ＣＤＦ実験の最新結果 筑波大学数理物質研究科 佐藤構二 日本物理学会第 61 回年次大会 愛媛大学、 2006 年 3 月 27 日

Tevatron Run II p – p collisions at  s = 1.96 TeV (1.8 TeV in Run I). Run II started in Summer Particle collider at the highest energy!

CDF Collaboration ~600 people from 12 Countries.

Tevatron Run II — Luminosity Status Peak Luminosity Record: 1.8  cm 2 s -1. Weekly Record: 27 pb -1 /week. Integrated Luminosity –Delivered: 1.6 fb -1,Recorded: 1.3 fb -1. Future: 4-8 fb -1 by Recent analyses typically use pb -1. Run II since Summer 2001

Collider Detector at Fermilab Multi-purpose detector Tracking in magnetic field.  Coverage |  |<~1. Precision tracking with silicon.  7 layers of silicon detectors. EM and Hadron Calorimeters.   E /E ~ 14%/  E (EM).   E /E ~ 84%/  E (HAD). Muon chambers.

Contents Top physics –Pair production cross section –Top mass –Search for ttbar resonance –Lifetime measurement –Search for single top Direct search for Higgs Boson –Standard Model Higgs B physics –Status of B s oscillation –B s  rare decay –B s and B c properties

Top Physics

Why is Top Physics Interesting? Direct study on top is only possible at Tevatron. Top is one of the least-well studied particles. –Does it couple to exotic particles? Top mass is unexpectedly heavy ~35  m b. –Special role in EWSB? Top datasets at CDF-II (7xCDF-I) is finally enough to start detailed studies on top. p p t b WW q q’ t b W+W+ ll X Production cross-section Resonance production Production kinematics ttbar Spin correlation Top Mass W helicity |V tb | Branching Ratios Rare/non SM Decays Anomalous Couplings CP violation Top lifetime Top Charge Top Width _ _ _ _ BR (%)Bkgd. Di-lep.5Low L+jets30Moderate All had.44High  +X 21  -ID hard ttbar decay modes:

Top Pair Cross Section Cross section is sensitive to both production and decay anomaly. The difference of the xs between different decay modes might indicate new physics. CDF measures xs with various decay modes/methods, and the results are consistent with SM.

Top Mass Measurement  Motivation Presise mass measurements of W and top can constrain the SM Higgs mass through radiative corrections. From Tevatron Run I : –M W =  59 MeV/c 2 (World Average :80410  32 MeV/c 2 ) –M top =  4.3 GeV/c 2  M higgs < 260 GeV/c 2 (95% C.L.) CDF Run II goal : –  M W ~30 MeV/c 2 –  M top ~2 GeV/c 2

Top Mass  l+jets Template Method New technique in Run II: Constrain the jet energy scale (JES) uncertainty by W  jj invariant mass in tt  l+jets candidate events. –The obtained scale is applied to both b- and light-jets. –Fit is done in m top vs JES plane. t t q q g g b b W+W+ W-W- l+l+ q’ q 15%85%  100% Use dijet invariant mass for in-situ JES calibration. Likelihood countour: Reconstracted top mass (kinematic fit) : M top (template) = ± 2.5 (stat. + JES) ± 1.3 (syst.) GeV (680 pb -1 ) World best single measurement: 佐藤・戸村・丸山・金 ( 筑波大）

Top Mass Measurements 土屋・近藤 ( 早稲田大） 28 日午後発表 予定 DLM Method in dilepton channel Event reconstruction with Matrix Element calculation. 寄田 ( 早稲田大、 現シカゴ 大）  M top ~2 GeV/c 2 achievable at L~2-3 fb -1

Top Mass Tevatron Combination Use only best analyses from each decay mode, each experiment. Correlation : uncorrelated  stat.  fit method  in situ JetEnergyScale(JES) 100% w/i exp (same period)  JES due to calorimeter 100% w/i channel  bkgd. model 100% w/i all  JES due to fragmentation,  signal model  MC generator

Updated Electroweak Fit Results New top mass world average : M top =  2.3 GeV/c 2. Updated preferred SM Higgs mass : –M higgs = GeV/c 2. –M higgs < 175 GeV/c 2 (95% CL). < 207 GeV/c 2 w/ LEP direct search limit. w/ Tevatron Run I average : M top =  2.7  3.3 GeV/c 2 m higgs = /-45 GeV/c 2 m higgs  260 GeV/c 2 (95% CL)

ttbar Resonance in Summer 2005 Search for new massive resonance decaying to top pairs such as top- color Z’. – Using lepton+>=4jets (no-btag) sample. –Event reconstruction by assuming LO matrix element. –Constraint top mass = 175GeV/c 2 Fix SM backgrounds to expected rate –Use theory prediction of 6.7pb for SM top pair production Interesting excess, 319pb -1 (2005 summer)

Updated Search for ttbar Resonance Same analysis was done using the 682pb -1 !! –Same selection, same mass fitting. –Previous 318pb -1 data is a sub-sample of the full dataset. Limit on a narrow vector resonance (  R =1.2% M R ): M R >725 GeV at 95%CL No significant excess

Top Lifetime SM prediction :  top ~0.4x s   top << 1/  QCD  s  top does NOT hadronize (unique about top quark). Measurement of  top helps in confirming SM top assumption. Measure lepton impact parameter (d 0 ) in L+jets events with  1 b-tagged jets. Use Z  ll to calibrate d 0 resolution. Signal template

Top Lifetime Result (318 pb -1 ) Data prefers  top =0. bkgd + signal(  top =0) c  top < 52.5  m (  top <1.75x % C.L. First direct limit on top lifetime

Motivation for Single Top Search Direct measurement of |V tb |. –Unitarity of the CKM matrix. Is |V tb | really ~1? –S-channel is sensitive to new resonance particles such as W’. s-channel t-channel s 1/2 =1.96TeV  (NLO) t-channel1.98 ± 0.25 pb s-channel0.88 ± 0.11 pb V tb SM prediction: Cross section is about half of ttbar. V tb *

Single Top Search Result (695 pb -1 ) SM prediction t+s combined NN output :Result of 2D NN fit : Neural Net is trained for t- and s- channels, both combined and separately. B-tagger output is input to NN as well as event kinematic variables. Bkgd categorized according to NN output shape: Bottom-like = Wbb, WZ, ZZ, Z , non-W; Charm-like = Wcc, Wc, WW, mistag  (t+s-chan.) < % C.L.  (t-chan.) < % C.L.  (s-chan.) < % C.L.  (t+s-chan.) = (stat) (syst) pb

Direct Search for SM Higgs Boson

SM Higgs Properties at Tevatron bbWW Recent top mass measurement favors small Higgs mass. Tevatron could compete with LHC if the Higgs is light.

SM Higgs Search  WH  l bb Event selection: Isolated e/  w/ E T >20 GeV, |  |<1. Missing E T >20 GeV. Two jets with E T >15 GeV, |  | < 2.0. At least one jet is b-tagged. Veto extra jets to reduce ttbar. Total acceptance ~ 1.5% including Br[W  l ] for m H =115. 石澤 ( 筑波大、現 triumph ）、 2006 年夏

SM Higgs Search  ZH  bb Event selection: Missing E T >70 GeV. 2 jets w/ jet E T >25 GeV, |  |<2.4. Veto e/  w/ E T >10 GeV. At least one jet is b-tagged. Veto additional jets w/ E T >15 GeV. Total acceptance ~ 3.6% including Br[Z  ] for m H =120.

SM Higgs Search  WW*  l l 2 opposite signed isolated e or . –1 st (2 nd ) lepton w/ E T >20(10) GeV. Veto jets to reduce ttbar bkgd. missing E T >M H /4. 16< m ll < M H /2-5 GeV to reduce resonance.. Total acceptance ~ 6% including Br[W  l ] 2 for m H =160. assuming mh~ １ 60 GeV/c 2

Summary of SM Search 小林 ( 筑波大）、 2004 年秋 95% exclusion upper limit SM prediction The results are mostly ~1/2 years old. They will be updated very soon.

Future Improvements on SM Higgs Search Improvement WH  l bbZH  b b ZH  llb b Mass resolution1.7 Continuous b-tag (NN)1.5 Forward b-tag1.1 Forward leptons Track-only leptons NN Selection WH signal in ZH Product of above CDF+D Ø combination2.0 All combined Luminosity Equivalent (s/  b) 2 Expect a factor of ~10 luminosity improvement per channel, and a factor of 2 from CDF+DØ Combination Start with existing channels, add in ideas with latest knowledge of how well they work (under studying) Analysis method will be improved with x2 dataset.

B Physics

B s  B s Oscillation Motivation from  m d from  m d /  m s Lower limit on  m s  m d ~|V td | 2 (B d  B d Oscillation) constrains a side of unitarity triangle. By taking ratio  m d /  m s we can rule out theoretical uncertainties and tighten the constraint on unitarity triangle. Orange band in the plot: the upper limit on |V td | is set by the lower limit of  m s. Frequency  m s ~|V ts | 2

B s  B s Oscillation Result (355 pb -1 ) Oscillation not yet observed. Frequency scan of the oscillation: –Fit for A for each  m s. –A=1 for true  m s. Results will be updated very soon! –With double data (765 pb -1 ). –Newly developed same-side kaon flavor tagging will improve  D 2 by a factor of ~3!! –Overall  D 2 =1.6% in current analyses.  m s > 8.6 ps -1 (95% CL limit) Frequency scan, semileptonic and hadronic channels combined :

Rare Decays B s / B d     b d, s t w w l+l+ l-l- b t w w l+l+ l-l- Z/  SM predictions on Branching Ratio : SUSY may enhance the rate : Event Selection (opposite sign di-muon) by likelihood discriminant composed with: –Isolation of tracks –Decay time –Direction of 2 nd vtx and P 

B s / B d      Result (780 pb -1 ) KK, K ,  decays of B d and B s, with  ID faked Observed : BR( B s → μμ ) < 1.0x10 CL (2.6 x in Run I ) BR( B d → μμ ) < 3.0x10 CL ( 8.6 x in Run I ) World Best Limits!! Likelihood Discriminant central+central : central+forward :

B s Lifetime (360 pb -1 ) Important input to B s oscillation. Use semi-leptonic decay : BsBs DsDs s s 魚住 ( 筑波大） 30 日午前発表予定 World second best value !!

bcbc cccc e J/  Bc B c Properties (360 pb -1 ) - 青木 ( 筑波大） 30 日午前発表予定 M(B c ) = ± 5.3 ± 1.2 MeV/c 2 σ(Bc)BR(Bc→J/ψeν)/σ(B + )BR(B + →J/ψK + ) = ± ±  (B c ) = ± ps

Exotics

3 rd Generation Vector Leptoquark Search (322 pb - 1 ) 秋元 ( 筑波大） 28 日午前発表予定 ℓ hh jet VLQ 3 ℓ   b b   pp 1 or 3 track(s) e or  VLQ 3  b  (pp  VLQ 3 VLQ 3 ) < 76 fb, m VLQ3 > 368 GeV/c 2 (95% C.L.) H T distributions for e  h channels (  2 jets) VLQ M=320 (  h channel also analyzed.)

Summary CDF Run II experiment is operating pretty well! CDF has already collected ~1.3 fb -1 of data. –~2.5 fb -1 by the end of 2006, ~8.5 fb -1 by Many impressive results are being reported. Many more results are already there! –Can not present everything in a limited time. –Please check www-cdf.fnal.gov for other results. Important results are coming up/updating shortly, mostly with ~800 pb -1 dataset. Stay tuned!! –Update on direct Higgs search. –Update on B s oscillation (measurement?). –1 st W mass measurement in Run II. –……………..