atlas records precise bᴼ meson lifetime lhc

Pioneering Precision: Scientists Record Electrically Neutral Beauty Meson Lifetime

New High-Precision Measurement of Bᴼ Meson Lifetime by ATLAS Collaboration

Researchers from the ATLAS collaboration at the Large Hadron Collider (LHC) have unveiled a new high-precision measurement of the electrically neutral beauty (Bᴼ) meson's lifetime, a hadron made up of a bottom antiquark and a down quark.

Understanding Beauty Mesons and Their Significance

Beauty (B) mesons consist of two qarks, including a bottom quark. For decades, their study has allowed physicists to probe rare, well-predicted phenomena, offering insights into weak force-mediated interactions and the dynamics of heavy-quark bound states. Accurate determination of the Bᴼ meson lifetime, the interval before its decay, remains crucial in this research domain.

ATLAS Collaboration's Latest Study on Bᴼ Meson Decay

The ATLAS collaboration's latest study on the Bᴼ meson focuses on its decay into an excited neutral kaon (K ͯ ᴼ) and a J/ψ meson. The J/ψ meson subsequently decays into two muons, while the k K ͯ ᴼ meson is analyzed through its decay into a charged pion and a charged kaon. This analysis leverages a substantial data set of 140 inverse femtobarns collected from proton-proton collisions during LHC Run 2 (2015-2018).

Measurement of Bᴼ Meson Lifetime

The ATLAS team reported a measurement of the Bᴼ meson lifetime at 1.5053 picoseconds (1 ps = 10⁻¹² seconds), with statistical and systematic uncertainties of 0.0012 ps and 0.0035 ps, respectively. This is the most precise determination to date, marking a significant enhancement over previous results, including prior ATLAS findings.

Overcoming Experimental Challenges

To achieve these precise measurements, researchers had to surmount various experimental challenges, such as systematic uncertainty minimization, advanced modeling, and refined detector alignment.

Decay Width Measurement and Its Implications

Beyond measuring the Bᴼ meson lifetime, the ATLAS team also determined its decay width, a fundamental property of unstable with finite lifetime. According to Heisenberg's uncertainty principle, shorter lifetime correspond to broader decay widths. The Bᴼ meson's decay width was measured as 0.664 inverse picoseconds (ps⁻¹), with a total uncertainty of 0.004 ps⁻¹.

Comparison with Bsᴼ Meson Decay Width

The researchers subsequently compared their result with an earlier measurement of the decay width of the Bsᴼ meson, which consists of a bottom quark and a strange quark. The ratio of the decay widths was found to be consistent with unity, indicating similar values for both measurements. These findings align with the predictions of the heavy-quark model and provide valuable data for refining these predictions.

Impact on Our Understanding of Weak-Force-Mediated Decays

The latest ATLAS precision measurements significantly deepen our understanding of weak-force-mediated decays within the Standard Model and offer crucial data for advancing future theoretical research.

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alice-antimatter-hyperhelium4-evidence-lhc

ALICE Unveils First Evidence of Antimatter Hyperhelium-4 Partner

Introduction: The Role of the Large Hadron Collider (LHC)

The Large Hadron Collider (LHC) facilitates collisions between heavy ions, generating quark—gluon plasma—a hot, dense state of matter believed to have existed a millionth of a second after the Big Bang. These collisions also offer an ideal environment for the formation of atomic nuclei, exotic hypernuclei, and their antimatter equivalents, including antinuclei and antihypernuclei.

Importance of Hypernuclei Research

The study of these matter forms is vital for multiple objectives, including:

• Deciphering how hadrons emerge from quarks and gluons in the plasma
• Exploring the matter-antimatter imbalance in the universe today

What are Hypernuclei?

Exotic Nuclear Structures

Hypernuclei are exotic nuclear structures composed of protons, neutrons, and hyperons—unstable particles that include one or more strange quarks. Despite their discovery in cosmic rays over 70 years ago, hypernuclei continue to captivate physicists due to their rarity in nature and the challenges associated with their creation and study in laboratory settings.

Hypernuclei Production in Heavy-Ion Collisions

Hypernuclei are produced in substantial numbers during heavy-ion collisions; however, until recently, only the lightest hypernucleus, the hypertriton, and its antimatter counterpart, the antihypertrition, have been detected. The hypertrition consists of a proton, a neutron, and a lambda particle (a hyperon with one strange quark), while the antihypertrition is composed of an antiproton, an antineutron, and an antilambda.

Antimatter Hypernuclei: A Milestone Discovery

First Evidence of Antihyperhelium-4

After the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) reported the observation of antihyperhydrogen-4 earlier this year—a bound state comprising an antiproton, two antineutrons, and an antilambda-the ALICE collaboration at the LHC has now provided the first evidence of antihyperhelium-4. This exotic particle is made up of two antiprotons, an antineutron, and an antilambda.

Significance of the Discovery

This result, showing a significance of 3.5 standard deviations, marks the first evidence of the heaviest antimatter hypernucleus observed at the LHC. The findings have been made available on the arXiv preprint server.

ALICE Experiment and Methodology

The 2018 Lead-Lead Collision Data

The ALICE experiment utilized lead-lead collision data from 2018, with an energy of 5.02 teraelectronvolts (TeV) for each colliding pair of nucleons (protons and neutrons). Employing an advanced machine-learning technique that exceeds the performance of standard hypernuclei search approaches, ALICE researchers examined the data for signs of hyperhydrogen-4, hyperhelium-4, and their antimatter equivalents.

Detection and Analysis Process

To identify candidates for (anti) hyperhydrogen-4, researchers searched for the (anti) helium-4 nucleus and the charged pion produced during its decay. In contrast, candidates for (anti) hy perhelium-4 were detected through their decay into an (anti) helium-3 nucleus, an (anti)  proton, and a charged  pion.

Measured Masses and Production Yields of Hypernuclei

Consistency with World-Average Values

The ALICE team not only found evidence of antihyperhelium-4 a significance of 3.5 standard deviations and antihyperhydrogen-4 with a significance of 4.5 standard deviations, but also measured the production yields and masses of both hypernuclei.

Both hypernuclei showed measured masses that are consistent with the current world-average values. The production yields were also analyzed and compared with predictions made by the statistical hadronization model, which accurately depicts hadron and nucleus formation in heavy-ion collisions.

Statistical Hadronization Model Predictions

The comparison shows that the statistical hadronization model's predictions are consistent with the data when both excited and ground states of hypernuclei are factored in. This supports the model's effectiveness in describing hypernuclei production, which are small, dense entities measuring roughly 2 femtometers in diameter (with 1 femtometer equal to 10¯¹⁵ meters).

Conclusion: Contribution to Understanding Matter and Antimatter

The researchers measured the antiparticle-to-particle yield ratios for both hypernuclei and found them to be consistent with unity, within the bounds of experimental uncertainty. This consistency aligns with ALICE's findings of equal matter and antimatter production at LHC energies and contributes to the broader study of the matter-antimatter imbalance in the universe.

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