ATLAS and CMS B-physics

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ATLAS and CMS B-physics Powered By Docstoc
					         ATLAS, CMS B-Physics Reach
              M.Smizanska, Lancaster University, UK




UK HEP FORUM The Cosener's House, Abingdon, 24th-25th April 2004
               'From the Tevatron to the LHC'
ATLAS,CMS: b-events from central pp LHC collisions
LHC pp                       s total     =    100 mb              ATLAS.CMS, LHCb three
                             s inelastic =     80 mb              different strategies to
                             s bb        =    500 mb              measure B production
                ATLAS/CMS               LHCb                      within partially overlapping
                Central detectors       Forward detector          phase space
 h - pT         |h| < 2.5               1.9 < h <4.9
after trigger   pT >10 GeV              pT > 2 GeV
and offline     s = 100 mb              s = 230 mb
s one B ‘in’
Luminosity      L = 2 × 1033 cm-2 s-1   L = 2 × 1032 cm-2 s-1
for B           rare B 1034 cm-2 s-1                                      100mb
physics
Statistics      1 y @ 1033 cm-2 s-1     1 y @ 2 × 1032 cm-2 s-                       230mb
                                        1
exclusive B         2.6 × 106
                dominated by B J/y          1.7 × 106 B  J/y
                But all hadronic with        1.7 × 106 hadronic
                muon tag




  ATLAS-CMS                                                                                  2
b-events: LHC vs Tevatron



               -
             sbb



                                        LHCb
                        ATLAS/CMS




                                    Bjorken x1 vs x2 for events
                                    that passed trigger&offline
                                        for at least one of B
                                              hadrons
                              CDF




 ATLAS-CMS                                                    3
b-events: LHC vs Tevatron, cont
  In hadron-hadron collisions b and
                                                  Implications:
    anti b quarks are produced with
 angular distances (0-p). At LHC a             B-Trigger strategies
                                                                  ATLAS/CMS
   contribution of topologies with b
                                               Tagging uncertaintes
     anti b different from ‘back-to
 back’ is expected to be even higher
            than in Tevatron.



     CDF                               ATLAS




 ATLAS-CMS                                                                    4
ATLAS,CMS B – physics Trigger strategies




ATLAS-CMS                                  5
               ATLAS Trigger Architecture
      Decision
                     2x 8
                      10       109 Hz
        times
    Implementatio
          n
      < 2.5 ms
      Hardware
       (FPGA)


         ~ 10
           Purpose
  General ms
Processors optimised
     algorithms      Higher Level
                      High Level
                        Trigger
                         Trigger
       ~ few sec
   General Purpose
  Processors : offline
    type algorithms

                     FPGA = Field Programmable Gate Array
ATLAS-CMS                                                   6
   ATLAS,CMS B – physics Trigger strategies
 Different scenarios for diff. luminosity   1. Di-muon trigger:
 conditions & rates                         L1 2m + L2 full precision m tracking
                                            Bd(Bs,Bc ) J/y (mm) + Ks0 (K0*,f,h),
                                            Lb (Sb, Xb) J/y (mm) L,
                       single-muon          B  mm, b  s mm

         h       all                        2. Muon-electron(g) trigger:
         b                                  L1 m + L1 E/g cluster (ET>2GeV)+ L2
         c                                  tracking in region
                                            Bd(Bs,Bc ) J/y (ee) + Ks0 (K0*,f,h) + B m
                                            Lb (Sb, Xb) J/y (ee) L + B  m
             b
                 all                        bsg + Bm
             h
                          di-muon
         J/y
                                            3. Muon-hadron triggers:
                                            L1 m + L1 Jet (ET>5GeV) + L2 tracking in
         c                                  region
                                            L1 m + L2 full-scan tracking in Inner
@1033cm-2s-1
                                            Detector
                                            B pure hadronic decays + B  m
    ATLAS-CMS                                                                        7
            ATLAS LVL1 Jet RoI                                      LVL1 Jet RoI
                                                                    ET > 6 GeV
For hadronic final states use LVL1 Jet RoI (events with LVL1
    muon)
•   LVL1 Jet Clusters in EM & Hadron Calorimeters.
•   Threshold of ET > 6 GeV (efficient for Bs with pT > ~ 16GeV)
•   Final threshold chosen will depend on RoI multiplicity
•   Preliminary simulation studies gives a mean multiplicity of 2
    for a 6 GeV threshold (final value may be higher).

                               LVL1 Jet
                               RoI ET > 6
                               GeV




    ATLAS-CMS                               Bs pT GeV                      ET GeV   8
                    CMS High-Level Trigger Tracking

Limited amount of CPU time available for trigger decision:
  500 ms on a 1GHz machine
  possibly 50 ms in 2007                  Regional seed generation

                                            Limited to some region
                                          identified by Lvl1 objects
                                        (e.g. cone around m direction)
     Reduce
            # of track seeds
            # of operations per seed
                                          Partial/Conditional Tracking
                                       Stopped when:
    HLT Tracking does not                N hits are reconstructed
  need to be as accurate as              PT resolution  given threshold
       in the offline                    PT value  given threshold
                                         ……………………………………..

ATLAS-CMS                                                            9
                          CMS BS m-m+
@ L1:
 2m trigger, PT  3 GeV, |h|  2.1
@ High Level Trigger:
 Regional tracking    look for pixel seeds only in a cone around
 the 2m, with PT  4 GeV and d0  1mm, and compatible with PV

 Conditional tracking  reconstruct tracks from good seeds
      Stop reconstruction if PT  4 GeV @ 5s
      Keep only tracks with σ(PT)/PT  2%, Nhit =6

  IF 2 Opposite Signs tracks found
  Calculate the invariant mass
  Retain pairs with a) |Mmm-MBS|  150 MeV
                    b) Vertex 2  20 & d0  150 mm

  Lvl-1 e         HLT e          Global e       Events/ 10fb-1     Trigger Rate
  15.2%           33.5%            5.1%               47             <1.7Hz



ATLAS-CMS                                                                     10
       ATLAS,CMS Inner detector and
       B-phys performance




ATLAS-CMS                             11
             CMS Tracker Design and Performances
 Pixel around interaction point            Radius ~ 110cm, Length/2 ~ 270cm
 4.2, 7, 10 cm and +- 60 cm in z
                                                  6 layers
                                                  TOB

                                                   4 layers
                                                   TIB


Silicon strip : sR = 10-60 mm                                3 disks TID 9 disks TEC
Pixel: sR, z = 10-20 mm, cell size ~ 100x150mm




ATLAS-CMS                                                                      12
                                                     The ATLAS Inner Detector

                                                  Three sub-detectors using different
                                                  technologies to match the
                                                  requirements of granularity and
                                                  radiation tolerance




Sub-
Detector            r(cm)       element size       resolution  hits/track
Pixel               5.0; 8.8   50mm x400mm         12mm x 60mm       3
(Silicon)           12.2        (3D)

SCT                   30-52     80mm x 12cm        16mm x 580mm         4
(Silicon Strip)                 (stereo)
Barrel: 4 cylinders; End-cap: 9 Wheels

TRT                 56-107     4 mm x 74cm         170mm                36
(Straw Tubes)                  (projective)

Initial LHC may be without: 1 pixel layer at 8.8cm, one of 3 endcap pixel
disks and forward TRT wheels: so called ‘Initial layout’
ATLAS-CMS                                                                               13
            ATLAS: Inner detector performance

            B proper time resolutions
            Single-Gauss fit   Com      Initial   1998
            s[fs]              plete
            Bs  Ds p          100      98        67

            B  mm             99       98        69

            Bs  J/y(mm) f     85       82        63

            Bd  J/y(mm)K0     89       86        69

            Lb  J/y(mm) L     101      95        73




ATLAS-CMS                                                14
Comparison of ATLAS and CMS
 impact parameter resolutions




ATLAS-CMS                       15
  ATLAS particle identification in B-physics events
                Low pT electron identification
Combined EM calorimeter-TRT               TRT electron identification
electron identification




Rejection of bb  m6X events
without electron vs efficiency of     Invariant mass for all track pairs
events bb m6e5X.                     in bb J/y (ee)K0 events before
Eff=70%,R=570, level-2 rate of        and after TRT selection cuts.
signal is 40Hz, fake rate 10Hz        Electrons have pT>1GeV.
due to hadrons misidentified as
electrons.
 ATLAS-CMS                                                                 16
        ATLAS particle identification in B-physics events, cont.
        Low and medium-pT muon performance
  Lowest pT muon identification            J/y(mm) reconstruction in the
  & reconstruction efficiency              environment of b-jet with pT~(50-80)
                                           GeV (for QCD b-production studies)

Inner detector +
Muon spectrometer




                                                                     the same
                                                                      in log scale


Inner detector +
Muon spectrometer
+ Hadron calorimeter
                                            Even in high pT jet a mass reconstruction
                                            is negligibly affected by fake pairs when a
                                            muon identified in Muon spectrometer
                                            match to a wrong track in Inner Detector.
    ATLAS-CMS                                                                        17
     Precise measurements of Bd  J/yKs0 decay
                                                    1year@1033cm-2 s-1   CMS      ATLAS
Method: maximum likelihood fit using                Trigger              4400k    800k
                                                    Offline              430k     170k
experimental inputs:                                S/B                  8        31
• proper time resolution
                                                    sin2 statistical
• tag probability                                   Lepton tag           0.031    0.039
• wrong tag fraction                                Jet/charge tag       0.021    0.026
• background contribution and composition           Total                0.015    0.017
                                                         Combined ATLAS
Neglected at present stage:
                                                         and CMS sin2
Direct CP violation term                                3y@1033cm-2s-1          0.007
Any new physics contributions
                                                         ATLAS, CMS
Production asymmetry – possibly fcn of (pT h)           3y@1033cm-2s-1 &
Wrong tag fraction – as fcn of (pT h)                   LHCb 5y@1032cm-2s-1     0.005
          The statistics used in the table includes:
          ‘dimuon triggers mu6mu3’, using LVL1 efficiency 80%/per muon.
          ‘di-electron LVL2 trigger e1e1’.
           With more realistic e4e4 the precision of ATLAS, CMS degrade by factor 1.2.


  ATLAS-CMS                                                                               18
                            sensitivity in Bd  p p                             + -


Signal yields                  Atlas   CMS LHCb
                                                              Max.likelihood computed
3y @1033cm2s-1                             5y                 from: *Proper time
                                                                                                  Simulateous fit of 6 contributing
                                                                                                  decays parametrized by 9
First trigger level            46k     52k       150k              *Invariant mass                coefficients, constrained by
                                                                   *Flavour at production
Offline 2-boby select.         2.3k    2.6k      4.9k                                             current experimental limits.
                                                                   *Specific ionisation:
Mass resol [MeV]               70      27        17
                                                                        Signal decay parametrized in terms of Adir , Amix:
Signal/2-body bck              0.19    0.33      15                          Adir cos( m t) + Amix sin( m t)
                                                                                                                         
Signal/other bck               1.6     5         >1           Adir , Amix    in SM depend on ,  ( or  eff ), ( PT  )
sAdir                          0.16    0.11      0.09                       were used to derive sensitivity to 
sAmix                          0.21    0.14      0.07
correlation                    0.25    0.51      0.47

                                             1. Divergencies appeare as sin
                                             or cos->1                                                             s | P T | 100%

                                             2. Linear |P/T| approximation
                                             is not justified for value 0.36
             Exact: |P/T|2
                                             suggested by current
                                             evaluations.                                                   s | P T | 30%
               Approx: |P/T|
                                             3. The current theoretical                                   s | P T | 0%
                                             uncertainty |P/T|~30%
                                             dominates other systematical
                                             and statistical errors of full
                                             LHC potential.
   ATLAS-CMS                                                                                                                     19
         Physics of Bs meson
  Program for precise measurements of Bs-anti-Bs system parameters : Gs, ms and
        probing Bs mixing phase fs -lh allowing to investigate new physics


ms from Bs  Ds p and Bs  Ds a1 already
 after 1 year sensitivity up to ms - 36 ps-1 fully explore
          SM allowed range ms (14.3 - 26) ps-1


     Gs and fs= - lh from Bs  J/yf
        or Bs J/yh both sensitive, but precision
              sufficient only in Bs  J/yf
                                                              f    q1

Angular analyses of cascade decay Bs  J/y (mm)f(KK)
                                                                                    q
determine Gs, Gs and fs simultaneously with 4                              Bs

parameters of 3 helicity amplitudes A||, AT, A0 : A||(t=0),
AT(t=0), 1, 2. Parameter ms will be measured by
flavor specific decays.
 ATLAS-CMS                                                                           20
CP - violation weak phase in Bs  J/y f

                                    Standard Model region-updated 2003
                                    New physics Left-right symmetric
                                    model (NP-LR) - needs update (2000
                                    version used here).
                                    ATLAS (3y): 1st level trigger 1m only. 2m 1st
                                    trigger under investigation, not included.
                                    TDR Detector, 240Evts.
                                    ATLAS - same – as above with Initial
                                    Detector
                                    CMS updated for realistic trigger in 2004
                                    3y@1033 : 252k Evts. The estimated
                                    precision between the two ATLAS curves.
                                    LHCb(5Y): full 1st Level trigger,
                                    performance parameters as given in 2000

                                    Experimental potential of both
                                    experiments not yet fully exploited:
                                    more studies on additional triggers,
                                    tagging.


ATLAS-CMS                                                                    21
         Potential for Rare decays
  B  mm              Will measure branching ration of Bs  mm which is in SM of
                      order Br < (10-9 Perform high sensitivity search on Bd  mm

                                        A study proved good performance at nominal LHC
                                        luminosity. After 1 year 1034cm-2 s-1
                                                          Signal Signal        BG
  Before LHC                                              Bs->mm Bd->mm
Bmm can be seen before LHC                    CMS        26      4            <6.4
only if drastically enhanced.
                                               ATLAS      92      14           660
    BK*mm will be measured
but mass and angular
distributions detailed enough to        3 years at 1033cm-2 s-1
show New Physics only at LHC.                               Signal        BG
                                                            Bs->mm
                                                 CMS        21            3
                                                 ATLAS      27            93

                                       Different conclusions about BG: 1.CMS - already
                                       exploit isolation cuts in calorimetry 2. Different
  ATLAS-CMS                               assumptions about tails in VTX resolution.      22
       Exclusive Rare decays of B mesons
 ATLAS statistics will allow angular analyses that can carry
 evidence for new physics. E.g. forward-backward
 asymmetry:       Bd-  K 0*m +m -
                                                1                               0

                                                                               
                                          1            d G
                                                         2
                                                                                        d 2G
                              A s
                                FB( ) 
                                        dG ds
                                                                  d cos(q ) -                      d cos(q )
                                                    dsd cos(q )                      dsd cos(q )
                                                0                               -1
                        Three points: mean values
                        of AFB in three q2/MB2
                        experimental regions with
                        error bars                           Lowest mass region:
                                      SM                     sufficient accuracy to
                                                             separate SM and MSSM if
                                      MSSM C7g >0
                                                             Wilson coefficient C7g <0
                                      MSSM C7g <0




ATLAS-CMS                                                                                             23
other studies of ATLAS, CMS b-physics group

Undergoing physics studies not mentioned here:
1.   Double heavy flavor mesons (b,c)
2.   QCD tests of beauty production at LHC central region. Correlations bb.
3.   Physics of Beauty baryons, production polarizations, decays.
4.   Rare decays of b  s gamma.
5.   Rare decays of L b  L mm




 ATLAS-CMS                                                                    24
ATLAS, CMS b-physics-related software

1.   ATLAS, CMS – B-related online software under development: reconstruction
     Algorithms, trigger simulations.
2.   ATLAS: offline MC simulation, reconstruction software, physics analyses
     software.
     •   Within a successful Data Chalenges-1 period 2002-2003 B-physics group
         studied B-performance for the Final version of detector layout.
     •   Data Chalenges-2 started 2004: grid production, Geant 4, databases, new
         Event Model
3.   ATLAS, CMS: B-event Generators software
     •   For bb production we use Pythia tuned to Tevatron data. Herwig – we
         never tried. NLOQCD ( MNR code) does not give whole events.
     •   Installation of B-decays dedicated package ‘EvtGen’ in common use and
         development with BaBar (main developer) , LHCb, CDF, D0.


 ATLAS-CMS                                                                         25
B-physics prospects with ATLAS, CMS - conclusions

1.   General purpose central LHC detectors are preparing a multi thematic B-
     physics program - including B-decays and B-production.
2.   ATLAS, CMS B-physics trigger strategy rely on dimuon trigger for luminosity
     2*1033 cm-2s-1 - extend selection menue at lower luminosities when there is
     spare processing capacity.
3.   In CP violation the main emphasis will be on underlying mechanisms and
     evidence of New physics. ATLAS, CMS is especially precise in measurement of
     . LHC ‘gold-platted’ mode is also Bs  J/y f
4.   Rare decays B  mm have the most favorable experimental signature allowing
     to measure also at nominal LHC luminosity 1034cm-2 s-1. Will measure
     branching ration of Bs  mm and sensitivity test for Bd  mm . Precision
     measurements will be done for B  K*mm.
5.   Beauty production at central LHC collisions will be measured for QCD tests.



 ATLAS-CMS                                                                         26

				
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