V. Ravindran

Research Summary:

Higgs physics at LHC is going to be one of the main interests to the particle physics community in the coming years when the LHC machine starts operating. In this context [1,2] I have computed the full next-to-leading order corrected differential distributions d²σ/dp_T/dy, dσ/dp_T and dσ/dy for the semi-inclusive process p + p → H+'X' and the full next to next to leading order correction to the total cross section for the fully inclusive Higgs production. 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 → ∞ 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 → H+'X' but the reaction g + q(\bar q) → 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. These corrections reduce the theoretical uncertainties coming from factorization and renormalization scales significantly making the prediction reliable.

The other topic which is very relevant is the study of the spin structure of the hadrons. RHIC at BNL is already at operational to do this important task. In this context, a precise computation of the spin observables is very important from the theory side to reduce various theoretical uncertainties. So I have computed the full next-to-next-to-leading order (NNLO) coefficient functions[3] for the polarized cross section dΔ&sigma/dQ for the Drell-Yan process p + p → 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+ q‾ → &gamma^*+'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. We give predictions for double longitudinal spin asymmetry measurements at the RHIC.

The spin dependent structure function g₂(x,Q²) can be measured in deep inelastic scattering experiments. Since the level of precision increases, a precise theoretical study on this becomes important. In this context I have studied[4] the twist--2 heavy flavor contributions to the polarized structure function g₂(x,Q²). We show that this part of g₂(x,Q²) is related to the heavy flavor contribution to g₁(x,Q²) by the Wandzura--Wilczek relation to all orders in the strong coupling constant. Numerical results are presented.

Publications:

• V. Ravindran, J. Smith and W. L. van Neerven, "Differential cross sections for Higgs production," Mod. Phys. Lett. A 18, 1721 (2003) [arXiv:hep-ph/0307005].

• V. Ravindran, J. Smith and W. L. van Neerven, "Higgs production at NNLO," Pramana 62, 683 (2004) [arXiv:hep-ph/0304005].

• V. Ravindran, J. Smith and W. L. van Neerven, "NNLO corrections to massive lepton-pair production in longitudinally polarized proton proton collisions," Nucl. Phys. B 682, 421 (2004) [arXiv:hep-ph/0311304].

• J. Blumlein, V. Ravindran and W. L. van Neerven, "Twist-2 heavy flavor contributions to the structure function g₂(x,Q^**2)," Phys. Rev. D 68, 114004 (2003) [arXiv:hep-ph/0304292].

• R. Basu and V. Ravindran, "Working Group Report: Quantum Chromodynamics (QCD) And Hadronic Structure," Pramana 60, 401 (2003).

• Linear Collider meeting (May'03) at TIFR, Mumbai.

• Linear Collider meeting (Oct'03) at CTS, Bangalore.

• International meeting on Linear Collider (Nov'03) at INSA, New Delhi.

• Linear Collider meeting (Dec'03) at TIFR, Mumbai.

• WHEPP (Jan'04) at IIT, Mumbai

Visits to other Institutes:

• Visited TIFR, Mumbai during the month of May from 6 to 24th.

• Visited IMSc, Chennai during the month of May from 26th to 30th.

• Visited University of Hyderabad during the month of December from 12th to 22nd.

Invited Lectures/Seminars:

• Invited talk at Linear Collider meeting at TIFR, Mumbai.

• Invited talk at Linear Collider meeting at CTS, Bangalore.

• Invited talk at the work group of WHEPP, IIT, Mumbai.

Other Activities:

Guiding Student:

• I guided two summer students.

• I taught the course on Electrodynamics to first year Ph.D students.

• Convener of the Transport committee.