Higgs Boson – Have we seen it? Outline � The excitement!! � What led to this? – The challenge and the effort � Have we found something new? � What the Indians did if any? Sunanda Banerjee May 2013 IOP, Bhubanswar
July 4, 2012 � Physicists get excited at times – for what? � Historic seminar at CERN with simultaneous transmission and live link at the large particle physics conference of 2012 in Melbourne, May 2013 New Particle at the Large Hadron Collider S. Banerjee 2
Media gets excited as well May 2013 New Particle at the Large Hadron Collider S. Banerjee 3
Constituents of matter Thomson Rutherford Chadwick SLAC 1897 1909 1932 1968 May 2013 New Particle at the Large Hadron Collider S. Banerjee 4
Finding so far � So far we have probed to a scale of 10 -19 m � Basic constituents of matters are all spin ½ objects (fermions) � The six basic types of quarks and leptons are arranged in 3 families � There are 4 types of interactions. We consider only 3: EM, weak & strong � These interactions are mediated through exchange of spin 1 objects (vector bosons) May 2013 New Particle at the Large Hadron Collider S. Banerjee 5
Evolution of Theory � Interaction is explained by exchange of a carrier of force � Theory of electromagnetic interaction reformulated during 40’s by Feynman, Schwinger and Tomonaga - gauge theory � Exchange particle has zero mass ⇒ photons � Try to apply gauge theory to other interactions – weak, strong � These interactions are short range – weak interaction needs exchange of massive particles; but mass cannot be easily included in theories satisfying gauge invariance May 2013 New Particle at the Large Hadron Collider S. Banerjee 6
The Guralnik-Hagen-Kibble-Higgs-Englert-Brout mechansim… � These six gentlemen during early 60’s came up with an idea which could rescue gauge theory approach to explain electroweak interactions. . – They, as 3 independent groups, wrote in the same 1964 volume of Physical Review Letters about a mechanism, which gives mass to particles, from different perspectives and each paper made a distinct contribution � Physical Review Letters volume 13 (1964): – Guralnik, Hagen, Kibble, "Global Conservation Laws and Massless Particles" – Higgs, "Broken Symmetries and the Masses of Gauge Bosons" – Englert, Brout, "Broken Symmetry and the Mass of Gauge Vector Mesons" May 2013 New Particle at the Large Hadron Collider S. Banerjee 7
The Standard Model � This idea is incorporated in unifying the theory of electromagnetic and weak interactions by Glashow, Weinberg and Salam � Strong interaction is also explained in terms of gauge theory: Quantum Chromo Dynamics ⇒ The Standard Model of high energy physics Sheldon Glashow Steven Weinberg Abdus Salam May 2013 New Particle at the Large Hadron Collider S. Banerjee 8
The Standard Model vs experiments |O meas − O fit |/ σ meas � Earlier experiments (particularly Measurement Fit 0 1 2 3 the experiments done at the LEP, ∆α (5) ∆α had (m Z ) 0.02750 ± 0.00033 0.02759 m Z [ GeV ] m Z [ GeV ] 91.1875 ± 0.0021 91.1874 CERN and Tevatron, Fermilab) Γ Z [ GeV ] Γ Z [ GeV ] 2.4952 ± 0.0023 2.4959 have tested the predictions of the σ 0 σ had [ nb ] 41.540 ± 0.037 41.478 20.767 ± 0.025 Standard Model to a high level of R l R l 20.742 A 0,l 0.01714 ± 0.00095 0.01646 A fb accuracy 0.1465 ± 0.0032 A l (P τ ) A l (P τ ) 0.1482 � All measurements agree with the 0.21629 ± 0.00066 0.21579 R b R b 0.1721 ± 0.0030 R c R c 0.1722 predictions which start with a few A 0,b 0.0992 ± 0.0016 A fb 0.1039 unknown parameters A 0,c 0.0707 ± 0.0035 A fb 0.0743 0.923 ± 0.020 A b A b 0.935 The Standard Model is a 0.670 ± 0.027 A c A c 0.668 0.1513 ± 0.0021 A l (SLD) A l (SLD) 0.1482 beautiful theory and sin 2 θ eff sin 2 θ lept (Q fb ) 0.2324 ± 0.0012 0.2314 arguably one that is most m W [ GeV ] m W [ GeV ] 80.399 ± 0.023 80.378 Γ W [ GeV ] Γ W [ GeV ] 2.085 ± 0.042 2.092 precisely tested m t [ GeV ] m t [ GeV ] 173.20 ± 0.90 173.27 0 1 2 3 July 2011 But where is Higgs boson? May 2013 New Particle at the Large Hadron Collider S. Banerjee 9
Indirect hints Prediction for the Higgs mass LEP: indirect determination of the top mass Possible due to � precision measurements � known higher order electroweak corrections t’ Hooft Veltman May 2013 New Particle at the Large Hadron Collider S. Banerjee 10
How to find Higgs boson? � It has to be produced in interactions – Collide particles with sufficient high energy – Protons are good choice for the colliding particles – Probability of Higgs production is small → need a large number of interactions � Higgs boson is unstable and will decay to other particles immediate after it is produced – Look at all possible signatures – Observation in multiple final state can only establish a new object bb ττ γγ WW-->l ν l ν ZZ-->4l ZZ-->2l2 τ ZZ-->2l2q ZZ-->2l2 ν 100 May 2013 Higgs boson mass, GeV/c 2 New Particle at the Large Hadron Collider S. Banerjee 11
The Large Hadron Collider at CERN � 27 km (17 miles) circumference � Accelerates beams of Lake Geneva protons to 99.9999991% CMS the speed of light CMS LHCb LHCb ALICE ALICE ATLAS ATLAS May 2013 New Particle at the Large Hadron Collider S. Banerjee 12 12 T. Virdee, ICHEP08
Large Hadron Collider Beam size (3.5-4.0) × 10 12 eV Beam Energy ~ 5.5 cm 7.8 × 10 33 cm − 2 s − 1 Luminosity ☓ 15 μ m ☓ 15 μ m Bunches/Beam 1377 1.4 × 10 11 Protons/Bunch 5.5 m (50 ns) (3.5-4.0) TeV Proton Proton colliding beams 1.5 × 10 7 Hz Bunch Crossing ν 0.1 - Hz e e 4.5 × 10 8 Hz Proton Collisions q µ + - χ 1 µ - ~ q Parton Collisions q Z ~ p g H p p p New Particle Production ~ q (Higgs, SUSY, ....) Z + µ µ + q − ~ µ χ 0 µ - 2 χ ~ 0 1 May 2013 New Particle at the Large Hadron Collider S. Banerjee 13
Facts about LHC � Energy stored in magnets: 10 GJ = A380 at a cruise speed of 700 km/h. Can heat and melt 12 tons of copper! � Energy stored in a single beam: 360MJ is equivalent to 90 kg of TNT or 15 Kg of chocolate � The amount of liquid helium in the machine is 60 tons or 120 thousand gallons � LHC is the coldest place within the solar system with the temperature of 1.9 o K � It is also the emptiest place in the solar system with the vacuum in the pipe containing the beams at 10 -13 atm. May 2013 New Particle at the Large Hadron Collider S. Banerjee 14
CERN accelerator complex (not to scale) 4 TeV 450 GeV CMS & ATLAS : General purpose, Higgs, SUSY ? ? 1.4 GeV 50 MeV 25 GeV LHC-b : B-Physics, CP-violation ALICE : Heavy Ion, QGP May 2013 New Particle at the Large Hadron Collider S. Banerjee 15
Total weight 14000 t CMS CMS Overall diameter 15 m 76k scintillating ECAL Overall length 28.7 m PbWO 4 crystals MUON ENDCAPS HCAL Scintillator/brass 473 Cathode Strip Chambers (CSC) Interleaved ~7k ch 432 Resistive Plate Chambers (RPC) 3.8T Solenoid IRON YOKE Preshower Si Strips ~16 m 2 ~137k ch 3 - YBO 1 Foward Cal E Y Steel + quartz YB1-2 Fibers 2 ~k ch Pixels & Tracker • Pixels (100x150 μ m 2 ) ~ 1 m 2 ~66M ch •Si Strips (80-180 μ m) ~200 m 2 ~9.6M ch MUON BARREL 250 Drift Tubes (DT) and May 2013 New Particle at the Large Hadron Collider S. Banerjee 16 480 Resistive Plate Chambers (RPC)
The CMS collaboration Belgium Bulgaria A large collaborative effort Austria 3600 Physicists, Engineers and students USA 38 Countries Finland CERN 182 Institutions France Germany Gradually Russia increasing Greece Uzbekistan Hungary Ukraine Italy Slovak Republic Georgia UK Belarus Poland Turkey Armenia India Portugal Spain China Estonia Pakistan Switzerland Cyprus Korea China (Taiwan) Croatia May 2013 New Particle at the Large Hadron Collider S. Banerjee 17
What may happen � Need a large number of interactions to probe at small cross section of the production process � LHC was generous for that – Provided excess of ~4x10 14 interactions during 2011 at 7 TeV cm energy and even larger number at 8 TeV during the first half of 2012 – The experiments collected the provided luminosity with very high efficiency � However this will produce ~10 9 unwanted interactions for each Higgs boson May 2013 New Particle at the Large Hadron Collider S. Banerjee 18
Success of LHC (Misery to Experiments) 2010 O(2) PU Bunch spacing 150 ns 30 pb -1 2011 O(10) PU Bunch spacing 75-50 ns 5.8 fb -1 k = # of bunches 2012 N = # of p’s/bunch O(20) PU f = rev. frequency Bunch spacing 50 ns 25 fb -1 σ = beam size F = geometry loss factor ε = beam emittance β = betatron function May 2013 New Particle at the Large Hadron Collider S. Banerjee 19
How much data is produced? � Nearly 1 GB of data is recorded every second – 15,000 TB/year = 15 PB/year – It’s like recording a DVD every 4 sec – Enough to fill your hard drive in 2 min � Processed all around the world via LHC Computing Grid May 2013 New Particle at the Large Hadron Collider S. Banerjee 20
Understand the detector first 10 May 2013 New Particle at the Large Hadron Collider S. Banerjee 21
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