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Inclusive Higgs Boson and Dijet Production Via Double Pomeron Exchange

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Inclusive Higgs Boson and Dijet Production Via Double Pomeron Exchange VOLUME 87, NUMBER 25 PHYSICAL REVIEW LETTERS 17DECEMBER 2001 Inclusive Higgs Boson and Dijet Production via Double Pomeron Exchange M. Boonekamp,1 R. Peschanski,2 and C. Royon1,3 1CEA, SPP, DAPNIA, CE-Saclay, F-91191 Gif-sur-Yvette Cedex, France 2CEA, SPhT, CE-Saclay, F-91191 Gif-sur-Yvette Cedex, France 3Brookhaven National Laboratory, Upton, New York 11973 and 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 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. DOI: 10.1103/PhysRevLett.87.251806 PACS numbers: 14.80.Bn, 12.40.Nn, 13.85.Rm, 13.87.Ce It has been shown [1] that Higgs boson and dijet pro- included in [1]) . We show that we are able to reproduce duction via double Pomeron (DP) exchange may be non- up to a rescaling (which will be fixed from experiment) the negligible. However, the lack of solid QCD theoretical observed distributions, in particular, the dijet mass fraction framework for diffraction makes an univocal theoretical spectrum. Using the same framework, we give predictions determination difficult [2,3]. An evaluation [4] of experi- for inclusive Higgs boson production via DP exchange at mental possibilities using outgoing (anti)proton tagging the Tevatron. and a missing mass method predicts a discovery potential The main lesson of our study is that an interesting dis- for the Higgs boson, but it strongly depends on the theo- covery potential for the Higgs boson particle at the Teva- retical framework. tron Run II can be expected in double (anti)proton tagged Our aim is to give predictions based on inclusive Higgs experiments. It is materialized in Table I for the number boson and dijet production at the Fermilab Tevatron col- of events as a function of MH depending on experimental lider via DP exchange. So far, the predictions have been cuts and decay products. based on exclusive production without accompanying Note that these estimates are sizably higher than the radiation, which is indeed present, e.g., in DP dijet more recent exclusive production predictions [3]. One rea- production at the Tevatron [5]. Thus, we (i) normalize son is the absence of a damping quark mass factor in in- the theoretical predictions to the observed dijet rate clusive dijet production. This renormalization enhances and obtain a more constrained prediction for the Higgs the tt¯ loop contribution for Higgs boson production. One boson, (ii) find sizable cross sections, and (iii) make may not, however, exclude the possibility of having a larger the first step in evaluating the specific inclusive signal͞ exclusive production cross section, as was obtained in pre- background ratio. vious analyses [1,2], if the rescaling factor for exclusive In the following we use as a starting point the Bialas- production is different from the one determined using in- Landshoff exclusive model for Higgs boson and heavy fla- clusive dijet production. vor jet production [1]. We modify it in order to take into Let us introduce the formulas for inclusive Higgs boson account inclusive Higgs boson and dijet production, adding and dijet production cross sections via DP exchange. also contributions from light quark jets and gluon jets (not µ ∂ µ ∂ Ω æ g g 2e 2 Y g x x s M g dx dj 2a0 y2 incl ෇ 1 2 H ͑ ͒ i i 2 i ͑ 2͒ dsH CH 2 d j1j2 2 g g GP xi , m g d yiji exp 22lyi , M x1 x2 s ෇ xi ji µ H ∂ µ i 1,2∂ Ω æ g g 2e X Y g x x s g dx dj 2a0y2 (1) incl ෇ 1 2 ͑2͒ ͑ ͒ ͑ ͒ i i 2 2 i ͑ 2͒ dsJJ CQQ¯ 2 FJJ d yi 1 ki GP xi , m g d yid ki ji exp 22lyi , MJJ¯ i෇1,2 i෇1,2 xi ji g g where x1 , x2 define the fraction of the Pomerons’ momen- Ref. [1] (except gg ! gg, not included in [1]) are recov- g g tum carried by the gluons involved in the hard process, ered by the substitution GP͑xi , m͒ ! d͑xi 2 1͒. g see Fig. 1, and GP͑x1,2, m͒, are, up to a normalization, the The formulas (1) are written for a Higgs boson of gluon structure function in the Pomerons extracted from mass MH and two jets (of total mass MJJ¯ ), respectively. HERA experiments; see [6]. m2 is the hard scale (for sim- The Pomeron trajectory is a͑t͒ ෇ 1 1e1a0t ͑e ϳ 2 0 22 plicity kept fixed at 75 GeV , the highest value studied at 0.08, a ϳ 0.25 GeV ͒, j1,2͑,0.1͒ are the Pomerons’ HERA; we neglect the small [6] contribution of quark ini- fraction of longitudinal momentum, y1,2, the 2-transverse tiated processes in the Pomeron). By construction of our momenta of the outgoing p,¯p, k1,2, those of the outgoing model, the known formulation for exclusive channels in quark jets, l ϳ 4 GeV22 the slope of the Pomeron pp¯ 251806-1 0031-9007͞01͞87(25)͞251806(4)$15.00 © 2001 The American Physical Society 251806-1 VOLUME 87, NUMBER 25 PHYSICAL REVIEW LETTERS 17DECEMBER 2001 21 TABLE I. Number of Higgs boson events for 1 fb : The p first column gives the number of events at the generator level x 1 , v 1 (all decay channels included), and the other columns after a fast P simulation of the detector. The second column gives the number of events decaying into bb¯ tagged in the dipole roman pot de- tectors (see text), the third one requiring additionally at least two jets of pT . 30 GeV, the fourth one gives the number of recon- g k structed and tagged events when the Higgs boson decays into t, x 1 1 H , QQ, gg and the fifth one when the Higgs boson decays into W 1W 2 (in this channel, the background is found to be negligible). g k x 2 2 MHiggs boson (1) (2) (3) (4) (5) 100 26.6 18.5 5.7 1.9 0.2 110 21.6 14.0 5.3 1.3 0.7 120 17.4 9.8 4.8 1.0 1.9 130 13.8 6.1 3.2 0.6 3.3 P 140 10.6 2.9 1.8 0.3 4.2 150 8.0 1.0 0.8 0.1 5.0 p x22 , v 160 5.7 0.2 0.1 0.0 4.5 FIG. 1. Inclusive production scheme: xi ϵ 1 2ji , yi are 170 3.7 0.0 0.0 0.0 2.9 the longitudinal and transverse 2-momenta of the diffracted g (anti)proton, xi , the Pomeron fraction momentum brought by the gluons participating in the hard cross section, ki , the transverse 2-momenta of the outgoing jets in the central coupling, and the constants CH , CQQ¯ are normalizations region from quarks, gluons, or the bb¯ decay products of the containing various factors related to the hard matrix Higgs boson. elements together with a common nonperturbative factor f f The dijet cross section sJJ depends on the gg ! Q¯ Q due to a nonperturbative gluon coupling [1], absent in the and gg ! gg cross sections [7]. This gives for five quark ͞ ratio CH CQQ¯ . flavors ͑f ෇ 1 ! 5͒ X f f f gg f 4mT1mT2 gg 4pT1pT2 ෇ ¯ f f ͑ ͒ ͑ ͒ ϵ ϵ FJJ FQ Q r 1 27Fgg r ; r 2 ; r 2 , M ¯ f f M f µ ∂µ ∂ Q Q µ gg∂ f f f gg 3 ϵ r r 9r ϵ 1 r (2) FQ¯ f Qf 2 f 2 f 1 2 1 2 ; Fgg 2 2 1 2 . mT1 mT2 2 16 pT1pT2 4 27 stands for the color factor fraction between gluon jets Fig. 1. The expected factorization breaking of hadropro- and quark jets partonic cross sections [7]. duction will appear in the normalization through a rescal- Note that the gg ! Q¯ fQf cross section depends on ing of the Pomeron fluxes, which are not the same as in transverse and not on rest quark masses. Thus, all five hard diffraction at HERA. Indeed, this ansatz remarkably quark flavors sizably contribute to the dijet cross section. reproduces the dijet mass fraction seen in experiment; see This is to be contrasted with the exclusive case for which Fig. 2. one finds [1] Let us compare our results with the measurements per- formed in the CDF experiment at Tevatron [5]. To this end, f ͑ f ͒ 2 f f r˜ 1 2 r˜ f 4mQ we interfaced our generator with SHW [8], a fast simulation F ¯ f f ͑r˜ ͒ ෇ ,˜r ϵ . (3) Q Q 2 f 2 f 2 of the D0 and CDF detectors. We chose as gluon content mT mT MQ¯ f Qf 1 2 of the Pomeron the result of the H1 “fit1” performed in 2 f The corresponding cross section is proportional to mQ Ref. [6], up to a normalization of the flux determined by and thus is quasizero for light quarks. This reflects the comparison with CDF results. known zero helicity constraint of the quark jet production We first compare our results for the dijet mass fraction mechanism of Ref. [1] (in fact, for light quarks, a zero ap- with the measurement of the CDF Collaboration [5] in DP pears in the forward anti(proton) direction; see dijet papers events.
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