I N S T I T U T E FOR HIGH ENERGY P H Y S I C S И В Э 81-в5 Н V.V.Ammosov, A.G.Denisov, P.F.Ermolov, G.S.Gapienko, V.A.Gapienko, V.I.Klyukhin, V.I.Koreshev, P.V.Pitukhin, V.I.Sirotenko, E.A.Slobodyuk, Z.U.Usubov, V.G.Zaetz (Institute of High Energy Physics, Serpukhov, USSR) J.P.Berge, D.Bogert, R.E^idorf, R.Hanft, J.A.Malko, F.A.Nezrick, R.Orava (Fermi National Accelerator Laboratory Batavia, Illinois 60510 USA) s V.I.Efremenko, A.V.Fedotov, R.A.Gorichev, V.S.Kaftanov, G.K.Kliger, V.Z.Kolganov, S.P.Rrutchinin, M.A.Kubantsev, I.V.Makhljueva, V.I.Shekeljan, V.G.Shevchenko (Institute for Theoretical and Experimental physics Moscow, USSR) J.Bell, C.T.Coffin, B.P.Roe, A.A.Seidl, D.Sinclair, E.Wang (University of Michigan,Ann Arbon, Michigan 481 USA) OBSERVATION OF /* + e + -EVENTS IN ANTINEUTRINO-NUCLEON INTERACTIONS Fermi'lab-IHEP-ITEP-Michigan University Collaboration Serpukhov 1981
V.V.Ammosov, A.G.Denisov, P.F.Ermolov, G.S.Gapienko, V.A.Gapienko, v.i.klyukhin, V.I.Koreshev, P.V.Pitukhin, V.I.Sirotenko, E.A.Slobodyuk, Z.U.Usubov, V.G.Zaetz (Institute of High Energy Physics, Serpukhov, USSR) J.P.Berge, D.Bogert, R.Endorf, R.Hanft, J.A.Malko, F.A.Nezrick, R.Orava (Fermi National Accelerator Laboratory Batavia, Illinois 60510 USA) V.I.Efremenko, A.V.Fedotov, P.A.Gorichev, V.S.Kaftanov, G.K.Kliger, V.Z.Kolganov, S.P.Krutchinin, M.A.Kubantsev, I.V.Makhljueva, V.I.Shekeljan, V.G.Shevchenko (Institute for Theoretical and Experimental Physics Moscow, USSR) J.Bell, C.T.Coffin, B.P.Roe, A.A.Seidl, D.Sinclair, E.Wang (University of Michigan,Ann Arbon, Michigan 481 USA) OBSERVATION OF ц + е + -EVENTS IN ANTINEUTRINO-NUCLEON INTERACTIONS Fermilab-IHEP-ITEP-Michigan University Collaboration Submitted to Phys. Lett.
M-24 Abstract Aaraosov V.V., Berge J.P., Bell J., Bogert D., Coffin C.T., Denisov A.G., Efremenko V.I., Endorf R., Ermolov P.F., Fedotov A.V., Gapienko G.S., Capienko V.A., Gorichev P.A., Hanft R., Kaftanov V.S., Kliger G.K., Xlyukhln V.I., Kolganov V.Z., Koreshev V.I., Krutchinin S.P., Kubantsev М.Л., Hakhljueva I.V., Halko J.A., Nezrick F.A., Orava R., Pitukhin P.V., Roe B.P., Seidl A.A., Shekeljan V.I., Shevchenko V.G., Sinclair D., Sirotenko V.I., Slobodyuk E.A., Usubov Z.V., Wang E., Zaetz V.G. Observation of p + e + Events in Antineutrino-Nucleon Interactions. Serpukhov, 1981. p.. (IHEP 81-65). Refs. 9. The first observation of ц + е + events produced from antineutrino interactions in the Fernilat/ 15 ft bubble chamber is reported. The relative yield of /i + e + events is (4.8 + - )10~ 4 of all charged-current events with antineutrino energy greater than 10 GeV. The observed V rate is 1.0 ti'i per ц*е* event. Possible sources of these events are discussed. Аннтация Аммсв В.В., Еэрге Дж.П., Белл Дж., Бгерт Д., Вант Е., Гапиенк В.А., Гапиекк Г.С., Грячев П.А., Денисв А.Г., Ермлв П.., Ефременк ВЛ., Заец В.Г., Кафтанв B.C., Клкгер Г.К., Клюхнк В.И., Крешев В.И., Клганв В.З., Кффин К.Т., Кручинин СП., Кубашев М.А., Малк Дж., Махлюе - ва И.В., Неэрик.А., рава Р., Питухкн П.В., Ре Б.П., Сейдл А.А., Синклер Д., Сиртекк В.И., Слбдюк Е.А., Усубв З.У, едтв A3., Ханфт Р., Шекелян В.И., Шевченк В.Г., Энарф Р. Наблюдение ц + е + -сбытия в ант«не*трик-яужлнных взаимдействиях. Серпухв, 1981. стр. с рис. (ИВЭ Н 81-65). Библигр. 9. Сбщается первм наблюдении ft e сбытий, бразванных в антинейтринных взаимдействиях на 15-футвй пузырьквй камере )кци1ич6. тнсительный выхд м + е + -сбытий сставляет (4.8^ i3)-10-* т всех сбытий зараженнг тка для энергии антинейтрин бльше 10 ГэВ. Средняя мнжественнсть видимых У -частиц в fi + e + -сбытиях равна l.o^j.g. бсуждаются взмжные истчники ц + е + -сбытий.
The production of opposite sign dileptons in charged current (CC) neutrino and antineutrino interactions is well studied and understood in the framework of the GDI scheme as the production and the subsequent decay of charmed hadrons. A study of the same sign dilepton events is a major experimental problem. There are indications of a signal in several experiments'*' 2 ', however a source of their production is still unclear. Here we report a clear observation of 4 ц + е* events three of which have neutral strange particle decay (V ю 's). Possible sources of these events are discussed. The data are based on a wide-band antineutrino exposure of 85 0 pictures obtained with the Fermilab 15 ft bubble chamber filled with a hydrogen-neon mixture containing 64% atomic neon. The mixture has a density of 0.74 g/cm, radiation length 39 cm and visible interaction length 140 cm. In contrast to our previous p+e' /3/ paper the analysis of p^e* events has been performed after all neutral induced events completely measured and processed by the geo- q
metry reconstruction program. The number of ^ CC events in the fiducial volume of 17 m passing E_ > 10 GeV*^ and P > 4 GeV/c cuts was 6 780 events. Jfuons were identified by the External ltuon Identifier (EMI) supplemented by a kinematic large transverse momentum procedure. After corrections for scanning efficiency (95%) and one to prong event losses (3.8%) we estimate the " CC sample to contain 7 410 events. These events have the average energy, <E->»32 GeV, and the average invariant hadronic energy, <W>~4 GeV. The selection criteria for positrons were the same as described in ref.' 3 Л A small electromagnetic background allowed one to make lower a cut for a positron momentum (P ) down to 0.4 GeV/c. e Four ^+e + candidates were selected which passed P > 4 GeV/c and P +> P e > 0.4 GeV/c cuts. In table 1 we list the properties of these events. Muons were identified both with the EMI and the kinematic procedure for all fi + e events. Positron energies were defined from curvature measurements and corrected, where appropriate, for detected brems - strahlung conversion.in each p*e* event the invariant mass of the positron with other negative noninteracting tracks was greater than the 7i mass. The V *s were detected in 3 ^" l "e + events. They were identified as K g -»jr"v~and Л ->p ff ~ decays with kinematic fitting. Kinematic values for p + e + events were calculated using event-by-event energy correction procedure' 5 '. E p for a usual Г СС event we» estimated using an average correction for hadron energy losses as described in ref.'*'. Lost one prong events лт» concentrated in the region of small jr. These losses were estimated using our measured y-distributlon.
In order to evaluate the significance of 4 ft + e + canditates the most important backgrounds are considered: (1) The v u CC events with asymmetric close-in у conversions having an undetected electron (P < 5 MeV/c). We determined that the e points of у conversions could not be separated within 1 cm from the primary vertex. This background estimated from experimental characteristics of у conversions is equal to 0.38 events. (2) Direct production of e + e~ pairs from scalar and vector meson decays having an undetected or unidentified electron. This background contributes 0.36 event. (3) Small-angle К decays. The minimal detectable angle of e3 emitted positron is determined from measured kinks to be 5 in space. The expected number of events is estimated by the K decay momentum spectrum to be 0.14, assuming the average К multiplicity of 0.1. (4) The v e CC events with leaving positive hadrons falsely identified as muons in the mi. The probability of misidertiification per event is determined from 3 " p + ц + events" in our experiment. Each of our p + e + events has P + >P + which is taken into account. The expected background is calculated from 74 observed events identified as? e CC events, then its contribution is 0.24 event. This leads to the total background of 1.1 events. The probability that the 4 p + e + events are caused by the background is 2.5%.
Three of p + e* events have V 's. Taking into account the rate for /6/ antineutrino CC events with V 's of 6.9%', the background for the 3 ft + e + V events is estimated to be 0.076 event. The probabi lity that 3 fi*e+v events are due to the background is equal to 7-10" 5. After subtracting the background and correcting for the positron selection efficiency (83%) we obtain the following yields of /* + e + and ii + e*v o events relative to»^cc events for E_ >10 GeV, P > 4 GeV/c and P + >0.4 GeV/c: V- e + + ff( /i e + )/a( M +) = (4.8 1з;!>-Ю- 4, а^+е+у 0 )/^) = (4.9 la!?)' 10 " 4 - The 90% confidence level lower limits for the relative production of /n + e + and /^e+v 0 events are 1.1 *10~ and 1.7* 10 ^, respectively. Our estimation for /z + e + production is by an order of magnitude greater than the CDHS rate of c(p + р+)/(ац + )= (4.3 ± 2.3)«10" 5/7/ obtained in a wide band v beam for E_>30 GeV/c and P>6.5 GeV/c. This may be due to a more severe cut on a muon momentum in the CDHS experiment. Using our previous estimation for the p+e~ rate of (0.36 ± 0.)% /3/ we obtain the ratio of o( M + * + )/o(/ob 0.13 +0.1*. -0.09 This rate is compatible with the CDHS value of (р+ + )/<т(р + р-) = = (4.2 2.3)-10~ 2/7/. The ratio of P /P e and the azimuthal angle ф m between muon and electron momenta in the plane normal to the neutrino direction 6
are generally used to determine the origin of direct electrons in opposite sign ц e events. For our /x + e + sample we have<p /P e "> = = 23 and <ф >= 340 (see table 1),which suggests a strong indication that positrons of p + e + events are likely to have a hadronic origin. There are 3 V 's associated with 4 ц + е + events. This differs markedly from 0.29 V 's expected for 4 ordinary CC events.the average multiplicity of the observed V ot s in ц + е + events after background sub- +1 2 traction is 1.0 _i*n«thus a semileptonic decay of charmed hadrons due to the quark decay: с -»se + i/ e is the only appropriate source for the production of ц + е + events in V CC interactions in the framework of 6 quark models. The V e + invariant masses shown in table 1 do not contradict usually treated semileptonic decays of charmed hadrons. Figure 1 shows distributions of P, ut, the transverse momentvm of a particle perpendicular to the well defined п /z + plane, and Z = E. /(S E ) for all particles from jfe + events excluding I y's and muons. The same distributions are displayed for ц + е~ and 1 /z + samples,and also for V 's and e + 's from p + e + events.the average values of P and Z are presented in table 2.There are no significant peculiarities of P, ut distribution for p + e + events compared to l/i and fi + e + samples. The Z-distribution for p+e* events is softer than V the ones for lp + and ц + ё~ samples. It seems that the Z-distribution for V 's and positrons of ft + e + events is harder than for all particles.
At least three possible interpretations of /x + e + pairs with associated strange particle production in i7 CC interactions exist now. They are (a) D production with the following 5 -»D regeneration, (b) cc production with a hadronic с decay, (c) beauty production with a subsequent hadronic decay of b-»cx. For all cases the creation of /* + e + pairs is due to the с-* se + i/ e quark transition. Consider these possibilities: (a) Using the upper limit for the D -D mixing of 0.025 obtai- /8/ ned from the DELCO experiment' ' we see that it is difficult to produce 4 fi + e + events. Furthermore from this hypothesis, it is a problem to understand the difference between <Z> of hadrons in ц+е~ and p+e events. (b) Three p + e* events have the invariant hadronic energy greater than 4 GeV and can be attributed to cc production. The yield of these (?е + events is relative to V CC events with E_> 10 GeV and P >4 GeV/c. It is significantly greater than the prediction of the gluon bremsstrahlung model /9/ which is~4-10~ 7 (m c =1.5 GeV, Br(c-»e + v.x) = 0.1) for our energy interval. However we observe one K s and one A decays in 3 ц + е events which does not contradict the expected value of 2 strange particles per event for cc production scheme. (c) In antineutrino interactions the simplest way of the beauty production is a two-body production of В baryons: v К-* u + B C 8
The mass of В baryons may be~5.6 GeV. Under the assumption on 2ц + е + events with Vf> 5.6 GeV to appear due to the beauty production we obtain that the rate of a { /i+ e + ; W > 5.6)/(^+) equals (2.7 ^-^)'10~ A for v,, CC sample with E_>10 GeV and P >4 GeV/c. Normalization to M v ft the РдСС sample with W>5.6 GeV gives aiv u-»bx)br(b -cx)br(c- + e i/x)/ CT (» + ) = (2.0 *?'б>-10. e 1#D P W>5.6 The observation of one Л decay in 2 fi + e events with W> 5.6 GeV does not contradict the expected 1.5 strange particles per event for the beauty product ion. Finally we conclude that the first clear signal of ц + е + pair production in v CC interactions has been observed. Positrons for those events have a hadronic origin. A significant excess of neutral strange particles for р + е + events is observed. A semileptonic charmed hadron decay due to the quark transition с-> se*i/ e is the only reasonable way to understand this phenomenon. The cc pair production in v CC interactions seems to be a possible source of с quark produc- At tion. However the observed yield of ц е events is significantly greater than the one expected in the frame of the current theoretical estimations. It cannot be excluded that production and decay of beauty hadrons are an additional source for the м +е+ event creation. We thank A.E.Asratyan, S.S.Gershtein, A.K.Likhoded, S.R.Slabospitsky and G.G.Volkov for valuable discussions. 9
ф гч 0) +> 8 к«н <а н +> ', I ф С се л Еч ft «н «Н 0 X ш а. *9- ft ft (GeV, \ L(Ge 1? 0 > > ее) hft (Ge (Ge ш < и eo с* 41* (0 1П 1» Т1 " 1 1П d CO f» on n n in CO n 1 1 4, (0 c. in en n S, d ГЧ 0) n t- o t» (0 ii ii гч Л м ф ce to а a н e л ев м to ф гн (ч 3, +>Н g «н с се я > м с ^ + з «н s гн «Н 3 + св-нпз. ф в Л 0 N1 <н ь 5 п н н Sol а to + н се п а и с +* ф + се + + ч» «^ / a A 1/>Н V ев 1П 4 и 5, г* ii f- -+1 ( t~ * ц л р н ft V в) и iin d r> +1 ю и d ±0.0 гн л N V W > in CO 26. 92. TP n 45. ri CO 10
(b) 20 СС sample (а) Ю 15 10 8 б (Л а: - \ ч ЯШ.... Ч I С С sample /** e^s from /л*е* -V. * : < с 10К - V s,e*'s f rom/ffe* je* j i л. i 0.0 0.1 0.2 03 0-5 06 07 OS Je* 0.1 02 03 05 0.6 2 Fig. 1. Distributions of (a) P ut and (b) Z for all particle*, excluding y's and muons In fl + e + events (solid histogram»), p+e~ events (dashed histograms) and ~ (t CC events (dashed-dotted curves). The p + e~ and CC samples are normalized to the (i + e + sample. Distributions for V е "» and e + 's of it + e + events are shown by dotted histograms. REFERENCES 1. M.J.lfurtagh. Proc. of the 1979 Intern. Symp. on Lepton and Photon Interactions at High Energy, Fermilab (USA), 1979,p.277. 2. S.Wojcicki. Proc. of the XX Intern. Conf. on High Energy Physics, Madison (USA), 1980. 3. J.P.Berge et al. Phys. Lett., 81B (1979) 89. 4. J.P.Berge et al. Phys. Rev. Lett., 39 (1977) 382. 5. G.Myatt. CERN/ECFA 72-4, (1972). 6. V.V.Ammosov et al. Preprint IHEP 80-124, Serpukhov, 1980. 7. J.De Groot et al. Phys. Lett., 86B (1979) 103. 8. K.Winter. Proc. of the 1979 Intern. Symp. on Lepton and Photon Interactions at High Energy, Fermilab (USA), 1979, p. 258. 9. K.Hagiwara. Nucl. Phys., B173 (1980) 487. Received 2 April 1981.
Цена в кп. - Институт физики выских энергий, 1961. Издательская группа И В Э Заказ 458. Тираж 270. 0,5 уч.-изд.л. Т-06888. Апрель 1961. Редактр А.А. Антипва.