The inclusive transverse momentum distributions of charged hadrons and K 's produced in tagged photon-photon collisions, are measured and compared to model calculations up to a p  of 5 GeV/c. The relative abundance of K 's favor the inclusion of charm. © 1993. 0 0 

Abrams, GS

Amidei, D

Baden, AR

Barklow, T

Boyarski, AM

Boyer, J

Burchat, PR

Burke, DL

Butler, F

Cords, D

Dorfan, JM

Feldman, GJ

Gidal, G

Gladney, L

Gold, MS

Goldhaber, G

Haggerty, J

Hanson, G

Hayes, K

Herrup, D

Hollebeek, RJ

Innes, WR

Jaros, JA

Juricic, I

Kadyk, JA

Karlen, D

Lankford, AJ

Larsen, RR

LeClaire, BW

Levi, ME

Lockyer, NS

Lüth, V

Nelson, ME

Ong, RA

Perl, ML

Riles, K

Rowson, PC

Schaad, T

Schellman, H

Schmidke, WB

Trilling, GH

Wood, DR

Yelton, JM

The inclusive transverse momentum distributions of charged hadrons and K0's produced in tagged photon-photon collisions, are measured and compared to model calculations up to a pT of 5 GeV/c. The relative abundance of K0's favor the inclusion of charm. © 1993

eScholarship - University of California

Inclusive charged hadron and K0 production in two-photon interactions

Cords, D.

Boyer, J.

Butler, F.

Gidal, G.

Abrams, G.S.

Amidei, D.

Baden, A.R.

Barklow, T.

Boyarski, A.M.

Burchat, P.R.

Burke, D.L.

Dorfan, J.M.

Feldman, G.J.

Gladney, L.

Gold, M.S.

Goldhaber, G.

Haggerty, J.

Hanson, G.

Hayes, K.

Herrup, D.

Hollebeek, R.J.

Innes, W.R.

Jaros, J.A.

Juricic, I.

Kadyk, J.A.

Karlen, D.

Lankford, A.J.

Larsen, R.R.

LeClaire, B.W.

Levi, M.E.

Lockyer, N.S.

Luth, V.

Nelson, M.E.

Ong, R.A.

Perl, M.L.

Riles, K.

Rowson, P.C.

Schaad, T.

Schellman, H.

Scmidke, W.B.

Trilling, G.H.

Wood, D.R.

Yelton, J.M.

Lawrence Berkeley National LaboratoryLBL PublicationsTitleInclusive Charged Hadron and K{sup 0} Production in Two-Photon InteractionsPermalinkhttps://escholarship.org/uc/item/7b20k879AuthorsCords, D.Boyer, J.Butler, F.et al.Publication Date1992-08-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaDISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information. apparatus. product. or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any age-ncy thereof or the Regents of the University of California. SLAC-PUB-5901 LBL-32903 August 1992 (fIE) Inclusive Charged Hadron and /(0 Production in Two-Photon Interactions· D. Cords, J. Boyer, F. Butler, G. Gidal, G. S. Abrams, D. Amidei, A. R. Baden, T. Barklow, A. M. Boyarski, P. R. Burchat, D. 1. Burke, J. M. Dorfan, G. J. Feldman, L. Gladney, M. S. Gold, G. Goldhaber, J. Haggerty, G. Hanson, K. Hayes, D. Herrup, R. J. Hollebeek, W. R. Innes, J. A. Jaros, 1. Juricic, J. A. Kadyk, D. Karlen, A. J. Lankford, R. R. Larsen, B. W. LeCliUre, M. E.Levi, N. S. Lockyer, V. Liith, M; E. Nelson, R. A. Ong, M. L. Perl, K. Riles, P. C. Rowson, T. Schaad, H. Schellman, W. B. Schmidke, G. H. Trilling, D. R. Wood, and J. M. Yelton Lawrence Berkeley Laboratory and Department of Physics University of Califomia, Berkeli'!y, Califomia 94720 Stanford Linear Accelerator Center Stanford University, Stanford, Califomia 94305 Department of Physics Harvard University, Cambridge, Massachusetts 02138 Abstract The inclusive transverse momentum distributions of charged hadrons and [(o's produced in tagged photon-photon collisions, are'measured and compared to model calculations up to a PT of 5 GeV /c. The relative abundance of /(o's favor the inclusion of charm. • This work was supported in part by the Department of Energy, contracts DE-AC03. 76SF00515 and DE-AC03-76SF00098. Submittedfor publications ~~~ ___ ~ ___ '.,.c~~ ......... ~_ .......... 1 ~BL Library LBL-32903 01/08/93 A process analogous to quark pair production in e+ e- annihilation is the hard-scattering quark exchange process in TY interactions. This hard-scattering process is expected to dominate I) the cross section at high transverse momenta of the produced quarks. Experimentally, one has looked for this process in two-jet 2) as well as inclusive particle 3,4) production and has found a relatively low PT onset of hard scattering in 'Y'Y interactions. This report examines the issue in more detail (high statistics) for charged particle inclusive production and checks if the heavier flavors display a similar behavior in inclusive /(0 production. The results5) are based on an integrated luminosity of 220 pb- I obtained with the Mark II detector at PEP operating at ECM = 29 GeV. The major features of the Mark II detector have been described elsewhere6). The combined track-ing information from the central drift chamber and the vertex drift chamber in a 2.3 kG magnetic field provided a momentum resolution of (u(PT)IPT)2 = (0.025)2 + (0.01lPT)2 (PT in GeV Ic). The small angle tagging system (SAT) measures electrons scattered between 21 and 83 mrad from the beam axis. It consists of three layers of drift chambers with a spatial resolution of 300 I'm in the xy plane, followed by three layers of acceptance defining scintillator and 18 alternating lay-ers of 1/4 inch lead and 1/2 inch scintillator. The energy resolution achieved for electrons is ulE = 15.5%IVE. We detect some 60,000 events tagged by an electron in the SAT corresponding to a Q2 interval between 0.075 and 1.00 GeV2. Since we do not observe the entire final state, the transverse momentum of hadrons, PT, is calculated in the usual man-ner, with respect to the e+e- beam axis. To eliminate the large QED background we accept only events with 3 or more charged tracks observed (in addition to the tagging electron). Events having identified leptons are removed using the Liquid Argon Calorimeter and the muon chambers. To minimize the beam-gas interaction background we also eliminate events with protons or deuterons identified by their time of flight. The background from e+e- -+ e+e- T+T- is subtracted using the Monte Carlo simulation of this process. The residual background from beam-gas interactions is simulated with events produced along the beam-line outside the in-2 ." teraction region. Both th'ese backgrounds vary between 5% and 10% with PT and are subtracted from the data. Taking advantage of the precision vertex chamber, a vertex finding program (VFINDP) is used to find KO,s which decay at least 2.5 mm from the primary vertex. After several quality cuts, tracks are combined into charge zero p~irs and the points of intersection are calculated. Of the two possible crossing points in the x-y plane, the program chooses the one which gives a posi-tive decay length and is nearest to'the interaction point. The track momenta are corrected for energy loss in the material traversed and the tracks are constrained to pass through a single point in space. The 7r+7r- pair mass distribution shows a clear KO peak with a resolution of 0-. = 7 MeV and an estimated background of less than 8%. We select events with masses in an interval ± 20 MeV about the actual KO mass. A Two-Photon Monte Carlo program 7) is used to simulate the hard scattering quark exchange process e+e- ...... e+e- qq, or for short 11 ...... qq. It incorporates transverse-transverse as well as transverse-longitudinal 11 luminosity functions 8), a summation over the four quark flavors u,d,s,c, and the subsequent fragmentation of the quarks according to the LUND scheme9): The ambiguities and variations in jet definitions at these low energies make it preferable to directly measure single particle inclusive cross sections. For this analysis we ,have ignored the Vector Dominance Model (VDM) contributions. The rather steep fall-off with PT makes this a negligible contribution above PT ",; 2 GeV Ic 12). The quark fragmentation parameters are taken as the set of values which best describe the e+ e- annihilation data at 29 GeV, and no attempt has been made to optimize the parameters for the lower two-photon energies. Since the quark flavors enter with the fourth power of their charges, the most important contributions come from the u and c quarks once the available two-photon energy exceeds the respective quark pajr thresholds. These Monte Carlo calculations describe the gross features of the data and are used to obtained the detection efficiencies for the various particle species. The efficiencies rise with PT and reach about 17% for charged hadrons and 3.3% for KO,s at PT = 2 GeV. They include the trigger simulation and the correct threshold 3 :. ~ __ ~_.a.,,-_._ behavior for charm production. As first pointed o~t by TASS03) the PT distribution of single charged hadrons does not follow a simple ,exponential Jall-off but flattens out for PT values above 1 GeV. Similar to th~ TASSO procedure, the Mark II analysis uses single tag data with Q2 values around 0.5 GeV2, but with its higher statistics Mark II can extend the sensitive range in PT from 3 to 5 GeV. In Fig. 1 the inclusive charged hadron cross section multiplied by p} is plotted as a function of PT . After the initial steep drop the data points are consistent with being constant for PT values above 3 GeV. This flat part of the distribution translates into a Pr4 bevaviour for do- / dPt and is an indication of the underlying structure of a scale-invariant point-like process, the simplest !llanifestation of which is the hard scattering quark exchange process 11 ...... qq. Several authors have calculated do-IdPt for this process in the quark parton model, and it 'has been shown earlier10) that any PT dependence due to quark hadronization is small compared to the Pr4 power law as long as one stays away from kinematic boundaries. Therefore, we can expect for our analysis a somewhat modified Pr4 behaviour for the inclusive particle spectrum, if the scaled transverse momentum XT = PT/Pbeam is small compared to 1. For the data in Fig. 1 XT is in the range between 0.07 and 0.34. , Nevertheless, the fragmentation introduces some uncertainty in the comparison of our data with the underlying hard scattering process. It is therefore more appropriate to compare the data with a Monte Carlo simulation of the process TY ...... qq, for which the fragmentation parameters have been adjusted in the clean environment of e+e- annihilation as mentioned above. The ratio of the measured and calculated inclusive cross-sections is shown in Fig. 2. The enhancement below 2 GeV is mainly due to vector dominance processes, which are not included in the the Monte Carlo. The remarkable feature is that the ratio is approximately constant and compatible with 1 for PT values above about 2 GeV. This means that the hard scattering process accounts for most of the high PT hadron production. Contributions from higher order hard scattering processes with 3 or 4 quarks and/or gluons can be important for moderate PT values and for Q2 = O. However, it has 4 ..... ~, .... -,.. fee •• , ':" _ ...... __ ...... IiIoi· .. • ... .-IIer ...... ·l!uioilllii .. __ ... ____ ....... .' been shown experimentally11) that any excess over the " -> qq process decreases dramatically as Q2 increases .. In addition, most detectors .are less sensitive to these higher order processes, since the additional spectator quarks and/or gluons are produced close to the beam direction. With its ability to identify gO's over a wide momentum range the Mark II detector can be used to look for the onset of charm production, because due to its charge, strange-quark production is expected to be suppressed by a factor of 16 with respect to charm quarks. With the same absolute normalization as above, the ratio of inclusive gO's from data and Monte Carlo is shown in Fig. 3 for PI' values up to 3 Ge V. Although the errors are much larger here, the data are consistent with the same general features observed for charged hadron production. The ratio of gO's to charged hadrons increases to about 30% at the highest PI' values as shown in Fig. 4. From the Monte Carlo simulations with and without charm one can ascertain that the charm quarks are responsible for about half the gO production (difference between solid and dashed lines) at high PI' . Combining the highest PI' bins we find R{PI' > 1.6 GeV /c) = 0.30 ± .08. This can be compared with Monte Carlo values of 0.32 and 0.16 with and without the charm-quark contributions. In an attempt to resolve the discrepancy between the Born term calculations and the untagged TASSO inclusive particle data4), Aurenche et al. have per-formed model calculations12) including higher order QCD terms and generalized vector dominance model contributions (motivated by photo-production data). The authors have subsequently expanded their calculations to include charm produc-tion and to extrapolate to the Mark II tagging range13). We have folded their single charged hadron inclusive spectrum with the PI' resolution expected for the Mark II detector. As seen in Fig. 5 the data points lie systematically above the predictions of Aurenche et al. for PT values larger than 1.5 GeV. However, the single-tag TASSO data 3) (in a similar Q2 range as Mark II) show an even higher , hadronic cross section. To be sure that the high PI' tail is not caused by the second ~ final state electron scattering at large angles, we removed all events with electron candidates in the end caps or central detector. From Monte Carlo simulations we 5 ,-.~ "-,-- -expect at most 5 electrons with PI' above 2 GeV to go undetected in regions not properly covered by shower counters. The discrepancy between the model calcu-lations and the Mark II data may be partially due to various effects: The tagging efficiency is only taken into account for an average Q2 whereas there exists a mod-erate Q2 dependence. The fragmentation may lead to uncertainties and is probably best handled with Monte Carlo methods. Analytic model calculations usually con-tain a number of approximations which may very well describe the overall features of a process but may lead to discrepancies in kinematic areas where the relative contributions have dropped by several orders of magnitude - as is the case for the high PI' tail discussed above. The model calculations have also not included multijet processes, for whic4 there is recent experimental evidence at TRISTAN15) confirming earlier indications at PEp16) and PETRA 11,14). However, the model calculations discussed here and our simple minded Monte Carlo simulations seem to describe different aspects (kinematic regions) of the data quite well. In summary, we extend the investigation of inclusive charged hadron produc-tion to 5 GeV in PI' and find evidence for the hard scattering process '" -+ qij in the PI' range from 3 to 5 GeV. With the first observation of inclusive gO production up to 3 GeV in PI' , we see the enhanced production expected from charm at high PI'values. References 1) S.M. Berman, J.D. Bjorken, J.B. Kogut, Phys. Rev. D4, 3388(1971) 2) W. Bartel et al., Phys. Lett. 107B, 163(1981); C. Berger et aI., Z. Phys. C33, 351(1987) 3) R. Brandelik et al., Phys. Lett. 107B,290(1981) 4) M. Althoff et al., Phys. Lett. 138B, 219(1984) 5) A preliminary report of these data was given in the proceedings of the VI lIth International Workshop on Photon-Photon Collisions, Shoresh, Jerusalem, Israel, April 1988 (World Scientific, Ed. U. Karshon) 6 6) R. Schindler et al., Phys. Rev. D24, 78(1981) 7) P. Bhattacharya eta!., Phys. Rev. D15, 3267(1977); J. Smith et a!., Phys. Rev D15, 3280(1977) 8) V.M. Budnev, I.F .. Ginzburg, G.V. Meledin, and V.G. Serbo, Phys. Rep. 15, 181(1975) 9) B. Anderson et al., Phys. Rep. 97,31(1983) 10) S. Brodsky et al., Phys. Rev D19, 1418(1979): K. Kajantie and R. Ratio, Nucl. Phys. B159, .528(1979) 11) C. Berger et al., Z. Phys. C26, 191(1984} 12) P. Aurenche, A. Douiri, R. Baier, M. Fontannez, D. Schiff, Z. Phys. C29, 423(1985) 13) P. Aurenche, R.Baier, M.Fontannez, D. Schiff, private communication 14) H.-J. Behrendet al., Z. Phys. CSI,365(1991) 15) R. Tanaka et al., Phys. Lett. B277, 215(1992) 16) H. Aihara et al., Phys. Rev. 41D, 2667(1990) 7 ., .,. FigureC aptions Fig. 1: Differential cross section p} du / dPT as a function of the charged hadron transverse momenta PT for single tagged events with 0.075 < Q2 < 1.0 Ge V 2. The dashed line represe~ts a PT4 fall-off in du/dp} .. Fig. 2: Inclusive charged hadron cross section ratio of experiment~l data to Monte Carlo "Y"Y -+ qij events as a function of PT (0.075 < Q2 < 1.0 GeV2). Fig. 3: Inclusive](o cross section ratio of experimental data to Monte Carlo "Y"Y -+ qijevents as a function of PT (0.075 < Q2 < 1.0 GeV2). Fig. 4: Ratio of ](0 to charg~d hadron production as a function of PT (0.075 < Q2 < 1.0.GeV2). The full/dashed histograms are for Monte Carlo "Y"Y -+ qij events with/without charm. Fig. 5: Differential cross section du/dpT as a function of the charged hadron transverse momenta PT (0.075 < Q2 < 1.0 GeV2). The solid line is an analytic calculation by Aurenche et el. ll •12). The dashed line is a best fit to the data from TASS03) and the dash-dotted lines an approximate 1 sigma contour around the data. 8 JJ <0 I\) 0> to N -u -l ..--.. G) CD < -(') ----"::1 -..J 0> » N 11 «5" --L o .0 J\) +:>-m to N -U -l .--.. G) CD < --() --:1 .... m ~ o o o 1 1 ----1 ~ =#:::"" 1 1 I\) 1 -e-1 ----1 1 ----1 ~ 1 +*-~ 1 1 -J--~ t 1 1 ::J 1 1 1+ ~ + 1 X 1 1 1 1 (j) Ratio (DataiMonteCarlo) ~ t ::r 1+ + x o I\) .. , ~ ! .. 1 Ratio (DatalMonteCarlo) o o I I I. I , . • • • -.-!- • I- -e-- --.--e-II--0 ; ~ >--. ~ "Tl -l l\) cO· ..--... G) w CD i < I ---(") --I"- --- ~ -l-t -A 0 I"- + -x I I I I I I ~ Ratio KO Ihadron (Produced) o , "Tl \J -; (.Q ...-.. r G) I ..p. CD < ---~ 1 1 1 1 1"--" ..--.. C C 0.. a.. ff) ff) ........ (") --" '" dcr/dpT [pb/(GeV/c)] .;,'" ...... ...... ~ 0 0 ...... ...... ...... ...... ...... ~ I 0 0 0 0 0 --4 0 --4 I\) U> .po. 0 •• •• ~ • / ~l • I\.) ; I I I . oj lJ .,. I.' ." ---i •. I I , <5" . ;t I . -- • / / ! U1 G) I I ~ CD I I J < I I ~ 0- * -~ ---- ~ ~ :::r-1+ + X ~ "" '" » en '" 1 

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Inclusive Charged Hadron and K{sup 0} Production in Two-Photon Interactions

https://escholarship.org/uc/item/7b20k879

Inclusive charged hadron and K0 production in two-photon interactions

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