RHIC-PV, April 27, 2007 M. Rijssenbeek 1 The Measurement of W ’s at the CERN and FNAL hadron colliders W ’s at RHIC ! W ’s at CERN – UA2 W ’s at FNAL - CDF

RHIC-PV, April 27, 2007 M. Rijssenbeek 2 W ’s at RHIC ! Measurement of W ’s in polarized-proton collisions at RHIC: –measure the u and d -quark and anti-quark contributions to the proton spin as function momentum fraction x. –use the W charge and the V–A structure of W production & decay to eν and μν to select quark flavor and quark helicity. For W – : u↔d

RHIC-PV, April 27, 2007 M. Rijssenbeek 3 Non-Hermetic Detectors RHIC detectors are not fully hermetic… electron and muon acceptance of the RHIC detectors varies strongly over the rapidity range… Thus: –missing transverse energy cannot be used to clean up the W signal –Trigger has to rely exclusively on high p T electrons and muons –The backgrounds to the W from Z→e/μ and QCD/fakes may be significant –enough Z -statistics for measurement/tuning of corrections? Detailed simulations will be crucial to determine acceptance corrections, efficiencies, and backgrounds –limited Z acceptance makes tuning of the simulations with Z→ee/μμ more difficult

RHIC-PV, April 27, 2007 M. Rijssenbeek 4 a “Non-Hermetic” Detector: UA2 – vs.1 Central tracking + Preshower + EM Calorimetry; |η|<1 Forward spectrometer + PS + EM Calorimetry; 1<|η|<3 a non-hermetic detector… UA2 collaboration: M Banner et al., Phys. Lett. 122B (1983) 476. UA2 collaboration: P Bagnaia et al., Phys. Lett. 129B (1983) 130.

RHIC-PV, April 27, 2007 M. Rijssenbeek 5 W and Z in UA2 strong quality selections on electron candidates necessary: –isolation, shower shape, preshower signal, track-PS- cluster match –even so: cut on missing p T for final sample… all good EM cluster pairs + Track & PS match Z W W

RHIC-PV, April 27, 2007 M. Rijssenbeek 6 W and Z in UA2 – vs : UA2 Upgrade program with hermetic calorimetry QCD UA2 collaboration: J.Alitti et al., Z.Phys.C47 (1990) 11.

RHIC-PV, April 27, 2007 M. Rijssenbeek 7 W ‘s at Fermilab the measurement of the W mass with a 0.05% accuracy (50 MeV or 100× M e ) requires the ultimate understanding of the detector!  simulations and cross checks & tuning with the data itself…

RHIC-PV, April 27, 2007 M. Rijssenbeek 8 Simulations the state of simulations of W and Z production (and decay) has much advanced over the past decades –forced by very high statistics W/Z samples for mass determination from LEP and Tevatron –much QCD calculational progress –improved detector simulations: showering –availability of raw computing power allows more detail and increased sophistication State-of-the-Art: –RESBOS: NLO W and Z production –CTEQ6M: NLO pdf’s with uncertainties Note: p T e/μ is quite sensitive to boson recoil M T less so, but is sensitive to y W/Z CRUCIAL for all precision W/Z measurements

RHIC-PV, April 27, 2007 M. Rijssenbeek 9 FNAL Example: CDF W Mass (from seminar by Dr. David Waters, UC London) CDF is a modern hermetic detector: hermetic detection of e, γ, jets; less hermetic for μ –recent M W measurement (e+μ) is single best in the world: M W CDF = ± 34 (stat) ± 34 (syst) MeV cfr: WA 2006: 80392±29 MeV CDF Note 8665, Jan 17, 2007; CDF

RHIC-PV, April 27, 2007 M. Rijssenbeek 10 W/Z Production in pp & Decay Modeling + Corrections: Higher orders (EW,QCD) Non-perturbative Leading Order picture: rapidity distribution angular & mass distributions : p T distribution 

RHIC-PV, April 27, 2007 M. Rijssenbeek 11 W Production Modeling: p T Use the best theoretical model on the market : –RESBOS  NLO QCD + resummation + non-perturabtive. Constrain the parameters g 1, g 2, g 3 and lineshape with the Z data:  W : 7 MeV  M W : 3 MeV (Landry et al., 2003)

RHIC-PV, April 27, 2007 M. Rijssenbeek 12 W→μν Backgrounds mostly Z→μμ : easy to lose a muon (at CDF !) But can estimate this background very reliably.

RHIC-PV, April 27, 2007 M. Rijssenbeek 13 Decay-In-Flight Background in W→ μ ν difficult background: very flat in transverse mass Use track quality:  2 and track impact parameter final cut value /NDF x x x x x x x x K,  fake high-p T track  W : 27 MeV  M W : 5 MeV Vary normalization & shape: Z  provides the template for real muons High impact parameter cuts provide the DIF template

RHIC-PV, April 27, 2007 M. Rijssenbeek 14 W→eν Backgrounds Z ’s ~ negligible QCD background dominates

RHIC-PV, April 27, 2007 M. Rijssenbeek 15 QCD Background in W→eν Multijet events: large σ  R fake (jet  e)  R fake (jet  E T ) final cut value QCD template from a background-rich “anti-electron“ sample  W : 32 MeV  M W : 7 MeV Vary normalization & shape:

RHIC-PV, April 27, 2007 M. Rijssenbeek 16 CDF W Mass 2007: sample size analyzed: 200/pb event selection: p T e,μ >30 GeV, p T ν >30 GeV Uncertainties in M W for fit to p T e/μ :

RHIC-PV, April 27, 2007 M. Rijssenbeek 17 W/Z Physics result: Van Neerven Plot: M W /M Z with M top constrain the SM Higgs range; 200/pb  Current data sets: 2/fb (CDF, DØ) FNAL Expectation: δM W ≈ 30 MeV /expt

RHIC-PV, April 27, 2007 M. Rijssenbeek 18 My Conclusions A precise measurement of Δu and Δd will bring new understanding of the spin structure of the baryons… However: in order to obtain the required precision, the measurement will need sophisticated simulations to understand and model the detector acceptance, efficiencies, and backgrounds –the physics and detector models must be tuned and checked with measurements of the Z (<10% of W statistics) –Dominant backgrounds must be measured with the data itself these simulations must be done beforehand to prove the measurement capability with RHIC’s “non- hermetic” detectors…