Cross sections for neutrino production of charmed particles

Volume 206 number 2 PHYSICS LETTERS B 19 May 1988

CROSS SECTIONS FOR NEUTRINO PRODUCTION OF CHARMED PARTICLES

F e r m i l a b E5 31 C o l l a b o r a t i o n

N. U S H I D A a, T. K O N D O b, S. T A S A K A c, I .G. P A R K d, J.S. S O N G d, T. H A R A ¢, Y. H O M M A e, Y. T S U Z U K I e, G. F U J I O K A f H. F U K U S H I M A f Y. T A K A H A S H I f, S. T A T S U M I ~, C. Y O K O Y A M A f K. F U J I W A R A g, K. T A R U M A g, S.Y. B A H K h, C.O. K I M h, J .N. P A R K h, D.C. B A I L E Y i, S. C O N E T T I i, p. M E R C U R E i, j . T R I S C H U K i, M. T U R C O T T E i, S. A O K I J, K. C H I B A J, H. F U C H I 3, K. H O S H I N O J, K. K O D A M A J, R. M A T S U I J, M. M I Y A N I S H I J, M. N A K A M U R A J, K. N A K A Z A W A J, K. N I U J, K. N I W A J, M. O H A S H I J, H. S A S A K I J, Y. T O M I T A J, N. T O R I I J, O. Y A M A K A W A J, Y. Y A N A G I S A W A J, G.J . A U B R E C H T II k J. D U N L E A k, S. E R R E D E k, A. G A U T H I E R k, M.J. G U T Z W I L L E R k, S. K U R A M A T A k, G. O L E Y N I K k, N .W. R E A Y k, K. R E I B E L k, R.A. S I D W E L L k, N .R . S T A N T O N k, K. M O R I Y A M A ~, H. S H I B A T A ~, O. K U S U M O T O m, y . N O G U C H I m, T. O K U S A W A m, M. T E R A N A K A m, J. Y A M A T O m, H. O K A B E n, j . Y O K O T A n, p. COTI~ o, S.G. F R E D E R I K S E N o, C.J .D. H I ' B E R T o, J. H I ' B E R T o, B. M c L E O D o, A. T H I B A U D E A U o, M. K A Z U N O P, H. S H I B U Y A P, I .A. L O V A T T q, J.F. M A R T I N q, D. P I T M A N q, J .D. P R E N T I C E q, B.J. S T A C E Y q, T.-S. Y O O N q and Y. M A E D A r

a Department of Physics, Aichi University of Education, lgaya-cho, Kariya-shi, Aichi 448, Japan b Fermi NationalAcceleratorLaboratory, Batavia, IL 60510, USA c Faculty of Education, Gifu University, Gifu 501-11, Japan d Department of Physics, Gyeongsang National University, Jinju 620, Korea c College ofLiberalArts, Kobe University, Tsurukabuto, Nada-ku, Kobe 657, Japan r Department of Physics, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657, Japan g Graduate School of Science and Technology, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657, Japan h Department of Physics, Korea University, Seoul 132, Korea + Department of Physics, McGill University, Montreal, Quebec, Canada H3A 2T8 J Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464, Japan k Department of Physics, The Ohio State University, Columbus, OH 43210, USA

Physics Department, Okayama University, Tsushimanaka, Okayama 700, Japan ,1 Physics Department, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558, Japan

Science Education Institute of Osaka Prefecture, Karita, Sumiyoshi-ku, Osaka 558, Japan o Department of Physics, University of Ottawa, Ottawa, Ontario, Canada KIN 6N5 P Physics Department, Toho University, Funabashi-shi, Chiba 274, Japan q Physics Department, University of Toronto, Toronto, Ontario, Canada M5S 1A 7

Faculty of Education, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240, Japan

Received 25 February 1988

We have found 122 charmed-particle decays among 3855 neutrino interactions located in the fiducial volume of a hybrid emulsion spectrometer installed in the Fermilab wide-band neutrino beam. We obtain an average relative charmed-particle production cross section of a(v~c~t-)/a(v~-,p--)=4.9_+o°:67%, at an average neutrino energy of 22 GeV. We also obtain a production rate of a(v,-+cev~)/a(v,~v,)=O.13+_°:31%; if we assume that there was an undetected muon, a limit of a(v,~ce~t- ) /a(v,~c~t- ) < 3% (90% CL) can be obtained. Other cross section ratios and limits are also presented.

F o r more than a decade , neu t r ino in te rac t ions have been expec ted to be a cop io u s source o f c h a r m e d par -

t ic les [ 1 ]. O n e o f the ear ly i nd i ca t i ons o f c h a r m e d par t i c les was the o b s e r v a t i o n o f oppos i t e - s ign d i lep-

0 3 7 0 - 2 6 9 3 / 8 8 / $ 03.50 © Elsev ie r Sc ience Pub l i she r s B.V. ( N o r t h - H o l l a n d Phys ics Pub l i sh ing D i v i s i o n )

375


ton events with a rate of about 1% in high-energy charged-current neutr ino interactions [2]. Using a charmed-particle semileptonic branching ratio of 10% [3], this translated into a 10% production rate of charmed particles.

Most of the data on charmed-particle production by neutr inos has been obtained using large neutr ino detectors. Usually the decays of the charmed particles cannot be seen directly and their presence is inferred from the observation of strange particles or final state leptons, necessitating large background subtractions.

Our experiment was designed to measure charmed- particle lifetimes by directly observing their decays in a nuclear emulsion target and reconstructing the events using the informat ion gathered in a down- stream spectrometer. The detector was installed at Fermilab in the wide-band neutr ino beam produced by 350 and 400 GeV protons during two separate running periods; both beam and detector have been described extensively elsewhere [4-11 ]. Our final data sample consists of 3855 neutr ino interactions ~1 among which 122 charmed-particle decays were found [ 9,10 ] ~2; a detailed breakdown of the sample is given in table 1. The estimated background was 0.2

~ An additional 31 neutrino interactions were found, but are not included in the final sample because the spectrometer magnet was turned off.

~2 Throughout this paper, all charmed particles also include their antiparticles except when the distinction is made explicitly.

and 3.6 events for the neutral and charged charmed- particle decays, respectively [ 9,10 ].

We have already published results on production cross sections and processes using the data from the first run of the experiment [ 12 ]. In this and the fol- lowing paper [ 13 ], we present final results obtained after a second running period which tripled the total data sample.

In order to correct for detection inefficiencies in our study of charmed-particle production, we used a Monte Carlo program (described in detail in ref. [ 10 ] ) to simulate the behavior of our apparatus. To test the Monte Carlo, its predictions were compared, where possible, with the data; for example, fig. 1 shows the agreement of the "visible" energy (Evis) distr ibution with the prediction of the Monte Carlo. The "correction factor" (Ev/Evis), obtained from the Monte Carlo, was used to calculate the true incident neutr ino energy from the observed visible energy for events without charm decays (typically, E v i s w a s 10% lower then Ev). Our charm events were studied in sufficient detail to permit an est imation of their in- coming neutr ino energy directly, without the Monte Carlo.

Each event was given a weight to compensate for inefficiencies. Charm-event weights were determined on an event-by-event basis with the help of the previously ment ioned Monte Carlo, and using the charmed-particle m o m e n t u m and direction. The weight is a product of two factors: the first is an esti-

Table l Charmed particles.

Charmed Number Weighted Rate a ) particle number (%)

D O 57 87+ 11 4 ~+6 v _ 5

D + 4 1 b) 6 0 + l l 3 " l + 6 - 2 0 J - - 8

D + 6.3 ~) 10+6 5_ 2 +4 A~ + 14.7 c) 2Q+ ,5 1~+8 u - 8 v _ 4

D O and D O o~ 1 1 <+3.5 "J 1.2

totals 121 ~) - 100

a~ Does not include ~ events. ,1 Most are ambiguous among D -+, D~, and A~ + [9,10]. c~ The fractional event comes from the weighting of one event

which fits both as a D + and as a A + . d ~ Two decays produced in a single neutrino interaction. ~) Does not include one candidate for a long-lived charmed neu-

tral baryon [ 8 ].

2 5 0

200

Z 150

>

1 0 0

5o

Z

i i i i

I I I I

2 0 4 0 6 0 8 0 1 0 0

g~ GeV)

Fig. 1. Total uncorrected energy visible (Ev,s) in the detector for the events with a tagged let-. The dashed curve is the prediction from the experiment Monte Carlo, normalized to the number of events observed.

376

Volume 206 number 2 PHYSICS LETTERS B 19 Ma/ J 'J,',;"

mate of the number of events with similar character-

istics present in the emulsion, while the second is an

estimate of what fraction of these events should have

been found. For each event, the first factor is deter-

mined from the probabili ty that any event with the

same kinematics would trigger the detector, be recon-

structed, and be found in the emulsion. The second factor compensates for the finite thickness of the

emulsion target and for scanning inefficiencies; for

this calculation we used the charmed-particle life-

t imes obtained by this experiment [4,5 ]. We also

compensate the single prong ( "k ink" ) decays for the

effect of using a 400 MeV/c transverse m o m e n t u m

cut to tag them as charmed-particle decays [7,10].

The total numbers of weighted charm events thus ob-

tained are listed in table 1. Neutr ino interactions

without charm were weighted in a similar manner ,

except that only an average weight was used (see ta-

ble 2), based only on the first factor. The errors on these weights [ 10 ] were determined

from the expected statistical fluctuations and from an

estimate of the systematic uncertainties; the errors

quoted in tables 1 and 2 include both contr ibut ions

added in quadrature. The systematic error was esti-

mated by varying the inputs to the weight-calculation

program, namely the efficiencies, the neutr ino en-

ergy spectra, and the parameters controlling the

Monte Carlo itself; it also includes a contr ibut ion

from the estimated background discussed above. Using the weighted number of events it is possible

to calculate the relative production rates for the var-

ious charmed-particle species produced in charged

current v, interactions (see table 1 ). The errors in-

Table 2 Neutrino interactions. CC: charged current; NC: neutral current.

Type Number ") Weighted number

v, CC 2952 36 l 4-+ 274 9, CC 152 195"+ 21 v, NC 649 1087"+ 122 v, NC 42 75+ 14 ve and 9c 60 69_+ 1 1

totals 3855 5040 _+ 301

"} Breakdown inferred from the distribution of found events and by using the results of the Monte Carlo.

Table 3 Cross section ratios.

Ratios Rates (%)

a(v,N~cp-X) 4 9 +o 7 l . o . 6 o-(v,N~g X)

¢r(vsN-*eP'+X) 5 Q+2 9 .o 2.0 2 cr(%N__.g+X)

3 a(v"n-~g-A+ ) +03 0.3_o2 a(v,N~g X)

4 ~} a(v,N--.v,c~X) 0.13 +°3L_ol, a(v~N-.v,X)

5 a) o'(vpN----~ccX ) 0.8 +--0.71"9 a(v,N~cX)

a) Includes neutrino and antineutrino interactions.

clude an extra systematic uncertainty due to the possible contaminat ion o l D + and A + among the events identified as D +- [5,9,10].

We also calculated the various cross section ratios summarized in table 3; we computed ratios since it was difficult to obtain an absolute normalizat ion for the number of neutr inos incident on the target and because ratios are less sensitive to any unforeseen inefficiencies a n d / o r biases. The charmed-particle production rate (for neutr ino interactions only) is a ( v , N _ _ , c g - X ) / ~ ( v , N - - , g - X ) = 4 . 9 + ° i 7 % ; fig. 2

shows the energy dependence of this cross section. The charm sample included three A~ + which were produced in quasi-elastic interactions: v , n ~ g - Ac + . After

12

- ~ 1 0

t 8 z

< 6

4 :X t z 2

T 0

50 100 150

E V (GeV)

Fig. 2. Relative charmed-particle production rate in charged-current v, interactions as a function of the incident neutrino energy. The solid curve is a prediction from ref. [ 14] [curve (b) of fig. 1 therein ] after correcting for the semileptonie branching ratios of charmed particles.

377


correcting for the relat ive f inding efficiencies (using the weights discussed above) , the quasi-elastic Ac + product ion rate was calculated to be a(v,n~ ~t-A~ + ) / a ( v . N - ~ p . - X ) = 0 . 3 + ° 1 3 % . Integrat ing the charged current cross section [ 3] over our energy spectrum [7-11 ] and using the above ratio, we f ind that the Ac + quasi-elastic cross section is a (v ,n- - . ~t-Ac + x 3 7 +3.7 10 -4o / = • --2.3 X cm 2.

We also have one event which is consistent with the neutral-current product ion of a pair o f charmed particles [ 7,15 ]. Using this event the neutral-current product ion rate for a pair of charmed part icles is a ( v , N - ~ cev,X ) / a ( v , N ~ v , X ) = 0.1J--O.l 1 " 7 l +0.31% (the errors were obta ined using Poisson statistics, and rep- resent a 68% CL interval) . I f we assume, instead, that a muon was not tagged in this event, we also obta in a l imit to charged-current ce product ion of a(v,N~c~l.t-X)/a(voN-,c~t-X) < 3% (90% CL). A lasting puzzle in neutr ino physics is the observat ion of same-sign dileptons. For example, the C H A R M Col laborat ion [ 16 ] repor ted a rate o f 14 + 4 + 3% for the ratio a(v~N~p-~-X)/a(v~,N-,l.t-~+X), while the CDHS Col laborat ion [17] repor ted a rate of 3.2 + 1.2%. A Fermi lab exper iment [ 18 ] using the 15 ft. bubble chamber and the same beam as used in our exposure also repor ted an upper l imit o f 5.3% (90% CL) on this ratio. The leading contr ibut ion to these same-sign di lepton events is expected to be the product ion of ce pairs f rom second-order QCD dia- grams. Our l imit of 3% shows how much o f the signal is due to c~ product ion, and is consistent with the en- t ire signal being due to charm.

We are also able to set l imits to various other processes, the most impor tan t of which are summar ized in table 4. In par t icular we observe no beauty-par t ic le decays ~3, no unambiguously ident i f ied wrong-sign charmed-par t ic le decay which could signal "new" product ion processes or possibly D ° - I ) ° mixing, and no evidence for f lavor-changing neutral current interactions.

This work was suppor ted in part by the Depar t - ment of Educat ion of the Province of Quebec, Can- ada; the Natura l Sciences and Engineering Research

,3 It was assumed that the b and c lifetimes and finding efficiencies were comparable.

Table 4 Limits to cross section ratios.

Ratios al 90% CL upper limits (%)

a(%N-,v~cX) l 2 a(v,N--,v~X )

2 a(v~N-,c~p.- X) 0.12 a(%N-,p-X)

3 a(v,N--,cep.- X) 3 a(v,N--,cp X)

4 a(v"N-*cla-X) 0.12 a(v,N~p.-X)

5 a(v,N--,~p.- X) 3 a(%N~ckt-X)

6 a(%N~bp-X) 2 a(v,N-~ckt-X)

7 a(v~N--,13y X) 3 a(v,N--,c~t-X)

a) All limits include neutrino and antineutrino interactions.

Counci l o f Canada; the Ashigara Research Labora- tories of the Fuji Photo F i lm Co. Ltd.; the Japan So- ciety for the Promot ion of Science; the J a p a n - U S Coopera t ive Research Program for High Energy Physics; the Minis t ry of Education, Science and Cul- ture of Japan; the Mitsubishi Foundat ion ; the Nish- ina Memor ia l Foundat ion; the Nissan Science Foundat ion ; the Korea Science and Engineering Foundat ion ; the Basic Science Research Inst i tute Program, Minis t ry of Education, Republ ic of Korea; the US Depar tmen t of Energy; and the US Nat ional Science Foundat ion .

R e f e r e n c e s

[ 1 ] M.K. Gaillard, B.W. Lee and J.L. Rosner, Rev. Mod. Phys. 47 (1975) 277; M.J. Murtagh, in: Proc. Intern. Symp. on Lepton and pho- ton interactions at high energies (Fermilab, Batavia, IL, 1979), ed. T.B.W. Kirk and H.D.I. Abarbanel (Fermilab, Batavia, 1979).

[2]A. Benvenuti et al., Phys. Rev. Len. 34 (1975) 419; 35 (1975) 1199; H.E. Fisk and F. Sciulli, Annu. Rev. Nucl. Part. Sci. 32 (1982) 499.

[3 ] Particle Data Group, M. Aguilar-Benitez et al., Review of particle properties, Phys. Len. B 170 (1986) 1.

[4] N. Ushida et al., Phys. Rev. Len. 45 (1980) 1049, 1053; 48 (1982) 844; 51 (1983) 2362; 56 (1986) 1771.

[5] N. Ushida et al., Phys. Rev. Lett. 56 (1986) 1767.

378


[ 6 ] N. Ushida et al., Nucl. lnstrum. Methods 224 (1984) 50; Phys. Rev. Lett. 47 ( 1981 ) 1694; 57 (1986) 2897; S.Y. Bahk, Ph.D. thesis, Korea University (1984); M.J. Gutzwiller, Ph.D. thesis, Ohio State University ( 1981 ); T. Hara, Ph.D. thesis, Osaka City University ( 1982); I.A. Lovatt, Ph.D. thesis, University of Toronto ( 1986 ); M. Miyanishi, Ph.D. thesis, Nagoya University ( 1983); D. Pitman, Ph.D. thesis, University of Toronto ( 1983); H. Shibuya, Ph.D. thesis, Nagoya University ( 1982); Y. Takahashi, Ph.D. thesis, Kobe University ( 1983 ); M. Turcotte, Ph.D. thesis, McGill University (1986).

[7 ] D.C. Bailey, Ph.D. thesis, McGill University (1983). [8] S. Errede, Ph.D. thesis, Ohio State University ( 1981 ).

[ 9 ] A. Gauthier, Ph.D. thesis, Ohio State University ( 1987 ). [10]S.G. Frederiksen, Ph.D. thesis, University of Ottawa

(1987). [ 11 ] A.J. Malensek, Fermilab Note FN-341 ( 1981 ), unpublished. [ 12] N. Ushida et al., Phys. Lett. B 121 (1983) 287, 292. [ 13 ] N. Ushida et al., Phys. Lett. B 206 (1988) 380. [ 14] R. Brock, Phys. Rev. Lett. 44 (1980) 1027. [ 15 ] E531 Collab., N.R. Stanton, in: Proc. Intern. Conf. on Neu-

trino physics and astrophysics, Vol. 1 (Maui, Hawaii, 1981 ) eds. R.J. Cence, E. Ma and A. Roberts (University of Ha- waii, Honolulu, 1981 ).

[ 16] M. Jonker et al., Phys. Lett. B 107 ( 1981 ) 241. [ 17] H. Burkhardt et al., Z. Phys. C 31 (1986) 39. [ 18] C. Baltay et al., Phys. Rev. Lett. 55 ( 1985 ) 2543.

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Cross sections for neutrino production of charmed particles