Precision measurement of the structure function ratios F e / F , FC / F and Fca

We present the s t ructure funct ion rat ios F~e/F2 ~ F2C/Fz ~ and F2ca/F2 D measured in deep inelastic muon-nuc leus scat ter ing at an incident m u o n m o m e n t u m of 200 GeV. The k inemat ic range 0.0035 < x <0 .65 and 0 . 5 < Q 2 < 9 0 G e V 2 is covered. At low x the three ra t ios are significantly smaller than uni ty and the size a Now at TRIUMF, Vancouver, BC V6T 2A3, Canada b Now at Trasys, 1930 Zaventem, Belgium c Now at INFN, Laboratori Nazionali del Grin Sasso, 67010 Assergi, Italy a Now at Universit6 de Gen~ve, 1211 Gen~ve 4, Switzerland e Now at GSt, W-6100 Darmstadt, FRG f Now at CEBAF, Newport News, VA 23606, USA g Now at CERN, 1211 Geneva 23, Switzerland h Now at University of Mainz, W-6500 Mainz, FRG i Now at Osaka University, Osaka 567, Japan J Now at DESY, W-2000-Hamburg 52, FRG k Now at Gruner and Jahr AG & Co KG, W-2210 Itzehoe, FRG J Now at IKP2-KFA, W-5170 Jfilich, FRG of the deplet ion grows with decreasing x and increasing mass n u m b e r A. At in termedia te x the rat ios show an enhancemen t of abou t 2% above uni ty for C / D and Ca /D, possibly less for He /D. There are indicat ions of some QZ dependence in the C a / D data. The integrals of the s t ructure funct ion differences Fz A Fz ~ are discussed. m Now at Carnegie Mellon University, Pittsburgh, PA 15213, USA n Now at EMPA, CH-8600 Dubendorf, Switzerland ~ On leave from Jozef Stefan Institut, Ljubljana 61111, Yugoslavia, now at DPhN Saclay, 91191 Gif-sur-Yvette, France P Now at University of Melbourne, Parkville, Victoria 3052, Australia q Now at Universit6 de Neuchfitel, CH-2000 NeuchMel, Switzerland r Supported by Bundesministerium fiir Forschung und Technologic Supported in part by FOM, Vrije Universiteit Amsterdam and NWO Supported by CPBR01.06 u Supported by CPBP.01.09