NEW RESULTS FROM ZEUS ON HIGH DEEP INELASTIC SCATTERING Qi MASAHIRO l\lJZE !\El\. lrMtitulc of Particle and :Vue/ear �tudies. J-:!- 1. Alidoricho Ta nashi. To�·yo 188-8.'iOJ .Japan Using the ZEUS <le lee Lor al ,.1HE R.A, we have analyzed 'i6.67i&-1 of deep p inelastic scattering data at. high Q2 region. Single diffe rent.ial crosse+ se ctions are pn•"'•ut.ed for neutral and charged current processes in the Q2 range cla/dQ2 from ·IOOGeV2 to ::::: 40, OOOGeV2. From the neutral u rrent data, fits to contact. int.era.ct.ion terms are performed and limits arc derived. These results include l:�p&-1 of new data taken after summer of c 1997. 177 1 Introduction Probi11p; 1 lw st rnct ure of 11urlrons with deep inelastic scat.trring (DIS) of high-energy leptons ha.s been 11iain tools in elenwnta.r�· pa t.irle physics. IIER.-\ at. DESY. coll di ng :ti .5Gr\' clrctrons 011<• of 1h1• r i .�:!OC:e\' pro1.0 1s. wi1 h 1 gives t.hr possibilit.y of studying DIS processt>s at. t.he center-of-mass energy of = :10o( :e\' which is about au order of magnit.ude higher than prPvious fixed target. experi111ent.s. Thi• 111om1•n1 um t.ra.nsfrr quar (Q2) bet.\\'rru rlPct.rou n proton has a. ma.ximu111 of 9x 10·1Ge\'2. � s ed a d s = llEH,\ ha lwru run uin g in ,+p mode since 199·1. s 199·1 1996, Hl 1 2 la From t h1• data t.a.kru during to both and ZEUS col borations reported that a.n was observed compared t.o the S audard Model (SM) predi ions in ueutral current. 1•:-;cpss of !'V<'nt.s t ct (\C') s!'a 1tl'ri11p; a t high Q2 a.nd high where is the moment.u111 fraction of the scattered pa rt.on iu t hP prot on. :\ u upd a.t. • with partial HJ97 data. has been reported in epton Photon Symposium in 1 L - lla111h11rg'1 i11d11ding t. hr harg d :c, da.rta. which show d tendency to lie a.t. high c e cu1Tent (CC) . e a.bovr SM a.1 Tlw preseutrd here are from the total l u mi 11osi -16 6pb collected by ZEUS from 1994 t.o <t. r1•sult.s t.y . - b 199·1-1 996 results 2 (20.171b- 1). HHJI. It. is more t.ha.n twice the luminosity used iu the pu lished 2 Neutral Current Results 1• vents a.re select by tagging the scatte d positron as an isolated cluster of energy deposits NC' ed re t.h<' lorimeter. The pos ron euergy has to be more than lOGeV, and an associated track with in ca it momentum larger than 5 eV is req uired in the central tracking detector. The longit udinal momentum . G conservation req u irement, :i8GeV 65GeV where E and P, are the total energy and z­ - P, , compouent'.' of the total momentum< b'measured < in the calorimeter, removes background events from phot.oprod uction. For very forward positrons outside the coverage of the central tracker, a m at chiug track is not. required but the energy requirements are tightened (Pr of the positron larger . (9 < 17°) and ·l·IGeV P, 65CeV). t.ha.n :lOGe\I - 2 The Q of the event is< calculaF: ted< with Dou ble A ngle (Di\)m ethod : 2 sin /H (l + cosO.) Q2 4 £ (1) = •sin 1H+sin 8. -si11(8c + !H) D.4 when• £, is t he iucident. po,itron energy, is the polar angle of the scattered positron and is the . 111 pola.r a nglr of t.hr t.ot.a.I hadronic system 9,calcula ted from calorimeter energy deposits. In the quark­ p>trt.on with rf t detector, corresponds to the angle of the scattered quark in the model and a pe ec /II 2 proton . The resolution of Q reconstruction is estimated from the Monte Carlo (MC) simulation , and 2 found t.o I)(' over the whole Q range used in the measurement. About 38,000 events a.re selected 2-:l% 2 with 400GeV . 2 Fip;11re shows the distribution of events in plane reconstructed in DA method Q / 8:c). oJJA - >1 y 2 (y = Th<'nu mber of observed and expected events above diffe n�ut Q cuts are shown in Table 1. There are 2 .1: 2 1.wo '""'n1.s with very high Q of more than 3.5,000GeV , but they are from 1994-1996 data and no urw in this region are observed in 1997 data. <'l'PU1.s 2 Fro111 thr Q2 distribution of t.he events, single diffcrent.ia.I cross sec:t:ions da/dQ are calculated . ll is at. most. 1 at. l backgrou nd fra.ctio11 is estimated fro111 lvIC a.nd statistica y subtracted. It % ow a.11d 111 11cli sma.ller a.t. high bins. The systematic uucertainties are estimated from various sou rces TIH' Q22 and . For Q lOOOGe\12, t he statistical error dominates the measu remen t. Figure (/ an• typically :.!-:�'Yr. :2 shows 1.IH' derived Flom level cross section, com pared with the theory curve from CTEQ<I D pa.rt.on > 2 OOG 2 dcnsit.y pa.ra.111Pt.eriiation. The cross sections arc in good agreement with SM up Lo Q ::::: :r n, O eV . 11'J'lw :: -coordinat.c is the direct.ion of llie incident prol.cm. 178 Number of obst:n·t>d l'!Xpec:ted NC' r.\ ·enl$ for different Q;n m cuts . 1V,,b •V t Tahll· l: 2500 a.nd18 17a 1792 rp± 93 Q.5000�tin 4-10 :!96 ± :.1� 10000 66 60 ±� 15000 17 ±2 :.10 3.5000 0.:29 ± 0.0:2 :2 ZEUS ° 0.9 94-97 94-96 � 0.8 • tprrlhllf•ry 1997 0.7 0.6 Q2 = GeV2 0.4 o.s 40000 0.3 Q' • .lOOOlleV G ' • 0.2 Q1 GeV1 = 0.1 Q2 20000GeV 2 1 Q1 =• GeV 1 10000 1 O 0.1 0.2 0-' 0.4 0.5 0.6 0.7 0.8 0.9 Q GeV 5000 X DA 1500 I Figure NC events with in plane. Q2 > ... 1: 2500GeV2 .1:n - YDA ZEUS Preliminary -- > 1994-97e•p � 10 '8. (."TE0.laQ40 " 10 • · PDF hand b 10 " � D . l 10 .. 10 . 10 .. stal. • . •y5l 10 , ""'{ t} ·• <B IO -' ' 10 10 Q2(Gc!V1) I.: j I llf l 11 ! I I! t ! 0.9 ' 0.8 '--.-�-----JJO 0 t=hf rn' Figure �: NC cross !::icct.ion da/d<J2 . Lower plot is the ratio between data and CTEQ4 prediction. The hand shows the unccrtaint.y estimated from the f'!xl.rapolation of low Q2 dala in QCD fit. a 179 ·1�>hl•· on contacr. interaction rcpresentati\'e models. fl4 denor.e LL + RR, LR + and .. nlt• .\'3,.\'� and LR + RL(up quark only ) model• r.. pect.h·oly. f\u for �= H Li111it Ill Fit Limit Limit. Limit Limit. fro111 from from from from from ZEllS ZF.l'S · OPAL5 ALF.PH " 3 coF 1 L ' Ty pr (TrV) .\ (To\') ;\ (Te\') .\ .\ (Te\') .\ (Te\') .\(Tc\') IT +I ·1.9 3.:l ·1.0 :1.5 :J.2 IT (I 10 ·1.3 3.9 - I •I.ti �.2 5.2 +I 2.•X· 2.0 3.8 4.9 .4.4 5 5.o 4.:l -1 > 4.8 3.1 :1.7 2.9 .·LI >JO 4.0 .\:l +I .x· 2.8 - :J .5 3.2 .\:1 -I ;1.7 3.6 1.5 - 2Jl 2.8 .\4 +I - 3.04.1 4.5 1.5 2.4 10 •1.9 .\'4 -I > 1.1 4.1 v +I :XO · - 2.0 2.1 1.8 '. · 4.li l' I -I - 2.2 · > 10 4.4 2.:1 2.(i ( ( ·X• 3 Contact Interaction From t.h0 n u current data we have er rmed tit on ossible contribution from eeqq contact !' tral , p fo p int<'raction tPrms Contact terms are re resented by additional terms to the SM Lagrangian . Here we . p o y the vector terms: a ronsider nl = L 1/af3(Ca/1,ea)(7if31''qµ) + h.c. (2) lNc lsM + ere ar or Among various combinations of four terms and w tested ll ;3 c /, R. o."t ,f) 11f,f,, llLR. 'IRL 1/RR, e nin<' modPls i n which the interaction couples to up and down quar s with equal strength, an d three k n. ou y r . models wher!' it couples l Lo up q ua k binned urnximum l kelihood tittiug is done for the observed Q d strib tion of the events, and A i 2 i u on dcnc level u pper limits are derived for the mass sca e of the possible nteraction A which is %'Ji, c fi <' l i rPla.ted to ·1'rn/A2, a 11 as 17 = ±1 . cross-check w th an al e ati e method is done which is a two-dimensional n i nned likelihood A i rn v u b = t fitting in dis ribution of the events. The two methods give consistent res lts. y t u TablP s mm ri e the results for sou1e of the models we l com rison with other experi­ 2 u a z s l pa :t , lll<'nl.s. for most. of the models he best tit g ves very large values of /\ which means co sistency wit.h t i n The limits from ZEUS data are ty pically a f w TcV audas om asar ble with those from and SM.