##### Document Text Contents

Page 1

CERN-OPEN-2008-020

December 2008

Expected Performance of the ATLAS Experiment

Detector, Trigger and Physics

The ATLAS Collaboration

A detailed study is presented of the expected performance of the

ATLAS detector. The reconstruction of tracks, leptons, photons,

missing energy and jets is investigated, together with the performance

of b-tagging and the trigger. The physics potential for a variety of

interesting physics processes, within the Standard Model and beyond, is

examined. The study comprises a series of notes based on simulations

of the detector and physics processes, with particular emphasis given to

the data expected from the first years of operation of the LHC at CERN.

Page 926

[GeV]QuarkE

50 100 150 200 250 300 350 400

)

Q

ua

rk

/E

Je

t

)/m

ea

n(

E

Q

ua

rk

/E

Je

t

(E

σ

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

ATLAS

R=0.40 Tower∆Cone

R=0.70 Tower∆Cone

Kt R=0.40 Tower

Kt R=0.60 Tower

Figure 2: Energy resolution for jets from light quarks (integrated over all η values), as a function

of the quark energy, for various jet algorithms (events simulated without pileup).

W-boson mass is shown in Figure 10.

To obtain mass values from the invariant mass spectra of Figure 10, the sum of a Gaussian and a

4th degree Chebychev polynomial is fitted to the distribution. The polynomial describes the background

from wrong jet combinations and from background events, whereas the mean value of the Gaussian and

its error are interpreted as the mass (mW) and its statistical error, σstat . The width of the Gaussian is

referred to as σGauss. Table 2 shows the obtained W-boson mass with the E recombination scheme for

various choices of the kT parameters.

The error resulting from 1% variation on the jet energy scale (JES) is obtained by varying the recon-

structed jet energies by ±1% followed by a linear fit across the three W-boson masses (-1%, nominal

value, +1%).

With increasing R and Dcut parameter values, the reconstructed W-boson (and also top quark) mass

rise monotonically. Higher parameter values lead to fewer but more energetic jets and thus their com-

bination has a higher invariant mass. Part of this effect could in principle be absorbed by the in-situ

calibration, but on the other hand, the event is more likely to be misreconstructed due to unwanted jet

merging, which makes the choice of the three jets maximizing the pT-sum unpredictable.

The efficiencies quoted in Table 2, defined as the number of events in the gaussian part of the mass

distribution divided by the initial number of events, which can be as high as 5.8%, drop to less than 4%

when the jets become too big.

Table 2 also shows the purity of the W-boson reconstruction, defined as the fraction of events in the

gaussian part of the distribution, in the range [−1σgaus, 1σgaus] from the mean value of the gaussian fit.

A purity around 64% can be obtained with some choices of the algorithms / parameters, for example

cone 0.4 or kT with R = 0.4, whereas other choices may lead to purities about 15% smaller.

This study indicates that, for the W-boson mass reconstruction in tt̄ events, the cone 0.4 algorithm

5

TOP – JETS FROM LIGHT QUARKS IN tt̄ EVENTS

33

902

Page 927

[GeV]QuarkE

50 100 150 200 250 300 350 400

)

Q

ua

rk

(M

C

J

et

)

/E

Je

t

)/m

ea

n(

E

Q

ua

rk

(M

C

J

et

)

/E

Je

t

(Eσ

0.05

0.1

0.15

0.2

0.25

ATLAS

R=0.40 Tower Quark-Jet∆Cone

R=0.70 Tower Quark-Jet∆Cone

R=0.40 Tower Monte Carlo Jet-Jet∆Cone

R=0.70 Tower Monte Carlo Jet-Jet∆Cone

Figure 3: Comparison of the jet energy resolutions with respect to the Monte Carlo hadrons

(“Monte Carlo jets”) and with respect to the initial quarks from the W-boson decay, for events

simulated without pileup.

[GeV]QuarkE

50 100 150 200 250 300 350 400

)

Q

ua

rk

/E

Je

t

)/m

ea

n(

E

Q

ua

rk

/E

Je

t

(E

σ

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

ATLAS

R=0.40 Topo∆Cone

R=0.40 Tower∆Cone

R=0.40 Topo with PileUp∆Cone

R=0.40 Tower with PileUp∆Cone

Figure 4: Comparison of the jet energy resolutions for events simulated with and without pile-up.

6

TOP – JETS FROM LIGHT QUARKS IN tt̄ EVENTS

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903

Page 1851

[7] Particle Data Group Collaboration, W. M. Yao et al., J. Phys. G33 (2006) 1–1232.

[8] S. Dimopoulos and G. L. Landsberg, Phys. Rev. Lett. 87 (2001) 161602,

arXiv:hep-ph/0106295.

[9] S. Hossenfelder, arXiv:hep-ph/0412265.

[10] P. Kanti, Int. J. Mod. Phys. A19 (2004) 4899–4951, arXiv:hep-ph/0402168.

[11] X. Calmet and S. D. H. Hsu, arXiv:0711.2306 [hep-ph].

[12] E. G. Adelberger, B. R. Heckel, and A. E. Nelson, Ann. Rev. Nucl. Part. Sci. 53 (2003) 77–121,

arXiv:hep-ph/0307284.

[13] P. Shukla and A. K. Mohanty, Pramana 60 (2002) 1117–1120, arXiv:hep-ph/0201029.

[14] CDF Collaboration, A. Abulencia et al., Phys. Rev. Lett. 97 (2006) 171802,

arXiv:hep-ex/0605101.

[15] ALEPH Collaboration, arXiv:hep-ex/0212036.

[16] S. Mele and E. Sanchez, Phys. Rev. D61 (2000) 117901, arXiv:hep-ph/9909294.

[17] D0 Collaboration, D0 Note 4336 (2004) .

[18] S. Hannestad and G. G. Raffelt, Phys. Rev. D67 (2003) 125008, arXiv:hep-ph/0304029.

[19] M. Casse, J. Paul, G. Bertone, and G. Sigl, Phys. Rev. Lett. 92 (2004) 111102,

arXiv:hep-ph/0309173.

[20] M. Fairbairn, Phys. Lett. B508 (2001) 335–339, arXiv:hep-ph/0101131.

[21] M. Fairbairn and L. M. Griffiths, JHEP 02 (2002) 024, arXiv:hep-ph/0111435.

[22] N. Kaloper, J. March-Russell, G. D. Starkman, and M. Trodden, Phys. Rev. Lett. 85 (2000)

928–931, arXiv:hep-ph/0002001.

[23] K. R. Dienes, Phys. Rev. Lett. 88 (2002) 011601, arXiv:hep-ph/0108115.

[24] G. F. Giudice, T. Plehn, and A. Strumia, Nucl. Phys. B706 (2005) 455–483,

arXiv:hep-ph/0408320.

[25] L. A. Anchordoqui, J. L. Feng, H. Goldberg, and A. D. Shapere, Phys. Rev. D68 (2003) 104025,

arXiv:hep-ph/0307228.

[26] L. A. Anchordoqui, J. L. Feng, H. Goldberg, and A. D. Shapere, Phys. Rev. D65 (2002) 124027,

arXiv:hep-ph/0112247.

[27] R. C. Myers and M. J. Perry, Ann. Phys. 172 (1986) 304.

[28] J. Pumplin et al., JHEP 07 (2002) 012, arXiv:hep-ph/0201195.

[29] M. R. Whalley, D. Bourilkov, and R. C. Group, arXiv:hep-ph/0508110.

[30] C. M. Harris and P. Kanti, JHEP 10 (2003) 014, arXiv:hep-ph/0309054.

[31] D. M. Gingrich, JHEP 11 (2007) 064, arXiv:0706.0623 [hep-ph].

25

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Page 1852

[32] C. M. Harris, P. Richardson, and B. R. Webber, JHEP 08 (2003) 033, arXiv:hep-ph/0307305.

[33] D. M. Gingrich, arXiv:hep-ph/0610219.

[34] G. Marchesini et al., Comput. Phys. Commun. 67 (1992) 465–508.

[35] G. Corcella et al., JHEP 01 (2001) 010, arXiv:hep-ph/0011363.

[36] D. F. E. Richter-Was and L. Poggioli, ATLAS Physics Note ATL-Phys-98-131 .

[37] J. Collins, Phys. Rev. D65 (2002) 094016, arXiv:hep-ph/0110113.

[38] T. Sjostrand, S. Mrenna, and P. Skands, JHEP 05 (2006) 026, arXiv:hep-ph/0603175.

[39] M. L. Mangano, M. Moretti, F. Piccinini, R. Pittau, and A. D. Polosa, JHEP 07 (2003) 001,

arXiv:hep-ph/0206293.

[40] J. P. Ottersbach, Diploma Thesis, Bergische Universitaet Wuppertal WU D 07-10 (2007) .

[41] G. C. Fox and S. Wolfram, Nucl. Phys. B149 (1979) 413.

[42] S. Brandt and H. D. Dahmen, Zeit. Phys. C1 (1979) 61.

[43] ATLAS Collaboration, CERN/LHCC 98-15 (1998) .

[44] ATLAS Collaboration, “Trigger for Early Running.” This volume.

[45] ATLAS Collaboration, “Reconstruction and Identification of Electrons.” This volume.

[46] C. M. Harris et al., JHEP 05 (2005) 053, arXiv:hep-ph/0411022.

[47] J. Tanaka, T. Yamamura, S. Asai, and J. Kanzaki, Eur. Phys. J. C41 (2005) 19–33,

arXiv:hep-ph/0411095.

26

EXOTICS – DISCOVERY REACH FOR BLACK HOLE PRODUCTION

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1828

CERN-OPEN-2008-020

December 2008

Expected Performance of the ATLAS Experiment

Detector, Trigger and Physics

The ATLAS Collaboration

A detailed study is presented of the expected performance of the

ATLAS detector. The reconstruction of tracks, leptons, photons,

missing energy and jets is investigated, together with the performance

of b-tagging and the trigger. The physics potential for a variety of

interesting physics processes, within the Standard Model and beyond, is

examined. The study comprises a series of notes based on simulations

of the detector and physics processes, with particular emphasis given to

the data expected from the first years of operation of the LHC at CERN.

Page 926

[GeV]QuarkE

50 100 150 200 250 300 350 400

)

Q

ua

rk

/E

Je

t

)/m

ea

n(

E

Q

ua

rk

/E

Je

t

(E

σ

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

ATLAS

R=0.40 Tower∆Cone

R=0.70 Tower∆Cone

Kt R=0.40 Tower

Kt R=0.60 Tower

Figure 2: Energy resolution for jets from light quarks (integrated over all η values), as a function

of the quark energy, for various jet algorithms (events simulated without pileup).

W-boson mass is shown in Figure 10.

To obtain mass values from the invariant mass spectra of Figure 10, the sum of a Gaussian and a

4th degree Chebychev polynomial is fitted to the distribution. The polynomial describes the background

from wrong jet combinations and from background events, whereas the mean value of the Gaussian and

its error are interpreted as the mass (mW) and its statistical error, σstat . The width of the Gaussian is

referred to as σGauss. Table 2 shows the obtained W-boson mass with the E recombination scheme for

various choices of the kT parameters.

The error resulting from 1% variation on the jet energy scale (JES) is obtained by varying the recon-

structed jet energies by ±1% followed by a linear fit across the three W-boson masses (-1%, nominal

value, +1%).

With increasing R and Dcut parameter values, the reconstructed W-boson (and also top quark) mass

rise monotonically. Higher parameter values lead to fewer but more energetic jets and thus their com-

bination has a higher invariant mass. Part of this effect could in principle be absorbed by the in-situ

calibration, but on the other hand, the event is more likely to be misreconstructed due to unwanted jet

merging, which makes the choice of the three jets maximizing the pT-sum unpredictable.

The efficiencies quoted in Table 2, defined as the number of events in the gaussian part of the mass

distribution divided by the initial number of events, which can be as high as 5.8%, drop to less than 4%

when the jets become too big.

Table 2 also shows the purity of the W-boson reconstruction, defined as the fraction of events in the

gaussian part of the distribution, in the range [−1σgaus, 1σgaus] from the mean value of the gaussian fit.

A purity around 64% can be obtained with some choices of the algorithms / parameters, for example

cone 0.4 or kT with R = 0.4, whereas other choices may lead to purities about 15% smaller.

This study indicates that, for the W-boson mass reconstruction in tt̄ events, the cone 0.4 algorithm

5

TOP – JETS FROM LIGHT QUARKS IN tt̄ EVENTS

33

902

Page 927

[GeV]QuarkE

50 100 150 200 250 300 350 400

)

Q

ua

rk

(M

C

J

et

)

/E

Je

t

)/m

ea

n(

E

Q

ua

rk

(M

C

J

et

)

/E

Je

t

(Eσ

0.05

0.1

0.15

0.2

0.25

ATLAS

R=0.40 Tower Quark-Jet∆Cone

R=0.70 Tower Quark-Jet∆Cone

R=0.40 Tower Monte Carlo Jet-Jet∆Cone

R=0.70 Tower Monte Carlo Jet-Jet∆Cone

Figure 3: Comparison of the jet energy resolutions with respect to the Monte Carlo hadrons

(“Monte Carlo jets”) and with respect to the initial quarks from the W-boson decay, for events

simulated without pileup.

[GeV]QuarkE

50 100 150 200 250 300 350 400

)

Q

ua

rk

/E

Je

t

)/m

ea

n(

E

Q

ua

rk

/E

Je

t

(E

σ

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

0.26

0.28

ATLAS

R=0.40 Topo∆Cone

R=0.40 Tower∆Cone

R=0.40 Topo with PileUp∆Cone

R=0.40 Tower with PileUp∆Cone

Figure 4: Comparison of the jet energy resolutions for events simulated with and without pile-up.

6

TOP – JETS FROM LIGHT QUARKS IN tt̄ EVENTS

34

903

Page 1851

[7] Particle Data Group Collaboration, W. M. Yao et al., J. Phys. G33 (2006) 1–1232.

[8] S. Dimopoulos and G. L. Landsberg, Phys. Rev. Lett. 87 (2001) 161602,

arXiv:hep-ph/0106295.

[9] S. Hossenfelder, arXiv:hep-ph/0412265.

[10] P. Kanti, Int. J. Mod. Phys. A19 (2004) 4899–4951, arXiv:hep-ph/0402168.

[11] X. Calmet and S. D. H. Hsu, arXiv:0711.2306 [hep-ph].

[12] E. G. Adelberger, B. R. Heckel, and A. E. Nelson, Ann. Rev. Nucl. Part. Sci. 53 (2003) 77–121,

arXiv:hep-ph/0307284.

[13] P. Shukla and A. K. Mohanty, Pramana 60 (2002) 1117–1120, arXiv:hep-ph/0201029.

[14] CDF Collaboration, A. Abulencia et al., Phys. Rev. Lett. 97 (2006) 171802,

arXiv:hep-ex/0605101.

[15] ALEPH Collaboration, arXiv:hep-ex/0212036.

[16] S. Mele and E. Sanchez, Phys. Rev. D61 (2000) 117901, arXiv:hep-ph/9909294.

[17] D0 Collaboration, D0 Note 4336 (2004) .

[18] S. Hannestad and G. G. Raffelt, Phys. Rev. D67 (2003) 125008, arXiv:hep-ph/0304029.

[19] M. Casse, J. Paul, G. Bertone, and G. Sigl, Phys. Rev. Lett. 92 (2004) 111102,

arXiv:hep-ph/0309173.

[20] M. Fairbairn, Phys. Lett. B508 (2001) 335–339, arXiv:hep-ph/0101131.

[21] M. Fairbairn and L. M. Griffiths, JHEP 02 (2002) 024, arXiv:hep-ph/0111435.

[22] N. Kaloper, J. March-Russell, G. D. Starkman, and M. Trodden, Phys. Rev. Lett. 85 (2000)

928–931, arXiv:hep-ph/0002001.

[23] K. R. Dienes, Phys. Rev. Lett. 88 (2002) 011601, arXiv:hep-ph/0108115.

[24] G. F. Giudice, T. Plehn, and A. Strumia, Nucl. Phys. B706 (2005) 455–483,

arXiv:hep-ph/0408320.

[25] L. A. Anchordoqui, J. L. Feng, H. Goldberg, and A. D. Shapere, Phys. Rev. D68 (2003) 104025,

arXiv:hep-ph/0307228.

[26] L. A. Anchordoqui, J. L. Feng, H. Goldberg, and A. D. Shapere, Phys. Rev. D65 (2002) 124027,

arXiv:hep-ph/0112247.

[27] R. C. Myers and M. J. Perry, Ann. Phys. 172 (1986) 304.

[28] J. Pumplin et al., JHEP 07 (2002) 012, arXiv:hep-ph/0201195.

[29] M. R. Whalley, D. Bourilkov, and R. C. Group, arXiv:hep-ph/0508110.

[30] C. M. Harris and P. Kanti, JHEP 10 (2003) 014, arXiv:hep-ph/0309054.

[31] D. M. Gingrich, JHEP 11 (2007) 064, arXiv:0706.0623 [hep-ph].

25

EXOTICS – DISCOVERY REACH FOR BLACK HOLE PRODUCTION

133

1827

Page 1852

[32] C. M. Harris, P. Richardson, and B. R. Webber, JHEP 08 (2003) 033, arXiv:hep-ph/0307305.

[33] D. M. Gingrich, arXiv:hep-ph/0610219.

[34] G. Marchesini et al., Comput. Phys. Commun. 67 (1992) 465–508.

[35] G. Corcella et al., JHEP 01 (2001) 010, arXiv:hep-ph/0011363.

[36] D. F. E. Richter-Was and L. Poggioli, ATLAS Physics Note ATL-Phys-98-131 .

[37] J. Collins, Phys. Rev. D65 (2002) 094016, arXiv:hep-ph/0110113.

[38] T. Sjostrand, S. Mrenna, and P. Skands, JHEP 05 (2006) 026, arXiv:hep-ph/0603175.

[39] M. L. Mangano, M. Moretti, F. Piccinini, R. Pittau, and A. D. Polosa, JHEP 07 (2003) 001,

arXiv:hep-ph/0206293.

[40] J. P. Ottersbach, Diploma Thesis, Bergische Universitaet Wuppertal WU D 07-10 (2007) .

[41] G. C. Fox and S. Wolfram, Nucl. Phys. B149 (1979) 413.

[42] S. Brandt and H. D. Dahmen, Zeit. Phys. C1 (1979) 61.

[43] ATLAS Collaboration, CERN/LHCC 98-15 (1998) .

[44] ATLAS Collaboration, “Trigger for Early Running.” This volume.

[45] ATLAS Collaboration, “Reconstruction and Identification of Electrons.” This volume.

[46] C. M. Harris et al., JHEP 05 (2005) 053, arXiv:hep-ph/0411022.

[47] J. Tanaka, T. Yamamura, S. Asai, and J. Kanzaki, Eur. Phys. J. C41 (2005) 19–33,

arXiv:hep-ph/0411095.

26

EXOTICS – DISCOVERY REACH FOR BLACK HOLE PRODUCTION

134

1828