Transcript Luminosity
Luminosity and ATLAS Boštjan Maček Adviser: prof. Marko Mikuž Overview introduction definition of luminosity the need for high luminosity LHC (Large Hadronic Collider) and luminosity ATLAS (A Toroidal LHC AparatuS) measurements detectors: BCM (Beam Conditions Monitor) 17 July 2015 Luminosity and ATLAS 2 Introduction particle identity protons available energy E=2*7 TeV =14 TeV luminosity L=1034cm-2s-1 data analysis quantitative measurements of particle physics world experimental conditions 17 July 2015 Luminosity and ATLAS 3 Luminosity scattering experiment d N d L ddt d 2 luminosity – experimental conditions differential cross-section - description of physics •experimental conditions measurements luminosity rate dN R L dt 17 July 2015 •rate of interactions •amount of data N Rdt Ldt integrated luminosity number of scattered particles Luminosity and ATLAS 4 17 July 2015 LHC - ATLAS Luminosity and ATLAS larger statistics bigger precision higher luminosity larger statistics The race for high luminosity 5 LHC and luminosity luminosity defined by parameters of collider protons grouped in bunches number of protons in a bunch - 1.15 1011 number of bunches - 2808 revolution frequency - 11.2 kHz relativistic factor - 7461 N n f rev r L F 4 2 b b beam optics parameters 17 July 2015 Luminosity and ATLAS 6 Beam optics I for high L bigger proton density is needed squeezing the beam typically systems of quadrupol magnets are used 17 July 2015 Luminosity and ATLAS 7 Beam optics II beam parameterization: x x’=dx/ds ... ... distance from optical axis inclination toward optical axis particle dynamics in quadrupol magnet C x’ magnet B B A particle trajectory A optical axis C magnet magnetic field, charge momentum 17 July 2015 x 2 x' 2 x a K Luminosity and ATLAS initial conditions 8 Beam optics III • passage trough magnet ellipse in x’-x plane • 1011 protons in a bunch bunch area x’ x’ x x’ x x • Liouville’s theorem bunch area is preserved 17 July 2015 Luminosity and ATLAS 9 x’ x’max Beam optics IV • goal: minimal xmax x xmax – minimal (shape) – minimal emittance xmax x'max (area) large smal Nb nb f rev r L F 4 2 17 July 2015 reduction by factor F=0.8 big x’ means that protons collide under 35 angle Luminosity and ATLAS rad 10 Luminosity measurements d 2N d L ddt d relate measured rate to cross-section feedback to the LHC fast measurements needed data preprocessing all four experiments have their luminosity measuring devices + LHC monitoring several complementary methods are used absolute luminosity measurements limited, calibration luminosity monitoring high luminosities 17 July 2015 Luminosity and ATLAS 11 Calculation from beam parameters hard to measure F, , and N b2 nb f rev r L F 4 transversal bunch size van der Meer scan beam-beam interactions limited by resolution of beam position monitor expected precision 5-10% 17 July 2015 Luminosity and ATLAS 12 Well calculable processes analyzing recorded data processes that can be precisely calculated most promising processes pp ppe+e- or W/Z production pp pp+- d 2N d L ddt d expected precision around 10% not a real-time measurement 17 July 2015 Luminosity and ATLAS 13 Optical theorem incident plain wave distance to the detector ikr e (r , ) eikz f ( ) r overall scattering scattering angle small angles x2 y2 r z 2z z detector response cross-section 17 July 2015 area of the detector (r, ) dS S 2 4 Im[ f (0)] k tot 4 Im[ f (0)] Luminosity and ATLAS 14 Small angle scattering tot=Rtot/L scattering under zero angle Re[f(0)]/Im[f(0)] 2 d el 2 ( 0) f (0) Im2 [ f (0)](1 2 ) tot2 (1 2 ) d 16 2 Rtot 1 L (1 2 ) 16 dRel / dp measuring: elastic rate at small angles and extrapolating to zero total rate (elastic rate + inelastic rate) Elastic Strong extremely small angles expected precision: 2% Elastic EM Inelastic no total rate needed !!! 17 July 2015 Luminosity and ATLAS 15 Luminosity monitoring only option for high luminosity measuring inelastic rate number of interactions in pp collision Poisson counting only ‘empty events’ 0 1 2 3 ... n ALi i BC n n e i pp possible bunch luminosity measurement needs to be calibrated (A) 17 July 2015 Luminosity and ATLAS 16 ATLAS detectors for W/Z analysis whole detector will contribute dedicated detectors absolute luminosity measurements ZDC (Zero Degree Calorimeter) Roman Pots luminosity monitoring BCM (Beam Conditions Monitor) LUCID (LUminosity measurement using a Cherenkov Integrating Detector) 17 July 2015 Luminosity and ATLAS 17 Beam Conditions Monitor • relative luminosity measurement – bunch luminosity measurement fast electronics – close to interaction point radiation hard • background suppression t + coincidences 4 modules on each side of IP 17 July 2015 Luminosity and ATLAS 18 Beam Conditions Monitor • something on both sides • rate of coincidences L R( L) P N , 1 e rTR P N 1 e rTR (1 P ) N L0 N 0 Poisson distribution probability for anything on + side simulation probability for particle detection on + side P N N N changes with interaction point position 17 July 2015 Luminosity and ATLAS 19 Conclusion luminosity is a parameter of collider detector must be adapted to measure in high luminosity precise measurement of luminosity is essential for physics interpretation of experiment for measuring more complementary approaches are needed ATLAS will be able to monitor luminosity to high precision 17 July 2015 Luminosity and ATLAS 20 Thank you ☺ 17 July 2015 Luminosity and ATLAS 21