A.T.Alan1, Z.Z.Ayd1n, S.F.Sultansoy2 Ankara University, Faculty of Sciences Department of Engineering Physics Tandogan, Ankara-Turkey

Transcription

1 AU/94-02(HEP) Associated Squark-Wino Production at TeV Energy yp Colliders A.T.Alan1, Z.Z.Ayd1n, S.F.Sultansoy2 Ankara University, Faculty of Sciences Department of Engineering Physics Tandogan, Ankara-Turkey The associated production of charged gauginos and scalar quarks in the high energy scattering of real photons off the protons and electrons is discussed. The conclusion is that capacities of yp and ye colliders in SUSY search are comparable with those of the well known pp colliders (LHC, SSC, UNK) and linear e"'c' colliders (CLIC, NLC, VLEPP) leave of absence from Inonii University, Dept. of Physics, Malatya, I urkey 2Permanent Address: Institute of Physics, Azerbaijan Academy of Sciences, Baku OCR Output

2 It is a well known fact that the Standard Model (SM) has been succesful in description of the elementary particles and their interactions up to the scale of 100 GeV. However, physicists believe that new physics beyond the standard model should exist at TeV scale. The reason is that the SM does not explain a number of principal problems, i.e. existence of three fermion families, the large difference between fermion masses (mv, < 10eV, mt > 100G'eV), fine tuning between Fermi and Planck scales etc,. Among the other ones (like technicolor, preons, extended electroweak symmetry etc.) supersymmetry (SUSY) seems to be one of the most promising candidates for TeV scale physics [1-3]. Standard type ep machines, first example of which is HERA, is fr from to reach TeV scale at a subprocess level. On the other hand, ep collisions played highly important role in understanding the structure of the microworld. For example, the success of quark parton model comes through the deep inelastic ep scattering. In order to reach TeV scale at the constituent level, a number of high energy machines have been built or proposed. Among these, the large hadron machines LHC and SSC and large linear e+ e' colliders are familiar and their research programs have been developed by a large number of high energy physicists. Colliding of protons from a large hadron machine with electrons from Linac is the sole way to reach TeV scale at the constituent level in ep collisions [4-6]. The other attractive feature of Linac-Ring type ep machines is the possibility of constracting of yp colliders on their basis [5,7,8]. This is realised by using the beam of high energy photons produced by the Compton backscattering of laser photons off a beam of linac electrons. This method was used originally to propose the construction of ye and yy colliders [9,10] on the bases of e+e` linacs. As mentioned above, physics research programs for TeV energy pp and e+e" col liders have been highly developed. Recently the physics goals of yy and ye colliders are being widely investigated (see for example [11-16]). On the physics programs for yp colliders there exist few papers [17-19] where physics at UNK+VLEPP is considered. In this paper we examine associated production of the winos and scalar quarks OCR Output

3 at yp collidcrs. With this study wc start to cxplorc the manifestations of SUSY at these machines. The Feynman diagrams for the associated production of chargino and squarks in 7p collisions are depicted in figure 1. The invariant amplitude for the subprocess yq > zi: is the sum of the following terms which correspond to fig.1-a, b and c, respectively (We use the notation of ref. [3]): mixing angle. The differential cross section of the subprocesses under consideration, which is calculated using the amplitudes (1), has the following form: d6 dt Ma = $ (1> )(1 vs)( 1 p + 7 kh <~(1>) Mb Y(1> )v ( r p v kl + Mw)(1 is)~(1>) 2(t M3,) Mc = $ Y(1> - v5) (p)(p 1 + k') 2(u M:) where s = (p + k)2, t = (p kl)? and u = (p p/) are the Lorentz invariant Mandelstam variables; Mw and Mg are the wino and squark masses; Qq, Qu, and Q, are the electric charges of the initial quark, chargino and produced squark, respectively. e = \/5, a is fine structure constant; g = c/sin0w, Ow is the weak 7:02 " (M3- ~ - {QQ S(M.?, + 2Mg,(M_g _ f) T- $2 $1112 aw + Q_gJ (M?;),, ;-2 ~ `" <*-Mai A A S(3 + t) + 2t(M3 ` 1123)* M3(2M.. QMZ d+3s) Q Q (M2_3 ) QW s Q ~ <M P+3s] } w ~ "., 5 w.+m )+2M3( M )-3M2M2 " *" ("M3)(M3 s-g " (1) One can easily perform the integration over df and get the total cross section 6 for the subprocess yq -> z'b. In order to obtain the total cross section for the OCR Output

4 _ ~ process 7p > 1]:QX one should integrate :9 over the quark and photon distributions: T ~ ~ * A dr d ;[r.<;>r.<x>1 <Mw.Mr.S) where fq(:c) is the distribution of quarks inside the proton [20], and 1 4 r. f y+; ; (i +mi$5l <3> (4) is the energy spectrum of the high energy real photons; y :-. E.,/E,, rc 2 4.8, D(;c) , and 3;,,,,,,, [10,14,15]. Since the proton contains two u-quarks it is clear that the main contribution to theicross section 0(*yp -+ u'3 jx) will come from the subprocesses 7u -> 17;+d. The inclusion of the other contribution coming from the subprocess 7d -> rb`:] will simply enhance the cross section by a factor of about 1.5. Bearing this fact in mind, we carry out the numerical integrations in eq.(3) only for the process yu + 11;+dX at this stage. Figures 2(a-d) display the dependence of the total cross section on the masses of SUSY particles for various yp colliders ( their parameters are given in Table 1). Usually the observation limit for new physics is taken to be 100 events per running year (107sec.). Taking into account the values of luminosities given in Table 1, one can easily extract from figures 2(a d) the upper mass limits for SUSY particle observations. The corresponding values are given in Table 1 where the fifth and sixth columns are formed according to the fixed mass values Mw = 0.1 TeV and Md = 0.1 TeV, respectively. The above consideration can be obviously applied to the process 7e -> 'IIJIAJ. In this case, the first two diagrams of figure 1 with appropriate changes (q -> c,< -> 17) will survive. The differential cross section is given by the sum of the first, second, and fourth terms of eq.(2) with the substitutions Q, -> -1, Qu, -> -1. Consequently, the total cross section reads 0.83 dyf1(y)6`(mwamvv g) (5) OCR Output

5 The cross sections for 76 + TIN; as a function of masses of SUSY particles are given in figures 3(a-b). In the case of equal masses for the wino and the sneutrino and L.,, = 1032cm' s 1 the observation limits are as follows: 350 GeV for X/E = 1 TeV and 300 GeV for \/E = 2 TeV. Depending on the mass spectrum of SUSY particlw following decay modes of winos and squarks will be possible: for squarks: d > dy, dfj, mb', {IW',. for winos: > l`*`17, uf"', ud}, J1], W+,. Note that,1d", W', I+ will further decay into lighter particles. Usually the photino and sneutrino are taken as the lightest SUSY particles. Therefore, the sig nature for the process under consideration will be in general lept0ns+jets -large missing py. It seems natural to assume that the hierarchy of the squark masses is similar to that of quarks. Let us consider, for definiteness, the case Md = Mw. Then, only following decay modes are left:.1-1 di l+z7,ul+,w+ } ar M, > M,. Taking into account further decays I+ - > H and W+ - > l+u or qq, one obtains j + I+ + p "i" and 3j + p?* as final states. If the gluino is lighter than the squark, the additional final states I+ 3 j + p ;} * and 5j + p'j~ will occur. The main background for the final state + I+ + p?*" will come from the process yp > W+X with the subsequent decay W+ > l+u. This background may be reduced, in principle, by cut p 1'?"" > 45GeV if Mw < Mw. Finally, our analysis shows that future cyp colliders will play an essential role in investigation of the SUSY manifestations. The polarization of high energy pho tons and, possibly, polarized proton beam will be additional advantage of these machines. We shall turn to polarization effects in a forthcoming study. After finishing this work we came across a paper by Buchmiiller and Fodor [21] OCR Output

6 who study 'IIJTIJ pair production at HERA-l-DLC yp collider. They give discovery limits according to the 10 events per year which seem to us rather small to a make firm decision. In addition, they assume a luminosity of 1033cm' s'1 which is pretty high to be realized. Note that we take 100 events per year with a luminosity of cm' s'1 to predict the discovery limits for SUSY at this machine. We are grateful to our colleagues associated with AU HEP group, especially S.Atag, for useful discussions. One of the authors (S.Sultansoy) is grateful to TUBITAK for partial support. The work is supported in part by TUBITAK under TBAG/CG. OCR Output

7 References [1] C.H.L1ewel1yn Smith, Phys. Rep. 105 (1984) 53. [2] H.P.Nilles, Phys. Rep. 110 (1984) 1. [3] H.E.Ha.ber and G.L.Kane, Phys. Rep, 117 (1985) 75. [4] S.I.Alekhi11 et al., Institute for High Energy Physics preprint IHEP 87 48, Ser pukhov (1987). [5] S.F.Su1tans0y, ICTP preprint IC/89/ 409, Trieste (1989). [6] P.Gr0sse Wiesmann, Nuc1.Instr.& Meth. A 274 (1989) 21. [7] Z.Z.Aydin, V.Ma.niev and S.Su1ta.ns0y, to be published in Particle World. [8] Z.Z.Aydin, A.Ciftci and S.Sultans0y, in preparation. [9] I.F.Gi11zburg et al., Piz ma ZhETF 34 (1981) 514. [10} I.F.Ginzburg et al., Nucl. Inst.& Meth. 205 (1983) 47;ibid. 219 (1984) 5. [11} J.A.Grifols and R.Pascual, Phys. Lett. B 135 (1984) 319. [12] E.Boos et al., Phys. Lett. B 273 (1991) 173. [13] E.Boos et al., DESY preprint , Hamburg (1991). [14] D.L.B0rden, D.A.Bauer and D.O.Caldwel1, SLAC preprint SLAC-PUB- 5715, Stanford (1992). [15] J.E.Cieza Montalvo and O.J.P.Eboli, Phys. Rev. D 47 (1993) 837. [16] M.Nadeau and D.London, Phys. Rev. D 47 (1993) [17] S.l.Alekhin et al., Int.J.of Mod. Phys. A 6 (1991) 23. [18] E.Boos et al., Proc. 26th Moriond Conf. on Electroweak Interactions and Unified Theories, Moriond, France, 1991, p.501. [19] G.Jikia, Nucl. Phys. B 333 (1990) 317. [20] E.Eichten et al., Rev. of Mod. Phys. 56 (1984) 579. [21} W.Buchmi`1ller and Z.F0dor, Phys. Lett. B 316 (1993) 510. OCR Output

8 FIGURE CAPTIONS Fig.1(a c): Feynman diagrams for chargin0 squark production in 7p collision. Fig.2(a d): Production cross sections of chargino and squarks as a function of their masses for various colliders. In each figure (1) stands for the case Mw = 100 GeV, (2) for the case Md = 100 GeV and (3) for the case Md = Mu,. Fig.3(a b): Cross sections for the process qc > [III;. In these figures (1) stands for the case Mw = 100 GeV, (2) for the case M, = 100 GeV and (3) for the case Mw = M,. OCR Output

9 Table 1. Parameters of the 7p colliders and discovery limits for SUSY search Center of mass energies and lumino- I Upper mass limits for SUSY sities for various 7p proposals Ref.[7] I particles to be observed Machines scp L7, Mw = Md I Md I Mw 103 cm'2.s"1 I (TeV) I (TeV) I (TeV) (TeV) HERA+DLC I I UNK+VLEPP I I LHC+TESLA I I 2.3 LHC+CLIC I I LHC+Linac1 I SSC+NLG I I SSC+LSC I I 3.1 SSC-}-Linac2 I I 3.2 (*) \/% = 0-9h/Q OCR Output

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