σ |V ub | at SuperB ??

σ|Vub|atSuperB ?? Benoit VIAUD LAL, Orsay Benoit VIAUD, SuperB workshop VI, Valencia

|Vub| Measurements Two complementary approaches Cleaner Theo. description more difficult Higher signal statistics Smaller theoretical errors Two complicated, but independent treatments: both the exp. and th. errors have different origins => Allows comparison to check reliability ! Benoit VIAUD, SuperB workshop VI, Valencia

|Vub| Measurements Two complementary approaches Cleaner Theo. description more difficult Higher signal statistics Smaller theoretical errors Presently HFAG, BNLP HFAG, FNAL |Vub|= (4.31 ± 0.17exp ± 0.35th)×10-3 |Vub|= (3.55 ± 0.22exp+0.6-0.4 th)×10-3 ~9% Benoit VIAUD, SuperB workshop VI, Valencia

|Vub| Measurements Two complementary approaches Higher signal statistics Smaller theoretical errors Cleaner Theo. description more difficult How better can we do with a super B Factory ? How to reach σ|Vub| = 1-2% ? With a reliable prediction ? -> Stat100 -> Better vertexing -> Better neutrino Benoit VIAUD, SuperB workshop VI, Valencia

The Key Issue: Control of the Backgrounds ! No (small) Background u u Main source of uncertainty σ~1 % => σ|Vub|~ 2.5 % Although open (?) questions - Use b-> s γmoments ? - Scheme ? Level of the other errors we should take into account ?? Benoit VIAUD, SuperB workshop VI, Valencia

The Key Issue: Control of the Backgrounds ! Reality Cuts ! => Extract |Vub| from partial BF, for which OPE does not converge… ΔBF sensitive to the Fermi motion of the b inside the B. => Need light cone Shape Function Often use parameterization, constrained by moments. Also by b->sγ Depends on hadronic quantities mb, 2( <- B->Xclv moments) Benoit VIAUD, SuperB workshop VI, Valencia

The Key Issue: Control of the Backgrounds ! Triggers a lot of theoretical work Benoit VIAUD, SuperB workshop VI, Valencia

The Key Issue: Control of the Backgrounds ! Many experimental analyses El endpoint El improved endpoint Look for the best trade-off between S, S/B and fu (selected fraction of phase space) => + - decides σth Tagged Complicated analyses… Subtle treatment of the Backgrounds… Results difficult to predict. No striking winner… Benoit VIAUD, SuperB workshop VI, Valencia

|Vub|determination pattern: complex ! It will be hard to evaluate precisely the Super B factory’s potential without a rigorous study (i.e. simulation, as accurate as possible). -> Too Many things to know, from many th. or exp. sources , having a complicated behavior (w.r.t the backgrounds, for example) to obtain reliable results otherwise… Benoit VIAUD, SuperB workshop VI, Valencia

So, where should we start from ? We want an evaluation of the Super B factory’s potential that : - is reliable - should reach σ|Vub| ~ 2% / tells us how to do so… - is not too hard to obtain o time o manpower o no need of full simulation / easy to extrapolate from present analyses… What we know about uncertainties should guide us. Usual dominant sources: - stat - detector efficiency / PID (trk/neutral) - background modelization - reconstruction precision - ?? Benoit VIAUD, SuperB workshop VI, Valencia

So, where should we start from ? We want an evaluation of the Super B factory’s potential that : - is reliable - should reach σ|Vub| ~ 2% / tells us how to do so… - is not too hard to obtain o time o manpower o no need of full simulation / easy to extrapolate from present analyses… What we know about uncertainties should guide us. Usual dominant sources: - stat - detector efficiency / PID (trk/neutral) - background modelization - reconstruction precision - σth expected small Good Candidate ? As dominant as possible Under control High S/B Something already good that would benefit from lower boost / better vertex Benoit VIAUD, SuperB workshop VI, Valencia Full spectrum

Tagged and Untagged analyses Untagged Semileptonic tag Hadronic tag oFirst find a Btag, then look for B->Xulv in its recoil: - Only one Xu-l pair in the rest of event - No other tracks, small residual energy o tag side: B->D(*)+(π±,K±), full reco. (~many modes) o Well defined event: full kinematics, charge, flavor. o Only one neutrino : precise reconstruction of m2miss ,q2 o tag side: B->D(*)lν o tag-B kinematics incomplete: 2 ν High signal statistics, More sensitive to Background simulation CleanSample + Purity + Efficiency Benoit VIAUD, SuperB workshop VI, Valencia

Illustration : MX Analysis • Hadronic tag • Signal extraction: • Binned X2 fit of B -> Xulv & B -> Xclv • MC distrib. to MX data distrib. • Continuum: mES fit in MX bins • MX reco improved by a kinematical fit, • σMX ~ 250 MeV • Originally designed for a “reduced SF dependence” analysis • Use SF universality to relate B->Xulv to B->Xsγ Leibovich, Low, Rothstein PLB 486:86 Weight function • Finally tried also with no MX cut 1.67 Benoit VIAUD, SuperB workshop VI, Valencia

MX Analysis at a Super B Factory ? • Main Contributions to σ|Vub| 88 fb-1 75 ab-1 18.6% 1% 3.8% 1% 3.8% 1% -> Experimental systematics mainly due to statistics (mES fit). Detection effects can also improve. -> B->Xclv improvement σ 1/4 • Additional improvements are possible: -> More elaborate fit : separate the various B->Xclv contributions… -> Better Vertexing should yield better σMX -> What else ?? σMX Benoit VIAUD, SuperB workshop VI, Valencia

MX Analysis at a Super B Factory ? • Main Contributions to σ|Vub| 88 fb-1 75 ab-1 18.6% 1% 3.8% 1% 3.8% 1% Again, σ|Vub|exp ~ 2% seems possible… -> Experimental systematics mainly due to statistics (mES fit). Detection effects can also improve. -> B->Xclv improvement 1/4 => σ(|Vub|)tot ~ 3% • Additional improvements are possible: -> More elaborate fit : separate the various B->Xclv contributions… -> Better Vertexing should yield better σMX -> What else ?? Benoit VIAUD, SuperB workshop VI, Valencia

MX analysis • Has good chance to eventually give good results • Already an analysis with the full spectrum • Btag is a complicated object, but not sure we need to care yet • (ex: should be under control with b->ulv/b->clv) • S/B not too BAD • MX should be better at SuperB. Benoit VIAUD, SuperB workshop VI, Valencia

[1] Gulez & al, hep-lat/0601021 [2] Okamoto & al, hep-lat/0409116 [3] Ball & al, hep-ph/0406232 Exclusive |Vub| • Unquenched LQCD (q2 > 16 GeV2): HPQCD[1], FNAL[2] • LCSR (q2 < 16 GeV2): Ball-Zwicky[3] o Need theory to calculate FF HFAG’s Average (FNAL) |Vub|= (3.55±0.22 +0.6-0.4 )10-3 ~12% o σth from LQCD could be down to ~ 3% in a few years (P. McKenzie, Vxb Workshop 2007) o FF shape could be known precisely enough to use the full measured BF… + Benoit VIAUD, SuperB workshop VI, Valencia

Belle, 535 MBB, hep-ex/0610054 Hadronic Tag Signal extraction based on the full knowledge of kinematics: - Mmiss2 = (pmiss= pY(4S)–pBtag– pπ– pl)2 Nsig = 48 ± 8 Nsig = 35 ± 7 o Very good bkg rejection: S/B~10 => Low Systematics ! (leading: detector effects) 75 ab-1 0.02 0.04 σ|Vub| ~ 4% Benoit VIAUD, SuperB workshop VI, Valencia

Discussion • I’ve certainly forgotten interesting things… • => you’re comments are needed… • - anything precise we already know ? • - ideas for the physics potential evaluation ? • - someone already having a to do list ? • - ?? Benoit VIAUD, SuperB workshop VI, Valencia

Back up Benoit VIAUD, SuperB workshop VI, Valencia

El Endpoint Analysis S/B ~ 1/10 • Select events with 2.0 < El < 2.6 GeV • pmiss used to reject Continuum Background • Large backgrounds: needs an accurate fit • -> Continuum: shape param. from offpeak, • normalisation from onpeak • -> Fit the B->Xclv composition: D, D*, D**, D(*) • How relaxed can the El cut be with a super B factory ? Benoit VIAUD, SuperB workshop VI, Valencia

El Endpoint Analysis relaxed / no cut ? • B-> c l v backgrounds are the concern : σstat due to S/B ; σsystFF + BF knowlegde… Benoit VIAUD, SuperB workshop VI, Valencia

El Endpoint Analysis relaxed / no cut ? • B-> c l v backgrounds are the concern : σstat due to S/B ; σsystFF + BF knowlegde… • Also improved with 75 ab-1 : • B-> (D, D*, D**, D(*)) lv presently • measured with σstat ~ σsyst . • => σstat will disappear • => σsyst0,5 (down to a few %, detector effects) • => σb->clv ~ 1 % • El cut relaxed: S/B goes from 1/10 to 1/50... • =>σb->clv ~ 5 %  2.5% on |Vub| • Other improvements ?? • Improved fitting technique ?? • Lower boost = better v will help for Continuum… • Also for B->c l v ? • Improved vertexing: D(*) veto ? • Very good control on tracks/neutrals reco. • How statistical is it ? • ?? • => May be σ(|Vub|)b->clv ~ 1.5 % • Not Crazy to expect σexp~ 2 % • Presently σmb~ 1-2 % (realistic ?) • Dominated by theory. • If σmb drops slightly <1 % • => σ(|Vub|)tot ~ ( 2%+2%) ~ 3% Benoit VIAUD, SuperB workshop VI, Valencia

Belle, 253 fb-1, hep-ex/0604024 Semileptonic Tag Simultaneous fit to B-->(0/0)lv + B+-> D(*,0)lv and B0->(+/+)lv + B+-> D(*,-)lv samples Signal extraction: global knowledge of the event - Fit to MX -xB2 (<1 for signal events with only the 2 νmissing) N(+lv) =156 ± 20 N(0lv) =69 ± 11 o Good bkg rejection: S/B~3 o Still limited by statistics ! o Systematic error: Btag efficiency. Use a control sample: events with 2 Btag decays. => “statistical” systematics ! Benoit VIAUD, SuperB workshop VI, Valencia

Summary • Inclusive decays are a mess • What to do to reach 1-2% (Ne pas oublier de poser cette question et de dire que a priori, il faut le spectre complet) ?? First, we have to work… To predict a very small quantity requires a precise/detailed work • Many things coming from many places • -> Need to know many things ( need to be aware of the improvement in many other stuffs…) • Need rigorous estimations (MC) to tell something • precise and reliable beyond what everybody knows… • Just a first look here… A few arguments to show that CDR is • in the right ballpark. • No cut… Extrapolate from current results (El,tagged Mx) • Define a roadmap / to do list… • bien reviser les coupures+systematiques… • the trade-off way: quid of subleading shape functions ?? Benoit VIAUD, SuperB workshop VI, Valencia

BaBar, 206 fb-1, hep-ex/0612020 Untagged B0->π-l+ν, loose ν-reconstruction No tight ν-reconstruction cuts : Signal Yield ↑ Purity ↓ High statistics allow a precise signal extraction in 12 q2 bins • Binned fit to ΔE-mES: renormalize histos from MC. High stat. also allows to control the systematics despite low S/B… -Bkg fitted in q2 bins: reduced σ from B->Xlv FF&BF (leading at high q2) -High stat. in data control samples: continuum bkg correction (leading at low q2) Total Nsig~5000 In q2 bins: Nsig ~ 430 to 500 S/B ~ 1/3 to 1/10 B(B->-lv)= (1.46±0.07stat±0.08syst)10-4 ΔB(B->-lv; q2>16GeV2)= (0.38±0.04stat±0.03syst)10-4 4.8% 5.5% |Vub|= ( 3.7±0.2±0.2+0.6-0.4 )10-3 FNAL Benoit VIAUD, SuperB workshop VI, Valencia

Status of BF’s and |Vub| Belle, semileptonic tags, B++B0 |Vub|= ( 3.6±0.41±0.20+0.6-0.4 )10-3 FNAL Babar, semileptonic+hadronic , B++B0 |Vub|= ( 4.0±0.5 ± 0.3+0.7-0.5 )10-3 FNAL CLEO, untagged |Vub|= (3.6±0.4 ±0.20+0.6-0.4 )10-3 HPQCD Babar Loose-v 1.37±0.15±0.11 |Vub|= (3.7±0.20±0.20+0.6-0.4 )10-3 FNAL Error on the FF determination dominates the most precise results. What improvements with the full B-factories dataset ? Benoit VIAUD, SuperB workshop VI, Valencia

BF’s &|Vub| with 1ab-1 (Belle) and 0.75 ab-1 (Babar) σ  ~ 0.5 o The Stat Error will drop, but also the Systematic Error: • Systematics based on data/MC comparisons -> Btag efficiency (semileptonic tag analysis) -> Continuum events correction (loose-v, low q2) • Improved track and neutral reconstruction • Better knowledge of b->Xlν backgrounds (BF and FF) -> loose-v measurement at high q2 harder… Guesstimated uncertainties, in terms of B0->π-l+v(Combine B+& B0 ) Belle (~similar for Babar) |Vub|= (3.7±0.30+0.6-0.4 )10-3 |Vub|= (x.x±0.10+0.6-0.4 )10-3 -> The untagged analysis is the most promising at short term to measure BF’s, |Vub|, and constrain the FF Benoit VIAUD, SuperB workshop VI, Valencia

[1] Ball & al, hep-ph/0406232 [2] Becirevic & al, Phys. Lett. B478, 417 [3] Ex: Becher&Hill, hep-ph/0509090 [4] P. Ball, hep-ph/0611108 Form Factors Several parameterizations of the FF shape proposed to extend LCSR and LQCD’s predictions to the whole q2 spectrum… -Ball-Zwicky (BZ)[1] -Becirevic-Kaidalov (BK)[2] -Boyd/Grinstrin/Lebed+Hill/Becher (BGL)[3] Constraints from the measured ΔB(q2) ? α= 0.52 ± 0.05 ± 0.03 All three parameterizations give the same fit to the data [4]… => Data constrain only one shape parameter… |Vubf+(0)| = (9.6 ± 0.3 ± 0.2 )×10-4 Benoit VIAUD, SuperB workshop VI, Valencia

[1] Ball & al, hep-ph/0406232 [2] Becirevic & al, Phys. Lett. B478, 417 [3] Ex: Becher&Hill, hep-ph/0509090 [4] P. Ball, hep-ph/0611108 Form Factors Several parameterizations of the FF shape proposed to extend LCSR and LQCD’s predictions to the whole q2 spectrum… -Ball-Zwicky (BZ)[1] -Becirevic-Kaidalov (BK)[2] -Boyd/Grinstrin/Lebed+Hill/Becher (BGL)[3] Constraints from the measured ΔB(q2) ? All three parameterizations give the same fit to the data [4]… => Data constrain only one shape parameter… Linear or more ?? Current measurements can’t see anything beyond linearity… Benoit VIAUD, SuperB workshop VI, Valencia

A few questions at that point… • Are there well grounded additional theoretical constraints (beyond unitarity) that can make BGL parameterization differ from the other ones when fitted to the data ? • Or does it take additional data ? • Can we use BGL to publish values of |Vub| from the full BF ? • Should we measure partial BF in bins of z ? • Should we try a particular binning in z or q2 ? Babar’s untagged measurement Full dataset ! Most improved point: High z Improved Continuum ! Benoit VIAUD, SuperB workshop VI, Valencia

[1] Ball & al, hep-ph/0406232, arXiv:07063628 Form Factors: B->η(η’) lv Recent theoretical calculations: LCSR[1] Last paper includes the gluonic singlet contribution (U(1)A anomaly) to the B->η(‘) FF’s. Affects mostly B->η’. Contribution constrained by measuring Rη’η = B(B->η’lv)/B(B->ηlv) Rising experimental sensitivity Benoit VIAUD, SuperB workshop VI, Valencia

[1] Ball & al, hep-ph/0406232, arXiv:07063628 Form Factors: B->η(η’) lv Recent theoretical calculations: LCSR[1] Last paper includes the gluonic singlet contribution (U(1)A anomaly) to the B->η(‘) FF’s. Affects mostly B->η’. Contribution constrained by measuring Rη’η = B(B->η’lv)/B(B->ηlv) Rising experimental sensitivity o Soon: Untagged Measurement @ BaBar (314 fb-1) η’-> η with η->γ γ /  σBFtot ~ 20% σRηη ~ 30% (?) Expect ~ 700 (2000) signal events for η’ (η) (If BF=0.8410-4) σΔBF(q2) ~ 15-30% at low q2 Also measure ΔBF(q2) in 4 bins. Very limited by combinatorial bkg for q2>12 (16) GeV2 for η’(η). σRηηprobably better with partial rate (low q2). Benoit VIAUD, SuperB workshop VI, Valencia

Summary • Our knowledge of B->(,η’, η)lv decays improves fast ! • -> All modes are or will soon be measured with several • independent approaches. • Important improvement in the very next years • -> Statistics 2-4 • -> Systematics begins to be harder to reduce • for the most precise measurements. • The untagged approach is still the best one with the full • B-factories dataset • -> |Vub| with a 5% experimental error • -> Start to constraint on the FF shape • -> B->η(η’)lv : soon a stronger constraint on • the gluonic singlet and hopefully the first • measurement of FF Benoit VIAUD, SuperB workshop VI, Valencia

Other Questions • What can we learn from combinations of B-> (,η,η’)lv and • D-> (,η,η’)lv ? Enough to make it an experimental priority ? • Improvements in LQCD ? Normalization and Shape (mNRQCD) ? • In back-up • -> Minimum cut on plep allowing to survive the bkg ? • -> q2 resolutions ? Benoit VIAUD, SuperB workshop VI, Valencia

Minimal cut on variables biasing q2 distribution • Cuts already loose in Tagged analyses: • - plep cut down to ~ 0.5 GeV (hadronic tag) • - plep > 0.5 to 1.0 GeV (loose-v). • Difficult to further loosen… • No big bias on q2 for B->lv… Many bins -> Small bias semileptonic tag… loose v Benoit VIAUD, SuperB workshop VI, Valencia

q2 resolution • Hadronic tag measurement: q2=(pl+pmiss)2 with pmiss= pY(4S)–pBtag– pπ– pl • => q2 ~ 0.2 GeV2 • Semileptonic tag measurement: q2=(pB-p)2 assuming B at rest in Y(4S) frame • => q2 ~ 0.8 GeV2 (slight improvement at high q2) • Loose neutrino Benoit VIAUD, SuperB workshop VI, Valencia

B->η/η’ lv • CLEO’s untagged Analysis (15.5 fb-1, hep-ex/0703041 ) • η->γγ, π+π-π0 / η’->ρ0γ , η(γγ)π+π • Precise pmiss (hermeticity) allows tight v-cuts • Binned fit to ΔE-mES • X-feed modes (,)lv fitted simultaneously • Leading systematics: detector effects • B->(η, η’) lv with a hadronic tag • η->γγ, π+π-π0, π0π0π0 / η’->ρ0γ (ρ0-> π+π-), η π+π • method analogous to B->πlν • VERY LOW statistics B(η’lv)= (2.66±0.80±0.56)10-4, 41±12 signal events B(ηlv) < 1.01 10-4, 14±7 signal events QCD anomaly: B(η’lv)/B(ηlv) > 2.5 (90% C.L) B(ηlv)= (0.84±0.27±0.21)10-4, ~46 signal events B(η’lv) < 1.3 10-4, ~24 signal events Benoit VIAUD, SuperB workshop VI, Valencia

Form Factors: B->η(η’) lv Recent theoretical calculations: LCSR[1] Last paper includes the gluonic singlet contribution (U(1)A anomaly) to the B->η(‘) FF’s. Affects mostly B->η’. Contribution constrained by measuring Rη’η = B(B->η’lv)/B(B->ηlv) Soon at Babar: • Untagged Measurement (314 fb-1) Expect ~ 700 (2000) signal events for η’ (η) (If BF=0.8410-4) η’-> η with η->γ γ /  σBFtot ~ 20% for both channels… σRηη ~ 30% (?) Will also measure ΔBF(q2) in 4 bins. Very limited by combinatorial bkg for q2>12 (16) GeV2 for η’(η). Expect σΔBF(q2) ~ 15-30 % elsewhere… Benoit VIAUD, SuperB workshop VI, Valencia

Tagged Measurements: Form Factors Babar, all tags and modes combined. With the full B-factories dataset: ->constraint on FF close to that currently reached by the untagged analysis. Belle, Hadronic tag Belle, 1/2leptonic tag Benoit VIAUD, SuperB workshop VI, Valencia

Results: |Vub| & Form Factors BF= 1.46 ±0.07stat ± 0.08syst BK fit: α= 0.52 ± 0.05 ± 0.03 |Vubf+(0)| = (9.6 ± 0.3 ± 0.2)×10-4 Benoit VIAUD, SuperB workshop VI, Valencia

Other Channels: B→(η,η’,ρ)lν 316 fb-1 , slac-pub-11996 • B->(η, η’) lv with a hadronic tag • analogous to B->πlν • η->γγ, π+π-π0, π0π0π0 / η’->ρ0γ (ρ0-> π+π-), η π+π • VERY LOW statistics 46-24 sig. events • Ready soon: B->ηlv , untagged analysis • Nsig ~ 400 events , in 3 q2 bins 318 fb-1 • Ready soon: B->ρlv , untagged analysis • Nsig ~ 1000 events, in 3 q2 bins • Even with 1/ab, will be difficult to extract the full 4-D rate (54 bins !) Would need help from th. : integrate over the angles ? FF ratios ? 318 fb-1 • These measurements will yield a nice improvement of the experimental knowledge of these channels. Theoretical progress needed to fully take advantage of this (|Vub| extraction, constraints on FF,…) • Existing model: Ball-Zwicky [3] (not for η‘) ; Nothing (?) from LQCD… • Something new by the end of 2008 ?? Benoit VIAUD, SuperB workshop VI, Valencia

B→πlν , Hadronic Tag Nsig = 31± 7 • Tag BB event with Btag: fully reconstructed hadronic decay • Select B→π lν signal in the recoil of Btag: • one π l pair : pe(pμ) > 0.5(0.8) GeV • No other tracks, Eres small • Full reco. of Btag =>precise νreconstruction • ΔE, mES,, pmiss= pY(4S) – pBtag – pπ–pl , m2miss • q2=(pl+pν)2 =(pl+pmiss)2 • B→π lνextracted in 3 q2 bins • mES fit in m2miss bins to subtract combinatorics/non BB events • other backgrounds: MC, rescaled with m2miss sideband • ΔBF(B→π lν) from the ratio of B-> π lν yields to B->Xlν yields + BF(B->Xlν): σsyst↓ Nsig = 26± 7 Benoit VIAUD, SuperB workshop VI, Valencia

B→πlν , semileptonic Tag • Tag BB event with Btag: B->D(*)lν • D0->K-(π+, 3πππ, π+π0), K0s π+π- ; D+-> K- 2π; D(*+)->D+/0π0/+ • mD , |pl| > 0.8 GeV, Dl vertex,… • Select B→π lν signal in the recoil of Btag: • one π lpair : pl >0.8 GeV • no other tracks, Eres small • q2=(mB-Eπ)2-|pπ|2(assume B at rest in Y(4S) frame) • Signalextraction: global event topology, 3 q2 bins Fit to cos2ΦB : - simultaneous to data and MC, - MD sideband included to constrain combinatorial background • ΔBF(B→π lν): εfrom MC +data control samples • events with 2 non-overlapping Btag’s Nsig = 57± 13 Nsig = 92± 25 Benoit VIAUD, SuperB workshop VI, Valencia

5 Untagged B0->π-l+ν, loose ν-reconstruction • Novel technique ! No tight ν-reconstruction cuts : Signal Yield ↑ Purity ↓ • πlpair: tight πand l ID criteria, |pe(μ)|>0.5(1) GeV, |cosθBY|<1 • Topology cuts to reduce non BB events. • Cuts optimized as a function of q2: Angle between Y and rest of event thrust axes, pmiss polar angle and m2miss , W helicity angle • Signal efficiency from 6.7% to 9.8 % (depending on q2) • q2=(pB-pπ)2 with the “Y-average frame” method average over arbitrary azimuth Φ, Φ+90°, Φ+180°, Φ+270° σ=0.53 GeV2 Corrected by an unfolding procedure Benoit VIAUD, SuperB workshop VI, Valencia

B→πlν , Hadronic and semileptonic Tags Nsig = 26± 7 Nsig = 31± 7 (B0) = 26 ±7 (B+) Once a BB event is tagged by finding a Btag … • Select B→π lν signal in the recoil of Btag: • Only one π-lpair, No other tracks, small residual energy • B→π lνextracted in 3 q2 bins hadr. tag: -q2=(pl+pmiss)2, pmiss= pY(4S)–pBtag– pπ–pl=pν -mES fit in m2miss bins to subtract combinatorics/ non BB -other backgrounds: MC, rescaled with m2misssideband -ΔBF(B→π lν) from the ratio of B-> π lν yields to B->Xlν yields + BF(B->Xlν): σsyst↓ ½-lep. tag: -q2=(mB- Eπ)2 -|pπ|2 ( hypo: B at rest in Y(4S) frame) -Fit to cos2ΦB -ΔBF(B→π lν): efficiency from MC & data control samples (events with 2 non-overlapping Btag’s) Nsig = 57± 7 (B0) = 92±7 (B+) Benoit VIAUD, SuperB workshop VI, Valencia

few definitions… In the Y(4S) frame: EB, pB= nominal values of the B energy and momentum, from 4-mom. conservation pY = pπ+pl |cosθBY| and |cos2ΦB| <1 if the ν’s are the only undetected particles… Benoit VIAUD, SuperB workshop VI, Valencia

211 fb-1 , hep-ex/0607089 B→πlν, Hadronic and semileptonic Tags Nsig = 31± 7 (B0) = 26 ±7 (B+) Once a BB event is tagged by finding a Btag … • Select B→π lν signal in the recoil of Btag: • Only one π-lpair, pe(pμ) > 0.5(0.8) GeV • No other tracks, small residual energy • B→π lνextracted in 3 q2 bins hadr. tag: -q2=(pl+pmiss)2, pmiss= pY(4S)–pBtag– pπ–pl=pν -Nsig = (data – Backgrounds from MC), MC rescaled with m2misssideband ½-lep. tag: -q2=(mB- Eπ)2 -|pπ|2 ( hypo: B at rest in Y(4S) frame) -Fit to cos2ΦB (<1 for clean signal events where only the νare undetected) Nsig = 57± 7 (B0) = 92±7 (B+) Benoit VIAUD, SuperB workshop VI, Valencia

Combine Hadronic & Semileptonic Tags, B+ & B0 ΔBF( ) ΔBF( )BF • weighted averages + isospin symmetry: Γ(B0->π-l+ν)=2Γ(B+->π0l+ν) LCSR HPQCD FNAL • Limited by statistics. Total exp. error already of the same order as th. error ! • Largest systematics: • hadronic: limited statistics of the signal MC sample, mES fit, neutral and μreconstruction BF of B->Xulν background decays. • 1/2leptonic: Btag efficiency, cos2ΦBshape for backgrounds, BF of semileptonic backgrounds Benoit VIAUD, SuperB workshop VI, Valencia

σ |V ub | at SuperB ??

σ |V ub | at SuperB ??

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