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

177 1 Introduction

Probi11p; 1 lw st rnct ure of 11urlrons with deep inelastic scat.trring (DIS) of high-energy 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 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 • 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 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

2 Neutral Current Results

1• vents a.re select by tagging the scatte d 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 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< calcula F: 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 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} ·•

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

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 - 4.13.0 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. e c p LEP Tevatrou expcrinwnt.s. a

4 Charged Current Results

eveul.s arc si n led by the mi sin in the ca.lorimetcr caused by the C:C g a s g transverse momentum (Pr) Psca piug ll<'lll.rino. Uncorrected Pr of gr ater than lOGcV is required. To reduce the background from e photoprod urtion, Pr / Er > is demauded , where is the total transverse energy mea.;ured in the O.'I Er calorimPl.Pr. For events with lOGeV direct on d 0 .5. i of l'T lll('

180 Number of ob�cr\"(�d aud for Q?,1111 Qf,1in nd errors Tahk J: Nobs cxpenetl.V CCa f'\·enl� different cuts. 1000 .)�6 liOO l".J"J> +.i:! -.i2 10000 22 1 I +.i.I -:i.2 1.5000 8 .9 .6 :J .9 + 1 -1 20000 0. 0.6.) :J 91 + -0.41 30000 l O.Oli +0.08 -0.0-1

Fi)?;lll'l' shows t.hr di ibution of in plane. The number of observed nd xpected :1 str CC i>vents - y a r Pn•11ts wit h diff<'rent 111i11i111u111 rnt.s r shown in T ble One outsta11ding event from Q2 ar a :1. 199·1-1996 li s :jO. OOOGeV2 but no dditional .r in this r<'gion is observed from data. Theri> <' ahovp = a event 1991 ""'' two C'V<'nt.s ll<'WC? from 1991 abov<'Q2 = :.!0, 000GeV�. Fro111 the Q2 distribution, du/dQ2 is calculated in eight Q2 bins. The background events are Pst 111a.!'d from and su btracted . They a.re t most in bin and much smaller .i t !WC statistically a 2.5% a 1 higher Q2. Systematic uncertain y is typically lO' but increases at high Q2 bins. The dominant i1 t i sourer is thr calorimeter energy scale (3%). Figur obtained cross sections Good e 4 shows the CC . agrrrment i h theory is observed up At higher the data t nd to w t thr to Q2 10, 000GrV2. Q2 e be above SM. but the ncer aint es both in s atistics and systematics are too large to draw a clear u t i t < condusion. 2 2 dependence of the cros.� e ti ns, fitto the W mass is erformed. From thr [Ma,/(Ma, + Q )] s c o a p 78.6:!:�:�(stat.J:!:U(syst.) Although the error is st ll large, this is good Tl((' rPsnlt is Mw = Ge\/. i co11firma.tion of the universality of CC interactio 1s in a com lementary kinematic region to fixed target 1 p nf'11trino s a te ing and e e /pp collisions. a r .t r + - 5 Su111111ary

-l6.671b-1 of e+p ZEUS data have been analyzed in term of du /dQ2, and NC and CC cross secti ns s o bc n measured in the ang from lOO e\12 OOOGe\12• The cro.<;Sec s tions are in good ha.vc r Q2 r e r G to 40, with M expectations up to 2 of OOOGe\12, seen from the expanded inset plots in agreement. S Q 10, ;::: Fign r<'s a.nd A few outstanding events exist at the highest bin in both channels, but no new 2 ,I. Q2 f u nd from 1997 data to confirm the significanc Fitsas to NC data set limits on contact t•vc•nl is o e. terms scale of typically 2 to 5 dependi11g on the model. The 1'V-mass de endence of a.I. pff�ctive Te V, p thr cross section allows the extraction of stat y t ) GeV CC Mw = 78.B ( .) �:g(s s . . ing massyears A will run in mode again, and comparable lumino.� ity with Dur the 1998-1999 H r:R e- p :!:U :!: da.ta. can be expect<'d . Comparison of DIS cross sect.ions gives import.ant infor­ cnrrent. e+ JI /c+ ma.t.io11 on com osition of proton and electroweak coupling of quarks. From t e year 2000 on, navor p - h ll A will be upgraded forhigher luminosity and it eis e cted to collect 1/b-1 of data in years, ER xpe few which should bring much exciting results in electroweak phy ic s s.

References

I. 1-1 1 Col labora.tio11, C. Adloff al., Z. l'hys. C 74, 191 (1997). '2. ZEllS Collabora.t.io11, .I . Breitwcg ftl., Z. Phys. C 74, 207 (1997). St.raub, - oton Symel posium 1997, Hamburg. :1. H. Ph el http ://www .desy . de/lp97-docs/proceedings/lp30/lp30 .ps Collaboratio11, F. Abe al., Lett. ·I. CDF Phys. /lm 79, 2198 ( 1997). 5. OPAL Collaboration, 11:. Ackerstaff el rt/. , CERN-PPE/97- 101(1997). J\Ll�Pll oll bo ation el for valu s from contributed paper #602 Ii. C a r , ALr:PH 98-02 1(1998), cxcept lJ4 e to !·:I'S Co11ference Jerusalem 1-ll·:P 1997, . et al., L:l Collaboration, M. Acciarri CERN-EP/98-3 1(1998). F ..Ja np1et. nd A. Blonde , Proceedings of thr study for n facility for urope, a. ! a cp E 1. DI·:SY p . 79-48(1979), :l91 X

181 ¥US 1994-97 Pre!iminary = 1 �c•p �vx ;;:0_9 199.1-1996 • \ 0.LI \0 1997 l>•U& \

'

.4 .5 .6 . events0 in0 0 0 7 plane.

Figure 3: CC x1n - YJB

10ZEUS Preliminary 1994-97 CTEQ4D ��! b

POF band

10 ·•

� 10 .7 Slal{: } Sia!. $ syst. 10 L..���.-, �������� -,���- '---'-" '" . 1 1 .. 1(CeY1) 1.2� Q 0.9 1 I ,: 1I0 ! 10, · o.s ' I 0 * f I l I I

!"t:c:t.io11 bar is sli-it.isl.ical and bar is statistic <.:ro�" da/dQ2 . added quadrature.

Figun� ·I: CC luuer error Llic outer ilncl y s stcmaLi<: errors in

182