Precise electroweak calculation of the charged current Drell-Yan process

Transcription

1 Precise electroweak calculation of the charged current Drell-Yan process Carlo M. Carloni Calame INFN, Sezione di Pavia Southampton, November 3, 26 thanks to Stefano and the SHEP group for the invitation! C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 1 / 41

2 Outline Motivations for precise predictions of Drell-Yan processes precise measurement of M W (and Γ W ) luminosity monitor PDFs constraint background to New Physics searches Overview of the literature QCD calculations EW calculations The event generator HORACE first version (with a QED Parton Shower) inclusion of exact O(α) electro-weak corrections technicalities results Conclusions & outlook C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 2 / 41

3 M W in the Standard Model G µ 2 = L SM = L SM (α, M W, M Z ; M H ; m f ; ckm) g2 8M 2 W (1 + r) r = r(m top, M W, M Z, M H,...) MW 2 (1 M W 2 MZ 2 ) = πα 2Gµ (1 r) the W mass can be predicted ( ) MW 2 = M Z 2 4πα(1 + r) M 2 G µ 2M 2 W = ±.32 GeV Z C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 3 / 41

4 Direct measurement of M W at LEP2, from e + e W W (at threshold and higher energies) at hadron colliders, from the M T distribution W-Boson Mass [GeV] TEVATRON ±.59 LEP ±.33 Average ±.29 χ 2 /DoF: 1.3 / 1 NuTeV ±.84 LEP1/SLD ±.32 LEP1/SLD/m t ±.2 Future goals for M W Tevatron Run II 27 MeV LHC 15 MeV Future goals for Γ W Tevatron Run II 3 MeV LHC 3 MeV m W [GeV] A small M W (and m top ) will constraint the indirect limit on M H M W = 27 [15] MeV and m top = 2.7 [1] GeV M H /M H 35 [18]% C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 4 / 41

5 M W at Hadron Colliders M W is extracted from the p l distribution, showing a (Jacobian) peak at M W /2 more reliable is MT 2p W = l pν (1 cos φ lν) less sensitive to QCD corrections (e.g. p W ) number of events W e ν M T (GeV) the ratio dσ/dm T W dσ/dmt Z high luminosities The th. description of M T spectrum has to match the aimed exp. accuracy can be also used to extract M W. Competitive at C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 5 / 41

6 Other motivations it is possible to monitor the collider luminosity, the parton luminosities or to measure the PDFs Frixione & Mangano 4 and refs. therein relevant observables: total cross section, W (and Z) rapidity distribution, lepton rapidity distribution σ exp 1 1 N obs BR(W lν) Ldt A = σtheory ab P ab ˆσ ab an accuracy of O(1%) is required/achievable DY processes are background to New Physics searches invariant mass (transverse mass) distribution tails have to be precisely simulated C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 6 / 41

7 Theoretical cross section at hadron colliders σ theory = i,j 1 dx 1 dx 2 f i,a (x 1, µ 2 )f j,b (x 2, µ 2 ) dσ H i,j(x 1 x 2 s, µ 2 ) it relies on factorization theorems f k,c (k = u, ū, d,, g, ) are the PDFs of hadron C dσk,l H describes the hard parton-parton process, as accurately as possible, including QCD Parton Shower evolution QCD fixed order corrections EW corrections µ 2 is the factorization scale. Evolution up to µ 2 is driven by DGLAP equations C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 7 / 41

8 Status of QCD calculations (& tools) NLO/NNLO corrections to W/Z total production rate G. Altarelli, R.K. Ellis, M. Greco and G. Martinelli, Nucl. Phys. B246 (1984) 12 R. Hamberg, W.L. van Neerven, T. Matsuura, Nucl. Phys. B359 (1991) 343 R.V. Harlander and W.B. Kilgore, Phys. Rev. Lett. 88 (22) 2181 resummation of LL/NLL p W T /M W logs (RESBOS) C. Balazs and C.P. Yuan, Phys. Rev. D56 (1997) 5558 NLO ME merged with HERWIG Parton Shower [PS] (MC@NLO) S. Frixione and B.R. Webber, JHEP 26 (22) 29 Matrix elements Monte Carlos (ALPGEN, SHERPA,...) matched with PS M.L. Mangano et al., JHEP 37, 1 (23) F. Krauss et al., JHEP 57, 18 (25) NNLO corrections to W/Z rapidity distribution (VRAP) C. Anastasiou et al., Phys. Rev. D69 (24) 948 K. Melnikov and F. Petriello, hep-ph/63182 C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 8 / 41

9 QCD predictions for W/Z total rates A.D. Martin et al., Eur. Phys. J. C18 (2) 117 Good convergence of α s expansion. NLO-NNLO difference 2% at the LHC C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 9 / 41

10 High-precision QCD: W/Z NNLO C. Anastasiou et al., Phys. Rev. D69 (24) 948 First calculation of a differential distribution at NNLO in α s. NNLO corrections at 2% at the LHC and residual scale dependence below 1%. O(α 2 S ) O(α em) need to worry about electroweak corrections! C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 1 / 41

11 EW calculations for W & tools Electroweak corrections to W production Pole approximation ( ŝ = M W ) D. Wackeroth and W. Hollik, PRD 55 (1997) 6788 U. Baur et al., PRD 59 (1999) 132 Complete O(α) corrections V.A. Zykunov et al., EPJC 3 9 (21) S. Dittmaier and M. Krämer, PRD 65 (22) 737 DK U. Baur and D. Wackeroth, PRD 7 (24) 7315 WGRAD2 A. Arbuzov, et al., EPJC 46, 47 (26) SANC C.M.C.C. et al., hep-ph/6917 HORACE Multi-photon radiation C.M.C.C. et al., PRD 69, 3731 (24), JHEP 55:19 (25), hep-ph/6917 HORACE S. Jadach, W. Płaczek, EPJC (23) WINHAC C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

12 EW calculations for W & tools Electroweak corrections to W production Pole approximation ( ŝ = M W ) D. Wackeroth and W. Hollik, PRD 55 (1997) 6788 U. Baur et al., PRD 59 (1999) 132 Complete O(α) corrections V.A. Zykunov et al., EPJC 3 9 (21) S. Dittmaier and M. Krämer, PRD 65 (22) 737 DK U. Baur and D. Wackeroth, PRD 7 (24) 7315 WGRAD2 A. Arbuzov, et al., EPJC 46, 47 (26) SANC C.M.C.C. et al., hep-ph/6917 HORACE Multi-photon radiation C.M.C.C. et al., PRD 69, 3731 (24), JHEP 55:19 (25), hep-ph/6917 HORACE S. Jadach, W. Płaczek, EPJC (23) WINHAC C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

13 O(α) EW correction effects U. Baur, S. Keller, D. Wackeroth, Phys. Rev. D59 (1999) 132 around the W peak, EW RC dominated by final-state [FS] (photonic) corrections FS radiation modifies the shape of the M T distribution at TeVatron, O(α) EW RC shift M W by O(1) MeV CDF coll., PRD (21) are QED higher orders (h.o.) important? Quoted as systematic uncertainty of O(1-2) MeV by TeVatron colls. C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

14 HORACE: first version The Monte Carlo event generator HORACE was originally developed to simulate QED multi-photon radiation in DY (W and Z) processes in LL accuracy, by means of a QED Parton Shower [PS]. Only final state radiation was accounted for C.M.C.C. et al., PRD (24) C.M.C.C et al., JHEP 55:19 (25) as in QCD, the QED PS solves the QED DGLAP equation, allowing for inclusion of QED LL corrections up to all orders (resummation) fully exclusive event generation (up to photons) by comparing the resummed PS and its O(α) truncation, the effects purely due to h.o. can be disentangled photons angular generation in W decay cos ϑ γ E 2 γ ( pl p l k γ p W p W k γ ) 2 C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

15 First HORACE vs WINHAC C.M.C.C et al., Acta Phys. Pol. B (24), hep-ph/42235 during the 23 MC4LHC CERN workshop, HORACE and WINHAC (Jadach & Płaczek) where compared WINHAC exploits the YFS approach to exponentiate exact O(α) EW corrections to W decay e.g., cross sections for W production (in nb) at parton (p) and hadron (h) level, with (c) and without (nc) cuts at LHC: Born O(α) with h.o. HORACE WINHAC HORACE WINHAC HORACE WINHAC p e (nc) (2) (1) p µ (nc) (1) (1) h e (nc) (4) (4) (1) (4) h µ (nc) (4) (1) (4) (4) h e (c) (1) (1) (1) (1) (1) (1) h µ (c) (1) (1) (1) (1) 3.161(1) (1) C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

16 First HORACE vs WINHAC: M T distribution W W W W dσ W dm T nb GeV W - e - ν e dσ W dm T nb GeV W - µ - ν µ WINHAC: Born HORACE: Born WINHAC: O( HORACE: O( α) WINHAC: Best α) HORACE: Best m W T [GeV] m W T [GeV].2 δ = O(α) - Born Born.2 δ = O(α) - Born Born WINHAC HORACE T m [GeV] T m [GeV].6 δ = Best - O(α Born ).6 δ = Best - O(α Born ) WINHAC HORACE T m [GeV] T m [GeV] for e, a calorimetric event selection [ES] criterium is used C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

17 First HORACE vs WINHAC: M T distribution differences dσ W dm T nb GeV - W e - ν e dσ W dm T nb GeV - - W µ ν µ WINHAC: Born HORACE: Born WINHAC: O( α) HORACE: O( α) WINHAC: Best HORACE: Best m W T [GeV] m W T [GeV] δ = W - H W δ = W - H W Born O(α) Best m W T [GeV] m W T [GeV] expected (.2%) differences at O(α). The relative effect of exponentiation is the same C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

18 First HORACE vs WINHAC: y W distribution dσ d y W [nb] W - e - ν e dσ d y W [nb] W - µ - ν µ WINHAC: Born HORACE: Born WINHAC: O( HORACE: O( α) WINHAC: Best α) HORACE: Best y W y W.1 δ = O(α) - Born Born.1 δ = O(α) - Born Born WINHAC HORACE W y W y.1.8 δ = Best - O(α Born ).1.8 δ = Best - O(α Born ) WINHAC HORACE y W y W C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

19 First HORACE vs WINHAC: y W distribution differences dσ [nb] d y W - W e - ν e dσ d y W [nb] - - W µ ν µ WINHAC: Born HORACE: Born WINHAC: O( α) HORACE: O( α) WINHAC: Best HORACE: Best y W y W δ = W - H W δ = W - H W Born O(α) Best y W y W expected (.2%) differences at O(α). The relative effect of exponentiation is the same C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

20 M W shift induced by h.o. QED RC by means of the first HORACE, we estimated the impact of multi-photon radiation on the extraction of M W from M T distr. a pseudo-experiment was performed (χ 2 analysis): 1 generate a sample of pseudo-data at Born level for M ref W 2 consider the M T spectrum and bin it into 1 bins within the fit region 65-1 GeV 3 consider N different M W around M ref W corrected M T spectra i=bins and generate N radiatively 4 for each mass, calculate the χ 2 between corrected and Born spectra χ 2 (M W ) = ( ) [ 2 ( ) 2 ( ) ] 2 dσi,qed dσi,born / dσi,qed + dσi,born σ QED σ Born σ QED σ Born 5 at the minimum of the χ 2 distribution, read the M W shift C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

21 M W shift induced by h.o. QED RC the execise was performed by including (naive) detector effects, which are important χ W µ ν W e ν order α χ W µ ν W e ν exponentiation M W (MeV) M α,e W M α,µ W M W (MeV),e 2 MeV MW 2 MeV,µ 11 MeV MW 1 MeV for the electron, a recombination criterium was adopted smaller effect W -mass shift due to multiphoton radiation is about 1% of that caused by one photon emission non negligible for precise W mass! C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 2 / 41

22 HORACE: new version C.M.C.C., G. Montagna, O. Nicrosini, A. Vicini, hep-ph/ HORACE now includes exact O(α) EW corrections, in order to go beyond the LL QED accuracy and include weak corrections (e.g. important at high M T ) virtual RC real RC C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

23 NLO EW calculation As usual, the (partonic) NLO EW calculation is split into two parts u d l + ν l M 2 2 = M + M virt α (λ) u d l + ν l γ M 2 3 = M soft α (λ, E) + M hard ( E) M soft α (λ, E) 2 = δ soft (λ, E) M cross section dσ 2 2 = dσ SV M 2 + 2R[M M virt α (λ)] + δ soft (λ, E) M cross section dσ 2 3 = dσ H M hard α ( E) 2 the phase space integration is performed with MC techniques infrared singularities are regularized with a small photon mass λ; collinear ones with a finite (unphysical) quark mass IS collinear singularities must be subtracted C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41 α

24 Subtraction of initial state collinear singularities IS quark masses regularize the collinear QED divergencies the QED IS singularities have to be subtracted from the hard cross section [in analogy with NLO QCD], since they are already accounted in the (QED) evolution of PDFs the set MRSTQED (24) includes the QED evolution δf [%] Q 1 = 1 GeV Q = 2 GeV u-quark d-quark gluon x e.g. M. Roth, S. Weinzierl, PLB (24) QED evolution modifies PDFs at.1% level for x <.1 dynamic generation of photon distr. function. Need to include photon induced processes in DY γ d ū W + νl l + γ d W W + ū νl l + C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

25 Subtraction of IS collinear singularities QED initial-state collinear singularities are universal are absorbed into PDFs, as in QCD the singular partonic cross section is convoluted with a modified PDF, subtracting IS singularities 1 f(x) f(x, µ 2 F ) { ( µ 2 ln F m 2 q { C(z) = x dz ( x ) α z f z, µ2 F 2π Q2 q ) [P ff (z)] + [P ff (z) (2 ln(1 z) + 1)] + + C(z) [ Pff (z) ( ln ( 1 z z ) ) ] MS z 4 + DIS } C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

26 Les Houches 25 comparison C. Buttar et al., hep-ph/6412 during the Les Houches 25 workshop, a tuned comparison among EW O(α) calculations was done DK (Dittmaier & Krämer), HORACE, SANC, WGRAD2 Setup for comparison (cuts & lepton ID) LHC, W + production p l > 25 GeV pmiss pν > 25 GeV η l < 2.5 l = bare µ +, bare e +, recombined e + recombination criteria (kill FS collinear α log s m, due to KLN 2 e theorem): if η γ > 2.5 and R e+ γ = (η e + η γ ) 2 + φ 2 e + γ.1 photon and electron momenta are summed (i.e. p e = p e + p γ ) similar comparison for the TeV4LHC workshop still going on. Naive-detector effects are also investigated here. C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

27 Les Houches comparisons, varying p l cut C. Buttar et al., hep-ph/6412 pp ν l l + s = 14 TeV (with MRSTQED4) p T,l /GeV σ /pb DK (1) (2).9452(1).11511(2).54816(3).26212(1) HORACE (4) (6).9451(1).11511(1).54812(4).26211(2) SANC (2) (2).9456(1).11516(1) (6).26218(3) WGRAD (1) (1).9451(5).11597(5).54818(2).2629(2) δ e + νe /% DK 5.19(1) 8.92(3) 11.47(2) 16.1(2) 26.35(1) 37.92(1) HORACE 5.23(1) 8.98(1) 11.49(1) 16.3(1) 26.36(1) 37.92(2) WGRAD 5.1(1) 8.55(5) 11.32(1) 15.91(2) 26.1(1) 38.2(2) δ µ + νµ /% DK 2.75(1) 4.78(3) 8.19(2) 12.71(2) 22.64(1) 33.54(2) HORACE 2.79(1) 4.84(1) 8.21(1) 12.73(1) 22.65(1) 33.57(1) SANC 2.8(1) 4.82(2) 8.17(2) 12.67(2) 22.63(2) 33.5(2) WGRAD 2.69(1) 4.53(1) 8.12(1) 12.68(1) 22.62(2) 33.6(2) δ recomb /% DK 1.73(1) 2.45(3) 5.91(2) 9.99(2) 18.95(1) 28.6(1) HORACE 1.77(1) 2.51(1) 5.94(1) 1.2(1) 18.96(1) 28.65(1) SANC 1.89(1) 2.56(1) 5.97(1) 1.2(1) 18.96(1) 28.61(1) WGRAD 1.71(1) 2.32(1) 5.94(1) 1.11(2) 19.8(3) 28.73(6) δ γq/% DK +.71(1) +5.24(1) +13.1(1) (2) +14.3(1) (1) C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

28 Les Houches comparisons: distributions EW corrections varying M T cut M T/GeV δ rec/% 1.73(1) 3.43(2) 6.52(2) 12.55(1) 19.51(1) δ γq/% +.567(3) (1) (1) (1) (1) perfect agreement between independent calculations on p l, M T distributions (δ due to EW O(α)) C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

29 The new HORACE: version 2. C.M.C.C., Montagna, Nicrosini, Vicini, hep-ph/6917, submitted to JHEP we would like to combine (merge, match) the old QED PS based formulation with the exact EW O(α) calculation, in order to preserve PS advantages (multi-photon effects, exclusive event generation) go beyond its approximation (LL accuracy, missing contributions already at O(α)) the matching has to avoid the double counting of O(α) LL, already accounted for by the PS, and to produce a formula well suited for Monte Carlo generation a solution to the problem has been found... the issue has a long story also in QCD (e.g. MC@NLO, POWHEG) C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

30 PS and exact O(α) matrix elements (at parton level) Consider the LL [LL P S] resummed, LL O(α) and exact O(α) cross sections dσ LL = Π(Q2, ε) n= 1 n! M n,ll 2 dφ n dσ α LL = [1 + C α,ll] M 2 dφ + M 1,LL 2 dφ 1 dσ SV (ε) + dσ H (ε) dσ α exact = [1 + C α ] M 2 dφ + M 1 2 dφ 1 F SV = 1 + (C α C α,ll ) F H = 1 + M 1 2 M 1,LL 2 M 1,LL 2 dσ α exact at O(α) = F SV (1 + C α,ll ) M 2 dφ + F H M 1,LL 2 dφ 1 dσmatched = F SV Π(Q 2, ε) 1 n= ( n n! i= F H,i) M n,ll 2 dφ n C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

31 Contents of the matched formula F SV and F H,i are infrared safe and account for missing EW O(α), avoiding double counting of QED LL [ ] σ matched O(α) = σα exact σmatched is made of exact O(α) one-loop building blocks resummation of higher-order LL contributions preserved the cross section is still fully differential in the momenta of the final state particles (including the photons) Problem: the O(α) calculation presents IS collinear singularities ( α log M 2 W m 2 q ), which are exponentiated in the matched formula. A subtraction procedure up to all orders needs to be devised! C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 3 / 41

32 Contents of the matched formula F SV and F H,i are infrared safe and account for missing EW O(α), avoiding double counting of QED LL [ ] σ matched O(α) = σα exact σmatched is made of exact O(α) one-loop building blocks resummation of higher-order LL contributions preserved the cross section is still fully differential in the momenta of the final state particles (including the photons) Problem: the O(α) calculation presents IS collinear singularities ( α log M 2 W m 2 q ), which are exponentiated in the matched formula. A subtraction procedure up to all orders needs to be devised! C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 3 / 41

33 IS subtraction to all orders the idea is to start with a subtracted O(α) cross section dσ α exact = dσ α exact dσ α sub + dσα sub d σα exact + dσ α sub where dσsub α contains the LL initial state collinear singularities, both for the S+V part and the real part (see hep-ph/6917 for explicit formulae) then the resummation and matching are performed by using the subtracted O(α) building blocks of d σ α exact, which is free of IS collinear singularities proof of the independence from quark masses e.g., W + cross section (nb) at LHC (within typical cuts) O(α) matched m q ± ±.26 m q / ± ±.33 m q / ± ±.5 C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

34 O(α) EW results with HORACE LHC, pp W + l + ν l, p,l and p,ν > 25 GeV, η l < 2.5 O(α) EW corrections to the M T distribution δ (%) M (GeV) rec. e + µ + δ (%) M (GeV) rec. e + µ + O(α) corrections at 5% - 1% level around the peak and increasingly large in the M T tail due to the presence of the EW Sudakov (logs) 2, α W log 2 s M 2 Z C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

35 Weak O(α) and QED non-log corrections on M T differences between matched result and final-state [FS] QED PS best minus exp. FS PS exact O(α) minus O(α) FS PS δ (%) best minus exp. FS PS exact O(α) minus O(α) FS PS δ (%) M (GeV) M (GeV) blue = (dσ α exact dσ α P S )/dσ red = (dσ matched dσ P S )/dσ Sum of weak O(α), QED FS non-logs and QED IS remnant flat around the peak, increasingly large in the tail the FS QED PS calculation is improved consistently by missing O(α) with the matching procedure C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

36 Effects of multi-photon radiation on M T higher-order EW corrections to the M T distribution pure h.o. FS PS pure h.o. best pure h.o. FS PS pure h.o. best.2.4 δ (%) δ (%) M (GeV) M (GeV) blue = (dσ matched dσα exact)/dσ red = (dσ P S dσα P S )/dσ QED h.o. around the peak distort the shape. In the tail, induced effects by EW Sudakov O(α) QED LL the O(α) calculation is improved consistently by h.o. with the matching procedure C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

37 Effects on lepton and W rapidities dσ (pb) dηl Born exact O(α) µ + exact O(α) e + best µ + best e dσ (pb) dyw δ (%) Born best µ + best e + µ + e yw ηl yw O(α) effects al the level of 2%, resummation negligible important for acceptances determination, luminosity and PDFs constraints C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

38 Effects on p W no QCD effects p W is defined as the p of the l + ν pair, different from zero because of photon radiation (pb/gev) dσ dp W exact O(α) O(α) FS PS best exp. FS PS p W (GeV) at high p W using the exact photon emission ME is crucial, both for O(α) and resummed distribution C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

39 Photonic observables (radiative events) besides leptonic cuts, we require η γ < 2.5 and E γ > 3 GeV for the hardest photon this signature can be used e.g. to study the W W γ trilinear vertex (pb/gev) dσ dp γ p γ (GeV) best exp. FS PS exact O(α) O(α) FS PS dσ dη (pb) γ best exp. FS PS exact O(α) O(α) FS PS as expected, the exact real emission ME gives large corrections w.r.t. the LL approximation here radiative events (one more α) are selected η γ C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

40 Combining EW & QCD corrections A unified tool simulating at best EW and QCD corrections would be highly desiderable for data analysis e.g., RESBOS combined with factorizable FS EW corrections of WGRAD2 RESBOS-A Q. Cao, C.P. Yuan, PRL (24) Q. Cao, C.P. Yuan, hep-ph/41171 dσ dp T e [pb/gev] 6 RES + NLO QED 5 RES + LO QED LO + NLO QED LO + LO QED 1 δ 8 6 RES + NLO QED LO + LO QED LO + NLO QED LO + LO QED e p + T (GeV) p T e + (GeV) C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

41 HORACE & QCD showering MCs HORACE is Les Houches Accord compliant. Its events can be passed through QCD Parton Shower & hadronization MCs (HERWIG or PYTHIA) to include at least LL QCD effects. e.g. HORACE (with QED PS)+PYTHIA vs. PYTHIA+PHOTOS courtesy of G. Polesello and M. Bellomo (ATLAS) HORACE+PYTHIA PYTHIA+PHOTOS C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41

42 HORACE & QCD showering MCs (II) interface to more refined QCD tools ALPGEN) is in progress... C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, 26 4 / 41

43 Conclusions & outlook DY processes are a fertile ground for (challenging) precision physics at hadron colliders precise M W measurement ( M W = 15 MeV at LHC) PDF constraints collider luminosity (with accuracy O(5%)) it is a background to New Physics searches Theoretical calculations are essential ingredients for the success of the physics program. Higher order QCD and EW corrections must be taken into account The Monte Carlo EW event generator HORACE has been developed, including exact O(α) EW corrections matched with a QED Parton Shower to simulate multi-photon radiation Combining QCD and EW generators is needed for data analysis Work in progress to interface at best HORACE with more refined QCD tools extend the EW matching to γ/z l + l channel thank you! C. M. Carloni Calame (INFN) EW radiative corrections to charged DY November 3, / 41