The curious history of the tetraquark X(4140)

2024-09-02 20:17:07

Particle physics seems simple, we observe an excess on an expected basis that is interpreted as a sign of a new particle, at first with a few sigmas, which accumulates up to five sigmas and the presence is announced. It can’t be easy. But it’s not always that easy. In 2008, the CDF detector of the Tevatron observed the Y(4140) resonance at 3.8 sigma (LCMF, Mar 19, 2009). It was confirmed by the CMS of the LHC in 2012 at 5.5 sigma, but we could not announce its presence; Neither Belle in 2010, nor LHCb in 2012, nor later BaBar in 2015 managed to confirm it (LCMF, December 5, 2012). An uncomfortable situation, especially for CDF, the first detective. Its sister experiment, DZero from the Tevatron, came to its aid, which observed it in 2014 at 3.1 sigma. CDF decided to re-analyze its original data until it reaches sigma 5 in 2017. With two tests that exceed this limit, a discovery should be announced. But serious skepticism and scientific articles were also published against the existence of Y(4140).

In this situation, the only option is to try to observe the particle with other production methods. DZero in 2015 published new evidence, but BESIII in 2015 still did not notice anything. It seems that the name Y (4140) has been jinxed; The name has to be changed to X(4140). The ball is in LHCb’s court, in its analysis of attacks from all LHC Run 1 (2011–2012). LHCb published the X(4140) observation with 8.4 sigma in 2017; Also, its quantum number is JPC = 1++, which indicates that it is a tetraquark. formed by two quark-antiquark pairs attractive type (c) and strange type (s). The issue is beyond doubt. In fact, LHCb published its discovery in LHC Run 2 collisions (2016–2018) in 2021, receiving 13 sigmas. Particles have been discovered outside of everything; For historical documents, your detector is CDF.

Obviously, you will wonder what happened, why Belle, BaBar, BESIII and LHCb, the latter in the beginning, could not observe this tetraquark. The reason is simple, as LHCb showed in 2017, there are four very close particles, X (4140), X (4274), X (4500) and behind. Only thanks to the resolution of the high power of the LHCb in clear levels in 2017 (as shown in the figure that opens this article); Therefore, these particles with quantum numbers JPC = 1++, 1++, 0++, and 0++ are observed with 8.4, 6.0, 6.1 and 5.6 sigma, respectively. In 2021 at LHCb they were observed in two production modes (as shown in the figure above) with 13 (16), 18 (18), 20 (20) and 17 (18) sigmas. Any hint of doubt disappears when faced with figures like these. In such large hadron studies, the LHCb is unbiased. But searcher X (4140) for history books is CDF.

Those interested in calculating the mass and size of these tetraquarks can consult the LHCb articles, from which I have extracted the figures, which is the LHCb Collaboration, “Observation of 𝐽/ 𝐽/𝜓⁢𝜙⁢𝐾+ Competition,” Physical Review Letters 118:022003 (11 January 2017), doi: https://doi.org/10.1103/PhysRevLett.118.022003, arXiv: 1606.07895 [hep-ex] (25 March 2016); y LHCb Collaboration, «Observation of New Resonances Lean to 𝐽/𝜓⁢𝐾+ and 𝐽/𝜓⁢𝜙,» Physical Review Letters. 127:082001 (17 August 2021), doi: https://doi.org/10.1103/PhysRevLett.127.082001, arXiv: 2103.01803 [hep-ex] (02 March 2021). El artículo que inicia esta historia es CDF Collaborative, “Evidence for a Near-Final Process in the 𝐽/𝜓⁢𝜙 Mass Spectrum in 𝐵+→𝐽/𝜓⁢𝜙⁢ 2 Revision: 15 June 2009), doi: https://doi.org/10.1103/PhysRevLett.102.242002, arXiv: 0903.2229 [hep-ex] (12 Mar 2009), y su reanálisis es CDF Collaboration, «Observation of the Y(4140) structure in the J/ψϕ Mass Spectrum in B±→J/ψϕK cays,» Modern Physics Letters A 32: 1750139 (27 Jul 2017 ) ), doi: https://doi.org/10.1142/S0217732317501395, arXiv: 1101.6058 [hep-ex] (Jan 31, 2011); This article appeared in 2011 on arXiv, submitted to Physical Review Letters, where it was written; It ended up being published in 2017, which is why I’m citing it as an article from 2017 (which, in addition, is good for the thread of the story; I apologize to anyone who feels deceived by the book- order of this poem). And I’m sorry for those who are interested, but I’m omitting the other mentioned books (CMS, Belle, LHCb, BaBar, Dzero and BESIII).