Contri6ution.s Revi.sta Mexicana de Fúica 39, No. Suplemento 1 (1993) 831-535

Production of neutral Higgs bosonsin high energy ep collisions

A. FERNÁNDEzt AND SULLY SÁNCIIEzt

Facultad de Ciencias Físico- MatemálicasUniversidad A utónoma de Puebla

AND

A. ROSADOtInstituto de Física, Universidad Autónoma de PueblaApartado postal )-48, 72570 Puebla, Pue., México

Departamento de Física, Centro de Investigación y de Estudios AvanzadosInstituto Politécnico Nacional, Apartado postal 14-740, 07000 México, D.F.

ABSTRACT.We discuss the /lo-production in the processes e-p - v/lo X and e-p - e- /10 Xin the context of the standard model SU(3), X SU(2)L x U(1) of the strong and elcetroweakinteractions, at llERA (fi = 314 GeY) and LEP /LlIC (fi = 1386 GeY) energies. Taking themass of the scalar Higgs in the range 50 GeY ~ Milo ~ 250 GeY, we find that the cross sectionrates are too small in the case of the llERA accelerator, but bceome measurables in the case of theLEP /LIIC accelerator. At LEP /LlIC collider, it would be produced around 1300 neutral Higgsbosons per year, provided that Mil '" 100 GeY. Finally we gel thal O'(e-p - vUo X)/O'(e-p-e-Uo X) '" 4.7, at LEP/LIIC energies.

RESUMEN.Disculimos la producción del bosón de Higgs /10 en los procesos e-p - v/lo Xy e-p _ e-Uo X en el conlexlo del modelo eslándar SU(3), x SU(2)L x U(I) de las in-teracciones fuerles y eleclrodébiles, para energías que serán alcanzables con llERA (fi =314 GeY) y con LEP /LIlC (fi = 1386 GeY). Variando la masa del escalar de Higgs enel inlervalo 50 GeY ~ MI/' ~ 250 GeY, encontramos que los resullados para la secciónlransversal son demasiados pequeños en el ca.<o del acelerador llERA, pero resultan medi-bies en el caso del acelerador LEP /LIlC. Con el colisionador LEP /LIIC se podrían pre>-ducir alrededor de 1300 bosones de Iliggs neulros por año, si MilO '" 100 GeY. Final-mente, oblenemos que O'(e-p - vUo X)/O'(e-p - e-Uo X) '" 4.7, a energías del LEP /LIIC.

PACS: 12.15.Cc; 13.60.lIb

At the present time, aH the available data on electroweak processes obtained at the bigaccelerators (SLC[I) and LEP[2]) can be explained within the context of the standard

ISupportcd in part by CONACyT and SN1(México).IWork prc.cnled in parlial fulfillment of the requirements for lhe Bachelor of Science degrcc alFacultad de Ciencias Físico Malemáticas, VAP.

32 A. FERNÁNDEZET AL.

q (q )

ZO-------HoZO

q(q') U(q)

v (p')

w-------- HOw+

(o ) (b)

FIGUREl. Feynman diagrams whieh eontribute to the amplitud oC processes 1 and 2, at the lowestorder in Q (u slands for u, e, J, Sjd for d, s, ü, e).

modcl (SM) of the eleetroweak interaetions hased on the gauge group SU(2)£ x U(I)[31.1I0wever, in spite of this sueeess, there are important features of the SM that have not heentested, sueh as the meehanism for symmetry hreaking. In this note we will he eoneernedwith this point, more specifieally we will study the produetion of the neutrallliggs bosonvia ep eollisions, in the range 50 Ce V $ M HO :s 250 Ce V. 01her authors have reportedealculations of the 1I0.produetion, hut taking 10 CeV :s Milo :s 60 CeV [41.The no canhe produeed through the following ep proeesses

ep --+ ello X,

ep --+ v liDX.

(1 )

(2)

\Ve will take all fermions massless and t1wrefore negleet the eontrihution eoming fromdiagrams in whieh the JIo couples to fermions. lIence, the only diagrams which contributein lowest order at the quark level to the processes (1) and (2) are those depicted in Fig.1. \Ve see from this figure that in reaction (2) only quarks with isospin 1/2 contri bu te.\Ve shall use the parton model [5) with the parlon distrihution functions of Duke andOwens (Set 1) [61, which take into account scaling violations and the charm contribution.The difTerential cross section da'P for (1) and (2) are given in terms of the cross sectionda'. for the parton suhprOCl>sses e- + q --+ e- + q + liD, e- + q --+ v + q' + liD, and theparton distribution functions ¡(x', (2)(x' is lhe fraction of the proton momentum earriee!hy the parlo n in a scat!ering process with momenlum transfer (2). \Ve are going lo usethe formulae given in [71 and the prescription (¿2 = (Q2 + Q'2)/2 in our computations.\Ve have checked that the results for the cross section rates do not depend strongly onthe identifieation of the scale Q2.

\Ve prosent the numerical results of our calculations taking Mw = 83 GeV for the massof the neutral boson ZO and sin2IJw = 0.23 for the electroweak mixing angle. \Ve give

PRODUCTION OF. • • 33

105')

x

~ 1041

•1

~ 1642•b

50 100 150M (GeV)

200 250

FIGURE 2. Logarilhmic plol of lhe dependen ce on Mil of lhe lolal cross seclion of lhe process(1),for llERA, llERA' and LEP /LHC energies.

TABLE I. Number of neutral IIiggs bosons expected to be produced per year accordingto our calculations, taking e = 15xl030 cm-2s-1 for HERA and e = 200xI030cm-2s-1for LEP /LIlC.

M/l.(GeV) e p-+e WX e p -+ v 11° XllERA LEP/LlIC llERA LEP/LIIC

50 I 400 7 1990

lOO O 230 I lOSO

150 O 130 O 620

200 O SO O 370

250 O 50 O 220

results for the case of Ilnpolarized deep ineJastic ep-scattering with i) Ee = 30 GeV andF:p = 820 GeV (HERA), ii) Ee = 50 GeV and F:p = 1..'; TeV (HERA') and ¡ii) F:e =60 GeV and Ep = 8 TeV (LEP /LIIC), and varying the mass of the neutral IIiggs in therangle 50 GeV :'5 Af/{o :'5250 GeV.

34 A. FERNÁNDEZET AL.

10-37

10-'8

"E 16'9 -U

Xo 10"40 .I

tQ. 1641

~b

1642

50

1-.-..(1---.(1---1:1• x_x

HERAHERA'LEP/LHC

100 150M (GeV)

200

\\\\\

250

FIGURE 3. Same as in Fig. 2, but for process (2).

10

x'1:'.la'.¡;,xoI~t 6Q.

~b

It-._. HERA6--6--6 HERA'X---l(-X LEP/LHC

____.- .----~---------o----.----.----.

250

---.--.~~--.~--.4+rm~~m~~~~m~~m--~50 100 150 200

M (GeV)

FIGURE 4. Comparison of the total cross sedion of processes (1) and (2).

In Fig. 2 we show in a logarithmic plot the depenrl~nce on /1.[RO of the total crosssection of the process (1), for HERA, llERA' and LEP /Llle energies. In Fig. 3, wedo the same, but for the process (2). In Fig. 4 we compare the total cross section ofprocesses (1) and (2), and we find that O"T(ep - vIlOX) is bigg~r than O"T(ep _ eIlOX).In particular, we find that l1T(ep - vllOX)/l1T(ep - ello X) :::::4.7.

PRO[)UCTION OF. •• 35

Finally, in Table 1, we show the number of neutral IIiggs bosons, whieh would be pro-dueed per year aeeording to our numerieal results for a luminosity of e = 15x 1030em-2s-1for llERA and e = 200 x 1030em-2s-1 for LEP/LIIC.

From our results we can eonclude the following: The HE RA aceelerator will be inap-propriate to look for evidenees of the existenee of the neutral Higgs boson. 1I0wever, inthe case of the LEP /LHC aeeelerator, our computations of the eross seetion rates yieldsto a measurable produdion of neutral IIiggs bosons. Further, at LEP /LIIC energies,(JT(e-p ~ vIJo X)/(J(e-p ~ el/o X) '" 4.7.

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