CMS OVERALL PERFORMANCE AND PHYSICS RESULTS IN 2010

The CMS detector is briefly described and status of its operation in 2010 is given. The performance of CMS subsystem is shown. Selected measurements from 2010 pp and HI runs are presented. Presented at Epiphany 2011: Cracow Epiphany Conference on the First Year of the LHC CMS overall performance and physics results in 2010 ∗


The CMS detector and its operation in 2010
CMS [1] is a general purpose experiment for physics discoveries at the highest luminosities of the LHC. Its main component is a large (6 m diameter and 13 m long) solenoid. It delivers strong, 3.8 T magnetic field in the inner part of the CMS detector and about 1.8 T in iron return yoke. CMS is traditionally divided into barrel part (with detectors roughly parallel to beam pipe) and two endcaps. Next to beam-beam interaction region there is a tracker system, consisting of silicon Pixel and silicon Strip Detectors. The CMS tracker provides excellent reconstruction of charged particle tracks and primary-and secondary-vertices. The tracker is surrounded by an electromagnetic calorimeter. It is a homogeneous calorimeter made of lead-tungstate crystals. The energy measurement is supplemented with a sampling brass-scintillator hadron calorimeter. The above subdetectors are positioned in the inner part of the CMS detector, inside the coil. In the outer part, outside the coil, a muon system is placed. It is dedicated for muon reconstruction and identification. The muon system is based on gaseous detectors: Drift-Tubes in the barrel, Cathode Strip Chambers in the endcaps and Resistive Plate Chambers. The pseudorapidity (η = − ln tan θ/2, where θ -a polar angle) coverage of CMS depends on a subsystem. The tracking detectors (muon system, tracker) provide reconstruction up to |η| ≈ 2.4 − 2.5. The calorimeter coverage is enlarged for the purposes of hermeticity and extends up to |η| ≈ 3 in a case of the electromagnetic calorimeter and up to |η| ≈ 5 in a case of the hadronic one.
After re-opening of the LHC, CMS started to collect proton-proton collisions data. The initial center-of-mass energy delivered by the LHC √ s = 0.9 TeV was followed by 2.36 TeV at the end of 2009. Since March 2010, till November 2010 the LHC energy was increased up to half of its designed energy, i.e. to √ s = 7 TeV. Although the instantaneous LHC luminosity at startup was small, during a few months of operation it was increased by 5 orders of magnitude and reached 2 · 10 32 cm −2 s −1 . The integrated luminosity delivered to CMS was 47pb −1 out of which above 43pb −1 was recorded by CMS. At the end of 2010, the LHC has entered into a heavy ion program, colliding lead-lead beams at nucleon-nucleon centre-ofmass energy √ s N N = 2.76 TeV.
During the whole year 2010 the CMS detector was performing very well. For each subdetector more than 98% channels were operational. Moreover the efficiency of taking data was very high (above 90%). The number of events passing strict CMS data-quality certification criteria correspond to integrated luminosity of about 36 pb −1 . These events are referred as full 2010 CMS data sample.

Detector performance results
The CMS detector was initially commissioned with a test beams data and cosmic runs [2] before the LHC startup. Commissioning was continued with an early LHC data. At this step the key aspects were calibration and alignment of subdetectors, validation of reconstruction algorithms, comparison of detector response (reconstructed physics objects) with simulation predictions, validation and tuning of trigger algorithms and menus.
A charged particle reconstruction is one of key aspects to understand an event content. CMS has demonstrated an excellent performance and a good understanding of tracking capabilities [3,4]. Tracker operation conditions were validated. Just after the LHC startup, timing readout windows were optimised. The early commissioning includes also measurements of Lorentz angle, energy loss (dE/dx) and detector efficiencies. The validation of tracking reconstruction algorithms includes studies of resolution and efficiency of track and primary vertices finding, multiple interaction extraction, determination of beam line position and width.
A good illustration of an overall tracking performance are searches for well known resonances. In Figure 1(a) one can see invariant mass histogram 3 of candidates for Ξ ± → Λ 0 /Λ 0 π ± decays. The analysis involves reconstruction of a secondary vertex (decay of Λ). It is formed by two opposite charge tracks (assumed to be pion and (anti)proton). Their transverse impact parameters should be not compatible with the beam spot. These tracks should form together a good secondary vertex with a proper invariant mass. In addition, since Ξ ± is a long lived baryon, there should be one more charged particle (pion) not compatible with beam spot, but should form a common vertex with Λ.
An excellent muon reconstruction is one of design points of the CMS experiment. Muons that are supposed to come from nearby the beam spot are reconstructed in two ways. A muon track can be initially reconstructed in the muon system and updated with information from the tracker. Alternatively, a track reconstructed in the tracker can be propagated to the muon system, and identified as a muon in case of agreement with a signal found therein. Since the CMS all-silicon tracker provides very precise measurements, both ways of reconstruction lead to equivalent resolutions up to transverse momenta of O(10 2 GeV)  The period of an early commissioning with proton beams was dominated by validation of local reconstruction inside muon stations, alignment, calibration and data synchronisation. It has been followed by studies of muon identification and reconstruction [5]. This includes analysis of reconstruction algorithms by comparison with generator expectations, validation of muon isolation algorithms, analysis of muon deposit in calorimeters, cosmic backgrounds, hadron decays in-flight, punch through probability and muon trigger performance. In all cases the agreement with simulation pre-4 dictions was met. In order to minimize bias in muon reconstruction efficiency measurement, CMS is applying tag-and-probe technique. It relies on J/Ψ → µ + µ − decays, with a possibility to extend to other resonances, especially Z muonic decays. It is required that one of the muons (tag) is reconstructed in the muon system and the second (probe) in the tracker. A probe track combined with a tag track must fulfil invariant mass criteria. In addition the probe track energy deposit in calorimeter should be compatible with that of minimum ionising particle. The check of reconstruction of a probe track in the muon system allows us to determine the muon reconstruction efficiency. An illustration of a very good performance of the muon system can be a di-muon invariant mas distribution as shown in Figure 1(b). One can note a clearly visible fine-structure of Υ family.
The precise measurement of electromagnetic cascades is a vital aspect for the Higgs boson searches as well as many exotic channels. Thus, the early 2010 data were used to finalise calorimeter commissioning [6]. This includes validation of crystal transparency, thermal stability and timing alignment. CMS observed unphysical high deposits in single crystals. They are caused by direct ionisation of the avalanche photodiode by highly ionising particles resulting from LHC collisions. Algorithms have been developed to flag these signal based on topological and timing characteristics and reject them. The commissioning of electromagnetic calorimeter with 2010 data has been completed by analyses of reconstruction performance [7,8], including efficiency measurement from data and calibration [9]. The CMS electromagnetic calorimeter has been pre-calibrated with laboratory measurements, test beams, cosmic rays and early LHC data. The final calibration is made in-situ using LHC collision data. The strategy to calibrate electromagnetic calorimeter in 2010 includes φ-symmetry inter-calibration method and π 0 /η calibration. The first one is exploring the φ symmetry of the detector around the beam axis and can be done with minimum bias events. It allows to inter-calibrate crystals at the same pseudorapidity. The π 0 and η calibration uses the photon pairs from decays. It extends crystal inter-calibration to different values of pseudorapidities and allows to investigate calorimeter energy scale. Both methods can be combined. The invariant mass of photons from π 0 decays is a quick illustration of calorimeter performance. The one obtained with only 18 nb −1 collected is shown in Figure 2(a). A good agreement with Monte-Carlo generator prediction is visible. Another method of calibration uses Z and W to electron decays. The electron measurement in the tracker can be used to correct the calorimeter energy scale. This method is expected to become the main one when integrated luminosity will reach ∼ 1 fb −1 . In addition, Z → e + e − and J/Ψ → e + e − decays can be used to monitor and correct the absolute energy scale as soon as large data sample is available. For a photon plus jet sample a relative response < p jet T /p γ T > is shown as a function of p γ T . The data agrees well with simulation prediction. In addition simulation truth response (p T ratio of simulated response and particle level jet) is also indicated.
Jets are another vital observables for CMS. They are among main tools to verify predictions of the Standard Model in the LHC energy regime. Moreover they are possible signatures of many New Physics processes. For the jet reconstruction CMS has adopted anti-k t clustering algorithm [10]. An important part of CMS commissioning is study of jet energy response and resolution [11][12][13]. Since the energy measured in the detector differs from the particle jet energy, a factorized procedure for the jet energy calibration was developed. There are three types of corrections applied. The energy offset correction is supposed to remove contributions from calorimeter electronic noise and pile-up. The relative correction compensates non-uniform pseudorapidity response of the calorimeter. The absolute correction removes variation in jet response as a function of jet transverse momentum (p T ). In order to determine jet energy corrections CMS is using Monte-Carlo truth information and physics processes for validation and in-situ calibration (resulting currently in small additional correction). The di-jet p T balance is 6 used for validation of relative corrected jet energy response while photon plus jet balance method provides measurement of the absolute energy scale. An initial CMS result, illustrating not only quality of preparation of CMS for data taking but also a high quality of CMS simulation is presented in Figure 2(b). The relative response agrees well with expectations justifying usage of 10% of jet energy uncertainties for early physics publications.
Calorimeter-only jet measurements can be improved with Particle-Flow method [14]. The CMS particle-flow event reconstruction attempts to identify and reconstruct individually all particles produced in collisions, using information from all CMS detectors. This information is used at the level of jet clusterization allowing for more precise jet reconstruction. The power of the method is well visible in Figure 3, obtained soon after LHC startup [15]. The jet energies extend to regimes not accessible with calorimeter-only jets. The jet production cross-sections agree very well with theoretical predictions. This first-data analysis is confirmed with full 2010 CMS data sample [16]. The Particle-Flow method applied to the reconstruction of missing transverse energy and jets is used in most of physics analyses in CMS.

Selected CMS measurements
Charge particle multiplicities and momentum spectra The charged particle multiplicities and momentum spectra in pp collisions at energies of 0.9, 2.36 and 7 TeV were the first measurements of the CMS experiment [17]. Since majority of pp collisions does not involve hard 7 scattering these measurements allow us to verify predictions of soft interactions which are modelled phenomenologically only. The CMS measurements refer to non-single-diffractive (NSD) interactions provided by event selection of non-diffractive and double-diffractive events. The charged particle multiplicities were obtained using three techniques. The counting of reconstructed hits and hit pairs in the Pixel Detector grant access to tracks with transverse momenta down to 30 and 50 MeV/c respectively. The third method relies on full track reconstruction based on at least three hits (often in the Pixel Detector) and allows not only track counting but also momentum measurements for p T above 100 MeV/c. These low p T reconstruction thresholds support measurements in soft particle regime. The CMS measured the average transverse momentum of charged tracks in the early 2010 √ s=7 TeV data to be < p T >= 0.545 ± 0.005(stat) ± 0.015(syst) GeV/c.
The CMS measurements use tracks in |η| < 2.4 and accounts for very soft tracks by extrapolation of momentum distributions down to p T =0. In Figure 4(a) the above result is compared with previous measurements taken at different beam energies. The same data were used to compute charged particle multiplicities as a function of η. CMS determined average charged multiplicity density in |η| < 0.5 to dN ch /dη = 5.57 ± 0.01(stat) ± 0.23(syst). The CMS result is shown in Figure 4(b) together with other measurements.
The CMS error bars are dominated by systematic uncertainties. In order to minimise these uncertainties measurements were done in very initial ment follows this trend. The choice of the jj interval can influence the average p T value by a few percent.
For jj < 0:5, the average charged multiplicity density is dN ch =d ¼ 5:78 AE 0:01ðstatÞ AE 0:23ðsystÞ for NSD events. The ffiffi ffi s p dependence of the measured dN ch = dj %0 is shown in Fig. 5, which includes data from various other experiments. The dN ch =d results reported here show a rather steep increase between 0.9 and 7 TeV, which is measured to be ½66:1 AE 1:0ðstatÞ AE 4:2ðsystÞ%. Using a somewhat different event selection, the ALICE Collaboration has found a similar increase of ½57:6 AE 0:4ðstatÞ þ3:6 À1:8 ðsystÞ% [5]. The measured charged-particle multiplicity is accurate enough to distinguish among most sets of event-generator tuning parameter values and various models. The measured value at 7 TeV significantly exceeds the prediction of 4.57 from PHOJET [9,10], and the predictions of 3.99, 4.18, and 4.34 from the DW [17], PROQ20 [18], and Perugia0 [19] tuning parameter values of PYTHIA, respectively, while it is closer to the prediction of 5.48 from the PYTHIA parameter set from Ref. [8] and to the recent model predictions of 5.58 and 5.78 from Refs. [20,21]. The measured excess of the number of charged hadrons with respect to the event generators is independent of and concentrated in the p T < 1 GeV=c [GeV] s [GeV] s    Fig. 5, which includes data from various other experiments. The dN ch =d results reported here show a rather steep increase between 0.9 and 7 TeV, which is measured to be ½66:1 AE 1:0ðstatÞ AE 4:2ðsystÞ%. Using a somewhat different event selection, the ALICE Collaboration has found a similar increase of ½57:6 AE 0:4ðstatÞ þ3:6 À1:8 ðsystÞ% [5]. The measured charged-particle multiplicity is accurate enough to distinguish among most sets of event-generator tuning parameter values and various models. The measured value at 7 TeV significantly exceeds the prediction of 4.57 from PHOJET [9,10], and the predictions of 3.99, 4.18, and 4.34 from the DW [17], PROQ20 [18], and Perugia0 [19] tuning parameter values of PYTHIA, respectively, while it is closer to the prediction of 5.48 from the PYTHIA parameter set from Ref. [8] and to the recent model predictions of 5.58 and 5.78 from Refs. [20,21]. The measured excess of the number of charged hadrons with respect to the event generators is independent of and concentrated in the p T < 1 GeV=c [GeV] s    period of data taking allowing to cope with a very small event pileup. The open, Minimum Bias trigger given by any hit in Beam Scintillator Counter (BSC) in coincidence with colliding bunches was used. The presented results were corrected for contamination of disfavoured single-diffractive events, acceptance, selection and reconstruction efficiency and extrapolation accuracies. The measurements of charged particle multiplicities and momentum spectra were not well reproduced by PHOJET [18] and PYTHIA [19] Monte-Carlo generators used by CMS with several tunings. It indicates need of further development of underlying models and tunings.

The reconstruction of W and Z bosons and production cross-section measurements
The production of W and Z bosons with a decay to leptons is and important process for the LHC. It is a benchmark channel for lepton reconstruction. Due to accurate theoretical prediction of the cross-section it is also a test of perturbative QCD and proton parton distribution functions (PDF). Moreover it is a first electroweak process for measurement at the LHC. CMS has published results after collecting only 198 nb −1 and then updated them [20] with integrated luminosity of 2.9 pb −1 .
The CMS results take into account fiducial and kinematical acceptance of the CMS detector. The selection efficiency is obtained from simulation and corrected with data as explained below.
The W events are characterised by a prompt isolated lepton and significant missing transverse energy. In the CMS analysis the W signal yields are obtained by fitting missing transverse energy (E T / ) distributions in the electron channel and transverse mass 1 (M T ) distributions in muon channel. The lepton p T threshold in the analysis is set to 20 GeV/c. The main backgrounds are QCD multi-jet, Drell-Yan and tt events. They are efficiently rejected by lepton isolation criteria and by single lepton required.
Similarly, the Z measurements are polluted by QCD multi-jet production which is efficiently suppressed by requirement of two isolated leptons. The additional processes with true leptons in final state from tt events, Z tauonic decays and di-bosons, result in small background level only.
The distribution of invariant and transverse mass in case of Z → e + e − and W → µν can be seen in Figure 5. Almost all 2010 certified data is used. The contributions from dominant processes are shown.
Wherever possible CMS is trying to minimise uncertainties from simulation. As example, a shape of QCD background in W → µν is determined from data. It is obtained from high-purity QCD sample passing all the signal selection criteria apart of muon isolation for which inverted criteria is used. The correction for isolation-E T correlation is taken into account. This procedure results in a QCD fixed shape template used in a likelihood fit to the M T distribution (keeping its normalisation as a free parameter). The difference between several templates used in signal yield allows us to estimate the systematic uncertainties related to QCD background shape. Among sources of systematic uncertainties other than background subtraction/modelling one can mention uncertainties in lepton reconstruction and identification, momentum and energy scale uncertainty of PDF for acceptance. The recent analysis [21] includes the full 2010 CMS data sample. The CMS measurement of production cross-section times branching fraction are combined in electron and muon decay channels to give σ(pp → W X) × BR(W → lν) = 10.31 ± 0.02(stat.) ± 0.09(syst.) ± 0.10(th.) ± 0.41(lumi.) nb and σ(pp → ZX) × BR(Z → l + l − ) = 0.975 ± 0.007(stat.) ± 0.007(syst.) ± 0.018(th.) ± 0.039(lumi.) nb.

Top-quark production
The top-quark physics is one of the key points of the LHC programme. Precise measurements of top-quark properties are necessary not only for its evidence. Many signatures in New Physics contain top quark. Top 10 production can be also a source of significant background for many discovery processes. With only approximately 3 pb −1 CMS has shown evidence for top-quark pairs at the LHC and measured [22] their production cross-section to be σ(pp → tt + X) = 194 ± 72(stat.) ± 24(syst.) ± 21(lumi.) pb.
The top decays almost exclusively to b and W, which in turn may decay leptonicaly. The CMS analysis use decay modes with di-lepton (with e,µ) and neutrinos in a final state. The lepton candidates are required to be isolated and have p T > 20 GeV/c. The lepton identification and isolation efficiency is measured from Z leptonic decays data and agrees well with simulation. Since leptonic Z decays are also considerable source of background a veto around Z mass value (± 15 GeV/c 2 ) in di-lepton invariant mass is applied. Events with a small di-lepton invariant mass are also rejected. Another signature of the signal events is possible large transverse energy. It is originating from neutrinos that escape detection. The required E T / threshold is 30 GeV, except for e ± µ ∓ events where much smaller background is expected from Drell-Yan events and softer, 20 GeV cut, is optimal. The distribution of number of jets with p T >30 GeV/c and all other cuts applied is shown in Figure 6 Expected yields from simulated signal and background processes, normalized to estimates from data where appropriate, are shown in Fig. 1 as a function of jet multiplicity for events satisfying the complete dilepton event selection criteria except the 2-jet requirement; the tt signal dominates the bins with at least two jets.
Eleven dilepton events (3 e + e − , 3 μ + μ − , 5 e ± μ ∓ ) are observed in the data after applying the event selection criteria, with a total of 2.1 ± 1.0 background events expected. We attribute the excess of events above the background expectation to top-quark pair production.
The top-quark mass reconstruction methods of [35] (KIN, i.e., KINematic, method) and [36] (MWT, i.e., Matrix Weighting Technique) are applied to the selected events. In both methods, numerical solutions to the kinematic equations appropriate for a tt decay with two charged leptons in the final state are found for each event. The solutions are based on an ensemble of values of jet momenta and missing energy, generated corresponding to their expected resolution around the measured values. In the KIN method the underconstrained system is solved by introducing an additional constraint on the longitudinal momentum of the tt system, whose probability distribution is expected to have a negligible  Expected yields from simulated signal and background processes, normalized to estimates from data where appropriate, are shown in Fig. 1 as a function of jet multiplicity for events satisfying the complete dilepton event selection criteria except the 2-jet requirement; the tt signal dominates the bins with at least two jets.
Eleven dilepton events (3 e + e − , 3 μ + μ − , 5 e ± μ ∓ ) are observed in the data after applying the event selection criteria, with a total of 2.1 ± 1.0 background events expected. We attribute the excess of events above the background expectation to top-quark pair production.
The top-quark mass reconstruction methods of [35] (KIN, i.e., KINematic, method) and [36] (MWT, i.e., Matrix Weighting Technique) are applied to the selected events. In both methods, numerical solutions to the kinematic equations appropriate for a tt decay with two charged leptons in the final state are found for each event. The solutions are based on an ensemble of values of jet momenta and missing energy, generated corresponding to their expected resolution around the measured values. In the KIN method the underconstrained system is solved by introducing an additional constraint on the longitudinal momentum of the tt system, whose probability distribution is expected to have a negligible dependence on the top-quark mass and is therefore assumed from simulation. The top-quark mass value corresponding to the largest     [23] and Matrix Weighting Technique (MWT) [24] are applied to data and to simulated signal-plus-background and background hypothesis. The predictions assume top-quark mass of 172.5 GeV/c 2 .

11
surements. The initial CMS evidence for a top quark at the LHC is based on eleven events passing all criteria. It agrees well with expected 7.7 ± 1.5 signal and 2.1 ± 1.0 background events. It can be further constrained by superimposing b-jet identification criteria. In Figure 6(b) the distribution of reconstructed top-quark mass is shown. Results of the two top-quark mass reconstruction methods are consistent with Tevatron measurements.
Several sources of systematics errors were evaluated. Among them there are uncertainties on the simulation of signal selection, di-lepton selection efficiency measured from data and the jet energy scale. The background sources were assumed to have 50% systematic uncertainties except for those measured with data, where uncertainty is obtained by comparing data and simulation.

Topological correlations in two-particle distributions
One of the most interesting CMS results is an observation of long-range (2 < |∆η| < 4.8) two-particle correlations [25]. The study of particle correlations at the LHC energy frontier provides important information helping to understand and model mechanism of hardonisation and possible collective effects due to high energy densities in collisions.
A typical long-range correlations in particle distributions arise from momentum conservation and away-side jet fragmentation. It has been demonstrated [26] at RHIC that hot and dense matter in heavy ion collisions modify that simple picture. Significant particle densities in highest multiplicity proton-proton events at the LHC are motivation to study possible correlations.
The data were collected in two ways: using CMS minimum bias trigger and dedicated high-multiplicity path. The latter one required energy deposit at calorimeters above 60 GeV at Level-1 and large number of pixel-tracks reconstructed at High-Level Trigger. The pixel-tracks are based on simplified track reconstruction inside Pixel Detector only. The online threshold for minimal number of pixel-tracks was 70-85, depending on the luminosity.
The two-particle correlations were analysed as a functions of their distance in azimuthal angle ∆Φ and pseudorapidity ∆η. The correlation function R(∆η, ∆Φ) is expressed in terms of normalised signal S N (∆η, ∆Φ) and background B N (∆η, ∆Φ) distributions ratio. The S N distribution counts a (∆η, ∆Φ) distance for all track pairs in an event. The B N denotes uncorrelated track pairs distributions by combining tracks from randomly selected different events. Both S N and B N are independently normalised to unit integral taking into account combinatorial factor. The CMS measurement of two-particle correlations is shown in Figure 7. The intermediate p T range (1 < p T < 3 GeV/c) where the effect is most pronounced is chosen. The has a qualitatively similar effect on the shape as the particle p T cut ompare Fig. 7b and Fig. 7c). However, it is interesting to note that hallow minimum at ∆φ ≈ 0 and |∆η| > 2 in high multiplicity p Tto be slightly less pronounced than that in minimum bias collisions. e p T range in high multiplicity events shown in Fig. 7d, an unexthe data. A clear and significant "ridge"-like structure emerges η| of at least 4 units. This is a novel feature of the data which has ticle correlation functions in pp or pp collisions. Simulations using such an effect. An identical analysis of high multiplicity events in relation functions which do not exhibit the extended ridge at ∆φ ≈0 ther structures of the correlation function are qualitatively reproto compare to these data since it produces more high multiplicity D6T tune . Several other PYTHIA tunes, as well as HERWIG++ [30] were also investigated. No evidence for near-side correlations cordata was found.
high multiplicity pp data is reminiscent of correlations seen in rel- ≥ 110) events with 1 < p T < 3 GeV/c. The sharp near-side peak from jet correlations is cut off in order to better illustrate the structure outside that region. of particles and, therefore, has a qualitatively similar effect on the shape as the particle p T cut on minimum bias events (compare Fig. 7b and Fig. 7c). However, it is interesting to note that a closer inspection of the shallow minimum at ∆φ ≈ 0 and |∆η| > 2 in high multiplicity p Tintegrated events reveals it to be slightly less pronounced than that in minimum bias collisions.
Moving to the intermediate p T range in high multiplicity events shown in Fig. 7d, an unexpected effect is observed in the data. A clear and significant "ridge"-like structure emerges at ∆φ ≈ 0 extending to |∆η| of at least 4 units. This is a novel feature of the data which has never been seen in two-particle correlation functions in pp or pp collisions. Simulations using MC models do not predict such an effect. An identical analysis of high multiplicity events in PYTHIA8 [34] results in correlation functions which do not exhibit the extended ridge at ∆φ ≈0 seen in Fig. 7d, while all other structures of the correlation function are qualitatively reproduced. PYTHIA8 was used to compare to these data since it produces more high multiplicity events than PYTHIA6 in the D6T tune . Several other PYTHIA tunes, as well as HERWIG++ [30] and Madgraph [35] events were also investigated. No evidence for near-side correlations corresponding to those seen in data was found.
The novel structure in the high multiplicity pp data is reminiscent of correlations seen in relativistic heavy ion data. In the latter case, the observed long-range correlations are generally ≥ 110) events c. The sharp near-side peak from jet correlations is cut off in order to cture outside that region. re, has a qualitatively similar effect on the shape as the particle p T cut ts (compare Fig. 7b and Fig. 7c). However, it is interesting to note that e shallow minimum at ∆φ ≈ 0 and |∆η| > 2 in high multiplicity p Tls it to be slightly less pronounced than that in minimum bias collisions. diate p T range in high multiplicity events shown in Fig. 7d, an unexd in the data. A clear and significant "ridge"-like structure emerges |∆η| of at least 4 units. This is a novel feature of the data which has -particle correlation functions in pp or pp collisions. Simulations using ict such an effect. An identical analysis of high multiplicity events in correlation functions which do not exhibit the extended ridge at ∆φ ≈0 ll other structures of the correlation function are qualitatively reprosed to compare to these data since it produces more high multiplicity the D6T tune . Several other PYTHIA tunes, as well as HERWIG++ [30] nts were also investigated. No evidence for near-side correlations corn in data was found.
the high multiplicity pp data is reminiscent of correlations seen in rel-. In the latter case, the observed long-range correlations are generally ≥ 110) events with 1 < p T < 3 GeV/c. The sharp near-side peak from jet correlations is cut off in order to better illustrate the structure outside that region. of particles and, therefore, has a qualitatively similar effect on the shape as the particle p T cut on minimum bias events (compare Fig. 7b and Fig. 7c). However, it is interesting to note that a closer inspection of the shallow minimum at ∆φ ≈ 0 and |∆η| > 2 in high multiplicity p Tintegrated events reveals it to be slightly less pronounced than that in minimum bias collisions.
Moving to the intermediate p T range in high multiplicity events shown in Fig. 7d, an unexpected effect is observed in the data. A clear and significant "ridge"-like structure emerges at ∆φ ≈ 0 extending to |∆η| of at least 4 units. This is a novel feature of the data which has never been seen in two-particle correlation functions in pp or pp collisions. Simulations using MC models do not predict such an effect. An identical analysis of high multiplicity events in PYTHIA8 [34] results in correlation functions which do not exhibit the extended ridge at ∆φ ≈0 seen in Fig. 7d, while all other structures of the correlation function are qualitatively reproduced. PYTHIA8 was used to compare to these data since it produces more high multiplicity events than PYTHIA6 in the D6T tune . Several other PYTHIA tunes, as well as HERWIG++ [30] and Madgraph [35] events were also investigated. No evidence for near-side correlations corresponding to those seen in data was found.
The novel structure in the high multiplicity pp data is reminiscent of correlations seen in relativistic heavy ion data. In the latter case, the observed long-range correlations are generally  N ≥ 110) subsample. The sharp peak around (∆η, ∆Φ) ≈ (0, 0) is truncated to better illustrate overall structure. Since particle order in computation of correlation is arbitrary, the plot is symmetries along ∆η = 0 and ∆φ = 0. peak at (∆η, ∆Φ) ≈ (0, 0) corresponds to particles inside the same jet, the away-side ∆Φ ≈ π ridge results from the fragmentation of back-to-back jets. In the subsample of events with high multiplicity the additional ridge appears at ∆φ ≈ 0 extending in several units of ∆η. This is the novel feature, not observed before in pp or pp collisions. It was also not predicted by any Monte-Carlo generators used by CMS (PYTHIA [19,27], HERWIG++ [28], Madgraph [29]).

Other CMS measurements
CMS has already performed over 25 measurement analyses resulting in publications. The CMS proton-physics measurements can be subdivided to results on soft QCD physics, particle correlations, perturbative QCD, bosons and heavy flavour. Among not described analyses the measurements of direct and in-direct J/ψ production [30], isolated prompt photon production [31], and reach b-physics program appear. Another class of analyses was opened when the LHC entered heavy ion program. Just after a few days of lead-lead collsions CMS has found first Z candidate. CMS has also observed [32] and studied the jet quenching phenomena which was one of proposed [33] signatures of quark-gluon plasma. It manifests as imbalance of jet energy resulting from parton energy loss in dense plasma. CMS has analysed momentum balance in di-jet events as a function of centrality. The imbalance is well visible for central events with leading jet p T > 120 GeV/c. 13 The imbalanced momentum can be recovered by looking at low p T tracks.

Summary
The performance of the LHC machine in 2010 was excellent. It allowed the CMS experiment to collect interesting data which are still under analysis. The early data were used to finalise commissioning and verify calibration and initial performance. This very early period was followed by measurement of already know or expected processes. The CMS measurement agrees well with pQCD and EWK predictions. The long-range near-side two-particle correlations were observed in pp collisions. The jetquenching phenomena was observe in lead-lead collisions. The exciting era of CMS searches has already started. More details about CMS searches are given in other contributions in these proceedings.