Two recent experiments at the BNL Multiparticle Spectrometer searched for charm production in the ..pi../sup -/p interactions at 16 and 17 GeV/c. One experiment looked for D/sup *//sup -/ production with a fast K/sup +/ trigger, while the other experiment triggered on single-electron events. The K/sup +/-trigger experiment finds that the D/sup *//sup -/ cross-section at 16 GeV/c is less than 130 nb at 95% confidence level

Chung, S. U.

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Talk given at theMoriond Workshop on New FlavoursLes Arcs, Savoie, FranceJanuary 1982SSL 31198OG 631Two Recent Charm Search Experimentswith the Multiparticle Spectrometer at BOT,presented byS.TJ. ChungENL—31198DE82 015243- DISCLAIMER -This book was prepared as an account of work sponsored by an agency of the United States Government.Neither ihe United States Gave*nmem nor any agency thereof, nor any of their employees, makes anywarranty, enures* or implied, or assumes any legal liability or responsibility 'or the accuracy,completeness, or usefulness of any information, op par at us. product, or process disclosed, orrepresents that its use vwuld not infringe privately owned rights. Reference herein to any sueciticcommercial product, process, or service by irade name, trademark, manufacturer, or otherwise, doesnot necessarily constitute or imply its endorsement, recommendation, or favoring by the UnitedStales Government or any agency thereof. The views and opinions of authors expressed herein do noinecessarily state or reflect thuse of trie United States Govern rent or any agency thereof.The submitted manuscript has been authored under contract DE-AC02-76CHOOOI6with the U.S. Department of Energy. Accordingly, the U.S. Governmentretains a nonexclusive, royalty-free license to publish or reproduce thepublished form of this contribution, or allow others to do so, for U.S.Government purposes.OF THIS DOCUMENT IS• ' - %TWO RECENT CHARM SEARCH EXPERIMENTSWITH THE MDLTIPARTICLE SPECTROMETER AT BNLS.U. ChungTalk given at theMoriond Workshop on New FlavoursLes Arcs, Savoie, FranceJanuary 1982TWO RECENT CHARM SEARCH EXPERIMENTSWITH THE MULTIPARTICLE SPECTROMETER AT BNLPresented by S.U. ChungK+ TRIGGER EXPERIMENT: S.U. Chunga\ A. Etkin, R.C. Fernow, K.J. Foley,J.H. Goldman^, H. Kirk, U.A. Love, T.W. Morris, S. Ozaki, E.D. Platner,S.D. Protopopescu, A. Saulys, D.P. Weygand, CD. Wheeler and E.H. Willen (BrookhavenNational Laboratory); J . Bensinger and W. Morris (Brandeis Univers i ty) ;S.J. Lindenbaum (Brookhaven National Laboratory and City College of New York);M.A. Kramer and U. Mal l ik c ) . (Ci ty College of New York); Y. Bar-Yam, J. Dowd,W. Kern and M. Winik^ (Southeastern Massachusetts Univers i ty ) ; J. Button-Shafer,S. Dhare) and R. Lichti*) (University of Massachusetts).ELECTRON TRIGGER EXPERIMENT: J. Stekas^) , G. Abshireh) , M.R. Adams, C. Brown*-),E. Crandell, J. Goldberger, P.D. Grannis and B.T. MeadowsJ) (State University ofNew York); L. Cornell (University of Pennsylvania); G.J. Donaldson^), H.A. Gordon,G.R. Morris^ and P. Rehak (Brookhaven National Laboratory).ABSTRACTTwo recent experiments at the BNL Mult ipart ic le Spectrometer searched for charmproduction in the ir~p interactions at 16 and 17 GeV/c. One experiment looked forD*~ production with a f a s t K+ tr igger, while the other experiment triggered ons ing le -a lec tron events . The K+-trigger experiment finds that the D*" cross - sec t ionat 16 GeV/c i s l e s s than 130 nb at 95% confidence l eve l .*a) V i s i t o r at CERN, Geneva, Switzerland.b) Present address: Florida State Univers i ty s Tallahassee, FL, USA.c) Present address: LAL, Or3ay, France.d) Now at Brookhaven National Laboratory, Upton, NY, USA.e) Present address: Mitre Corporation, Bedford, MA, USA.f) Present address: Texas Tech University, Lubbock, TX, USA.g) Present address: Bell Laboratories, Holmdel, NJ, USA.h) Present address: Computer Science Corporation, Silver Spring, MD, USA.i ) Present address: Syracuse University, Syracuse, NY, USA.j) Permanent address: University of Cincinnati, Cincinnati, OH, USA.k) Present address: Stanford Linear Accelerator Center, Stanford, CA, USA.1) Present address: Kaman Sciences Corp., Colorado Springs, CO, USA.The detection of charm production in hadronic processes has proved to bedifficult, mainly* because the cross-sections are ̂  10""* or less of the total cross-section and the detectable branching ratios are small1/. In order to achieve highsensitivity and good background rejection necessary for observation of charm atBNL, two separate approaches have been adopted with the BNL Multiparticle Spectro-meter. The method of one experiment utilized the small Q value (m^* - mD - m^ =- 5.7 ± 0.4 MeV) in the decay chain D*~ •+ D°ir~ and D° •*• K+r~ to reject the non-charm background2'3^. The strategy employed by the other experiment was to triggeron a single electron from the decay D~ •*• e~ + X° to suppress the hadronic back-ground1* ̂ . A brief description of the experiments and the results are presentedhere.The first experiment described here, the K+-trigger experiment, utilized theD* decay chain for the charm search5'6^. The layout of the experiment" is givenin Fig. 1. The central element of the trigger requirement was the identificationFig. 1 Layout of the K+-trigger experiment at the BNL MultiparticleSpectrometer. Tj and T2 are planar proportional wire chambers (PWCs);H5 and H? are scintillation counter hodoscopes; C6 and C7 are atmos-pheric and high-pressure Cerenkov counters. Also shown are the outlinesof three groups of spark-chamber modules around the liquid-hydrogentarget (LH2>t and in addition other detector elements not used in theK+ trigger.of a fast forward K+ with momentum in the range 6.5 to 11.0 GeV/c with two Cerenkovcounters and three-dimensional coincidence-matrix logic systems8^. In addition,there was also a minimum multiplicity requirement of three or more tracks aroundthe liquid hydrogen target.- 2 -This experiment searched for charm production in the inclusive reactionTT"p + D*~ + X (I)and also the exclusive reactionir-p + D *- + A* (2)with the D decayD° + ir". s D° •+ K+ + TT" (3)at the ir~ beam momentum of 16 GeV/c.A total of 2.5 x 10s K+ triggers were recorded and analysed, corresponding toa raw sensitivity of 68 events/nb. Figure 2a shows K+TT~ mass spectra for those33001.80 1,83 1.90M (K*ir - | . GtV.953o2.9 3.0 3.9MM IG»V)3szu>10 19 Z0Q (MeV)Fig. 2 a) K+ir" effective mass spectrum. Top histogram showsall events between 1.77 and 1.96 GeV. Bottom histogram showsremaining events after requiring at least one additional nega-tive track, MM > 2.0 GeV and Q < .25 MeV. b) Missing massspectrum off IC^T'IT" (MM) for K*"ir" mass between 1.77 and1.96 GeV and Q < 25 MeV. c) Q spectrum for events with K+TT~mass between 1.77 and 1.96 GeV and MM > 2.0 GeV.- 3 -events having one or more negative tracks in addition to the triggered K , and alsofor those with the additional requirements of Q < 25 MeV and the missing mass (MM)recoiling off K+ir"V greater than 2 GeV/c. The enormous reduction (by a factor of^ 100) in the data sample results mainly from the cut in Q. Figures 2b and 2cshow the MM and Q spectra for the reduced'data sample with the M(K+ir~) in the range1,77 to 1.96 GeV. The calculated K+ir" mass resolution is typically better than10 MeV, the MM resolution better than 45 MeV, and the Q resolution better than1 MeV.To estimate the acceptance, Monte Carlo events were generated with the D ~produced peripherally with an e^-?* distribution. The acceptance is actuallyfairly insensitive to the slope of the t distribution*'. These Monte Carlo eventswere processed through the same chain of data-reduction programs as that used forthe real data. The overall acceptance is 6.4% at the A* mass (2.26 GeV) and variesslowly as a function of MM between 2.2 GeV and 3.0 GeV; above 3.0 GeV it decreasesrapidly. There are additional losses due to inefficiencies of the trigger elements,beam losses, etc., which reduce the acceptance by an additional 30%. The visiblesensitivity for observing D*~ •* D°ir~ (D° • K+ir") is 3.0 events/nb for MM < 3.0 GeV.Figure 3 shows a scatter plot of Q vs MM for events with Kir effective massbetween 1.82 and 1.90 GeV. For MM < 3.0 GeV there are 10 events in the range20-~ 15-o10-» -I1•••••m• •• " . • . :* •f • • ••• * . * " *. . .L • • • .*• » •. • •! _ _ _ _ t • _i • •t 1 I2-0 2.4 2.3MM (GeV)3.2 3.8Fig. 3 Scatter plot of MM vs Q. The dotted lines indicatethe ranges 2.14 < MM < 2.38 GeV and 3.7 < Q < 7.7 MeV.*) The slope used for the t distribution corresponds to that expected from D° ex-change (assuming the Regge trajectory to have a slope of 0.4 GeV."2)._ 4 -3.7 < Q < 7.7 MeV. From studying events outside this Q range and also thoseoutside the selected Kir mass range, the background i s estimated to be 11 events.Thus one obtains a cross-section times branching ratio (o*B) upper limit for D*~production of 2.4 nb at 95Z confidence l eve l . Using the branching r a t i o s 1 ' 9 '0.64 ± 0.11 for D*~ -»• D°ir" and 0.03 ± 0.006 for D° •*• K+ir~ one obtains a cross-section upper limit of 130 ± 30 nb, where the error ref lects the uncertainties inthe branching ratios. In the MM range from 2.14 to 2.38 GeV and the Q range from3.7 to 7.7 MeV, there i s only 1 event and the estimated background i s 1 event.This gives a O»B upper limit of 1.3 nb for the exclusive reaction ir~p -»• D*~A+and a corresponding cross-section upper limit of 70 ± 18 nb ' .The second Multiparticle Spectrometer experiment to be reported here, theelectron-trigger experiment, was carried out again at. the BNL Multiparticle Spectro-meter with a IT" beam at 17 GeV/c on a hydrogen target. I t was sensitive to thefollowing specific reactions:ir-p * ACD~(D~ • e" + X, Ac «• lot* (4)Ac * pKs (5)Ac + Air+ir+ir~) (6)ir~p -»• D°D~p(D" •»• e" + X, D° + KgTT+ir~) (7)ir"p •*• D D~n(D~ - e" + X, D+ -* Ksu+) (8)The strategy employed was to trigger on a single electron of momentum greater than2.5 GeV/c and veto the Y and e+ which arise from the most l ikely source of suchelectrons, i . e . TT° •+• e+e~y (either internal or external conversions). The electrontrigger allowed a large suppression of the hadron background to these reactions.However, since there would always be a missing neutrino, the analysis required asignal in a two-dimensional plot of the MM of the D~ versus the effective mass ofthe other charmed partic le . In the case of reaction (8) one can only search forthe D~n mass. The effective mass in each required identification of Kg or A.*) The upper limits are based on Poisson s t a t i s t i c s . If the expected number ofevents to be observed i s 5 * 4.8, then the probability for observing 1 or 0event i s 5%. This gives then an upper limit signal of 3.8 events. Similarlyi f n * 17.0, then there i s a 5% probability of observing 10 or less eventsgiving an upper l imit signal of 7.0 events.- 5 -The charged particles in these reactions were measured in the planar chambersdownstream of the target, as well as the cylindrical chambers surrounding thetarget. The electron trigger was accomplished by using two lithium-foil transi-tion radiators each followed by a xenon-filled proportional chamber10' and alead/acrylic-scintillator sandwich shower detector11'. The experimental layoutis given in Fig. 4. On line, a triple coincidence was required between thesedevices, corresponding to the trajectory of a negative track. Off line, the hadronrejection exceeded 3000:1.ImXUVXSPK.CHCYLINDRICALTARGETMPS MAGNET COILBACKSOTRDTRIGGER PWCC6 H5Fig. 4 Layout of the electron-trigger experiment. The electron de-tection is achieved via two transition-radiation detectors (TRDs), aset of lead-scintillator shower detectors (SDs), and trigger PWCs. Inaddition, cylindrical and planar spark-chamber modules have been usedfor measurement of the electron and hadron tracks within the Multi-particle Spectrometer.A total good beam flux of 6.60 * 1010 pions was incident on a 90 cm hydrogentarget leading to ̂  1.3 x 106 events triggered. The analysis consisted of rejec-ting almost all these events since they did not meet the requirements of the re-actions (4) to (8). An-electron candidate was required to originate from a pro-duction vertex inside the target. To reduce the e+e" pair background further,the trigger electron was paired with all positive tracks to form an e+e~ hypothesis.If the invariant mass was less than 100 MeV, the event was rejected. The remainingevents were searched for neutral decay candidates which were separated from theproduction vertex. A final sample of 5700 events remained which had a single un-paired e~ of good quality, at least one Kg or A downstream of the production ver-tex, a good production vertex with at least three tracks and no visible y's with- 6 -an energy exceeding 1 GeV. Detailed Monte Carlo calculations simulated the experi-ment and, when subjected to the same cuts as the data, yielded the efficiency forfinding each reaction.Scatter plots of the effective mass versus the missing mass of the D~ weremade. Within a conservatively sized rectangle based on the mass resolution, noevents remained for the associated charm production reactions (4) to (6) and oneevent each remained for reactions (7) and (8).Using efficiencies and acceptances from this experiment and the measuredbranching ratios12^, upper limits for the total cross-sections for reactions (4)to (8) were determined at 95Z confidence level as follows:a(4)B2 < 6.3 nb , o(4) < 2.4 yb ,o(5)B2 < 7.3 nb , a(5) < 3.3 yb ,a(6)B*' < 69 nb , a(6) < 11 yb ,a(7)B2 < 13 nb , C</) < 1.5 yb ,a(8)B2 < 4.7 nb , a(8) < 1.6 yb •,The failure to observe any event for reactions (4) to (6) yields a combined upperlimit for the reaction ir~p -*• ACD~ of 1.6 yb.In conclusion, two separate searches for charm production at BNL energies havebeen carried out at the BNL Multiparticle Spectrometer. From these experiments onecan conclude that the charm cross-section is at least 20 times smaller than thoseat Fermilab or CERN energies. In particular, the cross-section upper limit for16 GeV/c 7T~p collisions *is less than 130 nb; this represents an improvement of afactor of 20 on a previous similar experiment5).This research supported by the U.S. Department of Energy under ContractNb. DE-AC02-76CH00016.- 7 -REFERENCES1) J.J. Aubert et al., Phys. Rev. Lett 3_5_, ̂ 15 (1975). Limits given in thispaper should be increased to > 10~ 3 2 cm2 if peripheral production is assumed.R. Cester et al., Phys. Rev. Lett. J7, 1178 (1976).2) G.J. Feldman et al., Phys. Rev. Lett. ^ 8 , 1313 (1977).3) J. Kirkby, Proc. 9th Int. Symposium on Lepton and Photon Interactions at HighEnergies, Batavia, 1979 (Fermilab, Batavia, 111., 1980), p. 107.J. Blietschau et al., Phys. Lett. 86B, 108 (1979).P. Avery et al., Phys. Rev. Lett. 44, 1309 (1980).J.E. Wiss, Proc. 6th Int. Conf. on Experimental Meson Spectroscopy, BrookhavenNational Laboratory, Upton, 1980 (Amer. Inst. Phys., NY, 1981), AIP Con-ference Proceedings No. 67, p. 257.4) E.S. Crandall, Search for charm production in 17 GeV/c ir~p reactions, Ph.DDissertation, State University of New York at Stony Brook (1981);E.S.. Crandall et al., to be submitted to Phys. Rev. D.5) R. Cester et al., Phys. Rev. Lett. 40, 138 (1978).6) V.L. Fitch et al., Phys. Rev. Lett. ^6, 761 (1981).7) ' S.U. Chung et al., Phys. Rev. Lett. 45, 1611 (1980).8) E.D. Platner et al., IEEE Trans. Nucl. Sci. Ik, 1225 (1977).9) R.H. Schindler et al., SLAC-PUB-2507, LBL-10905 (1981), submitted to Phys.Rev.10) R. Bosshard et a l . , Nucl. Instrum. Methods JL30, 365 (1975).11) G. Abshire et a l . , Nucl. Instrum. Methods 164, 67 (1979).12) G. Tril l ing, Phys. Reports .75, 57 (1981).

Two recent charm search experiments with the multiparticle spectrometer at BNL

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Two recent charm search experiments with the multiparticle spectrometer at BNL

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