In a study of interactions of 400 GeV protons in a totally absorbing iron calorimeter the authors report two observations indicating the hadronic production of heavy short-lived weakly decaying particles. First they have observed a prompt muon signal in the region .8<p/sub t /<2.5 GeV/c. The rate is comparable in magnitude to the prompt 2 mu rate in the same kinematic region. In addition to detecting mu /sup +/ mu /sup -/ events arising from electromagnetic sources (e.g. rho to mu /sup +/ mu /sup -/, psi to mu /sup +/ mu /sup -/ etc.) they have observed mu /sup +/ mu /sup -/ pairs associated with a significant amount of missing energy indicative of final state neutrinos. Interpreting these data as production of DD pairs followed by single or double muonic decays leads to a model dependent estimate of total production cross-section of order 15 mu b. (14 refs)

Barish, B.C.

Bartlett, J.F.

Bodek, A.

Brown, K.W.

Diamant-Berger, A.

Dishaw, J.P.

Faessler, M.

Liu, J.K.

Merritt, F.S.

Shaevitz, M.H.

Siskind, E.J.

Wojcicki, S.G.

CERN Document Server

672 Session IV OBSERVATION OF PROMPT SINGLE MUONS AND OF MISSING ENERGY ASSOCIATED WITHµ+µ- PAIRS PRODUCED IN HADRONIC INTERACTIONS* B.C.Barish, J.F.Bartlett**, A.Bodek***, K.W.Brown, M.H.Shaevitz, E.J.Siskind California Institute of Technology, Pasadena, CA. 91125, USA. A.Diament-Bergert, J.P.Dishaw, M.Faesslertt, J.K.Liuttt, F.S.Merritt, S.G.Wojcicki Stanford University, Stanford, CA. 94305, USA. Presented by A. Bodek (University of Rochester) ABSTRACT In a study of interactions of 400 GeV protons in a totally absorbinq iron calorimeter we report two observations indicating the hadronic production of heavy short-lived weakly decaying particles. First we have observed a prompt muon s i gna 1 in the region . 8 < Pt < 2. 5 GeV I c. The rate is comparable in magnitude to the prompt 2µ rate in the same kinematic region. In addition to detecting µ+µ- events arising from electromagnetic sources (e.g., p-+µ+µ-,ljJ+µ+µ- etc.) we have observed µ+µ- pairs associated with a significant amount of missing energy in-dicative of final state neutrinos. Interpreting these data as pro-duction of DD pairs followed by single or double muonic decays leads to a model dependent estimate of total production cross-section of order 15 µb. INTRODUCTION The hadronic production of charmed particles had recently received considerable ex-perimental and theoretical attention. QCD calculations predict cross-sections in the range 1-30 µbin 400 GeV p-N interactions1l, with gluon fusion probably giving the domi-nant contribution. Previous searches for charm production have produced widely varying resultsL-5), ranging from upper limits of ~1 µb/nucleon 2•3) at 400 GeV to a recently re-ported signal of zl50 µbat the ISR5l. The prompt neutrino signal reported by the CERN beam dump experiments6l, if interpreted as a charm signal, corresponds to a production cross-section of 25-50 µb/nucleon (assuming linear A dependence)?). One of the cleanest signatures of charm production would be the observation of a prompt single-muon signal, since the branching ratio of charm into µv+hadrons is large (~10%) and other sources of prompt single muons are negligible. Several experimental groups2•8•9) have reported sizable prompt muon production, but previously only two2•9) have attempted to separate 1-µ from 2-µ events (the latter are due primarily to e1ectro-magnetic rather than weak decays). The results of both of these groups were consistent with all the prompt muon signal originating from 2-µ events, but allowed a sizable single muon signal. PROMPT SINGLE r.UONS We report here on the observation of a prompt 1-µ signal in the moderately high Pt + + (0.8<p~ <2.5 GeV) and low xF (lO<Eµ <60 GeV) region produced by 400 GeV p-N interactions. We find approximately equal production cross-sections for 1-µ and 2-µ final states in this kinematic region. We also present evidence for the observation of missing energy + -(indicative of final state neutrinos) in association with hadronically produced µ µ pairs, and relate it to the observed single muon signal. * Work supported by the U.S.Dept. of Energy and the Nat. Sci. Foundation. ** Present address: Fermilab, Batavia, Illinois, 60510. ***Present address: University of Rochester, Rochester, N.Y., 14627. t Permanent address: Department de Physique des Particules Elementaires, Sac1ay, Fcance. tt Present address: CERN, Geneva, Switzerland. tHPresently with American Asian Bank, San Francisco, CA. Session IV 673 The experiment was performed in the Fermi lab N5 beam with 400 GeV protons at typical intensities of 3-5 105/sec. The primary elements of the detector (Fig. 1) were a fine-grained target-calorimeter of variable densitylO) (energy resolution of 3.5% at 400 GeV), a muon identifier (MI), and a toroidal muon spectrometer11 ). The data reported here were taken with a high-pt trigger, which required a coincidence of both a beam and a muon trigger component. The muon component required the muon to re-main in the same quadrant throughout the toroid system by requiring the appropriate coin-cidence of counters C, S2, ACR, T4 (which were divided into quadrants) and Sl, T2, T3, MV (divided into half-planes). This requirement preferentially selected muons with high Pt µ+ (pt > .8 GeV). The beam component required an incident proton to pass through counters BO and Bl (7.6x7.6 cm and 5.lx5.l cm) and to interact within the first 10 plates of the calorimeter. To reject any background from upstream interactions, triggers were vetoed by the presence of any additional particles in the beam or halo counters within 95 nanoseconds of the trig-ger. Further beam information was provided by the pulse height of the trigger counters and by the incident proton's trajectory and momemtum, as measured by a spectrometer immediately upstream of the calorimeter. Interactions satisfying the beam trigger alone were scaled, and one out of each 216 was recorded to provide a control sample of interactions without any muon requirement. In the data analysis, software cuts were made to insure that the muon trigger counters were associated with a good trajectory, that the µ+ enter the toroid system at least 17.5 cm from the axis (outside of the hole), and that the interaction point lie between plates 1 and 8 of the calorimeter. The muon trigger acceptance after all these cuts was + 4 greater than 50% over the range l.O<p~ <2.5 and 20<Eµ <60 GeV. The majority of muons which triggered the apparatus were due to pion and kaon decays. This background was measured by uniformly expanding the first 25 plates (1 meter of steel) of the calorimeter, thereby proportionally increasing the mean path length and decay prob-ability of hadrons in this region. Most of the hadrons decaying downstream of this region were produced by secondary or tertiary interactions, and consequently gave decay muons that were generally too low in energy to satisfy the trigger, The experiment collected data at three different densities (keeping the mean interac-tion point fixed in space): fully compacted, expanded by a factor of 1.5, and expanded by a factor of 2. The mean calorimeter density in the compacted configuration was 3/4 that of steel due to the gaps (1.3 cm) between plates. After all software cuts, the rates in each density configuration were normalized to the beam trigger rates and plotted as shown in Fig. 2. As expected, the 2-µ rate is flat, and the 1-µ rate shows a linear increase with the effective pion interaction length. The 1-µ slope measures the rate from non-prompt de-cays, and the intercept of (10.5±.5)10-6 at infinite density is the raw prompt 1-µ signal. To obtain the true prompt single muon rate, the raw prompt 1-µ rate had to be cor-rected for several background sources: a) µ+µ- events with a low energyµ- which ranged out in the calorimeter or muon identi-fier. A Monte-Carlo calculation using the measuredµ+µ- distributions gave a cor-rection of 10 ± 2% (systematic errors included) of the raw prompt 1-µ signal. This component was subtracted from the 1-µ signal and added to the 2-µ signal. b) Muons from decays of pions and kaons in the unexpanded part of the calorimeter (after 674 Session IV plate 25). A Monte-Carlo simulation of the hadron shower, which reproduced the mean shower profile measured in the experiment, gave a correction of 8±3% of the measured decay rate 12 ). This corresponds to 16±6% of the prompt 1-µ signal. c) A subtraction of 20±10% of the prompt 1-µ signal due to second order variation in the acceptance with density. These arise because, although the mean interaction point stays fixed, multiple scattering effects and production by secondaries move downstream when the calorimeter is expanded.Since the toroid hole subtends a larger angle for particles originating downstream, this yields a reduction of 4±2% in the acceptance of the expanded relative to the compacted configuration. This correction was obtained from theµ+µ- events (which should be constant with density). After all corrections, the measured prompt 1-µ rate was (5.8±1.5)xlo-6 per incident proton and the 2-µ rate was (5.9±.2)xl0-6; the errors are largely systematic. A natural ex-planation of this single muon signal would be production and subsequent decay via leptonic mode of new heavy hadrons, the most likely candidates being the charm particles. That same mechanism would also require a production (at a lower rate) of a pair of charged muons, both of which originate from the decay of charm particles. The muons from this process would have to be associated with a missing energy due to companion neutrinos emitted in the decay. TWO PROMP MUONS WITH MISSING ENERGY The total observed energy spectrum forµ+µ- events (Etot=E ++E _+Ecalorimeter) is shown in Fig. 3. The dashed curve shown for comparison is the E~ot ~pectrum exhibited by beam interactions without final state muon. There is a pronounced enhancement of missing energy events for mµ+µ-<2.4 GeV. We observe 227 µ+µ- events with missing energy in excess of 45 GeV. An estimate of the double TI,K decay background is provided by the 5 observed like sign dimuon events with large missing energy. Monte Carlo calculation of KK production and double decay also yields a background of 5 events. Also, since the toroid spectrometer is instrumented with acrylic calorimetry counters, we can rule out catastrophic muon energy loss in the steel as significant source of background. We conclude that all backgrounds are unlikely to contribute more than 10% of the observedµ+µ- with missing energy signal. INTERPRETATION To estimate a charm production cross-section from these data, we have assumed that all the signal comes from the semileptonic decays D-+Kµv (60%) and D+K*µv (40%) with a total semileptonic branching ratio of 8%. The inclusive D cross-section was assumed to increase linearly13 with the atomic number A of the nucleus and was parameterized as d3 6 -apt E ___Q. = C (1 - xF) e (for inclusive D production) dp3 ( 1) The single muon data were consistent with values in the range a=2.0-3.5 Gev-l and 6>3. Varying a and 6 over these allowed ranges yields charm cross-sections in the range 15-75 + µb/nucleon. For 6=5 and a=2.5, the acceptance for the produced µ 's was 2.5% and the cross-section for D production was a_ =36±9 µb/nucleon. This model, in which the two charmed states are uncorrelated gives ~R acceptance of 0.14% for theµ+µ- events with 45 GeV of + -missing energy and yields a charm cross-section of 22±8 µb. However, the µ µ mass and momentum distributions do not fit this model. In order to include the expected correlation between the D and 5 state we assume a Session IV 675 DD model production model 3 -ap ;s Ed~= 5:r (1-xF)S e t e- M/ s (for DD production) (2) dp M and calculated the fraction of DD double muonic decays which satisfy our trigger require-ment, give 2 µ's that pass the muon cuts, and yield a measured missing energy in excess of 45 GeV. Here the kinematic variables in the above cross-section equation refer to the com-posite DD system (and /5=27.4). The acceptance was rather insensitive (to ±30%) to varia-tions in a between 1.5 and 3.0 GeV-l and y between 0.0 and 17.5. For a=2.23, S=2.96 and y=l4.9 we obtain an acceptance of 0.39% yielding a charm cross-section of 8±3 µb. Using this same model we obtain a charm cross-section of 24±5 µb from the single muon data. Changing S from 2.96 to 6.0 changes theµ+µ- acceptance from 0.39% to 0.24%. In general, the 2µ with missing energy data yield lower cross-sections than the prompt single muon data. We are presently investigating various distributions that will bring the two sets of data into better agreement, and still fit the measured distributions. (For example, making S larger appears to help.) Besides finding better parameters, we are investigating whether we are using an improper production mechanism, e.g. improper correlation between the D and D state, the possibility of different branching ratios for the charge and neutral states, a possible contribution from charmed baryon production etc. Until these model uncertain-ties are resolved by more fits to the experimental distributions, charm cross sections be-tween 7 to 70 µbare consistent with the data. Also, the next run of Fermilab experiment14 E595, which measures prompt single muons over a larger kinematic range, will help resolve the model uncertainties. REFERENCES 1) C.Carlson and R.Suaya, SLAC-PUB-2212 (1978); and J.Babcock, D.Sivers, S.Wolfram, Phys. Rev. 018, 162 (1978); B.W.Lee, M.K.Gaillard, J.L.Rosner, Rev. Mod. Phys. 47, 277 (1975).- -2) H.Kasha et al., Phys. Rev. Lett. 36, 1007 (1976); M.J.Lauterbach, Phys. Rev. Dl7, 2507 (1978). -3) C.Coremans-Bertrand et al., Phys. Lett. 658, 480 (1976); also see D.Crennel et al., Phys. Lett. 788, 171 (1978) and W.Bozzol.,--et al., Lett. al Nuovo Cimento 12_,32 (1977). 4) W.Ditzler et al., Phys. Lett. Z_ll, 451 (1977); D.Spelbring et al., Phys. Rev. Lett. 40, 605 ( 1978). 5) D.Drijard et al., Phys. Lett. 818, 250 (1979); other relevant ISR results include A.G.Clark et al., Phys. Lett. 778, 339 (1978); and J.C.Alder et al., Phys. Lett. 668' 401 (1977). 6) P.Alibran et al., Phys. Lett. 748, 134 (1978); T. Hansl et al., Phys. Lett. 748, 139 (1978); P.C.Bosetti et al., Phys. Lett. 748, 143 (1978). 7) H.Wachsmuth, CERN/EP/PHYS 78-29 (presented at Topical Conference on Neutrino Physics, Oxford, England, July (1978)). 8) F.W.Busser et al., Phys. Lett. 538, 212 (1974). 9) J.G.Branson et al., Phys. Rev. Lett. I!_, 803 (1976). 10) J.P.Dishaw et al., (this experiment)--SLAC-PUB-2291 (March 1979), to be published in Physics Letters. 676 Session IV 11) E.J.Siskind et al., (this experiment)--CALT-68-665 (March 1979), submitted to Physical Review D. 12) Recent measurements of downstream decays, using a similar trigger in a modified ver-sion (Fermilab E595) of this experiment, have confirmed this Monte-Carlo estimate. 13) We have used a total inelastic p-Fe cross section of 690 mb which is 12.4 mb/nucleon (A.S.Carrol et al., Phys. Lett. BOB, 319 (1979). 14) Caltech-Fermilab-Rochester-Stanford Collaboration. ,,_ Soork Chombets - - - - J. Wide Angle Muon ldenlifier , Downsteom l--IJ2L. _IT•~ T 40cm -1------J 200cm 104 103 ~ ::?; 1£1 ' 102 Cf) I-z w > w 10 -Colonmeter ~V/y Acrylic Counters MQ9netized Steel FIGURE 1 lilj1llill~ ---Unbiased Proton ~ Interactions J ~ 320 360 400 440 480 520 Etotal (GeV) FIGURE 3 1. 2. 3. 60 "' c: 0 e 0. 40 lD 0 ::::: (/) I-z w > w 20 z 0 ::::> $3 :!: 0 2/3 -1µ ---- 2µ Prompt PFe/P 4/3 2 8/3 -- - - - - - - - - -o--- - --o-- - - - o-T4 0 0 20 40 EFFECTIVE >-" (cm) FIGURE 2 FIGURE CAPTIONS The experimental setup. The raw lµ and 2µ experimental rates 60 per io6 protons versus inverse density. After background subtractions the prompt lµ and 2µ rates are equal. + -The number of µ µ events versus the total observed energy (Etotal=E ++E _+Ecalorimeter}. µ µ 

Observation of prompt single muons and of missing energy associated with $\mu^{+}\mu^{-}$ pairs produced in hadronic interactions

Observation of prompt single muons and of missing energy associated with $\mu^{+}\mu^{-}$ pairs produced in hadronic interactions

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Observation of prompt single muons and of missing energy associated with μ+μ−\mu^{+}\mu^{-}μ+μ− pairs produced in hadronic interactions

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Observation of prompt single muons and of missing energy associated with $\mu^{+}\mu^{-}$ pairs produced in hadronic interactions