Scientists chasing a particle they believe may have played a vital role in creation of the universe indicated on Monday they were coming to accept it might not exist after all.
But they stressed that if the so-called Higgs boson turns out to have been a mirage, the way would be open for advances into territory dubbed "new physics" to try to answer one of the great mysteries of the cosmos.
The CERN research center, whose giant Large Hadron Collider (LHC) has been the focus of the search, said it had reported to a conference in Mumbai that possible signs of the Higgs noted last month were now seen as less significant.
A number of scientists from the center went on to make comments that raised the possibility that the mystery particle might not exist.
"Whatever the final verdict on Higgs, we are now living in very exciting times for all involved in the quest for new physics," Guido Tonelli, from one of the two LHC detectors chasing the Higgs, said as the new observations were announced.
CERN's statement said new results, which updated findings that caused excitement at another scientific gathering in Grenoble last month, "show that the elusive Higgs particle, if it exists, is running out of places to hide."
The centre's research director Sergio Bertolucci told the conference, at the Indian city's Tata Institute of Fundamental Research, that if the Higgs did not exist "its absence will point the way to new physics."
Under what is known as the Standard Model of physics, the boson, which was named after British physicist Peter Higgs, is posited as having been the agent that gave mass and energy to matter just after the Big Bang 13.7 billion years ago.
As a result, flying debris from that primeval explosion could come together as stars, planets and galaxies.
In the subterranean LHC, which began operating at the end of March 2010, CERN engineers and physicists have created billions of miniature versions of the Big Bang by smashing particles together at just a fraction under the speed of light.
The results of those collisions are monitored by hundreds of physicists not just at CERN but in linked laboratories around the world which sift through the vast volumes of information generated by the LHC.
Scientists at the U.S. Fermilab near Chicago have been in a parallel search in their Tevatron collider for nearly 30 years. Last month they said they hoped to establish if the Higgs exists by the end of September, when the Tevatron closes down.
For some scientists, the Higgs remains the simplest explanation of how matter got mass. It remains unclear what could replace it as an explanation. "We know something is missing, we simply don't quite know what this new something might be," wrote CERN blogger Pauline Gagnon.
"There are many models out there; we simply need to be nudged in the right direction," added Gagnon, an experimental physicist.