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V. Ravindran

Publications and source records attributed to V. Ravindran.

At least 127 records · Page 7Linked to original sources
arXiv2004

NNLO Corrections to the Polarized Drell-Yan Coefficient Function

We present the full next-to-next-to-leading order (NNLO) corrections to the coefficient function for the polarized cross section $d Δσ/d Q$ of the Drell-Yan process. We study the effect of these corrections on the process $p+p\to l^+l^-+`X'$ at an C.M. energy $\sqrt{S}=200 GeV$. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for a lepton pair invariant mass $Q<50 GeV$. For this reaction the dominant subprocess is given by $q+\bar q\to γ^*+`X'$ and its higher order corrections so that it provides us with an excellent tool to measure the polarized sea-quark densities.

hep-ph↗
arXiv2004

NNLO corrections to massive lepton-pair production in longitudinally polarized proton-proton collisions

We present the full next-to-next-to-leading order (NNLO) coefficient functions for the polarized cross section $dΔσ/dQ$ for the Drell-Yan process $p + p\to l^+l^- + 'X'$. Here $'X'$ denotes any inclusive hadronic state and $Q$ represents the invariant mass of the lepton pair. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for $Q<50$ GeV. Unlike the differential distribution w.r.t. transverse momentum the dominant subprocess for the integrated cross section is given by $q+\bar q \to γ^* + 'X'$ and its higher order corrections so that massive lepton pair production provides us with an excellent tool to measure the polarized anti-quark densities. Our calculations are carried out using the method of $n$-dimensional regularization by making a special choice for the $γ_5$ matrix. We give predictions for double longitudinal spin asymmetry measurements at the RHIC.

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arXiv2003

Twist-2 Heavy Flavor Contributions to the Structure Function $g_2(x,Q^2)$

The twist--2 heavy flavor contributions to the polarized structure function $g_2(x,Q^2)$ are calculated. We show that this part of $g_2(x,Q^2)$ is related to the heavy flavor contribution to $g_1(x,Q^2)$ by the Wandzura--Wilczek relation to all orders in the strong coupling constant. Numerical results are presented.

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arXiv2003

NNLO corrections to the total cross section for Higgs boson production in hadron-hadron collisions

We present the next-to-next-to-leading order (NNLO) corrections to the total cross section for (pseudo-) scalar Higgs boson production using an alternative method than those used in previous calculations. All QCD partonic subprocesses have been included and the computation is carried out in the effective Lagrangian approach which emerges from the standard model by taking the limit $m_t \to \infty$ where $m_t$ denotes the mass of the top quark. Our results agree with those published earlier in the literature. We estimate the theoretical uncertainties by comparing the $K$-factors and the variation with respect to the mass factorization/renormalization scales with the results obtained by lower order calculations. We also investigate the dependence of the cross section on several parton density sets provided by different groups. Further we study which part of the coefficient functions dominates the cross section. This is of interest for the resummation of large corrections which occur near the boundary of phase space. It turns out that depending on the definition of the total cross section the latter is dominated by the the soft-plus-virtual gluon corrections represented by $δ(1-x)$ and $(\ln^i(1-x)/(1-x))_+$ terms. PACS numbers: 12.38.-t, 12.38.Bx, 13.85.-t, 14.80.Gt.

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arXiv2003

Higgs Production at NNLO

We describe the calculation of inclusive Higgs boson production at hadronic colliders at next-to-next-to-leading order (NNLO) in perturbative quantum chromodynamics. We have used the technique developed in reference [4]. Our results agree with those published earlier in the literature.

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arXiv2002

NLO differential distributions of massive lepton-pair production in longitudinally polarized proton-proton collisions

We present the full next-to-leading order (NLO) corrected inclusive cross section $d^3Δσ/dQ^2/dy/dp_T$ for massive lepton pair production in longitudinally polarized proton-proton collisions $p + p\to l^+l^- + 'X'$. Here $'X'$ denotes any inclusive hadronic state and Q represents the invariant mass of the lepton pair which has transverse momentum p_T and rapidity y. All QCD partonic subprocesses have been included provided the lepton pair is created by a virtual photon, which is a valid approximation for $Q<50{\rm GeV}$. Like in unpolarized proton-proton scattering the dominant subprocess is given by $q(\bar q) + g \to γ^* + 'X'$ so that massive lepton pair production provides us with an excellent method to measure the spin density of the gluon. Our calculations are carried out using the method of n-dimensional regularization by making a special choice for the $γ_5$-matrix. Like in the case of many other prescriptions evanescent counter terms appear. They are determined by computing the NLO coefficient functions for $dΔσ/dQ^2$ and the polarized cross section for Higgs production using both n-dimensional regularization and a four dimensional regularization technique in which the $γ_5$-matrix is uniquely defined. Our calculations reveal that the non-singlet polarized coefficient function equals the unpolarized one up to a minus sign. We give predictions for double longitudinal spin asymmetry measurements at the RHIC.

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arXiv2002

Next-to-leading order QCD corrections to differential distributions of Higgs boson production in hadron-hadron collisions

We present the full next-to-leading order corrected differential distributions $d^2σ/dp_T/dy$, $dσ/dp_T$ and $dσ/dy$ for the semi-inclusive process $p + p\to H + 'X'$. Here $X$ denotes the inclusive hadronic state and $p_T$ and $y$ are the transverse momentum and rapidity of the Higgs-boson $H$ respectively. All QCD partonic subprocesses have been included. The computation is carried out in the limit that the top-quark mass $m_t \to \infty$ which is a very good approximation as long as $m_H,p_T < 200$ GeV. Our calculations reveal that the dominant subprocess is given by $g + g \to H + 'X'$ but the reaction $g + q(\bar q) \to H + 'X'$ is not negligible. Another feature is that the $K$-factor representing the ratio between the next-to-leading order and leading order differential distributions is large. It varies from 1.4 to 1.7 depending on the kinematic region and choice of parton densities. We show that a reliable determination of the differential cross sections requires good knowledge of the gluon density in the region where $x < 10^{-3}$. Further we study whether the differential distributions are dominated at large transverse momentum by soft-plus-virtual gluon contributions. This is of interest for the resummation of large corrections which occur near the boundary of phase space. We also compare our results with those previously reported in the literature.

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arXiv2002

QCD Corrections to Resonant Slepton Production in Hadron Colliders

We consider resonant production of sneutrino and slepton at hadronic colliders such as the Tevatron and the LHC within the context of a R-parity violating supersymmetric model. We present next to leading order QCD corrections to total cross sections which originate from both quark- as well as gluon-initiated processes. For couplings involving only the first generation quarks, the K factor at the Tevatron can be as large as 1.5 for a 100 GeV sfermion and falls to nearly 1.1 as the sfermion mass reaches 1 TeV. At the LHC, the variation is between 1.2 and 1.45 for masses less than 2 TeV. While the dependence on the parton density parametrization is found to be mild, this ceases to be true if the strange quark plays a dominant role in the production process. We also study the renormalization and factorization-scale dependence and find it to be less pronounced for the NLO cros sections as compared to the LO. The results obtained in this article are also applicable to resonant production of any color-neutral scalar.

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arXiv2001

QCD and power corrections to sum rules in deep-inelastic lepton-nucleon scattering

In this paper we study QCD and power corrections to sum rules which show up in deep inelastic lepton-hadron scattering. Furthermore we will make a distinction between fundamental sum rules which can be derived from quantum field theory and those which are of a phenomenological origin. Using current algebra techniques the fundamental sum rules can be expressed into expectation values of (partially) conserved (axial-) vector currents sandwiched between hadronic states. These expectation values yield the quantum numbers of the corresponding hadron which are determined by the underlying flavour group $SU(n)_F$. In this case one can show that there exist an intimate relation between the appearance of power and QCD corrections. The above features do not hold for phenomenological sum rules, hereafter called non-fundamental. They have no foundation in quantum field theory and they mostly depend on certain assumptions made for the structure functions like superconvergence relations or the parton model. Therefore only the fundamental sum rules provide us with a stringent test of QCD.

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arXiv2001

Twist-4 Gluon Recombination Corrections for Deep Inelastic Structure Functions

We calculate twist--4 coefficient functions for the deep inelastic structure function $F_2(x,Q^2)$ associated to 4--gluon operator matrix elements for general values of the Bjorken variable $x$ and study the numerical effect on the slope $\partial F_2(x,Q^2)/\partial \log Q^2$. It is shown that these contributions diminish the strongly rising twist--2 terms towards small values of $x$.

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arXiv2001

The Drell-Levy-Yan Relation: ep vs $e^+e^-$ Scattering to $O(α_s^2)$

We study the validity of a relation by Drell, Levy and Yan (DLY) connecting the deep inelastic structure (DIS) functions and the single-particle fragmentation functions in $e^+e^-$ annihilation which are defined in the spacelike ($q^2<0$) and timelike ($q^2>0$) regions, with respect to physical evolution kernels for the two processes to $O(α_s^2)$. We also comment on a relation proposed by Gribov and Lipatov.

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arXiv2000

On the Drell-Levy-Yan Relation to $O(α_s^2)$

We study the validity of a relation by Drell, Levy and Yan (DLY) connecting the deep inelastic structure (DIS) functions and the single-particle fragmentation functions in e^+e^- annihilation which are defined in the spacelike (q^2<0) and timelike (q^2>0) regions respectively. Here q denotes the momentum of the virtual photon exchanged in the deep inelastic scattering process or the annihilation process. An extension of the DLY-relation, which originally was only derived in the scaling parton model, to all orders in QCD leads to a connection between the two evolution kernels determining the q^2-dependence of the DIS structure functions and the fragmentation functions respectively. In relation to this we derive the transformation relations between the space-and time-like splitting functions up to next-to-leading order (NLO) and the coefficient functions up to NNLO both for unpolarized and polarized scattering. It is shown that the evolution kernels describing the combined singlet evolution for the structure functions F_2(x,Q^2), F_L(x,Q^2) where Q^2=|q^2| or $F_2(x,Q^2), \partial F_2(x,Q^2)/\partial \ln(Q^2)$ and the corresponding fragmentation functions satisfy the DLY relation up to next-to-leading order. We also comment on a relation proposed by Gribov and Lipatov.

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arXiv1999

Relations among Higher Order QCD corrections

We study the scheme transformation of next to leading order QCD corrections to various processes. An interesting relation by Drell, Levy and Yan (DLY) among space like and time like processes is studied carefully in the next to leading order level. We construct factorisation scheme invariants and show that they are DLY-invariant.

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arXiv1998

Relations among QCD corrections beyond leading order

The status of various relations among higher order QCD corrections is discussed. In particular, Drell-Levy-Yan relation and Supersymmetric relation are studied at the two-loop level. We have also investigated the validity of such relations for physical observables.

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arXiv1998

Second order QCD corrections to the forward-backward asymmetry in e^+e^- - collisions

The sentence, 11th line below Eq. (30), starting with "Further in [14] one has included all interference terms ...." is wrong and has been corrected. Second line below Eq. (40) m_bar(m)=m is replaced by m_bar(μ_0)=μ_0 with μ_0=4.10 GeV, μ_0=1.30 GeV and μ_0=166.1 GeV for bottom, charm and top respectively. The numbers in the second and third column of table 3 are a little bit changed. In the acknowledgement the funding agency is mentioned and one reference i.e. [20] is added.

hep-ph↗
arXiv1998

Heavy flavour mass corrections to the longitudinal and transverse cross sections in e^+e^- - collisions

The sentence, 7th line below Eq. (28), starting with "Further we exclude all interference terms ...." is wrong and has been corrected. Eq. (33) : f_k^{l,(i)} -> h_k^{l,(i)} i=0,1 Second line below Eq. (33) m_bar(m)=m is replaced by m_bar(μ_0)=μ_0 with μ_0=4.10 GeV and μ_0=166.1 GeV for bottom and top respectively. The numbers in the third column of tables 1 and 2 are a little bit changed.

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