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CLNS 97/1460CLEO 97-1Studies of the Cabbibo-suppressed decays D +→π0ℓ+νand D +→ηe +νe CLEO Collaboration (February 7,2008)Abstract Using 4.8fb −1of data taken with the CLEO II detector,the branching fraction for the Cabibbo suppressed decay D +→π0ℓ+νmeasured relative to the Cabibbo favored decay D +→
J.Bartelt,1S.E.Csorna,1V.Jain,1S.Marka,1A.Freyberger,2R.Godang,2K.Kinoshita,2
I.C.Lai,2P.Pomianowski,2S.Schrenk,2G.Bonvicini,3D.Cinabro,3R.Greene,3
L.P.Perera,3G.J.Zhou,3B.Barish,4M.Chadha,4S.Chan,4G.Eigen,4J.S.Miller,4
C.O’Grady,4M.Schmidtler,4J.Urheim,4A.J.Weinstein,4F.W¨u rthwein,4
D.M.Asner,5
D.W.Bliss,5W.S.Brower,5G.Masek,5H.P.Paar,5V.Sharma,5J.Gronberg,6T.S.Hill,6 R.Kutschke,6D.J.Lange,6S.Menary,6R.J.Morrison,6H.N.Nelson,6T.K.Nelson,6
C.Qiao,6J.
D.Richman,6D.Roberts,6A.Ryd,6M.S.Witherell,6R.Balest,7
B.H.Behrens,7K.Cho,7W.T.Ford,7H.Park,7P.Rankin,7J.Roy,7J.G.Smith,7 J.P.Alexander,8
C.Bebek,8B.E.Berger,8K.Berkelman,8K.Bloom,8
D.G.Cassel,8 H.A.Cho,8D.M.Coffman,8D.S.Crowcroft,8M.Dickson,8P.S.Drell,8K.M.Ecklund,8
R.Ehrlich,8R.Elia,8A.D.Foland,8P.Gaidarev,8B.Gittelman,8S.W.Gray,8
D.L.Hartill,8B.K.Heltsley,8P.I.Hopman,8J.Kandaswamy,8N.Katayama,8P.C.Kim,8 D.L.Kreinick,8T.Lee,8Y.Liu,8G.S.Ludwig,8J.Masui,8J.Mevissen,8N.B.Mistry,8 C.R.Ng,8
E.Nordberg,8M.Ogg,8,∗J.R.Patterson,8D.Peterson,8D.Riley,8A.Soffer,8 C.Ward,8M.Athanas,9P.Avery,9C.D.Jones,9M.Lohner,9C.Prescott,9J.Yelton,9 J.Zheng,9G.Brandenburg,10R.A.Briere,10Y.S.Gao,10D.Y.-J.Kim,10R.Wilson,10
H.Yamamoto,10T.E.Browder,11F.Li,11Y.Li,11J.L.Rodriguez,11T.Bergfeld,12 B.I.Eisenstein,12J.Ernst,
12G.E.Gladding,12G.D.Gollin,12R.M.Hans,12E.Johnson,12 I.Karliner,12M.A.Marsh,12M.Palmer,12M.Selen,12J.J.Thaler,12K.W.Edwards,13
A.Bellerive,14R.Janicek,14D.
B.MacFarlane,14K.W.McLean,14P.M.Patel,14
A.J.Sadoff,15R.Ammar,16P.Baringer,16A.Bean,16D.Besson,16D.Coppage,16
C.Darling,16R.Davis,16N.Hancock,16S.Kotov,16I.Kravchenko,16N.Kwak,16
D.Smith,16S.Anderson,17Y.Kubota,17M.Lattery,17S.J.Lee,17J.J.O’Neill,17
S.Patton,17R.Poling,17T.Riehle,17V.Savinov,17A.Smith,17M.S.Alam,18 S.B.Athar,18Z.Ling,18A.H.Mahmood,18H.Severini,18S.Timm,18F.Wappler,18 A.Anastassov,19S.Blinov,19,†J.E.Duboscq,19K.D.Fisher,19D.Fujino,19,‡R.Fulton,19 K.K.Gan,19T.Hart,19K.Honscheid,19H.Kagan,19R.Kass,19J.Lee,19M.B.Spencer,19 M.Sung,19A.Undrus,19,†R.Wanke,19A.Wolf,19M.M.Zoeller,19B.Nemati,20
S.J.Richichi,20W.R.Ross,20P.Skubic,20M.Wood,20M.Bishai,21J.Fast,21E.Gerndt,21 J.W.Hinson,21
N.Menon,21D.H.Miller,21E.I.Shibata,21I.P.J.Shipsey,21M.Yurko,21 L.Gibbons,22S.D.Johnson,22Y.Kwon,22S.Roberts,22E.H.Thorndike,22C.P.Jessop,23 K.Lingel,23H.Marsiske,23M.L.Perl,23S.F.Schaffner,23D.Ugolini,23R.Wang,23
X.Zhou,23T.E.Coan,24V.Fadeyev,24I.Korolkov,24Y.Maravin,24I.Narsky,24
V.Shelkov,24J.Staeck,24R.Stroynowski,24I.Volobouev,24J.Ye,24M.Artuso,25
A.Efimov,25F.Frasconi,25M.Gao,25M.Goldberg,25D.He,25S.Kopp,25G.C.Moneti,25 R.Mountain,25S.Schuh,25T.Skwarnicki,25S.Stone,25G.Viehhauser,25and X.Xing25
1Vanderbilt University,Nashville,Tennessee37235
2Virginia Polytechnic Institute and State University,Blacksburg,Virginia24061 3Wayne State University,Detroit,Michigan48202
4California Institute of Technology,Pasadena,California91125
5University of California,San Diego,La Jolla,California92093
6University of California,Santa Barbara,California93106
8Cornell University,Ithaca,New York14853
9University of Florida,Gainesville,Florida32611
10Harvard University,Cambridge,Massachusetts02138
11University of Hawaii at Manoa,Honolulu,Hawaii96822
12University of Illinois,Champaign-Urbana,Illinois61801
13Carleton University,Ottawa,Ontario,Canada K1S5B6
and the Institute of Particle Physics,Canada
14McGill University,Montr´e al,Qu´e bec,Canada H3A2T8
and the Institute of Particle Physics,Canada
15Ithaca College,Ithaca,New York14850
16University of Kansas,Lawrence,Kansas66045
17University of Minnesota,Minneapolis,Minnesota55455
18State University of New York at Albany,Albany,New York12222
19Ohio State University,Columbus,Ohio43210
20University of Oklahoma,Norman,Oklahoma73019
21Purdue University,West Lafayette,Indiana47907
22University of Rochester,Rochester,New York14627
酒会音乐23Stanford Linear Accelerator Center,Stanford University,Stanford,California94309 24Southern Methodist University,Dallas,Texas75275
25Syracuse University,Syracuse,New York13244
3
Interpretation of semileptonic decays of charm mesons is theoretically straightforward. Amplitudes of decay modes are proportional to the CKM matrix elements and the form factors describing the strong interactions between thefinal state quarks.In this paper we study the Cabibbo suppressed decays D+→π0ℓ+νand D+→ηℓ+νby measuring the ratios Rπ=B(D+→π0ℓ+ν)/B(D+→
(1−q2
K0ℓν.The factor c21 accounts for the d
d),and1for the s).There are several models that predict these rates[4,5]. Using the framework of Heavy Quark Effective Theory and symmetry arguments,measured form factors from semileptonic charm decays can be compared to those for the appropriate b→u decays[6]used to extract|V ub/V cb|.
王力宏扇刘谦While the Cabibbo-favored modes in charm semileptonic decay have been well measured [1,7],there are relatively few measurements of Cabibbo-suppressed semileptonic decays.Pre-vious CLEO results for the ratio Rπ[8]are based on a total luminosity of2.1fb−1,and are superceded by the results presented in this paper.The ratio of branching fractions R−=B(D0→π−ℓ+ν)/B(D0→K−ℓ+ν)is related to Rπby isospin(Rπ=0.5R−).Mark III[9],Fermilab E687[10],and CLEO[11]have reported results for B(D0
→π−ℓ+ν)giving
a current world average for R−=0.102+0.017
−0.016.
The data sample used for this analysis was recorded with the CLEO-II detector[12] operating at the CESR storage ring at Cornell University.A total luminosity of4.8fb−1of e+e−collisions was recorded at theΥ(4S)resonance and in the continuum nearby.
In D+decays,the combinatoric background can be suppressed by requiring that the D+ be produced in the decay chain D∗+→D+π0.The CLEO-II detector,with its excellent photon detection efficiency,is ideally suited for detecting the neutral pions from this decay. Because thefinal state neutrino is not detected in semileptonic decays,we defineδm=
cherylcoleMπ0
S h Fℓ+
−M h
Fℓ+
,where h F refers to the D+daughter meson,the“fast”π0(π0F),the
afromanElectrons with momenta above0.7GeV/c are identified by requiring that the ratio of the energy(E)deposited in the CsI calorimeter and the momentum(p)measured in the tracking system,E/p,be close to unity and that the energy loss measured by the tracking system be consistent with the electron hypothesis.Muons with momenta above1.4GeV/c are identified by their ability to penetratefive nuclear interaction lengths.Electrons(muons) within thefiducial volume are identified with an efficiency of94%(93%).The probability of a hadron being misidentified as a lepton is(0.20±0.06)%for electrons and(1.4±0.2)%for muons.We require the leptons to be found in the central region of the detector,where the resolution is best and the acceptance well-understood.
Isolated photons detected by the CsI calorimeter with a minimum energy of30MeV are paired to formπ0andηcandidates.For the slow pion,theγγmass is constrained to be within2.5standard deviations(about12.5MeV/c2)of the nominalπ0mass.For the fastπ0(η),the reconstructed mass is required to be within the range0.105-0.165GeV/c2 (0.510-0.585GeV/c2).The decay channelη→π+π−π0was not considered because of its low reconstruction efficiency.For the normalizi
ng D+→K0 through theπ+π−decay of its K S component.We require theπ+π−pair to form a secondary vertex of the correct mass that is displaced at least four standard deviations from the primary vertex.
Combinatoric backgrounds are reduced by several means.We impose the kinematic crite-
ria0.175≤pπ0
S <0.350GeV/c,p h
F
≥0.7GeV/c,and| p h
F
+ pℓ|≥2.1GeV/c.Backgrounds
from B meson decay are reduced by requiring that the ratio of Fox-Wolfram moments[13] R2=H2/H0satisfy R2≥0.2.Finally,we consider only well-measured tracks and events with a hadronic event structure.
Backgrounds can be divided into four classes:fake slow pions(fake D∗s),fake fast hadrons,fake leptons,and uncorrelated fast-hadron,lepton pairs(fake D+s).The major contribution to the fake D+background in the D+→π0ℓ+νchannel comes from feed-down from D+→K0→π0π0.We can correct for this background knowing only the ratio of the reconstruction efficiency for D+→π0ℓ+νto the efficiency to reconstruct D+→K0→π0π0asπ0ℓ+ν,which we determine from Monte Carlo simulation. Monte Carlo studies indicated that the feedthrough from other semileptonic charm decays and from B
K0,andηmodes. Figure3shows the fast hadron mass distributions.Thefits used a parametrization of the fast hadron mass obtained byfitting these one-dimensional projections.The signal shape in δm was determined fromfits to the distributions of reconstructed signal Monte Carlo.The fake lepton background was determined by performing afit to the distributions of events which satisfied all requirements except for the lepton identification requirement.The signal yields from thesefits were then scaled by the measured misidentification probabilities and subtracted from the yields from thefit to the data.The parameterization of the fake D∗background inδm was determined by looking at a sample of data events whose fast hadron mass was more than4sigma from the nominal mass.The si
gnal yields,fake lepton yields,and signal reconstruction efficiencies are presented in Table I.The efficiencies were determined
5
fromfits to the distributions from samples of reconstructed signal Monte Carlo.
With the results from thefits given in Table I,we proceed to calculate the ratio of branching fractions Rπ=[B(D+→π0ℓ+ν)]/[B(D+→
N(K0Sℓ+ν)ǫK0ℓ+ν)
K0ℓ+ν
(π0ℓ+ν)
K0ℓ+ν
(
K0ℓ+νdecay to be reconstructed as
K0ℓ+ν(π0ℓ+ν)is the
efficiency for a
K0e+νe channels.The systematic error in the ratio due to Monte Carlo simulations of K0S→π+π−andπ0F→γγis conservatively placed at10%.Other systematic errors for the electron channel include: statistical error on efficiencyfits from Monte Carlo samples(7%),fake lepton subtraction (7%),D+→
B feeddown(13%).The systematic errors are added in quadrature to obtain a total systematic error in the ratio for electrons of41%.
Thefit to the D+→ηe+νchannel yielded6±8events.We did not consider the muon channel due to the low detection efficiency.To obtain an upper limit on Rη,we scale this yield by the reconstruction efficiency of(0.26±0.02)%,and normalize to the average D+→π0ℓ+νyield of(4.39±2.22)×103events.The latter was estimated from our Rπmeasurement and the average of the efficiency-corrected yields for D+→
B(D+→π0ℓ+ν)=<1.5.at the90%confidence level.This result is
dominated by statistical error,but includes a30%systematic error that was combined in quadrature with the statistical error.
We have measured the branching fraction of the Cabibbo suppressed decay D+→π0ℓ+νrelative to D+→
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