Gluon emission and the transverse momentum (p/sub t/) of partons confined in nucleons were studied using deep-inelastic charged-current neutrino-nucleon interactions. For this analysis we use the flow of hadronic energy in the azimuthal direction around the momentum transfer referenced from the neutrino-muon scattering plane. A five standard deviation asymmetry was found. Analysis of this asymmetry indicates a (p/sub t/) of 0.35 +- 0.12 GeV/c if QCD corrections are included, and 0.56 +- 0.05 GeV/c if they are excluded. Some evidence was also observed for x dependence in p/sub t/. Data were taken at Fermilab in 1982 using a 200 ton (fiducial mass) fine grained calorimeter and a dichromatic neutrino beam

Bofill, J.

Busza, W.

Eldridge, T.F.

Friedman, J.I.

Fuess, S.

Goodman, M.C.

Kendall, H.W.

Lyons, T.F.

Magahiz, R.A.

Mukherjee, A.

Eldridge, T. F.

Friedman, J. I.

Goodman, M. C.

Kendall, H. W.

Lyons, T. F.

Magahiz, R. A.

UNT Digital Library

A Fermi National Accelerator Laboratory FERMILAB-Conf-86/102-E 7000.594 AZIMUTHAL ENERGY FLOW IN DEEP INELASTIC NEUTRINO SCATTERING* A. Mukherfeea, J. Bofilla, W. Busza, T.F. Eldridgeb, J.I. Friedma 2 S. Fuess, M.C. Goodmanc, H.W. Kendall, T.F. Lyons, R.A. Magahit , T. Mattison, L.S. Osborne, R. Pi@, L. Rosenson, A. Sandacz , F.E. Taylor, R. Verdier, J.S. Whitakerg, G.P. Yeha Massachusetts Institute of Technology, Cambridge, MA 02139 USA D. Bogert, R. Burnsteinh, J. Morfin, L. Stutte Fermi National Accelerator Laboratory, Batavia, IL 60510 USA M. Abolins, R. Brock, A. Cohen, D. Owen, J. Slateb, M. Tartaglia, H. Weerts Michigan State University, East Lansing, MI 48824 USA J.K. Walker University of Florida, Gainesville, FL 32601 USA June 12, 1986 *Submitted to the XXII.1 International Conference on High Energy Physics, California, July 16-23, 1986 Operated by Universities Research Association Inc. under contract with the United States Department of Energy Azimuthal energy flow in deep inelastic neutrino scattering A. Mukherjee=, J. Bofilla, W. Busza,T.F. Eldridgeb, J.I. Friedman, S. Fue~ss, M.C. Goodman’, H.W. Kendall, T.F. Lyons, R.A. Magahitd, T. Mattison, L.S. Osborne, R. Pitt*, L. Rosenson, A. Sandaczf, F.E. Taylor, R. Vsrdier, J.S. Whitakerg, G.P. Yeha Massachusetts Institute of Technology Cambridge, MA 02139 D. Bogert, R. Burnsteinh, J. Morfin, L. Stutte Fermi I ab Batavia, IL 60510 M. Abolins, R. Brock, A. Cohen, D. Owen, J. Slateb, hi. Tartaglia, H. Weerts Michigan State University East Lansing, MI 46824 J.K. Walker University of Florida Gainesville, FL 32601 Submitted to the XXIII International Conference on High Energy Physics June 12, 1986. -2- Abstract We study gluon emission and the transverse momentum (p,) of partons confined in nucleons using deep-inelastic charged- current neutrino-nucleon interactions. For this analysis we use the flow of hadronic energy in the azimuthal direction around the momentum transfer referenced from the neutri no- muon scattering plane. We find a five standard deviation asymmetry. Analysis of this asymmetry indicates a <pt> of 0.35+0.12 GeV/c if QCD corrections are included, and 0.56t0.05 GeV/c if they are excluded. We a Iso observe some evidence for x dependence in pt. Data were taken at Fermi lab in 1982 using a 200 ton (fiducial mass) fine gra i ned calorimeter and a dichromatic neutrino beam. PACS 13.15Em -3- Deep-inelastic neutrino-nucleon (vN) scatter i ng prov i des a tool to study the small-scale structure of nucleons. Previous experiments have concentrated on structure functions; these measure the longitudinal (along the momentum transfer) momentum distribution of struck partons. The evolution of the structure functions with increasing Q2 tests QCD radiative corrections. In our work we consider the flow of hadronic energy around the momentum transfer direction. This measures the transverse momentum of struck partons (p,), and provides a more sensitive test of perturbative QCD. Analyses of this kind have been done by bubble chambers’, but lower energies and lack of statistics have made the results ambiguous. An equivalent analysis using muon-nucleon deep-inelastic scattering has been performed by EMC2. Similar information can be extracted from dilepton production in hadron-hadron scattering via the Drell-Yan process3, but the purely hadronic interaction complicates the analysis. In our study of the azimuthal asymmetry in vN deep-inelastic scattering, we measure <pt> versus the Bj orken scaling variable x=Q2/ (2mv) and give more consideration to a threshold effect in production of 3-jet final states. Our detector was a 200-metric-ton (fiducial mass) calorimeter with 5mm lateral binning and 3cm (.25 radiation length, 0.03 absorption length) longitudinal segmentation4. The detector measured two orthogonal views of energy flow from which an azimuthal asymmetry is determined by looking at -4- a correlation between hadronic energy flow and the muon scattering angle 5 . The data sample consists of 9200 neutrino events obtained with three momentum sett i ngs of the dichromatic beam, and 1800 antineutrino events from one beam setting. To measure the flow of hadronic energy around the momentum transfer direction, we define the azimuthal angle #; for a single hadron i referenced from the neutrino-muon scattering plane as shown in Fig. 1. The quantity we wi I I study is the energy weighted average of COS#~ co+ Zcos~;E; (1) Ei where Ei is the energy of hadron i and the summations are over all particles in the hadronic final state. Equation (1) is for a single event; we us* <cos$> to refer to an average over events. With no gluon emission, the final hadron state has two jets: the current jet and target jet. If the struck parton has no component of momentum transverse to the exchanged W* boson which mediates the interaction, both jets are aligned with the momentum transfer direction. Therefore the mean value of co+ is zero. If the struck parton has nonzero transverse momentum, the current and target jet directions are shifted away from the momentum transfer d i rect i on and an asymmetry in the energy flow is possible. The UN cross section is proportional to s, the square of the center-of-mass energy of the incident -5 neutrino and parton. A kinematic analysis shows that s depends on the orientation of pt, giving events with the target jet between the outgoing I epton and current jet a larger cross section than other configurations. At the parton level for Q*>>p,* it has been shown that: <cos#>=- (PJQ) (l-y) *l’*, (2) where the “+I’ sign iS used for neutri no-quark or antineutrino-antiquark, the ,I _ II sign for antineutrino-quark or neutrino-antiquark scattering 6 . This effect causes <cos#> to be of order -.I for <pt>=0.3 GeV/c in the energy range of this experiment. First order QCD introduces an additional forward jet from gluon emission which is usually soft compared to the current jet. An interference between gluon emission from initial and final parton lines emphasizes events where this soft jet lies between the outgoing lepton and the currant jet. A similar affect occurs for 3-jet events from gluon fusion, but as this makes a much smaller contribution wa restrict our discussion to the gluon emission events. At the pat-ton level for small x we find: <cos#>=-as (Q*) f (x) (l-y) l l’* , (3) where the double sign has the same convention as in equation (2) , us (Qx) is the strong coupling constant, and f (xl is a convolution over structure functions’. The QCD contribution to <co+> is expected to be also of order -.l for the energy range of this experiment. -6- In converting the pa rton level first order QCD calculation to the correspond i ng result for observable particles we encounter some difficulties. The derivation of equation (3) included zero energy and col inear jets. The cross section for scattering with gluon emission (3-jet events) has nonintegrable singularities in these regions, some of which are cancelled by summing diagrams and the rest are factored into the structure functions. These analytic methods cannot be implemented in a phenomenological Monte Carlo calculation (MC) to convert the parton jets to observed particles. The nonintegrable regions of the cross section must somehow be excluded. Most popular MCs apply a cut on energy and col ineari ty (with the struck parton) of the radiated gluon* which results in very few 3-j et events and a negligible <co+> contribution. The treatment of 3-jet production in our MC is to duplicate the analytic pa rton level result as nearly as possible spectrum Since th i, Al I events conta i n three jets, with the gluon cut to keep the inclusive cross section fixed 5 . s strategy is not an obvious one, we also consider the other extreme, a *-jet MC (no event has 3-jets), which is equivalent to the MCs used in other experiments. The pt contribution to <cos#> (equation 2) can be viewed as absorbing all QCD terms not included in equation (3). In principle, a complete QCD calculation should predict <cos#> without any pt term, or equivalently should predict the pt to -7- use in equation (2). Note there is no theoretica I reason why this pt should be independent of the scaling variable x. Lacking a complete all-order QCD calculation, we can use the measured structure functions to predict the effective pt distribution by invoking spherical symmetry in the nucleon rest f ram*. The principal resu It is that <pt> is proportional to x at small x. The detailed validity of this calculation is however not clear since structure functions do not provide a good description of a nucleon in its rest frame . We note the x dependence predicted by this calculation is similar to those from other methods’, and wc will use it as a guide for an experimental study of <pt> versus x. The parton level asymmetry is reduced by hadronizatioo and secondary interactions. Our hadronization model and simulation of secondary interactions predict a reduction factor of about five, giving an expected <co+> of about - 0.02. The measured co+ distribution and its mean (- 0.016*0.003) are shown in Fig. 2. The plot is folded to emphasize that the mean of the distribution is small compared to the width, but it is not dominated by a few events in the tails of the distribution. We investigate’ d the fol lowing possible sources of systematic error: i, dentif ication of the muon track (to.0004 in <cos#>) ; remova I of leptonic energy deposition (+O.OOOl); shower containment (to. 0005) ; and bias in the determination -6- of the momentum transfer direction (*O.OOOS) The total systematic error, U <cos#> =0.0008, is found to be an order of magnitude smaller than the statistical error. Detai Is of the analysis and the study of systematic errors may be found in reference 5. If we assume <pt> is independent of x and fit <cos#> averaged over all events, we find <pt>=0.35*0.12 GeV/c using our 3-jet MC and <pt>=0.56*0.05 GeV/c using the 2-jet MC. Statistical and systematic errors have been combined in the quoted error. The best variable with which to separate the pt and first order QCD effects is Q*. The pt term (equation 2) varies as l/Q, while the 3-jet term (equation 3) varies logarithmically with Q* due to the running coup1 ing constant a,(Q*) . No matter what the x-dependence of <pt> is, at sufficiently low Q* the pt term should dominate, while at sufficiently high Q2 the QCD term should dominate. We are however limited at the low Q* end by the range over which events may be considered deep-inelastic, and at the high Q2 end by the finite energy of the beam. Fig. 3 shows the measured <cos#> sliced in Q for data, and <cos$> as predicted by 2- and 3-jet MG with pt independent of x. The agreement with either MC is poor, but is seen to be better in the 3-jet case compared to the 2-jet case. To improve the fits, we have allowed <pt> to be a function of x of the form <pt>=ax+b. We find the best in the 2- or 3-jet MC agreement is obtained with b=O, i.e. <pt> proportional to x. The result of this fit is presented in Fig. 4. The agreement is seen to be better than in Fig. 3, but there is I ittle distinction between the 2- and 3-jet cases. -9- We conclude that if <pt> is required to be x-independent, the data favor our 3-jet MC over the *-jet (standard) MC. Better fits are obtained with <pt> proportiona I to x. In this case, both 2- and 3-jet MCs give reasonable agreement, and the only point favoring the 3-jet MC is the unexpected large value of <pt> in the results are in agreement w ‘i In summary, we have asymmetry in the azimuthal *-jet case. Note that our 2-jet th EMC*, who used the Lund* MC. found a statistically significant distribution of hadronic energy in deep-inelastic charged-current neutrino-nucleon scattering. We interpret this as due to an intrinsic transverse momentum of partons confined in nut I eons, with a mean of 0.35t0.12 GeV/c if gluon emission is included in the calculation, or 0.56+0.05 GeV/c with no gluon emission. We have some evidence for pt being dependent on x. With the limited Q* range of our data, we cannot separate the QCD gluon radiation effect from intrinsic pt effects. We are in the process of analyzing a I arger, higher energy data sample which may significantly improve our measurement 10 . This work was supported by the Nationa I Science Foundation and the U.S. Department of Energy. The technical assistance of the Fermi lab staff is gratefully acknowledged. -lO- a)Present address: Fermi lab, Batavia, IL 60510 b) Present address: Hughes Aircraft, Los Angeles, CA 90009 ‘)Present address: Argonne National Lab, Argonne, IL 60439 4 Present address: Union College, Schnectady, NY e)Present address: Bell Labs, Naperville, IL f> Present address: Inst i tute of Physics, Warsaw University, Warsaw, Poland 9) Present address: Boston University, Boston, MA 02138 h) Present address: Illinois Institute of Technology, Chicago, IL 60616 ‘M. Derrick et al., Phys. Rev. D24 1071 (1981) - *J.J. Aubert et al., Phys. Lett. 8130 118 (1983) 3A.S. Ito et al., Phys. Rev. D23 604 (1981) - 4D. Bogert et al., IEEE Trans. Nucl. Sci., Vol. NS-29, No. 1, February 1986 5 A. Mukherjee, 1986 Ph.D. thesis, Massachusetts Institute of Technology, Cambridge MA 02139 (unpublished) 6R.N. Cahn, Phys. Lett. 788 269 (1978) - 7R.D. Peccei and R. Ruckl, Nucl. Phys. 8162 125 (1980) *B. Anderson et a I., Phys. Reports 97 31 (1983) - 9 V. El Iwanger, Nucl. Phys. 8154 358 (1979) 10 E-733 at FNAL Tevatron Quad Triplet beam -ll- Figure Captions Figure 1. Lab frame event geometry. Py and P,, define the I epton scattering plane. ‘h is the tota I f i na I state hadronic momentum; neglecting Fermi motion, this is also the momentum transfer. The azimuthal angle for a single hadron of momentum Pi is shown. Figure 2. Event-by-event co+ estimator with the negative half of the distribution folded onto the positive half. The arrow marks the mean, <cos#>=-0.016, folded onto the positive axis. Figure 3. -<cos#> versus Q <pt>=0.56 GeV/c, and 3-jet MC w vertical scale has been multipl Figure 4. -<cos#> versus Q <pt>=8.2x GeV/c, and 3-jet MC w for all data, *-jet MC with th <pt>=0.35 GeV/c. Note the ed by 1000. jet MC with for all data, 2- th <pt>=1.3x GeV/c -12- Fig. 1 P z 350 2.l 300 250 200 150 100 50 0 r 0 43-a -m-w- ET , , IVE , .,,ATIVE , I I 0.2 0.4 0.6 Fiq. 2 50 40 30 20 0 0 O( -14- . . b.. . t 4 4- f , . . . -t . I . . . . . . - - --_ -_ I + - 0 DATA Cl 2-JET 0 3-JET . . . . ..# I...... ------- +..--- I I I I 2 4 6 8 1 Fia . 3 Q(GeV/c) -15- 50 40 30 20 10 0 -10 0 DATA Cl 2-JET 0 3-JET I - . i 7.41 . . b.’ ‘... . ..r. s 1 12: . . . . . . . L . . . . . . . 1 _--mm- 1 I I I 2 4 6 a Fia . 4 QCGeV/C) 

Azimuthal energy flow in deep inelastic neutrino scattering

Azimuthal energy flow in deep inelastic neutrino scattering

Abstract

Similar works

Full text

Available Versions

UNT Digital Library