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NEW SEARCHES AT II ( ) TERUKI KAMON Department of Physics, Texas A&M University College Station, Texas 77843-4242 On behalf of the CDF and D0 Collaborations

Abstract Various recent results of new particle searches at the Fermi lab Tevatron are presented. No evi­ dence is found forsupersymmetric , gluino , and heavy gauge ( ) bosons in pfi collisions at TeV. Excluded mass regions foreach particle are determined. Js= 1.8 594

1 Introduction With the data from CERN's LEP - collider, DESY's HERA electron- collider and Fermilab's Tevatron proton- collider, the (SM) has received overwhelm­ ing experimental support. No new physics has been observed essentially at mass below �Mz. Thus, it is imperative that the Fermilab Tevatron, the world's highest energy particle collider, be used for searches of new phenomena. The CDF and D0 experiments have been actively studying their data for evidence of previously unobserved particles. Presented below are the latest results of searches at the Tevatron for supersymmetric particles (chargino, gluino), leptoquark bosons and heavy gauge bosons.

2 Search for and at CDF and D0 x[xg gg The Minimal Supersymmetric Standard Model (MSSM) [l) is a supersymmetrized SM with two Higgs doublets, which is one of the most appealing theories proposed to test grand unification [2). Conser­ vation of R-parity requires the SUSY particles to be produced in pairs and prevents decays of the lightest supersymmetric particle (lightest x?). The most distinctive signatures of chargino­ neutralino (xtxg) and gg (ijij,gij) pair production are trilepton events [3) and like-sign (LS) dileptons associated with large missing transverse energy (tr) plus multi-jets [4). Pair-produced xtxg decay as xt -+ e±vx0 and xg -+ e+e-x0. The striking signature of these events is thus three isolated plus tr. The CDF search is based on 100 pb-1data. Most of the events are from inclusive e and µ triggers at PT � 10 GeV/c. The trilepton requirements are Pr(l1) > 11 GeV /c and PT(£2,3) > 5 (4) GeV /c for e (µ), which is the same as in the previous analysis (based on 19 pb-1) [5) . Eight events are left which are consistent with the SM background. A further cut of tr> 15 GeV is imposed to reduce the background. There is no trilepton event candidate found, which is consistent with an expected background of 0.4 ± 0.1 for four trilepton (eee, eeµ, eµµ, µµµ) modes. The D0 trilepton analysis requires a lower cut of Pr(f1,2,a) > 5 GeV /c, although the events are from several trigger paths (inclusive e and µsamples and ee, eµ and µµ dilepton samples) . The acceptance difference due to those trigger thresholds are corrected using a Monte Carlo simulation. D0 also observes no trilepton event candidate in 14 pb-1 , which complies with an expected background of 0.8 ± 0.5 for eee, 0.8 ± 0.4 for eeµ, 0.6 ± 0.2 for eµµ, 0.1 ±0.1 for µµµ [6]. Both CDF and D0 have a similar constraint inspired by supergravity models [7). The CDF analysis [5) calculates slepton (l) and sneutrino masses from tan �, M(g), and M(ij) using the (v) renormalization group equations [8] , while D0 [6) uses a minimal supergravity model in ISAJET [9]. In those models, chargino and neutralino have three-body decays. The CDF analysis excludes M(xt) < 66 GeV/c2 (95% C.L.) at tan � = 2, M(ij) = l.05M(g) and µ= -400 GeV (the region of maximum experimental sensitivity). The CDF limit on xt (66 GeV /c2) is comparable to the LEPl.5 result [10]. The D0 result is not sensitive to set any mass limits for the ISAJET model. Limits on a· BR(4 trilepton modes) are also obtained: 0.6 pb (CDF) and 4 pb (D0) for 70-GeV /c2 chargino. CDF also examines one particular supergravity model, flipped SU(5) model [11]. In this model, M(lR) < M(xg) < M(h), so that the trilepton signal is nearly maximized via BR(xg l�fl') � 66% (e and µ) and BR(i� -+ £�x?) = 100%. However, the mass difference of lR and x? decreases-+ as M(xt) increases, so that the total trilepton acceptance as a function of M(xt) becomes flatat about 5% at 60 GeV /c2 and falls offfor M(xt)� 75 GeV /c2. Figure 1 shows the 95% C.L. upper limit curve on a· BR(xtxg -+ 3fX). The points in the figureare the ISAJET predictions for xtxg production in the supergravity model. The limit on M(xt) is 73 GeV /c2. The LS dilepton approach is complementary to the classic multi-jets+tr analysis in the search for gg, gij and ijij production. The signature arises mainly from gg production followed by dominant decays of g-+qq 'xt and g-+ qijxgif M(ij)> M(g) . Thus, the finalstate contains two or more leptons (from xt and xg decays) , tr and jets. Since the gluino is a Majorana , there is no charge correlation between these leptons. Such a data analysis begins with a dilepton sample (Pr(f1(2)) > t 12 (10) GeV /c) and subsequently requires r > 25 GeV and N(j) � 2 with Er(j1(2J) > 15 GeV in 595

3.0 CDF preliminary 100 Run lA + 18 data: pb-1 2.0 u SU(5) x U(l) model Rel: PRO 52, 4178 (1995) - 95% C. L. :;;- limit .£:: >< 1.0 .:!; = T 0.7 �� '>< 'ii: 0.5 '!i ' b K 73 0.3 GeV/c2

0.2 50 60 I70 80 90 100 / ' M;: (GeV c ) Figure 1: 95% C.L. upper limit on BR(xtxS --+ 3lX) vs. M(xt). The points are the predictions of ISAJET. Note that a3 · X) BR(xt --+ e±vx?) . BR(xg --+ i�l" ) . BR(i� --+ e�x?) BR(xtxg --+ l = for four trilepton modes.

1'7U1(2J)I < 1.1(2.4). Since the production cross section times branching ratio is small, CDF searched for the dilepton signature without the LS requirement. In 19 pb-1 , one event (µ+ µ-) is observed, which is consistent with an expected background of 2.39�g:��· The lower gluino massat 95% C.L. is 2 M(ij) M(g) 2 M(ij) M(g) calculated to be 154 GeV /c for � and 224 GeV /c for = at tan (J = 4 and 400 GeV (12]. Those limits weakly depend on the tan (J values (2-8) and the µ values (200 GeV µ = - < lµI < 1000 GeV).

3 Search for Leptoquark Bosons at CDF and D0 Leptoquark is a generic term for color-triplet bosons which couple both to a and a . They appear in many SM extensions which join the quark and lepton sectors at more fundamental levels (13]. Both CDF and D0 search for pair-produced lepton . The signatures are e+e- + 2 jets and e + tr + 2 jets. The D0 analyses of the first and second generation scalar (LQl and LQ2) searches using e+e-jj and lvjj events are based on 15 pb-1data (14, 15]. Neither analysis findsevidence fora leptoquark signal. The mass limits are 130 (116) GeV /c2 at (J 1 (0.5) for LQl with HMRS-B; 119 2 LQ2 =BR(LQ; --+ q (97) GeV /c at (J = 1 (0.5) for with CTEQ2pM. Here (J l; ;). Note that MT-LO is the nominal choice in D0's LQl and LQ2 analyses. The CDF= results on the LQl and LQ2 searches 1 1 are based on 4.1 pb- (16] and 67 pb- data (17]. The limits at (J = 1 (0.5) are 113 (80) GeV /c2 for LQl with HMR.S-B and 180 (141) GeV/c2 for LQ2 with CTEQ2pM. CDF also searches for the third generation leptoquark (LQ3) in r+r-jj mode, where one of the r leptons decays semileptonically and the second r has 1 or 3-prong hadronic decays. The r-decay lepton e or µ) is required to have PT > 20 GeV /c (1'71 1.1). The hadronic decay r must have uncorrected( Er > 15 GeV (1'71 1) associated 1 or 3 tracks< (the leading track > 10 GeV /c) in a < PT 10° cone around the energy cluster. The charge of the candidate is defined to be the total charge of 1 or 3 tracks and required to be an opposite sign tor the lepton charge. This reduces the QCD 596

Preliminary CDF 70 pb-' (1A + 1 B) .D a_ K= . �� �� / alfl Vector, 1, Pythia v5 6 b ,�: ���!��: ��j�/:;u�� v5 6 CTEQ2LO .

·.

957. C L. Upper L1m1ts

,f•100:;:o;,Vector, ,B•BR(LQ-hb}Km1, M>2 20 GeV/c2 • ·... Vedo r, M > 165 GeV/c' · . O Scalar, A"=O.M > 94 GeV/c2 · ... · A ··

·· · · · . ·· · · · ·· . ... 10 · · . · .. ·

50 75 100 125 150 175 200 225 250 Gen. Mass, GeV/c' 3" LO Figure 2: 95% C.L. upper limit on vs. M(LQ3) for /3 BR(LQ3 1. a = � Tb) = background by a factor of �2. The azimuthal separation between the lepton and tr directions should be less than 50° to reduce the W(� iv) + jets events. Finally, two jets are required with uncorrected Er > 10 GeV in 1'11 4.2. No events are left; consistent with the expected SM background of l.2±b:g < events including 1.0 Z event. Figure 2 shows the �results TT of the mass limits on LQ3 for the scalar and the vector bosons

(both = 0 and 1, where is an anomalous chromomagnetic moment). All limits on M(LQ3) are obtainedr;. at f3 1. r;. = 4 Search for W' WZ at CDF � � evjj In extended gauge models [21] proposed to restore left-right symmetry to the weak force, the right­ handed, charged bosons W' can decay with large probability to right-handed lniJn pairs. Both D0 and CDF have searched for the heavy W' through the process pji W' ev (or envn if M(vn) M(W')) � � <: in 74.4 pb-1and 19.7 pb-1 , respectively. The searches were made by assuming a standard strength W' WZ ( C of the coupling and the decay to be suppressed by a left-right mixing angle = [M(W)/M(W')]2 where C is 0(1). The� limits are 720 GeV /c2 [19) and 652 GeV /c2 [20). The CDF experiment is conducting a complementary search for W' in the decay to WZ evjj with Er (e) > 30 GeV /c2 1.05), tr > 30 GeV, Er(j1 }) > 50 (20) GeV. Additional tracking,� ( !JI< (2 isolation and electron identificationl criteria are also imposed. The previous result [17] is updated using llO pb-1data: 512 W' candidate events are left. We observe 7 events for M(W + jj) > 600 GeV/c2, compared to 4.2 expected events. We find no significant evidence for excess Z production produced in association with a W. The limits are obtained by a likelihood fitwith the data, background and signal shapes. The results of the excluded region in the (-M(W') plane are shown in Fig. 3. The range of 200-560 GeV /c2 is excluded at ( 1, which is consistent with the limits above. However, the CDF analysis is insensitive = C to setting any limit at = 1. 597

CDF Preliminar Statistical Uncertainties Onl (1 10 pb-') w � wz

0.8

""' � g' 0.6 < "' c ·x � 0.4

0.2 f = Cft7'

.. 0 JOO ::::::::·_::::·_:J_�-L:·__-_- 200 250 350 400 450c 500 550 ·600 W1 Moss (GeV/ ') 3: 95% BR(W' W - BR(W ev) for � vs. M(W'). Figure C.L. upper limit excluded region of u · --+ Z) --+C 1 3 Note that systematic uncertainties are not included. The dashed lines with = and are for illustration purposes only to show what an excluded region vs. C would look like.

Search for Z' -+ at CDF and D0 5 £+£- Neutral gauge bosons in addition to the zo are expected in many extensions of the SM [22]. These models typically specify the strength of the couplings of such bosons to quarks and leptons but make no mass prediction. Z' bosons may be observed directly via their decay to lepton pairs (e+e-, µ+ µ-). The CDF and D0 results presented below are derived assuming SM coupling strengths. For ee, the CDF criteria are Er(e) > 25 GeV in l1J(e1( ))1 1.1(2.4). The D0 requirements Z' --+ 2 < are similar: Er(e) > 30 GeV in l1J(e1(2))1 < 1.1(2.5). Additonal tracking, electron identification and isolation cuts are imposed. The only appreciable background is from Drell-Yan 'Y in the high mass region. For M(ee) > 250 GeV/c2, CDF D0 observes (1) events in 67.6 (14.4) pb-1data which is ( ) 8 (1.4) consistent with the expected background of 8.1 events. For µµ, the CDF criteria are PT(µ) > 20 GeV in l1J(µ1( ))1 0.6(1.1) with additional quality Z' --+ 2 < cuts. In 67 pb-1data, seven events with M(µµ) > 200 GeV /c2 are observed consistent with the expected rate from Drell-Yan production. The masslimits are extracted by a binned maximum likelihood analysis on the data comparing the data to a sum of the Drell-Yan background and the expectation. The Drell-Yan and Z' distributions Z' are modeled by the leading order Monte Carlo. The CDF mass limits on are 620 GeV / c2 for e+ e­ and 590 GeV /c2 for µ+ µ-. At this time, a combined limit of 650 GeVZ' /c2 is available from 67.6 pb-1e+e- data and 71.3 pb-1 µ+ µ- data [17]. The D0 masslimit from e+e- data is 490 GeV/c2 (23].

6 Summary The CDF and D0 experiments have searched for various new physics phenomena. In these studies, there is no evidence for physics beyond the Standard Model. 598

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