Theory seminar: Ankita Budhraja




Recoil-Sensitive Angularity Distributions using SCET

Jet angularities are a class of event shape observables whose sensitivity to the splitting angle of a collinear emission is controlled by a continuous parameter b, with b > 1 for infrared safety. Varying the exponent b changes the sensitivity of the observable to the substructure of the jet. When measured with respect to the standard thrust axis, this class of QCD observables is a generalization to the well known jet observables, thrust (b = 1) and jet broadening (b = 0). For b &1 (thrust-like angularities), the observable is insensitive to the recoil of soft against collinear radiation while when b is close to 0 (broadening-like angularities), recoil becomes an O(1) effect and cannot be ignored. In the literature, SCETI has been succesfully applied for thrust-like angularity distributions while jet broadening distribution has been worked out within an SCETII framework [1, 2, 3, 5]. In a recent publication [4], we formulated a universal framework based on SCETII that can be applied for the whole range of angularity exponents, thereby allowing us to smoothly connect the special limits of broadening (b = 0) and thrust
(b = 1), for the first time.

In this talk, I will first review the formalism developed in Ref. [4]. We find a good agreement of our one-loop results against the numerical results of the Event2 generator, for all the b values we tested. Interestingly, we find that the agreement against Event2 is improved in our framework for b = 0.5 in contrast to the well-known result from SCETI. Our results also suggest that though the cross-section is continuous around b = 0, the soft function itself is not, suggesting a discontinuity at the level of NLL cross-section at b = 0. I will discuss these results as well as some of our preliminary NLL findings.

[1] Hornig, A., Lee, C., & Ovanesyan, G., JHEP 0905 (2009) 122.
[2] Chiu, J., Jain, A., Neill, D., & Rothstein, I. Z. 2012, Phys. Rev. Lett., 108, 151601.
[3] Chiu, J., Jain, A., Neill, D., & Rothstein, I. Z. 2012, JHEP05, 084.
[4] Budhraja, A., Jain, A., & Procura, M. 2019, JHEP 1908 (2019) 144.
[5] Bell, G., Hornig, A., Lee, C., & Talbert, J., 2019, JHEP 01 (2019) 147.