SUMMARY OF THE SESSIONS ON LEPTON-HADRON PHYSICS D. Haidt To cite this version: D. Haidt. SUMMARY OF THE SESSIONS ON LEPTON-HADRON PHYSICS. Journal de Physique Colloques, 1982, 43 (C3), pp.C3-5-C3-21. 10.1051/jphyscol:1982301. jpa-00221854 HAL Id: jpa-00221854 https://hal.archives-ouvertes.fr/jpa-00221854 Submitted on 1 Jan 1982 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL DE PHYSIQUE CoZZoque C3, supple'rnent au no 12, Tome 43, de'cembre 1982 page C3-5 SUMMARY OF THE SESSIONS ON LEPTON-HADRON PHYSICS D. Haidt DESY, Notkestrasse 85, 2000 Hamburg 52, F.R.G. Introduction This report gives a short r6sum6 of the two sessions on lepton-hadron scattering. Three topics, namely structure functions, hadronic final states and prompt leptons in beam dump experiments, are summarized here, other topics are found in the summaries of L. Sehgal and V. Barger. 1. Structure Functions Deep inelastic lepton scattering off nucleons or nuclear targets has revealed the composite structure of nucleons. The lepton interacts with the quarks inside the nucleon through neutral and charged spacelike currents. All electroweak phenomena areso far well described by the standard model based on the gauge group U(1) x SU(2). These electroweak currents are therefore ideal tools to investigate the structure of the nucleon. The given gauge structure implies relations between the structure functions observed in charged lepton experiments and in charged and neutral current induced neutrino and antineutrino experiments. The major interest in measuring structure functions is the understanding of their scaling violation. Rather good and consistent data exist from various experiments on isoscalar targets. Least known is the longitudinal structure function related to the exchange of helicity 0 gauge bosons. Another class of experiments deals with lepton scattering off simple targets like hydrogen and deuterium. Although such experiments are based on smaller statistics they are of importance in disentangling the flavour composition of the quarks in the nucleon. Furthermore, in comparing measurements on deuterium with measurements on complex (almost isoscalar) targets nuclear effects may be tested. This topic can be kept short, since F. Eisele is dealing extensively with structure functions in his plenary talk. Table 1 summarizes the contributions to this Conference. (a) ~y~s_s_~~]~~~~]yn_I~m~:~-_su_~yu_~~ 1 This sumrule, I F3(x)dx = #q - #q = 3 (Q2 + a), originally derived from current 0 algebra measures the number of valence quarks in the nucleon, which equals 3 in the quark model. Fig. 1 shows the data of two experiments [3,41. The errors are statisti- cal. The sumrule is satisfied even at low Q" provided the contribution of elastic events is included. No or little variation with Q2 is observed. It should, however, Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982301 JOURNAL DE PHYSIQUE Experiment Quantity Speaker Contr. Paper Reference BEBC - ABCMO v,v H2 d/u Schmid # 596 1 - ABCDLOS v,v Ne F2, xF3 2 3 BEBC-GGM fF3 - CCFRR v,v Fe F2, xF3, /F3 Shaevitz 4 - - CDHS v,v Fe F2, xF3. q # 708 5 xG(x) # 706 6 # 318 7 R Merl o 8 CDHS v,V H~ dv/uv, T/U Merlo 8 i CHAR14 v ,: NC x-distr. # 590 9 BCDMS VC F2, R Edwards 10 EMC vFe, Hz, D2 F~RoN/F~~,R Edwards 10 P F2, F;, d/u Edwards 10 # 749 11 F2 .--------------------___--_-------_-_=---------------=------------------------------------------=--------------- .......................................... Table 1: Contributions to this Conference be noted that the integral gets important contributions at small x. For fixed Q2 and given-neutrino energy spectrum there is a smallest value of x. The small x region is therefore parametrized as xF3 (x) = AX^ with a = 0.5. 1 I . .......I . ..'...'I ' """'I ' """'1 x CCFRR (Ref.4 --Partonmob.lpr.diction -OCD prdietion XI-aJx 1. 2 Figure 1. The Gross-Llewellyn-Smith sumrule as a function of Q . New data were presented by CDHS r81, EMC pHZ and yFe [I01 and BCDMS 1101. R = uL/aT FL/F2 is related to the longitudinal structure function FL F2 - 2xF1. In the naive quark parton model FL = 0 (Callan-Gross relation). R is important for the extraction of F2. The differential y and v +T cross sections are proportional to 1 + (I-Y)~- y" and thus rather insensitive to R. The CDHS collaboration has presented considerably improved values for R at large x (see fig. 2). The idea of the new method consists in exploiting the quantity At large x the quantity A is known experimentally to be nearly zero, thus a tight upper limit can be obtained for R. Averaging over 0.4 < x < 0.7 gives <R> 5 0.006 2 0.012 + 0.025. In the region x < 0.4 R is still badly measured. JOURNAL DE PHYSIQUE x CDHS Figure 2. Pleasurements of R =FL/2xF1 averaged over the hadron energy as a function of the Bjorken variable x. The data from CDHS with the new method are - upper 1imi ts. New results from various experiments (see table 1) were presented. The high statistics experimentswithfinal results agree in shape with each other at the 10- 15% 1eve1 . However, the prel iminary data presented by the CCFRR coll aboration [4 1 disagree systematically when compared, for instance, with the data of the CDHS 1 collaboration 15 1 . A1 ready the quantities (ov+ ov) measured in the CCFRR experiment show a substantial energy dependence, unless the deviation from constant behaviour be ascribed to normalization differences. It should be noted that this experiment consists of a combination of 5 independent beam settings. The new, preliminary data of the BCDMS collaboration [lo] will be discussed in con- text with other data by F. Eisele. The EMC collaboration 1101 has extracted the structure function F2 both from their iron and deuterium data. The ratio is plotted in fig. 3 versus the scaling variable x and is not constant, as naively expected, but decreases systematically with increa- sing x by about 30%. No explanation has as yet been put forward. This effect under- lines the importance of lepton scattering experiments using simple targets like hydrogen and deuterium. I Q': 50 G~V' F202 - Figure 3. Ratio of the function F2 EMC measured on iron and deuterium vs x. 1.2 Fermi Smearing - \/' - The dashed line represents the / - / effect due to Fermi motion. The sys- -11 I, / tematic error (not included) amounts 1.0 --+---+- t +t-t-+-A/ 1, to about 0.1. - t 0.8 - I I: 0 .2 .4 .6 X The CHARM collaboration 191 has contributed a new piece of information in measuring the x distributions in v and < neutral current reactions. Under simplifying assump- tions one obtains: where u R,L, dR,L are the neutral current couplings and k referring to v resp. 7. The nucleon structure functions in neutral current interactions (see fig. 4) show no significant difference to those measured in charged current interactions as ex- pected by the quark model and the standard model of electroweak interactions. Figure 4. Neutral current x-distributions for v and ;interactions. ( e !_a-r_t._t- ?_t-r-u_c_t-u-r_e- f_~_n-c_t~i~o_n-s The sea quark distribution xq (x,Q2) = x (u + a + 2y) is well measured [51. With their < induced opposite sign dimuon sample the CDHS collaboration has deduced the structure function of the strange sea L7j. It agrees in shape with the measured anti- quark distribution q. Using further assumptions they get which suggests a nonsymmetric sea. However, a/ii is compatible with 1 within 30% 18). Three collaborations have presented results on the ratio of the d and u structure functions [I ,8,10]. The data agree with each other (fig. 5) for x > 0.3. The CDHS group deduced the valence distributions. No data exist beyond x = 0.8, where theoretical models give different predictions. JOURNAL DE PHYSIQUE Figure 5. Ratio of quark structure functions d(x)/u(x) vs x. The charmed sea is still rather badly known. The gluon distribution function is derived by the CDHS collaboration [6] from the Q2 evolution of F2 and xq. 2. Results, on Hadronic Final States New results on final states in lepton-hadron scattering experiments are summarized in table 2. Some contributions are already in their final form and published. They will not be commented here. Four bubble chamber experiments presented data on charged hadron multiplicities. The following table shows that the sizes of the v and < event samples are quite substantial. 1 I I Experiment SKAT 1 15' 1 BEBC ! BEBC / i I I 1 I Liquid Freon I ' D2 Hz-TST 1 I # u 1493 I , 400 t 4120 j ' 1 t I Contr. Paper 348 456 61 2 712 1 Table 2 ----------------------------------------------------=-------------------------------Exeeriment ------------ 4ua_n_t13~~~-~.~ ---S_eea_ker--- '_-~_on_tr~~ia_~er-~~-~~Re_f~---- BEBC WA21 mu1 tip1 icity Schmid # 712 13 charge properties # 711 14 WA24 # 612 15 WA25 fragmentation Vignaud # 543 16 WA59 cos @ # 737 17 15 ' FNAL IMSTT vDp multiplicity Snow # 456 18 Snow # 756 19 "'5 IIF 3 Ne p exclusive Sehgal # 303 p bremsstrahl ung 21 CDHS NC production # 704 2 2 c-fragmentation # 318 7 SKAT KO, A # 504 23 h* production # 347, # 348 24 GGM # 747 25 EMC - NA2 COS 6, PT Becks # 750, # 795 26,27 Q~ evolution # 748 28 nuclear targets # 751 29 heavy quarkonium # 752 30 open charm # 773 3 1 P/., p, B Becks 32 2 EMC - NA9 PT* Y Becks 3 2 C3-12 JOURNAL DE PHYSIQUE Two groups emphasize the importance of correct mass assignment.