Rare B–decays in ATLAS ITEP, Moscow, 05 - 09 December, 2005 : Rare B–decays in ATLAS ITEP, Moscow, 05 - 09 December, 2005
L.Smirnova,
N.Nikitine,
P.Reznicek (Prague Univ.),
S.Sivoklokov,
M.Smizanska (Lancaster Univ.),
K.Toms 1
LHC ATLAS Experiment : LHC ATLAS Experiment Date operating: 2007 year 2
Introduction - I : Introduction - I Physics: b → d, s transitions (FCNC) are forbidden at the tree level in SM and occur at the lowest order through one-loop-diagrams “penguin” and “box”.
The main points for study:
a) The good test of SM and its possible extensions
- SUSY, Two Higgs-doublet, LR, Extra Dimensions;
b) Information on the long-distance QCD effects;
c) Determination of the │Vtd│and │Vts│;
d) Some of rare decays as BG to other rare decays
(for example: B0d → π0 µ+ µ- as BG to B0d,s →µ+ µ-). 3
Introduction - II : Introduction - II Branching Ratios Hierarchy in SM:
Br(B0d →µ+ µ- ) ~ “a few” * 10-10
Br(B0d →µ+ µ- γ ) ~ “a few” * 10-10
Br(B0s →µ+ µ- ) ~ “a few” * 10-9
Br(B0s →µ+ µ- γ ) ~ “a few” * 10-8
Br(B0d → π0 µ+ µ- ) ~ “a few” * 10-8
Br(B0d → K µ+ µ-) = (5.6 ± 2.5) * 10-7 (BaBar, Belle, ‘02)
Br(Λb → Λ µ+ µ- ) ~ “a few” * 10-6
Br(B0s → φ µ+ µ- ) ~ “a few” * 10-6
Br(B0d → K* µ+ µ-) = (1.3 ± 0.4) * 10-6 (BaBar, Belle, ‘03)
Br(B0d → K*γ) = (4.3 ± 0.4) * 10-5 (CLEO, ‘93) 4 Green – already measured
decays
Cyan – decays probably can
be measured at ATLAS
Black – probably can’t be
measured at ATLAS
Current status of the differencial distributions for B0d → K* l+ l- : Current status of the differencial distributions for B0d → K* l+ l- Y.Kwon (BELLE Colab.), “EW Penguin & Leptonic
B decays”, Report on FPCP 2004, Oct. 4-9 2004. 5
Which new rare B-decays measurements can be performed by LHC in comparision with B-factories? : Which new rare B-decays measurements can be performed by LHC in comparision with B-factories? a) The rare decays of B0s – meson (B0s→φγ , B0s→φ µ+ µ- , and B0s →µ+ µ- (γ)) and Λb – baryon (Λb→ Λ µ+ µ-, Λb→ Λ γ);
b) Differential distributions for rare semileptonic B-meson decays (dimuon mass spectra, forward-backward asymmetries) with sufficient accuracy for distinguishing SM and it’s extentions;
c) Branching fractions of extremely rare decays
B0d,s →µ+ µ- and B0d,s →µ+ µ- γ decays have good sensi-
tivity for some SM extensions.
6
The basic theoretical description-I : The basic theoretical description-I Effective Hamiltonian for b → d,s transition:
Heff (b → q)~ GFV*tqVtb∑ Ci(µ) Oi (µ),
includes the lowest EW-contributions and perturbative
QCD corrections for Wilson coefficients Ci(µ) .
µ - scale parameter ~ 5 GeV : separates SD (perturba-
tive) and LD (nonperturbative) contributions of the
strong interactions.
SM NLO: A.Buras, M.Munz, PRD52, p.182, 1995
SM NNLO: C.Bobeth et al., JHEP 0404, 071, 2004
MSSM NNLO: C.Bobeth et al., NPB713, p522, 2005
7
The basic theoretical description-II : The basic theoretical description-II Oi (µ) – a set of the basic operators (specific for each
model: SM, MSSM, LR and others);
LD (nonperturbative) contribution of the strong inte-
ractions contained in the hadronic matrix elements:
and described in the terms of relativistic invariant
function - transition form factors, so
we need some nonperturbative methods (SR, QM, Lat) 8
ATLAS muon trigger strategy : ATLAS muon trigger strategy 1) The study of two-muons rare decays
(B0s →µ+ µ- , B0d →K*µ+ µ-) is based
on LVL1 di-muon trigger (can be
continued at nominal 1034 cm-2s-1).
2) The study of rare radiative decays
(B0s→φγ, B0d →K* γ) is based on single muon LVL1 (μ6) with photon reconstruction in EM CALO.
3) Rare decays (B0d → 0µ+ µ-,
B0s → µ+ µ- γ ) are based on 1) + 2). ATLAS LVL1, Trigger rates
@1033cm-2s-1 9
Simulation of rare B-decays for ATLAS detector : Simulation of rare B-decays for ATLAS detector 10
B-physics simulation history : B-physics simulation history 1) 1998-1999-years simulation
Early ATLAS Detector layout
CERN/LHCC/99-15, ATLAS TDR 15, 25 MAY 1999;
“1999 Workshop on SM Physics (and more) at the LHC”, CERN Yellow Reports
CERN-2000-004.
2) 2002-2003-years simulation
Final ATLAS Detector layout
ATLAS B-Physics Group, ATL-PHYS-2005-002
3) 2004-2005-years simulation
Final ATLAS Detector layout with new software
ATLAS Physics workshop (Rome),
http://agenda.cern.ch/fullAgenda.php?ida=a044738 11
Models used for MC generation : Models used for MC generation 12
“Rome production”: 2005 – Data Samples : “Rome production”: 2005 – Data Samples Generation (with theoretical matrix elements), full simulation, digitiza-
tion and reconstruction with 9.0.4 and 10.0.1 software releases, analysis
of AOD in 10.0.1 .
Signal channels:
B → μ6μ6 Rome production. 5 kEv in analysis (AOD)
B → K*0μ6μ4 Private (evgen-simul-digi-reco) 30 kEv (AOD)
B → φ μ6μ4 Private (evgen-simul-digi-reco) 12 kEv (AOD)
Λb → Λ μ5μ5 Private (evgen-simul-digi-reco) ~50 kEv (AOD)
Background samples:
bb→μ6μ6X ~50kEV included cut on M(μμ) ~ M(B0s)
bb→μ4μ4X ~23kEV for B-decays and ~31kEv for Λb-decays 13
B0d,s→µ+µ- simulation at ATLAS : B0d,s→µ+µ- simulation at ATLAS 1) 1998-1999-years simulation TDR ATLAS Detector layout
Full detector simulation and reconstruction for initial and nominal LHC luminosity,
signal + combinatorical background
After 3 year LHC at L=1033 cm-2s-1 (30 fb-1)
B0d : 4 signal ev., B0s : 27 signal ev., 93 BG ev. common to both
After 1 year LHC at L=1034 cm-2s-1 (100 fb-1)
B0d : 14 signal ev., B0s : 92 signal ev., 660 BG ev. common to both
B0d →µ+µ- : 3*10-10 upper limit at CL 95%
B0s →µ+µ- : 2.8σ at 3year@1033 and combining with 1year@1034 - 4.3σ
CERN/LHCC/99-15, ATLAS TDR 15, 25 MAY 1999;
“1999 Workshop on SM Physics (and more) at the LHC”, CERN Yellow Report, CERN-2000-004.
2) 2002-2005 simulations with Final ATLAS Detector layout and
with new software
DC1: ATLAS B-Physics Group, ATL-PHYS-2005-002
DC2+ Rome Production: ATLAS Physics workshop (Rome),
http://agenda.cern.ch/fullAgenda.php?ida=a044738 14
B0s →µ+µ- decays in ATLAS: Rome production at 2005 year : B0s →µ+µ- decays in ATLAS: Rome production at 2005 year Signal, BG and efficiencies of selection cuts (10 fb-1) 15
ATLAS sensitivity on Br(B0s→ µ+µ- ) with Final detector layout : ATLAS sensitivity on Br(B0s→ µ+µ- ) with Final detector layout 1) We get the cross section of B0s multiplied by acceptance of B0s →µ+µ- decay with pT(μ)>6 GeV and |η(μ) |<2.5 from Rome PYTHIA samples : σ(Bs )*α = 0.42 μb;
2) We get the background ( → μμX) cross section σ(BG) with pT(μ) > 6 GeV and |η(μ) |< 2.5 from Rome PYTHIA samples: σ(BG) = 600 pb;
3) SES - Single event sensitivity for B0s →µ+µ- SES = [(1 Bs →µ6µ6 event)/(total number of BG events)]×[σ(BG)/ (σ(Bs)*α) * εμ2];
4) For ATLAS upper limit calculation we have used CDF code http://www-cdf.fnal.gov/physics/statistics/statistics_software.html. 16
Λb → Λ µ+ µ- - motivation for study : Λb → Λ µ+ µ- - motivation for study AFB – is very sensitive to the SUSY [C-H.Chen et al., Phys.Rev.D64,074001 2001]
Standard model, W.C.: [A.J.Buras et al., Phys.Rev.D52,186 1995]
SUSY model: [E. Lunghi et al., Nucl.Phys.B568,120-144 2000] AFB in low di-muon invariant mass region (outside J/ψ resonances) shows significant sensitivity to effects of new physics Also sensitive, but:
higher ψ resonances
more sensitive to Λ0b→Λ0 transition form-factors
[C-H.Chen et al., Phys.Lett.B516,327-336, 2000] Main definition for AFB 17
Impact of Trigger Cuts for Λb → Λ µ+ µ- : Impact of Trigger Cuts for Λb → Λ µ+ µ- LVL1 cuts
All trigger cuts
No cuts 18 expected number of triggered events for 30 fb-1
trigger cuts slightly lower absolute value of AFB in region of lower di-muon masses
B0d→K*(892)µ+µ- decay at ATLAS : B0d→K*(892)µ+µ- decay at ATLAS Points to study in ATLAS:
Branching ratio - sensitive to the SUSY ;
Differencial distributions (dimuon-mass spectra, AFB)
very sensitive to the SUSY.
1998-1999 years simulations :
Full ATLAS Inner detector simulation and reconstruction at initial
luminosity (ATLAS TDR 15, Vol.II, 1999) using theoretical matrix
element from paper D.Melikhov, N.Nikitin, S.Simula, PRD57, 6814, 1998.
Results of 1998-1999 years simulation:
After 3 year LHC work at L=1033 cm-2s-1 (30 fb-1) is expected
~2000 signal events at 290 BG events 19
B0d→K*(892)µ+µ- decay at ATLAS 2005-year results : B0d→K*(892)µ+µ- decay at ATLAS 2005-year results ~120 kEv of signal before the cuts
for 30 fb-1.
Cuts:
pT(μ) > 6 Gev, |η(μ)| < 2.5
M(h+h-) = M(K*)±30 MeV
Vertexing procedure VkalVrt:
χ2 < 18, Lxy/σ >35
Isolation cut: no ch.trecs
pT>0.8 GeV in cone with θ < 5o
~ 3000 signal events after all cuts
< 3000 BG (events will be revised when high statistics available ) 20 Number of reconstructed events (2005 year) K*μμ – invariant mass (MeV) B0d - peak σBd=39 MeV
AFB for B0d→K*(892)µ+µ- decay : AFB for B0d→K*(892)µ+µ- decay 0.8 fb-1 5 fb-1 30 fb-1 hep-ex/0410006 21
CONCLUSION : CONCLUSION 1. Already during the first year of LHC, with luminosity just 100 pb-1 ATLAS can exceed best CDF and D0 current upper limit on branching ratios of B0s→µ+µ- decay.
2. After 30 fb-1 (equivalent to 3 years at initial luminosity) ATLAS will be able to achieve sensitivity at level of SM predictions for B0s→µ+µ-.
3. Under the same conditions ATLAS will have enough statistics for precise measurement of differential distributions of rare semileptonic decays.
4. Program of ATLAS rare muonic decays measurements can be continued at nominal LHC luminosity 1034 cm-2 s-1! 22