New Delhi: Indian equity indices BSE Sensex and NSE Nifty 50 reached historic highs on Thursday, buoyed by a strong rally in heavyweight stocks. NSE Nifty 50 surpassed its previous peak of 23,889.1 to touch a new record at 23,974.70, while Sensex breached the 79,000 mark for the first time, hitting a fresh lifetime high of 79,033.91.NIFTY all time high Initially opening marginally lower, Nifty 50 rose by 0.32% to 23,945 points by 10:30 a.m., while Sensex climbed 0.35% to 78,948.25 points after a slight 0.2% dip at the sessions start. Bank Nifty also achieved a significant milestone by crossing the 53,000 level for the first time.Ultratech Cement surged 4.3%Ultratech Cement, Indias largest cement producer by capacity, surged 4.3% following its announcement of acquiring a 23% stake in India Cements for $226 million. This move positioned Ultratech as the leading gainer in Nifty 50, prompting India Cements shares to soar by 12%.Know how Reliance Industries did Reliance Industries, the second-largest stock by weightage in Nifty 50, continued to drive the indices with a 1.25% increase. The company led by Mukesh Ambani had gained 4% in the preceding session, further bolstering market sentiment.The market rally was underpinned by positive investor sentiment driven by robust corporate earnings, strategic acquisitions, and favorable global cues. Analysts attributed the bullish trend to improved economic outlook and expectations of strong corporate performances in the upcoming quarterly results.Investors optimisticInvestors remained optimistic amidst signs of economic recovery post-pandemic, with key sectors like cement and banking witnessing substantial gains. Market participants are closely monitoring developments in sectors crucial to sustaining the current momentum, amidst evolving global and domestic economic dynamics.Which companies saw decline in stock prices Companies like Ultra Cement, Dr Reddys Laboratories, Grasim Industries, JSW Steel, and Tata Steel performed well and saw their stock prices rise. On the other hand, Tech Mahindra, TCS, HCL Technologies, Shriram Finance, and Nestle India were among those whose stock prices declined the most.