Presentation on theme: "India-CMS Collaboration Meeting Kajari Mazumdar Link-person (NOT Spokesperson), India-CMS collaboration July 28 – 29, 2011 BARC, Mumbai News from LHC,"— Presentation transcript:
India-CMS Collaboration Meeting Kajari Mazumdar Link-person (NOT Spokesperson), India-CMS collaboration July 28 – 29, 2011 BARC, Mumbai News from LHC, CMS Issues concerning India-CMS Pledges Conferences New institutes in CMS CMS upgrade ….
LHC Operation Machine performance much better than anticipated great time for high energy physics community many interesting results based on 2010 (~40 pb -1 ) and 2011 (~ 1 fb -1 ) data. Coordinated efforts across LHC experiments to achieve best possible science. Standard model Higgs boson is being chased extensively lot of attention from media! Important results by end of 2012 (few fb -1 ) Presently, Number of bunches per beam: 1380 instantaneous lumi: : / cm 2 /s Coming days: increasing in bunch charges (protons/bunch ->1.55E11) L= / cm 2 /s, pile up = 16 Further adjustment of machine parameters L= / cm 2 /s, pile up = 24 Only test operation with 25 ns bunch spacing in Heavy ion operation starts in Nov. with 100 ns b.s. Machine energy for 2012 operation yet to be decided
News from CMS Physics Search for Higgs Large range of Higgs mass excluded with 2011 data ~ 1 fb -1 For Lepton Photon conference ATLAS and CMS results will be combined better reach. More data required, in general for discovery ~ 2fb -1 by end of 2011 expected. Search for B s Lowest order process in standard model involves quantum loops branching ratio very small l ~ Contribution from New Physics can enhance the BR. CMS upper limit: ~1.9x10 -8, LHCb: ~1.8x10 -8 Expect combined limit ~ x10 -8 Compare with Tevatron result: Br(B s =1.8( )x10 -8 Very impressive publication list (~ 70 in journals + PAS), conference results (~ 30 in EPS), several updates expected for Lepton Photon conference.
Standard model Higgs combination results from CMS for 1.1 fb -1 Low mass: 22 channels, high mass: 18 (PAS HIG ) Issues for combination: Higgs boson signal is too small compared to background. Sensitivity of experiments are at their limits. eg., compare mass resolution of diff. channels with Higgs natural width at different mass values There are many systematics involved in measurements: nuisances Use “CLs” construction to be conservative in the presence of background fluctuations. Consider signal and background events as fn.s of nuisance parameters.
Statistical analysis: modelling The likelihood function built as a product L(data|μ, θ) = L obs (data|μ, θ) · L(θ 0 |θ) Prob. of observing the data given μ, θ. In the case of counting experiment with b(θ) background and s(θ) signal it’s just a Poisson( N | μ·s(θ) + b(θ) ) Likelihood of θ 0 given θ (Frequentist) Prob. of having θ given measurement θ 0 if it’s multiplied by a flat prior on θ(Bayesian) μ = σ/σ SM : strength of signal for standard model Higgs boson hypothesis μ=1, only background hypothesis μ = 0 Θ: nuisance parameter, ie, various systematic uncertainties relevant for different channels, unconstrained by a-priori considerations or measurements. Θ 0 : Observed value of nuisance parameter, evaluated from data. Giovanni Petrucciani’s talk at CMS WGM on
Statistical Analysis For each value of the signal strength μ = σ/σ SM 1. Evaluate on the data the test statistics profile likelihood ratio 2. Determine the values of the nuisance parameters θ that provide a best global fit to data and external measurements (θ obs ). Do it separately for the case of no signal and for the particular value of μ. 3. Use those values to generate an ensemble of pseudo-experiments for background-only and signal+background with θ obs 0,θ obs fixed. In the fit ot evaluate test-statistc, vary them Around best fitted value, acc. to suitable pdfs. If CL S < 0.05, then the value of μ is excluded at 95% CL. 4. Evaluate test statistics for pseudo-exp, compare with the one of data.
Exclusion Limit Expected exclusion: GeV Observed exclusion: GeV GeV + parts in between Expected exclusion: GeV Observed exclusion: GeV GeV + parts in between H , effective for m H =110,140 GeV/c 2 chance of observing a maximum excess as large as seen in data ~ 60% (HIG ) H WW: observed limits in the low mass range below 180 GeV/c 2 show a broad 2σ upward deviation, likely to be fluctuation. HIG
CMS Issues concerning us Pledges : shifts and other jobs Visibility of members of India-CMS Volunteering for CMS jobs Presentations in conferences on behalf of CMS collaboration September 2012 CMS week in India? Document containing contributions, relevant informations: publication,shifts,.. (Physics in simple terms, must include colourful pictures) Needed urgently informations about what all you have done. Everybody is requested to cooperate by providing as much information. Looking for volunteers to compile informations Need to have regular physics meetings within our community. Physics contacts of each group is requested to arrange for 1 seminar per month from the group. There are many students! EVO is still the only possibility, though not satisfactory.
Our service/tasks in CMS Task Force wants a report about how we are serving in the collaboration. Please enter urgently in the ESP tool the jobs you are involved in. Thanks to students who have also contributed in this! Though we have overshot in our “contribution” there are rooms to increase visibilty in about 4000 strong collaboration, mainly through physics at this stage. + for physicists, opting for review of analyses of individual liking. + Conference talks/posters by everybody contact subgroup leaders NOW!. Collaboration board discusses possibilities for various job openings which may also contribute to ESP (eg.documentation for the Workbook). CB members please circulate such mails as well as other interesting ones!.
How do you know about availability of a conference talk? get familiar with CINCO, subscribe to nominate yourself and arrange for others to nominate you, if possible also let me know Task Force is ready to approve extra deputation for this purpose group’s budget may be utilised, no extra resources, usually. Organizers are sometimes kind to waiver some of the expenses, must try for that Presentation of CMS results in International Conference Few members of India-CMS collab. have represented CMS in important conferences always, including Quark Matter, Moriond, EPS 2011, …. Contributions from India includes chairing of physics sessions in international conferences. In Lepton Photon conference there will be many posters. We need to be proactive for sustained visibility: I shall try to help as much as possible being in Conf. committee now. Jan, 2011
Physics requirement of upgraded CMS detector
Upgrade of LHC machine and CMS detector Commissioning of LHC machine triggered upgrade plan of whole LHC injector complex to be proposed! Presently includes ancient, crucial machines in the chain almost all need to be replaced. Phase1: LINAC4 etc. Phase2: upgrade of crucial components in main LHC ring for higher energy, much higher instantaneous luminosity. Shutdown plans of LHC are decided by physics output CMS has planned for subsystem upgrades acc. to physics needs but guided by LHC schedule and parameters. Much of CMS does not need significant upgradation! Phase1: only pixel, HCAL and RPC mainly For HCAL: replace HPDs and PMTs with SiPMs (HO most urgent) For RPC: main motivation is to increase the trigger capacity (lowering of threshold) For pixels easy replacement already foreseen during design convenient now. Presently, BARC+ PU in RPC TIFR, SINP, PU in HCAL barrel upgrade, HO upgrade by TIFR
New group in India-CMS
Phase 1 : Muons ME4/2 upgrade motivation Compare 3/4 vs. 2/3 stations: (Triggering on n out of n stations is inefficient and uncertain) Recent simulation with & without the ME4/2 upgrade: The high-luminosity Level 1 trigger threshold is reduced from 48 18 GeV/c Target Rate 5 kHz Rick Wilkinson, Ingo Bloch 1 July J. Nash - CMS Ugrades
Upgrade of CMS tracking detector during Phase1: only pixel Easy replacement already forseen during design Convenient now. Phase 2: 4 barrel layers Contribution in trigger
Phase 1 How well do detector components handle the increasing luminosity? Both instantaneous and integrated effects What detector elements will need replacement/modification to cope? Detectors will record >500 fb -1, can they withstand this? Phase 2 What detector elements will need replacement? Is there a requirement for a long shutdown? How long – 18 Months? (1 Full calendar year without beam +) When – sometime after the middle of the next decade Developing and building new tracking detectors will take many years ATLAS and CMS must agree on the dates No sense in having two long shutdowns Current planning ATLAS earliest date around 2015, CMS not earlier than 2017 Reach 700 fb -1 (potential limit) – most optimistic 2015, conservative 2017 Key Issues for experiments and required planning
Summary of limits There is not any evidence for a SM Higgs yet (but we have some nice fluctuations)
CLs of SM Higgs hypothesis CL: GeV GeV + pieces in between Expected exclusion: GeV CL: GeV Giovanni Petrucciani (UCSD)
The compatibility between the data and the backgroud model is quantified using p-values, computed comparing the prediction from (SM without higgs) w.r.t. (SM with a higgs of unknown cross section) In the gaussian limit, we’re doing a fit of all the data to extract a value of μ = σ/σ SM. The significance for μ ± Δμ is then Z = μ/Δμ In the combination, channels with little or no sensitivity contribute little or zero to p-value. Excesses not signal-like do not contribute. All channels are constrained to the same cros section: up and down fluctuations can compensate The p-value does not evaluate compatibility with the SM higgs boson signal (and can’t be made to do it). In PAS, p-values have been paired with plots of best fit cross section, to show how far from SM-like they are.