

 14 Nov 1995

University of California - Davis

UCD-95-25 UCSD/PTH 95-16 October 1995

Detection of the Minimal Supersymmetric Model Higgs Boson H0 in its h0h0 ! 4b and A0A0 ! 4b Decay Channels

J. Daia, J.F. Guniona, and R. Vegac aPhysics Department, University of California, La Jolla, CA 92093, USA bDavis Institute for High Energy Physics, University of California, Davis, CA 95616, USA

cPhysics Department, Southern Methodist University, Dallas, TX 75275

Abstract We demonstrate that detection of the heavier minimal supersymmetric model CP-even Higgs boson H0 will be possible at the LHC via its H0 ! h0h0 ! 4b and/or H0 ! A0A0 ! 4b decay channels for significant portions of the (mA0; tan fi) model parameter space. At low mA0 (!, 60 GeV), both the H0 ! A0A0 ! 4b and H0 ! h0h0 ! 4b modes yield a viable signal for most tan fi values; viability for the h0h0 channel extends up to mH0 , 2mt when the model parameter tan fi is not large. At the Tevatron, the h0h0 and A0A0 channels are both potentially viable at low mA0 for sufficiently good b-tagging efficiency and purity.

I. INTRODUCTION The minimal supersymmetric standard model (MSSM) is currently the most attractive theory for physics below the TeV energy scale. The two Higgs doublets of the model (H1 and H2) are precisely the number required for: i) anomaly cancellations; ii) giving masses to both up quarks (H2) and down quarks and leptons (H1); and iii) nearly precise gauge coupling constant unification. While extra singlet Higgs fields can be added without affecting these crucial features, extra doublets or any number of Higgs triplet fields would destroy unification. Thus, it is vital to assess our ability to fully explore the Higgs sector of the MSSM at future colliders.

The physical Higgs bosons of the MSSM are: two CP-even Higgs boson, the h0 and H0 (with mh0 ! mH0 by definition); one CP-odd Higgs boson, the A0; and a pair of charged Higgs bosons, H\Sigma . The h0 will very probably be detected at either LEP II or the LHC. However, the h0 might well have properties very like those of the single Higgs boson hSM of the minimal standard model (SM). The easiest, and perhaps only, way in which to verify that the Higgs sector is non-minimal would then be detection of a second Higgs boson. Unfortunately, our ability to do so at either the LHC or a future NLC is far from guaranteed. (The extensive literature on this subject is reviewed in Ref. [1].) Further, it would be highly desirable to be able to test the very explicit predictions for the self-couplings among the Higgs bosons of the MSSM. In this article, we demonstrate that, for the expected levels of b tagging efficiency and purity, the production/decay mode gg ! H0 ! h0h0 ! bbbb will be observable at the LHC in important regions of the parameter space of the model, thereby allowing both detection of the H0 and sensitivity to the H0h0h0 coupling. We also show that when kinematically allowed the H0 ! A0A0 ! 4b channel will be observable for most tan fi values. In addition, we explore the observability of these modes at an upgraded Tevatron with integrated luminosity in the vicinity of L = 30 fb\Gamma 1, and find statistically significant signals at small mA0 , provided the efficiency and purity of b tagging are both excellent.

To begin, we note some key features of the MSSM Higgs sector. At tree-level, the Higgs sector is completely determined by the two parameters mA0 and tan fi = v2=v1 (where v1 and v2 are the vacuum expectation values of the neutral components of the H1 and H2 doublets). After including

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radiative corrections at one-loop [2] and two-loops [3,4], other parameters of the model, especially the top-quark (pole) mass mt and the squark masses and mixings, have a strong influence on the Higgs sector. At large mA0 (?, 150 GeV), mh0 approaches an upper bound, while at small mA0, mH0 approaches a lower bound, and both these bounds increase with increasing mt and met. For mA0 between 20 and 70-80 GeV, mh0 , mA0 when tan fi ?, 4 \Gamma 6.

For all the calculations of this paper we shall take mt = 175 GeV, met = 1 TeV and neglect squark mixing. For these choices, one finds that mh0 is sufficiently small, even after radiative corrections, that the H0 ! h0h0 decay channel is essentially always open for small to moderate tan fi, although strongly kinematically suppressed for mA0 in the vicinity of , 90 GeV. For larger tan fi values, the H0 ! h0h0 decay is allowed only for mA0 !, 60 GeV and mA0 ?, 200 GeV. For mA0 !, 60 GeV, the H0 ! A0A0 channel is also kinematically allowed. These kinematics, in combination with the complicated coupling patterns of the Higgs bosons, yield the H0 ! h0h0 branching ratio contours plotted in Fig. 1 in (mA0; tan fi) parameter space. Full two-loop corrections to the H0 and h0 masses, mixing angles, and (very importantly) Higgs self-couplings have been included. We see that even though H0 ! h0h0 is generally kinematically allowed for mA0 ?, 200 GeV, BR(H0 ! h0h0) is not guaranteed to be large; it is suppressed at large tan fi values by the dominance of the enhanced H0 ! bb; o/ +o/ \Gamma modes and for mH0 , mA0 ?, 2mt by the dominance of tt decays. In addition, we note that the H0 ! A0A0 mode generally has a sizeable branching ratio whenever it is kinematically allowed, i.e. for mA0 !, 60 GeV. Finally, the decays of the h0 are essentially always dominated by bb, as are those of the A0 when mA0 is small.

These results assume that SUSY decay channels are absent or negligible. When kinematically allowed, SUSY decays will be important for small to moderate tan fi values and would suppress BR(H0 ! h0h0).

II. LHC RESULTS At the LHC, the channels that have been discussed for detection of the H0 at moderate tan fi and mA0 !, 2mt are gg ! H0 production followed by (a) H0 ! ZZ(\Lambda ) ! 4`, (b) H0 ! h0h0 ! bbbb

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and (c) H0 ! h0h0 ! bbflfl, the inclusive H0 ! bb channel having far too large a QCD background. The 4` channel (a) has been the object of numerous theoretical and ATLAS+CMS experimental studies [5,1]. It has been shown to be viable for (roughly) 120 GeV !, mA0 !, 2mt; tan fi !, 1:5 at low luminosity (L = 30 fb\Gamma 1) and 70 GeV !, mA0 !, 2mt; tan fi !, 3 \Gamma 5 at high luminosity (L = 300 fb\Gamma 1). ATLAS and CMS have recently explored the bbflfl mode (c). At L = 300 fb\Gamma 1 it is viable when BR(H0 ! h0h0) ?, 0:05 (see Fig. 1) and mA0 ?, 120 GeV [5,1]. The bbflfl channel has small backgrounds, but the expected number of events is quite limited since the h0 ! flfl branching ratio is of order 10\Gamma 3 for much of parameter space. Here, we study whether the much higher rates in the H0 ! h0h0 ! 4b channel can be utilized to detect the H0 ! h0h0 decays. In conjunction with the 2b2fl channel, this would also allow a model independent determination of the very important ratio BR(h0 ! flfl)=BR(h0 ! bb). In what follows, we demonstrate that the 4b channel will, indeed, allow detection of the H0 in its h0h0 decay mode in several important regions of parameter space, including a large region which overlaps that where the 2b2fl mode is viable. In addition, we find that, when kinematically allowed, the H0 ! A0A0 ! 4b channel will be detectable.

We will consider three b-tagging scenarios. The first is what now seems to be a relatively conservative scenario taken from the SDC detector Technical Design Report [7] and employed in our earlier work [6]. As a function of pT , eb\Gamma tag takes the values 0:16 at pT = 20 GeV, 0:22 at pT = 30 GeV, and is * 0:3 for large pT (yielding a rough average value of eb\Gamma tag , 0:25); the probability of mis-tagging is taken to be emis\Gamma tag = 0:01 for all pT * 20 GeV. For this btagging scenario we assume a maximal yearly integrated luminosity of L = 100 fb\Gamma 1. Current expectations further improve the situation. Canonical values now employed by ATLAS and CMS [5] are: eb\Gamma tag , 0:6 and emis\Gamma tag , 0:01 for jjj ^ 2:5 and pT * 15 GeV at low luminosity (applicable for accumulated luminosity of L = 30 fb\Gamma 1); and eb\Gamma tag , 0:5 and emis\Gamma tag , 0:02 for jjj ^ 2:5 and pT * 30 GeV at high luminosity (L = 300 fb\Gamma 1 accumulated). In the present work, we shall examine all three of these b-tagging scenarios; we shall label them (I), (II) and (III), respectively, in the order of the above discussion.

In this paper, we focus on gg ! H0 production followed by H0 ! h0h0 ! 4b or H0 ! A0A0 !

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4b decay. The gg ! bbH0 cross section is not significantly enhanced in the regions of parameter space where BR(H0 ! h0h0) is substantial (see Fig. 1), and, in fact, is small by comparison to the inclusive gg ! H0 cross section in these regions. Although there is no special enhancement for the H0 production rate, the gg ! H0 ! h0h0 ! 4b (gg ! H0 ! A0A0 ! 4b) channels have the advantage over the previously-studied gg ! bbH0 ! 4b channel that we can require two 2b combinations of mass , mh0 (, mA0 ) as well as a peak in the 4b mass. This considerably reduces both combinatoric and QCD backgrounds. Assuming 3 or 4 b-tagging, we find that the only possibly important backgrounds to the H0 ! h0h0 ! 4b process are the irreducible gg ! bbbb background and the mis-tag gg ! bbgg background (the intrinsic rate for this latter being very large). Because of the large size of mt, the rate for ttbb production is sufficiently smaller than that for bbbb as to be neglectable, and the rate for gg ! bbqq (summed over all light q 6= b) is much smaller than that for gg ! bbgg. (We compute signal and background processes using exact parton level matrix elements.)

For the original conservative b-tagging scenario (I) it is difficult to maintain adequate event rates if we demand that 4 jets be tagged as b's. Thus, in this case, we shall only require that 3 or 4 jets be tagged. The largest background is then from bbgg where at least one of the g's is mis-tagged. For b-tagging scenarios (II) and (III) eb\Gamma tag is sufficiently large that requiring 4 jets to be tagged as b's leaves an adequate signal rate while suppressing the potentially large gg ! bbgg background to a level below the irreducible gg ! bbbb background.

Semi-leptonic decays of the b-jets are included in our analysis. To incorporate detector resolution effects, we smear the lepton momenta using ffiE=E = 0:2=qE(GeV ) + 0:01 and the quark momenta using ffiE=E = 0:5=qE(GeV ) + 0:03. If a b-jet decays semi-leptonically, we replace the jet momentum by the sum of the (smeared) lepton and light quark momenta; otherwise, we employ the full (smeared) b-jet momentum. Approximate techniques for compensating for the momentum lost to the neutrino in the case of a semi-leptonic decay have not been employed here; implementation of such a technique might improve our results.

The precise cuts imposed are adjusted according to the (presumed) masses of the H0 and h0 (or

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A0). In the following we use the generic notation h for the h0 or light A0. First, we required that there be two jet pairs each having pair mass in the interval [0:88mh; 1:08mh]. Second, we required that the 4b mass be in an appropriate interval: [115; 135], [140; 160], [160; 185], [180; 210], [235; 260], [285; 310], [330; 360], [380; 415], [430; 465], and [475; 515] for mH0 = 125, 150, 175, 200, 250, 300, 350, 400, 450, and 500, respectively (all masses in GeV). These mass intervals in mh and mH0 are roughly optimal for the smearing outlined above. They extend further below the nominal mass than above so as to capture more of the low mass tail resulting from semi-leptonic b decays.

We will also impose a cut requiring that the transverse missing energy be less than 35 GeV. This cut does not significantly reduce the signal rate since signal events with substantial missing energy will not pass the mh cuts anyway. This is because there are typically several semi-leptonic b decays in events with large E= T , making it quite likely that one or more of the pairs of b quarks that come from the decay of the h's will not reconstruct to a pair mass close to mh. In contrast, the E= T ^ 35 GeV cut removes the substantial percentage of background events where the semileptonic b decays lead to large missing energy. We note that in computing the missing energy and determining the optimal cut, we have included an estimate of the missing energy associated with the underlying minimum-bias event structure.

For each choice of mH0 and mh we considered two possible pminT cut options and two possible cuts on the minimum separation required between any two of the b jets, \Delta Rmin. These were pminT = 15 or 30 GeV and \Delta Rmin = 0:7 or 1:2. (Note that the pminT = 15 GeV cut cannot be employed in the high luminosity scenario III, and that for scenario I the effective minimum is 20 GeV.) For any given combination of mH0, mh masses the choice among these four (\Delta Rmin; pminT ) options which gives the largest significance for the signal is chosen. Generally speaking, it is advantageous to impose the strongest cuts that one can without harming the efficiency of acceptance too severely. Roughly, for lower values of mH0 !, 200 GeV, the lower pminT must be employed, whereas for mH0 ?, 200 GeV the higher pminT was generally more optimal. When mH0 is large and mh is small, the h boost in the H0 center of mass is often such that the smaller \Delta Rmin must be employed.

Our procedure was to tabulate the signal and background rates for a series of mH0 masses and

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mh masses that scanned all mH0 values of possible interest and all mh values for which H0 ! hh is allowed by kinematics, for each of the four (\Delta Rmin; pminT ) options described above. (Of course, only the two \Delta Rmin options were examined in the high-luminosity b-tagging case (III) for which pminT = 30 GeV is required.) Rates corresponding to the best of these options for each mH0; mh (in terms of statistical significance) were then entered into a final summary table. SUSY relations between mH0 and mh were not implemented in constructing the tables. Signal event rates for gg ! H0 ! hh ! 4b were obtained assuming 100% branching ratio for the decays H0 ! hh and h ! bb and assuming a width \Gamma (H0 ! gg) = 5 \Theta 10\Gamma 4 GeV, that is typical of the values obtained in the MSSM. In order to determine the actual statistical significance of the gg ! H0 ! h0h0 ! 4b and gg ! H0 ! A0A0 ! 4b signals as a function of location in the MSSM parameter space, rates were obtained for the appropriate mH0 and mh = mh0 (or mh = mA0) values by interpolation between entries in the summary table, and the branching ratios and gg width were adjusted according to the predicted MSSM values. In our considerations, mh masses below 20 GeV are not considered nor are mH0 masses below 110 GeV. The contours presented below correspond to setting statistical significances to zero for such cases.

It is not appropriate here to detail the signal and background rates tabulated in the summary table. We confine ourselves to a few comments.

1. b-tagging option (I): 3 or 4 b-tags, L = 100 fb\Gamma 1 -- In this case, after cuts and tagging the

gg ! H0 ! 4b signal and gg ! 4b background rates are typically comparable, whereas the gg ! 2b2g mis-tag background rate is a factor of 3-9 higher.

2. b-tagging option (II): low luminosity (L = 30 fb\Gamma 1), 4 b-tags -- Here, the gg ! H0 ! 4b

rate is somewhat larger than the gg ! 4b irreducible background rate, which, in turn, is a factor of at least 10 larger than the bb ! 2b2g rate -- i.e. the latter background becomes unimportant when 4b's are tagged with excellent efficiency and purity.

3. b-tagging option (III): high luminosity (L = 300 fb\Gamma 1), 4 b-tags -- The pminT = 30 GeV rates

are obtained from those in option (II) by multiplying the rates for 4b final state channels

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by the factor (0:5=0:6)4 \Theta 10 ' 4:8 and the rates for the 2b2g background by (0:5=0:6)2 \Theta (0:02=0:01)2 \Theta 10 ' 27:8. In this case, the 2b2g background rates are typically comparable to the 4b background rates.

The relation between the option (I) and option (II) rates is easily understood. Very roughly, the signal and gg ! 4b rates for option (I) are

/ n4 \Theta (eb\Gamma tag , 0:25)3 \Theta [(1 \Gamma eb\Gamma tag) , 0:75] + (eb\Gamma tag , 0:25)4o \Theta 100 fb\Gamma 1 = 5:1 fb\Gamma 1 (the factor of 4 corresponding to any one of the 4 b's remaining untagged), while those for option (II) are / (eb\Gamma tag = 0:6)4 \Theta 30 fb\Gamma 1 = 3:9 fb\Gamma 1. In contrast, in going from option (I) to option (II) the gg ! 2b2g rates are suppressed by a factor of roughly

(0:6)2 \Theta (0:01)2 \Theta 30 fb\Gamma 1 (0:25)2 \Theta 0:01 \Theta 2 \Theta 100 fb\Gamma 1 , 0:0086

where the extra factor of 2 in the denominator corresponds to allowing either of the g's to not be (mis-)tagged in the 3 b-tag case. The result is that the 4b rates for option (II) are comparable to those for option (I), and that in option (II) the bbgg background is substantially smaller than the bbbb irreducible background. In option (III) the 4b and 2b2g backgrounds become comparable due to the lower efficiency for b tagging, coupled with a higher rate for mis-tagging. Clearly, b-tagging expectations (II) and (III) yield better statistical significance for the signal than the conservative choices of (I), for the same integrated luminosity.

Finally, we recall that at high luminosity it is assumed that 30 GeV is the lowest pminT value that can be employed. This effectively restricts the high luminosity option (III) case to mH0 values above about 150 GeV.

In order to compute the statistical significance of a signal when both the H0 ! A0A0 and H0 ! h0h0 decays are present (low mA0 ) we must take into account the fact that mh0 , mA0 at low mA0 once tan fi ?, 4\Gamma 6. Our procedure is to include in the h0h0 (A0A0) signal event rate the portion of the A0A0 (h0h0) signal event rate that overlaps into the double [0:88mh0 ; 1:08mh0 ] ([0:88mA0; 1:08mA0 ]) pair mass window. Obviously, when mA0 and mh0 are very close, this simply means the signal rates

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are added together before the statistical significance NSD = S=pB is computed. Our procedure implies that the contours for the h0h0 and A0A0 modes will converge for tan fi ?, 4 \Gamma 6.

We display in Fig. 2 the NSD = 2, 5, and 10 discovery contours for H0 ! h0h0 and H0 ! A0A0 for the L = 30 fb\Gamma 1 and L = 300 fb\Gamma 1 b-tagging options (II) (window 1) and (III) (window 2). It turns out that the results for b-tagging option (I) for L = 100 fb\Gamma 1 are almost identical to those for option (II) at L = 30 fb\Gamma 1 and so we do not present them here.

In the L = 30 fb\Gamma 1 option (II) case, we see two distinct regions. At low mA0 values there is a narrow band in the 20 GeV !, mA0 !, 60 GeV region for which NSD * 5 in both the h0h0 and A0A0 modes. (The h0h0 mode is viable for slightly more parameter space as indicated by its contours which bulge a bit beyond those for the A0A0 mode at lower tan fi !, 6 values.) The lower mA0 limits of these contours are an artifact of our zeroing all rates when the light Higgs mass is below 20 GeV -- in any case, we already know from LEP I that mA0 * 40 GeV. At higher mA0 values there is a NSD * 5 region for the h0h0 mode, extending from roughly mA0 , 100 GeV up to mA0 ?, 2mt for tan fi !, 4. Note that a viable signal is maintained for mH0 somewhat beyond 2mt, despite the fact that H0 ! tt decays rapidly become dominant. This is because the top-quark loop contribution to the gg ! H0 coupling is substantially enhanced in the vicinity of mH0 , 2mt, thereby enhancing the gg ! H0 production rate.

In the L = 300 fb\Gamma 1 option (III) case, the bands at low mA0 disappear; the pT ? 30 GeV cut eliminates them by virtue of kinematics. The NSD * 5 region for H0 ! h0h0 ! 4b at large mA0 extends to tan fi !, 5 and slightly higher mA0 values.

III. TEVATRON RESULTS In this section, we explore the capability of the Tevatron to observe the H0 ! h0h0 and H0 ! A0A0 signals in the 4b final state. CDF and D0 have dramatically increased their b-tagging efficiency and purity. At an upgraded Tevatron, they now expect to achieve eb\Gamma tag , 0:5 with emis\Gamma tag , 0:005 for a b-jet with pT ?, 15 GeV and jjj ! 2 at instantaneous luminosities capable of yielding L = 10 \Gamma 30 fb\Gamma 1 per year [8]. Their ability to obtain such a very small mis-tagging probability is crucial

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at the Tevatron, since the low event rates make it necessary to accept events in which either 3 or 4 b's are tagged.

Our results for L = 30 fb\Gamma 1 are displayed in Fig. 3. For the above-stated b-tagging efficiency and purity (left window of figure), a NSD = 4 (NSD = 2) signal is obtained for 33 !, mA0 !, 53 GeV (25 !, mA0 !, 55 GeV) in both the h0h0 and A0A0 modes (with the h0h0 mode contours again bulging a bit beyond the A0A0 contours for tan fi !, 6). If the detector design can be further improved, so as to achieve eb\Gamma tag , 0:75 and emis\Gamma tag , 0:0025, the h0h0 and A0A0 signals will be promoted to at least the NSD = 5 level (inner contours of the right-hand window) for most of this low mA0 band. The region for which H0 ! h0h0 is observable at higher mA0 is much more restricted than at the LHC.

We note that the near degeneracy of the A0 and h0 in the low-mA0 region is quite critical to there being an observable level for the H0 signal at the Tevatron. After cuts, tagging, and mass binning, the 4b background is typically of order fifty to two hundred events and the 2b2g background ranges from several hundred to more than a thousand events. The A0A0 and h0h0 signals, if not simultaneously present, would typically be just below the observable level; but in combination, they provide a just adequate event rate.

IV. DISCUSSION AND CONCLUSIONS We have demonstrated that detection of gg ! H0 ! h0h0 in 4b final states at the LHC will be possible for a substantial portion of parameter space, for anticipated integrated luminosities and b-tagging efficiency and purity. Should mA0 turn out to be small (!, 60 GeV), then both H0 ! h0h0 ! 4b and H0 ! A0A0 ! 4b yield viable signals. These channels add to the growing list of signals that can provide probes of the MSSM Higgs sector at the LHC [1]. Detection of the H0 in the h0h0 and A0A0 modes at the Tevatron is mostly limited to the mA0 !, 55 GeV portion of parameter space, and requires accumulated luminosity of L , 30 fb\Gamma 1 as well as excellent b-tagging efficiency and purity.

Although observation of e+e\Gamma ! h0A0 production at LEP II would also be possible in the low

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mA0 region of parameter space, the information gained about the Higgs sector from detection at the Tevatron (or LHC) of gg ! H0 ! h0h0; A0A0 would be very complementary.

In our analysis, we have assumed that it will be possible to trigger on the 4b final states, perhaps by requiring 4 jets with pT ? 15 to 20 GeV, or via a fast b-vertex trigger, or some combination of these approaches. This issue is under study by the ATLAS and CMS collaborations.

We note that our computations have not included higher-order QCD K factors for either signal or backgrounds. The K factor for gg ! H0 is known to be substantial (K , 1:6 [9]) and presumably those for the backgrounds will also be significant. Assuming that all K factors are of similar size (if anything the gg ! H0 K factor is likely to be the largest), the quoted statistical significances for observation will be increased by a factor of pK.

The rate for gg ! H0 ! h0h0; A0A0 probes the product, \Gamma (H0 ! gg) \Theta BR(H0 ! h0h0; A0A0), which is sensitive to the H0 ! gg one-loop coupling and the tri-linear Higgs self couplings. \Gamma (H0 ! gg) can deviate significantly from the values employed here if squarks are light, or if there are other unobserved heavy colored particles with significant couplings to the H0. The tri-linear Higgs couplings could also deviate from MSSM predictions if, for example, Higgs singlet fields are added to the minimal two-doublet structure. In the very substantial portion of parameter space where both H0 ! h0h0 ! 4b and H0 ! h0h0 ! 2b2fl can be observed at the LHC, the ratio of the h0 ! flfl and h0 ! bb couplings can be extracted. Clearly, much important information regarding the SUSY Higgs sector, and many important checks of the MSSM, will be made possible by observation of the H0 ! h0h0 and/or A0A0 modes.

In Ref. [6], we demonstrated that detection of gg ! bbH0 and/or gg ! bbA0 in 4b final states is possible for sufficiently large tan fi values (the required tan fi value increases as mA0 increases). Updated results that incorporate the current more optimistic expectations for b-tagging efficiency and purity will appear shortly [10]. The region of the (mA0; tan fi) parameter space for which the above modes are observable is largely complementary to that for which we have demonstrated viability for the 4b final states resulting from gg ! H0 ! h0h0 and/or gg ! H0 ! A0A0. In combination, these two different types of 4b modes allow H0 and/or A0 detection over a very

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sizeable fraction of the (mA0 ; tan fi) parameter space plane when mA0 !, 400 GeV. There is a wedge between the discovery regions at moderate tan fi ?, 5 that grows as mA0 increases above 400 GeV. Further improvements in b-tagging efficiency and purity would substantially reduce this wedge. Efforts by the ATLAS and CMS collaborations in this direction are thus highly desirable. Overall, the 4b modes have considerably enhanced the prospects for detecting the H0 and/or the A0 at the LHC. It is thus quite possible that the LHC will be able to fully explore the Higgs sector of the MSSM.

ACKNOWLEDGMENTS This work was supported in part by the U.S. Department of Energy. Further support was provided by the Davis Institute for High Energy Physics.

REFERENCES 1. An extensive review of the subject appears in J.F. Gunion, A. Stange, and S. Willenbrock,

`Weakly-Coupled Higgs Bosons', to appear in Electroweak Symmetry Breaking and Beyond the Standard Model, ed. T. Barklow, S. Dawson, H. Haber, and J. Siegrist, World Scientific Publishing.

2. For a review, see H. Haber, in Perspectives on Higgs Physics, ed. G. Kane, World Scientific

Publishing, p. 79.

3. M. Carena, J.R. Espinosa, M. Quiros and C.E.M. Wagner, CERN-TH/95-45; J.A. Casas, J.R.

Espinosa, M. Quiros and A. Riotto, Nucl. Phys. B436, 3 (1995).

4. H. Haber, R. Hempfling and A. Hoang, CERN-TH/95-216. 5. F. Gianotti (ATLAS), presented at the European Physical Society International Europhysics

Conference on High Energy Physics, Brussels, Belgium, July 27 - August 2, 1995, and private communication. R. Kinnunen (CMS), presentation at the Tahoe CMS Week, Tahoe City, CA,

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September 25-27, 1995. 6. J. Dai, J. Gunion, and R. Vega, Phys. Lett. B345, 29 (1995). 7. Technical Design Report, SDC Collaboration. 8. S. Kuhlmann, CDF note CDF/PHYS/ELECTROWEAK/PUBLIC/3342, September, 1995.

J. Womersley, private communication.

9. For a review and references, see B. Kniehl, Int. J. Mod. Phys. A10, 443 (1995.) 10. J. Dai, J.F. Gunion, and R. Vega, in preparation.

FIGURES 1. We show contours of fixed BR(H0 ! h0h0) = 0:5, 0:2, 0:1 and 0:05 in the (mA0; tan fi)

parameter space. We have taken mt = 175 GeV (pole mass) and met = 1 TeV, and neglected squark mixing. The 0:2, 0:1 and 0:05 contours in the vicinity of mA0 , 60 GeV are essentially indistinguishable; the H0 ! h0h0 decay becomes kinematically disallowed for mA0 values just beyond this boundary.

2. We show the (mA0 ; tan fi) parameter space contours within which H0 ! h0h0 ! 4b and

H0 ! A0A0 ! 4b can be observed at the 2, 5, or 10oe level assuming: 1) an integrated luminosity of L = 30 fb\Gamma 1 and 4-b-tagging option (II); and 2) L = 300 fb\Gamma 1 and 4-b-tagging option (III). See text for details. We take mt = 175 GeV and include two-loop radiative corrections, assuming met = 1 TeV and neglecting squark mixing. We also assume that SUSY decays are absent.

3. We show the (mA0 ; tan fi) parameter space contours within which H0 ! h0h0; A0A0 ! 4b

can be observed: 1) at the 2, 4 oe level assuming eb\Gamma tag = 0:5 and emis\Gamma tag = 0:005; and 2) at the 3, 5 oe level assuming eb\Gamma tag = 0:75 and emis\Gamma tag = 0:0025. We assume ps = 1:8 TeV, an integrated luminosity of L = 30 fb\Gamma 1 and accept events in which either 3 or 4 b's with pT ? 15 GeV and jjj ! 2 are tagged.

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FIGURES FIG. 1. We show contours of fixed BR(H0 ! h0h0) = 0:5, 0:2, 0:1 and 0:05 in the (mA0; tan fi) parameter space. We have taken mt = 175 GeV (pole mass) and met = 1 TeV, and neglected squark mixing. The 0:2, 0:1 and 0:05 contours in the vicinity of mA0 , 60 GeV are essentially indistinguishable; the H0 ! h0h0 decay becomes kinematically disallowed for mA0 values just beyond this boundary.

14 FIG. 2. We show the (mA0; tan fi) parameter space contours within which H0 ! h0h0; A0A0 ! 4b can be observed at the 2, 5, or 10oe level assuming: 1) an integrated luminosity of L = 30 fb\Gamma 1 and 4-b-tagging option (II); and 2) L = 300 fb\Gamma 1 and 4-b-tagging option (III). See text for details.

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FIG. 3. We show the (mA0; tan fi) parameter space contours within which H0 ! h0h0; A0A0 ! 4b can be observed: 1) at the 2, 4 oe level assuming eb\Gamma tag = 0:5 and emis\Gamma tag = 0:005; and 2) at the 3, 5 oe level assuming eb\Gamma tag = 0:75 and emis\Gamma tag = 0:0025. We assume ps = 1:8 TeV, an integrated luminosity of L = 30 fb\Gamma 1 and accept events in which either 3 or 4 b's with pT ? 15 GeV and jjj ! 2 are tagged.

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