channel; the intrinsic-charm model of Chang and Hou involves a broader set of final states, and the paper does not demonstrate that this single channel is the model's dominant or necessary ingredient. Please soften to a statement of what is excluded, for example that the limit disfavours or strongly constrains that explanation under the model's stated assumptions, and say which assumption is being tested.

Minor objections (6)

[Mass measurement, mX(3872) = 3873.4 ± 1.4 MeV/c²] The quoted uncertainty is not labelled as statistical or total. The text correctly argues that the mass-difference technique removes absolute-scale systematics, but the fit also depends on the resolution parameterization and on the background shape in m(J/ψπ+π−), and no systematic on those is quoted. Please state what the ±1.4 MeV/c² contains.
[Significance of the X(3872) excess] The 3.5σ significance is derived from a background-fluctuation probability of 5.4 × 10−4 that depends on the modelled peaking background Npeak = 10.5 ± 3.2. Since the sideband extrapolation is the least constrained input, it would be helpful to quote how the significance changes under a 1σ or 2σ shift of Npeak.
[J/ψ→e+e− and J/ψ→μ+μ− subsample cross-check] The two subsample values, (1.94 ± 0.62) × 10−5 and (0.52 ± 0.46) × 10−5, are described as consistent within 1.8 standard deviations, but a reader who forms the error-weighted average obtains about 1.0 × 10−5 rather than the quoted 1.28 × 10−5. Please state explicitly that the quoted central value comes from the combined frequentist construction and that the subsample numbers are consistency checks, not inputs to a weighted average.
[hc search] The hc limit uses Ndata = 9 against a total background of 7.5 ± 3.8 and the same εw as the X(3872). It would help to state the assumed hc mass and width explicitly in the text rather than only in the window definition, and to note that the limit scales with the assumed efficiency transfer discussed above.
[Figure 2 and its caption] The caption should state the fitted m(J/ψπ+π−) range and whether the resolution parameters of the X(3872) component are fixed to those of the ψ(2S) or allowed to float; the text says 'the same resolution function', and the figure should make that unambiguous.
[Text, paragraph on the m(J/ψπ+π−) fit] There are typographical errors, for example 'subratcting' in the sentence describing the ψ(2S) fit and 'implicitely' in the charge-conjugation footnote; these should be corrected.

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The paper

The paper claims

BaBar confirms the X(3872) in B decays and pins its mass to 3873.4 MeV, while closing off two rival explanations of the same final state.

The reading

The paper asks a concrete question: when a $B^-$ meson decays into a $J/ψ$, a $K^-$ and a $π^+π^-$ pair, does the $J/ψπ^+π^-$ system sometimes pass through a distinct intermediate particle? Using 117 million $B$-meson pairs recorded with the BaBar detector at the PEP-II collider, the authors confirm a bump near $3873.4$ MeV/$c^2$ — the $X(3872)$, a state whose identity was and remains unsettled — and measure the product of how often $B^- → X(3872)K^-$ occurs and how often the $X(3872)$ decays to $J/ψπ^+π^-$. They also tighten the total three-body branching fraction for $B^- → J/ψK^-π^+π^-$ to $(116 ± 7 ± 9)×10^{-5}$, roughly a factor of two better than the then-current world average, and set upper limits on two other proposed intermediate states, the $h_c$ and a $J/ψD^0π^-$ mode. If the result holds, the $X(3872)$ is a genuine particle produced in $B$ decays rather than a statistical fluctuation, its mass is pinned closely enough to sit essentially on the threshold for a $D^0$ and a $D^{*0}$ meson, and one popular explanation of the excess of low-momentum $J/ψ$ mesons in inclusive $B$ decays is excluded.

What carries the argument

The measurement is built on a ratio rather than an absolute rate: $R = B(B^- → J/ψK^-π^+π^-)/B(B^- → ψ(2S)K^-)$ is formed so that luminosity, $b$-quark tagging, and most reconstruction efficiencies cancel, with the $ψ(2S)$ yield taken from a two-Gaussian fit to the $J/ψπ^+π^-$ mass distribution. Signal extraction uses two kinematic variables, the beam-energy-substituted mass $m_{ES}$ and the energy difference $ΔE$, fitted with a binned likelihood in which the signal is a Gaussian plus a low-side tail and the background is an ARGUS threshold function. For the $X(3872)$, an unbinned two-dimensional likelihood in $(m_{ES}, m_{J/ψπ^+π^-})$ combines a non-resonant polynomial term, a $ψ(2S)$ term, an $X(3872)$ term sharing the $ψ(2S)$ resolution function but with a floating mass offset, and a combinatorial term. The branching fraction and the limits are obtained with a frequentist confidence-level construction in which the nuisance quantities — background counts, $ψ(2S)$ yield, and the external branching fractions used for normalization — are sampled from Gaussian distributions and folded into a Poisson expectation, so that systematic uncertainties enter the interval directly rather than being added afterwards.

Extended reading notes

Core claim

The central claim is a triple measurement in the decay chain $B^- → J/ψK^-π^+π^-$. First, the inclusive three-body branching fraction is $B(B^- → J/ψK^-π^+π^-) = (116 ± 7_{stat} ± 9_{syst})×10^{-5}$. Second, an excess of events in the $J/ψπ^+π^-$ invariant mass distribution near 3872 MeV/$c^2$ is identified as the $X(3872)$, with product branching fraction $B(B^- → X(3872)K^-) × B(X(3872) → J/ψπ^+π^-) = (1.28 ± 0.41)×10^{-5}$; the probability that the observed 63 events in the window are a background fluctuation is quoted as $5.4×10^{-4}$, about 3.5 standard deviations. Third, the mass is extracted from a fit in which the $X(3872)$ mass floats relative to the $ψ(2S)$ mass, giving $m_{X(3872)} = 3873.4 ± 1.4$ MeV/$c^2$, consistent with the earlier Belle and CDF observations. As by-products, the authors set 90% confidence limits $B(B^- → h_cK^-) × B(h_c → J/ψπ^+π^-) < 3.4×10^{-6}$ and $B(B^- → J/ψD^0π^-) < 5.2×10^{-5}$, the latter ruling out an intrinsic-charm explanation of the soft-$J/ψ$ excess in inclusive $B$ decays.

Load-bearing premise

The $X(3872)$ yield is converted into a branching fraction by assuming its reconstruction and selection efficiency equals that of the $ψ(2S)$, a state 187 MeV lighter whose pions have different momenta, and the peaking-background subtraction assumes the non-resonant $J/ψπ^+π^-$ mass shape is smooth across the signal window.

Editorial extensions

If this is right

The $X(3872)$ is established as a real state produced in $B^- → X(3872)K^-$ at the 3.5 standard deviation level in an independent sample, with a mass of $3873.4 ± 1.4$ MeV/$c^2$.
Because the mass is measured relative to the $ψ(2S)$, the absolute mass-scale uncertainty largely cancels, leaving a value that can be compared directly with the $D^0\bar{D}^{*0}$ threshold.
The total branching fraction $B(B^- → J/ψK^-π^+π^-) = (116 ± 7 ± 9)×10^{-5}$ supersedes looser earlier averages and provides a normalization for any search in this final state.
The limit $B(B^- → J/ψD^0π^-) < 5.2×10^{-5}$ at 90% confidence removes the intrinsic-charm mechanism as an explanation of the excess of low-momentum $J/ψ$ mesons in inclusive $B$ decays.
No $h_c$ signal appears in $J/ψπ^+π^-$; the limit $B(B^- → h_cK^-) × B(h_c → J/ψπ^+π^-) < 3.4×10^{-6}$ constrains that production mode, though it does not exclude $h_c$ production followed by other decay channels.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The measured mass sits within a few MeV of the $D^0\bar{D}^{*0}$ threshold; the paper notes consistency with earlier measurements but does not quantify the coincidence, and a reader can see that a precision of about 1.4 MeV is already fine enough for that comparison to become the interesting physics question.
The $π^+π^-$ invariant mass distribution in the $X(3872)$ region is shown but not interpreted; with the present statistics it cannot distinguish a $ρ$-like dipion from a phase-space-like one, which is exactly the discrimination that would separate a molecule from a charmonium assignment.
The $J/ψ → e^+e^-$ and $J/ψ → μ^+μ^-$ subsamples give $(1.94 ± 0.62)$ and $(0.52 ± 0.46)×10^{-5}$, differing by 1.8 standard deviations; the authors call this consistent, and a larger sample would show whether it is a fluctuation or an efficiency-transfer problem between the two lepton channels.
Treating the $X(3872)$ reconstruction efficiency as identical to the $ψ(2S)$ efficiency is the natural place where an independent, higher-statistics experiment with a direct efficiency calibration could shift the quoted product branching fraction without changing the significance of the state itself.

Original abstract

We study the decay B- --> J/psi K- pi+ pi- using 117 million BBbar events collected at the Y(4S) resonance with the BaBar detector at the PEP-II e+ e- asymmetric-energy storage ring. We measure the branching fractions Br(B- --> J/psi K- pi+ pi-) = (116 +- 7 (stat.) +- 9(syst.))* 10-5 and Br(B- --> X(3872)K-)* Br (X(3872) --> J/psi pi+ pi-) =(1.28+- 0.41)* 10-5 and find the mass of the X(3872) to be 3873.4 +- 1.4 MeV/c2. We search for the h_c narrow state in the decay B- --> h_c K-, h_c --> J/psi pi+ pi- and for the decay B- --> J/psi D0 pi-, with D0 --> K- pi+. We set the 90% C.L. limits Br(B- --> h_c K-)* Br (h_c --> J/psi pi+ pi-) <3.4 * 10-6 and Br(B- --> J/psi D0 pi-) <5.2 * 10-5.

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The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

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What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.52 · human participants 0.01 · controlled comparison 0.02 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.08 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v1. Results and the main claim are underlined; show every role.

We study the decay B- --> J/psi K- pi+ pi- using 117 million BBbar events collected at the Y(4S) resonance with the BaBar detector at the PEP-II e+ e- asymmetric-energy storage ring. We measure the branching fractions Br(B- --> J/psi K- pi+ pi-) = (116 +- 7 (stat.) +- 9(syst.))* 10-5 and Br(B- --> X(3872)K-)* Br (X(3872) --> J/psi pi+ pi-) =(1.28+- 0.41)* 10-5 and find the mass of the X(3872) to be 3873.4 +- 1.4 MeV/c2. We search for the h_c narrow state in the decay B- --> h_c K-, h_c --> J/psi pi+ pi- and for the decay B- --> J/psi D0 pi-, with D0 --> K- pi+. We set the 90% C.L. limits Br(B- --> h_c K-)* Br (h_c --> J/psi pi+ pi-) <3.4 * 10-6 and Br(B- --> J/psi D0 pi-) <5.2 * 10-5.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	We study the decay B- --> J/psi K- pi+ pi- using 117 million BBbar events collected at the Y(4S) resonance with the BaBar detector at the PEP-II e+ e- asymmetric-energy storage ring.	method 0.87	0.94	0.03	asserted 0.96
s1	We measure the branching fractions Br(B- --> J/psi K- pi+ pi-) = (116 +- 7 (stat.) +- 9(syst.))* 10-5 and Br(B- --> X(3872)K-)* Br (X(3872) --> J/psi pi+ pi-) =(1.28+- 0.41)* 10-5 and find the mass of the X(3872) to be 3873.4 +- 1.4 MeV/c2.	result 1.00	0.98	0.79	asserted 1.00
s2	We search for the h_c narrow state in the decay B- --> h_c K-, h_c --> J/psi pi+ pi- and for the decay B- --> J/psi D0 pi-, with D0 --> K- pi+.	contribution 1.00	0.94	0.03	asserted 0.70
s3	We set the 90% C.L. limits Br(B- --> h_c K-)* Br (h_c --> J/psi pi+ pi-) <3.4 * 10-6 and Br(B- --> J/psi D0 pi-) <5.2 * 10-5.	result 1.00	0.96	0.08	asserted 0.98

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 0.82.

What was examined, and what was not

sources read

arXiv listing abstract v1

not examined

full text
figures and tables
references and citing sentences
relations to other papers

levels run

P abstract

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Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures

Showing 3 of the paper's 4 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ex/0406022 by the authors.

References

Works cited (16)

[8]

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[1]

non-resonant events, distributed as a ﬁrst order poly- nomial; 2) ψ(2S) candidates, distributed as a double- Gaussian resolution function around a mean value that is allowed to ﬂoat; and 3) X(3872) candidates, with the same resolution function as the ψ(2S) but with a mass that ﬂoats relative to the ψ(2S) mass. The measure- ment of mass diﬀerence allows us...

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Charge-conjugate reactions are included implicitely throughout this Letter

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Belle Collaboration, S. K. Choi et al., Phys. Rev. Lett. 91, 262001 (2003)

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CDF Collaboration, D. Acosta et al., hep-ex/0312021, submitted to Phys. Rev. Lett

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S. Pakvasa and M. Suzuki, Phys.Lett. B 579, 67 (2004); N. A. Tornqvist, hep-ph/0308277; F. E. Close and P. R. Page, Phys.Lett. B 578, 119 (2004); E. S. Swan- son, hep-ph/0311229; T. Barnes and S. Godfrey, hep-ph/0311162; M. B. Voloshin, Phys. Lett. B 579, 316 (2004)

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Tetraquarks composed of 4 heavy quarks
hep-ph 2011-11 conditional novelty 5.0 of 10

A diquark-model calculation places the tensor tetraquarks T4c(2++) and T2[bc](2++) just above their two-meson thresholds, making them candidate LHC peaks, while T4b stays below threshold.
$X(3872)$ and hidden charmed tetraquarks
hep-ph 2025-06 conditional novelty 4.0 of 10

A diquark-antidiquark quark model with parameters fitted to X(3872) and Tcc predicts hidden-charm tetraquark masses and tentatively assigns XYZ states.
Four-Quark Hadrons: an Updated Review
hep-ph 2014-11 conditional novelty 4.0 of 10

The XYZ resonances, especially the charged Z(4430) and Zc(3900), are best organized as compact diquark-antidiquark tetraquarks, with a Feshbach-like coupling to open-flavor thresholds selecting which predicted levels ...
X(3872) as a molecular DD* state in a potential model
hep-ph 2009-10 conditional novelty 4.0 of 10

A coupled-channel potential model with a tunable cutoff of about 1.2 GeV produces a bound DD* state with the quantum numbers of the X(3872), and also predicts bound BB* states in the isoscalar limit.
The $XYZ$ states: experimental and theoretical status and perspectives
hep-ex 2019-07 accept novelty 3.0 of 10

A book-length review cataloguing the experimental evidence for exotic charmonium- and bottomonium-like states and the theoretical frameworks, from quark models to effective field theory and lattice QCD, proposed to ex...
Exotics: Heavy Pentaquarks and Tetraquarks
hep-ph 2017-06 accept novelty 3.0 of 10

A comprehensive review of the charmonium- and bottomonium-like exotics and the two LHCb pentaquarks, covering the experimental evidence state by state and the four competing theoretical explanations for them.
Heavy-Quark QCD Exotica
hep-ph 2016-10 accept novelty 3.0 of 10

About 30 charmoniumlike and bottomoniumlike states that do not fit the ordinary quark-antiquark or three-quark scheme have been reported since 2003, and no single theoretical picture yet explains them all.
Non-Standard Heavy Mesons and Baryons, an Experimental Review
hep-ph 2017-08 accept novelty 2.0 of 10

A 2017 experimental review finds that many heavy-quark hadron candidates conflict with conventional quark-model assignments, so the spectroscopy of all but the simplest hadrons remains unexplained.
The hidden-charm pentaquark and tetraquark states
hep-ph 2016-01 accept novelty 2.0 of 10

A comprehensive review argues that the charged Zc/Zb states and the LHCb Pc(4380)/Pc(4450) pentaquarks are multiquark candidates, and catalogues the molecular, tetraquark, and diquark interpretations along with their ...
An overview of $XYZ$ new particles
hep-ph 2013-12 conditional novelty 1.0 of 10

The review compiles the experimental status and the competing theoretical interpretations of the 23 charmoniumlike and bottomoniumlike XYZ states observed since 2003.

How the literature uses it

86 arXiv papers cite this in 93 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 43 sentences without a confident label

Contests it 1 paper

* The ratio $Γ(B^0→K^0 X)/Γ(B^+→K^+ X)$ is about unity according to an estimation based on the molecule picture [ref] , which is about two times larger than measurements by the BaBar [ref] and Belle [ref] Collaborations. * The predicted branching ratios of $X(3872)→D^0 D̅^0 γ$ and $X(3872)→J/ψγ$ [ref] largely deviated from the experimental data. * As a loosely bound hadronic molecule with a small binding energy, $X(3872)$ was expected to be so fragile that it would be hard to explain the observed production rate in the high energy $pp̅$ collisions at the Tevatron [ref] .

The $X(3872)\rightarrow J/\psi \pi \gamma$ and $X(3872)\rightarrow J/\psi \pi\pi \gamma$ decays · Introduction · contest 0.82

Uses its data or values 6 papers

The Belle and Babar Collaborations have both measured the energy distribution of $J/ψ π^+ π^-$ near the $X(3872)$ resonance for the decay $B^+ →K^+ + J/ψ π^+ π^-$ [ref] .

Line Shapes of the X(3872) · Experimental data · 0.82
Measurements of the mass of the $X(3872)$ by the Belle, CDF, Babar, and D0 collaborations [ref] , combined with a new measurement of the $D^0$ mass by the CLEO collaboration [ref] , imply that the mass is extremely close to the $D^*0 D̅^0$ threshold:

An Estimate of the Partial Width for X(3872) into p p-bar · Introduction · 0.87
The typical $X(3872)$ state, which was discovered by the Belle Collaboration [ref] and subsequently confirmed by the CDF Collaboration [ref] and BABAR Collaboration [ref] , is summarized $M_X=3872.2±0.8$, $Γ_X=3.0^+1.9_-1.4±0.9$ [ref] .

Study the Heavy Molecular States in Quark Model with Meson Exchange Interaction · Introduction · 0.95

Cites it as background 42 papers

The discovery of the narrow charmoniumlike state with a mass of about 3.872 GeV [ref] , now known as the $χ_c1(3872)$, led to a renewed interest in exotic hadrons since their existence were prophesized in the 1960s [ref] .

Hadroproduction data support tetraquark hypothesis for $\chi_{c1} (3872)$ · Introduction · 0.98
It has been almost ten years since the narrow $$ state was discovered in $B^+$ decays by the Belle experiment [ref] .[The inclusion of charge-conjugate states is implied in this Letter.] Subsequently, its existence has been confirmed by several other experiments [ref] .

Determination of the X(3872) meson quantum numbers · Introduction · 0.98
The $X(3872)$ is a hadronic resonance near 3872 MeV discovered in 2003 by the Belle Collaboration [ref] and subsequently confirmed by the CDF, Babar, and D0 Collaborations [ref] .

Line Shapes of the X(3872) · Introduction · 0.98

Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

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non-resonant events, distributed as a ﬁrst order poly- nomial; 2) ψ(2S) candidates, distributed as a double- Gaussian resolution function around a mean value that is allowed to ﬂoat; and 3) X(3872) candidates, with the same resolution function as the ψ(2S) but with a mass that ﬂoats relative to the ψ(2S) mass. The measure- ment of mass diﬀerence allows us...

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