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Measurements of forward physics in the TOTEM experiment at the LHC
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Measurements of forward physics in the TOTEM experiment at the LHC

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  1. Measurements of forward physics in the TOTEM experiment at the LHC High Energy Physics Seminar EPFL, Lausanne 26 November 2012 Hubert Niewiadomski CERN, on behalf of the the TOTEM collaboration

  2. Outlook • TOTEM Experiment • LHC Special Runs and TOTEM Data • pp Elastic Scattering Differential Cross-Section • Total, Elastic, Inelastic Cross-Sections @ √s = 7-8 TeV • Perspectives on Forward and Diffractive Physics Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  3. TOTEM EXPERIMENT Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  4. jet b jet TOTEM Physics Overview Total cross-section Elastic Scattering Forward physics Diffraction: soft (and hard with CMS) Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  5. Inelastic telescopes: charged particle vertex reconstruction in inelastic events T1: 3.1 <  < 4.7 T2: 5.3 <  < 6.5 HF (CMS) IP5 10 m T1 CASTOR (CMS) 14 m T2 Experimental Setup @ IP5 Roman Pots: measure elastic & diffractive protons close to outgoing beam IP5 RP147 RP220 Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  6. Forward trackers in TOTEM(with trigger capability) T1 (CSC) T2 (GEM) Fully installed, operational and providing trigger

  7. 24 Roman Pot detectors Microstrip silicon detectors inside a Roman Pot Fully installed and operational Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  8. Accelerator Optics Lattice between IP5 and RP220 • 6 quardupole magnets (Q1-Q5) • Dipoles, correctors, drift spaces Optics is defined by the lattice elements Ti, for e.g. focusing magnet transport matrix: Proton transport IP5  Roman Pot Measured in Roman Pots input prot. output prot. RP147 Reconstructed RP220 RP IP5 k() – magnet strength, l – length, =p/p Optics carefully optimised for TOTEM special runs

  9. TOTEM Collaboration • Countries: 7 • Institutes: 15 • Collaborators: 100 • Authors: 80 • Construction: 7 MCHF Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  10. LHC SPECIAL RUNS AND TOTEM DATA Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  11. First pp Elastic Scattering Event Candidates [LPCC July 2010] s = 7 TeV * = 3.5 m 2010 Data from Runs with RPs at 25s (1.5nb-1) Event scanning and analysis of constraints

  12. Large-t pp Elastic Scattering 100 Events (80nb-1) [LHCC Sep 2010] s = 7 TeV * = 3.5 m 2010 Data from Runs with RPs at 20s (total 185nb-1)

  13. Special run: 1st run with the b*=90 m optics and RP insertion, June 2011 Un-squeeze from injection optics b* = 11m to 90m Request of TOTEM (2005) Very robust optics with high precision • Two bunches with 1 and 2 x 1010 protons / bunch • Instantaneous luminosity: 8 x 1026 cm-2 s-1 • Integrated luminosity: 1.7 mb-1 • Estimated pile-up: ~ 0.5 % • Vertical Roman Pots at 10 s from beam center • Trigger rate : ~ 50 Hz • Recorded events in vertical Roman Pots: 66950 At the end of machine development 0.5 hours data taking by TOTEM Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  14. Runs & Data Statistics 2010-2011 Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  15. Runs & Data 2012 • Joint data-taking TOTEM-CMS @ √s = 8 TeV • 25 M events, 43nb-1 • Special optics b* 90m (July 2012) : 100 bunches • Bi-directional exchange of triggers (via new TOTEM electrical trigger) • TOTEM triggers on RP pp coincidences  full CMS readout • CMS triggers on di-jets  TOTEM RPs readout for protons signature • Ideal for studies of diffraction • *=1km optics runs + pPb ion runs (to come) Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  16. PP ELASTIC SCATTERING DIFFERENTIAL CROSS-SECTION Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  17. Proton reconstruction • Both angle projections reconstructed: Θx* and Θy* • Θx* fromΘx @ RP220 (through dLx/ds) Θx = dLx/ds Θx* • Θy* from y @ RP220 (through Ly) y = LyΘy* • → Fine alignment • Alignment between pots with overlapping tracks (1μm) • Alignment with respect to the beam – scraping exercise (20μm) • Mechanical constraints between top and bottom pots (10μm) • → Excellent optics understanding • Magnet currents measured • Measurements of optics parameters with elastic scatt. • Θleft* = Θright* (proton pair collinearity) • Proton position↔angle correlations • Lx=0 determination, coupling corrections Track based alignment Generally a difficult measurement, data driven analysis

  18. Optics systematic errors • In reality, due to machine imperfections, the transport matrix of each element is altered by Ti • Machine tolerances and imperfections leading to Ti • Beam momentum offset (p/p = 10-3) • Magnet transfer function error, IB, (B/B = 10-3) • Magnet rotations and displacements ( < 1mrad, x, y < 0.5mm, WISE database) • Power converter errors, kI, (I/I < 10-4) • Magnet harmonics (B/B = O(10-4) @ Rref= 17mm, WISE database) • Final transport matrix is a product of all the components (Ti + Ti) • The elements of TIP5RP220 are correlated and cannot take arbitrary values (Liouville’s theorem) • Measurements of some of the elements constrain the values of the others • Moreover, TOTEM uses 2 beams independently  more constraints – magnet imperfections – values needed for prot. reconstr.

  19. Optics reconstruction • Measured correlations between optical functions fitted, magnets’ strength altered within tolerance constraints • Principle Component Analysis (PCA) applied • Numerical method developed within MAD-X • Full nonlinear fitting with harmonics and displacements. • Mean pull = 0.043 • Pull RMS = 0.86 1 1 1.5 1.5 2 2

  20. MC verification of optics reconstruction Lengthy and difficult -beating measurements no longer critical ! Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  21. Cuts and data reduction • Topology • near and far units • diagonals • Low || selection (3σ) • |xRP,45|<3σx @Lx,45=0 • |xRP,56|<3σx @Lx,56=0 • corr. yRP216,45  yRP220,45 • corr. yRP216,56 yRP220,56 • Elastic collinearity (3σ) • θx,45* θx,56* • θy,45* θy,56* Intergrated luminosity : 6.2 nbarn-1 showers • Diagonals analysed independently Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  22. Proton tracks of a single diagonal(left-right coincidences) t = -p2q2 Sector 56 x = Dp/p y = LyQy x = LxQx + xD Lx ~ 0 Sector 45

  23. Cuts and data reduction • Topology • near and far units • diagonals • Low || selection (3σ) • |xRP,45|<3σx @Lx,45=0 • |xRP,56|<3σx @Lx,56=0 • corr. yRP216,45  yRP220,45 • corr. yRP216,56 yRP220,56 • Elastic collinearity (3σ) • θx,45* θx,56* • θy,45* θy,56* Intergrated luminosity : 6.2 nbarn-1 showers Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  24. Low  = Dp/p cuts yRP near,45  yRP far,45 (dLy/ds0) |x| < 3σx @ Lx = 0 Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  25. Cuts and data reduction • Topology • near and far units • diagonals • Low || selection (3σ) • |xRP,45|<3σx @Lx,45=0 • |xRP,56|<3σx @Lx,56=0 • corr. yRP216,45  yRP220,45 • corr. yRP216,56 yRP220,56 • Elastic collinearity (3σ) • θx,45* θx,56* • θy,45* θy,56* Intergrated luminosity : 6.2 nbarn-1 showers Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  26. Elastic collinearity cuts background signal background signal Data outside the 3σ cuts used for background estimation Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  27. Background and resolution determination –– signal –– background –– combined B/S = (8±1)% σ*=17.8rad (beam divergence) Data Combined background (t) -t [GeV2] θx/sqrt(2) Signal to background normalisation Signal vs. background (t) (also as a function of θy) σ(*) → t-reconstruction resolution: |t|=0.4GeV2: B/S = (11±2)% |t|=0.5GeV2: B/S = (19±3)% |t|=1.5GeV2: B/S = (0.8±0.3)%

  28. ty-acceptancecorrections |t|<0.36GeV2excluded from analysis |ty| (diagonal 1) Beam divergence |ty| (diagonal 2) Missing acceptance inθy* Correctionerror (ty): 0.31 GeV2 : 30% 0.33 GeV2 : 11% 0.35 GeV2 : 2% 0.4 GeV2 : 0.8% 0.5 GeV2 : 0.1% Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  29. -acceptance correction Total -acceptancecorrection Accepted (t) Diagonal 1 1 2 3 4 5 6 Θ*  |t|<0.36GeV2excluded from analysis Diagonal 2 Accepted (t) Critical at low t-acceptance limit Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  30. Analytical unfolding Smearing due to beam divergence Detector resolution negligible (divergence uncertainty) Verified by MC based approach Verified by stringent selection cuts Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  31. Systematics

  32. Statistical and Systematic uncertainties for the t and d/dtresults Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  33. dσ/dt Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  34. Elastic scattering – from ISR to Tevatron ISR ~1.4 GeV2 Diffractive minimum: analogous to Fraunhofer diffraction: |t|~ p2q2 • exponential slope B at low |t| increases • minimum moves to lower |t| with increasing s •  interaction region grows (as also seen from stot) • depth of minimum changes  shape of proton profile changes • depth of minimum differs between pp, pˉp  different mix of processes Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  35. TOTEM Result Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  36. s = 7 TeV Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  37. TOTEM vs. models comparison Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  38. [EPL 95 (2011) 41001] Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  39. TOTAL, ELASTIC, INELASTIC CROSS-SECTIONS @ √s = 7-8 TeV Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  40. Measurements and Results@ √s = 7 TeV Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  41. Cross-Section Formulae Optical Theorem: ; and r from COMPETE fit: Using luminosity from CMS: Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  42. “Raw Data” Jun’11 – Vertical RPs@10s b*= 90 m Sector 56 t = -p2q2 Ly 260 m Very low background Lx 0-3 m x = Dp/p Sector 45 Integrated luminosity : 1.65 mb-1 Inel. pile-up ~ 0.005 ev/bx Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  43. TOTEM: pp Elastic Cross-Section |t|= 0.02 GeV2 Extrapolation to t = 0: B = 20.1 GeV -2 Exponential slope: Integral Elastic Cross-Section

  44. Systematics and Statistics • t :[0.6:1.8]%syst optics  <1%align. [3.4:11.9]%stat (before unfolding) • ds/dt :4%syst lumin; 1%syst(acc.+eff.+backg.+tag) 0.7%syst unfold. • B :1%stat1%syst from t0.7%syst from unfolding • ds/dt(t=0) : 0.3%stat 0.3%syst (optics) 4%syst lumin 1%syst(acc.+eff.+backg.+tag) • ∫ ds/dt :4%syst lumin1%syst(acc.+eff.+backg.+tag) 0.8%stat extrap. • sTOT : (+0.8% -0.2%)syst   0.2%stat 2.7%syst = (+2.8%-2.7%)syst  0.2%stat • sEL :5%syst 0.8%stat • sINEL :(+2.4%-1.8%)syst  0.8%stat Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  45. TOTEM: pp Total Cross-Section Elastic exponential slope: Elastic diff. cross-section at optical point: Optical Theorem, Total Cross-Section Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  46. TOTEM: pp Inelastic Cross-Section Inelastic Cross-Section sinel (CMS) = (68.0  2.0(syst)  2.4(lumi)  4.0 (extrap)) mb sinel (ATLAS) = (69.4  2.4(exp)  6.9 (extrap)) mb sinel(ALICE) = (72.7  1.1(mod)  5.1 (lumi)) mb Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  47. Total, Elastic, Inelastic Cross-Section Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  48. Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012

  49. Luminosity-independent and • r-independent pp Total Cross-Sections@ 7 TeV Hubert Niewiadomski, CERN, TOTEM, EPFL, 26 November 2012