PoS(EPS-HEP2011)360 5. . 4 − 0 . http://pos.sissa.it/ within 2 µ η 120 GeV. In all cases collected by the LHCb ≤ 1 − Z m ≤ 8 pb ± ∗ lies in the range 60 Z m exceeding 20 GeV and pseudorapidity µ T p tara.shears@.ch experiment. All measurements are based on bosonwhich decays has with transverse at least momentum one inZ the final state, are reconstructed in decaysstates to involving muon two or , and one pairs muonwhere (the and latter the one reconstructed , reconstructed in within invariant final the mass same fiducial aceptance), results are consistent with next-to-next-to-leading order theoretical predictions. Speaker. We have measured the Wa and centre-of-mass Z energy of production 7 cross-sections TeV, in using -proton datasets collisions of at up to 240 ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

University of Liverpool E-mail: XXIst International Europhysics Conference on High21-27 Energy July Physics 2011 Grenoble, Rhône Alpes France Tara SHEARS, on behalf of the LHCb Collaboration Electroweak boson production in the forwardwith region LHCb PoS(EPS-HEP2011)360 ] 2 µµ 5). . 120 M 2 ≤ greater ≤ ), based Z analysis µ e η m T Z µ p ≤ ≤ 7 events, esti- . 1 ± 3 . boson production. We ]. Z between 60 4 . In addition, we present Z W m and A ]. The LHCb experiment [ W 1 and lie within pseudorapidities ] and [ 3 2 Tara SHEARS, on behalf of the LHCb Collaboration analysis are larger than for the pole. Z W 0 events. 04 events, estimated from simulation); . . ) and one muon and one electron ( 2 0 of data. We also present results for the cross- ± charge asymmetry, µµ ± 1 9 2 . − 61 W . exceeding 20 GeV µ 3 pb T . p 1 production, an invariant mass cross-sections constitute an important test of the Standard ± Z , and the 1 1 production around the . cross-sections inside our kinematic acceptance, where the final − ∗ Z γ W Z σ / and above 20 GeV. The invariant mass of the dimuon candidates, 5. As backgrounds to the and + and . 120 GeV. 1966 candidates are selected. Z µ 4 W T ≤ W W σ ≤ p µµ η and M 8 pb. Further information may be found in [ ≤ Z boson production in decays to pairs of tau within the same kinematic ± σ ≤ Z 5, with refers to both / . 5, and, in the case of . Z 4 W 4 5), and in a rapidity region which is in common to ATLAS and CMS (2 production (“heavy flavour"), with two semileptonic decays (4 σ . ≤ µ 2 c ≤ c where both taus decay to muons (0 1 events, determined from same sign dimuon combinations in data). 20 GeV. η µ µν > µµ η ± > ≤ ττ η → and T ≤ → p → b Note that units are quoted throughout this note with c=1. In this paper, The total background estimate is taken as 4 We report differential cross-section measurements and ratios of Candidate W events possess one well reconstructed isolated muon candidate with a The following background sources are considered: Measurements of the All candidates are triggered by requiring one identified muon within the LHCb acceptance, Candidate Z events possess two well reconstructed muons which lie within the pseudorapidity 0 Z W . b 2 1 Z acceptance, in final states containing two muons ( measurements of section ratios GeV. These results are based on 37 on a dataset of 240 of 2 present results for the total state muons have transverse momentum 2.2 is instrumented in thecapability forward between region pseudorapidities with of fullcan 1.9 test tracking, to the 4.9. calorimetry Standard and Model Consequently,region and measurements ( provide made identification input by to LHCb constrain the PDFs, both in the unique forward mated using data events with high(iii) muon generic impact QCD significance); events where pionsto or be falsely either identified as decay muons, in eitherdecay flight in (0 or pairs punch or through in conjunction the with detector a heavy flavour semileptonic than 20 GeV within 2 (i) (ii) with 2.1 range 2 Electroweak boson production in the forward region with LHCb 1. Introduction Model in proton-proton collisions withhave a uncertainties centre-of-mass of between energy 3% of and 7 10%,is TeV. depending Theoretical due on predictions rapidity, to where the knowledge dominant of uncertainty the parton distribution functions (PDFs) [ 2. Event selection must lie within 60 PoS(EPS-HEP2011)360 , ] ) 6 − cone W r ( greater + µ decay are W T boson, and p Z of all tracks / ∗ T W γ p 5 GeV, and both 5 GeV is required. > > T T ] and the CTEQ6m [ p p 5 5 surrounding the muon, . 0 , of the muon must be less than = production, taking branching ratios IP 2 spectrum to the shapes expected for φ W above 5 GeV. After these requirements ∆ Tara SHEARS, on behalf of the LHCb Collaboration T T p p + 2 η ∆ p 3 = r ] otherwise). The normalisation of (i) is constrained to the 7 ) candidates are observed. The efficiency of the selection is − 5. The sum of hadronic and electromagnetic calorimeter energies W . ( 4 + ≤ W η ≤ candidates in data, where one muon is removed to simulate a production, and (ii) to the observed rate of Z Z where the tau decays leptonically to a muon and ; where the tau decays leptonically to a muon and neutrinos; τ where one of the muons goes outside of the LHCb acceptance; τν ττ ττ µµ → → → → m to reduce backgrounds from heavy flavour production. Contributions from to muons into account. The contributions of (iii) and (iv) are estimated from simulation. The The following background sources have been considered: The signal yield is estimated by fitting the muon Backgrounds from punch-through are suppressed by requiring that the sum of hadronic In the muon-electron final state and additional electron candidate with Candidate events possess one well reconstructed isolated muon candidate with a Z Z W µ Z τ suppressed by vetoing any other muon inare the event made with a 15608 (12301) estimated using (i) (ii) varies between 45% and 80% depending on lepton pseudorapidity. (iii) (iv) Lower mass Drell-Yan production of dimuonacceptance; final states, where one muon is(v) outside b the and LHCb c events containing(vi) semileptonic generic decays QCD with events a where muon pions in(vii) or the generic kaons final QCD decay state; events in where flight; pions or kaons punch through to give muons. should be less than40 2 GeV. The unbiased impact parameter, signal (obtained from next-to-leading order simulation,parton using density POWHEG set) [ and eachsignal, and background background class. (vi), are allowed Inpseudorapidity to the bins vary. fit, The simultaneously. fit only The is the performed shapessimulation for overall (POWHEG for both for normalisations backgrounds charges (i), of (i) and Pythia over to the [ all (iv) are determined using shapes for backgrounds (v), (vi) andvariables (vii) to are enrich found these directly sources. fromthe data The exception by normalisations of anti-cutting are on decay fixed selection in to the flight rates which observed is in allowed data, to with vary in the fit. The purity of the observed rate of of are identified withindeposits the in same the pseudorapidity electromagnetic region and hadronicelectron as calorimeters, deposition. muons, and and preshower The detector must consistent leptonsthe have with must energy selection. be isolated, In and the back-to-back dimuon in final phi. state the 81 candidates additional pass muon must have and electromagnetic calorimeter energies associated withmomentum, the is muon candidate, less divided than by 0.04. the track Isolation is imposed by requiring that the summed Electroweak boson production in the forward region with LHCb we impose additional criteria onbe muon consistent identification with the and primary isolation, vertex. and ask that the muon should and identified inside a cone of radius sample is 80% (78%). 2.3 than 20 GeV within 2 associated with the muon candidate, divided by the track momentum, must be less than 0.2. PoS(EPS-HEP2011)360 is the Z ε )); superscript µµ ( W e ] generator. 8 µ ) channels. µµ 3) for ( can be written . in data above 80 GeV to 1 e y ∆ µ ± µµ , which is the probability of 6 . M , in a muon pseudorapidity inter- Z muon 3 (1 , which is the probability of these ε W Z ± σ sel , , ε 5 . W bkg 8) events in Z bkg . Tara SHEARS, on behalf of the LHCb Collaboration N L 1 N events, where one muon (the tag) is well L W − Z ± − ε ε asymmetry between both muons must exceed 5 W tot µµ . Z tot T N is the estimated number of background events, N production, P , which is the probability of reconstructing both → 2 (5 4 , which is the probability of triggering on such an . Z Z W bkg ) = 1 ) = Z Z track N trig y η ε ± ε ∆ ∆ ( ( µν µµ , using the same notation as above, but with a → → Z W W sel σ σ ε boson production in a rapidity region, W Z muon coverage. Cross-sections are corrected for final state radiation (FSR) ε π and where the efficiencies correspond to one, and not two muons. , for W track Z Z ε σ W , which is the proportion of events that should be reconstructed inside the trig ε Z A W A = significance must exceed 4, and the W IP ε is the number of selected events, Z tot as N η The cross-section, Muon trigger, muon identification and muon tracking efficiencies are determined directly from It should be noted that all cross-sections are quoted within the fiducial region we measure, and Similarly, we express the cross-section for The following backgrounds have been considered: ∆ is the integrated luminosity corresponding to the dataset used for the analysis, and decay products as tracks; a lepton reconstruction efficiency, identified and fires theis single tested muon to trigger, see andassociated how to the often it, other it depending muon also onof or the fires lepton efficiency track pseudorapidity. the under No candidate muon dependance test. (the on trigger, Efficiencies lepton is probe) are charge identified is determined observed. as as a a function muon, or has a track data. A tag and probe technique is adopted in (ii) Electroweak; diboson andgrounds top in backgrounds the are dimuon estimated channelthe from are expected simulation. shape estimated from from this Drell-Yan data, contribution back- by (3 fitting 3. Cross-section measurement where val where now or subscript in place of a to allow comparison with theory. Corrections are calculated using the3.1 HORACE [ Efficiencies are not corrected to the full 4 L Z Electroweak boson production in the forward region with LHCb leptons must be isolated andchannel the back-to-back. To suppress the higher Drell-Yan background in this overall efficiency for selecting signal events.acceptance This factor, efficiency can begiven expressed kinematic as region; a a product trigger of: efficiency, offline an selected event; a tracking efficiency, identifying both tracks as leptons; andleptons a passing additional selection selection efficiency, cuts. (i) QCD, estimated from same-sign and non-isolated data (9 0.2. 33 candidates pass thefrom selection. simulation, The and selection an efficiencies uncertainty for estimatedsimulation both from and selections comparing data. are agreement determined between distributions in PoS(EPS-HEP2011)360 1 8 (%) ± and 3 5 ) refer . . 9 7 11 0 3 W n/a ± ± µµ ± µµ ± ± (240 ( 1 σ − and ∆ µ e 1 pb ) . % 3 5 )( . . 9 5 10 µ 0 3 n/a ± ± e events. ± ± ± ( σ ee ∆ → . 1 Z 1 3 1 5 4 . . . . . 5 0 5 3 0 n/a (Z) (%) cross-sections. Note that ± ± ± ± ± σ Z Tara SHEARS, on behalf of the LHCb Collaboration ∆ and W ) (%) 7 3 2 2 5 6 ...... 5 − 1 2 0 3 3 1 ± ± ± ± ± ± cross-sections in table bosons have been measured using 37 ]. Both methods give similar results and are estimated (W production of tau leptons, the efficiency uncertainty 9 Z Z σ Z ∆ and and production within the LHCb fiducial are shown in figure W W Z ) (%) 6 9 5 2 5 5 ...... + 1 1 2 0 3 3 and ± ± ± ± ± ± (W σ W production. All values are quoted as percentages. The luminosity uncertainty ∆ ττ → Z Source Contributions to the systematic error for the total Efficiency Luminosity Backgrounds The cross-sections of The cross-sections and ratios of Systematic errors arise from: backgrounds; efficiencies; the FSR correction applied to the Electron tracking efficiencies are estimated from simulation, and scaled by the difference in FSR correction production in the muon channels. For Template shape (fit) Total systematic error to the final states for pb) of data insection the ratios, muon which provide (ditau) a more decay precisedensity test modes. functions. of Standard All The Model results predictions are luminosity and consistent probe uncertainty with of NNLO parton cancels predictions. in the cross- is quoted separately. 3.3 Results (left), together with the measured Wcoloured charge band asymmetry on (right). the The summary measurementsorder and are and are shown compared next-to-next-to-leading as a to order various calculationscharge predictions asymmetry (NNLO) based is and on shown a next-to-leading as varietyresults data of are points, consistent PDF compared with to sets. theoretical NNLO prediction. prediction. The W It can be seen4. that Conclusions all cross-section; the luminosity estimate. Thestatistics uncertainties and/or on available backgrounds statistics arise in fromprecision data. Monte of The Carlo the uncertainty efficiency in determination efficiencysimulation in is where taken data, calculated as on and Monte the encompasses Carlo statistical statistical differences data. uncertainty between on The data the FSR HORACE and correction estimate.Van uncertainty Der Meer The is scan, luminosity given and is by a beam determined the gas by method two [ methods, a Table 1: 3.2 Systematic errors to have a precision ofZ order 3.5%. This is the leading cause of systematic uncertainty for dominates. All the systematic errorpercentages), sources for are the combined total in measured quadrature. They are summarised (as tracking efficiency observed between simulationefficiency and is determined data from for data muons. using a The tag and electron probe identification method in Electroweak boson production in the forward region with LHCb PoS(EPS-HEP2011)360 44 33 (2004) 037301. -1 D69 Lepton PseudorapidityLepton Pseudorapidity 22 - cross-section measurements (b) W + and 11 MSTW08 ABKM09 JR09 2010 Data W , Tara SHEARS, on behalf of the LHCb Collaboration Z NNLO predictions (DYNNLO) LHCb preliminary, 37.1 pb

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- - 6 135 W- σ Z (pb) + (pb) σ (pb) (pb) CTEQ NNPDF W- W+ W+ Z Z W+ W- σ NLO σ σ σ σ σ σ , arXiv:0808.1847 [hep-ph], published online under 26 1100 MSTW08 ABKM09 JR09 100 NNLO 100 et al. 800 24 1.6 1000 LHCb-CONF-2011-041 LHCb-CONF-2011-039 90 JINST 3:S08005, 2008. 90 <4.5. 22 η 900 700 1.4 (a) 80 -1 et al. 20 80 , Computer Phys. Commun. (2008) 013004. [arXiv:0802.0007 [hep-ph]]. 800 600 70 18 1.2 >20 GeV, 2< T et al. 70 D78 charge asymmetry in bins of muon pseudo-rapidity compared to the NNLO prediction. The µ 700 µ 16 ) ) W → 60 1 µ µ 500 60 µ , W ν µ µ ( (e 600 (a) µ µ 14 Data: stat. and total error τ τ µ µ µ τ τ µ µ → → → → → 50 → → W Z Z Z Z W W 50 Phys. Rev. S. Frixione, P. Nason and C.S. Oleari, Alioli, JHEP P. 0711 Nason, (2007) C. 070, Oleari arXiv:0709.2092; and E. Re, JHEP 1006 (2010) 043, arXiv:1002.2581. M. Ferro-Luzzi, CERN-PH-EP/2005-023 (2005). [doi:10.3360/dis.2008.30 ]. [hep-ph/0303102]. 400 12 Kinematic cuts: charged leptons p LHCb Preliminary, 37.1 pb LHCb Preliminary, 0.8 500 [4] The LHCb Collaboration, [2] A. Augusto Alves [3] The LHCb Collaboration, [1] See, for example, R. Thorne [8] C. M. Carloni Calame, G. Montagna, O. Nicrosini, M. Treccani, Phys. Rev. [6] P. M. Nadolsky, H. -L. Lai, Q. -H. Cao, J. Huston, J.[7] Pumplin, D. T. Stump, Sjostrand W. -K. Tung, C. -P. Yuan, [5] P. Nason, JHEP 0411 (2004) 040, hep-ph/0409146; [9] S. Van Der Meer, ISR-PO/68-31, 1968; shaded and hatched areas represent thecentral uncertainty value of arising the from prediction the for PDF pseudorapidities sets below 2. tested. (b) The line represents the Electroweak boson production in the forward region with LHCb Figure 1: and ratios (coloured bands) compared to NNLO and NLO predictions (points), for the PDFReferences sets tested.