Wolfgang Menges Queen Mary Measuring Vub from Semileptonic

Wolfgang Menges, Queen Mary Measuring |Vub| from Semileptonic B Decays Wolfgang Menges Queen Mary, University of London, UK Institute of Physics: Particle Physics 2006 11 th April 2006

Introduction Wolfgang Menges, Queen Mary • CP violation is described by the CKM matrix in the SM • the consistency of the Unitarity Triangle is tested by measuring its angles and sides • one side is related to |Vub| • |Vub| can be measured in semileptonic, charmless B decays Vub Experimental challenge: • suppress continuum background • suppress charm decay Theoretical challenge: • extrapolate from partial to total BF

Unitarity Triangle Fits Wolfgang Menges, Queen Mary J/y. K 0: sin 2 interference in B DK: g Bd mixing: md kaon decays: εK b ul : |Vub| D*l : |Vcb| charmless two-body: a Bs mixing: ms / md http: //ckmfitter. in 2 p 3. fr

PEP 2 and Ba. Bar Detector Wolfgang Menges, Queen Mary Collected luminosity: ~ 330 fb-1 Analysed Luminosity: 80/210 fb-1 1. 5 T solenoid Electro. Magnetic Calorimeter 6580 Cs. I(Tl) crystals e+ (3. 1 Ge. V) Čerenkov Detector (DIRC) 144 quartz bars 11000 PMTs e- (9 Ge. V) Instrumented Flux Return iron/RPCs/LSTs (muon/neutral hadrons) Drift CHamber 40 stereo layers Silicon Vertex Tracker 5 layers, double sided strips

Inclusive b → uln : Strategies • B → Xuln decays are described by 3 variables El = lepton energy Wolfgang Menges, Queen Mary q 2 = lepton-neutrino mass squared u quark turns into one or more hadrons m. X = hadron system mass • Signal events have smaller m. X larger El and q 2 Not to scale!

Lepton Endpoint BABAR PRD 73: 012006, 2006 Wolfgang Menges, Queen Mary Selectrons with 2. 0 < El < 2. 6 Ge. V – Push below the charm threshold Larger signal acceptance Smaller theoretical error – Accurate subtraction of background is crucial! • off-resonance data • events with pe > 2. 8 Ge. V • fit b->clv composition in bkg subtraction – Measure the partial BF – S/B =1/15 for the endpoint El > 2. 0 Ge. V B (10 -4) = 5. 72 ± 0. 41 stat ± 0. 65 sys Luminosity: 80 fb-1 total BF is ~2 10 3 BABAR Data MC bkgd. b clv Data – bkgd. MC signal b ulv

El and q 2 BABAR PRL 95: 111801 q 2 (Ge. V 2) Wolfgang Menges, Queen Mary • Try to improve signal-to-background • Use pv = pmiss in addition to pe calculate q 2 – Define shmax(El, q 2) = the maximum m. X squared b ulv b clv El (Ge. V) • Cutting at shmax < m. D 2 removes b clv while keeping most of the signal – S/B = 1/2 achieved for El > 2. 0 Ge. V and shmax < 3. 5 Ge. V 2 Measured partial BF: BABAR B (10 -4) 3. 54 ± 0. 33 stat ± 0. 34 sys Luminosity: 80 fb-1 Smaller systematic errors Extract signal normalize bkg

m. X and q 2 BABAR hep-ex/0507017 • Must reconstruct all decay products to measure m. X or q 2 – Use (fully-reconstructed) hadronic B tag • Suppress b → c lv by vetoing against D (*) decays Wolfgang Menges, Queen Mary – Reject events with K – Reject events with B 0 → D *+(→ D 0 p+)l−v v • Measure the partial BF in regions of (m. X, q 2) – m. X < 1. 7 Ge. V and q 2 >8 Ge. V 2: DB (10 -4) = 8. 7 ± 0. 9 stat ± 0. 9 sys lepton X Luminosity: 211 fb-1

|Vub| from Branching Fraction Wolfgang Menges, Queen Mary For converting a branching fraction into |Vub|the phase space acceptance is needed: Results of different calculations/ HQE parameters using the same partial branching fraction: Example for mx/q 2 1) |Vub|=(5. 00± 0. 37 exp± 0. 46 SF± 0. 28 theo)´ 10 -3 +0. 46 2) |Vub|=(4. 65± 0. 34 exp – 0. 38 ± 0. 23 theo)´ 10 -3 SF 3) |Vub|=(4. 82± 0. 36 exp± 0. 46 SF+theo)´ 10 -3 4) |Vub|=(4. 86± 0. 36 exp± 0. 22 theo)´ 10 -3 1) BLNP: Ba. Bar B Xcl moments mb(SF) = 4. 61 ± 0. 08 Ge. V mπ2(SF) = 0. 15 ± 0. 07 Ge. V 2 2) BLNP: Belle B Xsg spectrum mb(SF) = 4. 52 ± 0. 07 Ge. V mπ2(SF) = 0. 27 ± 0. 23 Ge. V 2 3) BLL: Ba. Bar B Xcl moments mb(1 S) = 4. 74 ± 0. 06 Ge. V 4) DGE: HFAG average mb(MS) = 4. 20 ± 0. 04 Ge. V

Status of Inclusive |Vub| world average summer 2006 Wolfgang Menges, Queen Mary BLNP + SF from b->clv, b->sg |Vub| determined to 7. 4% Statistical 2. 2% Expt. syst. 2. 7% b clv model 1. 9% b ulv model 2. 1% SF params. (mb, mp 2) 4. 1% Theory 4. 2% – The SF parameters can be improved with b → sg, b clv measurements – What’s in theory error? Subleading SF and Weak Annihilation effects.

Exclusive b uln • Measure specific final states, e. g. , B → plv Wolfgang Menges, Queen Mary – Can achieve good signal-to-background ratio – Branching fractions are O(10 -4) statistics limited • Need form factors to extract |Vub| One FF for B → plv (massless lepton) – Theo. Uncertainties complementary to inclusive approach ! • f+(q 2) calculations exist based on: – Lattice QCD (q 2 > 15 Ge. V 2) • “quenched” calculations 15% uncertainty • new unquenched calculations (hep-lat/0409116, 0408019) – Light Cone Sum Rules (q 2 < 14 Ge. V 2) 10% uncertainty – Quark models (ISGW 2) … and other approaches

Status of Exclusive |Vub| • use BF and FF predictions to calculate |Vub| Wolfgang Menges, Queen Mary • needs also assumption of shape of full q 2 range All calculations consistent! incl. |Vub|[10 -3] = 4. 45 0. 20 0. 26 (BLNP)

The Unitarity Triangle: 2004 2006 • Precise determination of |Vub| complements sin 2 b to test the validity of the Standard Model – 7. 4% accuracy achieved so far 5% possible? Wolfgang Menges, Queen Mary • Close collaboration between theory and experiment is important Inclusive |Vub| : – Much exp. and theo. progress in the last 2 years Exclusive |Vub| : – Significant exp. progress in the last year, but further improvement in B → p FF calculations needed - Accuracy of 7 -8% for exclusive |Vub| in the next few years (? ) • Important to cross-check inclusive vs. exclusive results