Research in particle physics requires intense global collaboration and at times up to a hundred different laboratories have pooled their resources to conduct experiments at giant multi-million dollar facilities called accelerators.

But with TIFR being on Washington's ``restricted list'' of institutions after the Pokharan tests, that cooperation may now well be in jeopardy.

The eight scientists are from the prestigious Fermi National Accelerator Lab and the Argon National Lab, both supported by the US Department of Energy.

However, 25 other Americans, from private institutions and US universities, are attending. Two of the key scientists denied permission are Dan Green from Fermi and Rajendran Raja, another American, well-known for his work on elementary particles.

Reacting to the move, John Peoples, director of Fermi Lab, told Science magazine: ``We never did this (denial of permission even to Americans to visit India) with the Russians at the worst part of the Cold War, this is a precedent.''

Peoples said that last summer, the Department of Energy had asked him, in writing, to even remove the Indian flag from the UN-type display outside Fermi Lab's buildings in Chicago. This despite the fact that India has a collaboration with Fermi and has contributed hardware worth over half-a-million dollars.

Said TIFR scientist V S Narasimham who is also the meeting's local convenor: ``The US Government has been unfair and it was unnecessary to deny this permission for a purely scientific meeting.'' It amounted to ``mere harassment of the American scientists,'' as a result of which only science is going to suffer.

Incidentally, last year R Chidambaram, chief of the Indian atomic energy program, was denied a visa by the US to attend an international meeting of crystallographers at Arlington in USA. When contacted, the spokesperson of the American Embassy in New Delhi declined to comment.

About 130 scientists, half from abroad, are participating in the conference. Two Pakistani and a few Chinese scientists are also expected to participate. This conference is one in a series of international scientific meetings to better understand the mystery behind sub-atomic particles.