B and onia prodution in ATLAS
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Transcript of B and onia prodution in ATLAS
B and onia prodution in ATLAS
Else Lytken (CERN)
On behalf of the ATLAS collaboration
HERA-LHC workshop May 2008
E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 2
B and onia production in ATLAS
Measure cross sections at new energy , d/dpT, d/d(), d/d
B physics a window for new discoveries Observe rare decays, measure CP violation
parameters Detailed understanding of the bb
spectrum as background to other processes.
Commissioning/early physics: calibration, alignment, trigger efficiencies etc.
¯
¯
Take advantage of copious bb production at 14 TeV: (bb) ~500 b
_
Overlap
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Early physics with b’s and onia Focus of this talk is on the measurements during
commissioning phase/early physics: Linst = 1031 – 1032 cm-2s-1
Production of B’s and the quarkonia narrow resonances gives us a handle for first performance measurements complementary to and extending other SM “standard candles” such as W’s and Z’s. For instance crucial for Higgs and SUSY searches to
understand our performance with lower pT leptons Lower luminosities means lower pT trigger thresholds possible,
both for electrons and muons Given the high rates our trigger menus have the flexibility
to account for different luminosity scenarios
E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 4
~200 Hz
~1-2 kHz
Initial triggers: relevant examples
L2: confirm L1 signal + additional search in regions of interestEF: offline algorithms for final selection
2.5 s
40 ms
PS Rate (kHz) PS Rate (kHz)
Electrons
EM3 60 ~0.7 600 ~0.7
2EM3 1 ~6.5 10 ~6.5
Muons
MU6 1 ~0.6 1 ~6.4
MU10 1 ~0.3 1 ~3.6
2MU4 1 ~0.1 1 ~0.7
MU6JET10 10 ~1 100 ~1
L=1031 L=1032
For initial low luminosities can trigger on both low pT electrons and muons.Expected L1 rates and prescale factors:
4 s
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Inclusive b production cross section: +b-jet
fb found from fitting transverse relative pT to templates:
Transverse relative pT (GeV)
btrig =13.5%
brec = 85%
With 15 pb-1 such a fit gives us:
fbackgr = 77 ± 4 % (c; ,K )
fb = 23 ± 2 % (b ; bc )
ATLAS
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Inclusive cross section: dimuonsTo distinguish bb J/ X (indirect J/) from ppJ/ (prompt J/’s, ~ 2 ) Useful variable: the (pseudo-) proper time:
cJp
MLt
T
Jxy
)/(/
Lxy = transverse
decay length
_
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B measurements using excl. channels Due to high cross sections and dedicated triggers we can
reconstruct exclusive channels in early data Reconstruction of the mass and lifetime of the B± meson from B± J/ K± decay very useful for calibration and alignment performance.
Results with 10 pb-1: (mB+) = 42.2 ± 1.3 MeV (total) = 29.8 ± 0.84 %
Requirements: - dimuon trigger- displaced vertex (100 μm) - add. track with pT 1.5 GeV- track and μμ fit to same vertex- m(μμ,track) within 120 MeV of B+ mass.
ATLAS
T
xy
p
mL
E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 8
B cross section with excl. channels
Channel N (100 pb-1)
B+ J/ K+ 17000
B0 J/ K0* 8700
Bs J/ 900
b J/ 260
Available statisitics with 100 pb-1:
Measurement of dB/pT using B+J/ K+ after 10 pb-1:
10<pT<18 18<pT<26 26<pT<34 34<pT<42 10<pT<42
7.7 6.9 10.5 13.9 4.3
16.1 15.8 17.6 19.8 14.8Total uncertainty (%)
(GeV)
Acceptance + stat. (%)
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Quarkonia Among first measurements
+ theoretical interest: What is the production mechanism?
The Color Octet Mechanism agrees well with measured shape from Tevatron Polarization measurements:CDF sees no sign of pol. for J/, and DØ (1S) measurements not consistent with predictions.
More data with high-pT needed!
Coloroctet
Color singlet
Tevatron data
NRQCD
(1s)
J/
kT factorization model
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Quarkonia in ATLAS: J/ e+e-
Min bias ppJ/(ee)pp(ee)(1S)ppDrell-Yan(ee)
@ L1 trigger
L1 (trig) ~ 27%L2, EF under optimization
Initial data: take advantage of electron trigger paths as wellCurrent studies using 2EM3 Single-e triggers under investigationLater data (“low luminosity”, L=1033cm-2s-1) has to rely on single-μ b trigger also for J/(ee)X, (ee)X
N(J/) after L1: 4.2 M events
N() after L1: 1.2 M events
1031 cm-2s-1
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J/ e+e-
Two electron id methods explored: Low pT version of standard ATLAS
isolated electron cut based on shower shapes, associated to high quality tracks with E/p >0.7, conversion veto, and transition radiation hits
Less efficient for electrons from b’s
2nd method (pT 2 GeV/c) extrapolates in narrow window to calorimeter and uses likelihood ratio (similar variables)
After offline selection 100 pb-1: ~230k J/’s and ~43k ’s Expect to measure m(J/) to ~0.6%
N = # good pion tracks
Ne = same + misid. as e’s
R = N / Ne
“b-electrons”
L1 + offline selection
Mee (GeV)
d/
dm
(n
b/0
.5G
eV
)
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J/ μ+μ-
Current studies use a combination dimuon trigger, (trig) = 87% L1, 97% L2, with analysis cuts of 6 and 4 GeV
Rate 1 Hz expected at EF for all quarkonium μμ (incl ’, (2,3S) )
L1 combined L2 combined
J/ J/
10
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Dimuons: ResultsRequire: muons from same vertex and proper time < 0.2 ps
With pT1 6 GeV, pT2 4 GeV:
15k J/’s per 1 pb-1
2.5k ’s (1S) 1-2 days with L = 1031cm-2s-1
Bkg w/overtex cuts
With 10 pb-1: S/B = 60 for J/ and 10 for d/dpT ~ 1 % for J/ , ~5 % for
10 pb-1: also measurement of c J/()
~ 1 fb-1: b ()
E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 14
Polarization P(J/)P(-)
P(+)
*
Dimuon triggers: little or no information for high cos*Single-: combined with 0.5 GeV track gives access to these values (~ pT range but larger pT(+,-) )Single-u trigger => larger background Still: S/B = 1.2 (J/) and 0.05 (Upsilon)
6410+t
Measure high-pT polarization to distinguish production models
*2*
cos1cos
d
dN
x103
Combine and fit to measured distribution in slices of pT
Shown: 12 pT 13 GeV
Long. pol.( = -1)
Trvs. pol.( = +1)
ATLAS
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J/* = ATLAS~10 pb-1
* *** *
0.8 fb-1
Polarization resultsAlready with 10 pb-1: measure J/ pol. to same precision as TeV with 1.3 fb-1 - but with interesting high pT data!Same precision for polarization studies can be reached after ~100 pb-1
Crude superimpose of ATLAS stat uncertainties with 10 pb-1 assuming =0 :
NRQCD
*
*
*
*
* = ATLAS~10 pb-1
*
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Quarkonia as a monitoring tool Offline and online monitoring with
J/’s and ’s important to have a low pT data point in addition to Z’s
Given the large statistics expected should be able to use this already in the beginning
Check mass shift as a function of pT:
momentum scale, energy loss curvature diff:
detector misalignments and :
magnetic field, material effects
6 pb-1
1 week w. L=1031
Perfect alignment
Example of identifying a problem
E. Lytken (ATLAS Collaboration) HERA-LHC workshop May 2008 17
Summary and outlook
ATLAS well prepared for B and quarkonia cross section measurements in initial low luminosity period
Early data studies will also help us during commissioning For cross section measurements already enough statistics with
the early data! (10 pb-1 or less) Key measurements based on muon triggers but in initial period
will also have electron channels for comparison Stay tuned for the next chapter in J/ and Upsilon high-pT
polarization measurements!
Backup
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Single-muon trigger: S/BMost relevant for J/ studies …
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Polarization measurement
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More on polarization
Resolution of reconstructed cos* is ~0.0015
Combined measurement Unpolarized 17<pT <21 GeV
J/
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AcceptancepT cuts (trigger and offline) means pT(J/) 10 GeV, whereas non-zero A for Upsilons also at ~0RoI’s based on trigger towers of
x ~ 0.1 x 0.1 R separation between leptons also
affects sensitivity to material effects
J/
Upsilon(6,4)-cuts
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Electron efficiencies
“standard cuts”“b electrons”
Efficiency of single electronsbased on MC truth
(EM3:e5;e5)
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Inclusive b productionAfter fit
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The 3 production mechanisms
NLO: Gluon splitting
NLO: Flavour excitation, sensitive to PDF’s
LO: Flavour creation