Drell-Yan Research Articles

Symmetry-Scaling Based Complex Network Approach to Explore Exotic Hadronic States in High-Energy Collision

Conventionally invariant mass or transverse momentum techniques have been used to probe for any formation of some exotic or unusual resonance states in high energy collision. In this work, we have applied symmetry scaling based complex network approach to study exotic resonance/hadronic states utilizing the clustering coefficients and associated scaling parameter extracted with the complex network based technique of Visibility Graph. We have analyzed the data of Pb–Pb collision data sample at 2.76 TeV from ALICE Collaboration and analyzed different patterns of symmetry scaling, scale-freeness, correlation and clustering among the produced particles. This is a chaos-based complex network technique where simple parameters like Average Clustering Coefficient and Power of Scale-freeness of Visibility Graph (PSVG) may hint at formation of some exotic or unusual resonance states without using conventional methods. From this experiment we may infer that highest range of Average clustering coefficient, might be the resonance states/clusters from where the hadronic decay might have occurred and few clusters with highest value of this parameter may indicate that those clusters may be the ancestors of some strange particles. There have also been extensive study of dilepton production since the study of lepton pair generation in Drell–Yan processes is immensely important as these processes enable us to validate the Standard Model-SM predictions for the fundamental particles interaction at the new energy region and also to probe for new physics beyond SM. Hence we have applied the same methodology and extracted the same parameters for p–p collision data at 8 TeV from CMS, to detect possible resonance states eventually generating lepton pairs.

Production of Z bosons in the parton branching method

Transverse Momentum Dependent (TMD) parton distributions obtained from the Parton Branching (PB) method are combined with next-to-leading-order (NLO) calculations of Drell-Yan (DY) production. We apply the MCatNLO method for the hard process calculation and matching with the PB TMDs. We compute predictions for the transverse momentum, rapidity and $\phi^*$ spectra of Z-bosons. We find that the theoretical uncertainties of the predictions are dominated by the renormalization and factorization scale dependence, while the impact of TMD uncertainties is moderate. The theoretical predictions agree well, within uncertainties, with measurements at the Large Hadron Collider (LHC). In particular, we study the region of lowest transverse momenta at the LHC, and comment on its sensitivity to nonperturbative TMD contributions.

Direct determination of sin2ϑeffℓ at hadron colliders

We discuss the renormalization of the electroweak Standard Model at 1-loop using the leptonic effective weak mixing angle as one of the input parameters. We evaluate the impact of this choice in the prediction of the forward-backward asymmetry for the neutral current Drell-Yan process. The proposed input scheme is suitable for a direct determination of the effective leptonic weak mixing angle from the experimental data.

PDF profiling using the forward-backward asymmetry in Neutral Current Drell-Yan production

Non-perturbative QCD effects from Parton Distribution Functions (PDFs) may be constrained by using high-statistics Large Hadron Collider (LHC) data. Drell-Yan (DY) measurements in the Charged Current (CC) case provide one of the primary means to do this, in the form of the lepton charge asymmetry. We investigate here the impact of measurements in Neutral Current (NC) DY data mapped onto the Forward-Backward Asymmetry (AFB) on PDF determinations, by using the open source fit platform xFitter. We demonstrate the potential impact of AFB data on PDF determinations and perform a thorough analysis of related uncertainties.

Pion-induced Drell-Yan processes within TMD factorization

We extract the pion transverse momentum dependent (TMD) parton distribu- tion by fitting the pion-induced Drell-Yan process within the framework of TMD factoriza- tion. The analysis is done at the next-to-next-to-leading order (NNLO) with proton TMD distribution and non-perturbative TMD evolution extracted earlier in the global fit. We observe the significant difference in the normalization of transverse momentum differential cross-section measured by E615 experiment and the theory prediction.

The LHC Drell–Yan measurements as a constraint for the noncommutative space-time

The LHC measurements of the differential cross section of the Drell–Yan process is used to constrain the noncommutative space-time (NCST) phase space. A χ2 method is utilized to exclude the part of the parameters space which is not consistent with the LHC measurements. Depending on other NCST parameters, the scale can be pushed up to ΛNC > 655 GeV. The effect of other parameters is also investigated. To our knowledge, it is the first time that a detailed statistical analysis is performed to compare the NCST results with the Hadron Collider measurements.

Azimuthal asymmetries in unpolarized SIDIS and Drell-Yan processes: A case study towards TMD factorization at subleading twist

We consider the azimuthal distribution of the final observed hadron in semi-inclusive deep-inelastic scattering and the lepton pair in the Drell-Yan process. In particular, we focus on the cos⁡ϕ modulation of the unpolarized cross section and on its dependence upon transverse momentum. At low transverse momentum, for these observables we propose a factorized expression based on tree-level approach and conjecture that the same formula is valid in transverse-momentum dependent (TMD) factorization when written in terms of subtracted TMD parton distributions. Our formula correctly matches with the collinear factorization results at high transverse momentum, solves a long-standing problem and is a necessary step towards the extension of the TMD factorization theorems up to the subleading twist.

Explicit jet veto as a tool to purify the underlying event in the Drell–Yan process using CMS Open Data

The underlying event (UE) is an important part of high-energy collision events. In the event generators, the UE is tuned by fits to collision data. Usually, the UE observables are affected by the existence of extra jets and it is difficult to find a part of the phase space which is dominated by the UE. In this paper, we suggest to veto the jets in the considered region to disentangle these effects. The idea is verified to work on CMS Open Data. To our knowledge, it is the first time that such ideas are tested on real collision data.

Difficulties in the description of Drell-Yan processes at moderate invariant mass and high transverse momentum

We study the Drell-Yan cross section differential with respect to the transverse momentum of the produced lepton pair. We consider data with moderate invariant mass Q of the lepton pair, between 4.5 GeV and 13.5 GeV, and similar (although slightly smaller) values of the transverse momentum q_T. We approach the problem by deriving predictions based on standard collinear factorization, which are expected to be valid toward the high-q_T end of the spectrum and to which any description of the spectrum at lower q_T using transverse-momentum dependent parton distributions ultimately needs to be matched. We find that the collinear framework predicts cross sections that in most cases are significantly below available data at high q_T. We discuss additional perturbative and possible non-perturbative effects that increase the predicted cross section, but not by a sufficient amount.

Nuclear gluons at RHIC in a multiobservable approach

We explore the possibility of measuring nuclear gluon distributions at the Relativistic Heavy-Ion Collider (RHIC) with $\sqrt{s}=200 \, {\rm GeV}$ proton-nucleus collisions. In addition to measurements at central rapidity, we consider also observables at forward rapidity, consistent with proposed upgrades to the experimental capabilities of STAR and sPHENIX. The processes we consider consist of Drell-Yan dilepton, dijet, and direct photon-jet production. The Drell-Yan process is found to be an efficient probe of gluons at small momentum fractions. In order to fully utilize the potential of Drell-Yan measurements we demonstrate how the overall normalization uncertainty present in the experimental data can be fixed using other experimental observables. An asset of the RHIC collider is its flexibility to run with different ion beams, and we outline how this ability could be taken advantage of to measure the $A$ dependence of gluon distributions for which the current constraints are scarce.

Secondary Drell–Yan dileptons in heavy-ion reactions

We investigate the contribution of partonic interactions between incident nucleons and produced mesons to the dilepton continuum in heavy-ion reactions. A schematic model is employed in order to calculate the resulting Drell–Yan yield as a function of collision energy and for different scenarios concerning the formation of hadrons. The secondary Drell–Yan process is found to be significant for invariant masses [Formula: see text][Formula: see text]GeV in central [Formula: see text] collisions around [Formula: see text][Formula: see text]GeV, but less so at much lower or much higher energies. Secondary Drell–Yan dileptons should be observable in experiments due to their distinct rapidity dependence as a characteristic deviation from the well-known (primary) Drell–Yan contribution due to [Formula: see text] interactions. The predicted strong dependence of the secondary Drell–Yan contribution on the nuclear collision energy can be used to experimentally probe the effective hadronic formation time of secondaries.

Limits on R -parity-violating couplings from Drell-Yan processes at the LHC

We find constraints on R-Parity Violating (RPV) couplings of the minimal supersymmetric standard model, using Drell-Yan differential cross sections at the LHC. Specifically, we look at the constraints on $\lambda'LQD^c$ couplings from monolepton and dilepton data published by ATLAS, with either electrons or muons in the final state. Out of the 18 RPV couplings to which the LHC is at least potentially sensitive by this technique, we find new limits on 12 (or 13) of them, for squarks masses above 1 (or 2) TeV. We also show that one can employ our techniques to achieve significantly stronger bounds at a high-luminosity upgrade of the LHC.

Parton Distribution Functions from a Light Front Hamiltonian and QCD Evolution for Light Mesons.

We obtain the pion and the kaon parton distribution functions from the eigenstates of a light front effective Hamiltonian in the constituent quark-antiquark representation suitable for low-momentum scale applications. By taking these scales as the only free parameters, the valence quark distribution functions of the pion, after QCD evolution, are consistent with the data from the FNAL-E615 experiment. The ratio of the up quark distribution of the kaon to that of the pion also agrees with the CERN-NA3 experiment. Supplemented by known parton distribution functions for the nucleons, we further obtain the cross section consistent with experimental data for the π^{-}nucleus→μ^{+}μ^{-}X Drell-Yan process.

Hard exclusive processes involving kaons

Hard exclusive electroproduction of kaons as well as the kaon-induced exclusive Drell-Yan process are investigated within the handbag approach which is based on factorization in hard subprocesses and soft generalized parton distributions (GPDs). The kaon-hyperon transition GPDs occurring here, are related to the proton GPDs by flavor symmetry. The latter ones are taken from analyses of pion electroproduction. Like in hard processes involving pions the transversity GPDs play an important role in the processes of interest - the transverse cross sections are larger than (or, for the Drell-Yan process, about equal to) the longitudinal ones. The evolution of the transversity GPDs is taken into account for the first time but, as the analysis reveals, it is a minor effect in the range of photon virtualities of interest. The predictions for the cross sections agree fairly well with the sparse available electroproduction data.

The SeaQuest spectrometer at Fermilab

The SeaQuest spectrometer at Fermilab was designed to detect oppositely-charged pairs of muons (dimuons) produced by interactions between a 120 GeV proton beam and liquid hydrogen, liquid deuterium and solid nuclear targets. The primary physics program uses the Drell-Yan process to probe antiquark distributions in the target nucleon. The spectrometer consists of a target system, two dipole magnets and four detector stations. The upstream magnet is a closed-aperture solid iron magnet which also serves as the beam dump, while the second magnet is an open aperture magnet. Each of the detector stations consists of scintillator hodoscopes and a high-resolution tracking device. The FPGA-based trigger compares the hodoscope signals to a set of pre-programmed roads to determine if the event contains oppositely-signed, high-mass muon pairs.

Indirect probe of electroweak-interacting particles with mono-lepton signatures at hadron colliders

Electroweak-interacting massive particles (EWIMPs) exist in a broad class of new physics models beyond the Standard Model. Searching for such particles is one of most primary goal at the LHC and future colliders. The EWIMP generally affects the LHC signatures through quantum corrections even without direct productions. By measuring the Standard Model processes precisely, we can indirectly probe the EWIMPs. In this paper, we study the current constraint and future prospect of the EWIMPs by using the precision measurements of mono-lepton production from the charged Drell-Yan processes at hadron colliders. We found the mono-lepton signature can be a better probe than dilepton signature from the neutral Drell-Yan processes.

Final-State Two-Loop Radiative Corrections to the Drell-Yan Process at the LHC in the Soft-Photon Approximation

In the soft-photon approximation, compact expressions for two-loop final-state electromagnetic radiative corrections to the four-fermion process in the s channel are obtained on the basis of the on-shell renormalization scheme. As applied to the Drell—Yan process, an efficient procedure for numerically estimating final-state radiative effects is proposed for experiments at the LHC for high invariant masses.

Leading-logarithmic threshold resummation of the Drell-Yan process at next-to-leading power

We resum the leading logarithms αsn ln2n − 1(1 − z), n = 1, 2, . . . near the kine-matic threshold z = Q2/ŝ → 1 of the Drell-Yan process at next-to-leading power in the expansion in (1 − z). The derivation of this result employs soft-collinear effective theory in position space and the anomalous dimensions of subleading-power soft functions, which are computed. Expansion of the resummed result leads to the leading logarithms at fixed loop order, in agreement with exact results at NLO and NNLO and predictions from the physical evolution kernel at N3LO and N4LO, and to new results at the five-loop order and beyond.

Standard model EFT and the Drell-Yan process at high energy

The Drell-Yan process is a copious source of lepton pairs at high energy and is measured with great precision at the Large Hadron Collider (LHC). Barring any new light particles, beyond the Standard Model effects can be studied in Drell-Yan production using an effective field theory. At tree level, new 4-fermion interactions dominate, while at one loop operators modifying 3-gauge boson couplings contribute effects that are enhanced at high energy. We study the sensitivity of the neutral Drell-Yan process to these dimension-6 operators and compare the sensitivity to that of $W^+W^-$ pair production at the LHC.

The O(α2) initial state QED corrections to e+e− annihilation to a neutral vector boson revisited

We calculate the non-singlet, the pure singlet contribution, and their interference term, at O(α2) due to electron-pair initial state radiation to e+e− annihilation into a neutral vector boson in a direct analytic computation without any approximation. The correction is represented in terms of iterated incomplete elliptic integrals. Performing the limit s≫me2 we find discrepancies with the earlier results of Ref. [1] and confirm results obtained in Ref. [2] where the effective method of massive operator matrix elements has been used, which works for all but the power corrections in m2/s. In this way, we also confirm the validity of the factorization of massive partons in the Drell–Yan process. We also add non-logarithmic terms at O(α2) which have not been considered in [1]. The corrections are of central importance for precision analyses in e+e− annihilation into γ⁎/Z⁎ at high luminosity.