Measuring polarization of light quarks at ATLAS and CMS

Kats, Yevgeny

doi:10.1103/physrevd.92.071503

Cited by 13 publications

(22 citation statements)

References 57 publications

(85 reference statements)

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“…Moreover, sizable polarization was observed also for Λ (≈ sud) baryons in Z → qq, for Λ's carrying a large fraction, z 0.3, of the quark momentum [7]. This implies O(1) s-quark polarization retention in energetic Λ's (see [2] and references therein).…”

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confidence: 94%

“…If a new-physics source of top quarks is discovered, measuring their polarization will analogously teach us about their production mechanism. We asked whether this could be done also with other quarks: c and b in [1] and u, d and s in [2].…”

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confidence: 99%

“…Sensitivities turned out comparable. 2 Further inputs may come from polarized DIS and polarized pp collisions (e.g., [11]) and lattice QCD (e.g., [12]). Still, the correspondingly suppressed polarization transfer, as well as the smallness of f (u → Λ) and f (d → Λ) relative to f (s → Λ) (e.g., by factors of ∼ 4 for z > 0.3 [8]) and the expected large contamination from W + → cs decays (as a c-tag veto is only partially effective), imply that statistics beyond Run 2 will be required for the u and d quark polarization measurements in tt samples.…”

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confidence: 99%

“…u and d quark polarizations obviously cannot be measured using decays of protons or neutrons, one may again consider the Λ (≈ sud), as in the s-quark case. Even though in the naïve quark model the spin of the Λ is carried entirely by the s quark, the SU(3) flavor symmetry applied to the nucleon DIS data suggests that the u and d quarks each carry about −20% of the Λ spin[10] 2. …”

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confidence: 99%

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Measuring polarizations of bottom, charm, strange, up and down quarks in top decays

Kats

2016

Proceedings of 8th International Workshop on Top Quark Physics — PoS(TOP2015)

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Standard Model tt samples in ATLAS and CMS provide an opportunity to conduct measurements of the polarization of quarks produced in top-quark decays. The bottom quarks from the t → W + b decays, as well as the charm, strange, up and down quarks from the subsequent W + → cs, ud decays, are polarized. When a polarized quark hadronizes to a baryon, its polarization is partly preserved, and is reflected in the angular distributions of the baryon decay products. For the strange and bottom quarks, this effect has already been seen in hadronic Z decays at LEP. In Run 2 of the LHC, tt samples will have comparable statistics and several advantages from the point of view of flavor tagging. We propose strategies for such measurements in ATLAS and CMS. We estimate that precision of order 10% is attainable for the polarizations of the strange, charm and bottom quarks. In future higher-statistics runs, polarizations of up and down quarks might be measurable as well.

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confidence: 94%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Measuring polarizations of bottom, charm, strange, up and down quarks in top decays

Kats

2016

Proceedings of 8th International Workshop on Top Quark Physics — PoS(TOP2015)

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“…We note however, that given that no new physics has been discovered so far, and considering the price one needs to pay in fragmentation and branching fractions to measure quark polarizations, statistics will likely be a serious limitation for such measurements. 6. In tt and W c production, in the long term, in ATLAS, CMS, and LHCb:…”

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confidence: 99%

Measuring c-quark polarization in W +c samples at ATLAS and CMS

Kats

2016

J. High Energ. Phys.

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Being able to measure the polarization of quarks produced in various processes at the LHC would be of fundamental significance. Measuring the polarizations of quarks produced in new physics processes, once discovered, can provide crucial information about the new physics Lagrangian. In a series of recent papers, we have investigated how quark polarization measurements can be done in practice. The polarizations of heavy quarks (b and c) are expected to be largely preserved in the lightest baryons they hadronize into, the Λ b and Λ c , respectively. Furthermore, it is known experimentally that s-quark polarization is preserved as well, in Λ baryons. We study how ATLAS and CMS can measure polarizations of b, c and s quarks using certain decays of these baryons. We propose to use the Standard Model tt and W c samples to calibrate these measurements. We estimate that the Run 2 dataset will suffice for measuring the quark polarizations in these Standard Model samples with precisions of order 10%. We also propose various additional measurements for the near and far future that would help characterize the polarization transfer from the quarks to the baryons.

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Prospects for measuring quark polarization and spin correlations in $$b\overline{b }$$ and $$c\overline{c }$$ samples at the LHC

Kats,

Uzan

2024

J. High Energ. Phys.

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Polarization and spin correlations have been studied in detail for top quarks at the LHC, but have been explored very little for the other flavors of quarks. In this paper we consider the processes pp → $$q\overline{q }$$ with q = b, c or s. Utilizing the partial preservation of the quark’s spin information in baryons in the jet produced by the quark, we examine possible analysis strategies for ATLAS and CMS to measure the quark polarization and spin correlations. We find polarization measurements for the b and c quarks to be feasible, even with the currently available datasets. Spin correlation measurements for $$b\overline{b }$$ are possible using the CMS Run 2 parked data, while such measurements for $$c\overline{c }$$ will become possible with higher integrated luminosity. For the s quark, we find the measurements to be challenging with the standard triggers. We also provide leading-order QCD predictions for the polarization and spin correlations expected in the $$b\overline{b }$$ and $$c\overline{c }$$ samples with the cuts envisioned for the above analyses. Apart from establishing experimentally the existence of spin correlations in $$b\overline{b }$$ and $$c\overline{c }$$ systems produced in pp collisions, the proposed measurements can provide new information on the polarization transfer from quarks to baryons and might even be sensitive to physics beyond the Standard Model.

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Measuring polarization of light quarks at ATLAS and CMS

Cited by 13 publications

References 57 publications

Measuring polarizations of bottom, charm, strange, up and down quarks in top decays

Measuring polarizations of bottom, charm, strange, up and down quarks in top decays

Measuring c-quark polarization in W +c samples at ATLAS and CMS

Prospects for measuring quark polarization and spin correlations in $$b\overline{b }$$ and $$c\overline{c }$$ samples at the LHC

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