JHEP06(2009)034 May 5, 2009 June 9, 2009 May 17, 2009 : : : where the initial p Received Υ+ Published Accepted , → cross-section and conclude p + γp γ doi:10.1088/1126-6708/2009/06/034 Published by IOP Publishing for SISSA b [email protected] , and R.Sandapen a production at the and LHC Υ 0905.0102 QCD Phenomenology We compute the rate for diffractive Υ production at the Tevatron and J.R. Forshaw brian.cox@.ch a SISSA 2009 [email protected] School of Physics &Oxford Astronomy, Road, University Manchester of M13 Manchester, de 9PL,D´epartement Physique U.K. et d’Astronomie, Universit´edeMoncton, Moncton, N-B. E1A 3E9, Canada E-mail: b a c

is radiated offuse an low incoming angle proton proton detectors (or tothat antiproton). make a a We measurement measurement consider of of the the possible the possibility at cross-section to the at athemselves. LHC. centre This of is mass in energy the in excess region of whereKeywords: 1 TeV saturation is effects are likely to reveal ArXiv ePrint: Abstract: the LHC. The Υ is produced diffractively via the subprocess B.E. Cox, Diffractive JHEP06(2009)034 9 3. γp , 2 , = 1 n pair. The latter [1]. The Υ states where p qq p + )+ H + nS p → . +Υ( p p p + ). Work is currently in progress 1 p → − Υ + s p 2 → + − p p cm + γ 33 – 1 – ) in order to avoid problems with pileup. However, there is interest 1 primarily as a result of high quality data on the deep inelastic structure − 1 s 2 − cm cross-section6 cross-section2 31 pp γp 10 ∼ There already exist a number of papers predicting the rate for this process [5–10]. We In the following section we explain how to calculate the rate for this process. The The reaction is interesting primarily because the LHC will probe values of the Ordinarily this is a measurement that could only be performed at low LHC luminosi- At least for light quark scattering. 1 add to what hasof been [11] done that successfully by describes providingtimate a predictions of wide using the range effect of the of the dipole detector HERA acceptances model data and [12]. cross-section the We impact also offlux make measuring an of one es- of the off protons. determines an how the incoming photon proton produces is the Υ well after known, first as fluctuating into is a the ¯ dipole cross-section that to measure exclusive Υidentified centrally production produced at charm meson the states Tevatron [3] [2] and and centrally produced the dileptons CDF4]. [ collaboration has is well determined, are too light toof be one produced proton in is conjunction feasibleat with and instantaneous two that measured luminosities may protons in be but excess sufficient measurement to of control (10 pileup induced backgrounds in supplementing the LHC420 general m purpose from detectors theproduction interaction with of points; low new the physics, angle and primary proton in goal particular detectors being the at reaction the study of ‘central exclusive’ 1 Introduction In this paper we calculate the rate for the reaction 3 The 4 Results Contents 11 Introduction 2 The ties ( The Υ is producedillustrated diffractively in1, figure after i.e. one via of the the sub-process incomingcentre-of-mass protons energy radiates well a beyond photon,is those as an that opportunity were toexpected reached examine to QCD at be in HERA. important. the Asand In region a addition, an where the result, non-linear accurate odderon there (saturation) measurement isthe effects would expected odderon are help to in contribute to this at constrain some paper. the level theory. We shall not consider JHEP06(2009)034 p is V (2.3) (2.1) (2.2) ) where 2 where W ( p γp + σ (we neglect the is the fractional V ξ Y , ) → , Y p cosh 4 ) + Υ 2 γ → − M /µ 2 is denoted by 1 Y ≈ Q p collisions. At the Tevatron one Υ p E p pp ) + ( Υ+ (1 + 2 ξs reactions will be diffractive and leave → 1 ( Q p γp 2 γp ) σ Y system, the cross-section of interest is + ξ e ) γ 2 s Υ − pp ξ √ M ξ, Q – 2 – ( = then its energy ξ 1 + (1 γ/p Y π ξf em 2 α = ) p ) = 2 Υ p 2 p p Q ξ, Q → d ( Y pp γ/p d ( pair which is detected. At the LHC, there is opportunity to also detect one f fixes the electromagnetic form factor of the proton. σ 2 − 2 d µ ) is the photon flux given by [15]: + 2 µ cross-section measured at HERA [13, 14]. In section 3, we compute the photoproduction 71 GeV ξ, Q . ( 2 is the center-of-mass energy of the pp F . Diffractive photoproduction of the Υ meson in s γ/p = 0 √ f 2 µ If the Υ is produced at rapidity and energy loss of the proton. The cross-section for where where stands for an antiproton andΥ the decays other into for a a proton while at the LHC, both stand for protons. The the incoming proton intact. Amongst these will be the process transverse momentum of the meson). Defining of the protons. function Entirely in analogy to photoproductionated at off HERA, incoming where electrons almostthe according on-shell LHC photons to are can the distribution, radi- radiate Weisz¨acker-Williams protons almostopposite at real direction. photons A that significant can fraction then of scatter these off protons heading in the Figure 1 cross-section and compare our predictionspresent with our the predictions available HERA forthe data. the Tevatron In and rapidity section the distributions 4, LHC, of we including the the Υ effects of and2 proton the tagging. expected rates The at a vector meson and that is where our interest lies. JHEP06(2009)034 . b 2 4 ¯ 2 1 + b γ ± (2.9) (2.4) (2.6) (2.7) (2.5) (2.8) = h  , 3 3 ) } ξ ) , ( 1 r ) b A 3 m ( x, r . and helicity 1 + ( ) z σ 2 K is not uniquely defined ) ) b 1) photon wavefunction ξ Y ( m 3 ± W ] z, r A ( h = 2 ¯ 2 h ). → − yields the integrated flux]: [15 λ, λ Y − γ λ,h 2 Y zδ ) ψ ± ) ) Q ξ r 3 ( + b [12]. The dipole cross-section has h A m z, r exp( 2 ) + ( ( ( x 2 min − s 0 , ¯ + h ξs ∗ λ, 2 p ( √ K = 0) amplitude can be approximated by: δ /Q 6 Υ λ,h b 11 ) Υ m 2 then we are in the diffractive regime and γp t 2 z m µ σ ξ M 2 − h Υ z ψ ) − 2 ) d ξ ≈ = M ξ λ, ( – 3 – ( r δ 2 [(1 2 ¯ h A  γ/p d 2 min h, W ) = 1 + δ iλφ ln 2 Q ξf ξ e { Z (  ¯ h f ¯ h W = π A 2 − 2 ) ee ) h, X ξ λ,h, 2 p δ ) 2 1 ) are the light-cone wavefunctions of the photon and the Υ − Υ √ h ξ p C π ) is called the dipole cross-section and it represents the cross- z, r (2 4 i ) = ( N Y → 2 ¯ h d − structure function at low x, r r 1 + (1 and with the quark carrying energy fraction ( W Υ pp λ,h 2 ( ( σ r ψ . π F em σ ) = γp 2 2 d α A pair to scatter off a proton. The formalism we are describing has been z, r /W ( m b ¯ ) and ¯ h 2 ) = Υ b = ξ = 0. ( γ M λ,h ). They represent the amplitude for the vector meson to fluctuate into a centre of mass energy, i.e z, r Y ( ψ λ . If the invariant mass = γ/p ¯ h is the proton mass. Integrating eq. (2.3) over p γp f x p γ λ,h m ψ Υ + So much for the photon flux, we are now ready to tackle the cross-section for The cross-section The minimum virtuality of the photon is The photon wavefunction is well known and, since the longitudinal wavefunction of Except at By adding cross-sections, weWe are assume neglecting that the the interference Υ between retains the the two helicity amplitudes. of the photon. is the 2 3 4 → by the Υ’s rapidityThe since two any terms on one the of right-hand-side the of two eq. incoming (2.2) allow protons for can both radiate possibilities. the photon. where and thus the rapidity distribution of the Υ is given by p We take section for the very successful in explainingprecise a data very on wide the range of HERA data, including the extremely a real photon vanishes, we shall only need the transverse ( W with consequently the imaginary part of the forward ( been extracted, for light-quarkintroduced dipoles, in from [11]; HERA welight-cone data shall wavefunctions. and turn we to use this a shortly. parameterization First we address the calculationgiven by of the where pair of transverse size (of helicity JHEP06(2009)034 , nS (2.18) (2.17) (2.14) (2.13) (2.15) (2.10) (2.11) .  2  r ) 2 nS z , S ) R 2 2 3 − 2 b R m z, r (1 ( z  -space, we obtain 4 . r nS φ 2 − ) (2.12) exp } r r ) 1  z ∂ r, z  quark. ] 2 ( )] (2.16) 2 nS h r − b 2 ) R nS  z λ, r, z (1 2 b G ( ) + 4 z 2 nS − zδ S # 4 m R 2 ) 2 f r, z g + (1 − , − ( m z 1 h S ) ) r, z ) 2 2 2 b 2 3 ( S, z − z − g 2 k − m 2 nS 2 ) b  r, z 2 r λ, α − −  Ψ meson [12]. In this model, the meson ( z ˆ δ R 2 D + m ) S 2 f (1 S, h (1 1 2 z − J/ 3 2 z z − ∇ m k 2 nS exp G 4 α 4 λ, − )[1 + (1 2 f δ R  z  ¯ h + ) m – 4 – 4 [(1 ) = r, z ) + h, z ( nS δ 2 nS 2 nS nS,k S φ { − 2 iλφ r, z r, z R α ) = ) R ( e ( 2 b 1 z 2 f G (1 ¯ h → S S − =0 1 z 2 3 m − r, z ) m − k X n 8 g ( φ 2 h, √ " ) = ˆ 3 is the electric charge of the 1 − δ p − D (1 ) ( / S, z  1 h 3 r, z ) = C sch ( π α − (2 φ 4 S i N ) = 2 2 = r, z ) exp φ + ( 1 + r f z r, z e  ( nS − ) φ ) = nS 5 , acts on the Gaussian function g (1 2 and r r, z z z, r ( ∂ [16], and also for the heavier ( S ¯ h em 3 nS + φ ) is obtained by boosting a Schr¨odingergaussian wavefunction using the is their relative transverse momentum in the boosted frame. The subscript r G Υ λ,h N πα ∂ ψ k z, r r 1 = 1. The operator and ( ) = ) = 0 = 4 = ρ nS 2 2 r φ nS, r, z e is the relative three-momentum between the quark and antiquark in the meson’s rest r, z ( ( ∇ α S p The vector meson wavefunction is less well known. Various models are discussed in [16] 3 nS φ G where Explicitly we obtain and here we shallmesons, use the boosted gaussian wavefunction, which works well for the light where with light-cone wavefunction is given by and frame while reminds us we are to treattransformation the different of Υ the states seperately. resulting light-cone After a wavefunction two-dimensional to Fourier transverse with and where Brodsky-Huang-Lepage prescription [17]: JHEP06(2009)034 5. . (2.19) (2.20) 5 3 and 0 . 2 (dotted). . 0 ) (center) and 4 , S 2 = 0 . 3 z

r are fixed so as to = 0 2 z and nS pair with the light-cone 1 . R b ¯ 018 011 008 0 1 b . . . ) (left), Υ(2 − 0 0 0 e 0 S + ± ± ± 0.4 exp e r < r r > r S Γ 3 3 (dashed) and . F 340 612 443 . . . for for ), of the 1 0 0 1 5 = 0 − is fixed to be the value at which the − f , z e 4 0 r + 340 611 443 e . . . 3 ) = 1 0 0 (GeV Γ

1 r r 2 nS x, r 481 624 668 . . . ( 5 (solid), is used in eq. (2.13) instead of the Laplacian operator, 1 are shown in figure2 for . N 0 0 0 2 GeV. 2 r – 5 – . S /σ ∂ 2 3 ) = 0 0 0 φ . . = 4 217 , the dipole cross-section is determined by interpo- z nS, 0.4 0.8 0.4 . 1 b K K α H 0 r x, r λ m S ( 0) have been fixed by requiring that the wavefunctions and 2 − S 1 ≤ σ λ F x S 555 219 r . 2 2 − . . nS, r 5 k > 0 1 x φ α ≤ H S , − − 0 S 4 A A Boosted Gaussian parameters 1 r (for φ 2 nS = 567 831 028 3 . . . ) =

R 0 0 1 r nS,k 2 1 2 3 n α x, r ( 1 σ 0 1 1.5 0.5 S 1 wavefunction reduces to that presented in [18]. . The scalar part of the light-cone wavefunction for Υ(1 F S . Parameters and predicted electronic decay widths of the Boosted Gaussian light-cone ) (right) as a function of the transverse size, It remains to specify the parametric form of the dipole cross-section. Here we use the The parameters S We note that if the double partial derivative 5 , the 2 2 r saturation model presented in [11]It (which has we the subsequently refer following to form: as the “FSSat” model). reproduce the experimentally measuredparameters thus electronic obtained, decay together widthsand with [16]. the the resulting predicted wavefunctions The decay are values widths, shown in of are figure3. given the in table1 of different states be orthogonal to each other. The values of ∇ Υ(3 In the intermediate region lating linearly between the twohard forms component of is eq. some (2.19). specified fraction of the soft component, i.e. The scalar wavefunctions momentum fraction carried by the quark, Table 1 wavefunctions in appropriate GeVvalues based are units. taken The from [19] decay widths and we are take given in keV. Experimental Figure 2 JHEP06(2009)034 (3.1) (2.21) (2.22) (2.23) z 0.4 ) (left), pair and S 0.2 b ¯ b 0.0 5 4 ), of the 1 3 r − 2 2 1 data from HERA [11]. − (GeV 2 0 r F and compare it to existing 0.0 0.4 0.2

γp , σ 68 GeV . n z 2 0.4 B , | = 3 γp × 0.2 =0 p t  )

|A , for the transversely polarised Υ(1 0.0 2 π | nS γp t 1 + 1 5 Υ ) to muons. In4, figure we compare our σ d 16 Υ( 4 Ψ d . | 4 → 0 nS = Υ – 6 – γp 1 3 σ B r 0 =0 . t 2

GeV) 3 =1 = 14 / X n γp 1 t Υ γp σ d = σ 0 d M , carried by the quark. ( z ∗ γp 0.6 0.4 0.2 0.0  σ , is taken to be [16] Υ N B z = 0.4 Υ . Before presenting our predictions for hadron-hadron collisions, ) (right) as a function of the transverse size, 0.2 B , by a fit to the total structure function 2 S 1 − r 0.0 and 4 cross-section 55 GeV H . r , λ is the branching ratio of the Υ( 2 γp S is treated as a parameter that is determined, along with the other parameters . The light-cone wavefunction squared, = 0 n , λ B f H 0 N ) (center) and Υ(3 0 2 1 We now have almost all of the ingredients we need in order to compute the ampli- As can be seen, the theory curve (dotted) lies significantly below the HERA data. S ,A , i.e S | t and the total cross-section| is obtained by assuming an exponential fall-off with increasing where the diffractive slope, Figure 3 Υ(2 the light-cone momentum fraction, where A with we shall first compute the photon-proton cross-section To compare to the data, we compute HERA data. 3 The tude (2.8) for Υ production. The forward differential cross-section is given by However, we have ignored two important corrections. The first is the contribution from where predictions to the HERA data [20–22]. JHEP06(2009)034 (3.2) (3.3) (3.4) amplitude, γp 4 10 . 2) / 3 + 4) )  + 5 A| 10 λ λ λ /x m 2 π Γ( Γ(  |= ln (1 +3 W [GeV] π ln – 7 – ∂ λ 2 ∂ √ 2 = tan = β λ ) = λ ( g cross-section. Dotted curve — no skewedness correction and 2 R γp 10 is the ratio of the real to imaginary part of the , which we estimate using eq. (3.3). We have checked that ZEUS H1 ZEUS (2009) no real) FSSat (no skew, FSSat (no skew, real) FSSat (skew, real) FSSat (skew, real, x2) Fit λ β 1 3 2 0 4

10 10 10 10 10

p p

γ γ

[pb] ) where

σ 2 ∗ β is given by eq. (2.8). A . Predictions for the m = The second correction arises because the amplitude is not diagonal — the mass of the A few comments are in order regarding our estimation of the above two corrections. Figure5 shows the ratio of the real to imaginary parts of the amplitude for each state. Υ is large and timelike compareddipole to scattering the small, cross-section spacelike, was photonestimate virtuality. extracted the In from corrections contrast, from data our this at source zero by momentum multiplying transfer. the amplitude We by a factor of [23] Both of them depend on with where We note that thestates. calculation The dashed of curve this inreal figure4 part. ratioshows is the effect model-dependent of including especially the for correction due the to higher the Our prediction, with this correction included, is shown in4 figure as the dot-dashed curve. Figure 4 without the real part;real dashed part curve and — a includingHERA skewedness the data correction. and real the part; The double-dot-dashedin dot-dashed solid curve the curve curve is text — is the [6]. including the parameterization to the dot-dashed the curve HERA normalised data to described the the real part of thea amplitude factor and of including (1 it + given increases by the cross-section for each state by JHEP06(2009)034 · S 1 σ (3.5) ( 0 with / . ) 6 S and then state (see 2 s B ∗ γp · σ S 2 3. Since the Υ . σ = 0 λ 4 0319. We use eq. (3.5), . 10 0 ± ) in the amplitudes. The degree 155 6 . λ . 1 3  n=1 n=2 n=3 10 ) = 0 W S GeV 1  B · × W [GeV] S ). Both H1 and ZEUS measure 1 – 8 – 2 S σ ( . This is actually not the case as one can infer 10 / λ ) 12 pb S . 3 quark mass also affects the overall normalisation. For b B = 0 · for the excited states, relative to that of the 1 σ S r 3 1 σ 10

0.3 0.5 0.6

0.4

0.55 0.45 0.35 nS β 0484 and ( . 0 cross-section by assuming that the ratios of cross-section times branching ± S . The ratio of the real to imaginary part of the amplitude for the different states. 281 . 2 GeV) in order to achieve optimum agreement with the data. The result is the . Even with these corrections, the theory curve still lies below the data. This is not a In [6], the parametrisation ) = 0 = 4 The original fit of [6] did not include the most recent HERA data. Including it brings the fit down so Figure 5 S 6 b 1 that it is much closer to the FSSat prediction. our results do notwavefunction extends vary to very larger much uponfigure3), choosing one a might fixed naivelyresulting value expect in of that a the lower energy effective dependence value is of softer for the former, was found to fit the HERA data for Υ(1 from figure5. Thisto is a because partial the cancellationresults between excited in the state an soft effective wavefunctions and harder have hard energy nodes, dependence parts which (higher of leads the amplitude which in turn extract the 1 ratio are the same as those measured by the CDF collaboration [25], i.e. ( particularly surprising result andQuite it possibly, one is could typicalthat do of case better other the by dipole improving uncertaintyMoreover, model the the would calculations vector value mainly chosen meson [6, influence for wavefunctions24]. the the and in normalisation of the cross-section. solid curve in figure4. Byand doing skewedness this, corrections we in account a also purely for phenomenological the way. uncertainties in the real part of cancellation is ratherbeen sensitive to referred to the previously model as used the for node the effect dipole [18]. cross-section. This has these reasons, we followm the authors of [6] and rescale our results (by a factor 2 B together with the CDF ratios, to produce the double-dot-dashed curve in figure4. JHEP06(2009)034 (1 + (4.3) (4.2) (4.1) ∝ : 200 GeV, our + . µ ) Y # 2 < W <  → − ) θ Y 4 β 10 − cos θ β ) + ( ξ − ( . n=2 n=3 cos (1 β γ/p θ 2 f  ) − are emitted at an angle greater than 3 cos θ ξs 10 1 + β + ( is the polar angle relative to the direction 2 " µ , the emission angle of the γp ratio, in the range 50 θ 2 α − ) ) cos ξσ S θ 2 2 ) and W [GeV] 2 β β θ : 1 β – 9 – − cos N S µ − β 1 + d 2 (1 + 1 − d(cos Thus 10 = (1 = 7 α π ) 0. 3 p 16 } cos − β > = µ 0 Y + 0.1

0.2

φ

. The ratio of cross-sections for the different states.

µ 0.05 0.25 0.15

1S 1S nS

nS )d

.B / .B { )d σ σ θ p θ is the speed of the Υ and N 2 such that both the d Y → θ d(cos d(cos pp Figure 6 ( σ 2 = tanh d ratio is very sensitive to the details of the meson wavefunction and also to the β . S λ : 1 ), which corresponds to a distribution of dependence of the fit. We might take the difference to be indicative of the challenge ∗ S relative to the beam. To do that we need θ Note that the FSSat model predicts an energy dependence that is less steep than the We can also compute the cross-section ratios between the different Υ states in order to 6 Recall that we neglect the transverse momentum of the meson, which means it travels along the . 2 7 1 min beam axis. facing future experiments, i.e. they should be able4 to distinguish between the Results two. We are now readyassume to that present the our angular predictions distribution for of the the hadroproduction decay cross-section. muons in We the Υ rest frame is prediction is also below thewavefunction. value calculated However, in theoretical [7] predictions usingthe for perturbative 2 QCD these and ratios a are Gaussian value rather of uncertain since W We integrate over θ compare to the CDFobtained data. by CDF These quoted are above. shown For the in 2 6. figure Our results are below the values cos in the lab: in which the Υ travels when JHEP06(2009)034 8 7 (4.4) 5 6 LHC = 3 GeV and min t Y . At the LHC we P ◦ Fit FSSat 4 . 018 on the right-hand side = 15 . -4 -3 -2 -1 0 1 2 3 4 0 min -6 -5 θ ) luminosities. With one tagged 1 -7 − < ξ < ) s -8 0 2 θ −

002

5000

.

θ cos 20000 15000 10000 dY [fb] dY d σ/ cm β and rapidity and, in the case of the LHC, sin 32 t − 2 for both leptons. p Υ 10 (1 M . Υ min – 10 – t E P 2 5 6 = t P Tevatron Y (see also [26]). In all cases we show results for Fit FSSat 014 on the left-hand side. ◦ , whilst for the DØ detector we take . 7 ◦ 0 . 5 . = 7 < ξ < = 33 -4 -3 -2 -1 0 1 2 3 4 min θ . The Υ rapidity distribution without any cuts on the final state particles at the Tevatron min 0015 θ . = 4 GeV. At the LHC, we may also have the possibility to detect one of the protons -6 -5 0 Tagging one of the protons does severely limit the acceptance of a measurement: Cen- Figure7 shows the Υ rapidity distributions at the LHC and the Tevatron respectively For the Tevatron, we approximate the angular acceptance of the CDF muon detector

800 600 400 200

1000 min dY [fb] dY d d t σ/ proton, one could hope to control the pileup background after utilising the fact that the trally produced are cutmeasured out proton because loses the much 420large m more in detectors fact energy select that than events the indetecting the upsilon which always a unmeasured travels the proton in proton. does the have directionbe The the of performed potential boost the using advantage tagged is that data proton. the so collected However, measurement at need low not ( only the effect of observing one ofthat the although protons in the the strong proposedis sensitivity 420 diminished, m to detectors. it the is Our energy results still dependence show large on enough the that dipole one could cross-section hope to constrain the theory. before any cuts havebetween been the applied. shapes There of isparameterization the a of distributions striking the difference obtained photoproductionOne (especially using cross-section could at therefore the that the hope FSSat is that LHC) discriminate dipole based measurements between of dipole model on the models the and rapidity and distributions thereby HERAwe the contrain would indicate data. the be the able distribution. effect to of In figure8 cutting on the muon P in the region 420 mboth). from According the to interaction the point studiesacceptance presented (there for in will protons [1], not with forward detectors be fractionaland in energy any the 0 loss acceptance 420 0 to m region detect have assume, Figure 7 (left) and LHC (right) usingdata the FSSat described dipole in model the and text. the parameterization the photoproduction The transverse momentum of the muon (or anti-muon) is given by using and we also cut on a minimum value of JHEP06(2009)034 DZero Tevatron Y 5 > 3 > 4 > 4,1p tag t t t > 3 > 4 t t > 3 > 4 > 4, 1p tag t t t > 3 > 4 t t Fit, P Fit, P FSSat, P FSSat, P FSSat, P Fit, P Fit, P Fit, P FSSat, P FSSat, P -4 -3 -2 -1 0 1 2 3 4 (fb) 0

406 838

Fit 400 200 dY [fb] dY d σ/ σ 4 GeV). > Y (fb) t and above. In any case, it is worth noting that P – 11 – 350 685 1 FSSat − s σ 2 − per year. That translates to a total of over 5000 signal CDF DØ 1 cm CDF Tevatron − 33 -4 -3 -2 -1 0 1 2 3 4 LHC 10 Cross-sections at the Tevatron -5 × 0

4000 3000 2000 1000 dY [fb] dY d Y σ/ > 3 > 4 t t corresponds to 1 fb > 3 > 4 t t 1 − s 2 . The Υ rapidity distribution after cuts at the Tevatron (top) and LHC (bottom) using Fit, P Fit, P FSSat, P FSSat, P − . The predicted cross-sections for the Tevatron using the FSSat dipole model (first column) -4 -3 -2 -1 0 1 2 3 4 cm 0

32 200 400 dY [fb] dY d σ/ 10 two charged muons should pointvertex) to and a that single they vertexwith should (and the also no value other combine inferred tracks to from pointmomentum the produce fractions. to extracted an (one the Further Υ measured same detailed rapidity directly simulationsthis that and would method one is be will inferred) in required proton work agreement to at establish 2 whether and the power-law fitand to transverse the momentum photoproduction have data been (second applied column). ( Cuts on the muon rapidities Table 2 Figure 8 the FSSat dipole modeltext. and the the parameterization the photoproduction data described in the JHEP06(2009)034 8 100 MeV . Indeed T < p T p interaction per pp ) dependence implied by t Υ B (fb) = 1 TeV, which is well in the 6802 Fit 10351 σ W cut on the scattered proton, [27 28 ]. (fb) T p 5133 3035 FSSat above some value. This is equivalent to σ T p – 12 – cross-section at p Υ region can be measured by making the complementary 0 1 → W γp 4 GeV) have been applied (first row). The result of additionally Cross-sections at the LHC > t be sufficiently small, in which case the tagged proton most likely P No. of tagged protons T p distribution has been advertised as a means to probe the gap-filling , with gaps being filled in more often at larger values of T T p p . The predicted cross-sections for the LHC using the FSSat dipole model (first column) Finally, it is worth pointing out that should it be possible to make a cut on the measured After making such a cut, since we now have an enriched sample of events in which So far, we have made no mention of the issue of “gap survival” and as far as the The efficiency depends weakly upon the energy lost by the proton through eq. (2.4). (much larger than can be probed at HERA and the Tevatron) is obtained by insisting 8 proton’s transverse momentum thenment it of would the become photoproduction possibleprotons cross to that section. make radiate a photons This directprotons is is that measure- typically so do much since not, smaller the i.e. than eq. transverse the (2.3) momentum transverse is of momentum much softer of than the exp( bunch crossing. ThisQCD should models be of sufficient saturation. to produce a measurement that will constrain eq. (2.23). Requiring that the transverse momentum of the tagged proton Table 3 and the power-law fitand to transverse the momentum photoproduction ( data (second column). Cuts on the muon rapidities the tagged proton radiatedphotoproduction the cross-section. photon, we Figure9 canillustratesW eliminate the the possibilities. photon flux Thethat and the region extract tagged at proton the larger is at least 60% efficientThe for contamination selecting from events in events whichbe in the only which tagged 4%. the proton non-tagged radiates Ifconstitutes a proton the a photon. radiates very cut a significant is enhancement. photon lifted would to 300 MeV, the ratio decreases to 89% : 28%, which still radiated the photon. Thecut, lower i.e. by insisting that the proton have events in an environment where there will be, on average, less than one measuring one of the outgoing protons is shown in the second row. assuming that the untagged protonfacilitate emitted a the measurement photon. of the In this way, the proton detectors overall rate is concerned itis is typically not expected rather to peripheral.on provide much the suppression, However, since proton the the gap collision survival should depend rather strongly range where saturation effects are expected to reveal themselves. measuring the mechanism. This physics would needthe to photoproduction be cross-section under by control exploiting before a one could reliably extract JHEP06(2009)034 ] , TeV 96 . = 1 Υ s √ hep-ph/0702134 and ][SPIRES]. J/ψ ][SPIRES]. ][SPIRES]. arXiv:0902.1271 [SPIRES]. , boson production and ][SPIRES]. collisions at Z TeV ¯ p p (2007) 094023[ 96 . Exclusive hep-ph/0311164 = 1 The FP420 R&D Project: Higgs and s D 75 √ hep-ph/0412235 Hard exclusive production of a vector events in arXiv:0805.2113 > 4) arXiv:0806.0302 t p , arXiv:0805.0717 > 4) + ¯ t Exclusive photoproduction of upsilon: from HERA W [GeV] `` – 13 – Phys. Rev. Search for exclusive Observation of exclusive charmonium production and + (2004) 142003[ , (2005) 134[ p 92 → 146 (2008) 014023[ (2008) 126[ Diffractive and exclusive dilepton and diphoton production at γγ Photoproduction of quarkonium in proton proton and nucleus → FSSat (no muon cuts) FSSat (no cuts, P FSSat (muon cuts) Fit (no muon Fit (muon cuts, P ¯ p in p+pbar collisions at D 78 XVI international workshop on deep-inelastic scattering and related p Exclusive photoproduction at the Tevatron and LHC within the B 668 − 10 100 1000 10000 1 µ 10 + 100

µ

1000

p [SPIRES].

Phys. Rev. Lett. collaboration, M.G. Albrow et al., γ γ [pb]

σ ,

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