We evaluate Higgs boson and dijet cross-sections at the Tevatron collider via
Double Pomeron exchange when accompanying particles in the central region are
taken into account. Such {\it inclusive} processes, normalized to the observed
dijet rate observed at run I, noticeably increase the predictions for tagged
(anti)protons in the run II with respect to {\it exclusive} ones, with the
potentiality of Higgs boson detection.Comment: 6pages, 4 figure

A. Berera

A. Bialas

A. D. Martin

B. L. Combridge

C. Royon

J-R. Cudell

J. D. Bjorken

J. Pumplin

M. Boonekamp

R. Peschanski

T. Affolder

English

arXiv

We evaluate inclusive Higgs boson and dijet cross sections at the Fermilab Tevatron collider via double Pomeron exchange. Such inclusive processes, normalized to the observed dijet rate observed at Run I, noticeably increase the predictions for tagged (anti)protons in Run II with respect to exclusive production, with the potentiality of Higgs boson detection

Boonekamp, M.

Peschanski, R.

Royon, Christophe

KU ScholarWorks

VOLUME 87, NUMBER 25 P H Y S I C A L R E V I E W L E T T E R S 17 DECEMBER 2001251806-1Inclusive Higgs Boson and Dijet Production via Double Pomeron ExchangeM. Boonekamp,1 R. Peschanski,2 and C. Royon1,31CEA, SPP, DAPNIA, CE-Saclay, F-91191 Gif-sur-Yvette Cedex, France2CEA, SPhT, CE-Saclay, F-91191 Gif-sur-Yvette Cedex, France3Brookhaven National Laboratory, Upton, New York 11973and University of Texas, Arlington, Texas 76019(Received 11 July 2001; published 3 December 2001)We evaluate inclusive Higgs boson and dijet cross sections at the Fermilab Tevatron collider via doublePomeron exchange. Such inclusive processes, normalized to the observed dijet rate observed at Run I,noticeably increase the predictions for tagged (anti)protons in Run II with respect to exclusive production,with the potentiality of Higgs boson detection.DOI: 10.1103/PhysRevLett.87.251806 PACS numbers: 14.80.Bn, 12.40.Nn, 13.85.Rm, 13.87.CeIt has been shown [1] that Higgs boson and dijet pro-duction via double Pomeron (DP) exchange may be non-negligible. However, the lack of solid QCD theoreticalframework for diffraction makes an univocal theoreticaldetermination difficult [2,3]. An evaluation [4] of experi-mental possibilities using outgoing (anti)proton taggingand a missing mass method predicts a discovery potentialfor the Higgs boson, but it strongly depends on the theo-retical framework.Our aim is to give predictions based on inclusive Higgsboson and dijet production at the Fermilab Tevatron col-lider via DP exchange. So far, the predictions have beenbased on exclusive production without accompanyingradiation, which is indeed present, e.g., in DP dijetproduction at the Tevatron [5]. Thus, we (i) normalizethe theoretical predictions to the observed dijet rateand obtain a more constrained prediction for the Higgsboson, (ii) find sizable cross sections, and (iii) makethe first step in evaluating the specific inclusive signalbackground ratio.In the following we use as a starting point the Bialas-Landshoff exclusive model for Higgs boson and heavy fla-vor jet production [1]. We modify it in order to take intoaccount inclusive Higgs boson and dijet production, addingalso contributions from light quark jets and gluon jets (not0031-90070187(25)251806(4)$15.00included in [1]) . We show that we are able to reproduceup to a rescaling (which will be fixed from experiment) theobserved distributions, in particular, the dijet mass fractionspectrum. Using the same framework, we give predictionsfor inclusive Higgs boson production via DP exchange atthe Tevatron.The main lesson of our study is that an interesting dis-covery potential for the Higgs boson particle at the Teva-tron Run II can be expected in double (anti)proton taggedexperiments. It is materialized in Table I for the numberof events as a function of MH depending on experimentalcuts and decay products.Note that these estimates are sizably higher than themore recent exclusive production predictions [3]. One rea-son is the absence of a damping quark mass factor in in-clusive dijet production. This renormalization enhancesthe t̄t loop contribution for Higgs boson production. Onemay not, however, exclude the possibility of having a largerexclusive production cross section, as was obtained in pre-vious analyses [1,2], if the rescaling factor for exclusiveproduction is different from the one determined using in-clusive dijet production.Let us introduce the formulas for inclusive Higgs bosonand dijet production cross sections via DP exchange.dsinclH  CHµxg1 xg2 sM2H∂2edµj1j2 2M2Hxg1 xg2 s∂ Yi1,2ΩGPxgi , mdxgixgidjijid2yij2a0y2ii exp22ly2i æ,dsinclJJ  CQ̄Qµxg1 xg2 sM2J̄J∂2eFJJd2µ Xi1,2yi 1 ki∂ Yi1,2ΩGPxgi , mdxgixgidjijid2yid2kij2a 0y2ii exp22ly2i æ,(1)where xg1 , xg2 define the fraction of the Pomerons’ momen-tum carried by the gluons involved in the hard process,see Fig. 1, and GPxg1,2, m, are, up to a normalization, thegluon structure function in the Pomerons extracted fromHERA experiments; see [6]. m2 is the hard scale (for sim-plicity kept fixed at 75 GeV2, the highest value studied atHERA; we neglect the small [6] contribution of quark ini-tiated processes in the Pomeron). By construction of ourmodel, the known formulation for exclusive channels inRef. [1] (except gg ! gg, not included in [1]) are recov-ered by the substitution GPxgi , m ! dxgi 2 1.The formulas (1) are written for a Higgs boson ofmass MH and two jets (of total mass MJ̄J), respectively.The Pomeron trajectory is at  1 1 e 1 a0t e 0.08, a0  0.25 GeV22, j1,2,0.1 are the Pomerons’fraction of longitudinal momentum, y1,2, the 2-transversemomenta of the outgoing p, p̄, k1,2, those of the outgoingquark jets, l  4 GeV22 the slope of the Pomeron pp̄© 2001 The American Physical Society 251806-1VOLUME 87, NUMBER 25 P H Y S I C A L R E V I E W L E T T E R S 17 DECEMBER 2001TABLE I. Number of Higgs boson events for 1 fb21: Thefirst column gives the number of events at the generator level(all decay channels included), and the other columns after a fastsimulation of the detector. The second column gives the numberof events decaying into bb̄ tagged in the dipole roman pot de-tectors (see text), the third one requiring additionally at least twojets of pT . 30 GeV, the fourth one gives the number of recon-structed and tagged events when the Higgs boson decays into t,and the fifth one when the Higgs boson decays into W1W2 (inthis channel, the background is found to be negligible).MHiggs boson (1) (2) (3) (4) (5)100 26.6 18.5 5.7 1.9 0.2110 21.6 14.0 5.3 1.3 0.7120 17.4 9.8 4.8 1.0 1.9130 13.8 6.1 3.2 0.6 3.3140 10.6 2.9 1.8 0.3 4.2150 8.0 1.0 0.8 0.1 5.0160 5.7 0.2 0.1 0.0 4.5170 3.7 0.0 0.0 0.0 2.9coupling, and the constants CH , CQ̄Q are normalizationscontaining various factors related to the hard matrixelements together with a common nonperturbative factordue to a nonperturbative gluon coupling [1], absent in theratio CHCQ̄Q.251806-2gH ,  QQ, ggkk12xgx 12ppPP 1x   , v1x   , v2 2FIG. 1. Inclusive production scheme: xi  1 2 ji , yi arethe longitudinal and transverse 2-momenta of the diffracted(anti)proton, xgi , the Pomeron fraction momentum broughtby the gluons participating in the hard cross section, ki ,the transverse 2-momenta of the outgoing jets in the centralregion from quarks, gluons, or the b̄b decay products of theHiggs boson.The dijet cross section sJJ depends on the gg ! Q̄fQfand gg ! gg cross sections [7]. This gives for five quarkflavors f  1 ! 5FJJ XfFQ̄f Qf rf 1 27Fggrgg; rf 4mfT1mfT2M2Q̄fQf; rgg 4pT1pT2M2gg,FQ̄fQf rfm2 fT1 m2 fT2µ1 2rf2∂ µ1 29rf16∂; Fgg 1p2T1p2T2µ1 2rgg4∂3.(2)27 stands for the color factor fraction between gluon jetsand quark jets partonic cross sections [7].Note that the gg ! Q̄fQf cross section depends ontransverse and not on rest quark masses. Thus, all fivequark flavors sizably contribute to the dijet cross section.This is to be contrasted with the exclusive case for whichone finds [1]FQ̄fQf  r̃f r̃f1 2 r̃fm2 fT1 m2 fT2, r̃f 4m2 fQM2Q̄fQf. (3)The corresponding cross section is proportional to m2 fQand thus is quasizero for light quarks. This reflects theknown zero helicity constraint of the quark jet productionmechanism of Ref. [1] (in fact, for light quarks, a zero ap-pears in the forward anti(proton) direction; see dijet papersin [2]).The physical origin of our formulas (1) extended to theinclusive case is the following: Since the overall par-tonic configuration is produced initially by the long-range,soft DP interaction, we assume that, up to a normaliza-tion, the inclusive cross section is the convolution of the“hard” partons ! Higgs boson, partons ! jets subpro-cesses by the Pomeron structure function into gluons; seeFig. 1. The expected factorization breaking of hadropro-duction will appear in the normalization through a rescal-ing of the Pomeron fluxes, which are not the same as inhard diffraction at HERA. Indeed, this ansatz remarkablyreproduces the dijet mass fraction seen in experiment; seeFig. 2.Let us compare our results with the measurements per-formed in the CDF experiment at Tevatron [5]. To this end,we interfaced our generator with SHW [8], a fast simulationof the D0 and CDF detectors. We chose as gluon contentof the Pomeron the result of the H1 “fit 1” performed inRef. [6], up to a normalization of the flux determined bycomparison with CDF results.We first compare our results for the dijet mass fractionwith the measurement of the CDF Collaboration [5] in DPevents. As shown in Fig. 2, the dijet mass fraction spec-trum is well reproduced. The CDF measurement couldclearly not be described without radiation since the ob-tained dijet mass fraction would peak near one, up to de-tector resolution effects.To be more detailed, a tagged antiproton with 0.035 #jp̄ # 0.095 and jtj , 1 GeV2 was required. This quan-tity is reconstructed using the roman pot detectors installedby the CDF Collaboration. After the CDF cuts to tag an251806-2VOLUME 87, NUMBER 25 P H Y S I C A L R E V I E W L E T T E R S 17 DECEMBER 2001dijet mass fraction00.511.522.530 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Entries            3141FIG. 2. A comparison of the dijet mass fraction obtained in ourmodel and CDF data (open circles). With radiation: the shadeddistribution is the dijet distribution after radiation and simulationof the detector. Without radiation: dotted line: distribution atgenerator level; dashed line: after simulation of the detector.antiproton and the fast simulation of the detector, we ob-tain a cross section of 14.4 nb, to be compared with theCDF measurement of 43.6 nb. At the present stage, atleast two aspects are lacking in our study: first, our cross-section formulas do not include dissociation of the out-going (anti)protons. Second, some (difficult to evaluate)fractions of the proton-tagged events seen in experimentare in fact fake tags, coming namely from excited Nstates leaving an energetic decay proton in the detector.(A factor of 3 coming from the inclusion of excited Nstates has been predicted in the first reference in [2] in thecontext of exclusive Higgs boson production.) Both effectscontribute to enhance the measured cross section and thusthe difference between our prediction and the measuredvalue [9]. We thus scale up our cross sections by a factorof 43.614.4  3.We can now give predictions for the Higgs boson pro-duction cross sections in double diffractive events, by scal-ing our results by the above-determined factor. The resultsare given in Table I, first column. We note the high valuesof the cross sections, which predict more than ten eventsper fb21 for a Higgs boson mass below 140 GeV. (Theexpected luminosity is between 20 and 25 fb21 per ex-periment for Run-II.)After interfacing the generator with SHW [8], we canestimate the rates which could be observed in the experi-ments. The experimental resolution and acceptances ofthe roman pot detectors have been chosen to be similar tothe D0 ones for dipole detectors, namely, the t resolutionis 0.1pt, t acceptance is jtj # 0.5 GeV2, j resolution is0.2%, and the j acceptance is 100% if j . 0.04, 0% if251806-3e(1)025050075010001250150017502000900 925 950 975 1000Entries         100000QQ smeared mass11010 210 310 40 50 100 150 200Entries         100000(etjet1+etjet2)/205101520250 20 40 60 80 100Entries             468(etjet1+etjet2)/202.557.51012.51517.52022.50 20 40 60 80 100Entries             689(a) (b)(c) (d)FIG. 3. A comparison of diffractive dijet and Higgs boson dis-tributions: The Higgs boson distributions are here always on theright of the b̄b distribution. (a) shows the energy distribution ofthe tagged proton or antiproton, (b) the leading dijet mass dis-tribution, (c) the mean leading two jet transverse energy in caseradiation is added, and (d) is the same plot without radiation.Normalization is arbitrary in all figures.j , 0.01, and linear between 0% and 100% if 0.01 ,j , 0.04 [10]. The tagging efficiency (see second columnof Table I) is quite good if one uses a dipole detector oneach side. To be able to trigger these events, some activityinside the central detector will be required, and we give in Mx051015202530350 20 40 60 80 100 120 140 160 180 200Entries           37135 Mx0204060801001201401600 20 40 60 80 100 120 140 160 180 200Entries           38278FIG. 4. Higgs boson mass reconstruction: On top, with radia-tion; on bottom, without. The grey distribution is the result ofthe missing mass method, and the dashed line is the leading dijetmass distribution.251806-3VOLUME 87, NUMBER 25 P H Y S I C A L R E V I E W L E T T E R S 17 DECEMBER 2001Table I, third column, the number of events after requiringat least two jets of pT . 30 GeV [11].To enhance the signal to background ratio, it is possibleto cut on the proton and antiproton tagged energy at930 GeV (see Fig. 3a), on the jet topologies (the jetscoming from Higgs boson events are more central) andon the reconstructed mass distribution using the missingmass method [4] (see Figs. 3b and 4). We slightlymodified the original method to partly take into accountradiation and define MH pjpjp̄sEjet11Ejet21Ep1Ep̄2Ebeamwhere the Ejeti are the leading two jets energies and Epand Ep̄ are the tagged p and p̄ energies. We notice thatthe missing mass method is not working so nicely whenradiation is included. It is, however, still a competitivemethod to reduce background and reconstruct the Higgsboson mass [12]. Since we obtain quite high crosssections, other Higgs boson decay channels with smallerbranching ratios, such as H ! t1t2 (about 10% ofHiggs boson decay; see Table I) or H ! W1W2 are ofvery high interest since the expected background is verysmall. The background over signal ratio will be studiedin more detail in Ref. [13].We acknowledge fruitful discussions with M. Albrow,A. Bialas, A. Brandt, A. De Roeck, J. Feltesse, V. Khoze,M. Peskin, M. Ryskin, and L. Schoeffel.[1] J. D. Bjorken, Phys. Rev. D 47, 101 (1993); A. Bialasand P. V. Landshoff, Phys. Lett. B 256, 540 (1990);A. Bialas and W. Szeremeta, Phys. Lett. B 296, 191(1992); A. Bialas and R. Janik, Z. Phys. C 62, 487(1994).[2] Higgs boson: J-R. Cudell and O. F. Hernandez, Nucl. Phys.B471, 471 (1996); E. M. Levin, hep-ph/9912403, and ref-erences therein; Dijets: J. Pumplin, Phys. Rev. D 52, 1477(1995); A. Berera and J. C. Collins, Nucl. Phys. B474,183 (1996); A. D. Martin, M. G. Ryskin, and V. A. Khoze,Phys. Rev. D 56, 5867 (1997); A. Berera, Phys. Rev. D 62,014015 (2000).251806-4[3] V. A. Khoze, A. D. Martin, and M. G. Ryskin, hep-ph/0006005; hep-ph/0103007; Eur. Phys. J. C 19, 477 (2001);V. A. Khoze, hep-ph/0105224.[4] M. G. Albrow and A. Rostovtsev, hep-ph/0009336.[5] CDF Collaboration, T. Affolder et al., Phys. Rev. Lett. 85,4215 (2000).[6] C. Royon, L. Schoeffel, J. Bartels, H. Jung, andR. Peschanski, Phys. Rev. D 63, 074004 (2001).[7] B. L. Combridge and C. J. Maxwell, Nucl. Phys. B239, 429(1984).[8] SHW, a fast simulation package for D0 and CDF detectors;see www.physics.rutgers.edu/jconway/soft/shw/shw.html.[9] Note that the CDF cross section was measured after kine-matical cuts on the proton side: 0.01 # jp # 0.03. Thiscut is difficult to reproduce using a fast simulation of thedetector since it is very sensitive to the energy measurementinside the main CDF detector (the proton is not tagged).Thus, we did not apply this cut on our cross section. If onetries to apply these cuts in our fast simulation program, oneobtains a cross section 2 or 3 times smaller depending onthe energy corrections. We chose not to apply these ad-ditional factors to be on the safe side concerning our pre-dictions on the numbers of Higgs boson events. Thus, ourHiggs boson event rates may be conservative by a factorof 2 to 3 if one takes into account this effect.[10] D0 Collaboration, “Proposal for a Forward Proton Detectorat D0,” presented by A. Brandt, Proposal P-900 submit-ted to the Fermilab PAC, 1997; A Brandt et al., FermilabPUB-97-377.[11] This allows us to enhance our signalbackground ratio (thebb̄ diffractive background without any cuts is estimatedto be about 2.3 3 107 events per fb21 and becomes about8.3 3 104 events after those pT cuts), as shown in Figs. 3cand 3d. When we compare Figs. 2c and 2d, we also notethat radiation is more important for dijet events than forHiggs boson events, since the distribution for dijet events ismore shifted to the left after radiation than the Higgs bosonone. Hence, the pT cut is more efficient after radiation.[12] Because of radiation remnants which escape mostly intothe beam pipe, the missing mass method cannot work asit stands. However, it will be very useful to performconstrained fits and to have different ways of reconstructingthe Higgs boson mass.[13] M. Boonekamp, R. Peschanski, and C. Royon (to bepublished).251806-4

Inclusive Higgs boson and dijet production via Double Pomeron exchange

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