Higgs boson photoproduction at the LHC

Transcription

1 Higgs boson photoproduction at the LHC 1/ 22 Higgs boson photoproduction at the LHC G.G. Silveira High Energy Physics Phenomenology Group Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil work with M. B. Gay Ducati To appear in Phys. Rev. D

2 Higgs boson photoproduction at the LHC 2/ 22 Outline Motivation Predictions for the diffractive Higgs boson production Photoproduction approach Ultraperipheral Collisions (UPC) Photoproduction at the LHC Results Conclusions

3 Higgs boson photoproduction at the LHC 3/ 22 Motivation LHC will allow to probe a new kinematical region: CM energy: pp 7-14 TeV :: pa/aa TeV/A; pa: enhanced photon flux: σ tot Z 2. Higgs physics: the low luminosity regime is favorable to the Higgs boson production in diffractive processes. The Ultraperipheral Collisions (UPC) are a new way to study the Higgs boson production in hadronic collisions; The pa collisions have the best features to look for the Higgs boson at the LHC. Other processes of Higgs production are under study to allow its detection in hadron colliders; DPE allows the Higgs boson production through the leading ggh vertex in the mass range M H GeV. New evidences: considering the excluded mass ranges, we may explore the window mass 115 GeV < M H 158 GeV

4 Higgs boson photoproduction at the LHC 4/ 22 New results from the Tevatron Excluded range: The TEVNPH Working Group, arxiv: [hep-ex] 158 GeV M H 175 GeV EW fits: M H = GeV Goebel, arxiv: [hep-ph] Tevatron Run II Preliminary, <L> = 5.9 fb -1 95% CL Limit/SM 10 1 LEP Exclusion SM=1 Expected Observed ±1σ Expected ±2σ Expected Tevatron Exclusion Tevatron Exclusion July 19, m H (GeV/c 2 )

5 Higgs boson photoproduction at the LHC 5/ 22 Deeply Virtual Compton Scattering (DVCS) 1997: Ji PRD 55 (1997) 7114 γ p γp by Pomeron exchange in ep collisions. 2001: Munier, Staśto and Mueller NPB 603 (2001) 427 Vector meson production γ p Vp with GBW model. 2008: Motyka and Watt PRD 78 (2008) : Cisek, Schafer and Szczurek PRD 80 (2009) Vector particle production γp Ep in Ultraperipheral Collisions. γ γ γ, Υ,ω, J/ψ, ρ 0 J/ψ, Υ, Z 0 MW: Z 0 boson production { σγp = 4.2 fb, Tevatron p p y = 0 σ γp = 37. fb, LHC

6 Higgs boson photoproduction at the LHC 6/ 22 Electromagnetic Higgs boson production 1990: Cahn and Jackson PRD 42 (1990) 3690 Müller and Schramm PRD 42 (1990) 3699 Peripheral heavy-ion collision γγ annihilation 2007: Miller arxiv: [hep-ph] 2008: Levin and Miller arxiv: [hep-ph] Contribution from Electroweak boson loops to the γγ H. p, A p, A 2010: D Enterria and Lansberg PRD 81 (2010) Photon fluxes and Higgs effective Theory in γγ processes. γ γ H p, A p, A { M H = 150 GeV CJ: σpbpb = 7.0 pb s = 3.5 TeV/A MS:σ AA 100 pb M H = 120 GeV s = 14 TeV M: σ pp = 0.12 fb LM: σ pau(auau) = 0.6 pb (3.9 nb) DL: σ pp = 0.18 fb

7 Higgs boson photoproduction at the LHC 7/ 22 Diffractive Higgs production in pp and AA collisions p p 1991: Bialas and Landshoff PLB 256 (1991) 540 Regge Theory non-perturbative gluons 1997: Khoze, Martin and Ryskin PLB 401 (1997) : Levin and Miller arxiv: [hep-ph] QCD Pomeron hard-gluon exchange IP IP H { M H = 150 GeV BL : σ pp = 0.1 pb s = 16 TeV p p p, A p, A p, A H p, A { M H = 120 GeV KMR : σ exc/inc pp 3 fb/300 fb s = 14 / 8.8 (5.5) TeV/A LM : σ pa(aa) = 0.1 pb (3.9 pb)

8 Higgs boson photoproduction at the LHC 8/ 22 Diffractive Higgs photoproduction Proposal: γp process by DPE in pp collisions. γ COLOR DIPOLE q χ L t = 0 χ R q γ EFFECTIVE VERTEX SCREENING GLUON H HIGGS VERTEX GLUON-GLUON FUSION p f g (x,k 2 ) p NON-DIAGONAL PDF The loop is treated in impact factor formalism at t = 0.

9 Higgs boson photoproduction at the LHC 9/ 22 Scattering amplitude Partonic process: γq γ + H + q q(l µ ) γ(q µ ) γ(q µ ) q(q µ l µ ) g(k µ ) g(k µ ) H(q µ ) H g(r µ ) q(p µ ) q(p µ ) The scattering amplitude is obtained by the Cutkosky Rules Im A = 1 Z d(ps) 3 A (left) A (right) 2

10 Higgs boson photoproduction at the LHC 10/ 22 The amplitude in parton level The imaginary part of the amplitude has the form Im A = s «MH 2 Z α s αsc F Φ T 6 πv N c π γγ(k 2,Q 2 ) dk2 k 6 with the γγ impact factor given by Φ T γγ(k 2,Q 2 ) = 4πα sα X q e 2 q Z 1 0 dτ dρ k2 [τ 2 + (1 τ) 2 ][ρ 2 + (1 ρ) 2 ]. Q 2 ρ(1 ρ) + k 2 τ(1 τ) First remark: dependence on k 6 due to the presence of the color dipole. Computing the event rate in central rapidity «dσ dy H dq = α4 sk NLO M 2 2»Z 2 H αsc F 2 288π 5 B N cv π ΦT γγ(k 2,Q 2 ) dk2. k 6 γp: replace the quark contribution to the parton content into the proton.

11 Higgs boson photoproduction at the LHC 11/ 22 Parton Hadron The hadron coupling is represented by a non-diagonal PDF «α sc F [xg(x, k Khoze, Martin and Ryskin f g(x,k 2 2 )] ) = K π lnk 2 PLB 401 (1997) 330 The non-diagonality is approximated by a multiplicative factor K = (1.2) exp( Bp 2 /2) Shuvaev et al PRD 60 (1999) where B = 5.5 GeV 2 is the slope of the gluon-proton form factor. To correctly compute the pomeron coupling to the proton: x 0.01.

12 Higgs boson photoproduction at the LHC 12/ 22 Phenomenology inside Gluon Radiation at DLLA Khoze, Martin and Ryskin, PLB 650 (2007) 41 The real gluon emission from the ggh vertex needs to be suppressed. Sum the virtual graphs that include terms like ln `M H /k 2. The emission probability of 1-gluon is computed by Sudakov form factors S(k 2, µ 2 ) = Nc π Z µ 2 k 2 α s(ˆp 2 ) ˆp 2 dˆp 2 Z MH /2 p T «dê Ê = 3αs µ 2 4π ln2 k 2 Real emissions are not suppressed if the gluon color neutralization fails. Suppressing many gluons emission: It is included a factor e S to the cross section. Emissions below k 2 are forbidden. As k 2 0 the non-emission probability goes to zero faster than any power of k, like k 6. Ê,ˆp H Higgs rest frame

13 Higgs boson photoproduction at the LHC 13/ 22 Phenomenology inside Gluon Radiation at LLA Khoze, Martin and Ryskin, PLB 650 (2007) 41 Possibility of quark emissions from the production vertex. There will be contributions of single logarithms. The Sudakov form factors are rewritten as Z µ 2 T(k 2, µ 2 α s(ˆp 2 ) dˆp 2 Z " 1 2 ˆp /MH ) = zp gg(z) + X k 2 2π ˆp 2 0 q P qg(z) # dz The P ij are the DGLAP splitting functions; In this work, µ = M H /2. In order to correctly include these contributions to the amplitude, the unintegrated distribution is written as f (x,k 2, µ 2 ) = K»q T(k 2, µ lnk 2 2 )xg(x, k 2 ) Dokshitzer, Diakonov, Troian, Phys.Rept. 58 (1980) 269

14 Higgs boson photoproduction at the LHC 14/ 22 Phenomenology inside Rapidity Gaps KMR, EPJC 18 (2000) 167; Gotsman, Levin, Maor, arxiv: [hep-ph] The Rapidity Gap Survival Probability is calculated by R A(s, b) Sgap 2 2 e Ω(b) d 2 b = R = 2.7% 3% for LHC A(s, b) 2 N d 2 b where N = e Ω 0 is the relevant opacity at Ω = 0. Pomeron loops: Higgs boson production with Sgap 2 = 0.4% Miller, EPJC 56 (2008) 39 Central dijet production at HERA: diffractive ratio of 10%. Kaidalov, Khoze, Martin, and Ryskin, PLB 567 (2003) 61 γ p γ p H } } Gap Gap

15 Higgs boson photoproduction at the LHC 15/ 22 Cross section for central rapidity The cross section is calculated for central rapidity (y H = 0) «dσ = S 2 K NLO M 2 2 " Z # µ 2 2 H dk 2 gap dy H dt yh,t=0 288π 5 B α4 s f g(x,k 2, µ 2 )Φ T γγ(k 2,Q 2 ) N cv k 2 k 6 0 h Txg(x, i Proton content : α sc F /π f g(x,k 2 ) = K (ln k 2 ) k 2 ) Sudakov form factor : T(k 2, µ 2 ) = ˆα s(k 2 )/α s(µ 2 ) e S, S ln 2 (µ 2 /k 2 ) Gap Survival Probability : S 2 gap 3% and 10% for LHC Cutoff k 2 0 to regulate the infrared divergences: k 2 0 = 0.3 GeV 2. Electroweak vacuum expectation value: v = 246 GeV Gluon-proton form factor: B = 5.5 GeV 2 Khoze, Martin and Ryskin, EPJC 14 (2000) 525 Forshaw, hep-ph/ Gay Ducati and Silveira, PRD 78 (2008) Khoze, Martin and Ryskin, EPJC 18 (2000) 167

16 Higgs boson photoproduction at the LHC 16/ 22 Higgs boson production in UPC The γp process is a subprocess in Ultraperipheral collisions. b H Impact parameter: b > 2R NO STRONG INTERACTION! Only EM force acts in the second proton REAL PHOTONS

17 Higgs boson photoproduction at the LHC 17/ 22 Hadronic cross section For pp collisions, σ γp is convoluted with the photon flux σ tot = 2 Z ωmax ω min dω dni dω σγp(ω,m H), with ω min = MH/2x 2 s NN and ω max = p Q 2 γl 2β2 L. The photon flux is given by dn p dω = αem 2πω " ω «# 2 ln µ p 11 s «. µ p 2µ 2 p 3µ 2 p for protons, with µ p 1 + (0.71 GeV 2 ) s/2ω 2, and dn A dω = 2Z 2 α em πω for nuclei, with µ A = 2R A ω/γ L.» µ A K 0(µ A )K 1(µ A ) µ2 A 2 [K2 1 (µ A ) K 2 0 (µ A )] The photon virtuality can be written in terms of the ω and q. with γ L = (1 β 2 L) 1/2 = s/2m N. Q 2 = ω 2 /(γ 2 Lβ 2 L) q 2 1 R 2

18 Higgs boson photoproduction at the LHC 18/ 22 Results: Higgs boson in Ultraperipheral pp collisions σ pp: one order higher than the results from γγ processes ( fb). An optimistic approach for the GSP provides a cross section of 6 fb. LHC E CM = 14 TeV 10 1 σ pp (fb) 10 0 MRST2001LO :: GSP 3% MRST2001LO :: GSP 10% MSTW2008LO :: GSP 3% MSTW2008LO :: GSP 10% Higgs mass (GeV)

19 Higgs boson photoproduction at the LHC 19/ 22 Results: pa collisions σ pau 800 fb: competitive with the γγ process ; σ ppb : 4x higher than the approach with an Effective Field Theory LHC Pb Au 10 4 LHC Pb Au 10 3 σ pa (fb) 10 2 Ar 10 2 Ar 10 1 O O 10 0 MSTW2008LO GSP 3% 10 1 MSTW2008LO GSP 10% Higgs mass (GeV) Higgs mass (GeV) Levin and Miller, arxiv: [hep-ph] D Enterria and Lansberg, arxiv: [hep-ph]

20 Higgs boson photoproduction at the LHC 20/ 22 Gap Survival Probability The predicted cross section is competitive with other approaches; The Rapidity Gap Survival Probability (GSP) is not computed for the Higgs boson production in γp processes; Based on previous evidences from HERA: S 2 gap = 10%. Subprocess GSP (%) σ pp (fb) IPIP IPIP γγ γp γp The γp process may provide a good way to look for the Higgs boson in pp and pa collisions at the LHC. Khoze, Martin, Ryskin, JHEP 05 (2006) 36 Miller, EPJC 56 (2008) 39 Miller, arxiv:

21 Higgs boson photoproduction at the LHC 21/ 22 Event rates Taking the Branching ratio for BR(H b b) = 72 %, the event rate for the Higgs boson production can be predicted for LHC. Ahrens, Becher, Neubert and Yang, arxiv: (2010) Little chance to observe b b decay in LHC: γγ and τ + τ expected. CMS, Physics Technical Design Report (2007) σ (fb) BR σ L (fb 1 ) events/yr pp (30) 1 (30) pp (30) 6 (180) ppb ppb There is an one-month run scheduled to Nov./2010 of pa collisions. New data from pa collisions may be available in 2011.

22 Higgs boson photoproduction at the LHC 22/ 22 Conclusions We have computed the production cross section for the Higgs boson in UPC at the LHC: σ pp 2 6 fb σ pa pb The pa collisions provide a clean process to discover the Higgs boson at the LHC; The luminosity and pile-up in such processes will be favorable for the Higgs boson detection in LHC; A reasonably event rate predicted for future pa runs in LHC. Low sensitivity to the input parameter: infrared region under control; Taking the specific GSP for the photoproduction processes, the predictions may be higher than the ones from other approaches; The photoproduction approach allows a data analysis for the Higgs boson production in non-central events.