- Aubert, B;
- Bona, M;
- Boutigny, D;
- Karyotakis, Y;
- Lees, JP;
- Poireau, V;
- Prudent, X;
- Tisserand, V;
- Zghiche, A;
- Garra Tico, J;
- Grauges, E;
- Lopez, L;
- Palano, A;
- Pappagallo, M;
- Eigen, G;
- Stugu, B;
- Sun, L;
- Abrams, GS;
- Battaglia, M;
- Brown, DN;
- Button-Shafer, J;
- Cahn, RN;
- Groysman, Y;
- Jacobsen, RG;
- Kadyk, JA;
- Kerth, LT;
- Kolomensky, YG;
- Kukartsev, G;
- Lopes Pegna, D;
- Lynch, G;
- Mir, LM;
- Orimoto, TJ;
- Osipenkov, IL;
- Ronan, MT;
- Tackmann, K;
- Tanabe, T;
- Wenzel, WA;
- Del Amo Sanchez, P;
- Hawkes, CM;
- Watson, AT;
- Koch, H;
- Schroeder, T;
- Walker, D;
- Asgeirsson, DJ;
- Cuhadar-Donszelmann, T;
- Fulsom, BG;
- Hearty, C;
- Mattison, TS;
- McKenna, JA;
- Khan, A;
- Saleem, M;
- Teodorescu, L;
- Blinov, VE;
- Bukin, AD;
- Druzhinin, VP;
- Golubev, VB;
- Onuchin, AP;
- Serednyakov, SI;
- Skovpen, YI;
- Solodov, EP;
- Todyshev, KY;
- Bondioli, M;
- Curry, S;
- Eschrich, I;
- Kirkby, D;
- Lankford, AJ;
- Lund, P;
- Mandelkern, M;
- Martin, EC;
- Stoker, DP;
- Abachi, S;
- Buchanan, C;
- Foulkes, SD;
- Gary, JW;
- Liu, F;
- Long, O;
- Shen, BC;
- Vitug, GM;
- Zhang, L;
- Paar, HP;
- Rahatlou, S;
- Sharma, V;
- Berryhill, JW;
- Campagnari, C;
- Cunha, A;
- Dahmes, B;
- Hong, TM;
- Kovalskyi, D;
- Richman, JD;
- Beck, TW;
- Eisner, AM;
- Flacco, CJ;
- Heusch, CA;
- Kroseberg, J;
- Lockman, WS;
- Schalk, T;
- Schumm, BA;
- Seiden, A;
- Wilso, MG;
- Winstrom, LO
We present the first measurement of the B0 → X-u ℓ+νℓ partial branching fraction in the endpoint region of the lepton momentum spectrum, above the threshold for B → Xcℓνℓ decays. The analysis is based on a sample of 383 million γ(4S) decays into BB pairs collected with the BABAR detector at the PEP-II e+e- storage rings. We select B0B0 events by partially reconstructing one B meson via the B0 → Dz.ast;+ℓ- ̄νℓ decays then select B0 → X- u ℓ+νℓ decays identifying a second high momentum lepton. In the momentum interval ranging from 2.3 to 2.6 GeV/c we measure the partial branching fraction πB(B0 → Xuℓν) = (1.30 ± 0.21stat ± 0.07syst) × 10-4 where the first error is statistical and the second is systematic. By comparing this measurement with the one obtained from untagged B decays we obtain R+/0 = ΔB(B0 → Xuℓν)/ ΔB(B+ → Xuℓν) = 1.18 ± 0.35stat ± 0.17syst. Using this measurement we extract a limit on the contributions from processes breaking isospin symmetry in charmless semileptonic B decays.