scholarly journals Threshold resummation of new partonic channels at next-to-leading power

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Melissa van Beekveld ◽  
Leonardo Vernazza ◽  
Chris D. White
Keyword(s):  
Cross Section ◽  
Effective Theory ◽  
Boson Production ◽  
Theory Approach ◽  
Partonic Cross Section ◽  
Heavy Particles ◽  
Threshold Resummation ◽  
Turn On ◽  
Order Form ◽  
Fixed Order

Abstract Collider observables involving heavy particles are subject to large logarithmic terms near threshold, which must be summed to all orders in perturbation theory to obtain sensible results. Relatively recently, this resummation has been extended to next-to-leading power in the threshold variable, using a variety of approaches. In this paper, we consider partonic channels that turn on only at next-to-leading power, and show that it is possible to resum leading logarithms using well-established diagrammatic techniques in Quantum Chromodynamics. We first consider deep inelastic scattering, where we reproduce the results of a recent study using an effective theory approach. Next, we consider the quark-gluon channel in both Drell-Yan and Higgs boson production, showing that an explicit all-order form for the leading logarithmic partonic cross section can be obtained. Our results agree with previous conjectures based on fixed-order results.

scholarly journals Higgs boson production cross-section measurements and their EFT interpretation in the $$4\ell $$ decay channel at $$\sqrt{s}=$$13 TeV with the ATLAS detector

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
Cross Section ◽  
Decay Channel ◽  
Branching Ratio ◽  
Proton Collision ◽  
Boson Production ◽  
Theory Approach ◽  
Higgs Boson Production ◽  
The Standard Model

AbstractHiggs boson properties are studied in the four-lepton decay channel (where lepton = e, $$\mu $$ μ ) using 139 $$\hbox {fb}^{-1}$$ fb - 1 of proton–proton collision data recorded at $$\sqrt{s}=$$ s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for $$H\rightarrow ZZ^*$$ H → Z Z ∗ decay is measured to be $$1.34 \pm 0.12$$ 1.34 ± 0.12  pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of $$1.33 \pm 0.08$$ 1.33 ± 0.08  pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.

scholarly journals Phenomenology of combined resummation for Higgs and Drell-Yan

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Tanjona R. Rabemananjara
Keyword(s):  
Higgs Boson ◽  
Transverse Momentum ◽  
Entire Range ◽  
Fourier Transforms ◽  
Gluon Fusion ◽  
Boson Production ◽  
Threshold Resummation ◽  
Systematic Improvement ◽  
Fixed Order

Abstract We study the phenomenological impact of a recently suggested formalism for the combination of threshold and a so-called threshold-improved transverse momentum resummation, by using it to improve the fixed-order results. This formalism allows for a systematic improvement of the transverse momentum resummation that is valid in the entire range of pT by the inclusion of the threshold contribution. We use the Borel method as a suitable prescription for defining the inverse Mellin and Fourier transforms in the context of combined resummed expression. The study is applied to two QCD processes, namely the Higgs boson produced via gluon fusion and Z boson production via the Drell-Yan mechanism. We compare our results to the standard transverse momentum resummation, as well as to the fixed-order results. We find that the threshold-improved transverse momentum resummation leads to faster perturbative convergence at small pT while the inclusion of threshold resummation improves the agreement with fixed-order calculations at medium and large pT. These effects are more pronounced in the case of Higgs which is known to have slower perturbative convergence.

scholarly journals Defiducialization: providing experimental measurements for accurate fixed-order predictions

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
A. Glazov
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Production Cross ◽  
Vector Boson ◽  
Center Of Mass ◽  
Boson Production ◽  
Center Of Mass Energy ◽  
Full Phase Space ◽  
Theoretical Predictions ◽  
Fixed Order

AbstractAn experimental procedure is proposed to perform measurements of differential cross sections for vector boson production which can be compared to fixed-order QCD predictions with improved accuracy. The procedure relies on applying theoretical acceptance corrections computed as a function of the transverse momentum of the W/Z boson, $$p_T$$ p T , to the experimental measurement, rather than comparing data directly against fiducial fixed-order predictions. It is demonstrated that, contrary to standard fiducial computations, these acceptance factors vary little at low $$p_T$$ p T , so they can be reliably computed using fixed-order perturbation theory. An example analysis is performed using the ATLAS measurement of the Z-boson production cross section at center-of-mass energy of 8 TeV. The resulting full phase space measurement of the cross section differential in the boson rapidity is compared to theoretical predictions computed with next-to-next-to leading-order accuracy in QCD. Further extensions of the approach which include different types of measurements and improved theoretical predictions are discussed.

scholarly journals Searching for charged lepton flavor violation at ep colliders

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Stefan Antusch ◽  
A. Hammad ◽  
Ahmed Rashed
Keyword(s):  
Standard Model ◽  
Charged Lepton ◽  
Neutral Current ◽  
Effective Theory ◽  
Theory Approach ◽  
Lepton Flavor Violation ◽  
Lepton Flavor ◽  
Flavor Violation ◽  
The Standard Model ◽  
Order Of Magnitude

Abstract We investigate the sensitivity of electron-proton (ep) colliders for charged lepton flavor violation (cLFV) in an effective theory approach, considering a general effective Lagrangian for the conversion of an electron into a muon or a tau via the effective coupling to a neutral gauge boson or a neutral scalar field. For the photon, the Z boson and the Higgs particle of the Standard Model, we present the sensitivities of the LHeC for the coefficients of the effective operators, calculated from an analysis at the reconstructed level. As an example model where such flavor changing neutral current (FCNC) operators are generated at loop level, we consider the extension of the Standard Model by sterile neutrinos. We show that the LHeC could already probe the LFV conversion of an electron into a muon beyond the current experimental bounds, and could reach more than an order of magnitude higher sensitivity than the present limits for LFV conversion of an electron into a tau. We discuss that the high sensitivities are possible because the converted charged lepton is dominantly emitted in the backward direction, enabling an efficient separation of the signal from the background.

scholarly journals Forward dijets in proton-nucleus collisions at next-to-leading order: the real corrections

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Edmond Iancu ◽  
Yair Mulian
Keyword(s):  
Cross Section ◽  
Soft Gluon ◽  
Effective Theory ◽  
Dglap Evolution ◽  
Leading Order ◽  
Final State ◽  
Dijet Production ◽  
The Real ◽  
First Case ◽  
Subsequent Publication

Abstract Using the CGC effective theory together with the hybrid factorisation, we study forward dijet production in proton-nucleus collisions beyond leading order. In this paper, we compute the “real” next-to-leading order (NLO) corrections, i.e. the radiative corrections associated with a three-parton final state, out of which only two are being measured. To that aim, we start by revisiting our previous results for the three-parton cross-section presented in [1]. After some reshuffling of terms, we deduce new expressions for these results, which not only look considerably simpler, but are also physically more transparent. We also correct several errors in this process. The real NLO corrections to inclusive dijet production are then obtained by integrating out the kinematics of any of the three final partons. We explicitly work out the interesting limits where the unmeasured parton is either a soft gluon, or the product of a collinear splitting. We find the expected results in both limits: the B-JIMWLK evolution of the leading-order dijet cross-section in the first case (soft gluon) and, respectively, the DGLAP evolution of the initial and final states in the second case (collinear splitting). The “virtual” NLO corrections to dijet production will be presented in a subsequent publication.

scholarly journals The Spin Structure of the Nucleon

2016 ◽  
Vol 40 ◽  
pp. 1660001
Author(s):  
Xiangdong Ji ◽  
Yong Zhao
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Deeply Virtual Compton Scattering ◽  
Virtual Compton Scattering ◽  
Proton Spin ◽  
Effective Theory ◽  
Large Momentum ◽  
Theory Approach ◽  
The One ◽  
The Relationship

We justify the physical meaning of the spin and orbital angular momentum of free partons in the infinite momentum frame, and discuss the relationship between the Jaffe-Manohar and Ji’s sum rules for proton spin. The parton orbital angular momentum in the Jaffe-Manohar sum rule can be measured through twist-three GPD’s in hard scattering processes such as deeply virtual Compton scattering. Furthermore, we propose that the paton orbital angular momentum as well as the gluon helicity can be calculated in lattice QCD through a large momentum effective theory approach, and provide all the one-loop matching conditions for the proton spin content in perturbative QCD.

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