Eggert, Karsten

Morsch, Andreas

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9 September 1994 OCR OutputGeneva, Switzerlandbeauty acceptance and the reconstruction in forward spectrometers.closer the excited proton direction. This may offer some advantages for thePomeron hemisphere opposite to the underlying event which followstriggering on large diffractive masses the beauty system is boosted into thetopology for the beauty particles and the underlying event are given. Whencross-sections for beauty production at different diffractive masses and thecollisions at the LHC we discuss the beauty production in those events. TheUsing the framework of Pomeron exchange to describe diffractive ppAhsgactK. Eggert and A. MorschDiffractive Beauty Production at the LHC ColliderXu, 5) OCERN-AT—94-10- CERN AT/94 10 <¤¤llllllllllllllllllllllllllllllllllllillllCERN LIBRARIES, GENEVAEUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHthe presence of a pseudorapidity gap, a method frequently used in the past. OCR Outputproton momentum losses, which cannot be directly detected, can thus be identified bythe hemisphere opposite to the Pomeron. Low mass diffraction (M < 0.5 TeV) withmasses are sketched. The lower the mass the more forward the particles are emitted intoIn Fig. lc, the pseudo rapidity distributions of particles from two different excitedfavourable in these events.kinematics and the signal-to-background ratio for beauty particles may be moredifferent from the one of normal pp events. It is therefore not excluded that thediffractive events with most of the particles going along the diffractive system is quitediffractive events would lead to a substantial heavy flavour production. The topology oftherefore an interesting question to ask whether the possibly enhanced gluon flux inHeavy flavours, like beauty and top, are mainly produced by gluon interactions. It isinteracts with the proton constituents.function seems to be rather hard [4]. Thus the hard gluon beam from the Pomeronthe Pomeron is seen as a multi-gluon state. Measurements indicate that its structureway a Pomeron beam can be defined with momenta between 10 and 1000 GeV. Oftenof 10·3 to 10‘1 by means of Roman pots placed upstream in the straight section. In such aAs described in Ref. [3], the proton momentum loss écan be measured in the rangeproton in diffractive events at the LHC is therefore in the range of lO‘to 108 ‘1mass corresponds to the production of one additional pion. The momentum loss of themomentum of above 1 TeV is limited by the coherence condition, whereas the lowestThe largest momentum loss leading to an excited mass of around 4 TeV or a Pomeron(2)<;<T-¤ es 610`°<§<0.15{ (m’+m")physical meaningful range of ef is covered by:where ~/s=2pg is the centre of mass energy of the collision. At the LHC (~/s=14 T eV) the<1>1 · X = 6 =relative momentum loss §= Ap/po byx=1-Q. The mass M of the system X in which the other proton is excited is related to thisfraction 5 of the proton momentum leaving a proton with a beam momentum fractionmass M recoiling against the intact proton (Fig. 1a,b). The Pomeron has taken theof one proton, interacts with the other proton and thus produces an excited system withcurrently believed that single diffraction is mediated by a Pomeron which, being a partmomentum have been studied at the ISR and the proton-antiproton collider . It is[2][1]Inelastic diffractive processes in which one of the two protons stay intact but loosesOCR Output1. Introduction- .2(6) OCR Output-- = fs;/p(xi’Q2)fzi/P(xi’Q2)`E%dodo*(pIP —> QQXfunctions and the parton-parton cross section.The hard scattering cross-section is a product of the proton and Pomeron structure5(5)__ €¤\lX SD(.§m <§< gm) - 0.7mb lnpomeron momentum range §mm<§<§maXIntegrating over t and § one obtains for the total diffractive cross section in thediffractive c1·oss section of 12 mb/ side.The normalisation constant C was set to 2.3 mb GeV‘2 corresponding to a total singleand u=2.8, b=O.7 GeV?. o’(pIP —-> X) =2.3 mb is the total Pomeron proton cross section.·th “" 4m ‘ - at 1 p = .4.... .._. M 4m,2—t (1-t 7 zi)(4),f = ——-lt-; = -1;- ·— F f fP/Pg ) o·(pIP —>X) d§dt o·(pIP —+X) gl 1(1 do C 1 2dependence of the proton form factor F1(t) and an l/{dependence:As described in Ref. [7], the Pomeron flux factor was calculated from the tby the Pomeron and t symbolises an independent set of Mandelstam variables.momentum fraction of the Pomeron; t is the transverse momentum squared transferredHere, xi and xi denote the momentum fractions of the interacting partons and 5 thedifferential cross section of the hard scattering between the Pomeron and the proton.The first term on the right side is the pomeron flux factor and the second one thej=f (5 t) agatdxaxai “°’P ’ ax.ax.aE (3)d¤(p11¤ -> QQXd¤(pp —> Qijx)The differential cross section for pp diffractive hard scattering is:by G. Ingelrnan etal. [6]PY'l'l—HA 5.7 [5] in combination with POMPYT, a special diffractive event generator builtTo simulate heavy flavour production in single diffractive pp interactions we used2. Simulation of Diffractive Hard Scattering- 3 OCR Outputthe ones in the proton and hence the beauty particles are boosted along the Pomeronmomentum (1-10%) the gluons in the Pomeron have, on average, larger momenta thandirection (Fig. 5). When the Pomeron takes a substantial fraction of the protonthe beauty particles move into the opposite hemisphere, following the Pomeronhemisphere. With increasing diffractive masses the particle distribution gets wider andparticles and the underlying event particles go together into the excited protonthe hard structure fimction, in particular at large masses. At low masses the beautyparticles follow the underlying diffractive event the distributions are quite different fornegative ones of the Pomeron. Whereas for the soft structure function the beautyfunctions. Positive pseudorapidities denote the hemisphere of the excited proton,the underlying event are shown in Fig. 4 for (a) the hard and (b) the soft gluon structureevent. The average pseudorapidity 11 and the 11-range for beauty and the particles fromThe following figures illustrate the beauty kinematics with respect to the underlying4. Topology of Diffractive Beauty Eventsthese events.compared to normal pp events. We therefore study in the next chapter the topology ofPomeron, have a topology which allows an easier distinction of the beauty particleswhether diffractive events with an excited mass around 1 TeV, emitted opposite to thethe one in normal events, but at the larger energy of 14 TeV. It has now to be seenand charm content in diffractive events with a sub energy of ~ 1 TeV is comparable toIn our assumed scenario, in which the Pomeron consist of hard gluons, the beautynormal pp collisions (w/s=l4 TeV), whereas it is above 100 at low diffractive masses (Fig.masses. The charm-to-beauty ratio approaches at large masses 10-20, also similar tofunction of the Pomeron this beauty fraction would even exceed 2% at the highest100 times larger than in an LHC fixed target scenario. With the soft gluon structurefraction of 0.6% which is similar to pp collisions at w/s=14 TeV and more than a factormagnitude over the mass range (Fig. 2b), reaching at the highest masses a beautybins of log§. On the contrary, the beauty cross-section increases by two orders ofhaving in mind that the diffractive cross-section is constant (~1.5 mb! decade) in equaldiffractive mass M and for beauty production in this mass bin is plotted versus logl;ln Fig. 2a, the differential cross-sections do/dM for the inclusive production of the3. Diffractive Heavy Flavour Cross-sections(soft gluons)zfm, (z) = 6(1 - z)5(5)(hard gluons)zfg,,(z) = 6z(1 — z)Schlein [4] was used for the calculations and a soft structure function for comparison:is still an open question. The 'hard‘ structure function advocated by Ingelman andWe assume that the dominant structure of the Pomeron consists of gluons, although this- 4 OCR Outputover a probably much reduced background from the underlying event.energy of about 1 TeV thus providing very high momentum gluon·gluon interactionspp collider could thus be transformed into a Pomeron-Pomeron collider with a subwith Roman pot spectrometers double pomeron exchange reactions can be studied. Theperform detailed studies of the Pomeron structure. By equipping both forward armsstudy the nature of diffraction and, if the Pomeron would be a quasireal particle, toIn any case, beauty production in diffractive events would serve as an ideal tool toevents.further studied whether such a beauty sample would be cleaner compared to normalacceptance of a forward spectrometer, like e.g. the COBEX spectrometer. It has to bemass already on the 1. level trigger, the beauty particles can be boosted into thepot spectrometers. By choosing the proton momentum loss and hence the diffractiveloss of the protons can be measured in the range of 10‘to 10with the help of Roman3 `1signal-to-background ratio is more favourable in these events. The relative momentum(in the case of a hard structure function and large masses), the kinematics and thelower. It may be that, with most of the particles going opposite to the beauty particlescollisions at *}s=14 TeV, despite the fact that the sub energy in diffractive events isThe beauty production in high mass diffractive events is as large as in normal pp5. SummaryTeV.8 for three mass bins. The beauty momenta are lowest for diffractive masses around 1distributions of the underlying event particles and the beauty particles are shown in Fig.( M >3 TeV ) and increases above 100 GeV at masses below 0.1 TeV. The momentumThe average beauty momentum , shown in Fig. 7, is around 50 GeV for large massesbeauty production for masses below 0.3 TeV.mrad. In the proton hemisphere, COBEX would almost fully cover the diffractivepairs in high mass diffraction with most of the beauty particles being even within 200detector (Ref. [8]), placed in the Pomeron hemisphere, accepts more than 60% of the bBassumed spectrometer apertures. As an example, the forward (600 mrad) COBEXFig. 6 shows the acceptance of the bB pairs as a function of log§ for differentcombinatorial background for beauty reconstruction.most of the underlying event particles are in the proton hemisphere thus reducing theover only a few units can be boosted into the acceptance of the apparatus. Secondly,large diffractive mass the beauty particles with a pseudorapidity distribution extendingdirection. From the experimental point of view this has two advantages: by choosing a[8] COBEX Letter of Intent, CERN/LHCC/ 93-50. OCR Output[7] A. Donnachie and P.V. Landshoff, Nucl. Phys. B303 (1988) 634.Diffractive Hard Scattering Processes', DESY 93.[61 P. Bruni and G. Ingelman, 'POMPYT version 1.0- A Monte Carlo to simulateT. Sjostrand, Comp. Phys. Comm. 39 (1986) 347, ibid. 43 (1987) 367.[5] H.-U. Bengtsson, T. Sjostrand, Comp. Phys. Comm. 46 (1987) 43.[4] G. Ingelman and P. Schlein, Phys. Lett. 152B (1985) 256.LHC Low-/3 Insertion', CERN AT/ 94-09 (DI).[3] K. Eggert and A. Morsch, 'Leading Proton Detection in Difractive Events for an[2] M. Bozzo et al., Phys. Lett. B136 (1984) 217.[1] M.G. Albrow et ul., Nucl. Phys. B108 (1976) 1.References- 6 OCR OutputTeV and (c) M =3.6 TeV. The recoil protons show up at the right-hand side of the plots.assuming a hard gluon structure function for (a) diffractive mass M=0.2 TeV, (b) M=1.4Particle rate per event vs. momentum for underlying event and beauty particlesFig. 8(b) soft gluon structure function.Average momentum of the beauty particles vs. l0g(€) for (a) hard gluon structure andFig. 7200 rnrad (dashed line) and 100 mrad (dotted line) aperture.Beauty-antibeauty pair acceptance for forward spectrometers with 600 mrad (solid line),Fig. 6the plots.(b) M=1.4 TeV and (c) M=3.6 TeV. The recoil protons show up at the right-hand side ofparticles assuming a hard gluon structure function for (a) diffractive mass M=0.2 TeV,Particle density distribution vs. pseudo rapidity for underlying event and beautyFig. 5particle distribution.lines show the range of coverage of the underlying event and the width of the beauty(line) for (a) hard gluon structure and (b) soft gluon structure function. The verticalThe average pseudo rapidity for beauty particles (points) and underlying event particlesFig. 4Ratio of cE to bB cross-section.Fig. 3(b) Ratio of bil to total diffractive cross-section.(dotted curve) assuming a hard gluon structure function of the Pomeron.(a) Total diffractive cross—section vs. log(§) (solid curve) and diffractive bB cross-sectionFig. 2(c) Sketch of the single—diffractive event topology for two different diffractive masses M.(b) Single diffractive reaction represented by a t-channel Pomeron exchange diagram.diffractive reaction p+p—> p+X.(a) The initial state momentum vectors in the , overall centre—of-mass of the singleFig. 1Figure Captions

Diffractive beauty production at the LHC collider

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